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A role for both wild-type and expanded ataxin-7 in transcriptional regulation
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Medical and Clinical Genetics.
Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Clinical Neurophysiology.
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Medical and Clinical Genetics.
2005 (English)In: Neurobiology of Disease, ISSN 0969-9961, E-ISSN 1095-953X, Vol. 20, no 3, 646-655 p.Article in journal (Refereed) Published
Abstract [en]

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease primarily affecting the brainstem, retina and Purkinje cells of the cerebellum. The disease is caused by a polyglutamine expansion in ataxin-7, a protein found in two complexes TFTC and STAGA, involved in transcriptional regulation. Transcriptional dysregulation has been implicated in the pathology of several polyglutamine diseases. In this paper, we analyzed the effect of both wild-type and expanded ataxin-7 on transcription driven by the co-activator CBP and the Purkinje cell expressed nuclear receptor RORα1. We could show that transcription mediated by both CBP and RORα1 was repressed by expanded ataxin-7. Interestingly, repression of transcription could also be observed with wild-type full-length ataxin-7, not only on CBP- and RORα1-mediated transcription, but also on basal transcription. The repression could be counteracted by inhibition of deacetylation, suggesting that ataxin-7 may act as a repressor of transcription by inhibiting the acetylation activity of TFTC and STAGA.

Place, publisher, year, edition, pages
2005. Vol. 20, no 3, 646-655 p.
Keyword [en]
spinocerebellar ataxia type 7, polyglutamine, CAG repeat, acetylation, CREB-binding protein/genetics, cell nucleus/genetics/metabolism, cerebellum/*metabolism/pathology/physiopathology, child, histones/metabolism, humans, male, mutation/genetics, nerve tissue proteins/*genetics, promoter regions (genetics)/genetics, purkinje cells/metabolism/pathology, receptor protein-tyrosine kinases, receptors; cell surface/genetics, regulatory elements; transcriptional/*genetics, repressor proteins/genetics, silencer elements, transcriptional/genetics, spinocerebellar ataxias/*genetics/metabolism/physiopathology, trans-activation (genetics)/genetics, trinucleotide repeat expansion/genetics, tumor cells, cultured
National Category
Medical Genetics
URN: urn:nbn:se:umu:diva-3802DOI: 10.1016/j.nbd.2005.04.018PubMedID: 15936949OAI: diva2:142677
Available from: 2004-03-17 Created: 2004-03-17 Last updated: 2010-08-24Bibliographically approved
In thesis
1. Expression and functional analysis of the SCA7 disease protein ataxin-7
Open this publication in new window or tab >>Expression and functional analysis of the SCA7 disease protein ataxin-7
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Studier av uttrycket och funktionen av SCA7 sjukdomsproteinet ataxin-7
Abstract [en]

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease characterized by cerebellar ataxia and visual problems due to a progressive and selective loss of neurons within the cerebellum, brainstem and retina. The disease is caused by the expansion of a CAG repeat in the first coding exon of the SCA7 gene, resulting in an expanded polyglutamine domain in the N-terminal part of ataxin-7, a protein of unknown function.

To expand our knowledge of the ataxin-7 protein and the mechanism by which mutant ataxin-7 causes disease, we have studied the expression and function of both the normal and the mutated ataxin-7 protein.

Ataxin-7 expression was examination in brain and non-CNS tissues from SCA7 patients and age-matched controls. Expression was predominantly nuclear in neurons throughout the brain of both healthy and SCA7 individuals. We also observed aggregation of mutant ataxin-7 in the nuclei of neurons. No obvious difference in the expression level of ataxin-7 or the formation of aggregates could be observed between affected and non-affected brain regions in SCA7 patients. Based on these findings, we could conclude that the cell type specific neurodegeneration in SCA7 is not due to differences in expression levels or to the formation of ataxin-7 aggregates.

To widen our studies on ataxin-7 expression, we isolated and characterized the mouse SCA7 gene homolog. Cloning of the mouse SCA7 gene revealed two SCA7 mRNA isoforms that were highly homologous to their human counterparts. Immunohistochemical analysis also revealed a conserved expression pattern of ataxin-7 in adult mouse brain. In addition, ataxin-7 expression was observed during embryonic development in brain as well as in several non-neuronal tissues such as heart, liver and lung.

Besides SCA7, eight neurodegenerative disorders are known to be caused by expanded polyglutamine repeats, including SCA 1-3, 6 and 17, DRPLA, SBMA and Huntington’s disease. The polyglutamine disorders have many features in common and a common pathological disease mechanism involving transcriptional dysregulation has been proposed. To investigate the possible involvement of transcriptional dysregulation in SCA7 pathology, we analyzed the effects of both wild-type and expanded ataxin-7 on transcription driven by the co-activator CBP, the Purkinje cell-expressed nuclear receptor RORα1 or a basic TATA promoter. As previously shown for other polyglutamine disease proteins, expansion of the polyglutamine domain in ataxin-7 leads to reduced transcription. Surprisingly, strong repression of CBP-mediated, RORα1-mediated and basal transcription was also observed with wild-type ataxin-7, suggesting that the normal ataxin-7 protein may have a role in transcriptional regulation.

129 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 886
Molecular biology, Polyglutamine disease, CAG repeat, Spinocerebellar ataxia type 7, Molekylärbiologi
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
urn:nbn:se:umu:diva-214 (URN)91-7305-628-6 (ISBN)
Public defence
2004-04-16, Hörsal Betula, 6M, Umeå Universitet, Umeå, 09:00
Available from: 2004-03-17 Created: 2004-03-17Bibliographically approved

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