Figure 1.

miRNA biogenesis. The biogenesis of miRNAs involves a series of steps. It begins with the transcription of primary miRNA (pri-miRNA) by RNA polymerase II/III. The pri-miRNA is then cleaved by the Drosha-DGCR8 complex, resulting in the formation of pre-miRNA. The next step involves the export of pre-miRNA from the nucleus to the cytoplasm with the assistance of Exportin-5 and Ran-GTP. In the cytoplasm, the Dicer-TRBP complex further processes pre-miRNA, leading to the generation of a miRNA duplex. The duplex is then unwound, resulting in a mature miRNA strand that is loaded onto the Ago2 protein and incorporated into the RNA-induced silencing complex (RISC). The passenger strand of the miRNA duplex is degraded. Finally, the mature miRNA within the RISC can bind to target mRNAs, leading to mRNA cleavage, repression of translation, or degradation of the mRNA. It is worth noting that miRNAs can be selectively released through microvesicles and exosomes.