Figure 1: Representative scheme summarizing the biogenesis of the miRNA. The cartoon depicts the four main pathways followed by miRNA after extranuclear cleavage by DICER. The miRNA duplex can be processed to single mature miRNA and loaded into exosomes or microvesicles ready for extracellular release (1) or aggregates in P-bodies (2), a new model of mRNA regulation involving miRNA and other specific proteins [122]. However, miRNAs are preferentially loaded into the RISC complex in the cytoplasm, inducing silencing of target mRNA (3). Alternatively, miRNAs are able to enter back into the nucleus and directly bind the promoter region of target genes (4) and influence their expression. Argn = argonaute.