Figure 1.

A schematic of miRNA biogenesis. miRNA biogenesis begins in the nucleus, where genes are mainly transcribed by RNA polymerase II into pri-miRNAs. Pri-miRNAs are processed into pre-miRNA by the RNase III enzyme, Dorsha and DGCR8. After being transported into cytoplasm by Exportin-5/Ran-GTP, pre-miRNAs are further processed by Dicer and TRBP to yield miRNAs duplex. An functional miRNA strand is unwound from the miRNAs duplex and then loaded into the RISC to form an miRISC assembly, which are the functional forms of miRNAs and the regulator of gene expression in posttranscriptional level by interacting with the target mRNA.