RESUMO
Spinocerebellar ataxia type 3 is caused by the expansion of the coding CAG repeat in the ATXN3 gene. Interestingly, a -1 bp frameshift occurring within an (exp)CAG repeat would henceforth lead to translation from a GCA frame, generating polyalanine stretches instead of polyglutamine. Our results show that transgenic expression of (exp)CAG ATXN3 led to -1 frameshifting events, which have deleterious effects in Drosophila and mammalian neurons. Conversely, transgenic expression of polyglutamine-encoding (exp)CAA ATXN3 was not toxic. Furthermore, (exp)CAG ATXN3 mRNA does not contribute per se to the toxicity observed in our models. Our observations indicate that expanded polyglutamine tracts in Drosophila and mouse neurons are insufficient for the development of a phenotype. Hence, we propose that -1 ribosomal frameshifting contributes to the toxicity associated with (exp)CAG repeats.
Assuntos
Drosophila/genética , Mudança da Fase de Leitura do Gene Ribossômico , Proteínas do Tecido Nervoso/genética , Neurônios/metabolismo , Proteínas Nucleares/genética , Fatores de Transcrição/genética , Animais , Animais Geneticamente Modificados , Ataxina-3 , Drosophila/metabolismo , Imuno-Histoquímica , Doença de Machado-Joseph/genética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Proteínas do Tecido Nervoso/metabolismo , Proteínas Nucleares/metabolismo , Peptídeos/química , RNA Mensageiro/metabolismo , Fatores de Transcrição/metabolismo , Transfecção , Expansão das Repetições de TrinucleotídeosRESUMO
Autosomal dominant sensory ataxia is a rare genetic condition that results in a progressive ataxia that is caused by degeneration of the posterior columns of the spinal cord. To date only two families have been clinically ascertained with this condition, both from Maritime Canada. We previously mapped both families to chromosome 8p12-8q12 and have now screened the majority of annotated protein-coding genes in the shared haplotype region by direct DNA sequencing. We have identified a putative pathogenic mutation in the gene encoding ring-finger protein RNF170, a potential ubiquitin ligase. This mutation is a rare non-synonymous change in a well-conserved residue and is predicted to be pathogenic by SIFT, PolyPhen, PANTHER and Align-GVD. Microinjection of wild-type or mutant orthologous messenger RNAs into zebrafish (Danio rerio) embryos confirmed that the mutation dominantly disrupts normal embryonic development. Together these results suggest that the mutation in RNF170 is causal for the sensory ataxia in these families.