Epidermal growth factor in human follicular fluid stimulates mouse oocyte maturation in vitro

Objective: To study the effect of human follicular fluid (FF) and the specific contribution of its epidermal growth factor (EGF) component on the in vitro maturation of cumulus-enclosed mouse oocytes. Design: A previously described mouse oocyte model system was used to study the effect of FF on oocyte maturation before and after extraction of EGF by immunoprecipitation. Follicular fluid specimens enclosing both mature and immature human oocytes were tested. Main Outcome Measures: The endpoints assessed were the percentage of oocytes undergoing germinal vesicle breakdown (GVBD) and polar body one formation at different intervals over a 24-hour period and the final degree of cumulus expansion achieved. Results: A concentration-related stimulatory effect of mature FF was noted when compared with the spontaneous increase of GVBD and polar body one formation observed for the EGF-free control medium. Overall, the effect of immature FF was inhibitory. After extraction of EGF from FF by immunoprecipitation from both immature and mature FF, the rates of GVBD and polar body one formation were decreased in both groups. The addition of 5 ng/mL of EGF to the extracted groups reversed this effect on polar body one formation. Cumulus expansion was maximal for oocytes incubated with mature FF and minimal for those incubated with EGF- free media. Conclusions: The positive effect of mature human FF on mouse oocyte maturation and cumulus expansion is to a large extent because of the presence of EGF.