Primary structure and developmental expression of Dp ZP2, a vitelline envelope glycoprotein homolog of mouse ZP2, in Discoglossus pictus, one of the oldest living Anuran species

Abstract

A glycoprotein of the Xenopus vitelline envelope, gp 69/64, which mediates sperm binding, is closely related to the components of ZPA family, such as the mouse zona pellucida ZP2. To test the generality of these findings, we studied Discoglossus pictus, a species evolutionary distant from Xenopus and identified as a protein of 63 kDa in the vitelline envelope. Preliminary studies suggest that this protein may bind sperm at fertilization. We found that the 63-kDa protein is glycosylated and contains both N- and O-linked chains. We have cloned the cDNA encoding the Discoglossus protein of 63 kDa (Dp ZP2) by screening a Discoglossus cDNA library using Xenopus gp 69/64 cDNA as a probe. Analysis of the deduced sequence of Discoglossus protein revealed 48% identity with Xenopus gp 69/64 and 37-40% identity with mouse ZP2. The sequence conservation included a ZP domain, a potential furin cleavage site and a putative transmembrane domain. The N-terminus region of Dp ZP2 was 40% identical to the corresponding region of Xenopus gp 69/64 which has been shown to be essential for sperm binding to the VE. Although, as of yet, there is no evidence for sperm binding at the Dp ZP2 N-terminus, it is interesting that in this region three potential O-glycosylation sites are conserved in both species, in contrast to N-glycosylation sites. It was found that the Dp ZP2 mRNA is expressed in stage 1 oocytes and in the follicle cells surrounding the oocyte. Similarly, in Xenopus oocytes, the gp 69/64m RNA, was found in the oocytes, as well as in the somatic cells. Mol. Reprod. Dev. 59:133-143, 2001.

Texture of the zona pellucida of the mature pig oocyte. The mammalian egg envelope revisited

“…Depending on the species, ZPA in the mouse [40] or ZPB in the pig [3,41] would constitute sperm receptors. More generally, it appears that all egg envelope glycoproteins of vertebrates belong to the same family [10,12,21,42].…”

“…The site of ZP synthesis is the oocyte during its growth phase, at least in the mouse [6][7][8] and/or the follicular cells in other species [3,9]. A unifying hypothesis, at least on the composition of these envelopes, has been offered by molecular biology: the constitutive proteins are homologous and all belong to the ZP protein family [3,[10][11][12]. Does a common composition induce a similar structure of egg envelopes?…”

Organization of the vitelline envelope in ovarian follicles of Torpedo marmorata Risso, 1810 (Elasmobranchii: Torpediniformes)

“…Our investigations performed with the polyclonal antibody to gp69/64 indicate that the VE in T. marmorata is characterized by the presence of a glycoprotein of 66 kDa probably homologous to the gp69/64 reported in the VE of various amphibians (Tian et al, '97, '99;Vaccaro et al, 2001;Kubo et al, 2002;Infante et al, 2004). The positive reaction recorded in 120 kDa may be because of the presence of an epitope in the glycoprotein that is recognizable with the anti-gp69/64 antibody.…”

Egg jelly of the newt, Cynops pyrrhogaster contains a factor essential for sperm binding to the vitelline envelope

“…Binding of sperm to the vitelline envelope at fertilization is a universal event among animal species (Dan, '67;Vacquier and Moy, '77;Bleil et al, '88;Vacquire et al, '95;Tian et al, '97a;Nakai et al, '99;Vaccaro et al, 2001;Barisone et al, 2002). In vertebrates, it is caused by sperm binding to ZP proteins, which are components of the vitelline envelope or zona pellucida.…”

“…The ZPA, a ligand for acrosome-reacted mouse sperm (Bleil et al,'88), binds to proacrosin/acrosin that is exposed in the region around the sperm head during the acrosome reaction (Howes et al, 2001). The ZPA homologue is one of the sperm-binding proteins in the anuran amphibians Xenopus laevis (Tian et al,'97a,b) and D. pictus (Vaccaro et al, 2001) and in the latter species, it binds only to acrosome-reacted sperm (Infante et al, 2004). In X. laevis, the ZPC also acts as a major ligand for sperm binding (Vo and Hedrick, 2000;Vo et al, 2003).…”