EFFECTS OF WHEAT-GERM-AGGLUTININ ON TUNICATE EGG ACTIVATION AND FERTILIZATION - IS THERE A PLASMA-MEMBRANE SPERM RECEPTOR SYSTEM ON ASCIDIACERATODES EGGS

Little work has been carried cut on the sperm recognition systems pres ent on the egg plasma membrane. Here it is shown that wheat germ agglu tinin (WGA) interferes with the sperm-interacting system on the plasma membrane of eggs of the ascidian, Ascidia ceratodes. The WGA activate s the dechorionated egg, indicating that a plasma membrane sugar resid ue can be directly tied to egg activation. Low concentrations of this lectin do not activate the eggs, but reduce fertilizability. This obse rvation suggests that the WGA binding site might be part of a sperm re ception-activation complex in the plasma membrane. While WGA also affe cts sperm binding to the chorion, the mechanisms of sperm interaction at the plasma membrane and chorion show different sensitivities to lec tins, sugars and enzymes.