MicroRNA-21 in extracellular vesicles contributes to the growth of fertilized eggs and embryo development in mice

Human preimplantation embryo development is susceptible to high rates of early embryo wastage. We determined the miR-21 expression of extracellular vesicles (EVs) in fertilized eggs and embryos of varying stages and their response to miR-21 microinjection. Sexually mature female and male mice were mated. Next, the expression and immunohistochemistry intensity of surface markers (CD9 and CD63) of EVs were detected in pregnant and non-pregnant mice. Exosomes were co-cultured with embryos for detection of blastocyst formation rate, and embryo apoptosis. Moreover, the expressions of Bcl-2 associated X protein (Bax), B cell lymphoma 2 (Bcl-2), and octamer-binding transcription factor-4 (Oct4) were determined. Finally, we detected miR-21 expression in EVs of uterus in pregnant mice, in embryos after embryo implantation and after embryo co-cultured with exosomes in uterine luminal fluid. MiR-21 was up-regulated in EVs of uterus, and higher immunohistochemistry intensity of CD9 and CD63, suggesting more EVs secreted in uterine luminal fluid in pregnant mice. After microinjection, miR-21 inhibitor suppresses embryo development of mice. Moreover, embryos co-cultured with exosomes display higher blastocyst formation rate, reduced apoptotic rate of embryos in pregnant mice. In addition, miR-21 was down-regulated with the development of embryos after embryo implantation, while miR-21 expression in embryos was up-regulated by exosomes in uterine luminal fluid in the pregnant mice. Increased miR-21 expression in EVs of uterus and increased miR-21 expression after implantation, which indicate the key role in the growth of fertilized eggs and embryo development in mice.