INHIBITION OF GAMETE MEMBRANE FUSION IN THE SEA URCHIN BY QUERCETIN

Abstract

Human Anatomy, University of Milano, Milano, Italy We have treated sea urchin gametes with quercetin to investigate the effects of this drug on fertilization and egg activation. High concentrations of this drug gradually inhibited sperm motility, but pretreatment of sperm with the drug did not affect their fertility. Treatment of eggs with quercetin at micromolar concentrations completely blocked fertilization. The drug did not block the acrosome reaction of sperm, nor did it affect the binding of the acrosomal filament to the vitelline layer of the egg. However, fertilization was prevented. Inseminated quercetin-treated eggs could be activated by ionophore A23187, but still failed to incorporate sperm. Quercetin blocked fertilization if added after primary gamete binding, but 30 s before the beginning of the cortical reaction in experiments in which eggs were inseminated at low temperature. Drug added 10 s before the beginning of the cortical reaction was ineffective. Electron microscopy confirmed normal primary gamete binding and failure of fertilization. Vitelline layer removal by trypsin did not restore fertilizability to quercetin-treated eggs. Thus quercetin prevented fertilization by blocking gamete membrane fusion. These results indicate that quercetin can be a useful probe for the mechanism of membrane fusion in fertilization.