Role of EGF, IGF-I, sera and cumulus cells on maturation in vitro of bovine oocytes

We examined the effects of epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), the presence/absence of cumulus cells, and sera (fetal calf serum, FCS or estrous cow serum, ECS) on cumulus expansion and meiotic maturation during in vitro bovine oocyte maturation. The oocytes obtained (n=4491) were divided into cumulus-oocyte complexes (COG) or denuded oocytes and were then cultured in 3 groups comprising TCM-199 and sera: Group I(without serum), Group II (10% FCS), and Group III (10% ECS). Each group was subjected to 4 predefined treatments with growth-factors: control (no growth factor), EGF, IGF-I, and EGF+IGF-I. At the end of the 24-h culture period, the oocytes were assessed for degree of cumulus expansion and metaphase II stage. Treatments with EGF enhanced the incidence of full cumulus expansion in all 3 groups. Maximal stimulation for both cumulus expansion and nuclear maturation occurred with EGF+IGF-I in all groups, mainly in the groups with serum. Regarding the denuded oocytes, no positive effects on nuclear maturation rates were observed for any treatment. These results suggest that: 1) EGF, with or without IGF-I, stimulates cumulus expansion and meiotic maturation significantly; and 2) the presence of FCS or ECS enhances the effect of these growth factors in bovine cumulus-oocyte complexes.