Repeat ‐associated non‐AUG translation from antisense CCG repeats in fragile X tremor/ataxia syndrome

ObjectiveRepeat‐associated non‐AUG (RAN) translation drives production of toxic proteins from pathogenic repeat sequences in multiple untreatable neurodegenerative disorders. Fragile X‐associated tremor/ataxia syndrome (FXTAS) is one such condition, resulting from a CGG trinucleotide repeat expansion in the 5′ leader sequence of the FMR1 gene. RAN proteins from the CGG repeat accumulate in ubiquitinated inclusions in FXTAS patient brains and elicit toxicity. In addition to the CGG repeat, an antisense mRNA containing a CCG repeat is also transcribed from the FMR1 locus. We evaluated whether this antisense CCG repeat supports RAN translation and contributes to pathology in FXTAS patients. MethodsWe generated a series of CCG RAN translation‐specific reporters and utilized them to measure RAN translation from CCG repeats in multiple reading frames in transfected cells. We also developed antibodies against predicted CCG RAN proteins and used immunohistochemistry and immunofluorescence on FXTAS patient tissues to measure their accumulation and distribution. ResultsRAN translation from CCG repeats is supported in all 3 potential reading frames, generating polyproline, polyarginine, and polyalanine proteins, respectively. Their production occurs whether or not the natural AUG start upstream of the repeat in the proline reading frame is present. All 3 frames show greater translation at larger repeat sizes. Antibodies targeted to the antisense FMR polyproline and polyalanine...
Source: Annals of Neurology - Category: Neurology Authors: Tags: Research Article Source Type: research