Human Sperm Do Not Bind to Rat Zonae Pellucidae Despite the Presence of Four Homologous Glycoproteins

Abstract

The specificity of sperm-egg recognition in mammals is mediated primarily by the zona pellucida surrounding ovulated eggs. Mouse sperm are quite promiscuous and bind to human eggs, but human spermatozoa will not bind to mouse eggs. The mouse zona pellucida contains three glycoproteins, ZP1, ZP2, and ZP3, which are conserved in rat and human. The recent observation that human zonae pellucidae contain a fourth protein raises the possibility that the presence of four zona proteins will support human sperm binding. Using mass spectrometry, four proteins that are similar in size and share 62-70% amino acid identity with human ZP1, ZP2, ZP3, and ZP4/ZPB were detected in rat zonae pellucidae. However, although mouse and rat spermatozoa bind to eggs from each rodent, human sperm bind to neither, and the presence of human follicular fluid did not alter the specificity of sperm binding. In addition, mutant mouse eggs lacking hybrid/complex N-glycans or deficient in Core 2 O-glycans were no more able to support human sperm binding than normal mouse eggs. These data suggest that the presence of four zona proteins are not sufficient to support human sperm binding to rodent eggs and that additional determinants must be responsible for taxon-specific fertilization among mammals.After passage through the lower female reproductive tract, mammalian spermatozoa fertilize ovulated eggs in the ampulla of the oviduct. A key event in successful fertilization is sperm binding to the surface of the extracellular zona pellucida that surrounds the egg. Following zona penetration and fusion with the egg plasma membrane, peripherally located cortical granules within the egg exocytose their contents, which modify the zona matrix such that sperm no longer bind. These events are carefully orchestrated to ensure that a single sperm fertilizes a single egg (1).Despite decades of investigation, the molecular basis of mammalian sperm-egg recognition remains controversial. Human sperm are particularly fastidious and bind to old world primate eggs but not to eggs of other species. In contrast, mouse sperm are quite promiscuous, binding with near universality to eggs from other mammalian orders (2). The mouse zona pellucida is composed of three major glycoproteins, ZP1, ZP2, and ZP3, one of which, ZP2, is proteolytically cleaved following fertilization (3). Mouse lines have been established that lack each of the zona proteins as well as lines in which human ZP2 and/or human ZP3 replace endogenous mouse proteins (4). Mice without ZP1 form a zona pellucida matrix to which mouse sperm bind and Zp1 null females are fertile, albeit with decreased fecundity (5). Mice in which endogenous proteins are replaced with human ZP2, human ZP3, or both are also fertile but do not support human sperm binding (6, 7). Thus, mouse ZP1 is not required for sperm-egg recognition, and human ZP2 and ZP3 are not sufficient to support human sperm binding.These results suggest that "humanized" zona matrices either lack a factor or contain a factor that prevents the binding of h...

Zona pellucida protein ZP2 is expressed in the oocyte of Japanese quail (Coturnix japonica)

“…These egg envelopes are mainly constructed of glycoproteins belonging to different subclasses of the zona pellucida (ZP) gene family (Spargo & Hope 2003, Conner et al 2005, Smith et al 2005. The components of this matrix include three or four glycoproteins (i.e., ZP1, ZP2, ZP3, and ZP4) in mammalian species (Lefievre et al 2004, Hoodbhoy et al 2005, Litscher & Wassarman 2007, Ganguly et al 2008, Izquierdo-Rico et al 2009). In the cases of nonmammalian vertebrate such as amphibians (i.e.…”

Molecular characterization of egg envelope glycoprotein ZPD in the ovary of Japanese quail (Coturnix japonica)

“…The components of this matrix include three glycoproteins (i.e., ZP1, ZP2, and ZP3, which are also known as ZPB1, ZPA, and ZPC respectively, according to Spargo & Hope (2003) and Smith et al (2005)) in most mammalian species (Harris et al 1994) and four glycoproteins in several organisms including humans, bonnet monkeys, and rats (ZP1, ZP2, ZP3, and ZP4 (ZPB2); Lefievre et al 2004, Hoodbhoy et al 2005, Ganguly et al 2008, while non-mammalian vertebrates such as amphibians (i.e., Xenopus laevis and X. tropicalis), five ZP glycoproteins (ZP2, ZP3, ZP4, ZPD, and ZPAX) have been identified (Lindsay et al 2003, Goudet et al 2008. ZP gene family proteins are characterized by a highly conserved amino acid sequence called the ZP domain, consisting of about 260 amino acid residues with eight or ten conserved Cys residues (Bork & Sander 1992).…”

Acrosome reaction: relevance of zona pellucida glycoproteins

“…However, the ZP matrices of rats, hamsters, bonnet monkeys and humans are composed of four glycoproteins: ZP1, ZP2, ZP3 and ZP4. [8][9][10][11][12][13] In humans, ZP1 has a 638-aa polypeptide backbone; ZP2 has 745 aa; ZP3 has 424 aa and ZP4 has 540 aa. The ZP glycoproteins are heavily glycosylated and have N-as well as O-linked glycans, which have crucial roles in the spermatozoon-ZP interaction and AR induction.…”

“…75 In this context, a fusion construct consisting of human IgG (Fc) and either exon 7 or 8 of mouse Zp3 were prepared. An EC cell line carrying the recombinant gene was produced that secreted chimeric glycoproteins designated either EC-huIgG (Fc)/mouse ZP3 (7) or EC-huIgG (Fc)/ mouse ZP3 (8). It was observed that only EC-huIgG (Fc)/mouse ZP3 (7) bound specifically to the plasma membrane overlying the sperm head to a similar extent as mouse ZP3 isolated from eggs, and at nanomolar concentrations EC-huIgG (Fc)/mouse ZP3 (7) inhibited the binding of mouse sperm to eggs in vitro.…”