Impact of circRNA on the complex regulatory network of the cell

MicroRNAs (miRNAs) are small nucleotides that can bind to messenger RNA (mRNA) preventing its translation. Different mRNA targets can have the same miRNA binding site leading to a miRNA-mediated cross-talk between competitive endogenous RNA (ceRNA) species (1-3). Circular RNAs (circRNAs) are yet another example of ceRNAs (4), first discovered by electron microscopy in an RNA virus in 1976 (5). These are single stranded non-coding RNAs that have their 3' and 5' ends covalently linked due to back-splicing, thus acquiring a circular form. Due to their low transcript abundance, circRNAs were originally thought to be a byproduct of aberrant splicing of mRNA (6). In recent years, however, progress in high-throughput technologies and bioinformatics lead to the identification of many new circRNAs.