Figure 1.

The Biogenesis of microRNAs by Canonical Pathway: Maturation of miRNA sequence by transcription of primary miRNAs or Pri-miRNAs from the miRNA gene by RNA polymerase II followed by the cleavage of Pri-miRNAs to precursor or Pre-miRNAs through Drosha/DGCR8. The Pre-miRNAs are then exported from nucleus to cytoplasm with the help of Exportin 5. In the cytoplasm, Dicer cleavage of the hairpin structure takes place, where one of the strands of the miRNA duplex is loaded onto the RISC via the Argonaut or Ago proteins. Finally, the RISC-loaded miRNAs regulate the repression of gene expression by base complementarity inducing transcriptional repression or mRNA degradation.