Figure 1.

Biogenesis (a) and main pathways (b) of miRNA-21. (a) MiR-21 biogenesis looks similar to that of other miRNA molecules: pri-miR-21 is processed by Drosha endonuclease and DGCR8 protein to pre-miR-21 (this is done in the cell nucleus); then, pre-miR-21 is transferred to the cytoplasm by the enzyme exportin 5. In the cytoplasm, the Dicer enzyme removes the final loop of the pre-miR-21 structure to form a mature miR-21. (b) Mature miR-21 can act intracellularly by silencing mRNA, or it can be secreted outside the cell and regulate among others inhibition of apoptosis, induction of angiogenesis, and proliferation and survival of fibroblasts.