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At the time of fertilization, mammalian eggs are enveloped by an egg-specific extracellular matrix, the zona pellucida (zp). For fertilization to occur, sperm must recognize and bind to the zp. ZP-binding triggers exocytosis in the acrosomal region of the sperm head (the acrosome reaction, AR), which is mandatory for sperm passage through the zp and access to the egg plasma membrane where gamete fusion occurs. Thus, the related events of sperm-zp binding and zp-triggered ARs are key regulators of fertilization. Although sperm-zp interaction carries species specificity, the fundamental mechanisms of communication between gametes at this level appear conserved among many animals (Saling 1989; Wassarman 1988). |
