Circular RNA identified from Peg3 and Igf2r.

Circular RNA is a newly discovered class of non-coding RNA generated through the back-splicing of linear pre-mRNA. In the current study, we characterized two circular RNAs that had been identified through NGS-based 5'RACE experiments. According to the results, the Peg3 locus contains a 214-nucleotide-long circular RNA, circPeg3, that is detected in low abundance from the neonatal brain, lung and ovary. In contrast, the Igf2r locus contains a group of highly abundant circular RNAs, circIgf2r, showing multiple forms with various exon combinations. In both cases, the expression patterns of circPeg3 and circIgf2r among individual tissues are quite different from their linear mRNA counterparts. This suggests potential unique roles played by the identified circular RNAs. Overall, this study reports the identification of novel circular RNAs specific to mammalian imprinted loci, suggesting that circular RNAs are likely involved in the function and regulation of imprinted genes.