Figure 1.

miRNA biogenesis. In the nucleus, canonical miRNAs are processed by the endoribonuclease, Drosha, in partnership with DGCR8. In contrast, mirtrons are processed by the spliceosome. The pre-miRNA is then exported from the nucleus into the cytoplasm by Exportin-5, and it is processed into a mature miRNA by Dicer. After RISC incorporation, mature miRNAs inhibit translation or promote degradation of their target mRNA transcripts depending on the degree of complementarity between the 3′-UTR of the target mRNA and the seed region of the miRNA.