Figure 1.

Overview of miRNA Biogenesis. (A) Intergenic primary miRNAs (pri-miRNAs) undergo co-transcriptional microprocessing via DGCR8/DROSHA to produce precursor miRNA (pre-miRNA). (B) In intronic miRNAs, microprocessing occurs during intron commitment for splicing and generally completes before the intron is spliced. (C) Mirtrons are a special class of intronic miRNAs whereby pre-miRNAs are derived directly from intron splicing and (D) lariat debranching by DBR1. (E) Canonical and mirtron pre-miRNAs join a common pathway of Exportin-5 mediated cytoplasmic export, after which (F) DICER cleavage produces a miRNA duplex. (G) miRNA duplexes are loaded onto Argonaute (Ago) proteins whereby strand selection occurs. (H) Retention of the miRNA guide strand by Ago is critical to the formation of the RNA induced silencing complex (RISC) which (I) targets protein-coding mRNAs promoting either transcript degradation or inhibiting translation. Pol II = RNA Polymerase II.