Expression and Regulation Profile of Mature MicroRNA in the Pig: Relevance to Xenotransplantation

Figure 1

Biogenesis of miRNA and assembly into miRISC and possible mechanisms of miRISC-mediated repression. In animals, the pri-miRNA is transcribed by RNA polymerase II from genomic DNA and is processed by Drosha with the aid of DGCR8 to generate a pre-miRNA species, which is exported from the nucleus and processed by Dicer to form the mature miRNA/miRN duplex. Generally, only one strand of the duplex is then assembled into miRISC. When RISCs bind to mRNAs, they can repress initiation of translation at the stage of cap recognition (I) or 60S recruitment (II). Alternatively, they can induce mRNA deadenylation and thereby inhibit its circularization (III). They can also repress translation at the postinitiation stage through inducing ribosomes to dissociate prematurely (IV). They can also induce deadenylation followed by decapping to facilitate mRNA degradation (V). Without repression, mRNAs recruit initiation factors and ribosomal subunits and form circularized structures (VI).