#fertilization envelope

Regeneration -ll

The fertilization envelope is formed by:

Fertilization envelope does not arise de novo but represents transformed vitelline envelope. Before fertilization vitelline envelope tightly apposes egg plasma membrane and bears sperm receptors. Upon calcium-triggered cortical granule exocytosis, glycosaminoglycans released become highly hydrated osmotically drawing seawater into perivitelline space lifting envelope. Serine protease removes bound sperm and cleaves EBR1, hyalin creates inner supporting layer, ovoperoxidase catalyzes dityrosine crosslinks hardening envelope against mechanical penetration. This elevated modified structure is fertilization envelope, mechanically strong and biochemically non-adhesive, protecting embryo. Hyalin, glycosaminoglycans, or acrosomal proteins alone cannot form envelope without vitelline precursor.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Vitelline to fertilization envelope conversion via cortical granule components.

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Sea urchin -l

Slow block to polyspermy is stabilized by:

After initial elevation triggered by mucopolysaccharide swelling, vitelline envelope transformed into fertilization envelope requires chemical hardening to provide durable mechanical barrier against supersperm and environmental stress. Two cortical granule enzymes accomplish covalent stabilization: egg-specific ovoperoxidase catalyzes oxidative crosslinking forming dityrosine bridges between adjacent envelope glycoproteins using hydrogen peroxide, while transglutaminase catalyzes formation of ε-(γ-glutamyl)lysine isopeptide bonds. Together these enzymatic crosslinks convert soluble vitelline envelope into insoluble, tough, impermeable protective coat encasing embryo. Glycosaminoglycans drive swelling but not stabilization, hyalin builds hyaline layer for cell adhesion, Na+ mediates fast electrical block. Thus stabilization depends on peroxidase-transglutaminase system.

Ref: Foerder & Shapiro, PNAS 1977, Peroxidase hardening; Gilbert, Developmental Biology, Chapter 7: Envelope crosslinking.

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Sea urchin -l

The fertilization envelope is formed by:

After successful sperm fusion, cortical granule exocytosis rapidly releases paracrystalline protein fraction and enzymatic cocktail into perivitelline space between plasma membrane and vitelline layer. Mucopolysaccharide hydration induces osmotic water influx elevating vitelline envelope away from egg surface. Simultaneously proteases sever connections linking bindin receptors to envelope, while transglutaminase and ovoperoxidase catalyze covalent crosslinking of glycoproteins and newly deposited structural proteins hardening envelope into fertilization envelope, tough impermeable protective coat preventing further sperm entry and shielding embryo from mechanical stress. Hyalin, glycosaminoglycans and acrosomal proteins contribute but driving mechanism is vitelline envelope modification and crosslinking.

Ref: NCBI Bookshelf, Developmental Biology, Chapter 7: Fertilization envelope formation from vitelline envelope.

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Sea urchin -lll

Fertilization envelope hardening involves:

Hardening of fertilization envelope after cortical granule release requires enzymatic cross-linking to provide mechanical strength. Granules release calcium-dependent enzymes including ovoperoxidase that utilizes hydrogen peroxide generated by calcium-dependent respiratory burst NADPH oxidase to form di-tyrosine covalent bonds between envelope proteins, and transglutaminase forming epsilon-gamma glutamyl-lysine cross-links, plus proteoliaisin remodeling vitelline structure. Calcium is required for activation and substrate binding of these enzymes. Result is tough, elevated envelope impermeable to sperm, providing permanent polyspermy block and protection from shear. Sodium, potassium, and magnesium ions alone do not drive hardening process.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Fertilization envelope hardening calcium-dependent enzymes ovoperoxidase.

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Sea urchin -lll

The fertilization envelope in sea urchins originates from:

Unfertilized sea urchin egg is surrounded by vitelline membrane, thin extracellular coat containing sperm receptors, overlaid by thick jelly coat. Upon calcium-triggered cortical granule exocytosis, structural proteins and enzymes detach vitelline membrane and harden it via cross-linking by transglutaminase and ovoperoxidase using hydrogen peroxide from respiratory burst. Elevated hardened coat becomes fertilization envelope. Plasma membrane remains beneath, zona pellucida is mammalian equivalent not present in urchins, egg jelly dissolves. Thus fertilization envelope originates directly from modified vitelline membrane repurposed as protective barrier essential for embryonic development.

Ref: Alberts, Molecular Biology of the Cell, Chapter: Fertilization envelope derived from vitelline membrane sea urchin.

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