title: Prophase I mouse oocytes are deficient in the ability to respond to fertilization by decreasing membrane receptivity to sperm and establishing a membrane block to polyspermy.
abstract: Changes occurring as the prophase I oocyte matures to metaphase II are critical for the acquisition of competence for normal egg activation and early embryogenesis. A prophase I oocyte cannot respond to a fertilizing sperm as a metaphase II egg does, including the ability to prevent polyspermic fertilization. Studies here demonstrate that the competence for the membrane block to polyspermy is deficient in prophase I mouse oocytes. In vitro fertilization experiments using identical insemination conditions result in monospermy in 87% of zona pellucida (ZP)-free metaphase II eggs, while 92% of ZP-free prophase I oocytes have four or more fused sperm. The membrane block is associated with a postfertilization reduction in the capacity to support sperm binding, but this reduction in sperm-binding capacity is both less robust and slower to develop in fertilized prophase I oocytes. Fertilization of oocytes is dependent on the tetraspanin CD9, but little to no release of CD9 from the oocyte membrane is detected, suggesting that release of CD9-containing vesicles is not essential for fertilization. The deficiency in membrane block establishment in prophase I oocytes correlates with abnormalities in two postfertilization cytoskeletal changes: sperm-induced cortical remodeling that results in fertilization cone formation and a postfertilization increase in effective cortical tension. These data indicate that cortical maturation is a component of cytoplasmic maturation during the oocyte-to-egg transition and that the egg cortex has to be appropriately primed and tuned to be responsive to a fertilizing sperm.
authors.affiliation: Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland 21205, USA.
authors.forename: Cassie A
authors.initials: CA
authors.lastname: Kryzak
authors.forename: Maia M
authors.initials: MM
authors.lastname: Moraine
authors.forename: Diane D
authors.initials: DD
authors.lastname: Kyle
authors.forename: Hyo J
authors.initials: HJ
authors.lastname: Lee
authors.forename: Caelin
authors.initials: C
authors.lastname: Cubeñas-Potts
authors.forename: Douglas N
authors.initials: DN
authors.lastname: Robinson
authors.forename: Janice P
authors.initials: JP
authors.lastname: Evans
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D005260:Female; D005306:Fertilization / Q000502:physiology*; D008297:Male; D049469:Meiotic Prophase I / Q000502:physiology*; D008677:Metaphase / Q000502:physiology; D051379:Mice; D009865:Oocytes / Q000502:physiology*; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D015044:Zona Pellucida / Q000502:physiology
keywords: CD9; activation competence; block to polyspermy; cytoplasmic maturation; polyspermy