Epidermal growth factor induces acrosomal exocytosis in bovine sperm.

At the time of fertilization mammalian spermatozoa undergo a Ca(2+)-dependent exocytotic event, which is known as the acrosome reaction (AR). We describe here that EGF-receptor (EGFR) is localized in the head of bull spermatozoa and that epidermal growth factor (EGF) can induce the occurrence of the AR in its typical dose-dependent manner. Previously we showed that protein kinase C (PKC) is involved in the cascade leading to AR in bull spermatozoa. Here, we show that PKC is involved in the mechanism in which EGF exerts its effect on AR. These findings together with our results which show inhibition of AR by tyrosine-phosphorylation inhibitors, indicate that ejaculated bull sperm contain a typical 170-kDa EGFR which is active in the mechanism leading to AR.