Ultrastructure, Composition, and Possible Roles of the Egg Coats in Haliotis asinina

Spawned eggs of a tropical abalone Haliotis asinina have 2 protective barriers: the egg jelly coat and the vitelline envelope. At the electron microscopic level, the egg jelly is composed of a network of large fibers (40-50 nm thick) cross-linked by smaller fibers (15-20 nm thick), whereas the vitelline envelope is a thin, tough sheet containing pores that might be channels for sperm contact and entry. Electrophoretically, the egg jelly contains 2 major glycoproteins at 107 kDa and 178 kDa, whereas the vitelline envelope contains a broad spectrum of protein bands ranging from 15-200 kDa, which also includes the corresponding egg jelly protein bands. Glycoproteins of egg jelly and vitelline envelope exhibit strong cross-reactivities, and they appear in late oocytes (Oc4, Oc5). Glucose is the major sugar composition of both egg jelly and vitelline envelope glycoproteins, whereas minor proportions of arabinose, fructose, galactose, and fucose are present in both the egg jelly and vitelline envelope. Our findings suggest that a sperm acrosome reaction could be induced by isolated vitelline envelope glycoproteins, whereas acceleration of sperm motility could be stimulated by egg jelly glycoproteins.