Figure 1.

miRNA biogenesis and mode of action. miRNA biogenesis embodies a multistep process catalyzed by specific RNA polymerases. miRNAs are initially transcribed as a long, capped and polyadenylated pri-miRNA, cropped by the Drosha complex into a hairpin pre-miRNA. Following translocation to the cytoplasm by Exportin-5, the pre-miRNA is further processed by the Dicer complex, generating a ~22-nucleotide mature miRNA–miRNA duplex. The guide strand is then selected by the Argonaute protein and integrated into an RNA-induced silencing complex (RISC) to form the miRNA–RISC. This will act on target mRNAs, including aquaporin (AQP) mRNAs, by binding to the 3′-UTR and leading to translational inhibition or mRNA degradation (see text for more details).