Figure 1.

Mechanisms for circRNA biogenesis. CircRNA formation may proceed through a direct back-splicing pathway (dashed arrow) driven by intron pairing or RNA-binding protein interaction (a, see Figure 2), through an exon skipping lariat mechanism (dashed arrow) during alternative splicing events (b) and alternatively, circRNAs may be produced through the canonical splicing pathway depending on the presence of lariats resistant to debranching activity (c).