title: Nuclear speckles are detention centers for transcripts containing expanded CAG repeats.
abstract: The human genetic disorders caused by CAG repeat expansions in the translated sequences of various genes are called polyglutamine (polyQ) diseases because of the cellular "toxicity" of the mutant proteins. The contribution of mutant transcripts to the pathogenesis of these diseases is supported by several observations obtained from cellular models of these disorders. Here, we show that the common feature of cell lines modeling polyQ diseases is the formation of nuclear CAG RNA foci. We performed qualitative and quantitative analyses of these foci in numerous cellular models endogenously and exogenously expressing mutant transcripts by fluorescence in situ hybridization (FISH). We compared the CAG RNA foci of polyQ diseases with the CUG foci of myotonic dystrophy type 1 and found substantial differences in their number and morphology. Smaller differences within the polyQ disease group were also revealed and included a positive correlation between the foci number and the CAG repeat length. We show that expanded CAA repeats, also encoding glutamine, did not trigger RNA foci formation and foci formation is independent of the presence of mutant polyglutamine protein. Using FISH combined with immunofluorescence, we demonstrated partial co-localization of CAG repeat foci with MBNL1 alternative splicing factor, which explains the mild deregulation of MBNL1-dependent genes. We also showed that foci reside within nuclear speckles in diverse cell types: fibroblasts, lymphoblasts, iPS cells and neuronal progenitors and remain dependent on integrity of these nuclear structures.
authors.affiliation: Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14 Str., 61-704 Poznan, Poland.
authors.forename: Martyna O
authors.initials: MO
authors.lastname: Urbanek
authors.affiliation: Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14 Str., 61-704 Poznan, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Jazurek
authors.affiliation: Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14 Str., 61-704 Poznan, Poland.
authors.forename: Pawel M
authors.initials: PM
authors.lastname: Switonski
authors.affiliation: Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14 Str., 61-704 Poznan, Poland.
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Figura
authors.affiliation: Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14 Str., 61-704 Poznan, Poland. Electronic address: wlodkrzy@ibch.poznan.pl.
authors.forename: Wlodzimierz J
authors.initials: WJ
authors.lastname: Krzyzosiak
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D002460:Cell Line; D022003:Cell Nucleus Structures / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D006367:HeLa Cells; D020271:Heredodegenerative Disorders, Nervous System / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006801:Humans; D000071058:Huntingtin Protein / Q000235:genetics / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D051379:Mice; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D012313:RNA / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D014158:Transcription, Genetic; D019680:Trinucleotide Repeat Expansion
chemical_list: C086055:HTT protein, human; D000071058:Huntingtin Protein; C493663:MBNL1 protein, human; D010455:Peptides; D016601:RNA-Binding Proteins; C097188:polyglutamine; D012313:RNA
keywords: CAG foci; CUG foci; Polyglutamine diseases; RNA toxicity; Splicing speckles