Figure 1.

The canonical pathway of miRNA biogenesis. Pri-miRNA is then cleaved by the Drosha/DGCR8 complex to form pre-miRNA, which is exported from the nucleus to the cytoplasm by exportin 5. Once in the cytoplasm, the pre-miRNA is cut into a small, immature dsRNA duplex that contains both the mature miRNA strand and complementary strand by another RNase-III–type endonuclease, Dicer. One strand of the mature miRNA forms a complex with Dicer and the Argonaute protein, also called miRNA-containing RISC, and the miRNA binds to the 3′-UTR of its target mRNA, resulting in target mRNA degradation or translational repression. AGO, Argonaute; DGCR8, DiGeorge syndrome critical region 8; miRISC, miRNA-containing RNA-induced silencing complex; 3′-UTR, 3′-Untranslated regions.