Sperm-egg interaction

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Abstract
In this paper we discuss the events leading to the recognition and fusion of sperms and eggs. In the course of evolution a glycoprotein coat, the vitelline coat, has differentiated around the egg. This coat carries the sperm receptors and is a product of the oocyte. The receptors are glycoprotein molecules; in most of the species studied fucose appears to be the most important component as regards receptor function. In most, though not in all, animals the interaction of the spermatozoa with the sperm receptors triggers the acrosome reaction. Some observations further suggest that the vitelline coat may also serve to repress the metabolism of the unfertilized egg. Fusion of the spermatozoon with the egg plasma membrane does not require specific receptors. Interaction of the spermatozoon with the sperm receptors elicits profound changes in sperm metabolism that are described as “sperm activation” which in fact precede the acrosome reaction. Prevention of polyspermic fertilization is a complex process: in some species it depends on changes in the molecular organization of the egg plasma membrane triggered by the interaction with the first spermatozoon. In naturally polyspermic eggs it depends on cytoplasmic events that are set in motion once one sperm pronucleus has merged with the egg pronucleus.