ABSTRACT
miRNAs are small RNAs that participate in post-transcriptional gene regulation. miRNAs are important regulators of most cellular processes. Therefore, the levels of miRNAs need to be tightly regulated, specialized to the cell type, developmental state and cellular conditions. This variation of miRNA content between cells is achieved by the regulation of its biogenesis pathway, thus, allowing the generation of specific sets of miRNAs in specific cellular conditions. In eukaryotes, most miRNAs are produced by the canonical miRNA biogenesis pathway. In this pathway, a primary transcript is first produced from the miRNA gene by the action of RNA polymerases. This primary transcript then undergoes several processing steps in nucleus and cytoplasm to finally form the mature miRNA which performs its function of post-transcriptional gene regulation by translational repression or mRNA degradation. Each step of the canonical miRNA biogenesis pathway involves different sets of enzymes and cofactors that can be regulated by different factors to alter the mature miRNA levels. This chapter focuses on the regulation at different steps of the canonical miRNA biogenesis pathway. The steps of canonical miRNA biogenesis pathway are explained in detail. The manipulation of each step by different regulatory factors is elucidated. Finally, the mechanism of function of mature miRNA (mRNA degradation) is also covered.
