Internal Ribosome Entry Segment Activity of ATXN8 Opposite Strand RNA

Spinocerebellar ataxia type 8 (SCA8) involves the expansion of CTG/CAG repeats from the overlapping ataxin 8 opposite strand (ATXN8OS) and ataxin 8 (ATXN8) genes located on chromosome 13q21. Although being transcribed, spliced and polyadenylated in the CTG orientation, ATXN8OS does not itself appear to be protein coding, as only small open reading frames (ORFs) were noted. In the present study we investigated the translation of a novel 102 amino acids containing-ORF in the ATXN8OS RNA. Expression of chimeric construct with an in-frame ORF-EGFP gene demonstrated that ATXN8OS RNA is translatable. Using antiserum raised against ORF, ATXN8OS ORF expression was detected in various human cells including lymphoblastoid, embryonic kidney 293, neuroblastoma IMR-32, SK-N-SH, SH-SY5Y cells and human muscle tissue. The biological role of the ATXN8OS ORF and its connection to SCA8 remains to be determined.