Fig. 1
From: Targeting miRNA by CRISPR/Cas in cancer: advantages and challenges
A graphical illustration of miRNA biogenesis. The pre-miRNAs have one or more incomplete hairpin structures that have a stem of about 33 base pairs. Ribonucleases Drosha and Dicer process the pri-miRNA precursor in two separate processes. In the nucleus, Drosha first cuts the pri-miRNA into a pre-miRNA about 70 nucleotides in length, which is then transferred to the cytoplasm by XPO5. The mature, functional, ds miRNA is then processed by Dicer using the pre-miRNA as a template. After maturation, the miRNA is covalently linked to RISC, a multiprotein complex that contains the AGO protein and is essential for RNA silencing. Exon 1 and exon 2 are connected together when the RNA splicing process takes place and leads to the formation of the lariat RNA (circular molecules with a short tail). Following RNA splicing and additional processing, the intron-containing spliced lariat may function as a pri-miRNA for intronic miRNA synthesis. XPO5 exportin-5, ds double-stranded, RISC RNA-induced silencing complex, AGO argonaute, ADAR adenosine deaminase RNA specific, TRBP tar RNA-binding protein, EGFR epidermal growth factor receptor