#sperm activation

Regeneration -ll

Sperm motility in sea urchins is initiated by:

Sea urchin sperm are kept quiescent in gonads where pH is acidic and carbon dioxide high, maintaining intracellular pH around 7.2. Upon spawning into seawater pH 8.0, sodium-hydrogen exchangers extrude protons driven by sodium gradient, raising internal pH to 7.6. Alkalization activates dynein ATPase, increases mitochondrial oxygen consumption, enhances flagellar beat frequency, and sensitizes guanylate cyclase to chemotactic peptides. Acidifying agents inhibit motility, while artificial alkalization with ammonium chloride activates motility without egg factors. Thus increased internal pH, not decreased pH or mere external pH change without internal effect, initiates forward motility and chemosensory competence.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Sperm activation via intracellular pH increase and Na+/H+ exchange.

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Regeneration -ll

In sea urchins, the sperm acrosomal reaction begins when sperm contacts:

The acrosome reaction is triggered before sperm contacts vitelline envelope or egg plasma membrane, ensuring bindin exposure at correct time. Initial stimulus comes from fucose-sulfate-rich glycoconjugates and low molecular weight peptides within egg jelly surrounding egg. Jelly components induce calcium influx via voltage-gated channels and activation of Na+/H+ antiport raising intracellular pH, causing outer acrosomal membrane fusion with plasma membrane releasing acrosomal enzymes and polymerizing actin to project acrosomal process. Vitelline envelope interaction follows jelly-induced priming; egg membrane fusion occurs afterwards, and nuclear contact never directly triggers reaction.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Acrosome reaction triggered by egg jelly polysaccharides.

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Regeneration -ll

Which ion is primarily involved in sperm activation in sea urchins?

Sea urchin sperm remain immotile in testes due to low pH and high CO2, then activate upon spawning into alkaline seawater. Egg jelly peptides speract and resact bind receptor guanylate cyclase on flagellar membrane, elevating cGMP, opening K+ channels, hyperpolarizing membrane, and activating Na+/H+ exchanger raising intracellular pH. Alkalization triggers CatSper channels opening causing calcium influx. Calcium pulses transform flagellar beat from symmetric low-amplitude to asymmetric high-amplitude turning events, accelerating respiration and preparing acrosomal exocytosis. Thus calcium acts as central second messenger linking chemotactic sensing to motility activation and readiness for fertilization.

Ref: NCBI Bookshelf, Molecular Biology of the Cell, Chapter 21: Sperm chemotaxis and CatSper-mediated Ca2+ influx in sea urchin.

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Sea urchin -l

Which ion is primarily involved in sperm activation in sea urchins?

Sea urchin sperm activation and chemotaxis involve dramatic intracellular ion fluxes coordinating motility. Egg jelly peptides like resact bind receptor guanylate cyclase localized on flagellar membrane, raising cGMP that opens K+ selective channels hyperpolarizing membrane, then Na+/H+ exchanger SLC9C1 raises intracellular pH activating dynein motor. Crucially Ca2+ influx through CatSper-associated channels in flagellum triggers increased asymmetric beating and acrosome reaction exocytosis. Intracellular Ca2+ oscillations also regulate turning behavior during chemotactic navigation toward egg. While K+, Na+, Mg2+ modulate excitability, Ca2+ acts as central second messenger orchestrating flagellar beat changes and secretory events.

Ref: Kaupp et al., Nature Reviews Mol Cell Biol 2008, Sperm chemotaxis and Ca2+ signaling in sea urchins.

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