MECHANISMS OF MAMMALIAN FERTILIZATION

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The zona peltucida (ZP) is a thick extracellular c0at that surrounds all mammalian eggs. The mouse egg ZP consists of three glycoproteins, called mZP1-3. Genes encoding the glycoproteins are expressed exclusively by growing mouse oocytes during a 2-3 week period and the nascent glycoproteins are assembled into crosslinked filaments that constitute the ZP. One of the glycoproteins, mZP3, is recognized in a species-specific manner by free-swimming, acrosome-intact sperm when they bind to unfertilized eggs. Binding to mZP3 induces sperm to undergo the acrosome reaction, a form of cellular exocytosis. Only acrosome-reacted sperm can penetrate the ZP and fuse with egg plasma membrane to form a zygote. In this application, experiments are described that continue to address significant questions about ZP glycoproteins and the egg ZP, The Specific Aim of this proposal is to evaluate relationships between mZP2 and mZP3 polypeptide primary structures and secretion and assembly of these glycoproteins into filaments using growing mouse oocytes, transgenic mice, and transfected mammalian cells. It is proposed that secretion and assembly of ZP glycoproteins is regulated by specific domains of rnZP2 and mZl>3 polypeptides. Many of the experiments proposed are possible because of results obtained and methodolgy developed during the previous grant period. The experiments include the use of mutated and wild-type mZP genes, a variety of epitope-tagged mZP cDNA constructs microinjected into growing mouse oocytes, transgenic mice carrying mutated transgenes, and transfected mammalian cells. Results of these experiments should provide important molecular information about possible relationships between ZP glycoprotein primary structures, secretion of ZP glycoproteins from growing oocytes, and assembly of ZP glycoproteins into long filaments. In view of the great similarities between mouse and human ZP glycoproteins and between fertilization in mice and humans, it is very likely that information obtained here will apply to humans as well. Furthermore, the research could have important consequences for development of novel reversible contraceptive methods that prevent ZP formation during oogenesis in humans.