In vitro developmental competence of ICSI-derived activated ovine embryos

Abstract

The present study was conducted to determine the necessity for activation after intracytoplasmic sperm injection (ICSI) in sheep. The effect of chemical stimulation with either 5 μM ionomycin (I) for 5 min or ionomycin + 2 mM 6-dimethylaminopurine (6-DMAP) for 3 h on the efficiency of ICSI, was compared in six experimental groups: (1) ICSI, (2) ICSI + I, (3) ICSI + I + 6DMAP, (4) Sham, (5) Sham + I, and (6) parthenogenetics (Sham and parthenogenetic groups were used as controls). In the present study, ovine oocytes needed additional chemical stimulation, after conventional ICSI, to activate (female pronucleous formation) and to form zygotes with male and female pronuclei (2PN). The percentage of cleaved embryos obtained and developed to blastocyst stage was higher ( P < 0.001) for ICSI-derived zygotes, followed by activation (I and I + 6DMAP; 18.2 and 22.5%, respectively) than ICSI and Sham injection without activation (3.0 and 0.0%, respectively). There was, however, no significant difference between activation protocols I or I + 6DMAP. Furthermore, there was no significant difference among chemically activated, ICSI-derived zygotes in term of hatchability rate; however, the percentage was significantly higher in parthenogenetic and IVF groups than ICSI and Sham injection. In conclusion, neither sperm alone nor mechanical activation was sufficient for ovine oocyte activation and pronuclei formation. Therefore, in our study conditions for in vitro embryo development, chemical activation of oocytes must be considered an essential part of the ICSI procedure in sheep.