Figure 1.

miRNA biogenesis and their functions. A miRNA gene is transcribed by RNA polymerase II (Pol II) to form a primary transcript (pri‐miRNA) with a hairpin loop. The hairpin in the pri‐miRNA is identified by the Drosha‐DGCR8 microprocessor complex, and the pri‐miRNA is converted into the pre‐miRNA. The pre‐miRNA is exported from the nucleus into the cytoplasm by Exportin‐5. Then the pre‐miRNA is processed by the RNase III endonuclease Dicer, yielding a miRNA‐double duplex, which is loaded into Argonaute (Ago) protein to generate the RNA‐induced silencing complex (RISC), then one strand of the duplex is degraded while the other guides the RISC to the target mRNA, thus leading to direct mRNA cleavage or translational repressing