Protein synthesis and acrosome reaction-inducing activity of human cumulus cells

The acrosome reaction of human spermatozoa is a prerequisite to fertilization. It has been hypothesized that secretions of cumulus cells could be involved in the induction of this sperm reaction. A source of variation in the in-vitro fertilization of human oocytes could be the maturational differences in the cumulus cells which affect the acrosome reaction. In order to investigate this possibility, we have studied the capability of secretions obtained from cumulus cells of different maturational stages to induce the acrosome reaction. Capacitated spermatozoa were exposed to the culture medium containing cumulus cell secretions and their acrosomal status was evaluated using the triple stain technique. The maturational status of the cumulus or fertilization of the enclosed oocyte did not influence the percentage of acrosome-reacted live spermatozoa. In order to further document these observations, cumulus cells were submitted to [35S]methionine incorporation and total and secreted proteins were analysed by SDS-PAGE electrophoresis. Neither quantitative nor qualitative changes were detected in the electrophoretic patterns of the proteins obtained from cumulus cells of different maturational status. Thus, variation of the acrosome reaction-inducing activity of cumulus cells does not appear to be involved in the variable fertilization of oocytes obtained from follicles of differing maturity.