co-evolving with the CAG-repeat tract - modulates Huntington's disease phenotypes.

Circular RNA (circRNA) molecules have critical functions during brain development and in brain-related disorders. Here, we identified and validated a circRNA, , stemming from the Huntington's disease (HD) gene locus that is most abundant in the central nervous system (CNS). We uncovered its evolutionary conservation in diverse mammalian species, and a correlation between levels and the length of the CAG-repeat tract in exon-1 of in human and mouse HD model systems. The mouse orthologue, , is expressed during embryogenesis, increases during nervous system development, and is aberrantly upregulated in the presence of the expanded CAG tract. While an IRES-like motif was predicted in , the circRNA does not appear to be translated in adult mouse brain tissue. Nonetheless, a modest, but consistent fraction of associates with the 40S ribosomal subunit, suggesting a possible role in the regulation of protein translation. Finally, c overexpression experiments in HD-relevant ST striatal cells revealed its ability to modulate CAG expansion-driven cellular defects in cell-to-substrate adhesion, thus uncovering an unconventional modifier of HD pathology.