A sperm factor as the counterpart to the sperm-binding factor of the homologous eggs

Interactions between sperm and sea urchin egg jelly

The addition of egg jelly to sea urchin sperm induces multiple changes in morphology and behavior. When jelly is added to sperm diluted in seawater, the acrosome reaction is triggered, the mitochondrion rounds up, the internal pH is transiently alkalinized and then reacidified, and respiration becomes uncoupled and rapidly decreases. Sperm also become unable to fertilize eggs within a few minutes after jelly addition. In order to explore in more detail the effect of egg jelly on sperm, we have studied the response to jelly in the presence of inhibitors of the acrosome reaction. When jelly is added to sperm under conditions which are inhibitory for the acrosome reaction, an alkalinization takes place without the subsequent reacidification, the mitochondria remain coupled, and respiration and intracellular ATP levels remain high. Sperm viability is prolonged by some of these conditions, but not others. The addition of jelly to sperm in the absence of calcium elicits an internal alkalinization but no other rapid change in sperm physiology. The capacity of egg jelly to alter sperm physiology even when the overall acrosome reaction is inhibited indicates that some of the physiological changes either are early events in the triggering pathway that happen before the inhibitory step or are unrelated to the acrosomal reaction itself. The reacidification of the internal pH, the uncoupling and decrease of the respiration, and the decrease of the ATP levels might be linked together by the large influx of calcium that occurs after the acrosome reaction.

Isolation of a glycopeptide fraction from the surface of the sea urchin egg that inhibits sperm-egg binding and fertilization

The role of cell surface glycoproteins of the sea urchin egg in binding sperm has been examined by studying the biological activity of glycopeptides derived from these glycoproteins. Glycopeptides were produced from egg surface glycoproteins by Pronase digestion. After fractionation by gel filtration the glycopeptides were tested for their ability to inhibit the binding of sperm to eggs, presumably by competing with the egg surface glycoproteins for binding sites on the sperm. One glycopeptide fraction with an apparent molecular weight of approximately 6,000 was found to be a potent inhibitor of sperm-egg binding, as well as fertilization, even at nanomolar concentrations. This activity was heat stable and exerted its effect against the sperm and not the egg. Experiments with a radiolabeled form of the glycopeptide fraction directly demonstrated that at least one component of it bound to sperm. Specific binding of the radiolabeled glycopeptide occurred only to acrosome-reacted sperm. Because the isolated glycopeptide fraction has many of the characteristics that one would expect of a biologically active fragment of an egg surface receptor for sperm, these findings are consistent with the idea that one or more glycoconjugates on the surface of the egg are involved in sperm binding.

Fertilization in brown algae. III. Preliminary characterization of putative gamete receptors from eggs and sperm of Fucus serratus

Membrane fractions have been isolated from eggs of Fucus serrratus which inhibit fertilization in a species-specific manner. This activity is destroyed by alpha-fucosidase and alpha-mannosidase. Some 6% of the protein of this membrane fraction binds to Con A-agarose, following SDS solubilization, and when eluted with alpha-methyl mannoside inhibits fertilization when preincubated with sperm, but not eggs. This inhibitory activity is species-specific and destroyed by alpha-fucosidase but not by trypsin. SDS-gel electrophoresis reveals 1 band staining strongly with Coomassie Brilliant Blue G and weakly with the PAS reagent. This major band represents a glycoprotein with an approximate molecular weight of 30 000 Daltons. Membrane fractions from sperm of Fucus serratus solubilized in KC1 yielded a protein-containing fraction, after affinity chromatography on desulphated focoidan-Sepharose. This fraction is 100-fold more effective in inhibiting fertilization after preincubation with eggs than either Con A or fucose-binding protein. It is species-specific and inhibition is reversed when pretreated eggs are washed with fucoidan. Activity is destroyed by heat and trypsin and only one diffuse band is apparent on SDS gels. This stains positively with Coomassie Brilliant Blue G but not with PAS and has a molecular weight of approximately 60 000 Daltons. Tentative calculation of the numbers of putative receptor molecules gives a figure of 2.5 X 10(9) receptors per egg and 1.8 X 10(6) receptors per sperm.