title: Establishment of the mammalian membrane block to polyspermy: evidence for calcium-dependent and -independent regulation.
abstract: One crucial result of egg activation is the establishment of blocks on the zona pellucida and the egg plasma membrane to prevent fertilization by additional sperm. The mechanism(s) by which a mammalian egg regulates the establishment of the membrane block to polyspermy is largely unknown. Since Ca(2+) signaling regulates several egg activation events, this study investigates how sperm-induced Ca(2+) transients affect the membrane block to polyspermy, building on our previous work (Biology of Reproduction 67:1342). We demonstrate that mouse eggs that experience only one sperm-induced Ca(2+) transient establish a membrane block that is less effective, than in eggs that experience normal sperm-induced Ca(2+) transients but that is more effective than in eggs with completely suppressed [Ca(2+)](cyt) increases. Sperm-induced increases in [Ca(2+)](cyt) regulate the timing of membrane block establishment, as this block is established more slowly in eggs that experience one or no sperm-induced Ca(2+) transients. Finally, our studies produce the intriguing discovery that there is also a Ca(2+)-independent event that is associated with fertilization in the pathway leading to membrane block establishment. Taken together, these data indicate that Ca(2+) plays a role in facilitating membrane block establishment by regulating the timing with which this change in egg membrane function occurs, and also that the membrane block differs from other post-fertilization egg activation responses as Ca(2+) is not the only stimulus. The membrane block to polyspermy in mammalian eggs is likely to be the culmination of multiple post-fertilization events that together modify the egg membrane's receptivity to sperm.
authors.affiliation: Division of Reproductive Biology, Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Room W3606, 615 N. Wolfe St., Maryland, USA.
authors.forename: Allison J
authors.initials: AJ
authors.lastname: Gardner
authors.forename: Carmen J
authors.initials: CJ
authors.lastname: Williams
authors.forename: Janice P
authors.initials: JP
authors.lastname: Evans
mesh_terms: D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism; D020013:Calcium Signaling; D002462:Cell Membrane / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D005307:Fertilization in Vitro; D008297:Male; D008322:Mammals / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D009866:Oogenesis; D010312:Parthenogenesis; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013480:Superovulation; D015053:Zygote / Q000378:metabolism*
chemical_list: D002614:Chelating Agents; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D002118:Calcium