Circular RNAs

Circular RNAs (circRNAs) are generated by back-splicing of lncRNA or mRNA exons. High-throughput sequencing has uncovered thousands of circRNA species in human cells and tissues and circRNAs are particularly abundant in the brain. As with lncRNAs, the number of circRNAs with important biological functions is more challenging to estimate. circRNAs are exceptionally stable, with an average half-life of ~20 hours (compared to ~2 hours for mRNAs). This stability is presumably because the majority of eukaryotic RNA degradation pathways, including those recruited by miRNAs, act at the 5′ or 3′ end of transcripts. However, some circRNAs are more rapidly turned over. One such circRNA is Cdr1as, which is highly expressed in the brain, contains 70+ conserved sites for miR-7, and is post-transcriptionally regulated by miR-7. How and where does Cdr1as turnover occur? Are similar mechanisms used to degrade other circRNAs?