Following passage through the oviduct, the coelomic envelope of Discoglossus pictus (amphibia) acquires fertilizability upon reorganization, conversion of gp 42 to gp 40, extensive glycosylation, and formation of a specific layer

This paper describes the morphological and biochemical changes in Discoglos sus pictus coelomic oocyte envelope (CE) following passage through the ovid uct. As in other anurans, in this species, the transformation of the envelo pe into vitelline envelope (VE) leads to the acquisition of fertilizability and involves the cleavage of a glycoprotein. In addition, several features , typical of Discoglossus pictus, were observed. A new layer, VE-D, forms u nderneath the VE region facing the site of sperm entrance, the dimple. In t he VE, arrowhead-like bundles of fibrils are perpendicularly oriented towar d the dimple. Ultrastructural observations and staining with UEA-I suggeste d that VE-D might have a role in supporting sperm penetration into the dimp le by orienting VE bundles and exposing sugar residues such as fucose, In ' in vitro' tests, VE binding of sperm occurs only if sperm are exposed to A2 3187, in agreement with previous data (Campanella et al., 1997: Mot Reprod Dev 47:323-333). Sperm binding occurs all over the VE. Accordingly, extract s of the VE covering the animal or the vegetal hemisphere have the same aff inity to lectins (DBA, DSA, GNA, MAA, SEA, SNA, UEA-I, WGA). The CE contain s six main glycoproteins. Peptide mapping indicated that during CE transfor mation into VE, gp 42 shifts to an apparent M-r of 40 and gp 61 is converte d to an apparent M-r of 63 kDa. Lectin blot analyses showed extensive chang es in cross-reactivity of most glycoproteins during the CE-->VE transition. The fact that DBA and UEA-I stain gp 63 rather than gp 61 and that this ch ange is related only to gp 63, suggested that O-glycosylation and terminal fucose might be acquired by gp 63 in preparation of fertilization. Gp 63 ha s recently been cloned (Vaccaro et at., submitted) and shown to exhibit hig h homology to Xenopus gp 69/64, a VE sperm ligand (Tian et at., 1997a: J. C ell Biol. 136: 1099-1108; Tian et al., 1997b: Dev Biol 187:143-153), and to ZP2 of mammals. (C) 2001 Wiley-Liss, Inc.