Fig. 1

Schematic representation of canonical miRNA biogenesis pathway. The miRNA biogenesis is a multistep process. miRNA genes are transcribed by polymerase II or III resulting in primary precursors (pri-miRNAs). Second, pri-miRNAs are cleaved into pre-miRNA by the Microprocessor complex (Drosha-DGCR8) in the nucleus and then transported from the nucleus to the cytoplasm by Exportin-5-Ran-GTP. Drosha/DGCR8 is subjected to complex regulation by positive and negative factors, represented on the figure. In the cytoplasm, Dicer1, TRBP and Paz protein cleave and digest the pre-miRNA to produce a mature duplex miRNA. The functional strand of the mature miRNA is loaded together with AGO-2 proteins into the RISC. The mature miRNA silences target mRNAs through mRNA cleavage or translational repression