Fig. 2.

The biogenesis of miR-18a. Model of miR-18a biogenesis, function and secretion. The miR-18a gene is transcribed into pri-miR-18a in the nucleus and is processed by the Microprocessor complex, which is composed of Drosha and DGCR8, to generate pre-miR-18a. Pre-miR-18a is then exported into the cytoplasm by exportin 5 (EXP 5) and cleaved by Dicer into a miRNA duplex. One strand of the duplex is selectively loaded into the RNA-induced silencing complex (RISC) along with argonaut (AGO). Mature miR-18a in the RISC complex can engage in base pairing with its target mRNA and induce translational repression or can be transferred into recipient cells directly by microvesicles or loaded into multivesicular bodies (MVBs) and exosomes, which are subsequently secreted into the extracellular space