RAN translation and frameshifting as translational challenges at simple repeats of human neurodegenerative disorders

Wojciechowska, Marzena; Olejniczak, Marta; Galka-Marciniak, Paulina; Jazurek, Magdalena; Krzyzosiak, Wlodzimierz J.

Frameshifting frequency also depends on the experimental model, with higher frequencies in transfected cells compared with in vivo models. Frameshifted products were observed in intranuclear aggregates within the caudate/putamen of brains from HD patients and in the cortex of HD transgenic mice (29) . However, frameshiftpositive aggregates represented a mere 4% of the total huntingtin-positive inclusions, as demonstrated in the mouse cortex via double immunofluorescence. As a result of occurrence at low level, no frameshift products were detected on western blots of murine brains. Frameshifted huntingtin was also not detected in stable, inducible PC12 cells even after expression of an Htt exon 1 Q74 fragment for 1 month, when the vast majority of cells contained Htt-Gln aggregates as detected by immunocytochemistry (Supplementary Table S3 ). This result suggests that huntingtin frameshifting is time-dependent and occurs at low levels. When N2a cells stably expressing Htt exon 1 with Q65 fragments were additionally transfected with constructs containing 51 CAG repeats, the frequency of frameshifting was >60% (30) .