The Interactions of Sea Urchin Gametes During Fertilization

Abstract

The interactions between sea urchin spermatozoa and ova during fertilization usually exhibit a high degree of species specificity. Under natural conditions and reasonable gamete concentrations, most interspecific inseminations fail to yield zygotes. Macromolecules on the external surfaces of the apposing gametes must surely be responsible for successful gamete recognition, adhesion and fusion. Species specific recognition between surface components of sperm and egg could occur during at least three events comprising the fertilization process. The first event is the interaction of the sperm plasma membrane with the egg jelly coat. This induces the sperm acrosome reaction resulting in the exocytosis of the “bindin” -containing acrosome granule and also the extrusion of the acrosome process from the anterior tip of the sperm. The second event is the adhesion of the bindin-coated acrosome process to glycoprotein “bindin receptors” on the external surface of the egg vitelline layer. The third event is the penetration of the vitelline layer and the fusion of sperm and egg plasma membranes. With the isolations of the component of egg jelly which induces the acrosome reaction, sperm bindin from the acrosome vesicle and the egg surface bindin receptor from the vitelline layer, there is hope of discovering the molecular basis of this most interesting intercellular interaction which results in the activation of embryonic development.