Spinocerebellar Ataxia

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Note: Keyword search: ataxin (i.e. Search Criteria =  Spinocerebellar Ataxia+ ataxin)

(108 References)


Zuhlke, C., A. Dalski, et al. (2002). "Spinocerebellar ataxia type 1 (SCA1): phenotype-genotype correlation studies in intermediate alleles." Eur J Hum Genet 10(3): 204-9.
CAG repeat expansions with loss of CAT interruptions in the coding region of the ataxin-1 gene are associated with spinocerebellar ataxia type 1 (SCA1). For molecular genetic diagnosis it is necessary to define the limits of normal and pathological size ranges. In most studies, normal alleles as measured by PCR range from 6-39 units with interruptions of 1-3 CAT trinucleotides that are thought to be involved in the stability of the trinucleotide stretch during DNA replication. Expanded alleles have been reported to carry 39-81 CAG trinucleotides without stabilising CAT interruptions. To evaluate the limits between normal and disease size ranges we analysed the repeat length and composition of the SCA1 gene in 15 individuals with alleles ranging from 36 and 41 triplets for genotype-phenotype correlation studies. We found the 39 trinucleotide-allele to be either interrupted by CAT repeats or formed by a pure CAG stretch. The clinical features of individuals carrying 39 uninterrupted CAG repeats did not differ from the SCA1 phenotype in general with dysphagia, pale discs, pyramidal signs and cerebellar tremor being more frequent as compared to other SCA genotypes. In contrast, the interrupted 39 trinucleotide-allele is not correlated with the SCA1 phenotype.

Yoshida, H., T. Yoshizawa, et al. (2002). "Chemical chaperones reduce aggregate formation and cell death caused by the truncated machado-joseph disease gene product with an expanded polyglutamine stretch." Neurobiol Dis 10(2): 88-99.
Machado-Joseph disease/spinocerebellar ataxia-3 (MJD/SCA-3) is an inherited neurodegenerative disorder caused by expansion of the polyglutamine stretch in the MJD gene-encoded protein ataxin-3. The truncated form of mutated ataxin-3 causes aggregation and cell death in vitro and in vivo. Abnormal conformation and misfolding of the pathological protein are assumed critical to pathogenesis. To test this hypothesis, we transfected BHK-21 and Neuro2a cells transiently with N-terminal truncated ataxin-3 with an expanded polyglutamine stretch. We then studied the effects of organic solvent dimethyl sulfoxide (DMSO), cellular osmolytes glycerol, and trimethylamine N-oxide (TMAO) on aggregate formation and cell death. These reagents stabilize proteins in their native conformation and called chemical chaperones based on their influence on protein folding. Aggregate formation and cytotoxicity induced by truncated expanded ataxin-3 were reduced by exposing cells to these chemical chaperones. Our results indicate the potentially useful therapeutic strategy of the chemical chaperones in preventing cell death in MJD.

Watase, K., E. J. Weeber, et al. (2002). "A long CAG repeat in the mouse Sca1 locus replicates SCA1 features and reveals the impact of protein solubility on selective neurodegeneration." Neuron 34(6): 905-19.
To faithfully recreate the features of the human neurodegenerative disease spinocerebellar ataxia type 1 (SCA1) in the mouse, we targeted 154 CAG repeats into the endogenous mouse locus. Sca1(154Q/2Q) mice developed a progressive neurological disorder that resembles human SCA1, featuring motor incoordination, cognitive deficits, wasting, and premature death, accompanied by Purkinje cell loss and age-related hippocampal synaptic dysfunction. Mutant ataxin-1 solubility varied with brain region, being most soluble in the neurons most vulnerable to degeneration. Solubility decreased overall as the mice aged; Purkinje cells, the most affected in SCA1, did not form aggregates of mutant protein until an advanced stage of disease. It appears that those neurons that cannot sequester the mutant protein efficiently and thereby curb its toxicity suffer the worst damage from polyglutamine-induced toxicity.

Takahashi, J., H. Fujigasaki, et al. (2002). "Two populations of neuronal intranuclear inclusions in SCA7 differ in size and promyelocytic leukaemia protein content." Brain 125(Pt 7): 1534-43.
Spinocerebellar ataxia type 7 (SCA7) is a hereditary progressive cerebellar ataxia with retinal degeneration associated with an abnormally expanded polyglutamine stretch. Neuronal intranuclear inclusions (NIIs), as in other polyglutamine diseases, are pathological hallmarks of these disorders. NIIs in polyglutamine diseases contain not only the protein with the expanded polyglutamine stretch but also other types of proteins. Several chaperone proteins related to the ubiquitin proteasome pathway, transcription factors and nuclear matrix proteins have been detected in NIIs. The composition of NIIs might reflect the process of NII formation and part of the pathogenesis of these diseases. To investigate how these proteins relate to the pathogenesis of SCA7, we performed immunohistochemical analyses of the composition of NIIs in two cases of SCA7. We demonstrated that there are two types of NIIs in SCA7 that differ in size and immunoreactivity to promyelocytic leukaemia protein (PML), one of the essential components of nuclear bodies (NBs; also called PML oncogenic domains). Small and large NIIs contained ataxin-7, human DnaJ homologue 2 (HDJ-2) and proteasome subunit 19S. In contrast, PML was found only in small NIIs. CREB-binding protein (CBP), another component of NBs, was distributed like PML in NIIs. Our results suggest that NIIs are formed by the accumulation of ataxin-7 in NBs, which become enlarged as they recruit related proteins.

Strom, A. L., J. Jonasson, et al. (2002). "Cloning and expression analysis of the murine homolog of the spinocerebellar ataxia type 7 (SCA7) gene." Gene 285(1-2): 91-9.
Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease caused by the expansion of a polyglutamine tract in the protein ataxin-7, a protein of unknown function. In order to analyze the expression pattern of wild type ataxin-7 in detail, the murine SCA7 gene homolog was cloned and the expression pattern in mice analyzed. The SCA7 mouse and human gene exhibit a high degree of identity at both DNA (88.2%) and protein (88.7%) level. The CAG repeat region, known to be polymorphic in man, is conserved in mouse but contained only five repeats in all mouse strains analyzed. The arrestin homology domain and the nuclear localization signal found in human ataxin-7 is also conserved in the murine homolog. Expression of ataxin-7 was detected during mouse embryonic development and in all adult mouse tissues examined by northern and western blots. In brain, immunohistological staining revealed an ataxin-7 expression pattern similar to that in human, with ataxin-7 expression in cerebellum, several brainstem nuclei, cerebral cortex and hippocampus. Our data show high conservation of ataxin-7 both structurally and at the level of expression, suggesting a conserved role for the protein in mice and humans.

Skinner, P. J., C. A. Vierra-Green, et al. (2002). "Amino acids in a region of ataxin-1 outside of the polyglutamine tract influence the course of disease in SCA1 transgenic mice." Neuromolecular Med 1(1): 33-42.
Spinocerebellar ataxia type 1 (SCA1) belongs to a family of polyglutamine induced neurodegenerative disorders. Transgenic mice that overexpress a mutant allele of the SCA1 gene develop a progressive ataxia and Purkinje cell pathology. In this report, the pathological importance of a segment of ataxin-1 previously shown to be important for protein-protein interactions was examined. While the absence of a 122 amino acid segment from the protein-protein interaction region of ataxin-1 did not effect the initiation of disease, its absence substantially suppressed the progression of disease in SCA1 transgenic mice. Thus, these data suggest that this region of ataxin-1 has a role in disease progression. Furthermore, these results provide evidence that ataxin-1-induced disease initiation and disease progression involve distinct molecular events.

Rub, U., R. A. De Vos, et al. (2002). "Spinocerebellar ataxia type 3 (Machado-Joseph disease): severe destruction of the lateral reticular nucleus." Brain 125(Pt 9): 2115-2124.
The lateral reticular nucleus (LRT) of the medulla oblongata is a precerebellar nucleus involved in proprioception and somatomotor automatisms. We investigated this nucleus in five individuals with clinically diagnosed and genetically confirmed spinocerebellar ataxia type 3 (SCA3, Machado-Joseph disease). Polyethylene glycol-embedded 100 micro m thick sections stained for lipofuscin granules and Nissl material as well as Nissl-stained paraffin-embedded sections revealed severe destruction of the LRT in all SCA3 brains examined. Some of the few surviving neurones contained ataxin-3-immunopositive intranuclear inclusion bodies, as noted in other affected brain regions in SCA3. Along with the severe neuronal depletion, obvious astrogliosis was seen in the LRT of all SCA3 patients. The findings suggest that the LRT is a consistent target of the pathological process underlying SCA3. In view of its afferent and efferent connections, destruction of the LRT probably contributes to gait ataxia in individuals suffering from SCA3.

Okazawa, H., T. Rich, et al. (2002). "Interaction between mutant ataxin-1 and PQBP-1 affects transcription and cell death." Neuron 34(5): 701-13.
PQBP-1 was isolated on the basis of its interaction with polyglutamine tracts. In this study, using in vitro and in vivo assays, we show that the association between ataxin-1 and PQBP-1 is positively influenced by expanded polyglutamine sequences. In cell lines, interaction between the two molecules induces apoptotic cell death. As a possible mechanism underlying this phenomenon, we found that mutant ataxin-1 enhances binding of PQBP-1 to the C-terminal domain of RNA polymerase II large subunit (Pol II). This reduces the level of phosphorylated Pol II and transcription. Our results suggest the involvement of PQBP-1 in the pathology of spinocerebellar ataxia type 1 (SCA1) and support the idea that modified transcription underlies polyglutamine-mediated pathology.

Meunier, C., D. Bordereaux, et al. (2002). "Cloning and characterization of a family of proteins associated with Mpl." J Biol Chem 277(11): 9139-47.
Thrombopoietin (TPO) controls the formation of megakaryocytes and platelets from hematopoietic stem cells via activation of the c-Mpl receptor and multiple downstream signal transduction pathways. We used two-hybrid screening to identify new proteins that interacted with the cytoplasmic domain of Mpl, and we found a new family of proteins designated A2D (for Ataxin-2 Domain protein). The A2D are 130-kDa proteins that have three regions similar to those of Ataxin-2, the gene product causing familial type 2 spinocerebellar ataxia. A2D has several isoforms with different C-terminal domains, all produced from a single gene by alternative splicing. Northern blotting indicated that the A2D gene is widely expressed in immortalized cell lines and hematopoietic and fetal tissues. A2D proteins were constitutively associated with Mpl in vivo in human hematopoietic UT7 cells. TPO also caused the release of A2D from the activated receptor, and the phosphorylation of A2D on tyrosines residues was dependent on the Mpl C-terminal domain. Finally, A2D bound to the unstimulated erythropoietin receptor, whereas erythropoietin caused dissociation from the erythropoietin receptor, suggesting that A2D proteins are new components of the cytokine signaling system.

Kettner, M., D. Willwohl, et al. (2002). "Intranuclear aggregation of nonexpanded ataxin-3 in marinesco bodies of the nonhuman primate substantia nigra." Exp Neurol 176(1): 117-21.
Marinesco bodies (MB) are intranuclear inclusion bodies predominantly found in melanin-pigmented neurons of the substantia nigra. MB are demonstrable not only in humans but also in nonhuman primates. In the present study MB of aged rhesus monkeys (Macaca mulatta; n = 15; mean age 16 years) and aged baboons (Papio anubis; n = 13; mean age 25 years) were examined immunohistochemically. MB were found to be immunoreactive for ubiquitin, a protein involved in initiation of proteasome-mediated proteolysis. We also demonstrate that MB in monkeys are intensely immunoreactive for the protein ataxin-3 as detected by using two monoclonal anti-ataxin-3 antibodies (1H9 and 2B6). The abnormally expanded form of this polyglutamine protein is known to be causally involved in spinocerebellar ataxia type 3 or Machado-Joseph disease. The monoclonal antibody 1C2 was employed to examine whether ataxin-3 in MB in monkeys contains such an abnormally expanded polyglutamine stretch. MB were consistently 1C2-immunonegative, indicating that they are composed of normal wild-type ataxin-3. In conclusion MB in nonhuman primates permit experimental examination of mechanisms involved in transnuclear localization, intranuclear aggregation, and ubiquitination of nonexpanded polyglutamine proteins.

Jonasson, J., A. L. Strom, et al. (2002). "Expression of ataxin-7 in CNS and non-CNS tissue of normal and SCA7 individuals." Acta Neuropathol (Berl) 104(1): 29-37.
Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder primarily affecting the cerebellum, brain stem and retina. The disease is caused by an expanded polyglutamine tract in the protein ataxin-7. In this study we analyzed the expression pattern of ataxin-7 in CNS and non-CNS tissue from three SCA7 patients and age-matched controls. SCA7 is a rare autosomal dominant disorder, limiting the number of patients available for analysis. We therefore compiled data on ataxin-7 expression from all SCA7 patients ( n=5) and controls ( n=7) published to date, and compared with the results obtained in this study. Expression of ataxin-7 was found in neurons throughout the CNS and was highly abundant in Purkinje cells of the cerebellum, in regions of the hippocampus and in cerebral cortex. Ataxin-7 expression was not restricted to regions of pathology, and there were no apparent regional differences in ataxin-7 expression patterns between patients and controls. The subcellular distribution of ataxin-7 was primarily nuclear in all brain regions studied. In cerebellar Purkinje cells, however, differences in subcellular distribution of ataxin-7 were observed between patients and controls of different ages. Here we provide an increased understanding of the distribution of ataxin-7, and the possible implication of subcellular localization of this protein on disease pathology is discussed.

Hong, S., S. J. Kim, et al. (2002). "USP7, a ubiquitin-specific protease, interacts with ataxin-1, the SCA1 gene product." Mol Cell Neurosci 20(2): 298-306.
Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 has been known to associate with elongated polyglutamine tract in ataxin-1, the SCA1 gene product. Using the yeast two-hybrid system, we have found that USP7, a ubiquitin-specific protease, binds to ataxin-1. Further experiments with deletion mutants indicated that the C-terminal region of ataxin-1 was essential for the interaction. Liquid beta-galactosidase assay and coimmunoprecipitation experiments revealed that the strength of the interaction between USP7 and ataxin-1 is influenced by the length of the polyglutamine tract in the ataxin-1; weaker interaction was observed in mutant ataxin-1 with longer polyglutamine tract and USP7 was not recruited to the mutant ataxin-1 aggregates in the Purkinje cells of SCA1 transgenic mice. Our results suggest that altered function of the ubiquitin system can be involved in the pathogenesis of spinocerebellar ataxia type 1.

Garden, G. A., R. T. Libby, et al. (2002). "Polyglutamine-expanded ataxin-7 promotes non-cell-autonomous purkinje cell degeneration and displays proteolytic cleavage in ataxic transgenic mice." J Neurosci 22(12): 4897-905.
Spinocerebellar ataxia (SCA) type 7 is an inherited neurodegenerative disorder caused by expansion of a polyglutamine tract within the ataxin-7 protein. To determine the molecular basis of polyglutamine neurotoxicity in this and other related disorders, we produced SCA7 transgenic mice that express ataxin-7 with 24 or 92 glutamines in all neurons of the CNS, except for Purkinje cells. Transgenic mice expressing ataxin-7 with 92 glutamines (92Q) developed a dramatic neurological phenotype presenting as a gait ataxia and culminating in premature death. Despite the absence of expression of polyglutamine-expanded ataxin-7 in Purkinje cells, we documented severe Purkinje cell degeneration in 92Q SCA7 transgenic mice. We also detected an N-terminal truncation fragment of ataxin-7 in transgenic mice and in SCA7 patient material with both anti-ataxin-7 and anti-polyglutamine specific antibodies. The appearance of truncated ataxin-7 in nuclear aggregates correlates with the onset of a disease phenotype in the SCA7 mice, suggesting that nuclear localization and proteolytic cleavage may be important features of SCA7 pathogenesis. The non-cell-autonomous nature of the Purkinje cell degeneration in our SCA7 mouse model indicates that polyglutamine-induced dysfunction in adjacent or connecting cell types contributes to the neurodegeneration.

Aleman, T. S., A. V. Cideciyan, et al. (2002). "Spinocerebellar Ataxia Type 7 (SCA7) Shows a Cone-Rod Dystrophy Phenotype." Exp Eye Res 74(6): 737-45.
Autosomal dominant spinocerebellar ataxia 7 is associated with retinal degeneration. SCA7, the causative gene, encodes ataxin-7, a ubiquitous 892 amino acid protein of variable sub-cellular localization, and the disease is due to expansion of an unstable CAG repeat in the coding region of the gene. Recent increases in understanding of the mechanisms ofSCA7 -related retinopathy from in vitro and murine model studies prompted us to perform a detailed study of the retinal phenotype of affected members of a family with SCA7 mutation (45-47 CAG repeats). There was a spectrum of severity from mild to severe dysfunction. Early functional abnormalities were at both photoreceptor and post-receptoral levels. When cone and rod photoreceptor dysfunction was present, it was approximately equal. Regional retinal dysfunction was evident: there was more dysfunction centrally than peripherally with least effect in the midperiphery. In vivo cross-sectional retinal images with optical coherence tomography showed an early disease stage of altered foveal lamination (abnormal area of low reflectivity splitting the outer retina-choroidal complex) accompanied in the parafovea by reduced retinal thickness. Later disease stages showed foveal and parafoveal retinal thinning. The phenotype in this family with SCA7 is that of a cone-rod dystrophy. These observations increase interest in a recent hypothesis that ataxin-7 may interfere with the function of CRX (cone-rod homeobox), a transcription factor regulating photoreceptor genes and a cause of a cone-rod dystrophy phenotype in man.

Zhou, Y. X., W. H. Qiao, et al. (2001). "Spinocerebellar ataxia type 1 in China: molecular analysis and genotype-phenotype correlation in 5 families." Arch Neurol 58(5): 789-94.
BACKGROUND: Twelve genetic types of autosomal dominant hereditary ataxia have been recently identified and the genes responsible for most of them cloned. Molecular identification of the type of ataxia is important to determine the disease prevalence and its natural history in various populations. OBJECTIVES: To perform molecular analysis of 75 Chinese families affected with spinocerebellar ataxia (SCA) and to evaluate the spectrum of mutations in these genes and the correlation between genotypes and phenotypes in Chinese patients. SETTING: Neurogenetics Unit, China-Japan Friendship Hospital, Beijing, China. METHODS: One hundred nine patients from 75 kindreds diagnosed as having autosomal dominant SCA, 16 patients with sporadic SCA or spastic paraplegia, 280 control chromosomes of the Chinese population, and 120 control chromosomes of the Sakha population were selected for this study. We conducted detailed mutational analysis by direct sequencing of polymerase chain reaction products amplified from genomic DNA. RESULTS: Spinocerebellar ataxia type 1 (SCA1) was identified in 5 families with 12 studied patients. All affected family members were heterozygous for a CAG repeat expansion in the SCA1 gene containing 51 to 64 trinucleotide repeats. Normal alleles had 26 to 35 repeats. Spinocerebellar ataxia type 1 accounted for 7% of the studied Chinese families with ataxia. In addition, we determined the frequency of a single vs double CAT interruption in 120 control chromosomes of the Siberian Sakha population, which has the highest known prevalence of SCA1, and compared this with 280 control chromosomes from the Chinese populations. The results show that 64.7% of the Siberian normal alleles contain a single CAT interruption, whereas 92% of the Chinese had more than 1 interruption. CONCLUSIONS: Spinocerebellar ataxia type 1 is responsible for 7% of affected families in the Chinese population. A correlation between the prevalence of SCA1 and the number of CAT interruptions in the trinucleotide chain suggests that a CAT-to-CAG substitution may have been the initial event contributing to the generation of expanded alleles and influencing relative prevalence of SCA1.

Zander, C., J. Takahashi, et al. (2001). "Similarities between spinocerebellar ataxia type 7 (SCA7) cell models and human brain: proteins recruited in inclusions and activation of caspase-3." Hum Mol Genet 10(22): 2569-79.
Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant polyglutamine disorder presenting with progressive cerebellar ataxia and blindness. The molecular mechanisms underlying the selective neuronal death typical of SCA7 are unknown. We have established SCA7 cell culture models in HEK293 and SH-SY5Y cells, in order to analyse the effects of overexpression of the mutant ataxin-7 protein. The cells readily formed anti-ataxin-7 positive, fibrillar inclusions and small, nuclear electron dense structures. We have compared the inclusions in cells expressing mutant ataxin-7 and in human SCA7 brain tissue. There were consistent signs of ongoing abnormal protein folding, including the recruitment of heat-shock proteins and proteasome subunits. Occasionally, sequestered transcription factors were found. Activated caspase-3 was recruited into the inclusions in both the cell models and human SCA7 brain and its expression was upregulated in cortical neurones, suggesting that it may play a role in the disease process. Finally, on the ultrastructural level, there were signs of autophagy and nuclear indentations, indicative of a major stress response in cells expressing mutant ataxin-7.

Yvert, G., K. S. Lindenberg, et al. (2001). "SCA7 mouse models show selective stabilization of mutant ataxin-7 and similar cellular responses in different neuronal cell types." Hum Mol Genet 10(16): 1679-92.
Accumulation of expanded polyglutamine proteins and selective pattern of neuronal loss are hallmarks of at least eight neurodegenerative disorders, including spinocerebellar ataxia type 7 (SCA7). We previously described SCA7 mice displaying neurodegeneration with progressive ataxin-7 accumulation in two cell types affected in the human pathology. We describe here a new transgenic model with a more widespread expression of mutant ataxin-7, including neuronal cell types unaffected in SCA7. In these mice a similar handling of mutant ataxin-7, including a cytoplasm to nucleus translocation and accumulation of N-terminal fragments, was observed in all neuronal populations studied. An extensive screen for chaperones, proteasomal subunits and transcription factors sequestered in nuclear inclusions (NIs) disclosed no pattern unique to neurons undergoing degeneration in SCA7. In particular, we found that the mouse TAF(II)30 subunit of the TFIID initiation complex is markedly accumulated in NIs, even though this protein does not contain a polyglutamine stretch. A striking discrepancy between mRNA and ataxin-7 levels in transgenic mice expressing the wild-type protein but not in those expressing the mutant one, indicates a selective stabilization of mutant ataxin-7, both in this model and the P7E/N model described previously. These mice therefore provide in vivo evidence that the polyglutamine expansion mutation can stabilize its target protein.

Yue, S., H. G. Serra, et al. (2001). "The spinocerebellar ataxia type 1 protein, ataxin-1, has RNA-binding activity that is inversely affected by the length of its polyglutamine tract." Hum Mol Genet 10(1): 25-30.
Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disease caused by the expansion of a polyglutamine tract within the SCA1 product, ataxin-1. Previously, using transgenic mice, it was demonstrated that in order for a mutant allele of ataxin-1 to cause disease it must be transported to the nucleus of the neuron. Using an in vitro RNA-binding assay, we demonstrate that ataxin-1 does bind RNA and that this binding diminishes as the length of its polyglutamine tract increases. These observations suggest that ataxin-1 plays a role in RNA metabolism and that the expansion of the polyglutamine tract may alter this function.

Vig, P. J., S. H. Subramony, et al. (2001). "Calcium homeostasis and spinocerebellar ataxia-1 (SCA-1)." Brain Res Bull 56(3-4): 221-5.
Spinocerebellar ataxia-1 (SCA-1) belongs to a group of polyglutamine neurodegenerative disorders characterized by the expansion of a glutamine tract within the mutant disease-causing protein. In SCA-1, the expression of mutant ataxin-1 induces a progressive functional loss and the subsequent degeneration of a set of neurons including cerebellar Purkinje cells. Studies on SCA-1 transgenic mice have provided further understanding of the molecular and cellular events important for the disease. This review discusses what has been learned about the pathogenesis of SCA-1 through the transgenic mouse models in reference to Ca(2+) dependent pathways. This article also discusses the role of Ca(2+) regulating cytoplasmic and nuclear proteins in the pathogenesis of SCA-1. Finally, we discuss the use of double mutant mouse models to understand the association between Ca(2+) binding proteins and Purkinje cell pathology in SCA-1.

Uchihara, T., H. Fujigasaki, et al. (2001). "Non-expanded polyglutamine proteins in intranuclear inclusions of hereditary ataxias--triple-labeling immunofluorescence study." Acta Neuropathol (Berl) 102(2): 149-52.
Neuronal intranuclear inclusions (NIIs) found in CAG/polyglutamine-expansion disorders contain both expanded polyglutamine and the gene product without the CAG repeat. The gene product containing expanded polyglutamine has, therefore, been considered to be a major component of NIIs. In this immunohistochemical study, we showed recruitment of ataxin-2, ataxin-3 and TATA box binding protein (TBP) into NIIs of the pontine neurons of spinocerebellar ataxia type (SCA) 1, SCA2, SCA3 and dentatorubral-pallidoluysian atrophy brains. Triple-labeling immunofluorescence demonstrated colocalization of ataxin-2 and ataxin-3 in NIIs containing expanded polyglutamine, irrespective of the disease examined. These in vivo findings indicate that polyglutamine proteins recruited into NIIs are not restricted to their expanded form. Among these proteins, recruitment of ataxin-2 was least frequent in every case examined, suggesting that the rate of recruitment partly depends on the protein transported into NIIs. Because other proteins lacking polyglutamine motif were not detected in NIIs, it is suggested that the presence of polyglutamine is a prerequisite for these proteins to be recruited into nucleus and to form NIIs. Interaction between expanded and non-expanded polyglutamine may play roles during these processes.

Srivastava, A. K., S. Choudhry, et al. (2001). "Molecular and clinical correlation in five Indian families with spinocerebellar ataxia 12." Ann Neurol 50(6): 796-800.
Spinocerebellar ataxia 12 (SCA12) is a recently identified form of autosomal dominant cerebellar ataxia associated with the expansion of an unstable CAG repeat in the 5' untranslated region of the gene PPP2R2B. We analyzed 77 Indian families with autosomal dominant cerebellar ataxia phenotype and confirmed the diagnosis of SCA12 in 5 families, which included a total of 6 patients and 21 family members. The sizes of the expanded alleles ranged from 55 to 69 CAG repeats, and the sizes of the normal alleles ranged from 7 to 31 repeats. We believe our study is the first to demonstrate that SCA12 may not be as rare in some populations as previously thought.

Skinner, P. J., C. A. Vierra-Green, et al. (2001). "Altered trafficking of membrane proteins in purkinje cells of SCA1 transgenic mice." Am J Pathol 159(3): 905-13.
Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disease caused by the expression of mutant ataxin-1 that contains an expanded polyglutamine tract. Overexpression of mutant ataxin-1 in Purkinje cells of transgenic mice results in a progressive ataxia and Purkinje cell pathology that are very similar to those seen in SCA1 patients. Two prominent aspects of pathology in the SCA1 mice are the presence of cytoplasmic vacuoles and dendritic atrophy. We found that the vacuoles in Purkinje cells seem to originate as large invaginations of the outer cell membrane. The cytoplasmic vacuoles contained proteins from the somatodendritic membrane, including mGluR1, GluRDelta1/Delta2, GluR2/3, and protein kinase C (PKC) gamma. Further examination of PKCgamma revealed that its sequestration into cytoplasmic vacuoles was accompanied by concurrent loss of PKCgamma localization at the Purkinje cell dendritic membrane and decreased detection of PKCgamma by Western blot analysis. In addition, the vacuoles were immunoreactive for components of the ubiquitin/proteasome degradative pathway. These findings present a link between vacuole formation and loss of dendrites in Purkinje cells of SCA1 mice and indicate that altered somatodendritic membrane trafficking and loss of proteins including PKCgamma, are a part of the neuronal dysfunction in SCA1 transgenic mice.

Shahbazian, M. D., H. T. Orr, et al. (2001). "Reduction of Purkinje cell pathology in SCA1 transgenic mice by p53 deletion." Neurobiol Dis 8(6): 974-81.
The expansion of a polyglutamine tract in the ataxin-1 protein beyond a critical threshold causes spinocerebellar ataxia type 1 (SCA1). To investigate the mechanism of neuronal degeneration in SCA1, we analyzed the phenotype of an SCA1 transgenic mouse model in the absence of p53, an important regulator of cell death. p53 deficiency did not affect the early features of SCA1 mice such as impaired motor coordination and ataxin-1 nuclear inclusion formation but caused a notable reduction in later pathological features, including Purkinje cell heterotopia, dendritic thinning, and molecular layer shrinkage. To determine if this protective effect was mediated by an anti-apoptotic property of p53 deficiency, we looked for apoptosis in SCA1 mice but failed to detect any evidence of it even in the presence of p53. We propose that p53 acts after the initial pathogenic events in SCA1 to promote the progression of neuronal degeneration in SCA1 mice, but this activity may be unrelated to apoptosis.

Savic, D., I. Topisirovic, et al. (2001). "Is the 31 CAG repeat allele of the spinocerebellar ataxia 1 (SCA1) gene locus non-specifically associated with trinucleotide expansion diseases?" Psychiatr Genet 11(4): 201-5.
A number of human hereditary neuromuscular and neurodegenerative disorders are caused by the expansion of trinucleotide repeats within certain genes. The molecular mechanisms that underlie these expansions are not yet known. We have analyzed six trinucleotide repeat-containing loci [spinocerebellar ataxias (SCA1, SCA3, SCA8), dentatorubral-pallidoluysian atrophy (DRPLA), Huntington chorea (HD) and fragile X syndrome (FRAXA)] in myotonic dystrophy type 1 (DM1) patients (n = 52). As controls, we analyzed two groups of subjects: healthy control subjects (n =133), and a group of patients with non-triplet neuromuscular diseases (n = 68) caused by point mutations, deletions or duplications (spinal muscular atrophy, Charcot-Marie-Tooth disease, type 1A, hereditary neuropathy with liability to pressure palsies, and Duchenne and Becker muscular dystrophy). Allele frequency distributions for all tested loci were similar in these three groups with the exception of the SCA1 locus. In DM1 patients, the SCA1 allele with 31 CAG repeats account for 40.4% of all chromosomes tested, which is significantly higher than in two other groups (11.3% in healthy controls and 6.6% in the group of non-triplet diseased patients; P < 0.001, Fisher's exact test). This is consistent with our previous findings in HD patients. The absence of this association in non-triplet diseases as well as in healthy controls could indicate a possible role of this SCA1 allele with 31 repeats in triplet diseases. Here we discuss a possible role of the SCA1 region in pathological trinucleotide repeat expansions.

Popova, S. N., P. A. Slominsky, et al. (2001). "Polymorphism of trinucleotide repeats in loci DM, DRPLA and SCA1 in East European populations." Eur J Hum Genet 9(11): 829-35.
A normal polymorphism at three triplet repeat loci (myotonic dystrophy (DM), dentatorubral-pallidoluysian atrophy (DRPLA) and spinocerebellar ataxia type 1 (SCA1)) were examined in healthy unrelated individuals from the Siberian Yakut (Mongoloid) population, the Adygei (Caucasian) population and nine East European populations: populations from Russia (Holmogory, Oshevensk, Kursk, Novgorod, Udmurts, Bashkir), two Ukrainian populations (Lviv and Alchevsk) and one Belarussian. The distribution of alleles for DRPLA and SCA1 were similar for all East-European populations. For the DM locus, East European populations had typical allele distribution profiles with two modes, (CTG)5 and (CTG)11-14, but some differences were found for the Bashkir population where alleles containing 11-14 CTG repeats had relatively higher frequency. The Yakut population had different allele spectra for all types of repeats studied. Higher heterozygosity levels and insignificant differences between expected and observed heterozygosity were found for all tested loci. The latter led us to suggest that the trinucleotide repeat loci analysed are not influenced by selection factors and could be useful for genetic relationship investigations in different populations.

Parker, M. E. (2001). "Attacking ataxia." Minn Med 84(9): 8-11.

Orr, H. T. and H. Y. Zoghbi (2001). "SCA1 molecular genetics: a history of a 13 year collaboration against glutamines." Hum Mol Genet 10(20): 2307-11.
Spinocerebellar ataxia type 1 (SCA1) is a relatively rare autosomal-dominant neurological disorder. SCA1 has the intriguing feature that the disease-causing mutation is the expansion of an unstable trinucleotide repeat, specifically a CAG repeat that encodes the amino acid glutamine in ataxin-1. During the past 10 years, substantial progress has been made towards understanding the pathogenic mechanism in this disease. The nucleus has been identified as the subcellular site where the mutant protein acts to cause disease. Evidence indicates that expansion of the glutamine tract alters the folding properties of ataxin-1. Finally, several cellular pathways have been identified which are able to impinge on the SCA1 disease process. The characterization of these pathways and their role in SCA1 will guide research over the next several years.

Orr, H. T. (2001). "Hereditary ataxia. An unfolded protein." Lancet 358 Suppl: S35.

Nozaki, K., O. Onodera, et al. (2001). "Amino acid sequences flanking polyglutamine stretches influence their potential for aggregate formation." Neuroreport 12(15): 3357-64.
Expanded polyglutamine stretches have been shown to form aggregates and to be toxic to cells. In this study, we hypothesized that amino acid sequences flanking the polyglutamine stretches influence the aggregate formation potential of these stretches. Green fluorescent protein (GFP) fusion proteins containing glutamine repeats of various lengths and a fixed number of flanking amino acids of ataxin-2, huntingtin, dentatorubral-pallidoluysian atrophy protein (DRPLAP) or ataxin-3 were transiently expressed in COS-7 cells. The aggregate formation potential of ataxin-2 and DRPLAP increased in a CAG-repeat-length-dependent manner, with a threshold between 34 and 36. Truncated ataxin-2-Q56-GFP and truncated huntingtin-Q56-GFP showed a significantly higher aggregate formation potential than truncated DRPLAP-Q56-GFP or truncated ataxin-3-Q56-GFP. These results are in agreement with the clinical observation that ages of disease onset in patients with spinocerebellar ataxia type 2 or Huntington's disease are lower than those in patients with DRPLA or Machado-Joseph disease having expanded CAG repeats of the same length. Furthermore, mutagenesis of the flanking sequence of ataxin-2 markedly reduced its aggregate formation potential. These results indicate that the amino acid sequences flanking the polyglutamine stretches significantly influence their aggregate formation potential.

Mori, M., Y. Adachi, et al. (2001). "A genetic epidemiological study of spinocerebellar ataxias in Tottori prefecture, Japan." Neuroepidemiology 20(2): 144-9.
We investigated the genotype frequencies of patients with spinocerebellar ataxias (SCA), using a community-based prevalence study among 613,349 inhabitants in Tottori prefecture, Japan. Prevalence date was April 1, 1998. On this date, 109 SCA patients were identified in this community. The prevalence of SCA was 17.8 per 100,000 individuals. The most common cause of inherited SCA was a mutation at the SCA6 locus (25%), followed by mutation at the SCA1 locus (15%), SCA3 locus (5%) and dentatorubral-pallidoluysian atrophy locus (5%). None of the expanded alleles was found in SCA2, SCA7 or Friedreich's ataxia. Mutation at SCA6 was also the most common form of sporadic SCA at 11%. Prevalences per 100,000 individuals were as follows: SCA6, 2.40; SCA1, 0.48; DRPLA, 0.32, and SCA3, 0.16.

McNeil, D. E., W. M. Linehan, et al. (2001). "Comorbid genetic diseases, von Hippel-Lindau disease and spinocerebellar ataxia type 2, confounding the diagnosis of cerebellar dysfunction in an adolescent." Clin Neurol Neurosurg 103(4): 216-9.
The authors report a 15-year-old female who presented with difficulties in ambulation as well as difficulties with balance and penmanship. She had a known genetic risk of von Hippel-Lindau (VHL; MIM 193300) disease, with a unique VHL mutation, but had no tumors of the brain or spine to explain her symptoms. Laboratory analysis of peripheral blood lymphocytes was targeted at genetic loci associated with ataxic disorders. Allelic expansion of the ataxin-2 gene was identified. Spinocerebellar ataxia type 2 (SCA2) was diagnosed as a comorbid genetic condition in this patient.

McEwan, I. J. (2001). "Structural and functional alterations in the androgen receptor in spinal bulbar muscular atrophy." Biochem Soc Trans 29(Pt 2): 222-7.
The androgen receptor is a member of the nuclear receptor superfamily, and regulates gene expression in response to the steroid hormones testosterone and dihydrotestosterone. Mutations in the receptor have been correlated with a diverse range of clinical conditions, including androgen insensitivity, prostate cancer and spinal bulbar muscular atrophy, a neuromuscular degenerative condition. The latter is caused by expansion of a polyglutamine repeat within the N-terminal domain of the receptor. Thus the androgen receptor is one of a growing number of neurodegenerative disease-associated proteins, including huntingtin (Huntington's disease), ataxin-1 (spinocerebellar ataxia, type 1) and ataxin-3 (spinocerebellar ataxia, type 3), which show expansion of CAG triplet repeats. Although widely studied, the functions of huntingtin, ataxin-1 and ataxin-3 remain unknown. The androgen receptor, which has a well-recognized function in gene regulation, provides a unique opportunity to investigate the functional significance of poly(amino acid) repeats in normal and disease states.

Matilla, A., C. Gorbea, et al. (2001). "Association of ataxin-7 with the proteasome subunit S4 of the 19S regulatory complex." Hum Mol Genet 10(24): 2821-31.
Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder characterized by ataxia and selective neuronal cell loss caused by the expansion of a translated CAG repeat encoding a polyglutamine tract in ataxin-7, the SCA7 gene product. To gain insight into ataxin-7 function and to decipher the molecular mechanisms of neurodegeneration in SCA7, a two-hybrid assay was performed to identify ataxin-7 interacting proteins. Herein, we show that ataxin-7 interacts with the ATPase subunit S4 of the proteasomal 19S regulatory complex. The ataxin-7/S4 association is modulated by the length of the polyglutamine tract whereby S4 shows a stronger association with the wild-type allele of ataxin-7. We demonstrate that endogenous ataxin-7 localizes to discrete nuclear foci that also contain additional components of the proteasomal complex. Immunohistochemical analyses suggest alterations either of the distribution or the levels of S4 immunoreactivity in neurons that degenerate in SCA7 brains. Immunoblot analyses demonstrate reduced levels of S4 in SCA7 cerebella without evident alterations in the levels of other proteasome subunits. These results suggest a role for S4 and ubiquitin-mediated proteasomal proteolysis in the molecular pathogenesis of SCA7.

Lebre, A. S., L. Jamot, et al. (2001). "Ataxin-7 interacts with a Cbl-associated protein that it recruits into neuronal intranuclear inclusions." Hum Mol Genet 10(11): 1201-13.
Spinocerebellar ataxia 7 (SCA7) is a neurodegenerative disease caused by expansion of a CAG repeat in the coding region of the SCA7 gene. The disease primarily affects the cerebellum and the retina, but also many other central nervous system (CNS) structures as the disease progresses. Ataxin-7, encoded by the SCA7 gene, is a protein of unknown function expressed in many tissues including the CNS. In normal brain, ataxin-7 is found in the cytoplasm and/or nucleus of neurons, but in SCA7 brain ataxin-7 accumulates in intranuclear inclusions. Ataxin-7 is expressed ubiquitously, but mutation leads to neuronal death in only certain areas of the brain. This selective pattern of degeneration might be explained by interaction with a partner that is specifically expressed in vulnerable cells. We used a two-hybrid approach to screen a human retina cDNA library for ataxin-7-binding proteins, and isolated R85, a splice variant of Cbl-associated protein (CAP). R85 and CAP are generated by alternative splicing of the gene SH3P12 which we localized on chromosome 10q23-q24. The interaction between ataxin-7 and the SH3P12 gene products (SH3P12GPs) was confirmed by pull-down and co-immunoprecipitation. SH3P12GPs are expressed in Purkinje cells in the cerebellum. Ataxin-7 colocalizes with full-length R85 (R85FL) in co-transfected Cos-7 cells and with one of the SH3P12GPs in neuronal intranuclear inclusions in brain from a SCA7 patient. We propose that this interaction is part of a physiological pathway related to the function or turnover of ataxin-7. Its role in the pathophysiological process of SCA7 disease is discussed.

La Spada, A. R., Y. H. Fu, et al. (2001). "Polyglutamine-expanded ataxin-7 antagonizes CRX function and induces cone-rod dystrophy in a mouse model of SCA7." Neuron 31(6): 913-27.
Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant disorder caused by a CAG repeat expansion. To determine the mechanism of neurotoxicity, we produced transgenic mice and observed a cone-rod dystrophy. Nuclear inclusions were present, suggesting that the disease pathway involves the nucleus. When yeast two-hybrid assays indicated that cone-rod homeobox protein (CRX) interacts with ataxin-7, we performed further studies to assess this interaction. We found that ataxin-7 and CRX colocalize and coimmunoprecipitate. We observed that polyglutamine-expanded ataxin-7 can dramatically suppress CRX transactivation. In SCA7 transgenic mice, electrophoretic mobility shift assays indicated reduced CRX binding activity, while RT-PCR analysis detected reductions in CRX-regulated genes. Our results suggest that CRX transcription interference accounts for the retinal degeneration in SCA7 and thus may provide an explanation for how cell-type specificity is achieved in this polyglutamine repeat disease.

Kozlov, G., J. F. Trempe, et al. (2001). "Structure and function of the C-terminal PABC domain of human poly(A)-binding protein." Proc Natl Acad Sci U S A 98(8): 4409-13.
We have determined the solution structure of the C-terminal quarter of human poly(A)-binding protein (hPABP). The protein fragment contains a protein domain, PABC [for poly(A)-binding protein C-terminal domain], which is also found associated with the HECT family of ubiquitin ligases. By using peptides derived from PABP interacting protein (Paip) 1, Paip2, and eRF3, we show that PABC functions as a peptide binding domain. We use chemical shift perturbation analysis to identify the peptide binding site in PABC and the major elements involved in peptide recognition. From comparative sequence analysis of PABC-binding peptides, we formulate a preliminary PABC consensus sequence and identify human ataxin-2, the protein responsible for type 2 spinocerebellar ataxia (SCA2), as a potential PABC ligand.

Kim, J. Y., S. S. Park, et al. (2001). "Molecular analysis of Spinocerebellar ataxias in Koreans: frequencies and reference ranges of SCA1, SCA2, SCA3, SCA6, and SCA7." Mol Cells 12(3): 336-41.
Spinocerebellar ataxias (SCAs) are a heterogeneous group of neurodegenerative disorders. CAG repeat expansions in the causative genes have been identified as the basic cause of several types of SCAs, and have been used for the diagnoses and classifications of patients with ataxia. In order to assess the frequency and CAG repeat size ranges of SCAs, and to establish an effective strategy for molecular diagnosis, we performed a molecular analysis of SCA1, SCA2, SCA3, SCA6, and SCA7 in 76 patients. These patients were as follows: 32 with dominant inheritance, 39 sporadic cases, and 5 with unknown family histories. The normal and affected CAG repeat size ranges were established at five SCA loci in Koreans, which was consistent with previous reports. The total prevalence of the five types of SCAs was 39.5% in the 76 patients with ataxia, regardless of their family history. It was 75.0% in the 32 families with a dominant inheritance. The most frequent type was SCA3 (15.8%), followed by SCA2 (14.5%). Both types combined formed 76.7% of the 30 patients with CAG expansions. SCA1, SCA6, and SCA7 were less frequent, affecting 3.9%, 2.6%, and 2.6% of the cases, respectively. This mutation spectrum is quite different from a previous report concerning Koreans, but is similar to the distributions that are seen in several ethnic populations worldwide. For a correct and effective diagnosis of SCAs, we suggest that a molecular diagnosis be undertaken, even in patients without a family history, as well as those with a family history. A stepwise approach is also recommended. Patients with ataxia should be tested for SCA2 and SCA3. Individuals testing negative should be tested for SCA1, SCA6, and SCA7.

Kiehl, T. R., H. Shibata, et al. (2001). "Identification and expression of a mouse ortholog of A2BP1." Mamm Genome 12(8): 595-601.
Human ataxin-2 contains a polyglutamine repeat that is expanded in patients with spinocerebellar ataxia type 2 (SCA2). Ataxin-2 is highly conserved in evolution with orthologs in mouse, Caenorhabditis elegans, and Drosophila melanogaster. It interacts at its C-terminus with ataxin-2 binding protein 1, A2BP1. This study presents a highly conserved mouse ortholog of A2BP1, designated A2bp1. The amino acid sequence of the human and mouse protein is 97.6% identical. This remarkable degree of conservation supports the fact that these proteins have an important basic function in development and differentiation. Sequence analysis reveals the existence of RNA binding motifs. The A2bp1 transcript was found in various regions of the CNS including cerebellum, cerebral cortex, brain stem, and thalamus/hypothalamus. The A2bp1 protein was detected by immunocytochemistry in the CNS and connective tissue of the mouse embryo starting at stage E11, as well as in the heart at all stages. Mouse embryos showed varying expression of A2bp1 at all stages. Previous studies in other model systems had implicated the orthologs of ataxin-2 and A2BP1 in development. This study suggests a role for A2bp1 in embryogenesis as well as in the adult nervous system, possibly mediated by a function in RNA distribution or processing.

Kaemmerer, W. F., C. M. Rodrigues, et al. (2001). "Creatine-supplemented diet extends Purkinje cell survival in spinocerebellar ataxia type 1 transgenic mice but does not prevent the ataxic phenotype." Neuroscience 103(3): 713-24.
It is not known why expression of a protein with an expanded polyglutamine region is pathogenic in spinocerebellar ataxia, Huntington's disease and several other neurodegenerative diseases. Dietary supplementation with creatine improves survival and motor performance and delays neuronal atrophy in the R6/2 transgenic mouse model of Huntington's disease. These effects may be due to improved energy and calcium homeostasis, enhanced presynaptic glutamate uptake, or protection of mitochondria from the mitochondrial permeability transition. We tested the effects of a 2% creatine-supplemented diet and treatment with taurine-conjugated ursodeoxycholic acid, a bile constituent that can inhibit the mitochondrial permeability transition, on ataxia and Purkinje cell survival in a transgenic model of spinocerebellar ataxia type 1. After 24 weeks, transgenic mice on the 2% creatine diet had cerebellar phosphocreatine levels that were 72.5% of wildtype controls, compared to 26.8% in transgenic mice fed a control diet. The creatine diet resulted in maintenance of Purkinje cell numbers in these transgenic mice at levels comparable to wildtype controls, while transgenic mice fed a control diet lost over 25% of their Purkinje cell population. Nevertheless, the ataxic phenotype was neither improved nor delayed. Repeated s.c. ursodeoxycholic acid injections markedly elevated ursodeoxycholic acid levels in the brain without adverse effects, but provided no improvement in phenotype or cell survival in spinocerebellar ataxia type 1 mice.These results demonstrate that preserving neurons from degeneration is insufficient to prevent a behavioral phenotype in this transgenic model of polyglutamine disease. In addition, we suggest that the means by which creatine mitigates against the neurodegenerative effects of an ataxin-1 protein containing an expanded polyglutamine region is through mechanisms other than stabilization of mitochondrial membranes.

Inoue, T., X. Lin, et al. (2001). "Calcium dynamics and electrophysiological properties of cerebellar Purkinje cells in SCA1 transgenic mice." J Neurophysiol 85(4): 1750-60.
Cerebellar Purkinje cells (PCs) from spinocerebellar ataxia type 1 (SCA1) transgenic mice develop dendritic and somatic atrophy with age. Inositol 1,4,5-trisphosphate receptor type 1 and the sarco/endoplasmic reticulum Ca(2+) ATPase pump, which regulate [Ca(2+)](i), are expressed at lower levels in these cells compared with the levels in cells from wild-type (WT) mice. To examine PCs in SCA1 mice, we used whole-cell patch clamp recording combined with fluorometric [Ca(2+)](i) and [Na(+)](i) measurements in cerebellar slices. PCs in SCA1 mice had Na(+) spikes, Ca(2+) spikes, climbing fiber (CF) electrical responses, parallel fiber (PF) electrical responses, and metabotropic glutamate receptor (mGluR)-mediated, PF-evoked Ca(2+) release from intracellular stores that were qualitatively similar to those recorded from WT mice. Under our experimental conditions, it was easier to evoke the mGluR-mediated secondary [Ca(2+)](i) increase in SCA1 PCs. The membrane resistance of SCA1 PCs was 3.3 times higher than that of WT cells, which correlated with the 1.7 times smaller cell body size. Most SCA1 PCs (but not WT) had a delayed onset (about 50--200 ms) to Na(+) spike firing induced by current injection. This delay was increased by hyperpolarizing prepulses and was eliminated by 4-aminopyridine, which suggests that this delay was due to enhancement of the A-like K(+) conductance in the SCA1 PCs. In response to CF stimulation, most PCs in mutant and WT mice had rapid, widespread [Ca(2+)](i) changes that recovered in <200 ms. Some SCA1 PCs showed a slow, localized, secondary Ca(2+) transient following the initial CF Ca(2+) transient, which may reflect release of Ca(2+) from intracellular stores. Thus, with these exceptions, the basic physiological properties of mutant PCs are similar to those of WT neurons, even with dramatic alteration of their morphology and downregulation of Ca(2+) handling molecules.

Fusco, F. R., M. T. Viscomi, et al. (2001). "Localization of ataxin-2 within the cerebellar cortex of the rat." Brain Res Bull 56(3-4): 343-7.
Spinocerebellar ataxia type 2 is caused by a polyglutamine stretch in the protein ataxin-2 that is due to an expansion of a CAG repeat in the spinocerebellar ataxia-2 gene. The function of wild-type ataxin-2 has not been clarified. A widespread distribution of this protein throughout the brain has been reported. We examined the expression of ataxin-2 in cortical cerebellar cells of the adult rat. We performed a single label immunohistochemical study of ataxin-2 and a single label immunofluorescence study of ataxin-2 and zebrin on adjacent sections, to compare the distribution of the observed parasagittal band pattern. We also performed a double label immunofluorescence study of ataxin-2 and one of each parvalbumin, calbindin, and calretinin. Single label studies revealed that between 50% and 70% of the Purkinje cells express ataxin-2. The abundance of ataxin-2 was different between hemisphere and vermis, with a clear prevalence for the former. Furthermore, the distribution of ataxin-2-positive Purkinje cells showed a peculiar alternating parasagittal band pattern. Among the other cortical cerebellar cells only basket and granule cells showed ataxin-2 staining. Our dual label studies showed that about 50% of calbindin and more than 70% of parvalbumin-immunoreactive Purkinje cells were also labeled for ataxin-2. The uneven distribution of ataxin-2 expression in the Purkinje cell layer does not support the hypothesized link between ataxin-2 content and cell vulnerability. The differences in ataxin-2 expression among the cell types of cerebellar cortex, on the other hand, suggest a possible correlation between ataxin-2 content and cell function.

Evert, B. O., I. R. Vogt, et al. (2001). "Inflammatory genes are upregulated in expanded ataxin-3-expressing cell lines and spinocerebellar ataxia type 3 brains." J Neurosci 21(15): 5389-96.
Spinocerebellar ataxia type 3 (SCA3) is a polyglutamine disorder caused by a CAG repeat expansion in the coding region of a gene encoding ataxin-3. To study putative alterations of gene expression induced by expanded ataxin-3, we performed PCR-based cDNA subtractive hybridization in a cell culture model of SCA3. In rat mesencephalic CSM14.1 cells stably expressing expanded ataxin-3, we found a significant upregulation of mRNAs encoding the endopeptidase matrix metalloproteinase 2 (MMP-2), the transmembrane protein amyloid precursor protein, the interleukin-1 receptor-related Fos-inducible transcript, and the cytokine stromal cell-derived factor 1alpha (SDF1alpha). Immunohistochemical studies of the corresponding or associated proteins in human SCA3 brain tissue confirmed these findings, showing increased expression of MMP-2 and amyloid beta-protein (Abeta) in pontine neurons containing nuclear inclusions. In addition, extracellular Abeta-immunoreactive deposits were detected in human SCA3 pons. Furthermore, pontine neurons of SCA3 brains strongly expressed the antiinflammatory interleukin-1 receptor antagonist, the proinflammatory cytokine interleukin-1beta, and the proinflammatory chemokine SDF1. Finally, increased numbers of reactive astrocytes and activated microglial cells were found in SCA3 pons. These results suggest that inflammatory processes are involved in the pathogenesis of SCA3.

Einum, D. D., J. J. Townsend, et al. (2001). "Ataxin-7 expression analysis in controls and spinocerebellar ataxia type 7 patients." Neurogenetics 3(2): 83-90.
Expansion of polymorphic CAG repeats encoding polyglutamine cause at least eight inherited neurodegenerative diseases, including Huntington disease and the spinocerebellar ataxias. However, the pathways by which proteins containing expanded polyglutamine tracts cause disease remain unclear. To gain insight into the function of the SCA7 gene product, ataxin-7, as well as its contribution to cell death in spinocerebellar ataxia type 7 (SCA7), polyclonal antibodies were generated and ataxin-7 expression was examined within neuronal tissues from controls and three SCA7 patients. Immunoblotting demonstrates that ataxin-7 is widely expressed but that expression levels vary between tissues. Immunohistochemical analyses indicate that ataxin-7 is expressed within neurons both affected and unaffected in SCA7 pathology and that subcellular localization varies depending upon the neuronal subtype. Additionally, ataxin-7 staining was detected throughout control retina, including intense staining within the cell bodies and photosensitive outer segments of cone photoreceptors. Anti-ataxin-7 antibodies revealed intranuclear inclusions within surviving inferior olivary and cortical pyramidal neurons, as well as within surviving photoreceptor and ganglion cells of SCA7 patients harboring either 42 or 66 CAG repeats at the SCA7 locus. In contrast, inclusion formation was not detected within neurons of a patient with 41 repeats. This study broadens the current understanding of ataxin-7 localization and incorporates for the first time analysis of late-onset SCA7 patients where polyglutamine tract lengths are relatively shorter and disease course less severe than in previously described infantile-onset cases.

Cummings, C. J., Y. Sun, et al. (2001). "Over-expression of inducible HSP70 chaperone suppresses neuropathology and improves motor function in SCA1 mice." Hum Mol Genet 10(14): 1511-8.
Many neurodegenerative diseases are caused by gain-of-function mechanisms in which the disease-causing protein is altered, becomes toxic to the cell, and aggregates. Among these 'proteinopathies' are Alzheimer's and Parkinson's disease, prion disorders and polyglutamine diseases. Members of this latter group, also known as triplet repeat diseases, are caused by the expansion of unstable CAG repeats coding for glutamine within the respective proteins. Spinocerebellar ataxia type 1 (SCA1) is one such disease, characterized by loss of motor coordination due to the degeneration of cerebellar Purkinje cells and brain stem neurons. In SCA1 and several other polyglutamine diseases, the expanded protein aggregates into nuclear inclusions (NIs). Because these NIs accumulate molecular chaperones, ubiquitin and proteasomal subunits--all components of the cellular protein re-folding and degradation machinery--we hypothesized that protein misfolding and impaired protein clearance might underlie the pathogenesis of polyglutamine diseases. Over-expressing specific chaperones reduces protein aggregation in transfected cells and suppresses neurodegeneration in invertebrate animal models of polyglutamine disorders. To determine whether enhancing chaperone activity could mitigate the phenotype in a mammalian model, we crossbred SCA1 mice with mice over-expressing a molecular chaperone (inducible HSP70 or iHSP70). We found that high levels of HSP70 did indeed afford protection against neurodegeneration.

Chai, Y., L. Wu, et al. (2001). "The role of protein composition in specifying nuclear inclusion formation in polyglutamine disease." J Biol Chem 276(48): 44889-97.
Intracellular inclusions are a unifying feature of polyglutamine (polyQ) neurodegenerative diseases, yet each polyQ disease displays a unique pattern of neuronal degeneration. This implies that the protein context of expanded polyQ plays an important role in establishing selective neurotoxicity. Here, in studies of the spinocerebellar ataxia type 3 disease protein ataxin-3, we demonstrate that the protein sequence surrounding polyQ specifies the constituents of nuclear inclusions (NI) formed by the disease protein. The nuclear proteins cAMP response element-binding protein-binding protein (CBP) and Mastermind-like-1 strongly colocalize only to NI formed by full-length ataxin-3, whereas the splicing factor SC35 colocalizes only to NI formed by a polyQ-containing, carboxyl-terminal fragment of ataxin-3. These differences in NI formation reflect specific protein interactions normally undertaken by ataxin-3, as both normal and mutant full-length ataxin-3 co-immunoprecipitate with CBP and sediment on density gradients as macromolecular complexes. Moreover, normal ataxin-3 represses cAMP response element-binding protein-mediated transcription, indicating a functional consequence of ataxin-3 interactions with CBP. Finally, we show that mutant ataxin-3 forms insoluble intranuclear complexes, or microaggregates, before NI can be detected, implying a precursor-product relationship. These results suggest that protein context-dependent recruitment of nuclear proteins to intranuclear microaggregates, and subsequently to NI, may contribute to selective neurotoxicity in polyQ diseases.

Calabresi, V., S. Guida, et al. (2001). "Phenotypic effects of expanded ataxin-1 polyglutamines with interruptions in vitro." Brain Res Bull 56(3-4): 337-42.
Spinocerebellar ataxia type 1 is a neurodegenerative disease caused by expansion of an uninterrupted glutamine repeat in ataxin-1 protein. Protein aggregation and immunoreactivity to 1C2 monoclonal antibody are two distinct pathognomonic features of expanded ataxin-1, as well as of other polyglutamine disorders. Rare cases of non-affected elderly subjects carrying expanded ataxin-1 alleles were found in random population. However, in these alleles the glutamine stretch was interrupted by histidines. Due to lack of phenotype, these alleles should be considered "normal". Most importantly, occurrence of these unusual alleles provides a unique opportunity to investigate which molecular properties of expanded ataxin-1 are not coupled to polyglutamine pathogenesis. Towards this goal, we compared in vitro the immunoreactivity to 1C2 antibody and the ability to form aggregates of interrupted and uninterrupted alleles. Immunoblotting showed that expanded-interrupted ataxin-1 had an affinity to 1C2 resembling that of normal ataxin-1. On the contrary, filter assay showed that aggregation rate of expanded-interrupted ataxin-1 resembles that of expanded-uninterrupted ataxin-1. These observations indicate that affinity for 1C2 does not directly correlate with self-aggregation of ataxin-1. Moreover, self-aggregation is not directly affected by histidine interruptions. In conclusion, these results support the hypothesis that mechanisms underlying neuronal degeneration are triggered by protein misfolding rather than by protein aggregation.

Bevivino, A. E. and P. J. Loll (2001). "An expanded glutamine repeat destabilizes native ataxin-3 structure and mediates formation of parallel beta -fibrils." Proc Natl Acad Sci U S A 98(21): 11955-60.
The protein ataxin-3 contains a polyglutamine region; increasing the number of glutamines beyond 55 in this region gives rise to the neurodegenerative disease spinocerebellar ataxia type 3. This disease and other polyglutamine expansion diseases are characterized by large intranuclear protein aggregates (nuclear inclusions). By using full-length human ataxin-3, we have investigated the changes in secondary structure, aggregation behavior, and fibril formation associated with an increase from the normal length of 27 glutamines (Q27 ataxin-3) to a pathogenic length of 78 glutamines (Q78 ataxin-3). Q78 ataxin-3 aggregates strongly and could be purified only when expressed with a solubility-enhancing fusion-protein partner. A marked decrease in alpha-helical secondary structure accompanies expansion of the polyglutamine tract, suggesting destabilization of the native protein. Proteolytic removal of the fusion partner in the Q78 protein, but not in the Q27 protein, leads to the formation of SDS-resistant aggregates and Congo-red reactive fibrils. Infrared spectroscopy of fibrils reveals a high beta-sheet content and suggests a parallel, rather than an antiparallel, sheet conformation. We present a model for a polar zipper composed of parallel polyglutamine beta-sheets. Our data show that intact ataxin-3 is fully competent to form aggregates, and posttranslational cleavage or other processing is not necessary to generate a misfolding event. The data also suggest that the protein aggregation phenotype associated with glutamine expansion may derive from two effects: destabilization of the native protein structure and an inherent propensity for beta-fibril formation on the part of glutamine homopolymers.

Affaitati, A., T. de Cristofaro, et al. (2001). "Identification of alternative splicing of spinocerebellar ataxia type 2 gene." Gene 267(1): 89-93.
Spinocerebellar ataxia 2 (SCA-2) is a neurodegenerative disorder caused by the expansion of an unstable CAG/polyglutamine repeat located at the NH(2)-terminus of ataxin-2 protein. Ataxin-2 is composed by 1312 aminoacids and it is expressed ubiquitously in human tissues. To date, the function of ataxin-2 is not known. In this study, we report the characterization of an alternative splice variant of human ataxin-2. The splice transcript lacks the exon 21 and connects exon 20 to exon 22 with the same reading frame of the full length mRNA. This novel isoform of ataxin-2 is conserved in the mouse. It is named type IV to differentiate it from type II splice variant lacking exon 10 (present in human and mouse cDNAs) and from type III, lacking exon 10 and exon 11 seen in mouse. Type IV of human ataxin-2 cDNA is predicted to encode a protein of 1294 residues. Both the full length and the type IV transcript of ataxin-2 are present in several human tissues, including brain, spinal cord, cerebellum, heart and placenta. These findings allow the hypothesis that type I, II and IV of human ataxin-2 might perform different functions.

Abe, T., K. Abe, et al. (2001). "Ophthalmological findings in patients with spinocerebellar ataxia type 1 are not correlated with neurological anticipation." Graefes Arch Clin Exp Ophthalmol 239(10): 722-8.
BACKGROUND: Optic atrophy, attenuation of the oscillatory potentials (OPs) of the electroretinogram (ERG), and enlargement of corneal endothelial cells, have been reported in patients with spinocerebellar ataxia type 1 (SCA1). These patients have a trinucleotide repeat expansion in the SCA1 gene and show neurological anticipation. The purpose of this study was to determine whether the ophthalmological findings are correlated with the neurological disorders, and whether ophthalmological anticipation is present in patients with SCA1. METHODS: The visual acuity, ERGs, and corneal endothelial cell density were examined in 14 patients whose DNA analysis revealed an expanded trinucleotide repeat in an allele of the SCA1 gene. The results of the tests were compared with the trinucleotide repeat number and the duration of the neuronal disease. RESULTS: The neurological disorders in the patients showed anticipation. The negative correlation between the trinucleotide repeat number and the neurological disorder was statistically significant (P<0.0001). However, the correlations between trinucleotide repeat number and visual acuity, amplitude of OPs, and corneal endothelial cell density were not significant. Statistically significant correlations were found between the duration of the neuronal disease and the visual acuity, OPs, and corneal endothelial cell density (P<0.0001, P=0.0004, and P<0.0001, respectively). The ophthalmological disorders were prominent in patients who had neuronal disease for more than 10 years. CONCLUSION: Unlike the neurological findings, the ophthalmological disorders in patients with SCA1 were not correlated with the trinucleotide repeat number of the SCA1 gene. The ophthalmological findings were most highly correlated with the duration of the neuronal disease.

Yvert, G., K. S. Lindenberg, et al. (2000). "Expanded polyglutamines induce neurodegeneration and trans-neuronal alterations in cerebellum and retina of SCA7 transgenic mice." Hum Mol Genet 9(17): 2491-506.
Among the eight progressive neurodegenerative diseases caused by polyglutamine expansions, spinocerebellar ataxia type 7 (SCA7) is the only one to display degeneration in both brain and retina. We show here that mice overexpressing full-length mutant ataxin-7[Q90] either in Purkinje cells or in rod photoreceptors have deficiencies in motor coordination and vision, respectively. In both models, although with different time courses, an N-terminal fragment of mutant ataxin-7 accumulates into ubiquitinated nuclear inclusions that recruit a distinct set of chaperone/proteasome subunits. A severe degeneration is caused by overexpression of ataxin-7[Q90] in rods, whereas a similar overexpression of normal ataxin-7[Q10] has no obvious effect. The degenerative process is not limited to photoreceptors, showing secondary alterations of post-synaptic neurons. These findings suggest that proteolytic cleavage of mutant ataxin-7 and trans-neuronal responses are implicated in the pathogenesis of SCA7.

Vig, P. J., S. H. Subramony, et al. (2000). "Relationship between ataxin-1 nuclear inclusions and Purkinje cell specific proteins in SCA-1 transgenic mice." J Neurol Sci 174(2): 100-10.
Spinocerebellar ataxia-1 (SCA-1), like other polyglutamine diseases, is associated with aggregation of mutant protein ataxin-1 in the nuclei of susceptible neurons. The role of ataxin-1 aggregates in the pathogenesis of susceptible neurons, especially cerebellar Purkinje cells, is unknown. The present study was initiated to determine the temporal relationship between ataxin-1 aggregation and the sequence of specific biochemical changes in Purkinje cells in SCA-1 transgenic mice (TM). Earlier, we demonstrated that SCA-1 TM with no Purkinje cell loss and no alterations in home cage behavior show decreased expression of calcium-binding proteins calbindin-D28k (CaB) and parvalbumin (PV) in Purkinje cells. To determine if increased expression of mutant ataxin-1 in TM is also associated with earlier biochemical changes in Purkinje cells, both heterozygous and homozygous (B05 line of SCA-1) TM were used. The age of onset of ataxia in SCA-1 TM was at 12 weeks in heterozygotes and 6 weeks in homozygotes. In 6 week old heterozygous TM, Western blot analysis of growth associated protein 43 (GAP-43) and synaptophysin revealed no significant alterations as compared with the age-matched nontransgenic mice (nTM), whereas CaB was significantly reduced. beta-III-Tubulin was used as a specific Purkinje cell marker protein, immunohistochemical localization showed strong beta-III-tubulin immunoreactivity (IR) in Purkinje cells in 6 week old heterozygous TM, whereas CaB and PV IR were markedly reduced in the same neurons (double immunofluorescence staining). Most Purkinje cells from heterozygous (12 weeks old) and homozygous (6 weeks old) TM contained ataxin-1 nuclear inclusions (NIs). Cells with and without visible NIs revealed reduced PV and CaB IR; however, the changes were overtly more severe in cells with visible NIs. In contrast, the same cells were strongly immunoreactive to beta-III-tubulin. CaB, which is also present in the nucleus, colocalized with ataxin-1 and ubiquitin positive NIs. Further, RT-PCR analysis of CaB mRNA in the cerebellum in 6 week old heterozygous TM demonstrated a significant decrease in mRNA in comparison with the aged-matched nTM. These data suggest that there are selective alterations in the expression of CaB and PV in Purkinje cells which possibly occur earlier than ataxin-1 aggregation. Further, we speculate that ataxin-1 aggregates may not be toxic in general; however, they may deplete specific proteins essential for Purkinje cell viability in SCA-1 TM.

Tang, B., C. Liu, et al. (2000). "Frequency of SCA1, SCA2, SCA3/MJD, SCA6, SCA7, and DRPLA CAG trinucleotide repeat expansion in patients with hereditary spinocerebellar ataxia from Chinese kindreds." Arch Neurol 57(4): 540-4.
OBJECTIVE: To assess the frequency of SCA1 (spinocerebellar ataxia type 1), SCA2, SCA3/MJD (spinocerebellar ataxia type 3/Machado-Joseph disease), SCA6, SCA7, and DRPLA (dentatorubropallidoluysian atrophy) CAG trinucleotide repeat expansions [(CAG)n] among persons diagnosed with hereditary SCA from Chinese families. PATIENTS AND METHODS: Spinocerebellar ataxia type 1, SCA2, SCA3/MJD, SCA6, SCA7, and DRPLA (CAG)n mutation were detected with the polymerase chain reaction, highly denaturing polyacrylamide gel electrophoresis, and silver staining technique in 167 patients with autosomal dominant SCA from 85 Chinese families and 37 patients with sporadic SCA. RESULTS: Spinocerebellar ataxia type 1 (CAG)n mutation in 7 patients from 4 kindreds (4.70%) was expanded to 53 to 62 repeats. Spinocerebellar ataxia type 2 (CAG)n mutation in 12 patients from 5 kindreds (5.88%) was expanded to 42 to 47 repeats. Spinocerebellar ataxia type 3/Machado-Joseph disease (CAG)n mutation in 83 patients from 41 kindreds (48.23%) was expanded to 68 to 83 repeats. Sixty-five patients from 35 kindreds (41.19%) and 37 patients with sporadic SCA did not test positive for SCA1, SCA2, SCA3/MJD, SCA6, SCA7, or DRPLA. There was a predictable inverse relationship between the number of CAG repeats and the age at onset for SCA3/MJD and SCA2. Clinically, dementia and hyporeflexia were more frequent in patients with SCA2, while spasticity, hyperreflexia, and Babinski signs were more frequent in patients with SCA3/ MJD, and those might be helpful in clinical work to primarily distinguish patients with SCA3/MJD and SCA2 from others with different types of SCA. CONCLUSIONS: The frequency of SCA3/MJD is substantially higher than that of SCA1 and SCA2 in patients with autosomal dominant SCA from Chinese kindreds, who are non-Portuguese. Clinical expressions of the various types of SCAs overlap one another; therefore, for clinical study it is important to make a gene diagnosis and genetic classification for patients with SCA.

Shibata, H., D. P. Huynh, et al. (2000). "A novel protein with RNA-binding motifs interacts with ataxin-2." Hum Mol Genet 9(9): 1303-13.
Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of a polyglutamine tract in ataxin-2, a protein of unknown function. Using the yeast two-hybrid system, we identified a novel protein, A2BP1 (ataxin-2 binding protein 1) which binds to the C-terminus of ataxin-2. Northern blot analysis showed that A2BP1 was predominantly expressed in muscle and brain. By immunocfluorescent staining, A2BP1 and ataxin-2 were both localized to the trans -Golgi network. Immunocytochemistry showed that A2BP1 was expressed in the cytoplasm of Purkinje cells and dentate neurons in a pattern similar to that seen for ataxin-2 labeling. Western blot analysis of subcellular fractions indicated enrichment of A2BP1 in the same fractions as ataxin-2. Sequence analysis of the A2BP1 cDNA revealed an RNP motif that is highly conserved among RNA-binding proteins. A2BP1 had striking homology with a human cDNA clone, P83A20, of unknown function and at least two copies of A2BP1 homologs are found in the Caenorhabditis elegans genome database. A2BP1 and related proteins appear to form a novel gene family sharing RNA-binding motifs.

Orr, H. T. (2000). "The ins and outs of a polyglutamine neurodegenerative disease: spinocerebellar ataxia type 1 (SCA1)." Neurobiol Dis 7(3): 129-34.
Polyglutamine neurodegenerative disorders are characterized by the expansion of a glutamine tract within the mutant disease-causing protein. Expression of the mutant protein induces a progressive loss of neuronal function and the subsequent neurodegeneration of a set of neurons characteristic to each disease. Spinocerebellar ataxia type 1 (SCA1) is one polyglutamine disease where various experimental model systems, in particular transgenic mice, have been utilized to dissect the molecular and cellular events important for disease. This review summarizes these findings and places them in a context of potential future research directions.

Onodera, Y., M. Aoki, et al. (2000). "High prevalence of spinocerebellar ataxia type 1 (SCA1) in an isolated region of Japan." J Neurol Sci 178(2): 153-8.
Autosomal dominant cerebeller ataxias (ADCAs) are a heterogeneous group of neurodegenerative disorders that differ in both the clinical manifestations and modes of inheritance. At present, eight different genes causing ADCAs have been found: spinocerebeller ataxia type 1 (SCA1), SCA2, SCA3/Machado-Joseph disease (MJD), SCA6, SCA7, SCA8, SCA12 and dentatorubropallidoluysian atrophy (DRPLA). The relative prevalence of each mutation varies according to race and native place. We studied 117 unrelated ADCA families that originated from the Tohoku District in the northernmost part of Honshu Island in Japan (mainly Miyagi Prefecture in the central part of Tohoku District). The SCA1 mutation was the most frequent among the known disorders (24.8% of all such families). The relative prevalence of SCA1 in the Tohoku District is very high compared with the values already reported from other regions in the world. Because the population of this area had seldom moved, the alleles with SCA1 mutations (including alleles with an intermediate CAG repeat number) are assumed to have been present in this area for a long time.

Lorenzetti, D., K. Watase, et al. (2000). "Repeat instability and motor incoordination in mice with a targeted expanded CAG repeat in the Sca1 locus." Hum Mol Genet 9(5): 779-85.
To elucidate the pathophysiology of spinocerebellar ataxia type 1 (SCA1) and to evaluate repeat length instability in the context of the mouse Sca1 gene, we generated knock-in mice by inserting an expanded tract of 78 CAG repeats into the mouse Sca1 locus. Mice heterozygous for the CAG expansion show intergenerational repeat instability (+2 to -6) at a much higher frequency in maternal transmission than in paternal transmission. The majority of changes transmitted through the female germline were small contractions, as in humans, whereas small expansions occurred more frequently in paternal transmission. The frequency of intergenerational changes was age dependent for both paternal and maternal transmissions. Mice homozygous for mutant ataxin-1 on a C57BL/6J-129/SvEv mixed background performed significantly less well on the rotating rod than did wild-type littermates at 9 months of age, although they were not ataxic by cage behavior. Histological examination of brain tissue from mutant mice up to 18 months of age revealed none of the neuropathological changes observed in other transgenic models overexpressing expanded polyglutamine tracts. These data suggest that, even with 78 glutamines, prolonged exposure to mutant ataxin-1 at endogenous levels is necessary to produce a neurological phenotype reminiscent of human SCA1. Pathogenesis is thus a function of polyglutamine length, protein levels and duration of neuronal exposure to the mutant protein.

Lindenberg, K. S., G. Yvert, et al. (2000). "Expression analysis of ataxin-7 mRNA and protein in human brain: evidence for a widespread distribution and focal protein accumulation." Brain Pathol 10(3): 385-94.
Spinocerebellar ataxia 7 (SCA7) is an autosomal dominant neurodegenerative disorder caused by the expansion of a CAG-trinucleotide repeat in the coding region of the SCA7 gene. The expansion is translated into an extended polyglutamine stretch in the protein ataxin-7, a protein of unknown function. By Northern blot analysis expression of ataxin-7 was detected in numerous regions of human brain and some peripheral tissues. It is unknown, however, if ataxin-7 is enriched at sites of the SCA7 pathology. We studied the regional and cellular expression pattern of ataxin-7 at the mRNA level by in situ hybridization histochemistry in normal human brain. Furthermore we used a monoclonal and two polyclonal antibodies raised against the normal ataxin-7 to establish the distribution of this protein in brain, retina and peripheral organs. At the mRNA level ataxin-7 was preferentially expressed in neurons; the regional distribution reflected neuronal packing density. Ataxin-7 immunoreactivity (IR) was similarly widely expressed. In most neurons, ataxin-7 IR was preferentially localized to the cytoplasmatic compartment although some nuclear ataxin-7 IR was detected in most neurons. A more intense and more prominently nuclear ataxin-7 IR was observed in neurons of the pons and the inferior olive, brain regions severly affected by the disease, suggesting that the subcellular localization and abundance of ataxin-7 is regulated in a regionally specific way. Since neurons displaying more intense and more prominently nuclear ataxin-7 IR belonged to the class of susceptible cells in SCA7, an enrichment of normal ataxin-7 in the nuclear compartment may contribute to neurodegeneration. However not all sites of SCA7 pathology displayed a strong cytoplasmatic and nuclear immunoreactivity.

Lin, X., B. Antalffy, et al. (2000). "Polyglutamine expansion down-regulates specific neuronal genes before pathologic changes in SCA1." Nat Neurosci 3(2): 157-63.
The expansion of an unstable CAG repeat causes spinocerebellar ataxia type 1 (SCA1) and several other neurodegenerative diseases. How polyglutamine expansions render the resulting proteins toxic to neurons, however, remains elusive. Hypothesizing that long polyglutamine tracts alter gene expression, we found certain neuronal genes involved in signal transduction and calcium homeostasis sequentially downregulated in SCA1 mice. These genes were abundant in Purkinje cells, the primary site of SCA1 pathogenesis; moreover, their downregulation was mediated by expanded ataxin-1 and occurred before detectable pathology. Similar downregulation occurred in SCA1 human tissues. Altered gene expression may be the earliest mediator of polyglutamine toxicity.

Kiehl, T. R., H. Shibata, et al. (2000). "The ortholog of human ataxin-2 is essential for early embryonic patterning in C. elegans." J Mol Neurosci 15(3): 231-41.
Ataxin-2, the gene product of the human spinocerebellar ataxia type 2 (SCA2) gene, is a protein of unknown function. Ataxin-2 interacts with ataxin-2-binding-protein 1 (A2BP1), a member of a novel family of putative RNA-binding proteins. Because the sequences of ataxin-2 and A2BP1 are evolutionarily conserved, we investigated functional aspects and expression pattern in the nematode Caenorhabditis elegans. Human ataxin-2 has 20.1% amino acid identity and 43.9% similarity to its C. elegans ortholog, designated ATX-2, that encodes a predicted 1026 aa protein. One of the worm orthologs of human A2BP1 is the numerator element FOX-1, with an overall 29.8% aa identity. We studied the expression pattern of atx-2 using the endogenous promotor coupled with a GFP expression vector. Atx-2 was widely expressed in the adult worm with strong expression in muscle and nervous tissue. It was also heavily expressed in the embryo. In order to elucidate the function of atx-2 and fox-1, we conducted RNA interference (RNAi) studies. The interfering dsRNA was introduced into larval L4 stage worms of the N2 strain by microinjection or soaking. DsRNA representing the full-length atx-2 gene resulted in arrested embryonic development in the offspring of all 58 microinjected worms. Nomarski imaging showed embryos in different stages of developmental arrest, indicating an essential role of atx-2 for early embryonic development. When fox-1 was targeted by RNAi, there was a marked reduction in the number of eggs per worm. The results presented here underline previous findings about the interaction of human ataxin-2 and A2BP1.

Jager, M., F. von Rosen, et al. (2000). "[Typical anticipation in type 7 spinocerebellar ataxia]." Nervenarzt 71(10): 835-8.
Spinocerebellar ataxia type 7 (SCA7) belongs to the category of autosomal dominant cerebellar ataxias (ADCA). The clinical picture is characterised by progressive ataxia and macular degeneration. Other common signs are slow saccades, external ophthalmoplegia, and pyramidal tract signs. The disease is caused by the expansion of an unstable CAG trinucleotide repeat in the gene for ataxin 7 on chromosome 3. SCA7 is a rare disorder. The first case in Germany was described only recently. We report two additional patients, father and son, with the molecular genetic diagnosis of SCA7. The father carries a trinucleotide expansion of 42 CAG repeats, the son 51. Normal alleles range from 7 to 35 CAG repeats. Both patients show the typical picture with progressive ataxia and macular degeneration. We found a pronounced anticipation (earlier disease onset in subsequent generations), which is highly characteristic of CAG repeat disorders.

Huynh, D. P., K. Figueroa, et al. (2000). "Nuclear localization or inclusion body formation of ataxin-2 are not necessary for SCA2 pathogenesis in mouse or human." Nat Genet 26(1): 44-50.
Instability of CAG DNA trinucleotide repeats is the mutational mechanism for several neurodegenerative diseases resulting in the expansion of a polyglutamine (polyQ) tract. Proteins with long polyQ tracts have an increased tendency to aggregate, often as truncated fragments forming ubiquitinated intranuclear inclusion bodies. We examined whether similar features define spinocerebellar ataxia type 2 (SCA2) pathogenesis using cultured cells, human brains and transgenic mouse lines. In SCA2 brains, we found cytoplasmic, but not nuclear, microaggregates. Mice expressing ataxin-2 with Q58 showed progressive functional deficits accompanied by loss of the Purkinje cell dendritic arbor and finally loss of Purkinje cells. Despite similar functional deficits and anatomical changes observed in ataxin-1[Q80] transgenic lines, ataxin-2[Q58] remained cytoplasmic without detectable ubiquitination.

Hayes, S., G. Turecki, et al. (2000). "CAG repeat length in RAI1 is associated with age at onset variability in spinocerebellar ataxia type 2 (SCA2)." Hum Mol Genet 9(12): 1753-8.
Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant disorder caused by the expansion of a polymorphic (CAG)(n) tract, which is translated into an expanded polyglutamine tract in the ataxin-2 protein. Although repeat length and age at disease onset are inversely related, approximately 50% of the age at onset variance in SCA2 remains unexplained. Other familial factors have been proposed to account for at least part of this remaining variance in the polyglutamine dis-orders. The ability of polyglutamine tracts to interact with each other, as well as the presence of intra-nuclear inclusions in other polyglutamine disorders, led us to hypothesize that other CAG-containing proteins may interact with expanded ataxin-2 and affect the rate of protein accumulation, and thus influence age at onset. To test this hypothesis, we used step-wise multiple linear regression to examine 10 CAG-containing genes for possible influences on SCA2 age at onset. One locus, RAI1, contributed an additional 4.1% of the variance in SCA2 age at onset after accounting for the effect of the SCA2 expanded repeat. This locus was further studied in SCA3/Machado-Joseph disease (MJD), but did not have an effect on SCA3/MJD age at onset. This result implicates RAI1 as a possible contributor to SCA2 neurodegeneration and raises the possibility that other CAG-containing proteins may play a role in the pathogenesis of other polyglutamine disorders.

Fujigasaki, H., T. Uchihara, et al. (2000). "Ataxin-3 is translocated into the nucleus for the formation of intranuclear inclusions in normal and Machado-Joseph disease brains." Exp Neurol 165(2): 248-56.
Machado-Joseph disease (MJD)/spinocerebellar ataxia type 3 (SCA3) is one of the dominantly inherited cerebellar ataxias. The gene responsible for the disease, a novel gene of unknown function, encodes ataxin-3 containing a polyglutamine stretch. Although it has been known that ataxin-3 is incorporated into neuronal intranuclear inclusions (NIIs) in neurons of affected regions, the relationship between NII formation and neuronal degeneration still remains uncertain. In the present study we show two different conditions in which ataxin-3 is recruited into the nucleus and suggest a process to form nuclear inclusions. In normal brains, wild-type ataxin-3 localizes within the ubiquitin-positive nuclear inclusion, the Marinesco body, indicating that ataxin-3 is recruited into the nuclear inclusion even in the absence of pathologically expanded polyglutamine. In MJD/SCA3 brains, immunohistochemical analyses with anti-ataxin-3 antibody, anti-ubiquitin antibody, and monoclonal antibody 1C2 known to recognize expanded polyglutamine revealed differences in frequency and in diameter among NIIs recognized by each antibody. These results were confirmed in the same inclusions by double immunofluorescent staining, suggesting that expanded ataxin-3 forms a core, thereby recruiting wild-type ataxin-3 into the nucleus around the core portion, and then followed by activation of the ubiquitin/ATP-dependent pathway. Recruitment of ataxin-3 into the nucleus and formation of nuclear inclusion under two different conditions suggest that ataxin-3 may be translocated into the nucleus under certain conditions stressful on neuronal cells such as aging and polyglutamine neurotoxicity.

Fernandez-Funez, P., M. L. Nino-Rosales, et al. (2000). "Identification of genes that modify ataxin-1-induced neurodegeneration." Nature 408(6808): 101-6.
A growing number of human neurodegenerative diseases result from the expansion of a glutamine repeat in the protein that causes the disease. Spinocerebellar ataxia type 1 (SCA1) is one such disease-caused by expansion of a polyglutamine tract in the protein ataxin-1. To elucidate the genetic pathways and molecular mechanisms underlying neuronal degeneration in this group of diseases, we have created a model system for SCA1 by expressing the full-length human SCA1 gene in Drosophila. Here we show that high levels of wild-type ataxin-1 can cause degenerative phenotypes similar to those caused by the expanded protein. We conducted genetic screens to identify genes that modify SCA1-induced neurodegeneration. Several modifiers highlight the role of protein folding and protein clearance in the development of SCA1. Furthermore, new mechanisms of polyglutamine pathogenesis were revealed by the discovery of modifiers that are involved in RNA processing, transcriptional regulation and cellular detoxification. These findings may be relevant to the treatment of polyglutamine diseases and, perhaps, to other neurodegenerative diseases, such as Alzheimer's and Parkinson's disease.

Evidente, V. G., K. A. Gwinn-Hardy, et al. (2000). "Hereditary ataxias." Mayo Clin Proc 75(5): 475-90.
There are many causes of hereditary ataxia. These can be grouped into categories of autosomal recessive, autosomal dominant, and X-linked. Molecularly, many of them are due to trinucleotide repeat expansions. In Friedreich ataxia, the trinucleotide repeat expansions lead to a "loss of function." In the dominant ataxias, the expanded repeats lead to a "gain of function," most likely through accumulation of intranuclear (and less commonly cytoplasmic) polyglutamine inclusions. Channelopathies can also lead to ataxia, especially episodic ataxia. Although phenotypic characteristics are an aid to the clinician, a definitive diagnosis is usually made only through genotypic or molecular studies. Genetic counseling is necessary for the testing of symptomatic and asymptomatic individuals. No effective treatment is yet available for most ataxic syndromes, except for ataxia with isolated vitamin E deficiency and the episodic ataxias.

Davidson, J. D., B. Riley, et al. (2000). "Identification and characterization of an ataxin-1-interacting protein: A1Up, a ubiquitin-like nuclear protein." Hum Mol Genet 9(15): 2305-12.
Expansion of a polyglutamine tract within ataxin-1 causes spinocerebellar ataxia type 1 (SCA1). In this study, we used the yeast two-hybrid system to identify an ataxin-1-interacting protein, A1Up. A1Up localized to the nucleus and cytoplasm of transfected COS-1 cells. In the nucleus, A1Up co-localized with mutant ataxin-1, further demonstrating that A1Up interacts with ataxin-1. Expression analyses demonstrated that A1U mRNA is widely expressed as an approximately 4.0 kb transcript and is present in Purkinje cells, the primary site of SCA1 cerebellar pathology. Sequence comparisons revealed that A1Up contains an N-terminal ubiquitin-like (UbL) region, placing it within a large family of similar proteins. In addition, A1Up has substantial homology to human Chap1/Dsk2, a protein that binds the ATPase domain of the HSP70-like Stch protein. These results suggest that A1Up may link ataxin-1 with the chaperone and ubiquitin-proteasome pathways. In addition, these data support the concept that ataxin-1 may function in the formation and regulation of multimeric protein complexes within the nucleus.

Clark, H. B. and H. T. Orr (2000). "Spinocerebellar ataxia type 1--modeling the pathogenesis of a polyglutamine neurodegenerative disorder in transgenic mice." J Neuropathol Exp Neurol 59(4): 265-70.
Spinocerebellar ataxia type 1 (SCA1) is one of a group of dominantly inherited neurodegenerative diseases caused by a mutant expansion of a polyglutamine-repeated sequence within the affected gene. One of the major cell types affected by the gene (ataxin-1) mutation in SCA1 is the cerebellar Purkinje cell. Targeted expression of mutant ataxin-1 in Purkinje cells of transgenic mice produces an ataxic phenotype with pathological similarities to the human disease. Other transgenic experiments using altered forms of mutant ataxin-1 have shown that nuclear localization of the mutant protein is necessary for pathogenesis and that nuclear aggregates of ubiquitinated mutant protein, while a feature of SCA1 and other polyglutamine diseases, are not a requirement for pathogenesis in transgenic models of SCA1. Present and future generations of transgenic mouse models of SCA1 will be valuable tools to further address mechanisms of pathogenesis in polyglutamine-related disorders.

Cancel, G., C. Duyckaerts, et al. (2000). "Distribution of ataxin-7 in normal human brain and retina." Brain 123 Pt 12: 2519-30.
Spinocerebellar ataxia 7 (SCA7) is a neurodegenerative disease caused by the expansion of a CAG repeat encoding a polyglutamine tract in the protein ataxin-7. We developed antibodies directed against two different parts of the ataxin-7 protein and studied its distribution in brain and peripheral tissue from healthy subjects. Normal ataxin-7 was widely expressed in brain, retina and peripheral tissues, including striated muscle, testis and thyroid gland. In the brain, expression of ataxin-7 was not limited to areas in which neurones degenerate, and the level of expression was not related to the severity of neuronal loss. Immunoreactivity was low in some vulnerable populations of neurones, such as Purkinje cells. In neurones, ataxin-7 was found in the cell bodies and in processes. Nuclear labelling was also observed in some neurones, but was not related to the distribution of intranuclear inclusions observed in an SCA7 patient. In this patient, the proportion of neurones with nuclear labelling was higher, on average, in regions with neuronal loss. Double immunolabelling coupled with confocal microscopy showed that ataxin-7 colocalized with BiP, a marker of the endoplasmic reticulum, but not with markers of mitochondria or the trans-Golgi network.

Basu, P., B. Chattopadhyay, et al. (2000). "Analysis of CAG repeats in SCA1, SCA2, SCA3, SCA6, SCA7 and DRPLA loci in spinocerebellar ataxia patients and distribution of CAG repeats at the SCA1, SCA2 and SCA6 loci in nine ethnic populations of eastern India." Hum Genet 106(6): 597-604.
To identify various subtypes of spinocerebellar ataxias (SCAs) among 57 unrelated individuals clinically diagnosed as ataxia patients we analysed the SCA1, SCA2, SCA3, SCA6, SCA7 and DRPLA loci for expansion of CAG repeats. We detected CAG repeat expansion in 6 patients (10.5%) at the SCA1 locus. Ten of the 57 patients (17.5%) had CAG repeat expansion at the SCA2 locus, while four had CAG expansion at the SCA3/MJD locus (7%). At the SCA6 locus there was a single patient (1.8%) with 21 CAG repeats. We have not detected any patient with expansion in the SCA7 and DRPLA loci. To test whether the frequencies of the large normal alleles in SCA1, SCA2 and SCA6 loci can reflect some light on prevalence of the subtypes of SCAs we studied the CAG repeat variation in these loci in nine ethnic sub-populations of eastern India from which the patients originated. We report here that the frequency of large normal alleles (>31 CAG repeats) in SCA1 locus to be 0.211 of 394 chromosomes studied. We also report that the frequency of large normal alleles (>22 CAG repeats) at the SCA2 locus is 0.038 while at the SCA6 locus frequency of large normal alleles (>13 repeats) is 0.032. We discussed our data in light of the distribution of normal alleles and prevalence of SCAs in the Japanese and white populations.

Sharma, D., S. Sharma, et al. (1999). "Peptide models for inherited neurodegenerative disorders: conformation and aggregation properties of long polyglutamine peptides with and without interruptions." FEBS Lett 456(1): 181-5.
Several neurodegenerative diseases are caused by expansion of polyglutamine repeats in the affected proteins. In spino-cerebellar ataxia type 1 (SCA1), histidine interruptions have been reported to mitigate the pathological effects of long glutamine stretches. To understand this phenomenon, we investigated the conformational preferences of peptides containing both the uninterrupted polyglutamine stretches and those with histidine interruption(s) as seen in SCA1 normals. Our study suggests that substitution of histidines by glutamines induces a conformational change which results in decreased solubility and increased aggregation. Our findings also suggest that all the polyglutamine peptides with and without interruption(s) adopt a beta-structure and not random coil.

Sanpei, K. (1999). "[The function of spinocerebellar ataxia type 2 (SCA2) gene product, ataxin-2 and the mechanism of pathogenesis for SCA2]." Nippon Rinsho 57(4): 822-4.
This review summarizes the current progress in the research on the function of ataxin-2 and the mechanism of pathogenesis for SCA2. Recent studies on genomic structure of the human gene for SCA2 and on the mouse homolog of the SCA2 gene have shed light on the molecular mechanism of pathogenesis of SCA2. Analysis of the expression pattern of ataxin-2 in human brain revealed that both wild-type and mutant form of ataxin-2 were expressed and the wild-type ataxin-2 was localized in the cytoplasm with strong labeling of Purkinje cells and that intranuclear inclusions were not seen in SCA2 brain.

Pujana, M. A., J. Corral, et al. (1999). "Spinocerebellar ataxias in Spanish patients: genetic analysis of familial and sporadic cases. The Ataxia Study Group." Hum Genet 104(6): 516-22.
Autosomal dominant cerebellar ataxias (ADCA) are a clinically heterogeneous group of neurodegenerative disorders caused by unstable CAG repeat expansions encoding polyglutamine tracts. Five spinocerebellar ataxia genes (SCA1, SCA2, SCA3, SCA6 and SCA7) and another related dominant ataxia gene (DRPLA) have been cloned, allowing the genetic classification of these disorders. We present here the molecular analysis of 87 unrelated familial and 60 sporadic Spanish cases of spinocerebellar ataxia. For ADCA cases 15% were SCA2, 15% SCA3, 6% SCA1, 3% SCA7, 1% SCA6 and 1% DRPLA, an extremely rare mutation in Caucasoid populations. About 58% of ADCA cases remained genetically unclassified. All the SCA1 cases belong to the same geographical area and share a common haplotype for the SCA1 mutation. The expanded alleles ranged from 41 to 59 repeats for SCA1, 35 to 46 [corrected] for SCA2, 67 to 77 for SCA3, and 38 to 113 for SCA7. One SCA6 case had 25 repeats and one DRPLA case had 63 repeats. The highest CAG repeat variation in meiotic transmission of expanded alleles was detected in SCA7, this being of +67 units in one paternal transmission and giving rise to a 113 CAG repeat allele in a patient who died at 3 years of age. Meiotic transmissions have also shown a tendency to more frequent paternal transmission of expanded alleles in SCA1 and maternal in SCA7. All SCA1 and SCA2 expanded alleles analyzed consisted of pure CAG repeats, whereas normal alleles were interrupted by 1-2 CAT trinucleotides in SCA1, except for three alleles of 6, 14 and 21 CAG repeats, and by 1-3 CAA trinucleotides in SCA2. No SCA or DRPLA mutations were detected in the 60 sporadic cases of spinocerebellar ataxia, but one late onset patient was identified as a recessive form due to GAA-repeat expansions in the Friedreich's ataxia gene.

Perez, M. K., H. L. Paulson, et al. (1999). "Ataxin-3 with an altered conformation that exposes the polyglutamine domain is associated with the nuclear matrix." Hum Mol Genet 8(13): 2377-85.
Spinocerebellar ataxia type-3 or Machado-Joseph disease (SCA3/MJD) is a member of the CAG/polyglutamine repeat disease family. In this family of disorders, a normally polymorphic CAG repeat becomes expanded, resulting in expression of an expanded polyglutamine domain in the disease gene product. Experimental models of polyglutamine disease implicate the nucleus in pathogenesis; however, the link between intranuclear expression of expanded polyglutamine and neuronal dysfunction remains unclear. Here we demonstrate that ataxin-3, the disease protein in SCA3/MJD, adopts a unique conformation when expressed within the nucleus of transfected cells. The monoclonal antibody 1C2 is known preferentially to bind expanded polyglutamine, but we find that it also binds a fragment of ataxin-3 containing a normal glutamine repeat. In addition, expression of ataxin-3 within the nucleus exposes the glutamine domain of the full-length non-pathological protein, allowing it to bind the monoclonal antibody 1C2. Fractionation and immunochemical experiments indicate that this novel conformation of intranuclear ataxin-3 is not due to proteolysis, suggesting instead that association with nuclear protein(s) alters the structure of full-length ataxin-3 which exposes the polyglutamine domain. This conformationally altered ataxin-3 is bound to the nuclear matrix. The pathological form of ataxin-3 with an expanded polyglutamine domain also associates with the nuclear matrix. These data suggest that an early event in the pathogenesis of SCA3/MJD may be an altered conformation of ataxin-3 within the nucleus that exposes the polyglutamine domain.

Pang, J., R. Allotey, et al. (1999). "A common disease haplotype segregating in spinocerebellar ataxia 2 (SCA2) pedigrees of diverse ethnic origin." Eur J Hum Genet 7(7): 841-5.
The identification of a CAG trinucleotide repeat expansion, located within the coding sequence of the ataxin-2 gene, as the mutation underlying spinocerebellar ataxia 2 (SCA2) has facilitated direct investigation of pedigrees previously excluded from linkage analysis due to insufficient size or pedigree structure. We have previously described the identification of the ancestral disease haplotype segregating in the Cuban founder population used to assign the disease locus to chromosome 12q23-24.1. We now report evidence for the segregation of the identical core haplotype in pedigrees of diverse ethnic origin from India, Japan and England, established by the analysis of the loci D12S1672 and D12S1333 located 20kb proximal and 200 kb distal to the triplet repeat motif respectively. Interpretation of this data is suggestive that for these pedigrees at least, the mutation has arisen on a single ancestral or predisposing chromosome.

Mauger, C., J. Del-Favero, et al. (1999). "Identification and localization of ataxin-7 in brain and retina of a patient with cerebellar ataxia type II using anti-peptide antibody." Brain Res Mol Brain Res 74(1-2): 35-43.
Autosomal dominant cerebellar ataxias (ADCAs) are a complex group of neurodegenerative disorders characterized by progressive degeneration of the cerebellum, brain stem and spinal cord. The spinocerebellar ataxia type 7 (SCA7) is associated with pigmentary macular dystrophy and retinal degeneration leading to blindness caused by a CAG/polyglutamine (polyGln) expansion in the coding region of the SCA7 gene/protein. The SCA7 gene codes for ataxin-7, a protein of unknown function. To investigate its cellular and subcellular localization, we have developed a sequence-specific polyclonal antibody against the N-terminal part of the protein. Immunohistochemical analysis indicated that ataxin-7 accumulates as single nuclear inclusion (NI) in the cells of the brain and retina of a SCA7 patient but not of controls. The 1C2 antibody, directed against expanded polyGln, confirmed the aggregation of mutant ataxin-7 in these NIs. Furthermore, ubiquitin was found in these aggregates, suggesting that mutant ataxin-7 is a target for ubiquitin-dependent proteolysis, but resistant to removal. Electron microscopic studies using immunogold labeling showed that ataxin-7 immunoreactive NIs appear as dense aggregates containing a mixture of granular and filamentary structures. Together, these data confirm the presence of NIs in brain and retina of a SCA7 patient, a common characteristic of disorders caused by expanded CAG/polyGln repeats.

Matsuura, T., H. Sasaki, et al. (1999). "Mosaicism of unstable CAG repeats in the brain of spinocerebellar ataxia type 2." J Neurol 246(9): 835-9.
Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of unstable CAG repeats within the coding region of the novel gene, ataxin-2, on chromosome 12q24.1. We analyzed CAG repeat size of the SCA2 allele in two deceased patients (father and daughter) to investigate the repeat mosaicism in CNS regions. The CAG repeat size was examined using lymphoblastoid cell lines, frozen brain tissues, and paraffin-embedded tissues. In each patient the major repeat size of the expanded allele varied within the brain or spinal cord (father, 39-42; daughter, 39-47 repeats), and was smaller by three to eight repeats in the cerebellum than in other CNS regions. Our results are in agreement with the findings in other polyglutamine disorders showing somatic mosaicism.

Koyano, S., T. Uchihara, et al. (1999). "Neuronal intranuclear inclusions in spinocerebellar ataxia type 2: triple-labeling immunofluorescent study." Neurosci Lett 273(2): 117-20.
Spinocerebellar ataxia type 2 (SCA2) is associated with an expansion of CAG/polyglutamine-repeat of a gene of unknown function. We performed an immunohistochemical study to identify the immunolocalization of the disease protein ataxin-2 in normal and SCA2 patients. Although normal and expanded ataxin-2 were ubiquitously localized to the cytoplasm of neurons, ubiquitinated intranuclear inclusions were observed selectively in 1-2% of neurons of affected brain regions except the cerebellum. Triple-labeling immunofluorescence revealed that ataxin-2, expanded polyglutamine and ubiquitin were colocalized to these neuronal intranuclear inclusions (NIs), indicating that SCA2 shares morphological characteristics common to other neurological disorders associated with an expansion of CAG/polyglutamine-repeat. Lack of NIs in the cerebellar lesion, however, suggests the discrepancy between formation of NIs and neuronal degeneration in SCA2.

Kaytor, M. D., L. A. Duvick, et al. (1999). "Nuclear localization of the spinocerebellar ataxia type 7 protein, ataxin-7." Hum Mol Genet 8(9): 1657-64.
Spinocerebellar ataxia type 7 (SCA7) belongs to a group of neurological disorders caused by a CAG repeat expansion in the coding region of the associated gene. To gain insight into the pathogenesis of SCA7 and possible functions of ataxin-7, we examined the subcellular localization of ataxin-7 in transfected COS-1 cells using SCA7 cDNA clones with different CAG repeat tract lengths. In addition to a diffuse distribution throughout the nucleus, ataxin-7 associated with the nuclear matrix and the nucleolus. The location of the putative SCA7 nuclear localization sequence (NLS) was confirmed by fusing an ataxin-7 fragment with the normally cytoplasmic protein chicken muscle pyruvate kinase. Mutation of this NLS prevented protein from entering the nucleus. Thus, expanded ataxin-7 may carry out its pathogenic effects in the nucleus by altering a matrix-associated nuclear structure and/or by disrupting nucleolar function.

Kaemmerer, W. F. and W. C. Low (1999). "Cerebellar allografts survive and transiently alleviate ataxia in a transgenic model of spinocerebellar ataxia type-1." Exp Neurol 158(2): 301-11.
Spinocerebellar ataxia type 1 (SCA-1) is one of several neurodegenerative diseases, including Huntington's disease, spinobulbar muscular atrophy, dentatorubral-pallidoluysian atrophy, and SCA-2, SCA-3, SCA-6, and SCA-7, each caused by an expanded number of CAG repeats in the coding region of their respective genes. The mechanism by which the resulting proteins are pathogenic is unknown. Clinical trials of neural transplants in Huntington's disease patients are under way. While initial reports are encouraging, definitive evidence of graft survival in patients despite the ongoing disease process is not possible with current imaging techniques. Transplants in primates have shown long-term survival of striatal grafts and recovery of function, but have used lesioning to model Huntington's phenotypically. Studies of striatal grafts in a transgenic mouse model of Huntington's have not yet shown a behavioral benefit. We describe a behavioral benefit of cerebellar grafts in a transgenic model of SCA-1 in which the ataxic phenotype results from expression of an expanded ataxin-1 protein. Mice were transplanted at an age when their ataxic phenotype is just becoming evident. Compared with sham-operated littermates, grafted mice showed better performance on multiple behavioral tests of cerebellar function. Differences persisted for 10 to 12 weeks posttransplant, after which there was a progressive decline in motor performance. At 20 weeks postsurgery, donor Purkinje cell survival was evident in 9 of 12 graft recipients. These results indicate that transplants can have behavioral benefits and grafts can survive long-term despite the ongoing pathological process in a brain actively expressing an expanded polyglutamine protein.

Joo, E. J., J. H. Lee, et al. (1999). "Possible association between schizophrenia and a CAG repeat polymorphism in the spinocerebellar ataxia type 1 (SCA1) gene on human chromosome 6p23." Psychiatr Genet 9(1): 7-11.
The gene for spinocerebellar ataxia type 1 (SCA1) is a potential candidate gene for schizophrenia because of previous positive linkage findings in this region (6p22-24), and because the reported correlation between SCA1 onset and the number of CAG repeats suggests anticipation. To test the involvement of this gene in the development of schizophrenia, we examined genotypes of the SCA1 CAG repeat polymorphism for 49 Caucasian patients with schizophrenia, and 88 Caucasian controls. We found a significant association between the frequencies of alleles of this gene and schizophrenia (chi 2 = 18.40, df = 8, P = 0.018). Among 13 alleles, one allele (31 trinucleotide repeat) was significantly more frequent in patients with schizophrenia than in controls (chi 2 = 9.57, df = 1, P = 0.002). This association was sustained after applying a Bonferroni correction for multiple testing (P = 0.05/13 = 0.004), and the chi-square results were shown to be robust through Monte Carlo simulation. We observed no allelic association with three flanking microsatellite markers (D6S288, D6S1605, and D6S337), suggesting that our result was not due to population stratification. Further studies of this locus are needed to confirm this finding, and to determine a potential role for this gene in the development of schizophrenia.

Huynh, D. P., M. R. Del Bigio, et al. (1999). "Expression of ataxin-2 in brains from normal individuals and patients with Alzheimer's disease and spinocerebellar ataxia 2." Ann Neurol 45(2): 232-41.
Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of a CAG trinucleotide repeat located in the coding region of the human SCA2 gene. The SCA2 gene product, ataxin-2, is a basic protein with two domains (Sm1 and Sm2) implicated in RNA splicing and protein interaction. However, the wild-type function of ataxin-2 is yet to be determined. To help clarify the function of ataxin-2, we produced antibodies to three antigenic peptides of ataxin-2 and analyzed the expression pattern of ataxin-2 in normal and SCA2 adult brains and cerebellum at different developmental stages. These studies revealed that (1) both wild-type and mutant forms of ataxin-2 were synthesized; (2) the wild-type ataxin-2 was localized in the cytoplasm in specific neuronal groups with strong labeling of Purkinje cells; (3) the level of ataxin-2 increased with age in Purkinje cells of normal individuals; and (4) ataxin-2-like immunoreactivity in SCA2 brain tissues was more intense than in normal brain tissues, and intranuclear ubiquitinated inclusions were not seen in SCA2 brain tissues.

Hsieh, M., S. Y. Li, et al. (1999). "Identification of five spinocerebellar ataxia type 2 pedigrees in patients with autosomal dominant cerebellar ataxia in Taiwan." Acta Neurol Scand 100(3): 189-94.
OBJECTIVES: The autosomal dominant cerebellar ataxias (ADCAs) are a group of genetically diverse neurological conditions linked by progressive deterioration in balance and coordination. Spinocerebellar Ataxia Type 2 (SCA2) is one of the ADCAs and also belongs to a special group caused by the expansion of an unstable CAG repeat encoding a polyglutamine tract. We aimed to investigate the frequency of SCA2 mutation in the ataxia patients referred to the clinic. MATERIALS AND METHODS: We screened 58 families with inherent cerebellar ataxia and 57 normal individuals by the use of radioactive genomic polymerase chain reaction (PCR) method. A simple non-radioactive PCR for rapid detection of the expanded SCA2 alleles via agarose gel electrophoresis was also employed. RESULTS: Eight SCA2 affected patients and 1 at-risk individual in 5 unrelated SCA2 families were identified. The CAG repeats of normal alleles in the sample studied range in size from 16 to 30 repeat units, while those of SCA2 chromosomes are expanded to 34 to 49 repeat units. Our results also showed that unlike SCA 1 and SCA3/MJD, the size distribution of the normal alleles showed few polymorphisms, with the 22 repeat allele accounting for 90.1%. Homozygosity in normal individuals was 80.2%. No overlap in ataxin-2 allele size between normal and expanded chromosomes was observed. CONCLUSION: This is the first report of the SCA2 gene distributions in the population of Taiwan. The SCA2 mutation accounts for 8.6% of ADCA type I families referred to us, intermediate between SCA1(1.7%) and SCA3/MJD (24%) of the ADCA type I families in our collection.

Frontali, M., A. Novelletto, et al. (1999). "CAG repeat instability, cryptic sequence variation and pathogeneticity: evidence from different loci." Philos Trans R Soc Lond B Biol Sci 354(1386): 1089-94.
Different aspects of expanded polyglutamine tracts and of their pathogenetic role are taken into consideration here. (i) The (CAG)n length of wild-type alleles of the Huntington disease gene was analysed in instability-prone tumour tissue from colon cancer patients to test whether the process leading to the elongation of alleles towards the expansion range involves single-unit stepwise mutations or larger jumps. The analysis showed that length changes of a single unit had a relatively low frequency. (ii) The observation of an expanded spinocerebellar ataxia (SCA)1 allele with an unusual pattern of multiple CAT interruptions showed that cryptic sequence variations are critical not only for sequence length stability but also for the expression of the disease phenotype. (iii) Small expansions of the (CAG)n sequence at the CACNA1A gene have been reported as causing SCA6. The analysis of families with SCA6 and episodic ataxia type 2 showed that these phenotypes are, in fact, expressions of the same disorder caused either by point mutations or by small (CAG)n expansions. A gain of function has been hypothesized for all proteins containing an expanded polyglutamine stretch, including the alpha 1A subunit of the voltage-gated calcium channel type P/Q coded by the CACNA1A gene. Because point mutations at the same gene with similar phenotypic consequences are highly unlikely to have this effect, an alternative common pathogenetic mechanism for all these mutations, including small expansions, can be hypothesized.

Evert, B. O., U. Wullner, et al. (1999). "High level expression of expanded full-length ataxin-3 in vitro causes cell death and formation of intranuclear inclusions in neuronal cells." Hum Mol Genet 8(7): 1169-76.
Spinocerebellar ataxia type 3 (SCA3) is caused by a CAG/polyglutamine repeat expansion in the SCA3 gene. To analyse the pathogenic mechanisms in SCA3, we have generated ataxin-3-expressing rat mesencephalic CSM14.1 cells. In these cells, a post-mitotic neuronal phenotype is induced by temperature shift. The isolated stable cell lines provided high level expression of non-expanded (Q23) or expanded (Q70) human full-length ataxin-3. CSM14.1 cells expressing the expanded full-length ataxin-3 developed nuclear inclusion bodies, strong indentations of the nuclear envelope and cytoplasmic vacuolation. These ultrastructural alterations were present prior to a significantly decreased viability of neuronally differentiated cells expressing expanded ataxin-3. The observed spontaneous cell death did not correlate with formation of intranuclear inclusions and was not apoptotic by ultrastructural analysis. No increased susceptibility to staurosporine-induced apoptosis was found for the expanded or non-expanded ataxin-3-expressing cell lines. These data show that high level expression of expanded full-length ataxin-3 in a neuron-like cell line generates ultrastructural alterations of SCA3 pathogenesis and results in increased spontaneous non-apoptotic cell death.

Duyckaerts, C., A. Durr, et al. (1999). "Nuclear inclusions in spinocerebellar ataxia type 1." Acta Neuropathol (Berl) 97(2): 201-7.
Spinocerebellar ataxia type 1 is due to a CAG repeat expansion in the gene encoding ataxin-1. In a case with an expansion of 56 repeats, intranuclear inclusions were found only in neurons, both in severely affected regions (such as the pons) and in areas where the lesions were inconspicuous (such as the cortex or the striatum). The inclusions were labelled by a monoclonal antibody directed against long polyglutamine stretches (1C2); they were also detected by the anti-ubiquitin antibody. They were faintly eosinophilic, Congo red negative and were not stained by thioflavin S or by ethidium bromide.

Cummings, C. J., H. T. Orr, et al. (1999). "Progress in pathogenesis studies of spinocerebellar ataxia type 1." Philos Trans R Soc Lond B Biol Sci 354(1386): 1079-81.
Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited disorder characterized by progressive loss of coordination, motor impairment and the degeneration of cerebellar Purkinje cells, spinocerebellar tracts and brainstem nuclei. Many dominantly inherited neurodegenerative diseases share the mutational basis of SCA1: the expansion of a translated CAG repeat coding for glutamine. Mice lacking ataxin-1 display learning deficits and altered hippocampal synaptic plasticity but none of the abnormalities seen in human SCA1; mice expressing ataxin-1 with an expanded CAG tract (82 glutamine residues), however, develop Purkinje cell pathology and ataxia. These results suggest that mutant ataxin-1 gains a novel function that leads to neuronal degeneration. This novel function might involve aberrant interaction(s) with cell-specific protein(s), which in turn might explain the selective neuronal pathology. Mutant ataxin-1 interacts preferentially with a leucine-rich acidic nuclear protein that is abundantly expressed in cerebellar Purkinje cells and other brain regions affected in SCA1. Immunolocalization studies in affected neurons of patients and SCA1 transgenic mice showed that mutant ataxin-1 localizes to a single, ubiquitin-positive nuclear inclusion (NI) that alters the distribution of the proteasome and certain chaperones. Further analysis of NIs in transfected HeLa cells established that the proteasome and chaperone proteins co-localize with ataxin-1 aggregates. Moreover, overexpression of the chaperone HDJ-2/HSDJ in HeLa cells decreased ataxin-1 aggregation, suggesting that protein misfolding might underlie NI formation. To assess the importance of the nuclear localization of ataxin-1 and its role in SCA1 pathogenesis, two lines of transgenic mice were generated. In the first line, the nuclear localization signal was mutated so that full-length mutant ataxin-1 would remain in the cytoplasm; mice from this line did not develop any ataxia or pathology. This suggests that mutant ataxin-1 is pathogenic only in the nucleus. To assess the role of the aggregates, transgenic mice were generated with mutant ataxin-1 without the self-association domain (SAD) essential for aggregate formation. These mice developed ataxia and Purkinje cell abnormalities similar to those seen in SCA1 transgenic mice carrying full-length mutant ataxin-1, but lacked NIs. The nuclear milieu is thus a critical factor in SCA1 pathogenesis, but large NIs are not needed to initiate pathogenesis. They might instead be downstream of the primary pathogenic steps. Given the accumulated evidence, we propose the following model for SCA1 pathogenesis: expansion of the polyglutamine tract alters the conformation of ataxin-1, causing it to misfold. This in turn leads to aberrant protein interactions. Cell specificity is determined by the cell-specific proteins interacting with ataxin-1. Submicroscopic protein aggregation might occur because of protein misfolding, and those aggregates become detectable as NIs as the disease advances. Proteasome redistribution to the NI might contribute to disease progression by disturbing proteolysis and subsequent vital cellular functions.

Cummings, C. J., E. Reinstein, et al. (1999). "Mutation of the E6-AP ubiquitin ligase reduces nuclear inclusion frequency while accelerating polyglutamine-induced pathology in SCA1 mice." Neuron 24(4): 879-92.
Mutant ataxin-1, the expanded polyglutamine protein causing spinocerebellar ataxia type 1 (SCA1), aggregates in ubiquitin-positive nuclear inclusions (NI) that alter proteasome distribution in affected SCA1 patient neurons. Here, we observed that ataxin-1 is degraded by the ubiquitin-proteasome pathway. While ataxin-1 [2Q] and mutant ataxin-1 [92Q] are polyubiquitinated equally well in vitro, the mutant form is three times more resistant to degradation. Inhibiting proteasomal degradation promotes ataxin-1 aggregation in transfected cells. And in mice, Purkinje cells that express mutant ataxin-1 but not a ubiquitin-protein ligase have significantly fewer NIs. Nonetheless, the Purkinje cell pathology is markedly worse than that of SCA1 mice. Taken together, NIs are not necessary to induce neurodegeneration, but impaired proteasomal degradation of mutant ataxin-1 may contribute to SCA1 pathogenesis.

Chai, Y., S. L. Koppenhafer, et al. (1999). "Evidence for proteasome involvement in polyglutamine disease: localization to nuclear inclusions in SCA3/MJD and suppression of polyglutamine aggregation in vitro." Hum Mol Genet 8(4): 673-82.
Spinocerebellar ataxia type 3, also known as Machado-Joseph disease (SCA3/MJD), is one of at least eight inherited neurodegenerative diseases caused by expansion of a polyglutamine tract in the disease protein. Here we present two lines of evidence implicating the ubiquitin-proteasome pathway in SCA3/MJD pathogenesis. First, studies of both human disease tissue and in vitro models showed redistribution of the 26S proteasome complex into polyglutamine aggregates. In neurons from SCA3/MJD brain, the proteasome localized to intranuclear inclusions containing the mutant protein, ataxin-3. In transfected cells, the proteasome redistributed into inclusions formed by three expanded polyglutamine proteins: a pathologic ataxin-3 fragment, full-length mutant ataxin-3 and an unrelated GFP-polyglutamine fusion protein. Inclusion formation by the full-length mutant ataxin-3 required nuclear localization of the protein and occurred within specific subnuclear structures recently implicated in the regulation of cell death, promyelocytic leukemia antigen oncogenic domains. In a second set of experiments, inhibitors of the proteasome caused a repeat length-dependent increase in aggregate formation, implying that the proteasome plays a direct role in suppressing polyglutamine aggregation in disease. These results support a central role for protein misfolding in the pathogenesis of SCA3/MJD and suggest that modulating proteasome activity is a potential approach to altering the progression of this and other polyglutamine diseases.

Chai, Y., S. L. Koppenhafer, et al. (1999). "Analysis of the role of heat shock protein (Hsp) molecular chaperones in polyglutamine disease." J Neurosci 19(23): 10338-47.
Polyglutamine (polygln) diseases are a group of inherited neurodegenerative disorders characterized by protein misfolding and aggregation. Here, we investigate the role in polygln disease of heat shock proteins (Hsps), the major class of molecular chaperones responsible for modulating protein folding in the cell. In transfected COS7 and PC12 neural cells, we show that Hsp40 and Hsp70 chaperones localize to intranuclear aggregates formed by either mutant ataxin-3, the disease protein in spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD), or an unrelated green fluorescent protein fusion protein containing expanded polygln. We further demonstrate that expression of expanded polygln protein elicits a stress response in cells as manifested by marked induction of Hsp70. Studies of SCA3/MJD disease brain confirm these findings, showing localization of Hsp40 and, less commonly, Hsp70 chaperones to intranuclear ataxin-3 aggregates. In transfected cells, overexpression of either of two Hsp40 chaperones, the DNAJ protein homologs HDJ-1 and HDJ-2, suppresses aggregation of truncated or full-length mutant ataxin-3. Finally, we extend these studies to a PC12 neural model of polygln toxicity in which we demonstrate that overexpression of HDJ-1 suppresses polygln aggregation with a parallel decrease in toxicity. These results suggest that expanded polygln protein induces a stress response and that specific molecular chaperones may aid the handling of misfolded or aggregated polygln protein in neurons. This study has therapeutic implications because it suggests that efforts to increase chaperone activity may prove beneficial in this class of diseases.

Burk, K., T. Klockgether, et al. (1999). "[New insights in the molecular genetics and pathophysiology of hereditary ataxias]." Nervenarzt 70(6): 491-5.
The hereditary ataxias are a heterogeneous group of inherited neurodegenerative disorders characterised by progressive ataxia that results from degeneration of the cerebellum and its afferent and efferent connections. With respect to the pathogenic mechanisms, the hereditary ataxias may be tentatively divided into three groups: (1) The recessive ataxias are induced by the functional impairment of a protein that is essential for the survival of specific neurons while the autosomal dominant ataxias are either caused by (2) mutations of genes coding for ion channels thus resulting in a channelopathy or by (3) a novel deleterious function of a extended polyglutamine sequence within the proteins encoded by the respective genes.

Yabe, I., H. Sasaki, et al. (1998). "SCA6 mutation analysis in a large cohort of the Japanese patients with late-onset pure cerebellar ataxia." J Neurol Sci 156(1): 89-95.
Spinocerebellar ataxia type 6 (SCA6) is caused by small CAG repeat expansion in the gene encoding the alpha1A-voltage-dependent-calcium channel subunit (CACNLIA4) on chromosome 19p13, and is a subgroup of the late-onset pure cerebellar ataxia (ADCA III). To investigate the prevalence of SCA6 in the Japanese, we analyzed this mutation in 23 families and 12 probands with ADCA III. The specificity and stability of the CAG repeat were examined in additional individuals and families with other miscellaneous dominant SCAs. The CAG expansion of SCA6 gene was exclusively observed in 12 of 23 families (52%) and 12 proband cases with ADCA III, but not in others. The CAG repeat was 21-33 in the disease-associated alleles (n=56), and 4-18 in normal alleles (n=1148). Expanded alleles were stable during transmission, and a significant inverse correlation for CAG repeat number with age at onset was noted. Our results indicate that SCA6 shares approximately half of the ADCA III in the Japanese, and that gene mutations causing the remaining, have yet to be identified.

Ueyama, H., T. Kumamoto, et al. (1998). "Clinical and genetic studies of spinocerebellar ataxia type 2 in Japanese kindreds." Acta Neurol Scand 98(6): 427-32.
OBJECTIVES: We report the results of clinical and genetic studies from 2 related Japanese kindreds with spinocerebellar ataxia type 2 (SCA2). MATERIAL AND METHODS: Family A showed 19 patients through 4 generations, while family B showed 6 patients, including dizygotic twin brothers, through 3 generations. We performed clinical, radiological, neurophysiological, and genetic analyses in the family members. RESULTS: Neurologic analysis of 13 affected patients revealed a mean age at onset of 43.5 years. The most common neurologic finding was cerebellar ataxia with deep sensory disturbance. Slow saccades was found only in the younger patients below age 35 years. Nerve conduction studies revealed subclinical sensory neuropathy. Brain MRI showed the presence of pontocerebellar atrophy. Genetic study using PCR revealed that all affected patients had an expanded CAG allele in the ataxin-2 gene, which led to a final diagnosis of SCA2. CONCLUSION: SCA2 may be more clinically heterogeneous than previously thought. PCR is useful in differentiating SCA2 from other types of inherited ataxia.

Trottier, Y., G. Cancel, et al. (1998). "Heterogeneous intracellular localization and expression of ataxin-3." Neurobiol Dis 5(5): 335-47.
Spinocerebellar ataxia type 3 or Machado-Joseph disease (SCA3/MJD) is an autosomal dominant neurodegenerative disorder caused by an unstable and expanded CAG trinucleotide repeat that leads to the expansion of a polyglutamine tract in a protein of unknown function, ataxin-3. We have generated and characterized a panel of monoclonal and polyclonal antibodies raised against ataxin-3 and used them to analyze its expression and localization. In Hela cells, multiple isoforms are expressed besides the major 55-kDa form. While the majority of ataxin-3 is cytosolic, both immunocytofluorescence and subcellular fractionation studies indicate the presence of ataxin-3, in particular, of some of the minor isoforms, in the nuclear and mitochodrial compartments. We also show that ataxin-3 can be phosphorylated. In the brain, only one ataxin-3 isoform containing the polyglutamine stretch was detected, and normal and mutated proteins were found equally expressed in all patient brain regions analyzed. In most neurons, ataxin-3 had a cytoplasmic, dendritic, and axonal localization. Some neurons presented an additional nuclear localization. Ataxin-3 is widely expressed throughout the brain, with a variable intensity specific for subpopulations of neurons. Its expression is, however, not restricted to regions that show intranuclear inclusions and neurodegeneration in SCA3/MJD.

Silveira, I., P. Coutinho, et al. (1998). "Analysis of SCA1, DRPLA, MJD, SCA2, and SCA6 CAG repeats in 48 Portuguese ataxia families." Am J Med Genet 81(2): 134-8.
The spinocerebellar ataxias (SCAs) are clinically and genetically a heterogeneous group of neurodegenerative disorders. To date, eight different loci causing SCA have been identified: SCA1, SCA2, Machado-Joseph disease (MJD)/SCA3, SCA4, SCA5, SCA6, SCA7, and dentatorubropallidoluysian atrophy (DRPLA). Expansion of a CAG repeat in the disease genes has been found in five of these disorders. To estimate the relative frequencies of the SCA1, DRPLA, MJD, SCA2, and SCA6 mutations among Portuguese ataxia patients, we collected DNA samples from 48 ataxia families and performed polymerase chain reaction (PCR) amplification of the CAG repeat mutations on chromosomes 6p, 12p, 14q, 12q, and 19p, respectively. Fifty-five individuals belonging to 34 dominant families (74%) had an expanded CAG repeat at the MJD gene. In five individuals from two kindreds with a dominant pattern of inheritance (4%), an expanded CAG repeat at the SCA2 gene was found. In MJD patients, the normal allele size ranged from 13 to 41, whereas the mutant alleles contained 65 to 80 repeats. For the SCA2 patients, normal alleles had 22 or 23, while expanded alleles had between 36 and 47 CAG units. We did not find the SCA1, DRPLA, or SCA6 mutations in our group of families. The MJD mutation remains the most common cause of SCA in Portugal, while a small number of cases are caused by mutations at the SCA2 gene, and 22% are due to still unidentified genes.

Perez, M. K., H. L. Paulson, et al. (1998). "Recruitment and the role of nuclear localization in polyglutamine-mediated aggregation." J Cell Biol 143(6): 1457-70.
The inherited neurodegenerative diseases caused by an expanded glutamine repeat share the pathologic feature of intranuclear aggregates or inclusions (NI). Here in cell-based studies of the spinocerebellar ataxia type-3 disease protein, ataxin-3, we address two issues central to aggregation: the role of polyglutamine in recruiting proteins into NI and the role of nuclear localization in promoting aggregation. We demonstrate that full-length ataxin-3 is readily recruited from the cytoplasm into NI seeded either by a pathologic ataxin-3 fragment or by a second unrelated glutamine-repeat disease protein, ataxin-1. Experiments with green fluorescence protein/polyglutamine fusion proteins show that a glutamine repeat is sufficient to recruit an otherwise irrelevant protein into NI, and studies of human disease tissue and a Drosophila transgenic model provide evidence that specific glutamine-repeat-containing proteins, including TATA-binding protein and Eyes Absent protein, are recruited into NI in vivo. Finally, we show that nuclear localization promotes aggregation: an ataxin-3 fragment containing a nonpathologic repeat of 27 glutamines forms inclusions only when targeted to the nucleus. Our findings establish the importance of the polyglutamine domain in mediating recruitment and suggest that pathogenesis may be linked in part to the sequestering of glutamine-containing cellular proteins. In addition, we demonstrate that the nuclear environment may be critical for seeding polyglutamine aggregates.

Nechiporuk, T., D. P. Huynh, et al. (1998). "The mouse SCA2 gene: cDNA sequence, alternative splicing and protein expression." Hum Mol Genet 7(8): 1301-9.
Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of a CAG trinucleotide repeat located in the coding region of the human SCA2 gene. Sequence analysis revealed that SCA2 is a novel gene of unknown function. In order to provide insights into the molecular mechanisms of pathogenesis of SCA2 and to identify conserved domains, we isolated and characterized the mouse homolog of the SCA2 gene. Sequence and amino acid analysis revealed 89% identity at the nucleotide and 91% identity at the amino acid level. However, there was no extended polyglutamine tract in the mouse SCA2 cDNA, suggesting that the normal function of SCA2 is not dependent on this domain. Northern blot analysis of different mouse tissues indicated that the mouse SCA2 gene was expressed in most tissues, but at varying levels. Alternative splicing seen in human SCA2 was conserved in the mouse. By northern blot analysis, SCA2 was expressed during embryogenesis as early as day 8 of gestation (E8). Immunohistochemical staining using affinity-purified antibodies demonstrated that ataxin 2 was expressed in the cytoplasm of Purkinje cells as well as in other neurons of the CNS.

Matilla, A., E. D. Roberson, et al. (1998). "Mice lacking ataxin-1 display learning deficits and decreased hippocampal paired-pulse facilitation." J Neurosci 18(14): 5508-16.
Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disorder characterized by ataxia, progressive motor deterioration, and loss of cerebellar Purkinje cells. To investigate SCA1 pathogenesis and to gain insight into the function of the SCA1 gene product ataxin-1, a novel protein without homology to previously described proteins, we generated mice with a targeted deletion in the murine Sca1 gene. Mice lacking ataxin-1 are viable, fertile, and do not show any evidence of ataxia or neurodegeneration. However, Sca1 null mice demonstrate decreased exploratory behavior, pronounced deficits in the spatial version of the Morris water maze test, and impaired performance on the rotating rod apparatus. Furthermore, neurophysiological studies performed in area CA1 of the hippocampus reveal decreased paired-pulse facilitation in Sca1 null mice, whereas long-term and post-tetanic potentiations are normal. These findings demonstrate that SCA1 is not caused by loss of function of ataxin-1 and point to the possible role of ataxin-1 in learning and memory.

Koeppen, A. H. (1998). "The hereditary ataxias." J Neuropathol Exp Neurol 57(6): 531-43.
Efforts to classify the hereditary ataxias by their clinical and neuropathological phenotypes are troubled by excessive heterogeneity. Linkage analysis opened the door to a new approach with the methods of molecular biology. The classic form of autosomal recessive ataxia, Friedreich's ataxia (FA), is now known to be due to an intronic expansion of a guanine-adenine-adenine (GAA)-trinucleotide repeat. The autosomal dominant ataxias such as olivopontocerebellar atrophy (OPCA), familial cortical cerebellar atrophy (FCCA), and Machado-Joseph disease (MJD) have been renamed the spinocerebellar ataxias (SCA). Specific gene loci are indicated as SCA-1, SCA-2, SCA-3, SCA-4, SCA-5, SCA-6, and SCA-7. In 5 of them (SCA-1, SCA-2, SCA-3, SCA-6, and SCA-7), expanded cytosine-adenine-guanine (CAG)-trinucleotide repeats and their abnormal gene products cause the ataxic condition. The most common underlying loci for olivopontocerebellar atrophy (OPCA) are SCA-1 and SCA-2, although other genotypes may be added in the future. A major recent advance was the identification of the gene for SCA-3 and MJD, and the high prevalence of this form of autosomal dominant ataxia. In FA and the SCA with expanded CAG-trinucleotide repeats, clinical and neuropathological severity are inversely correlated with the lengths of the repeats. Anticipation in the dominant ataxias can now be explained by lengthening of the repeats in successive generations. Progress is being made in the understanding of the pathogenesis of FA and SCA as the absent or mutated gene products are studied by immunocytochemistry in human and transgenic murine brain tissue. In FA, frataxin is diminished or absent, and an excess of mitochondrial iron may cause the illness of the nervous system and the heart. In SCA-3, abnormal ataxin-3 is aggregated in neuronal nuclei, and in SCA-6, a mutated alpha1A-calcium channel protein is the likely cause of abnormal calcium channel function in Purkinje cells and in the death of these neurons.

Koefoed, P., L. Hasholt, et al. (1998). "Mitotic and meiotic instability of the CAG trinucleotide repeat in spinocerebellar ataxia type 1." Hum Genet 103(5): 564-9.
Spinocerebellar ataxia type 1 (SCA1) is an autosomal, dominantly inherited neurodegenerative disease caused by an unstable CAG trinucleotide repeat expansion in the ataxin-1 gene located on chromosome 6p22-p23. The expanded CAG repeat is unstable during transmission, and a variation in the CAG repeat length has been found in different tissues, including sperm samples from affected males. In order further to examine the mitotic and meiotic instability of the (CAG)n stretch we have performed single sperm and low-copy genome analysis in SCA1 patients and asymptomatic carriers. A pronounced variation in the size of the expanded allele was found in sperm cells and peripheral blood leucocytes, with a higher degree of instability seen in the sperm cells, where an allele with 50 repeat units was contracted in 11.8%, further expanded in 63.5% and unchanged in 24.6% of the single sperm analysed. We found a low instability of the normal alleles; the normal alleles from the individuals carrying a CAG repeat expansion were significantly more unstable than the normal alleles from the control individuals (P<0.001), indicating an interallelic interaction between the expanded and the normal alleles.

Klockgether, T. and B. Evert (1998). "Genes involved in hereditary ataxias." Trends Neurosci 21(9): 413-8.
The hereditary ataxias are a group of inherited neurodegenerative disorders characterized by progressive ataxia that results from degeneration of the cerebellum and its afferent and efferent connections. Recent molecular research has led not only to the discovery of a number of causative mutations, but also shed light on the likely mechanisms by which these mutations cause the respective phenotypes. In Friedreich's ataxia (FRDA), the most common type of autosomal recessive ataxia, the loss of a mitochondrial protein, frataxin, results in overload of mitochondrial iron and oxidative stress. The autosomal dominant ataxias, spinocerebellar ataxia type I (SCAI), SCA2, SCA3 and SCA7, are caused by inheritance of an unstable, expanded CAG trinucleotide repeat.These disorders are assumed to be due to a novel deleterious function of the extended polyglutamine sequences within the proteins encoded by the respective genes. Recent observations in transgenic mice and in human post-mortem tissue suggest that the extended proteins are transported into the nucleus of neurons where they form intranuclear inclusions that disrupt normal nuclear function. In another group of dominant disorders, episodic ataxia type I and type 2 (EA-I, EA-2) and SCA6, the mutations affect genes that code for ion channels.

Klement, I. A., P. J. Skinner, et al. (1998). "Ataxin-1 nuclear localization and aggregation: role in polyglutamine-induced disease in SCA1 transgenic mice." Cell 95(1): 41-53.
Transgenic mice carrying the spinocerebellar ataxia type 1 (SCA1) gene, a polyglutamine neurodegenerative disorder, develop ataxia with ataxin-1 localized to aggregates within cerebellar Purkinje cells nuclei. To examine the importance of nuclear localization and aggregation in pathogenesis, mice expressing ataxin-1[82] with a mutated NLS were established. These mice did not develop disease, demonstrating that nuclear localization is critical for pathogenesis. In a second series of transgenic mice, ataxin-1[77] containing a deletion within the self-association region was expressed within Purkinje cells nuclei. These mice developed ataxia and Purkinje cell pathology similar to the original SCA1 mice. However, no evidence of nuclear ataxin-1 aggregates was found. Thus, although nuclear localization of ataxin-1 is necessary, nuclear aggregation of ataxin-1 is not required to initiate pathogenesis in transgenic mice.

Giunti, P., G. Sabbadini, et al. (1998). "The role of the SCA2 trinucleotide repeat expansion in 89 autosomal dominant cerebellar ataxia families. Frequency, clinical and genetic correlates." Brain 121 ( Pt 3): 459-67.
The spinocerebellar ataxia type 2 (SCA2) is caused by a trinucleotide (CAG) expansion in the coding region of the ataxin 2 gene on chromosome 12q.89 families with autosomal dominant cerebellar ataxia (ADCA) types I, II and III, and 47 isolated cases with idiopathic late onset cerebellar ataxia (ILOCA), were analysed for this mutation. The identification of the SCA2 mutation in 31 out of 38 families with the ADCA I phenotype, but in none of those with ADCA II, ADCA III or ILOCA confirms the specificity of this mutation. A clinical comparison of the ADCA I patients with the three known mutations (SCA1, -2 or -3) highlights significant differences between the groups; SCA2 patients tended to have a longer disease duration, a higher frequency of slow saccades and depressed tendon reflexes. However, these neurological signs were also seen in an ADCA I family in which the SCA2 mutation was not identified, illustrating the importance of a direct genetic test. The SCA2 families were from different geographical and ethnic backgrounds. However, haplotype analysis failed to show evidence of a founder mutation, even in families from the same geographical origin. The range of normal alleles varied from 17 to 30 CAG repeats and from 35 to 51 repeats for the pathological alleles. Similar to the other diseases caused by unstable trinucleotide repeats, a significant inverse correlation has been found between the number of repeats and age of onset, and there is a significantly higher paternal instability of repeat length on transmission to offspring. The SCA2 mutation is the most frequent amongst ADCA I patients, accounting for 40%, compared with SCA1 and SCA3 which account for 35% and 15%, respectively.

Cummings, C. J., M. A. Mancini, et al. (1998). "Chaperone suppression of aggregation and altered subcellular proteasome localization imply protein misfolding in SCA1." Nat Genet 19(2): 148-54.
Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder caused by expansion of a polyglutamine tract in ataxin-1. In affected neurons of SCA1 patients and transgenic mice, mutant ataxin-1 accumulates in a single, ubiquitin-positive nuclear inclusion. In this study, we show that these inclusions stain positively for the 20S proteasome and the molecular chaperone HDJ-2/HSDJ. Similarly, HeLa cells transfected with mutant ataxin-1 develop nuclear aggregates which colocalize with the 20S proteasome and endogenous HDJ-2/HSDJ. Overexpression of wild-type HDJ-2/HSDJ in HeLa cells decreases the frequency of ataxin-1 aggregation. These data suggest that protein misfolding is responsible for the nuclear aggregates seen in SCA1, and that overexpression of a DnaJ chaperone promotes the recognition of a misfolded polyglutamine repeat protein, allowing its refolding and/or ubiquitin-dependent degradation.

Culvenor, J. G., A. Henry, et al. (1998). "Subcellular localization of the Alzheimer's disease amyloid precursor protein and derived polypeptides expressed in a recombinant yeast system." Amyloid 5(2): 79-89.
Different isoforms and derived polypeptides of the Alzheimer's disease amyloid protein precursor (A beta PP) have been expressed in the yeast Pichia pastoris. The expression characteristics of the different A beta PP polypeptides were studied by post-embedding immunogold electron microscopy with various A beta PP antibodies. The site of intracellular expression could be readily identified with specific antibodies. Full length A beta PP was expressed in association with the nuclear membrane and the endoplasmic reticulum. Secretory derivatives of A beta PP were localized in membrane-bound secretory vesicles. A construct encoding two copies of beta A4[1-42] linked head-to-tail (beta A4duplex) accumulated as irregular dense cytoplasmic and intranuclear inclusions which reacted with all beta A4 antibodies tested. A beta A4-C-terminal construct accumulated into membranous structures in the cytoplasm and nucleus and reacted with most antibodies to beta A4 and the cytoplasmic domain of A beta PP. The two shorter constructs containing the beta A4 sequence formed similar intranuclear aggregates to those reported for intranuclear inclusions of polyglutamine peptides from huntingtin (in Huntington's disease) and ataxin protein fragments (in spinocerebellar ataxia). This is of interest because intracellular aggregation of the polyglutamine and beta A4 peptides may affect cells by similar toxic mechanisms. These studies demonstrate clear differences in the expression properties of different A beta PP polypeptides.

Cancel, G., I. Gourfinkel-An, et al. (1998). "Somatic mosaicism of the CAG repeat expansion in spinocerebellar ataxia type 3/Machado-Joseph disease." Hum Mutat 11(1): 23-7.
An expanded and unstable CAG repeat in the coding region of the MJD1 gene is the mutation responsible for spinocerebellar ataxia 3/Machado-Joseph disease. In order to determine whether there was a higher degree of instability in affected regions, the size of the expanded CAG repeat was analyzed in different regions of the central nervous system, in two unrelated SCA3/MJD patients. The degree of somatic mosaicism was quantified and compared to that in a SCA1 patient. Instability of the expanded CAG repeat was observed in peripheral tissues as well as in CNS of the three patients, but there was no correlation between the degree of mosaicism and the selective vulnerability of CNS structures. As in the other diseases caused by expanded CAG repeats, a lower degree of mosaicism was found in the cerebellar cortex of both SCA1 and SCA3/MJD patients, probably reflecting specific properties of this structure. In SCA3/MJD, the degree of mosaicism seemed to correlate with age at death rather than with the size of the expanded CAG repeat. Finally, somatic instability was more pronounced in SCA1 than in SCA3/MJD patients.

Tang, B., D. Wang, et al. (1997). "[SCA1, SCA2, MJD/SCA3 (CAG)n mutation detection and analysis in patients with hereditary spinocerebellar ataxia from Chinese families]." Zhonghua Yi Xue Za Zhi 77(11): 819-22.
OBJECTIVE: To assess the frequency of the SCA1, SCA2, MJD/SCA3 CAG trinucleotide repeat expansions ((CAG)n) among individuals diagnosed with hereditary spinocerebellar ataxia (SCA) from Chinese families. METHOD: The SCA1, SCA2, MJD/SCA3 (CAG)n mutation were detected with the polymerose chain reaction (PCR), denaturing polyacrylamide gel and silver staining technique in 79 patients with autosomal dominant SCA from 50 Chinese families. RESULTS: Among 50 kindreds, 2% (1/50) had the SCA1, (CAG)n, 6% (3/50) had the SCA2, (CAG)n, whereas 48% (24/50) were positive for the MJD/SCA3 (CAG)n. Thus, together SCA1, SCA2, and MJD/SCA3 represent 56% (28/50) of the autosomal dominant ataxias in our group. In two SCA1 patients the CAG repeat was expanded to 53-62 repeats, whereas in normal ivdividuals was 12-36 repeats. In seven SCA2 patients the CAG repeat was expanded to 43-47 repeats, whereas in normal ivdividuals was 22-30 repeats. In forty-two MJD/SCA3 patients the CAG repeat was expanded to 63-78 repeats, whereas in normal ivdividuals was 15-38 repeats. The SCA1, SCA2, MJD/SCA3 (CAG)n mutation were excluded in the other 28 SCA patients from 22 families. CONCLUSION: The frequency of MJD/SCA3 is substantially higher than that of SCA1 and SCA2 in the autosomal dominant SCA from Chinese families. Chinese patients with MJD/SCA3 are non-Portuguese patients with MJD/SCA3. Clinical expressions of the various SCAs overlap one another, making a diagnostic classification based on phenotype inaccurate in many instances. It is important for SCA clinical study to make a SCA gene diagnosis and genomic classification.

Schmitt, I., T. Brattig, et al. (1997). "Characterization of the rat spinocerebellar ataxia type 3 gene." Neurogenetics 1(2): 103-12.
Machado-Joseph disease (MJD) belongs to a group of clinically and genetically heterogeneous neurodegenerative disorders characterized by progressive cerebellar ataxia. The disease-causing mutation has recently been identified as an unstable and expanded (CAG)n trinucleotide repeat in a novel gene of unknown function. In Caucasians, repeat expansions in the MJD1 gene have also been found in patients with the clinically distinct autosomal dominant spinocerebellar ataxia type 3 (SCA3). In order to gain insight into the biology of the MJD1/SCA3 gene we cloned the rat homologue and studied its expression. The rat and human ataxin-3 genes are highly homologous with an overall sequence identity of approximately 88%. However, the C-terminal end of the putative protein differs strongly from the published human sequence. The (CAG)n block in the rat cDNA consists of just three interrupted units suggesting that a long polyglutamine stretch is not essential for the normal function of the ataxin-3 protein in rodents. The expression pattern of the SCA3 gene in various rat and human tissues was investigated by Northern blot analyses. The mature transcript is approximately 6 kb in length. In rat testis, a smaller transcript of 1.3 kb was identified. Transcription of rsca3 was detected in most rat tissues including brain. Analyzing the expression level of the SCA3 gene in several human brain sections revealed no significant higher mRNA level in regions predominantly affected in MJD. Thus additional molecules and/or regulatory events are necessary to explain the exclusive degeneration of certain brain areas.

Leggo, J., A. Dalton, et al. (1997). "Analysis of spinocerebellar ataxia types 1, 2, 3, and 6, dentatorubral-pallidoluysian atrophy, and Friedreich's ataxia genes in spinocerebellar ataxia patients in the UK." J Med Genet 34(12): 982-5.
Accurate clinical diagnosis of the spinocerebellar ataxias (SCAs) can be difficult because of overlap in phenotype with other disorders and variation in clinical manifestations. Six SCA loci have been mapped and four disease causing genes identified, in addition to the causative gene for Friedreich's ataxia (FA). All of the identified mutations are expansions of trinucleotide repeat tracts. The SCA2 and SCA6 genes were published recently. The extent of the normal CAG size ranges at these loci and the relative frequencies of the known causes of SCA in the UK are not known. This study first investigated the normal size ranges of the SCA2 and SCA6 loci by genotyping control populations of West African and South African subjects, since African populations generally show the greatest allelic diversity. We found one allele larger than the previously determined normal range for SCA2, and our results at the SCA6 locus agreed with the previously reported normal range. The second component of the study assessed the relative frequencies of the SCA1, 2, 3, and 6, DRPLA, and FA trinucleotide repeat mutations in 146 patients presenting with SCA-like symptoms referred to genetic diagnostic laboratories in the UK. We detected mutations in 14% of patients referred with a diagnosis of autosomal dominant SCA, and in 15% of patients referred with spinocerebellar ataxia where we did not have sufficient family history data available to allow categorisation as familial or sporadic cases. Friedreich's ataxia accounted for 3% of the latter category of cases in our sample, but the most common causes of SCA were SCA2 and SCA6.