miRNA biogenesis and function. (A) The canonical miRNA biosynthesis pathway. Drosha indicates an RNase type III endonuclease; DGCR8, DiGeorge syndrome critical region 8; Dicer, another RNase type III endonuclease; TRBP, TAR RNA-binding protein; RISC, RNA-induced silencing complex; Ago, Argonaute 2; and ORF, open reading frame. (B) The seed region of the miRNA (bp 2-8) binds to complementary sites on the 3′-UTR of target mRNAs where it predominantly causes a decrease in mRNA levels but may also inhibit translation.