The coelomic envelope to vitelline envelope conversion in eggs of Xenopus laevis

Abstract

An amphibian egg recovered from the body cavity is enclosed by a coelomic egg envelope. Upon transport down the oviduct, the envelope is converted to the vitelline envelope. The coelomic and vitelline envelopes are distinct in terms of sperm penetrability, ultrastructural morphology, and radioiodination profiles. In this study, the macromolecular compositions of these two envelopes were determined. Isolated envelopes were compared by one- and two-dimensional gel electrophoresis, peptide mapping, and radiolabeling. A protein with a molecular weight of 57,000 (57K) was present in the vitelline envelope but was absent in the coelomic envelope. A glycoprotein with a molecular weight of 43K in the coelomic envelope was converted to a component with a molecular weight of 41K in the vitelline envelope. The 43K-molecular weight component of the coelomic envelopes could be radioiodinated by lactoperoxidase but no labeling of the 41K-molecular weight component occurred in the vitelline envelope. Peptide mapping using limited proteolysis established that the 43K-molecular weight component of the coelomic envelope was a precursor to the 41K-molecular weight component of the vitelline envelope. These molecular alterations may underlie the ultrastructural and physiological changes occurring in these envelopes.

The Synthesis and Localization of Envelope Glycoproteins in Oocytes of Xenopus laevis using Immunocytochemical Methods

“…vealed that the anti-VE serum reacted with the major components of the CE. After absorption with egg extracts, the antiserum retained reactivity against most components of CE reported by Gerton and Hedrick (6) (Fig. 1).…”

“…Besides these, our antiserum was also reactive to molecules with the M.W. smaller than 29K which have not been detected by ordinary Coomassie brilliant blue staining (6).…”

“…Intriguing in relation to its functions in gamete interaction is that certain glycoprotein components of this envelope undergo conversions both before (6) and after (7) fertilization. The coelomic envelope (CE) of a body cavity egg differs from the VE of an oviposited egg by conversion of a 43K to a 41 K envelope glycoprotein and addition of a 57K protein secreted by the oviduct (6,7). In view of these findings, the exact 85 mode of envelope synthesis during oogenesis merits investigation.…”

Xenopus Cdc6 confers sperm binding competence to oocytes without inducing their maturation

“…We asked if these alterations could contribute to the acquisition of sperm binding capacity during oocyte maturation. Because the proteolytic processing of gp43 in the oviduct is essential for unmasking the putative sperm binding sites in coelomic eggs (8,16,17,21), initially we determined if this processing can occur in immature oocytes. By analyzing the envelope proteins isolated from the immature stage 6 oocytes that have been forced to pass through the oviduct, we found that gp43 was cleaved to gp41 (Fig.…”

“…This process involves ultrastructural changes in the envelope and processing of a major 43-kDa glycoprotein (gp43) in the CE to 41 kDa by a protease secreted from the oviduct (8,16,17). After several hours the coelomic egg passes through the oviduct and emerges as an oviposited egg.…”