Hopkins Marine Station Student Paper

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Title: The effects of a homogenate of the fucoid algae Fucus gardneri on the fertilization of the eggs of the purple sea urchin, Strongylocentrotus purpuratus
Student Author(s): Freed, Peter
Faculty Advisor(s): Epel, David
Pages: 23
Location: Final Papers Biology 175H
Date: June 2001
Abstract: Crude homogenates of the algae Fucus vesiculosus contain a factor(s) capable of inhibiting the fertilization of Strongylocentrotus purpuratus (purple sea urchin) eggs. Previous studies indicated that this effect might have been due to the polysaccharide fucoidan. I here examined the effect of the homogenate at a molecular, cellular and ecological level. Inhibitory activity was present in seawater homogenates of the algae at a concentration of approximately 2 mg fresh weight/ml. The inhibitory factor was heat stable and molecular sieve centrifuge filtration showed the active fraction had a molecular weight above 10,000. Comparison of the >10,000 MW fraction with fucoidan indicates that the inhibitor in the homogenate is not fucoidan or is not fuciodan alone. Sperm binding experiments showed that the factor(s) prevents sperm from penetrating the jelly layer of the eggs and possibly from penetrating the vitelline layer. This suggests that the factor(s) inhibit a sperm enzyme that allows sperm to penetrate the jelly layer and perhaps the vitelline layer. Studies assessing whether intact F. vesiculosus might leak the inhibitory factor into the surrounding seawater—as in a tide pool—and thereby affect fertilization were inconclusive. Characterization of this potent inhibitor could provide new insights into the sperm-egg interactions leading to fertilization.