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Unformatted text preview: BICD 130 Embryos, Genes, and Development Four major components of fertilization Contact and recognition between sperm and egg -- quality control (same species) Regulation of sperm entry into the egg -- quantity control (essential that only a single sperm fertilizes egg) Fusion of genetic material of sperm and egg -- yields diploid cell (zygote) Activation of egg metabolism to initiate development Sea urchin fertilization Sea urchin acrosome reaction Initiated by contact of sperm with egg jelly Mediated by sea urchin receptors for egg jelly (suREJs) located directly above acrosomal vesicle Involves species-specific carbohydrates in egg jelly Acrosome reaction: Activation of sperm by contact with egg Exocytosis: fusion of acrosomal membrane with sperm cell membrane; release of contents of acrosomal vesicle Polymerization of actin monomers into actin microfilaments; extension of acrosomal process Exposure of bindins The acrosome reaction of sea urchin sperm The acrosome reaction of sea urchin sperm Mammalian fertilization Capacitation: Fresh mammalian sperm must reside for a time in the female reproductive tract before being competent to undergo the acrosome reaction Mouse fertilization The acrosome reaction of hamster sperm Species specificity of sea urchin fertilization Evidence for the identification of a sea urchin egg receptor for sperm Foltz et al. (1993) Science 259: 1421-1425 Limited number of bindin receptors on sea urchin eggs Fibrillar structure of the mouse zona pellucida Carbohydrate groups on ZP3 are essential for binding to sperm ZP3-binding proteins are located in the mouse sperm cell membrane, overlying the acrosome
Antibody to ZP3-binding protein Radioactively labeled ZP3 binds to capacitated mouse sperm Entry of sea urchin sperm into the egg Entry of sperm into hamster egg Tangential fusion of hamster sperm acrosome with egg microvilli Sea urchin fast block to polyspermy: Rapid change in egg electrical potential Contents of cortical granules serine protease mucopolysaccharides peroxidase hyalin Sea urchin: Cortical granules lie adjacent to the egg cell membrane Sea urchin: Cortical granule exocytosis and the slow block to polyspermy Sea urchin: Cortical granule exocytosis and the slow block to polyspermy Wave of calcium release during fertilization of sea urchin egg Cleavage: Series of mitotic divisions that divides the egg cytoplasm into smaller cells These cells are called blastomeres Very rapid increase in cell number during cleavage in the frog embryo An abbreviated cell cycle during cleavage Yolk distribution defines the animal-vegetal axis of the egg
Animal pole yolk Vegetal pole Amount and distribution of yolk Isolecithal: sparse, evenly distributed yolk Mesolecithal: moderately dense yolk, concentrated toward vegetal pole Telolecithal: dense yolk throughout most of egg; one pole relatively yolk-free Centrolecithal: dense yolk in center of egg ...
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