Fig. 2.

Step-by-step illustration of miRNA pathway in regulating gene expression within a eukaryotic cell: (1) Transcription of DNA into pri-miRNA. (2) Dorsha processes pri-mRNA into pre-miRNA (hairpin shape). (3) Pre-miRNA is transported to cytoplasm by Exportin-5. (4a) pre-miRNAs can be released from the cytoplasm into extracellular environment, or (4b) Pre-miRNA is processed by Dicer to generate mature miRNA duplex in the cytoplasm. (5a) Binding miRNA to proteins to form RNA-induced silencing complex (RISC)*. One of the double strands (i.e., the passenger strand) is removed, and only the guide strand is present, or (5b) secretion of mature miRNAs to outside of the cell. (6a) RISC binds to mRNA with perfect match. (6b) RISC binds to mRNA with some mismatches. (7a) mRNA degradation when the RISC binds to a perfect match mRNA sequence, or (7b,c) either translation inhibition, or mRNA deadenylation leading to mRNA destabilization when some mismatches of mRNA sequence and the RISC. *RISC is also known as miRISC in miRNA-mediated RNA interference pathway