Fig. 1.

The linear biogenesis of miRNA. miRNA biogenesis involves transcription of pri-miRNA by RNA polymerase II/III, cleavage by the Drosha-DGCR8 complex to pre-miRNA, followed by export to the cytoplasm by Exportin-5 in the presence of Ran-GTP cofactor. In the cytoplasm, pre-miRNA is cleaved by the Dicer-TRBP complex to a miRNA duplex, which is unwound to a guide strand that is bound to Ago2 and incorporated into the RISC, and a passenger strand, which is degraded. Ultimately, miRNA binding to target mRNAs results in mRNA target cleavage, translational repression, or mRNA decay. A more novel fate of the miRNAs is the selective secretion via microvesicles or exosomes