Abnormal RNA structures (RNA foci) containing a penta‐nucleotide repeat (UGGAA)_n in the Purkinje cell nucleus is associated with spinocerebellar ataxia type 31 pathogenesis

Abstract

Spinocerebellar ataxia type 31 (SCA31) is an autosomal-dominant cerebellar ataxia showing a Purkinje cell (PC)-predominant neurodegeneration in humans. The mutation is a complex penta-nucleotide repeat containing (TGGAA)n , (TAGAA)n , (TAAAA)n and (TAGAATAAAA)n inserted in an intron shared by two different genes BEAN1 and TK2 located in the long arm of the human chromosome 16. Previous studies have shown that (TGGAA)n is the critical component of SCA31 pathogenesis while the three other repeats, also present in normal Japanese, are not essential. Importantly, it has been shown that BEAN1 and TK2 are transcribed in mutually opposite directions in the human brain. Furthermore, abnormal RNA structures called "RNA foci" are observed by a probe against (UAGAAUAAAA)n in SCA31 patients' PC nuclei, indicating that the BEAN1-direction mutant transcript appears instrumental for the pathogenesis. However, it is not known whether the critical repeat (TGGAA)n contributes to the formation of RNA foci, neither do we understand how the RNA foci formation is relevant to the pathogenesis. To address these issues, we investigated two SCA31 cerebella by fluorescence in situ hybridization using a probe against (UGGAA)n . We also asked whether the mutant BEAN1-transcript containing (UGGAA)n exerts toxicity compared to the other three repeats in cultured cells. Histopathologically, we confirm that the PC is the main target of SCA31 pathogenesis. We find that the RNA foci containing (UGGAA)n are indeed observed in PC nuclei of both SCA31 patients, whereas similar foci were not observed in control individuals. In both transiently and stably expressed cultured cell models, we also find that the mutation transcribed in the BEAN1-direction yields more toxicity than control transcripts and forms RNA foci detected with probes against (UGGAA)n and (UAGAAUAAAA)n . Taking these findings together, we conclude that the RNA foci containing BEAN1-direction transcript (UGGAA)n are associated with PC degeneration in SCA31.

Characterization of Target mRNA Reduction Through In Situ RNA Hybridization in Multiple Organ Systems Following Systemic Antisense Treatment in Animals

“…Recent advances in whole genome sequencing have revealed significant complexity in the molecular ''lesions'' underlining human diseases and many of the gene products associated with these lesions are considered ''undruggable'' with traditional therapeutic approaches (Wheeler et al, 2012;NiiMi et al, 2013). Oligonucleotide-based antisense technology is theoretically ideal for treatment of these otherwise ''undruggable'' targets.…”

Spinocerebellar ataxia type 36 exists in diverse populations and can be caused by a short hexanucleotide GGCCTG repeat expansion

“…These findings may suggest that SCA36 pathological features are distinct from those of non-coding repeat expansion disorders. Future investigations should search for abnormal RNA structures (‘RNA foci’) in these affected neuronal cells, as have been detected in other related diseases caused by repeat expansions in introns: myotonic dystrophy type 2 (DM2),7 SCA1020 and SCA31 8 21…”

Modulation of error-sensitivity during a prism adaptation task in people with cerebellar degeneration

“…The impairments that we observed in the abrupt protocol reproduced results of a number of previous prism adaptation studies (Martin et al 1996;Milder and Reinecke 1983;Weiner et al 1983). Although lesions in these previous studies were not necessarily restricted to the cerebellum, all patients studied here had pure cerebellar type deficits with little involvement of other systems: SCA6 is characterized mainly by degeneration of Purkinje cell in the superior parts of the vermis and hemispheres (Ishikawa et al 1999;Sasaki et al 1998;Takahashi et al 1998), and SCA31 also results mainly in degeneration of Purkinje cells (Niimi et al 2013;Seidel et al 2012), although regions other than the cerebellar cortex may also be affected in SCA6 or SCA31 (Seidel et al 2012;Wang et al 2010). The present results expand previous findings by suggesting that Purkinje cell dysfunction leads to impairments in prism adaptation in humans.…”