title: RNA gain-of-function in spinocerebellar ataxia type 8.
abstract: Microsatellite expansions cause a number of dominantly-inherited neurological diseases. Expansions in coding-regions cause protein gain-of-function effects, while non-coding expansions produce toxic RNAs that alter RNA splicing activities of MBNL and CELF proteins. Bi-directional expression of the spinocerebellar ataxia type 8 (SCA8) CTG CAG expansion produces CUG expansion RNAs (CUG(exp)) from the ATXN8OS gene and a nearly pure polyglutamine expansion protein encoded by ATXN8 CAG(exp) transcripts expressed in the opposite direction. Here, we present three lines of evidence that RNA gain-of-function plays a significant role in SCA8: 1) CUG(exp) transcripts accumulate as ribonuclear inclusions that co-localize with MBNL1 in selected neurons in the brain; 2) loss of Mbnl1 enhances motor deficits in SCA8 mice; 3) SCA8 CUG(exp) transcripts trigger splicing changes and increased expression of the CUGBP1-MBNL1 regulated CNS target, GABA-A transporter 4 (GAT4/Gabt4). In vivo optical imaging studies in SCA8 mice confirm that Gabt4 upregulation is associated with the predicted loss of GABAergic inhibition within the granular cell layer. These data demonstrate that CUG(exp) transcripts dysregulate MBNL/CELF regulated pathways in the brain and provide mechanistic insight into the CNS effects of other CUG(exp) disorders. Moreover, our demonstration that relatively short CUG(exp) transcripts cause RNA gain-of-function effects and the growing number of antisense transcripts recently reported in mammalian genomes suggest unrecognized toxic RNAs contribute to the pathophysiology of polyglutamine CAG CTG disorders.
authors.affiliation: Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN, USA.
authors.forename: Randy S
authors.initials: RS
authors.lastname: Daughters
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Tuttle
authors.forename: Wangcai
authors.initials: W
authors.lastname: Gao
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Melinda L
authors.initials: ML
authors.lastname: Moseley
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Ebner
authors.forename: Maurice S
authors.initials: MS
authors.lastname: Swanson
authors.forename: Laura P W
authors.initials: LP
authors.lastname: Ranum
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D002460:Cell Line; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D006801:Humans; D045586:Intranuclear Inclusion Bodies / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D012313:RNA / Q000235:genetics / Q000378:metabolism*; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020754:Spinocerebellar Ataxias / Q000235:genetics* / Q000378:metabolism; D019680:Trinucleotide Repeat Expansion
chemical_list: C415906:ATXN8OS gene product, human; C493663:MBNL1 protein, human; D009419:Nerve Tissue Proteins; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D016601:RNA-Binding Proteins; D012313:RNA
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