Figure 4: MicroRNA (miRNA) biogenesis and gene expression control in human cells. (1) Canonical pathway produces pre-miRNA by Drosha/DGCR8 cleavage of pri-miRNA. (2) Noncanonical pathway mirtrons are produced by spliced introns debranched by debranching enzyme (Dbr), after which they fold into pre-miRNA hairpins. Pre-miRNA hairpins are exported from the nucleus to cytosol by exportin-5 (Expo-5) and cleaved by Dicer to produce 22 nucleotides RNA duplexes. One strand of the duplex is transferred to Argonaute complex (Ago) and guided to base-pair with its target mRNA throughout its seed sequence. TRBP: tar-RNA binding protein.