Skip to content
Login Register

#gamete recognition

3 public questions tagged with this topic.

Regeneration -ll

The primary role of the bindin protein in sea urchin sperm is:

Bindin is a thirty-five kilodalton insoluble protein sequestered within sperm acrosomal vesicle and exposed at tip of acrosomal process after calcium-dependent exocytosis. It contains lectin-like domains recognizing sulfated polysaccharides on Egg Bindin Receptor EBR1 glycoprotein embedded in vitelline envelope. Interaction confers species-specific binding, constituting major barrier to heterospecific fertilization and reproductive isolation. Beyond adhesion, bindin exhibits amphipathic fusogenic activity promoting mixing of sperm and egg lipid bilayers facilitating membrane fusion. It does not power dynein-driven motility, regulate intracellular alkalization, or mediate chromatin condensation occurring during spermiogenesis.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Bindin - species-specific adhesion and membrane fusion in sea urchin.

View Details
Sea urchin -l

Species specificity during fertilization in sea urchins primarily depends on:

While initial sperm attraction by egg jelly provides coarse guidance, lasting species-specific recognition at binding step depends critically on precise molecular complementarity between sperm protein bindin and its large glycoprotein receptor EBR1 on vitelline envelope. Bindin sequence shows hypervariable regions among sea urchin species, and receptor binding pocket compatibility determines adhesion strength and specificity. Heterologous bindin experimentally fails to agglutinate eggs despite vigorous motility and intact flagellar proteins. Flagellar components, actin filaments or ATPase enzymes do not confer selectivity. Competition with recombinant bindin isoforms blocks fertilization species-specifically, demonstrating bindin-receptor complex as primary determinant enforcing prezygotic isolation during broadcast spawning.

Ref: Glabe & Vacquier, Nature 1977, Species-specific bindin receptor; Gilbert Chapter 7: Gamete binding specificity.

View Details
Fertilization in mammals-iv

Izumo interacts with egg protein:

Izumo1 is conserved immunoglobulin-like transmembrane protein exposed on inner acrosomal membrane after acrosome reaction in mouse and human sperm. Its essential egg counterpart is Juno, a GPI-anchored folate receptor family member enriched on oolemma microvilli. Izumo1-Juno binding mediates tight adhesion between gamete membranes, preceding CD9-organized fusion complex formation. Genetic deletion of either protein results in sperm accumulation in perivitelline space without fusion, proving interaction indispensability. CD9 is tetraspanin facilitating fusion but not direct Izumo ligand, while ZP3 and fertilin participate in zona adhesion and earlier steps, not final fusion recognition.

Ref: Satouh et al., Science 2012 & Inoue et al., Nature 2005: Izumo1-Juno interaction essential for sperm-egg membrane adhesion and fusion.

View Details