Intron-mediated enhancement boosts Rtn4 circRNA expression: A robust method for exploring circRNA function

CircRNAs are expressed in many important biological processes. Studying their function requires an effective expression method. When we used intron-mediated enhancement (IME) to improve circRNA expression of mouse Rtn4 (Nogo, a key protein in Nogo-Rho pathways) circRNA as a test case, we achieved a 4-6-fold improvement compared to an existing method. We further developed this approach into a general circRNA expression vector pCircRNA-DMo. An unexpected feature of our approach is its ability to promote translation of circRNA into detectable amounts of proteins. Intriguingly, both monomer and multimer repeating peptides can be observed as a result of rolling circle translation of RTN4 circRNA. We also confirmed the presence of both peptide forms in human and mouse brains, highlighting the significance of circRNA translation in vivo. In summary, we demonstrate the significant advantage of IME in enhancing circRNA biogenesis and hence our vector offers a robust platform for exploring potential circRNA peptide-encoding functions.