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Spinocerebellar ataxia type 7 (SCA7) is a genetic neurodegenerative disorder caused by a CAG-polyglutamine repeat expansion. Purkinje cells (PCs) are central to the pathology of ataxias, but their low abundance in the cerebellum underrepresents their transcriptomes in sequencing assays. To address this issue, we developed a PC enrichment protocol and sequenced individual nuclei from mice and patients with SCA7. Single-nucleus RNA sequencing in SCA7-266Q mice revealed dysregulation of cell identity genes affecting glia and PCs. Specifically, genes marking zebrin-II PC subtypes accounted for the highest proportion of DEGs in symptomatic SCA7-266Q mice. These transcriptomic changes in SCA7-266Q mice were associated with increased numbers of inhibitory synapses as quantified by immunohistochemistry and reduced spiking of PCs in acute brain slices. Dysregulation of zebrin-II cell subtypes was the predominant signal in PCs of SCA7-266Q mice and was associated with the loss of zebrin-II striping in the cerebellum at motor symptom onset. We furthermore demonstrated zebrin-II stripe degradation in additional mouse models of polyglutamine ataxia and observed decreased zebrin-II expression in the cerebella of patients with SCA7. Our results suggest that a breakdown of zebrin subtype regulation is a shared pathological feature of polyglutamine ataxias. Editor's summary: Spinocerebellar ataxias (SCAs) are neurodegenerative diseases affecting coordination and movement. Purkinje cells (PCs) are especially vulnerable in SCAs, but their low abundance makes cell type–specific transcriptomic profiling difficult. Using a PC enrichment protocol for snRNA-seq, Bartelt et al. discovered that genes contributing to zebrin-II PC subtype identity were dysregulated in the SCA7-266Q mouse model. Immunohistochemistry revealed a loss of zebrin-II striping in the cerebella of SCA7-266Q mice and mouse models of other SCA subtypes. snRNA-seq on postmortem cerebellar tissue from patients with SCA7 demonstrated zebrin-II dysregulation in molecular layer interneurons. These results suggest that dysregulation of zebrin-II cell subtypes in the cerebellum is a shared feature across SCAs. —Daniela Neuhofer [ABSTRACT FROM AUTHOR]

Many neurodegenerative disorders, such as Alzheimer's, Parkinson's and polyglutamine diseases, share a common pathogenic mechanism: the abnormal accumulation of disease-causing proteins, due to either the mutant protein's resistance to degradation or overexpression of the wild-type protein. We have developed a strategy to identify therapeutic entry points for such neurodegenerative disorders by screening for genetic networks that influence the levels of disease-driving proteins. We applied this approach, which integrates parallel cell-based and Drosophila genetic screens, to spinocerebellar ataxia type 1 (SCA1), a disease caused by expansion of a polyglutamine tract in ataxin 1 (ATXN1). Our approach revealed that downregulation of several components of the RAS-MAPK-MSK1 pathway decreases ATXN1 levels and suppresses neurodegeneration in Drosophila and mice. Importantly, pharmacological inhibitors of components of this pathway also decrease ATXN1 levels, suggesting that these components represent new therapeutic targets in mitigating SCA1. Collectively, these data reveal new therapeutic entry points for SCA1 and provide a proof-of-principle for tackling other classes of intractable neurodegenerative diseases., The increasing prevalence of neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease in the ageing population is one of our most pressing public health issues (1,2). There is no [...]

Transgenic mice homozygous for a spinocerebellar ataxia type 1 (SCA1) gene containing an expanded CAG trinucleotide repeat show degeneration of the cerebellar cortex Purkinjie cells and develop ataxia. Mice containing a normal SCA1 gene do not develop ataxia. Mice heterozygous for the CAG repeat do not develop ataxia, although a small amount of Purkinjie cells degenerate. Thus the phenotype of ataxia is seen only if a sufficient number of Purkinjie cells degenerate. The CAG trinucleotide repeat is present in the coding region of SCA1 gene.

A conditional transgenic mouse model of spinocerebellar ataxia type 1 (SCA1) is used to delay the postnatal expression of mutant ATXN1 until after completion of cerebellar development in order to examine the effect of development on SCA1. The analysis has shown that a decrease of ROR[alpha]-mediated gene expression during development is a key factor in the susceptibility of Purkinje cells to SCA1.

Spinocerebellar ataxia type 1 (SCA1) is a dominant trinucleotide repeat neurodegenerative disease characterized by motor dysfunction, cognitive impairment, and premature death. Degeneration of cerebellar Purkinje cells is a frequent and prominent pathological feature of SCA1. We previously showed that transport of ATXN1 to Purkinje cell nuclei is required for pathology, where mutant ATXN1 alters transcription. To examine the role of ATXN1 nuclear localization broadly in SCA1-like disease pathogenesis, CRISPR-Cas9 was used to develop a mouse with an amino acid alteration (K772T) in the nuclear localization sequence of the expanded ATXN1 protein. Characterization of these mice indicates that proper nuclear localization of mutant ATXN1 contributes to many disease-like phenotypes including motor dysfunction, cognitive deficits, and premature lethality. RNA sequencing analysis of genes with expression corrected to WT levels in Atxn1 175QK772T/2Q mice indicates that transcriptomic aspects of SCA1 pathogenesis differ between the cerebellum, brainstem, cerebral cortex, hippocampus, and striatum. • An SCA1 knockin mouse model with a mutated NLS in ATXN1-polyQ was generated • NLS mutation mitigates ATXN1-polyQ-related lifespan, motor, and cognitive deficits • Gene expression alterations and molecular pathology differ across brain regions • Nuclear localization of ATXN1-polyQ is a critical aspect of SCA1 disease pathology SCA1, a lethal polyglutamine (polyQ) neurodegenerative disease, displays motor and cognitive impairments. Here, CRISPR-Cas9 was used to mutate the nuclear localization sequence of ATXN1-polyQ in a knockin SCA1 mouse model. The results indicate that ATXN1-polyQ nuclear localization contributes to all SCA1-like phenotypes. However, disease-associated changes in gene expression differ between affected brain regions. [ABSTRACT FROM AUTHOR]

Previous studies indicate that while transgenic mice with ATXN1[30Q]-D776-induced disease share pathological features caused by ATXN1[82Q] having an expanded polyglutamine tract, they fail to manifest the age-related progressive neurodegeneration seen in spinocerebellar ataxia type 1. The shared features include morphological alterations in climbing fiber (CF) innervation of Purkinje cells (PCs). To further investigate the ability of ataxin-1 (ATXN1) to impact CF/PC innervation, this study used morphological and functional approaches to examine CF/PC innervation during postnatal development in ATXN1[30Q]-D776 and ATXN1[82Q] cerebella. Notably, ATXN1[30Q]-D776 induced morphological alterations consistent with the development of the innervation of PCs by CFs being compromised, including a reduction of CF translocation along the PC dendritic tree, and decreased pruning of CF terminals from the PC soma. As previously shown for ATXN1[82Q], ATXN1[30Q]-D776 must enter the nucleus of PCs to induce these alterations. Experiments using conditional ATXN1[30Q]-D776 mice demonstrate that both the levels and specific timing of mutant ATXN1 expression are critical for alteration of the CF-PC synapse. Together these observations suggest that ATXN1, expressed exclusively in PCs, alters expression of a gene(s) in the postsynaptic PC that are critical for its innervation by CFs. To investigate whether ATXN1[30Q]-D776 curbs the progressive disease in ATXN1[82Q]-S776 mice, we crossed ATXN1[30Q]-D776 and ATXN1[82Q]-S776 mice and found that double transgenic mice developed progressive PC atrophy. Thus, the results also show that to develop progressive cerebellar degeneration requires expressing ATXN1 with an expanded polyglutamine tract. [ABSTRACT FROM AUTHOR]

The article focuses on a study related to neuronal dysfunction in ataxin-1 (ATXN1) in mice. It says that the hypothesis of abnormalities in climbing fiber (CF)-Purkinje cell (PC) and parallel fiber (PF) were tested using flavoprotein autofluorescence optical imaging and extracellular field potential recordings and found that they contributed to ATXN1 dysfunction. It also says that prevention of transgene expression during postnatal cerebellar development causes amelioration of the abnormalities.

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant, polyglutamine-induced neurodegenerative disorder that results in loss of motor coordination caused primarily by a disruption of cerebellar Purkinje cell function. In this study, we developed a conditional SCA1 mouse model to examine whether stopping expression of mutant ataxin-1 alters the disease phenotype. After cessation of SCA1[82Q] transgene expression, mutant ataxin-1, including that in nuclear inclusions, was cleared rapidly from Purkinje cells. At an early stage of disease, Purkinje cell pathology and motor dysfunction were completely reversible. After halting SCA1 expression at later stages of disease, only a partial recovery was seen. Interestingly, restoration of the ability to perform a complex motor task, the accelerating Rotarod, correlated with localization of mGluR1α to the Purkinje cell-parallel fiber synapse. These results show that the progression of SCA1 pathogenesis is dependent on the continuous expression of mutant ataxin-1. Of note, even at a late stage of disease, Purkinje cells retain at least some ability to repair the damage caused by mutant ataxin-1. [ABSTRACT FROM AUTHOR]

Identifies an ataxin-1-interacting ubuiquitin-like protein (A1Up) using the yeast two-hybrid system. Presence of A1U mRNA in Purkinje cells; Role of ataxin-1 in the formation and regulation of multimeric protein complexes within the nucleus; Relationship between the co-localization of A1Up with ataxin-1 in transfected cells and the extent of A1Up expressed and the number of glutamines in ataxin-1.

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. [ABSTRACT FROM AUTHOR]

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant, polyglutamine-induced neurodegenerative disorder that results in loss of motor coordination caused primarily by a disruption of cerebellar Purkinje cell function. In this study, we developed a conditional SCA1 mouse model to examine whether stopping expression of mutant ataxin-1 alters the disease phenotype. After cessation of SCA1[82Q] transgene expression, mutant ataxin-1, including that in nuclear inclusions, was cleared rapidly from Purkinje cells. At an early stage of disease, Purkinje cell pathology and motor dysfunction were completely reversible. After halting SCA1 expression at later stages of disease, only a partial recovery was seen. Interestingly, restoration of the ability to perform a complex motor task, the accelerating Rotarod, correlated with localization of mGluR1alpha to the Purkinje cell-parallel fiber synapse. These results show that the progression of SCA1 pathogenesis is dependent on the continuous expression of mutant ataxin-1. Of note, even at a late stage of disease, Purkinje cells retain at least some ability to repair the damage caused by mutant ataxin-1.