| Abstract: | We have developed an inexpensive in vitro system for studying cumulus penetration and fertilization by using physiological numbers of sperm. This system simulates conditions believed to exist in vivo more closely than any in current usage. In this system, 1–100 hamster sperm are used to challenge fresh hamster oocyte-cumulus complexes (OCC). Only fresh (nonoviducal) OCC are used, as they present the most stringent challenge to sperm. Because sperm numbers are low, OCC do not disperse, and sperm can be studied microscopically during penetration of the cumulus oophorus and corona radiata. These conditions permit microscopic assessment of the sperm acrosome. Video tapes of experiments allow easy review and analysis of experiments. Results obtained employing this technique show that, in vitro, (1) capacitated, acrosome-intact hamster sperm can penetrate the extracellular matrix between cumulus cells and bind to the zona pellucida; (2) the “figure-eight motility” characteristic of hyperactivated hamster sperm swimming in culture medium is suppressed when sperm swim in the extracellular matrix between cumulus cells; and (3) fertilization occurs in capillary tubes when low numbers of sperm are used. The in vitro system that we have described will be useful in analyzing the mechanisms used by sperm to penetrate the cumulus and corona radiata and to clarify the role of the acrosomal enzymes in fertilization. |
