Figure 1.

The biogenesis and function of circRNAs. There are three main types of circRNAs, including exonic circRNAs, which consist of only exon(s), exon-intron circRNAs (ElciRNA), which consist of both exon(s) and intron(s), and intronic circRNAs (CiRNA), which consist of only intron(s). An exon-intron circRNA can regulate the expression of its parental gene through binding to its promoter. The mechanism of regulation by exonic circRNAs include serving as a decoy for binding to microRNAs (miRNAs); interacting with specific binding elements on RBPs and acting as a sponge to regulate the functions of RBPs and to affect the activities of associated proteins; regulating transcription; and acting as templates to encode proteins.