Bidirectional Expression of CUG and CAG Expansion Transcripts and Intranuclear Polyglutamine Inclusions in Spinocerebellar Ataxia Type 8

Nat Genet. 2006 Jul;38(7):758-69. doi: 10.1038/ng1827. Epub 2006 Jun 25.

Abstract

We previously reported that a (CTG)n expansion causes spinocerebellar ataxia type 8 (SCA8), a slowly progressive ataxia with reduced penetrance. We now report a transgenic mouse model in which the full-length human SCA8 mutation is transcribed using its endogenous promoter. (CTG)116 expansion, but not (CTG)11 control lines, develop a progressive neurological phenotype with in vivo imaging showing reduced cerebellar-cortical inhibition. 1C2-positive intranuclear inclusions in cerebellar Purkinje and brainstem neurons in SCA8 expansion mice and human SCA8 autopsy tissue result from translation of a polyglutamine protein, encoded on a previously unidentified antiparallel transcript (ataxin 8, ATXN8) spanning the repeat in the CAG direction. The neurological phenotype in SCA8 BAC expansion but not BAC control lines demonstrates the pathogenicity of the (CTG-CAG)n expansion. Moreover, the expression of noncoding (CUG)n expansion transcripts (ataxin 8 opposite strand, ATXN8OS) and the discovery of intranuclear polyglutamine inclusions suggests SCA8 pathogenesis involves toxic gain-of-function mechanisms at both the protein and RNA levels.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Chromosomes, Artificial, Bacterial / genetics
  • Disease Models, Animal
  • Humans
  • Mice
  • Mice, Transgenic
  • Molecular Sequence Data
  • Nerve Tissue Proteins / chemistry
  • Nerve Tissue Proteins / genetics*
  • Nerve Tissue Proteins / metabolism
  • Peptides / genetics
  • Peptides / metabolism
  • Phenotype
  • RNA, Long Noncoding
  • RNA, Untranslated
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Spinocerebellar Ataxias / genetics*
  • Spinocerebellar Ataxias / pathology
  • Spinocerebellar Ataxias / physiopathology
  • Trinucleotide Repeat Expansion*

Substances

  • ATXN8OS gene product, human
  • Nerve Tissue Proteins
  • Peptides
  • RNA, Long Noncoding
  • RNA, Untranslated
  • Recombinant Proteins
  • polyglutamine