The uptake of [3H] glucosamine-labelled glycoconjugates into the perivitelline space of preimplantation mouse embryos

Identification of bovine sperm acrosomal proteins that interact with a 32-kDa acrosomal matrix protein

Mammalian fertilization is accomplished by the interaction between sperm and egg. Previous studies from this laboratory have identified a stable acrosomal matrix assembly from the bovine sperm acrosome termed the outer acrosomal membrane-matrix complex (OMC). This stable matrix assembly exhibits precise binding activity for acrosin and N-acetylglucosaminidase. A highly purified OMC fraction comprises three major (54, 50, and 45 kDa) and several minor (38-19 kDa) polypeptides. The set of minor polypeptides (38-19 kDa) termed "OMCrpf polypeptides" is selectively solubilized by high-pH extraction (pH 10.5), while the three major polypeptides (55, 50, and 45 kDa) remain insoluble. Proteomic identification of the OMC32 polypeptide (32 kDa polypeptide isolated from high-pH soluble fraction of OMC) yielded two peptides that matched the NCBI database sequence of acrosin-binding protein. Anti-OMC32 recognized an antigenically related family of polypeptides (OMCrpf polypeptides) in the 38-19-kDa range with isoelectric points ranging between 4.0 and 5.1. Other than glycohydrolases, OMC32 may also be complexed to other acrosomal proteins. The present study was undertaken to identify and localize the OMC32 binding polypeptides and to elucidate the potential role of the acrosomal protein complex in sperm function. OMC32 affinity chromatography of a detergent-soluble fraction of bovine cauda sperm acrosome followed by mass spectrometry-based identification of bound proteins identified acrosin, lactadherin, SPACA3, and IZUMO1. Co-immunoprecipitation analysis also demonstrated the interaction of OMC32 with acrosin, lactadherin, SPACA3, and IZUMO1. Our immunofluorescence studies revealed the presence of SPACA3 and lactadherin over the apical segment, whereas IZUMO1 is localized over the equatorial segment of Triton X-100 permeabilized cauda sperm. Immunoblot analysis showed that a significant portion of SPACA3 was released after the lysophosphatidylcholine (LPC)-induced acrosome reaction, whereas the IZUMO1 and lactadherin polypeptides remain associated to the particulate fraction. Almost entire population of bovine sperm IZUMO1 relocates to the equatorial segment during the LPC-induced acrosome reaction. We propose that the interaction of OMC32 matrix polypeptide with detergent-soluble acrosomal proteins regulates the release of hydrolases/other acrosomal protein(s) during the acrosome reaction.

Altered pregnancy outcomes in mice following treatment with the hyperglycaemia mimetic, glucosamine, during the periconception period

Exposure of cumulus–oocyte complexes to the hyperglycaemia mimetic, glucosamine, during in vitro maturation impairs embryo development, potentially through upregulation of the hexosamine biosynthesis pathway. This study examined the effects of in vivo periconception glucosamine exposure on reproductive outcomes in young healthy mice, and further assessed the effects in overweight mice fed a high-fat diet. Eight-week-old mice received daily glucosamine injections (20 or 400 mg kg–1) for 3–6 days before and 1 day after mating (periconception). Outcomes were assessed at Day 18 of gestation. Glucosamine treatment reduced litter size independent of dose. A high-fat diet (21% fat) for 11 weeks before and during pregnancy reduced fetal size. No additional effects of periconception glucosamine (20 mg kg–1) on pregnancy outcomes were observed in fat-fed mice. In 16-week-old mice fed the control diet, glucosamine treatment reduced fetal weight and increased congenital abnormalities, but did not alter litter size. As differing effects of glucosamine were observed in 8-week-old and 16-week-old mice, maternal age effects were assessed. Periconception glucosamine at 8 weeks reduced litter size, whereas glucosamine at 16 weeks reduced fetal size. Thus, in vivo periconception glucosamine exposure perturbs reproductive outcomes in mice, with the nature of the outcomes dependent upon maternal age.

SLLP1, a unique, intra-acrosomal, non-bacteriolytic, c lysozyme-like protein of human spermatozoa

We report the presence of a unique, non-bacteriolytic, c (chicken or conventional type) lysozyme-like protein, SLLP1, in the acrosome of human sperm. C lysozymes are bacteriolytic and can also bind to N-acetylglucosamines linked by beta-1,4 glycosidic bonds. Most of the invariant residues (17 out of 20), including all the cysteines, were conserved in SLLP1, but the two catalytic residues E35 and D52 of c lysozymes were replaced with T and N, respectively. The full-length cDNA encodes a protein of 215 aa with a predicted protease cleavage site between A87 and K88. The processed form of SLLP1, which showed an exon-intron organization similar to human c lysozyme, was the major isoform in the acrosome of ejaculated sperm. As expected, based on its sequence, the mature protein secreted from yeast showed no bacteriolytic activity. A significant decrease (54%, P < or = 0.001) in the number of sperm bound to zona-free hamster eggs was observed in the presence of antisera to recombinant SLLP1. SLLP1 mRNA (size, approximately 1 kb) appeared to be expressed only in the testis and in the Burkitt lymphoma Raji cell line. The gene SPACA3 encodes SLLP1 and contains five exons at locus 17q11.2. Because of its typical c lysozyme-like sequence, genomic organization, conservation of putative substrate-binding sites even in the absence of catalytic residues, and localization in the acrosomal matrix, we hypothesize that, after acrosome reaction, SLLP1 could be a potential receptor for the egg oligosaccharide residue N-acetylglucosamine, which is present in the extracellular matrix over the egg plasma membrane, within the perivitelline space, pores of zona pellucida, and cumulus layers.

Exogenous transferrin is taken up and localized by the neurulation-stage mouse embryo in vitro

We have screened neurulation-stage mouse embryos for regional differences in protein distribution, by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The screen has revealed an 83-kD protein (pI 6.8) that is present in embryo regions where neurulation is in progress but not in regions where neurulation is complete. The 83-kD protein is not synthesized in the neurulation-stage embryo or in the yolk sac, but is taken up from the culture serum in vitro and, probably, from the maternal serum in utero. The 83-kD protein has been identified as transferrin on the basis of its electrophoretic migration and recognition on Western blots by an antitransferrin antibody. Culture of embryos in serum containing 125I-transferrin, followed by autoradiography of embryo sections, shows that transferrin is taken up and localized in the gut beneath the closing neural folds at several levels of the body axis in 8.5- and 9.5-day embryos. In situ hybridization studies show that the transferrin receptor mRNA is expressed in all cells of the 9.5-day embryo, including the gut endoderm. These findings are consistent with a role for transferrin in development of the gut and perhaps, indirectly, in completion of neurulation during early mouse embryogenesis.