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#fertilization cone

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Regeneration -ll

Fertilization cone formation involves:

After sperm-egg plasma membrane fusion, egg cortex reorganizes beneath fusion site into funnel-like protrusion called fertilization cone that engulfs sperm head and midpiece drawing nucleus inward. This structure depends on rapid polymerization of cortical actin microfilaments orchestrated by small GTPases RhoA, Rac, and Arp2/3 complex nucleating branched filaments. Actin mesh pushes membrane around sperm and provides traction. Myosin II later contracts cone, tubulin microvilli elongate slightly, and dynein remains sperm flagellar motor. Inhibition of actin polymerization with cytochalasin D prevents cone formation leaving sperm attached externally, proving actin assembly essential for incorporation of male pronucleus.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Fertilization cone formation via actin polymerization in egg cortex.

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Sea urchin -l

Fertilization cone formation involves:

Immediately after sperm-egg plasma membrane fusion, egg cortex locally remodels beneath bound spermatozoon to form conspicuous fertilization cone. Process begins with transient depolymerization of cortical actin followed by rapid GTPase-dependent actin polymerization involving Arp2/3 complex and formins, pushing plasma membrane outward into blunt protrusion engulfing sperm head and midpiece while drawing sperm nucleus into ooplasm. Myosin II contractility and microtubule-based transport assist later incorporation and pronuclear migration but initial protrusion itself driven by localized actin polymerization triggered by calcium and small GTPases. Cytochalasin B inhibition blocks cone formation preventing sperm internalization, demonstrating dependence on actin dynamics.

Ref: Gilbert, Developmental Biology, Chapter 7: Fertilization cone - actin-based engulfment of sperm.

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