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#egg coat

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Fertilization in mammals-l

Zona pellucida analogous to invertebrate structure:

Zona pellucida is mammalian extracellular coat synthesized by oocyte and granulosa cells composed of sulfated glycoproteins forming porous matrix. It is evolutionarily and functionally homologous to vitelline envelope surrounding sea urchin and other invertebrate eggs. Both mediate species-restricted sperm binding, stimulate acrosome reaction, and after fertilization undergo cortical granule-induced modifications causing envelope elevation or hardening establishing block to polyspermy. Vitelline envelope can be distinguished from jelly layer external to it, much as zona distinct from cumulus. Analogy underscores conserved fertilization strategy across phyla, reproductive biology and developmental patterning principles.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Homology of zona pellucida and vitelline envelope in fertilization.

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Fertilization in mammals-iv

Zona pellucida analogous to:

Zona pellucida is thick extracellular glycoprotein matrix surrounding mammalian oocyte and early embryo, composed of ZP1-ZP4 secreted by oocyte and granulosa cells. Evolutionarily it corresponds to vitelline envelope described in non-mammalian vertebrates and invertebrates like sea urchins and Xenopus, providing species-specific sperm binding barrier, block to polyspermy after hardening and protection during preimplantation development. Jelly coat is additional gelatinous layer outside vitelline envelope in echinoderms, chorion is insect or teleost outer envelope, micropyle is sperm entry canal in fish and insects, making vitelline envelope closest functional and structural analogy to mammalian zona.

Ref: Wassarman & Litscher, Curr Top Dev Biol 1995: Comparative biology of vitelline envelope and zona pellucida glycoprotein families.

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