A study in The Journal of Cell Biology describes how a secreted enzyme helps egg cells avoid being fertilized by more than one sperm. Because polyspermy disrupts embryonic development, oocytes take several steps to ensure they only fuse with a single sperm. One key step is to prevent additional sperm from binding to the surface of an already-fertilized egg, a blockade that involves the release of secretory granules and cleavage of a protein called ZP2, a component of the zona pellucida matrix that surrounds eggs...
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