STRUCTURAL FEATURES OF THE ABALONE EGG EXTRACELLULAR-MATRIX AND ITS ROLE IN GAMETE INTERACTION DURING FERTILIZATION

Abalone eggs are surrounded by a complex extracellular coat that conta ins three distinct elements: the jelly layer, the vitelline envelope, and the egg surface coat. In this study we used light and electron mic roscopy to describe these three elements in the red abalone (Haliotis rufescens) and ascribe function to each based on their interactions wi th sperm. The jelly coat is a spongy matrix that lies at the outermost margin of the egg and consists of variably sized fibers. Sperm pass t hrough this layer with their acrosomes intact and then go on to bind t o the vitelline envelope. The vitelline envelope is a multilamellar fi brous layer that appears to trigger the acrosome reaction after sperm binding. Next, sperm release lysin from their acrosomal granules, a no nenzymatic protein that dissolves a hole in the vitelline envelope thr ough which the sperm swims. Sperm then contact the egg surface coat, a network of uniformly sized filaments lying directly above the egg pla sma membrane. This layer mediates attachment of sperm, via their acros omal process, to the egg surface. (C) 1995 Wiley-Liss, Inc.