Figure 1.

MicroRNAs biogenesis and function. In the nucleus, pri-miRNAs are transcribed by RNA Polymerase II (Pol II) to pre-miRNAs after processing by the microprocessor complex, which consists of Drosha and DGCR8. Pre-miRNAs are exported from the nucleus to the cytoplasm by exportin-5 and processed into the miRNA-miRNA* duplex by Dicer. The duplex is separated into two strands: one strand is selected as the mature miRNA, and the other strand is degraded. Mature miRNAs are incorporated into RISC (RNA-induced silencing complex) to produce target mRNA repression (imperfect complementarity) or mRNA cleavage (perfect complementarity). pri-miRNAs: Primary miRNAs; Pol II: RNA Polymerase II; pre-miRNAs: MiRNAs precursor; DGCR8: DiGeorge syndrome critical region gene; miRNA: MicroRNA; RISC: RNA-induced silencing complex.