Fig. 1.

Biogenesis, sorting, releasing and uptaking of miRNAs from MSC-derived exosomes. After miRNAs and EXOs are generated, some miRNAs specifically bind to RNA-binding proteins or membrane proteins according to specific motifs in miRNAs and are transported to EXOs by them. An RNA-binding proteins or membrane proteins can bind to different miRNAs with the same motifs. An RNA-binding proteins or membrane proteins also bind to more than one motif miRNA. EXOs are released extracellular through exocytosis, and miRNA can be protected from extracellular degradation under the protection of EXOs. Recipient cells absorb released EXOs through three mechanisms. (1) Direct fusion with the plasma membrane, (2) Phagocytosis, (3) Receptor-mediated endocytosis