Role of epidermal growth factor in bovine oocyte maturation and preimplantation embryo development in vitro.

Epidermal growth factor (EGF) has been shown to have a positive effect during in vitro maturation (IVM) and has been reported in follicular fluid at levels capable of stimulating meiosis in a variety of species. The aim of the present work was to study the effect on subsequent development of EGF present in defined medium during bovine 1) oocyte maturation or 2) embryo culture. The presence of EGF during IVM, irrespective of concentration (1, 10, 100 ng/mg), stimulated cumulus expansion and significantly increased the proportion of oocytes attaining metaphase II, the rate of cleavage, and the proportion of embryos reaching the 5- to 8-cell stage at 72 h postinsemination. Blastocyst rates on Days 7 and 9 were also significantly improved for oocytes matured in the presence of EGF (10% vs. 18-24% on Day 7 and 21% vs. 31-32% on Day 9, for Tissue Culture Medium 199 [M199] and M199 + EGF, respectively). The presence of fetal calf serum (FCS) during IVM resulted in similarly elevated rates of development. There was no cumulative effect when EGF and FCS were present together during IVM. The presence of EGF also altered the pattern of proteins neosynthesized during maturation. The maturation-promoting effect of EGF was evident for denuded oocytes also, suggesting that EGF may act, at least in part, directly on the oocyte. Immunofluorescence studies revealed the EGF receptor on immature cumulus-oocyte complexes. When present during postfertilization culture in defined medium (synthetic oviduct fluid), EGF stimulated development in comparison to that of the control but could not replace serum. The results suggest a physiological role for EGF in the regulation of bovine oocyte maturation and development.