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#sea urchins

7 public questions tagged with this topic.

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

Bindin receptors in sea urchins are located on the:

Species-specific sperm binding occurs on vitelline envelope where Egg Bindin Receptor glycoprotein complex is concentrated. Biochemical isolation shows EBR1 is 350 kDa transmembrane protein with large extracellular domain containing sulfated oligosaccharides recognized by bindin lectin domain. Immunofluorescence localizes EBR1 to vitelline envelope before fertilization, not soluble jelly, internal cortical granules, or deep plasma membrane domains. After cortical granule serine protease cleaves EBR1 extracellular domain, binding sites are lost, contributing to permanent block. Egg plasma membrane contains fusogenic lipids and integrins mediating final membrane merger after initial vitelline anchoring, but primary bindin receptor resides in envelope.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Localization of bindin receptor EBR1 on vitelline envelope.

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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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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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Regeneration -ll

Sea urchins belong to which phylum?

Sea urchins display classic echinoderm traits that place them firmly within phylum Echinodermata alongside starfish, brittle stars, and sea cucumbers. Adults show pentaradial symmetry, endoskeletal ossicles with spines, and a water vascular system operating tube feet for locomotion and feeding. Embryologically they are deuterostomes with radial cleavage, enterocoelic coelom formation, and blastopore becoming anus, aligning them phylogenetically closer to chordates than molluscs or arthropods. Bilateral larvae metamorphose into radial adults, confirming echinoderm affiliation rather than chordate, molluscan, or arthropod body plans.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 1: Echinoderm embryology and phylogenetic position within Deuterostomia.

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Controls Ecosystem

Sea urchins' role in kelp forest ecosystems?

“Primary herbivore” for sea urchins' role in kelp forest ecosystems. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Ecosystem processes are constrained by energy conservation and by the cycling of matter. Energy enters mainly through primary production, is lost as metabolic heat at every transfer, and therefore cannot be recycled in the way that carbon, nitrogen, phosphorus, or water can. The remaining alternatives—“Top predator”, “Primary producer”, “Secondary carnivore”—refer to different states, processes, or scales and therefore do not express the same causal relationship. The relevant inference should follow the pathway from resource supply to organismal uptake and then to ecosystem-level flux. Productivity, trophic transfer, decomposition, and nutrient regeneration are connected, but each measures a different part of that pathway. Linking the wording to measurable consequences for fitness, abundance, or flux gives the conclusion its scientific meaning and prevents a purely mnemonic interpretation.

Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 4

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