The Primary Egg Envelope of the Anuran Lepidobatrachus laevis: Physicochemical and Macromolecular Alterations During Development

Abstract

The coelomic egg envelope (CE) of the frog Lepidobatrachus laevis has a network of fibrillar bundles which disperse after transit through the oviduct. Following oviposition, the egg vitelline envelope (VE) has an additional amorphous zone on the exterior surface. The fertilization envelope (FE) formed after fertilization, appears to be very similar to the VE. The CEs, VEs, FEs and hatched envelopes (FE,,) were manually isolated. The CE, VE and FE were solubilized at 100°C using denaturing conditions, but were only partially solubilized in phosphate buffer, pH 7.0. All envelopes and several purified polypeptides from the VE and FE were analyzed using gel electrophoresis and one-dimensional peptide mapping. Each of the envelopes contained 9 major polypeptides ranging from 11 8.5 to 22 kD and 8-1 2 minor polypeptides. Several envelope components were added/removed in the conversions based on the results of experiments in which preparations were incubated with activated egg exudate and crude hatching enzyme; some of these transformations were mimicked by tryptic and chymotryptic digestions. Therefore, serine proteases may be involved in envelope processing in vivo. Lepidobatrachus CE polypeptides and several major components from the VE, FE and FEh were crossreactive with antibodies against Xenopus VE*.

Anuran and pig egg zona pellucida glycoproteins in fertilization and early development

“…Individual envelope ZP glycoproteins were separated and purified by preparative SDS-PAGE (Gerton et al, 1982). Envelopes from other anuran eggs have been isolated and characterized (Barisone et al, 2002;Caputo et al, 2005;Peavy and Carroll, 1993;, as well as the CE obtained from body cavity eggs after oviduct ligation (Grey et al, 1977). The methods used for X. laevis envelope preparation were applied in principle to isolation of the ZP from pig eggs (Dunbar et al, 1980).…”

“…This is perhaps most readily demonstrated by the distinct morphological forms of envelopes as visualized with transmission and scanning electron microscopy [X. laevis (Hedrick and Nishihara, 1991;Larabell and Chandler, 1989); L. laevis (Peavy and Carroll, 1993); B. arenarum (Mariano and Cabada, 1978;Mariano et al, 1984); B. japoncius ; D. pictus (Campanella et al, 1992;Caputo et al, 2001); R. japonica (Yoshizaki and Katagiri, 1981)]. The ZP glycoproteins are organized into filaments and filament arrangements are distinguishable in the CE, VE, and FE.…”

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

“…Interestingly, in Bufo, gps 36 and 39 may have sperm binding activity (Omata and Katagiri, 1996). More complex changes occur in Lepidobatracus laevis, where a 56/53 kDa doublet of the CE is absent from the VE, and a CE 68 kDa glycoprotein shifts to 66 kDa in the VE (Peavy and Carroll, 1993).…”