Function of the Acrosomal Matrix: Zona Pellucida 3 Receptor (ZP3R/sp56) Is Not Essential for Mouse Fertilization1

Abstract

In mammalian fertilization, sperm-zona pellucida binding is considered to be a critical aspect of gamete interaction. In this study, we examine the mouse sperm acrosomal matrix protein zona pellucida 3 receptor (ZP3R; formerly called sp56) because of our interest in defining the function of the acrosomal matrix, the particulate compartment within the sperm secretory acrosome. Using targeted deletion of the Zp3r gene by homologous recombination, we examined the fertility of nullizygous animals. Our experiments showed that males and females homozygous for the affected gene exhibited no differences in litter sizes compared to wild-type and heterozygous animals. Testis weights of nullizygous males were equivalent to those of wild-type and heterozygous males, and no differences in the number of sperm produced by mice of three genotypes were found. In vitro fertilization rates using cumulus-intact and cumulus-free oocytes were also equivalent. Examination of sperm-binding zonae of unfertilized eggs and the ability of the sperm to undergo acrosomal exocytosis in response to calcium ionophore A23187 displayed no differences between wild-type, heterozygous, and nullizygous mouse sperm. These results provide further evidence that either ZP3R is not involved in sperm-zona pellucida binding or this process might be functionally redundant, involving multiple proteins for gamete interactions.

The cell biology of mammalian fertilization

“…Moreover, glycosylation was not observed on these residues on native ZP proteins (Boja et al, 2003). Furthermore, disruption of the ZP3-binding protein SP56 (ZP3R -Mouse Genome Informatics) on spermatozoa (Bookbinder et al, 1995) resulted in almost no phenotype in fertilization (Muro et al, 2012). Finally, enzymes that make core glycans have also been disrupted, and eggs lacking complex and hybrid N-glycans as well as core-1-derived O-glycans were fertilized normally (Shi et al, 2004;Williams et al, 2007).…”

“…However, the gene disruption of these factors resulted in no significant phenotype in fertilization [e.g. GalTase (Lu and Shur, 1997), Sp56 (Muro et al, 2012), zonadhesin (Tardif et al, 2010), Crisp1 (Da Ros et al, 2008, acrosin (Baba et al, 1994)]. Thus, although these factors may play a role in inducing the acrosome reaction, the importance of these factors, and a zona-induced acrosome reaction, during fertilization is unclear.…”

Molecular interaction of zp3 to zp3r reveals a cross-species fertilization mechanism

“…Disruption of these proteins like zonadhesin (Zan) [11], 毬 1,4-galactosyltransferase-I [16], and ZP3R [17] do not make the null individual sterile. However, Zannull mice sperm exhibit a loss of species-specific properties; thus, these sperm can bind to the egg cells of other species.…”

Epididymal C4b-binding protein is processed and degraded during transit through the duct and is not essential for fertility

“…For example, the knockout mice of PH-20 (Baba et al 2002) and clusterin (Bailey et al 2002) discussed in the previous paragraphs showed normal fertility. Moreover, unexpectedly, gene-targeting of the C4BP-related protein, ZP3R/sp56, had no effect on mouse fertilization, and it has been suggested that the sperm-zona pellucida binding system might be functionally redundant (Muro et al 2012). The sperm maturation system is likely to involve multiple redundant proteins, and C4BP might be one of them.…”