Effects of different activation regimens on pronuclear formation and developmental competence of in vitro-matured porcine oocytes after intracytoplasmic sperm injection.

To improve the activation protocol for in vitro-maturated porcine oocytes after intracytoplasmic sperm injection (ICSI), we examined the combined effect of U0126, a specific inhibitor of mitogen-activated protein kinase kinases, and an electrical pulse on pronuclear formation and developmental competence. Two approaches were tested: (i) 6-h treatment of ICSI oocytes with U0126 applied at different intervals (0, 2, 3 or 4 h) after the electrical pulse and (ii) treatment of ICSI oocytes with U0126 applied 4 h after the electrical pulse over an additional 4, 6 or 8 h. Another protein kinase inhibitor, 6-dimethylaminopurine, was used as a chemical activator in control experiments. The highest rates of diploid embryo formation, normal fertilization and blastocyst formation were observed after 6 h of exposure to U0126 starting 4 h after the electrical pulse. Therefore, U0126 can be used as an activating agent for porcine oocytes fertilized by ICSI.