Oocyte Galα1,3Gal Epitopes Implicated in Sperm Adhesion to the Zona Pellucida Glycoprotein ZP3 Are Not Required for Fertilization in the Mouse

Abstract

The Gal␣133Gal structure is displayed on the zona pellucida glycoprotein ZP3 on murine oocytes. This trisaccharide has been implicated in sperm-zona pellucida adhesive events thought to be essential to fertilization in the mouse. To determine directly if this molecule is required for fertilization, we have generated mice that are deficient in a gene (␣1,3GT) encoding the UDPGal:␤-D-Gal-␣133Gal-galactosyltransferase enzyme responsible for Gal␣133Gal synthesis and expression. These mice develop normally and exhibit no gross phenotypic abnormalities. The Gal␣133Gal epitope is absent from the vascular endothelium and other tissues in ␣1,3GT (؊/؊) adult mice. By contrast, ␣1,3GT (؊/؊) mice, like humans, develop naturally occurring anti-␣-galactoside antibodies normally absent in wild type mice. Female ␣1,3GT (؊/؊) mice yield oocytes that are devoid of the Gal␣133Gal epitope; however, these mice are fully fertile. These observations indicate that the Gal␣133Gal moiety is not essential to sperm-oocyte interactions leading to fertilization or to essentially normal development. They further suggest that ␣1,3GT (؊/؊) mice will find utility for exploring approaches to diminish anti-Gal-dependent hyperacute xenograft rejection, which presents a major barrier to the use of porcine and other non-primate organs for xenotransplantation in humans.Fertilization in mammals involves an adhesive interaction between sperm and the zona pellucida, a glycoprotein-containing shell that surrounds the oocyte. Sperm receptor activity of the murine oocyte resides in the zona pellucida glycoprotein ZP3 (1). Sperm recognition of murine ZP3 depends upon Olinked oligosaccharides displayed by ZP3 (Ref. 2;. Treatment of purified egg ZP3 and ZP3-derived O-linked oligosaccharides with ␣-galactosidase eliminates sperm receptor activity (6). These observations have been taken to imply that terminal ␣-galactosides on ZP3 glycoconjugates are critical for sperm binding activity (6). This notion is supported by more recent observations demonstrating that structurally defined bi-and tetraantennary blood group I-related oligosaccharides containing terminal Gal␣133Gal moieties inhibit binding of sperm to eggs in a dose-dependent manner (7).In the mouse, at least one UDP-Gal:␤-D-Gal-␣133Gal-galactosyltransferase (␣1,3GT) 1 is responsible for the synthesis of terminal Gal␣133Gal␤134GlcNAc trisaccharides from common lactosamine-terminated glycoconjugates (8, 9). Mice and other placental mammals express the Gal␣133Gal␤134GlcNAc trisaccharide products of ␣1,3GT on a variety of glycoproteins and in a variety of tissues (10, 11). Aside from the postulated role of Gal␣133Gal moiety in murine fertilization, the function(s) of this structure are not known.By contrast, humans, apes, and Old World monkeys lack the ability to synthesize these oligosaccharide moieties, because the genetic homologues of the murine ␣1,3GT locus are pseudogenes incapable of encoding a functional ␣1,3GT (12, 13). Consequently, these latter species are reciprocally replete with immunoglobulins...

Induction of molecular chimerism by gene therapy prevents antibody-mediated heart transplant rejection

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Ig Knock-In Mice Producing Anti-Carbohydrate Antibodies: Breakthrough of B Cells Producing Low Affinity Anti-Self Antibodies

“…␣Gal-deficient mutant mice lacking a functional ␣GT gene (GT 0/0 mice) generated by gene targeting in embryonic stem cells lack expression of ␣Gal epitopes and consequently develop ␣Gal-specific natural Abs, the majority of which are IgM (23)(24)(25). The serum titer of ␣Gal-specific Abs in GT 0/0 mice increases in an age-dependent fashion.…”

Protease activity involvement in the passage of mammalian sperm through the zona pellucida

“…One is a terminal β-1,3 galactose (Bleil and Wassarman, 1988) and the other is a terminal N-acetylglucosamine proposed to bind β-1,4 galactosyl transferase, a putative sperm receptor (Miller and Ax, 1990;Miller et al, 2002). Furthermore, the continued fertility of mutant mice lacking either the enzyme that adds terminal β-1,3 galactose (Thall et al, 1995)or b-1,4 galactosyltransferase (Shi et al, 2001) makes it unlikely that these are the sole determinants of mouse sperm binding. Therefore, the mechanism of interaction between zona pellucida and the sperm remains unsolved.…”