Sperm-Egg Interactions

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Molecular mechanisms of the acrosome reaction, sperm-binding to and sperm penteration through the vitelline coat, and membrane fusion were studied by using echinoderms and ascidians.Starfish egg jelly contains a sulfated glycoprotein (ARIS), a high-mannose glycoprotein with saccharide chains having 0-3 glucose residues at the non-reducing termini, sulfated steroidal saponins including Co-ARIS I, II, and III, and oligopeptides including SAP. In alkaline or high Ca^<++> sea water, ARIS induces the acrosome reaction. In normal sea water, a combination of ARIS and Co-ARIS induces the acrosome reaction whithout incresing PH_i.Three novel ceramide dihexosides; melibiosyl,gentibiosyl and from echinoderm gametes. Their possible roles in the acrosome reaction and fusion of sperm and egg plasma membranes are under investigation.N-Acetylhexosaminidase, the most potent glycosidase in the sperm of Halocynthia roretzi, was purified and characterized. The second potent was -L-fucosidase that seems to serve as vitelline coat-binding protein. Sperm receptor in the vitelline coat was suggested to have terminal L-Fuc, D-GalNAc and D-GlcNAc. Indeed, major N-glycoside chains of the vitelline coat have such structures. A 60K protein was suggested to be a physiological substrate of vitelline coat lysin(s).During the course of oocyte maturation triggered by 1-methyl-adenine in Asterina, a 39K Gi protein and a trypsin-type protease of high substrate specificity participate in the steps befor and after MPF formation, respectively.