#resact

Regeneration -ll

Calcium channels activated by resact in sea urchin sperm are encoded by:

Chemotactic calcium signaling in sea urchin sperm relies on specific ion channels opened downstream of resact binding. Resact activates receptor guanylate cyclase raising cGMP, opening tetraKCNG channels causing hyperpolarization, then depleting cGMP leading to depolarization that activates voltage-dependent calcium entry. Electrophysiology and molecular cloning identified entry path as CatSper channel complex encoded by four homologous CatSper1-4 genes forming heterotetramer in principal piece of flagellum, associated with auxiliary subunits. CatSper null sperm lack calcium pulses and chemotaxis. Bindin, resact, or hyalin genes encode structural adhesion proteins or chemoattractants, not calcium channel subunits responsible for chemosensation.

Ref: EMBO Journal, Seifert et al., The CatSper channel controls chemosensation in sea urchin sperm.

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Regeneration -ll

The protein that provides direction for sperm toward eggs in sea urchins is:

Sea urchin eggs release diffusible peptides into surrounding jelly that establish chemical gradients guiding sperm navigation. Resact, a fourteen amino acid peptide purified from Arbacia punctulata jelly, serves as potent chemoattractant for conspecific sperm, while speract functions in Strongylocentrotus purpuratus. Resact binds to transmembrane guanylate cyclase receptor on sperm flagellum, boosting cGMP, activating cyclic nucleotide-gated K+ channels, causing hyperpolarization, intracellular alkalization, and periodic CatSper calcium influxes that steer flagellum toward higher gradient. Bindin mediates adhesion after arrival, hyalin supports embryonic adhesion, not chemotactic directionality.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Egg-sperm chemotaxis - resact, speract and guanylate cyclase signaling.

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Sea urchin -l

Calcium channels activated by resact in sea urchin sperm are encoded by:

Resact peptide binding to receptor guanylate cyclase on sperm flagellum activates cGMP synthesis opening K+ channels and triggering Ca2+ oscillations critical for chemotactic steering. Electrophysiology and genomics identified cation channel of sperm, CatSper, as major Ca2+ entry route mediating oscillations. CatSper genes encode four homologous subunits forming pH-sensitive channel enriched in flagellar principal piece. Sea urchin genome contains CatSper orthologs; blocking pore abolishes Ca2+ influx and turning. Bindin, resact and hyalin encode adhesion proteins unrelated to conductance. Thus calcium channels activated by resact are encoded by CatSper genes.

Ref: Seifert et al., Nature 2015, CatSper channelosome in sperm; Kaupp Lab - resact/CatSper signaling.

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Sea urchin -l

The protein that provides direction for sperm toward eggs in sea urchins is:

Sea urchin eggs release small soluble peptides into surrounding seawater to actively guide sperm navigation. Speract modulates intracellular Ca2+ to increase flagellar beat frequency aiding vicinity search, while resact is definitive 14-amino-acid chemotactic peptide purified from Arbacia punctulata jelly that attracts sperm directionally. Resact binds receptor guanylate cyclase and elicits rapid cGMP-dependent Ca2+ bursts that transiently increase curvature and steer swimming up concentration gradient, analogous to bacterial chemotaxis. Bindin is sperm adhesion protein, hyalin mediates blastomere adhesion. Resact thus provides precise directional information orienting sperm toward egg center, greatly increasing encounter efficiency during broadcast spawning.

Ref: Ward et al., J Biol Chem 1985, Discovery of resact; Gilbert Chapter 7: Sperm chemotaxis by resact and speract.

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Sea urchin -lll

Resact specifically attracts:

Resact is fourteen amino acid peptide purified from egg jelly of Arbacia punctulata that guides sperm chemotaxis toward egg. It binds high-affinity receptors on sperm flagellum coupled to guanylate cyclase, increasing cGMP and calcium oscillations altering flagellar waveform and steering toward gradient source. Chemotactic response is highly selective; Arbacia sperm respond strongly to Resact at picomolar concentrations, while Strongylocentrotus sperm show minimal response, preferring Speract. This species specificity enhances conspecific fertilization assurance when multiple species spawn simultaneously, contributing to reproductive isolation and preventing hybridization in broadcast spawning marine environment, improving fertilization success significantly.

Ref: Ward et al., Chemotaxis: Resact species-specific attraction conspecific sperm sea urchin reproductive isolation.

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