Sperm binding and formation of the fertilization envelope by surface complexes isolated from sea urchin eggs
During fertilization of the echinoderm egg the sperm cell undergoes the acrosomal reaction and binds species-specifically to the vitelline layer, which is attached to the exterior surface of the egg plasma membrane. Following initial interaction and fusion of the limiting membranes of the egg and the sperm, the cortical vesicles attached to the inner surface of the egg plasma membrane (Fig. 1) fuse and secrete components which appear to modify the vitelline layer, giving rise to the fertilization envelope.Recently, the surface and associated secretory vesicles of the egg were isolated from homogenates by differential centrifugation in sea water containing 25 mM EGTA (Fig. 2) (2). Determination of the extent to which this cell surface-secretory complex can be induced to mimic fertilization related events observed with intact eggs is currently in progress.