FIG. 1.

miRNAs biogenesis and mechanisms of action. Briefly, miRNA genes are transcribed by RNA polymerase II as pri-miRNAs. pri-miRNAs with 5′ cap (m⁷G) and 3′ polyadenylate are further cleaved into pre-miRNA by Drosha/DGCR8 complex. Pre-miRNAs are actively exported from nucleus to cytoplasm by exportin5/Ran-GTP. In cytoplasm, pre-miRNAs are recognized by Dicer/TRBP complex and cut to generate double-strand miRNAs. One of the two strands is selected as guide and assembled RISC to bind 3′ UTR of target genes and suppress its expression, while the complementary one is degraded. After completing its task, the mature miRNA is degraded by the 5′-3′ exoribonuclease or 3′-5′ exoribonucleases. miRNA, microRNAs; pri-miRNAs, primary miRNAs; RISC, RNA-induced silencing complex; TRBP, transactivating response RNA-binding protein; UTR, untranslated region.