Two major acrosomal proteins act on different parts of the oocyte vitelline coat in the abalone, Haliotis discus

Abstract

Two proteins of molecular weights 20,000 (20K) and 15,500 (15.5K) are the major soluble substances released from the acrosomal vesicle of the abalone, Haliotis discus, spermatozoon. A crude preparation of them has been shown to possess lytic activity on the oocyte vitelline coat (VC). To elucidate the role(s) of each acrosomal protein (AP) in VC lysis, oocytes were examined after treatment with various AP preparations. The VC, which is about 1 micron thick, is composed of thin outer and inner electron-dense layers and a thick main layer of a fine filamentous feltwork. When oocytes were treated with a crude preparation containing both APs, the outer layer disappeared and the feltwork of the main layer loosened extensively. A preparation containing predominantly the 20K AP dissolved the outer layer completely and the main layer to some extent, whereas another preparation containing predominantly the 15.5K AP caused loosening of the main layer without alteration of the outer layer, suggesting that the 20K AP acts on the outer layer, whereas the 15.5K AP acts on the main layer. However, when purified, each AP by itself failed to dissolve the VC, although lysis occurred in a 1:1 mixture of these preparations. Moreover, when the oocytes were pretreated with the 20K AP and thoroughly washed, the 15.5K AP alone could induce lysis. These results suggest that the lysis of the outer layer requires both APs but not simultaneously. The 15.5K AP, which is located posteriorly in the acrosomal vesicle, must be released to act on the VC following the action of the 20K AP.

Extraordinary divergence and positive Darwinian selection in a fusagenic protein coating the acrosomal process of abalone spermatozoa.

“…Previous work (38) with a Japanese abalone, Haliotis discus, suggested that the 18-kDa protein dissolves an outermost zone of the egg VE and that the actions of both the 18-kDa and 16-kDa acrosomal proteins are required to dissolve the VE. Eggs of H. rufescens with intact jelly layers and VEs were exposed to purified 16-kDa and 18-kDa proteins for time periods of hours and microscopically assessed for any effect on the VE.…”

Purification and characterization of a vitelline coat lysin from Ciona intestinalis spermatozoa

“…In many marine invertebrates, and in mammals, the main barrier is the continuous noncellular coat, consisting mainly of glycoproteins, called vitelline coat (VC) and zona pellucida, respectively. Sperm molecules localized on the sperm head or within the acrosomal vesicle are involved in the opening of a passageway through these egg coats (Hoshi, 1985;Pinto et al, 1990;Vacquier et al, 1990;Usui and Haino-Fukushima, 1991). Several sperm hydrolases (Hoshi, 1985) have been implicated in this process in ascidians, echinoderms, and mammals.…”

“…Several sperm hydrolases (Hoshi, 1985) have been implicated in this process in ascidians, echinoderms, and mammals. Some marine mollusc spermatozoa possess acrosomal proteins that create a hole in the egg vitelline envelope by a nonenzymatic mechanism (Haino-Fukushima, 1974;Vacquier et al, 1990;Usui and Haino-Fukushima, 1991). Collectively, these sperm-borne lytic agents have been termed "lysins," regardless of their mechanism of action and localization of their storage (Dan, 1967;Hoshi, 1985).…”

Structural features of the abalone egg extracellular matrix and its role in gamete interaction during fertilization

“…Previous ultrastructural studies using thin-sectioning have indicated that the VE contains three sublayers (Lewis et al, 1982;Usui and Haino-Fukushima, 1991). In this study we have identified these layers with QFIDEIRS and further delineated substructure within them.…”