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#cortical granule reaction

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Regeneration -ll

During cortical granule reaction, glycosaminoglycans:

Cortical granules discharge heterogeneous mixture; glycosaminoglycans such as chondroitin sulfate proteoglycans are major osmotically active component. Upon release into narrow perivitelline space they rapidly hydrate and swell, generating high colloid osmotic pressure drawing water between vitelline envelope and plasma membrane. Resulting influx expands space beneath envelope lifting it outward to create perivitelline space and nascent fertilization envelope. Hardening occurs later via ovoperoxidase-mediated dityrosine crosslinking, while receptor removal depends on protease cleavage. Glycosaminoglycans do not harden envelope, digest receptors, or induce acrosomal exocytosis; their physical swelling provides elevating force essential for block.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Glycosaminoglycans and osmotic elevation of fertilization envelope.

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Regeneration -ll

The cortical granule reaction requires an increase in intracellular:

Cortical granule exocytosis is strictly calcium-dependent exocytosis analogous to neurotransmitter release. Fertilization activates phospholipase C producing IP3 that triggers calcium release from endoplasmic reticulum via IP3 receptors. Cytoplasmic free calcium increases from nanomolar resting to micromolar levels propagating as wave across cortex. Calcium binds synaptotagmin-like calcium sensors on granule membranes promoting assembly of SNARE complexes driving membrane fusion and content discharge. Elevation of sodium, potassium, or magnesium accompanies fertilization potential but cannot substitute. Chelation of calcium by intracellular BAPTA injection completely abolishes cortical reaction demonstrating absolute requirement for intracellular calcium surge.

Ref: NCBI Bookshelf, Egg Activation: IP3-mediated calcium wave and cortical granule exocytosis in sea urchin.

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Sea urchin -l

During cortical granule reaction, glycosaminoglycans:

Among cortical granule components massively released during slow block to polyspermy are large sulfated mucopolysaccharides, hyaline and glycoproteins that hydrate explosively upon discharge into extracellular space. Their high colloid osmotic pressure and water-binding capacity draws surrounding seawater and ovular fluid into perivitelline space between egg plasma membrane and elevated vitelline envelope, causing dramatic space expansion and envelope elevation that physically separates sperm receptors from oolemma. Subsequent hardening by peroxidase-mediated dityrosine crosslinking and transglutaminase isopeptide crosslinking then freezes envelope in raised position. Glycosaminoglycan-driven swelling crucially creates space for lifting envelope, while proteases digest receptors and ovoperoxidase hardens structure independently.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Perivitelline space expansion by mucopolysaccharides.

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