Schematic of microRNA transfer by exosomes. miRNAs were overexpressed via transfected with miRNAs expression vector and then microRNAs are selectively incorporated into the intraluminal vesicles of a multivesicular bodies (MVBs). Exosomes containing miRNAs are derived from the MVBs and could be released into the extracellular environment by either fusion of MVBs with the cell surface or budding pathway. Exosomes may bind to the plasma membrane of a target cell. Recruited exosomes may either fuse directly with the plasma membrane or first be endocytosed and then fuse with the delimiting membrane of an endocytic compartment. Both pathways result in the delivery of the exosomal miRNAs to the cytoplasm of the target cell where it may associate with and silence corresponding mRNA.
The maturation process of miRNAs. In nucleus, the RNA Pol II transcribes pri-miRNA and be cleaved by DROSHA/DGCR8 complex to form pre-miRNA. Then the pre-miRNA will be transported to the cytoplasm by Exportin-5, where they are further processed by the RNase III endonuclease DICER to form the mature single stranded miRNA. Then the strand will enter the RNA induced silencing complex (RISC) to suppress the target mRNA either by translational repression (Partial complementarity) or by target degradation (complete complementarity).
Selected miRNAs reportedly involved in UV-induced skin response:
Biosynthesis of miRNAs and their role in Pancreatic cancer: