Carbohydrates and fertilization in animals

Molecular Biomarkers of Canine Reproductive Functions

The aim of the current study is to review potential molecular biomarker substances selected so far as useful for assessing the quality of dog semen. Proteins, lipids, carbohydrates, and ions can serve as molecular biomarkers of reproductive functions (BRFs) for evaluating male reproductive health and identifying potential risk factors for infertility or reproductive disorders. Evaluation of BRF levels in semen samples or reproductive tissues may provide insights into the underlying causes of infertility, such as impaired sperm function, abnormal sperm-egg interaction, or dysfunction of the male reproductive tract. Molecular biomarker proteins may be divided into two groups: proteins that are well-studied, such as A-kinase anchoring proteins (AKAPs), albumins (ALBs), alkaline phosphatase (ALPL), clusterin (CLU), canine prostate-specific esterase (CPSE), cysteine-rich secretory protein 2 (CRISP2), lactotransferrin (LTF), metalloproteinases (MMPs), and osteopontin (OPN) and proteins that are not well-studied. Non-protein markers include lipid-based substances (fatty acids, phosphatidylcholine), carbohydrates (glycosaminoglycans), and ions (zinc, calcium). Assessing the levels of BRFs in semen samples may provide valuable information for breeding management and reproductive assessments in dogs. This review systematizes current knowledge that could serve as a starting point for developing practical tests with the use of biomarkers of canine reproductive functions and their predictive value for assisted reproductive technique outcomes and semen preservation.

Effective Organotin-Mediated Regioselective Functionalization of Unprotected Carbohydrates

Regioselective functionalization of unprotected carbohydrates at a secondary OH group in the presence of primary OH groups based on the commonly used organotin-mediated reaction has been improved. We found that the preactivation of the dibutylstannylene acetal intermediate with tetrabutylammonium bromide in toluene is a key to the improved condition for the efficient, high-yielding, and regioselective tosylation, benzoylation, or benzylation of unprotected carbohydrates. The counteranion of tetrabutylammonium ion with a weak coordination ability plays a crucial role in the improved regioselective reactions. A convenient access to the intermediates of synthetic value is also demonstrated in the organotin-mediated regioselective tosylation of unprotected carbohydrates, followed by the nucleophilic inversion reaction to give sulfur-containing and azide-modified carbohydrates.

Glyphosate Interference in Follicular Organization in the Wall Lizard Podarcis siculus

Glyphosate (Gly) is a broad-spectrum herbicide widely used thanks to its high efficiency and low toxicity. However, evidence exists of its toxic effects on non-target organisms. Among these, the animals inhabiting agricultural fields are particularly threatened. Recent studies demonstrated that exposure to Gly markedly affected the morphophysiology of the liver and testis of the Italian field lizard Podarcis siculus. The present study aimed to investigate the effects of the herbicide on the female reproductive system of this lizard in order to have a full picture of Gly-induced reproductive impairment. The animals were exposed to 0.05 and 0.5 μg/kg of pure Gly by gavage for 3 weeks. The results demonstrated that Gly, at both doses tested, profoundly interfered with ovarian function. It induced germ cells' recruitment and altered follicular anatomy by anticipating apoptotic regression of the pyriform cells. It also induced thecal fibrosis and affected oocyte cytoplasm and zona pellucida organizations. At the functional levels, Gly stimulated the synthesis of estrogen receptors, suggesting a serious endocrine-disrupting effect. Overall, the follicular alterations, combined with those found at the level of the seminiferous tubules in males, suggest serious damage to the reproductive fitness of these non-target organisms, which over time could lead to a decline in survival.

Targeted delivery of oligonucleotides using multivalent protein-carbohydrate interactions

Cell surface protein-carbohydrate interactions are essential for tissue-specific recognition and endocytosis of viruses, some bacteria and their toxins, and many glycoproteins. Often protein-carbohydrate interactions are multivalent - multiple copies of glycans bind simultaneously to multimeric receptors. Multivalency enhances both affinity and binding specificity, and is of interest for targeted delivery of drugs to specific cell types. The first such example of carbohydrate-mediated drug delivery to reach the clinic is Givosiran, a small interfering ribonucleic acid (siRNA) that is conjugated to a trivalent N-acetylgalactosamine (GalNAc) ligand. This ligand enables efficient uptake of the nucleic acid by the asialoglycoprotein receptor (ASGP-R) on hepatocytes. Synthetic multivalent ligands for ASGP-R were among the first 'cluster glycosides' developed at the birth of multivalent glycoscience around 40 years ago. In this review we trace the history of 'GalNAc targeting' from early academic studies to current pharmaceuticals and consider what other opportunities could follow the success of this delivery technology.

Mating in the Closest Living Relatives of Animals Is Induced by a Bacterial Chondroitinase

We serendipitously discovered that the marine bacterium Vibrio fischeri induces sexual reproduction in one of the closest living relatives of animals, the choanoflagellate Salpingoeca rosetta. Although bacteria influence everything from nutrition and metabolism to cell biology and development in eukaryotes, bacterial regulation of eukaryotic mating was unexpected. Here, we show that a single V. fischeri protein, the previously uncharacterized EroS, fully recapitulates the aphrodisiac-like activity of live V. fischeri. EroS is a chondroitin lyase; although its substrate, chondroitin sulfate, was previously thought to be an animal synapomorphy, we demonstrate that S. rosetta produces chondroitin sulfate and thus extend the ancestry of this important glycosaminoglycan to the premetazoan era. Finally, we show that V. fischeri, purified EroS, and other bacterial chondroitin lyases induce S. rosetta mating at environmentally relevant concentrations, suggesting that bacteria likely regulate choanoflagellate mating in nature.

Egg envelopes of Armadillidium vulgare (Latreille, 1804) (Crustacea, Isopoda Oniscidea): Ultrastructure and lectins binding

The ultrastructural study carried out on (a) oocytes of Armadillidium vulgare during vitellogenesis, (b) mature eggs taken from the ovaries during the parturial moult of the posterior half of the body, and (c) fertilized eggs collected within a few hours of their release into the brood pouch, has clearly demonstrated that before the fertilization the chorion is the only envelope present in the egg of oniscidean isopods. In the mature eggs, the chorion appears as a uniformly electron-dense lamina, about 0.4-0.5 µm thick, which does not show any specialized area. A second envelope, described by other authors as vitelline envelope, is formed above the oolemma only right after fertilization and appears separated from the chorion by a space full of liquid. The ways in which the genesis of this envelope is realized are not yet clear; it could be interpreted rather as a fertilization membrane. The investigations carried out with the aid of a battery of FITC-lectins have highlighted the presence at the chorion surface of unfertilized eggs of various saccharide residues distributed in uniform way. No significant change was observed in the pattern of lectins binding to the chorion of eggs taken from the brood pouch, thus demonstrating how, after the fertilization, no significant rearrangement in the distribution of saccharide residues present on the egg surface occurs in A. vulgare. The ways in which, therefore, the recognition, the binding and the entry of the peculiar sperm of oniscidean isopods into the egg occur, still remain all to be deciphered. Microsc. Res. Tech. 79:792-798, 2016. © 2016 Wiley Periodicals, Inc.

Effect of aglycon structure on saccharide elongation by cells

Alkyl N-acetyl-β-D-glucosaminide (GlcNAc primers) with different aglycon moieties were synthesized and used to determine the effect of the aglycon structure on cellular saccharide elongation. Dodecyl N-acetyl-β-D-glucosaminide (GlcNAc-C12), tridecan-7-yl N-acetyl-β-D-glucosaminide (GlcNAc-2C6), and pentacosan-13-yl N-acetyl-β-D-glucosaminide (GlcNAc-2C12) primers were synthesized by glycosylation of dodecan-1-ol, tridecan-7-ol, and pentacosan-13-ol, respectively, with peracetylglucosamine. These primers were introduced to mouse B16 melanoma cells to prepare glycolipids. After 48 h incubation, results showed that GlcNAc-C12 was elongated to give NeuAc-Gal-GlcNAc-C12. GlcNAc-2C6 was also elongated to afford Gal-GlcNAc-2C6 and NeuAc-Gal-GlcNAc-2C6. On the other hand, GlcNAc-2C12 primer was not elongated. Significantly, the results demonstrated that the amount of glycosylated product increased 1.5-times by modifying the aglycon structure of GlcNAc from C12 to 2 C6 despite having almost the same number of C-units.

Diagnosis and prognosis of male infertility in mammal: the focusing of tyrosine phosphorylation and phosphotyrosine proteins

Male infertility refers to the inability of a man to achieve a pregnancy in a fertile female. In more than one-third of cases, infertility arises due to the male factor. Therefore, developing strategies for the diagnosis and prognosis of male infertility is critical. Simultaneously, a satisfactory model for the cellular mechanisms that regulate normal sperm function must be established. In this regard, tyrosine phosphorylation is one of the most common mechanisms through which several signal transduction pathways are adjusted in spermatozoa. It regulates the various aspects of sperm function, for example, motility, hyperactivation, capacitation, the acrosome reaction, fertilization, and beyond. Several recent large-scale studies have identified the proteins that are phosphorylated in spermatozoa to acquire fertilization competence. However, most of these studies are basal and have not presented an overall mechanism through which tyrosine phosphorylation regulates male infertility. In this review, we focus of this mechanism, discussing most of the tyrosine-phosphorylated proteins in spermatozoa that have been identified to date. We categorized tyrosine-phosphorylated proteins in spermatozoa that regulate male infertility using MedScan Reader (v5.0) and Pathway Studio (v9.0).

Glycobiology of reproductive processes in marine animals: the state of the art

Glycobiology is the study of complex carbohydrates in biological systems and represents a developing field of science that has made huge advances in the last half century. In fact, it combines all branches of biomedical research, revealing the vast and diverse forms of carbohydrate structures that exist in nature. Advances in structure determination have enabled scientists to study the function of complex carbohydrates in more depth and to determine the role that they play in a wide range of biological processes. Glycobiology research in marine systems has primarily focused on reproduction, in particular for what concern the chemical communication between the gametes. The current status of marine glycobiology is primarily descriptive, devoted to characterizing marine glycoconjugates with potential biomedical and biotechnological applications. In this review, we describe the current status of the glycobiology in the reproductive processes from gametogenesis to fertilization and embryo development of marine animals.

Lectin-binding pattern of the Senegalese sole Solea senegalensis oogenesis

The glycoconjugate pattern of developing ovarian follicles in wild and cultured Senegalese sole Solea senegalensis was investigated by means of lectin histochemistry. Ovaries from cultured fish contained oocytes up to the late vitellogenic stage, whereas they reached the hydration stage in wild specimens. The follicular cells bound MAL II, SBA, HPA, DBA, Con A, KOH-sialidase (K-s)-WGA, GSA I-B(4) in the late vitellogenic stage, and in wild fish also SNA and K-s-PNA, whereas in the hydration stage SBA, HPA, DBA, and GSA I-B(4) only. The zona radiata reacted with SBA, HPA, DBA, Con A, and GSA I B(4) in the late vitellogenic stage and in cultured fish also with UEA I, whereas in the hydration stage it stained with SBA only. The cortical alveoli bound SBA, HPA, RCA(120) during the late vitellogenic stage, also SNA, PNA, K-s-PNA, GSA I-B(4) in cultured fish, DBA, and K-s-WGA in wild ones which stained with SBA, HPA, and GSA I-B(4) in the hydrated stage. The yolk reacted with Con A in the late vitellogenic oocytes, and also with MAL II, SNA, K-s-PNA, SBA, HPA, K-s-WGA, GSA I-B(4), UEA I in the hydrated ones. From perinucleolus to late vitellogenic stages, the oocyte nucleoplasm bound Con A, GSA I-B(4), GSA II, UEA I, and in wild fish also MAL II, SNA, LTA but only GSA I-B(4) reactivity in the early maturation stage. These findings demonstrate that the glycan pattern of fish ovarian follicles changes during the maturative stages and that it is affected by culture-rearing conditions.

Sulphated glycoconjugates are powerful inhibitors of spermatozoa binding to the vitelline envelope in amphibian eggs

BACKGROUND INFORMATION

In amphibians, the role of sulphated glycans has not been determined in spermatozoa-egg interaction, although they are known to be involved in other systems. In previous studies, it was found that, in Discoglossus pictus, a VE (vitelline envelope) glycoprotein of 63 kDa exhibits high homology to Xenopus laevis gp69/gp64 and to ZP2 of mammals. gp63 and a glycoprotein of 75 kDa are both capable of binding the spermatozoa in in vitro assays and, having similar peptide maps and different glycosylation, are probably two glycoforms of the same protein.

RESULTS

In the present study, binding assays performed by treating dejellied eggs with metaperiodate suggest that hydroxy groups of sugars are not directly involved in spermatozoa-vitelline envelope binding. Competition assays between dejellied eggs and spermatozoa preincubated with dextran, dextran sulphate or fucoidan indicated that sulphated oligosaccharides have an inhibitory effect on spermatozoa binding. In similar competition assays, Le(x) (Lewis(x)) trisaccharide 3'-sulphate inhibited spermatozoa binding to VE in contrast with 3'-sialyl-Le(x) tetrasaccharide. Assays performed with gp75- or gp63-coated beads and spermatozoa treated with fucoidan or dextran sulphate indicated that sulphated oligosaccharides competitively inhibit spermatozoa binding to gp75-coated beads, yet not to gp63-coated beads. Finally, solubilized VE digested with N-glycosidase F retains the inhibitory activity in spermatozoa-VE binding assays in contrast with VE treated with alpha-N-acetylgalactosaminidase.

CONCLUSION

It was concluded that VE sulphate groups are involved in spermatozoa binding. These groups are present in gp75 glycoconjugates and are probably located in O-linked glycoconjugates.

Polypeptide encoded by mouseZP3 exon-7 Is Necessary and Sufficient for binding of mouse sperm in vitro

Fertilization in mice is initiated by species-specific binding of sperm to mZP3, one of three mouse zona pellucida (ZP) glycoproteins. At nanomolar concentrations, purified egg mZP3 binds to acrosome-intact sperm heads and inhibits binding of sperm to eggs in vitro. Although several reports suggest that sperm recognize and bind to a region of mZP3 encoded by mZP3 exon-7 (so-called, sperm combining-site), this issue remains controversial. Here, exon-swapping and an IgG(Fc) fusion construct were used to further evaluate whether mZP3 exon-7 is essential for binding of sperm to mZP3. In one set of experiments, hamster ZP3 (hZP3) exon-6, -7, and -8 were individually replaced with the corresponding exon of mZP3. Stably transfected embryonal carcinoma (EC) cell lines carrying the recombinant genes were produced and secreted recombinant glycoprotein was purified and assayed for the ability to inhibit binding of sperm to eggs. While EC-hZP3, a recombinant form of hZP3 made by EC cells, is unable to inhibit binding of mouse sperm to eggs in vitro, the results suggest that substitution of mZP3 exon-7 for hZP3 exon-7, but not mZP3 exon-6 or -8, can impart inhibitory activity to EC-hZP3. In this context, a fusion construct consisting of human IgG(Fc) and mZP3 exon-7 and -8 was prepared, an EC cell line carrying the recombinant gene was produced, and secreted chimeric glycoprotein, called EC-huIgG(Fc)/mZP3(7), was purified and assayed. It was found that the chimeric glycoprotein binds specifically to plasma membrane overlying sperm heads to a similar extent as egg mZP3 and, at nanomolar concentrations, inhibits binding of mouse sperm to eggs in vitro. Collectively, these observations provide new evidence that sperm recognize and bind to a region of mZP3 polypeptide immediately downstream of its ZP domain that is encoded by mZP3 exon-7. The implications of these findings are discussed.

Contribution of mouse egg zona pellucida glycoproteins to gamete recognition during fertilization

For sperm to fertilize eggs, they must first bind to the thick zona pellucida (ZP) that surrounds the plasma membrane of all unfertilized mammalian eggs. An extensive literature suggests that mouse sperm recognize and bind to a specific ZP glycoprotein called mZP3. However, the role of individual ZP glycoproteins in binding of mouse sperm to eggs has been called into question by recent transgenic experiments with null mice. Results of such experiments have been interpreted to mean that binding of sperm depends on the supramolecular structure of the ZP, not on an individual ZP glycoprotein. Here, it is argued that results of these transgenic experiments actually are consistent with the prevailing view of gamete recognition that implicates a specific ZP glycoprotein in both binding of mouse sperm to eggs and induction of the acrosome reaction.

Analysis of the participation of N-acetylglucosamine in the different steps of sperm-zona pellucida interaction in hamster

Glycoproteins and lectin-like proteins mediate sperm-zona pellucida interaction. The present study analysed the participation of carbohydrates in the different stages of sperm interaction with the zona pellucida in hamster, by determining the effects of different monosaccharides. N-acetylglucosamine (GlcNAc, 1 mM) reduced sperm ability to bind to the zona pellucida. Surprisingly, spontaneous acrosome reaction (AR) was also inhibited by this sugar. In order to analyse the effect of GlcNAc on sperm-zona pellucida binding, independent of its effect on the AR, strontium (Sr) was used as a calcium (Ca) replacement in the sperm capacitation and co-incubation medium. Sr seemed to be able to replace Ca for sperm capacitation, at least when measured as the ability to bind to the zona pellucida, and undergo AR when Ca is provided. Moreover, sperm-zona pellucida binding could also take place in a Sr-modified medium. When binding assays were carried out in the Sr medium, GlcNAc also produced an inhibitory effect. This could be reproduced when sperm, but not oocytes, were pre-incubated with the monosaccharide. IVF assays were also carried out to analyse the participation of GlcNAc in the different steps of sperm-oocyte interaction. Taken together, the results support the involvement of the GlcNAc residues of the zona pellucida in the early steps of the interaction with sperm.

The Contribution of d-Mannose, l-Fucose, N-Acetylglucosamine, and Selectin Residues on the Binding of Glycodelin Isoforms to Human Spermatozoa1

Previous data showed that glycodelin-A from amniotic fluid and glycodelin-F from follicular fluid inhibited sperm-zona pellucida binding. Solubilized zona pellucida reduced the binding of glycodelin-F to sperm extract dose dependently. This study demonstrated that the zona pellucida proteins also reduced the binding of glycodelin-A to sperm extract. Ionophore-induced acrosome reaction reduced the binding of iodinated glycodelin-A and -F to sperm, indicating that the glycodelin-binding sites are on the outer acrosomal membrane or on the sperm plasma membrane overlying the acrosome. While the binding of glycodelin-A to sperm was suppressed by mannose and fucose neoglycoproteins, that of glycodelin-F was also reduced by acetylglucosamine neoglycoprotein. Pretreatment of sperm with inhibitors of mannosidase and acetylglucosaminidase reduced the binding of glycodelin-F to sperm. On the other hand, inhibitor of mannosidase but not of acetylglucosaminidase inhibited the binding of glycodelin-A. In a competition binding assay, mannosidase reduced both glycodelin-A and -F binding whereas acetylglucosaminidase reduced only glycodelin-F binding. While fucosidase reduced the binding of both glycodelins, fucosidase inhibitor was marginally active in suppressing the binding of glycodelins to human sperm. Among the selectins tested, only E-selectin had a slight inhibitory effect on the binding of glycodelin-A to sperm. The binding of glycodelin-F was unaffected by selectins and their antibodies. In conclusion, the binding of glycodelin-A to sperm involves mannose, fucose, and possibly E- selectin residues, while that of glycodelin-F involves mannose, fucose, and N-acetylglucosamine but not the selectin residue.

Glycoconjugate histochemistry of the seminal vesicles of the Japanese miniature (Shiba) goat

The present study localizes and characterizes complex glycoconjugates in the seminal vesicles of the Japanese Shiba goat, using several carbohydrate histochemical procedures, including lectin techniques at light and electron microscopic levels. Glandular epithelial cells and luminal secretions were shown to contain neutral and acidic glycoconjugates with various saccharide residues, such as alpha-D-Man, alpha-D-Glc, alpha-L-Fuc, beta-D-Gal, GalNAc, GlcNAc, and NeuAc (sialic acid). The terminal oligosaccharide chains of sialoglycoconjugates present in the seminal vesicles were NeuAc alpha 2-3Gal beta 1-3GalNAc and NeuAc alpha 2-3Gal beta 1-4GlcNAc. In addition, in lysosomes of the glandular epithelial cells alpha-D-Man, alpha-D-Glc, GlcNAc and NeuAc (sialic acid) residues could be detected, the secretory vesicles contained alpha-L-Fuc, and the endoplasmic reticulum exhibited alpha-D-Man and alpha-D-Glc residues. The complex glycoconjugates with various sugar residues found in the seminal vesicles of the goat may be involved in various fertilization-related events.

Murine and human zona pellucida 3 derived from mouse eggs express identical O-glycans

Murine sperm initiate fertilization by binding to the outer covering of the egg known as the murine zona pellucida (mZP). This binding is thought to require the interaction of O-glycans linked to a specific mZP glycoprotein (mZP3) with egg-binding proteins coating the sperm plasma membrane. The precise molecular basis of this interaction remains to be resolved. In this study, we analyzed the O-glycosylation of the individual mZP glycoproteins by using ultrasensitive MS methods. We found that the majority of the O-glycans that are linked to mZP3 are core type 2 sequences terminated with sialic acid, lacNAc (Galbeta1-4GlcNAc), lacdiNAc (Gal-NAcbeta1-4GlcNAc), Galalpha1-3Gal, and NeuAcalpha2-3[GalNAcbeta1-4]Galbeta1-4 (Sda antigen). Many of these terminal sequences have been implicated previously in murine sperm-egg binding. Core type 1 O-glycans are also present and are generally unmodified, although some are terminated with sialic acid, beta-linked N-acetylhexosamine, or NeuAcalpha2-3[GalNAcbeta1-4]Galbeta1-4. Eggs expressing human ZP (huZP) glycoprotein huZP3, derived from transgenic mice, bind murine but not human sperm, implying that huZP3 acquires the same O-glycans as native mZP3. Sequencing of huZP3-associated O-glycans confirms that this implication is correct. The data obtained in this investigation may prove to be very useful for studies to determine the precise molecular basis of initial murine sperm-egg binding.

In vitro maturation and fertilization of buffalo oocytes: effects of storage of ovaries, IVM temperatures, storage of processed sperm and fertilization media

Studies were conducted to examine the possibility of preserving slaughterhouse-derived buffalo ovaries at 4 degrees C for 0 (control), 12 and 24 h to maintain the developmental competence of the oocytes (experiment 1), to assess the effect of incubation temperature during oocyte maturation on rates of in vitro maturation (IVM) and in vitro fertilization (IVF) of buffalo oocytes and embryo development (experiment 2), and to examine the effect of storage at 25 degrees C for 0 (control), 4 and 8 h of frozen-thawed buffalo sperm and BO and H-TALP as sperm processing and fertilization media on cleavage and embryo development in vitro of buffalo oocytes (experiment 3) in order to optimize the IVF technology in buffalo. Results suggested that storage of ovaries at 4 degrees C for 12 or 24 h significantly (p < 0.05) reduced the developmental potential of oocytes. Incubation temperatures during the IVM influenced the fertilization rate but had no significant effect on maturation and subsequent embryo development. The incubation temperature of 38.5 degrees C during IVM was found to be optimum for embryo production in vitro. Storage of frozen-thawed sperm at 25 degrees C for 8 h significantly (p < 0.05) decreased its ability to cleave the oocytes. Sperm processed in BO medium had significantly (p < 0.05) higher ability to cleave the oocytes than the H-TALP medium.

Circadian rhythm of glycoprotein secretion in the vas deferens of the moth, Spodoptera littoralis

BACKGROUND

Reproductive systems of male moths contain circadian clocks, which time the release of sperm bundles from the testis to the upper vas deferens (UVD) and their subsequent transfer from the UVD to the seminal vesicles. Sperm bundles are released from the testis in the evening and are retained in the vas deferens lumen overnight before being transferred to the seminal vesicles. The biological significance of periodic sperm retention in the UVD lumen is not understood. In this study we asked whether there are circadian rhythms in the UVD that are correlated with sperm retention.

RESULTS

We investigated the carbohydrate-rich material present in the UVD wall and lumen during the daily cycle of sperm release using the periodic acid-Shiff reaction (PAS). Males raised in 16:8 light-dark cycles (LD) showed a clear rhythm in the levels of PAS-positive granules in the apical portion of the UVD epithelium. The peak of granule accumulation occurred in the middle of the night and coincided with the maximum presence of sperm bundles in the UVD lumen. These rhythms persisted in constant darkness (DD), indicating that they have circadian nature. They were abolished, however, in constant light (LL) resulting in random patterns of PAS-positive material in the UVD wall. Gel-separation of the UVD homogenates from LD moths followed by detection of carbohydrates on blots revealed daily rhythms in the abundance of specific glycoproteins in the wall and lumen of the UVD.

CONCLUSION

Secretory activity of the vas deferens epithelium is regulated by the circadian clock. Daily rhythms in accumulation and secretion of several glycoproteins are co-ordinated with periodic retention of sperm in the vas deferens lumen.

Characterization of the sperm receptor for acrosome reaction-inducing substance of the starfish, Asterias amurensis

Acrosome reaction-inducing substance (ARIS) in the jelly coat of starfish eggs is a highly sulfated proteoglycan-like molecule of an apparent molecular size over 10(4) kDa and plays a pivotal role in the induction of acrosome reaction in homologous spermatozoa. It is known in Asterias amurensis that ARIS binds to a restricted area of the anterior portion of sperm head, and that a glycan fragment of ARIS, named Fragment 1, consisting of 10 repeats or so of a pentasaccharide unit retains the biological activity of ARIS to an appreciable extent. In this report, we have shown the binding of Fragment 1, a relatively small pure glycan fragment of ARIS, to the putative ARIS receptor on the sperm surface by three independent methods. First, the specific binding of P-ARIS to isolated sperm membranes was monitored in real-time by using a surface plasmon resonance detector, namely a Biacore sensor system. The specific and quantitative binding of Fragment 1 to the intact sperm and to isolated sperm membranes was similarly monitored. Secondly, the binding of 125I-labeled Fragment 1 to the intact sperm was stoichiometrically measured, for which we had developed a unique procedure for radioiodination of saccharide chains. It is found that Fragment 1 competes with P-ARIS for the binding to ARIS-receptor, suggesting that Fragment 1 is a useful ligand in the search for ARIS receptor protein(s). Thirdly, the putative receptor molecules were specifically labeled by using Fragment 1 as a ligand for photoaffinity crosslink technique. Taking these results into account, we conclude that starfish sperm have the ARIS receptor, which consists most probably of 50 to 60 kDa proteins, of reasonably high affinity (for Fragment 1, Kd = 15 microM, Bmax = 8.4 x 10(4) per cell).

Expression of lectin receptors on the membrane surface of sperm of fertile and subfertile boars by flow cytometry

Studies suggest that carbohydrates are important in different stages of fertilization. Plasma membrane changes accompanying in vitro capacitation and acrosome reaction (AR), such as removal or appearance of specific glycoproteins, have been studied using lectins that bind specifically to carbohydrate residues. In specialized artificial insemination farms and semen production centers, identification of boars with decreased fertilization ability (subfertility) is a newborn necessity. This investigation is a sequential study to determine the kinetics of surface carbohydrates turnover during in vitro capacitation and AR in fertile and subfertile boar sperm. Flow cytometry determinations of the binding of three FITC-labeled lectins were assessed. WGA binding was significantly lower in fresh, capacitated, and acrosome-reacted sperm of subfertile boars than in fertile boars. Con-A binding was not significantly different in fresh sperm of fertile and subfertile boars. However. Con-A labeling in capacitated, and acrosome-reacted sperm differed significantly in both groups. UEA binding increased only in capacitated sperm of subfertile boars. These findings could be used as indicators of capacitation and AR and may also be a good indicator of sperm fertilizing ability in boars.

Glycohistochemistry of the zona pellucida of developing oocytes in the rabbit and hare

Lagomorpha are often used as animal models in reproductive experiments. The aim of the present study was to examine the glycoconjugate modifications occurring mainly in the zona pellucida during oocyte growth in the rabbit and hare, using a battery of lectins combined with sialidase digestion and chemical treatments. This histochemical approach made it possible to identify sulpho- and asulpho-carbohydrates in the terminal and/or subterminal position linked to sialic acid residues. The lectins that stained the zona pellucida of both species most effectively were SBA, PNA and WGA, indicating the presence of beta-D-N-acetylgalactosamine, beta-D-galactosamine and N-acetylglucosamine residues. The differences in the glucidic residue content and in their spatial distribution that depended on the species and stage of follicle development were also detected.

Mechanical forces imposed on echinoid eggs during spawning: mitigation of forces by fibrous networks within egg extracellular layers

Many echinoderms spawn large numbers of eggs in rapid spawning bouts directly into the water column. During spawning, the eggs pass from the gonad along a narrow oviduct and through a rigid gonopore before reaching the water. As the eggs traverse this pathway, they are exposed to shear stress induced by the development of a velocity gradient within the fluid formed by the eggs. In some species, the diameter of the eggs is larger than the diameter of the gonopore. In these cases, the eggs also experience strain resulting from compression of the egg as it passes through the relatively small gonopore. The magnitude of shear stress experienced by eggs differs among species depending upon the viscosity of the eggs. The degree of strain experienced by eggs differs among species depending upon the relative sizes of the egg and gonopore and also changes within species as they grow. Recent evidence suggests that these forces have the propensity to damage eggs, thereby reducing their fertilizability, or to destroy them. Experimental evidence shows that the jelly coat around the eggs can protect them from shear stresses and reduce the strain imposed on them under a compressive force. Echinoderm eggs are surrounded by a jelly coat that has a composite structure of irregularly arranged fibrous networks embedded in a jelly matrix. These fibrous networks have characteristics that are similar to those of engineered and biological materials that are known to reduce the transmission of mechanical forces to other structures. Given this similarity to other materials, three possible mechanisms for the action of the jelly coat may be identified. First, the apparent viscosity of the eggs of echinoids declines as the rate at which they are sheared during spawning increases. This reduction in viscosity with increasing shear rate (shear-thinning) may, in part, be due to the structure of the jelly coat and its resultant non-Newtonian nature. Second, experimental evidence indicates that the jelly coat preferentially deforms under a compressive load, reducing the transmission of that load to the egg. Third, the jelly (but not the fibers in the coating) may deform in a nearly viscous manner. In this case, the fibers may serve to provide an elastic ‘backbone’ to the layer and remain in place to stiffen the outer layer of the egg. The composite structure of the jelly coat and the morphology of the fibrous network are likely to be critical to all these mechanisms.

Differential effects of polysulphates between mouse and hamster during in vitro fertilization

The interaction between zona pellucida polysulphates and sperm receptors appears to be a widespread mechanism used by mammals during gamete interaction. In this work, the effect of heparin on binding, penetration and fertilization of mouse and hamster oocytes was assessed. We found that heparin inhibited oocyte penetration and fertilization in both species. Heparin as well as fucoidan (a fucose-sulphate polymer) inhibited the proteolytic activity of acrosomal enzymes in both species. Our results suggest that zona pellucida penetration in both species may be modulated by polysulphates acting on either the proteolytic rate of degradation of the zona and/or its interaction with acrosome-reacted sperm (secondary binding).

Dynamics of the mammalian sperm plasma membrane in the process of fertilization

Sexual reproduction requires the fusion of sperm cell and oocyte during fertilization to produce the diploid zygote. In mammals complex changes in the plasma membrane of the sperm cell are involved in this process. Sperm cells have unusual membranes compared to those of somatic cells. After leaving the testes, sperm cells cease plasma membrane lipid and protein synthesis, and vesicle mediated transport. Biophysical studies reveal that lipids and proteins are organized into lateral regions of the sperm head surface. A delicate reorientation and modification of plasma membrane molecules take place in the female tract when sperm cells are activated by so-called capacitation factors. These surface changes enable the sperm cell to bind to the extra cellular matrix of the egg (zona pellucida, ZP). The ZP primes the sperm cell to initiate the acrosome reaction, which is an exocytotic process that makes available the enzymatic machinery required for sperm penetration through the ZP. After complete penetration the sperm cell meets the plasma membrane of the egg cell (oolemma). A specific set of molecules is involved in a disintegrin-integrin type of anchoring of the two gametes which is completed by fusion of the two gamete plasma membranes. The fertilized egg is activated and zygote formation preludes the development of a new living organism. In this review we focus on the involvement of processes that occur at the sperm plasma membrane in the sequence of events that lead to successful fertilization. For this purpose, dynamics in adhesive and fusion properties, molecular composition and architecture of the sperm plasma membrane, as well as membrane derived signalling are reviewed.

Evidence for the participation of beta-hexosaminidase in human sperm-zona pellucida interaction in vitro

Mammalian sperm-zona pellucida (ZP) interaction is mediated by sperm lectin-like proteins and ZP glycoproteins. We have previously reported the participation of binding sites for N-acetylglucosamine (GlcNAc) residues in human sperm function, including sperm interaction with the ZP. Additionally, previous results from our laboratory suggested that some of these events may be mediated by the glycosidase N-acetylglucosaminidase (beta-hexosaminidase, Hex, in mammals). In this study, we report the possible participation of Hex in human sperm-ZP interaction. Human recombinant Hex (hrHex) was obtained by expression in a stable transfected CHO cell line. When the recombinant enzyme was present during hemizona (HZ) assays, the number of sperm bound per HZ was significantly reduced. The same result was obtained when HZ were preincubated with hrHex. Additionally, the presence of a Hex-specific substrate during the HZ assay produced the same inhibitory effect. These results suggest the participation of a sperm Hex in the interaction with human ZP in vitro.

Effect of recombinant boar beta-acrosin on sperm binding to intact zona pellucida during in vitro fertilization

In a previous paper we demonstrated that boar beta-acrosin recombinant proteins were able to bind non-enzymatically to solubilized pig zona pellucida (ZP) glycoproteins. Here we report the participation of boar beta-acrosin in the secondary binding of sperm to intact pig ZP. This was achieved by using two boar recombinant proteins: beta-acrosin and a mutant of the catalytic site, beta-acrosin Ser/Ala(222). Assays of binding between the iodinated recombinant beta-acrosin and whole ZP showed that this binding could be saturated, was specific, and was stable over time. Using autoradiography, we determined that recombinant beta-acrosin bound on the entire surface of the ZP but initially was distributed heterogeneously. This suggests that the ligands for beta-acrosin may not be homogeneously distributed on the ZP. To study the contribution of acrosin in sperm secondary binding to the ZP, we preincubated in vitro-matured oocytes with these recombinant proteins and then performed in vitro fertilization assays. Under the experimental conditions used, binding of beta-acrosin recombinant proteins did not block sperm penetration. These results suggest that there may be other proteins that participate in the secondary binding, and that these proteins may recognize ligands that are different from those blocked by beta-acrosin recombinant proteins.

Shear stress experienced by echinoderm eggs in the oviduct during spawning: potential role in the evolution of egg properties

Shear stresses experienced by eggs in the oviduct of the echinoid Arbacia punctulata during spawning were calculated using engineering equations that describe laminar flow through pipes. Shear stresses in the oviduct ranged from 0 to 58.7 Pa. Two properties of eggs were identified that have the potential either to minimize the shear stress in the oviduct or to reduce the damage experienced by eggs exposed to high shear stress. These properties are the viscosity of the eggs and the presence of extracellular layers on eggs of A. punctulata. The viscosity of eggs decreases with increasing shear rates, which reduces the magnitude of shear stress experienced in the oviduct, while the extracellular layers mitigate the effect of shear stress on the eggs. Eggs with intact extracellular layers were damaged less frequently than were those with the extracellular layers removed. The results of this research indicate that physical stresses may be important selective factors in the evolution of gamete properties.

Isolation and biological characterization of boar sperm capacitation-related antigen

PROBLEM

Monoclonal anti-capacitated sperm antibody has been used as a probe to identify, isolate, and characterize specific, fertilization-related antigen with some characteristic features that point to its possible significance in immunocontraception.

METHOD OF STUDY

Fast protein liquid chromatography (FPLC), enzyme-linked immunosorbent assay (ELISA), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and isoelectrofocusing were used for isolation, immunochemical and physicochemical characterization of a monoclonal antibody (mAb) 1F10 cognate antigen. Sperm-zona pellucida binding and hemizona assay were used for testing the biological roles of mAb 1F10 and Ag 1F10 in boar and human fertilization processes.

RESULTS

The Ag 1F10 was found to be eluted in the eighth protein peak of FPLC-fractionated Nonidet P40 (NP40) extracts of capacitated boar spermatozoa. The SDS-PAGE and immunoelectrofocusing experiments showed that Ag 1F10 is a protein composed of a single peptide chain with a relative molecular mass of 68/70 kDa and an isoelectric point of 3.5. It was demonstrated that the zona binding activity of spermatozoa preincubated in the presence of mAb 1F10 was significantly inhibited both in porcine and human in vitro fertilization (IVF) systems. A dose-dependent manner of inhibition of the sperm/ligand activities of porcine and human zona pellucida was observed when the effect of purified Ag 1F10 was investigated by its preincubation with zona pellucida.

CONCLUSIONS

It is assumed that the protein bearing the epitope recognized by mAb 1F10 may be accepted as one of the molecules with receptor function in sperm-zona pellucida interaction during fertilization.

Glycohistochemical investigation of canine and feline zonae pellucidae of preantral and antral oocytes

Glycoconjugate modifications were analysed in the zona pellucida during development of oocytes in dog and cat using conventional histochemical staining methods with or without previous carbohydrate digestion. A series of lectins combined with desulphation and sialic acid degradation were applied. No differences were observed between dog and cat follicles using conventional histochemical staining methods. In both species, the zona pellucida and follicular fluid/intercellular matrix strongly reacted with PAS and high iron diamine stain (HID) and reacted moderately with low iron diamine stain (LID). Treatment with testicular hyaluronidase, chondroitinase ABC, chondroitinase AC and chondroitinase B treatment diminished HID and LID positivity of follicular fluid and intercellular matrix. Lectins that gave the most intense staining of the zona pellucida of both species were SBA, PNA, RCA-I, GSA-IB4 and WGA, indicating the presence of beta-D-GalNAc, D-Gal and GlcNAc residues. Sulpho- and asulpho-carbohydrates were identified in terminal and/or subterminal positions linked to sialic acid residues. In conclusion, the results indicate that glycosaminoglycans are not present in the zona pellucida of both species. Differences were observed in carbohydrate residues and in their spatial distribution, depending on species and developmental stage of the follicles. The similarity in lectin affinity between ooplasm and zona pellucida of oocytes present in follicles at different stages of development confirm the involvement of oocytes in zona pellucida production.

Isolation and characterization of heparin- and phosphorylcholine-binding proteins of boar and stallion seminal plasma. Primary structure of porcine pB1

In the bovine, seminal plasma heparin-binding proteins bind to sperm lipids containing the phosphorylcholine group and mediate the capacitating effects of heparin-like glycosaminoglycans during sperm residence in the female genital tract. We report the characterization of heparin- and phosphorylcholine-binding proteins of stallion and boar seminal plasma. Horse seminal plasma proteins HSP-1 and HSP-2, and boar protein pB1, belong to the same family as the bull heparin- and phosphorylcholine-binding proteins BSP-A1/2, BSP-A3, and BSP-30K. We have determined the amino acid sequence and posttranslational modifications of boar glycoprotein pB1. It contains 105 amino acids arranged into a mosaic structure consisting of a N-terminal 18-residue O-glycosylated polypeptide followed by two tandemly organized 40-45-residue fibronectin type II domains. pB1 displays 60-65% amino acid sequence similarity with its equine and bovine homologues. However, in their respective seminal plasmas, the BSP and the HSP proteins associate into 90-150-kDa oligomeric complexes, whereas pB1 forms a 35-40-kDa complex with spermadhesin AQN-1. In addition, pB1 appears to be identical to the recently described leukocyte adhesion regulator of porcine seminal fluid pAIF-1. Our results tie in with the hypothesis that homologous proteins from different mammalian species may display distinct biological activities, which may be related to species-specific aspects of sperm physiology.

Proteolytic release and partial characterization of human sperm-surface glycopeptides

Sperm-surface glycopeptides were obtained from intact sperm membranes after proteolytic release by different enzymatic treatments such as autoproteolysis, trypsin, papain and pronase. Glycopeptides were isolated, their properties and composition were examined, and their monosaccharide and amino acid constituents were characterized. The monosaccharides identified were fucose, mannose, galactose, N-acetylglucosamine, and N-acetylgalactosamine, which form part of more than one type of oligosaccharide units. Autoproteolytic treatment mainly provided O-glycosidic type oligosaccharides, while a mixture of O- and N-glycosidic oligosaccharides was obtained in variable proportions when treated with trypsin, papain or pronase. The highest degree of peptide cleavage was obtained with pronase. Despite the higher yields reached with trypsin, these glycopeptides contain the lowest percentage of oligosaccharide chains. Proteolytic treatment provides a simple, rapid procedure for the isolation of glycopeptides from the sperm surface.

Gender-specific glycosylation of human glycodelin affects its contraceptive activity

We have recently demonstrated that a human amniotic fluid-derived glycoprotein, glycodelin-A (GdA; previously known as PP14 or PAEP), potently inhibits gamete binding in an established sperm-egg binding system and expresses immunosuppressive activities directed against a variety of different immune cell types. GdA has high mannose-, hybrid-, and complex-type biantennary oligosaccharides including structures with fucosylated or sialylated N, N'-diacetyllactosediamine (GalNAcbeta1-4GlcNAc) sequences, which are rare in other human glycoproteins. We now report the characterization of glycodelin-S (GdS). This is a human seminal plasma glycoprotein that is immunologically indistinguishable from GdA, but unlike the latter, does not inhibit human sperm-zona pellucida binding under hemizona assay conditions. Analysis of the N-glycans of GdS by mass spectrometry revealed that all glycoforms of GdS are different from those of GdA. GdS glycans are unusually fucose-rich, and the major complex-type structures are biantennary glycans with Lewisx (Galbeta1-4(Fucalpha1-3)GlcNAc) and Lewisy (Fucalpha1-2Galbeta1-4(Fucalpha1-3)GlcNAc) antennae. It is probable that these highly fucosylated epitopes contribute to the immunosuppressive activity of human seminal plasma and to the low immunogenicity of sperm. This study provides the first evidence for gender-specific glycosylation that may serve to regulate key processes involved in human reproduction.

Two-dimensional polyacrylamide gel electrophoresis of bovine semen after cryopreservation in half- milliliter straws

One of the problems encountered with two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) is the streaking of proteins so that individual spot identification is compromised. This study was conducted to determine whether a low loading dose (50 microg) of protein would permit resolution of more discrete protein spots using megapixel camera technology, and if so, to present a nomenclature for future comparisons of the identified proteins. If the major proteins could be identified in a 50-microg sample we aimed to determine whether they could be identified in the supernatant (seminal plasma plus extender) of cryopreserved semen. Two ejaculates were obtained from each of 6 bulls and bovine seminal plasma (BSP) protein concentration was standardized to 50 microg/10 microl. Isoelectric points (pI) and molecular weights (MWt) of BSP proteins were determined by measuring spot mobility on 2-D PAGE (15% polyacrylamide). Three distinct protein spot constellations (a,b,c) could be readily seen by the naked eye and a faintly stained constellation "d" was identified by the megapixel camera. The image analysis software located 6 protein spots in both constellation "a" (MWt 26 kDa; pI 4.2 to 4.8) and "b" ( MWt 27 kDa; pI 6.6 to 8.0). Constellation "c" contained 13 protein spots distributed in a right-angled triangle with its base towards the acidic end of the gel (MWt 14.7 to 18.8 kDa; pI 5.3 to 7.4). Only spots c(2), c(3), c(5), c(8), and c(13) were present in all 12 samples. Streaking can be eliminated by using 50 microg protein for 2-D PAGE, and the major protein spots are readily identified by megapixel camera technology. Protein spots c(3), c(5), c(13) and constellation "a" appear to correspond with Manjunath's proteins (BSP-A(1), -A(2); -A(3); -30 kDa). Killian's 2 low fertility proteins may lie in the "c" constellation, and 1 of the high fertility proteins may lie in the "b" constellation. The 3 major BSP proteins can be visualized in the supernatant of cryopreserved semen. We believe that the technique may prove useful for retrospective analysis of processed semen batches that achieve less than satisfactory results in the field.

Post-fertilization changes in the zona pellucida glycoproteins of rat eggs

The zona pellucida (ZP) is the extracellular coat surrounding the mammalian egg. Numerous evidence supports the role of ZP carbohydrate residues as the specific sperm receptors. In this study we used lectins to study different distribution patterns of carbohydrate residues in the rat ZP, and to follow changes at fertilization. ZP were collected from follicular, ovulated, and fertilized eggs, incubated with one of 11 different biotin-labeled lectins, followed by avidin-fluorescein isothiocyanate (FITC) complex, and visualized by epifluorescent microscopy. For electron microscope (EM) histochemistry, eggs were embedded in LR white and ultrathin sections were stained with the complex Ricinus communis lectin (RCA-1)-colloidal gold. Some lectins (RCA-I, Glycine max) bound to the entire ZP while others were restricted to the inner or outer zones [Griffonia simplicifolia, Concanovalia ensiformis, Triticum vulgaris (WGA), succinyl-WGA]. Other lectins (Lens culinaris, Ulex europhaeus) were totally excluded. The RCA-1 binding pattern changed following sperm penetration, from homogeneous in ZP of ovulated eggs (57%) to uneven in ZP of fertilized (71%) or activated (68%) eggs. Our results demonstrate an uneven distribution of different sugar residues in the rat ZP, and a post-fertilization change in the distribution of beta-galactose, which is specifically recognized by RCA-I, presumably correlated with other changes in the ZP that lead to the block to polyspermy.

Estimation by radiation inactivation of the minimum functional size of acrosome-reaction-inducing substance (ARIS) in the starfish, Asterias amurensis

In the starfish Asterias amurensis, the jelly coat of the eggs contains a glycoprotein essential for the induction of the acrosome reaction in homologous spermatozoa that is termed the acrosome-reaction-inducing substance (ARIS). ARIS is a highly sulphated and fucose-rich glycoprotein of extremely high molecular mass (> 10(4) kDa). ARIS was irradiated with high-energy electrons in order to estimate the minimum size required for its biological activity. The minimum functional unit or target size of ARIS was estimated to be c. 14 kDa by target size analysis. ARIS was significantly disintegrated by the irradiation, yet the total sugar content was not apparently reduced. The binding of 125I-labelled ARIS to spermatozoa competed with that of irradiated ARIS, although the affinity of ARIS was much reduced after irradiation.

Structural analysis of the oligosaccharides derived from glycodelin, a human glycoprotein with potent immunosuppressive and contraceptive activities

Glycodelin, also known as placental protein 14 (PP14) or progesterone-associated endometrial protein (PAEP), is a human glycoprotein with potent immunosuppressive and contraceptive activities. In this paper we report the first characterization of glycodelin-derived oligosaccharides. Using strategies based upon fast atom bombardment and electrospray mass spectrometry we have established that glycodelin is glycosylated at Asn-28 and Asn-63. The Asn-28 site carries high mannose, hybrid and complex-type structures, whereas the second site is exclusively occupied by complex-type glycans. The major non-reducing epitopes in the complex-type glycans are: Gal beta 1-4GlcNAc (lacNAc), GalNAc beta 1-4GlcNAc (lacdiNAc), NeuAc alpha 2-6Gal beta 1-4GlcNAc (sialylated lacNAc), NeuAc alpha 2-6Gal beta 1-4GlcNAc (sialylated lacdiNAc), Gal beta 1-4(Fuc alpha 1-3)GlcNAc (Lewisx), and GalNAc beta 1-4(Fuc alpha 1-3)GlcNAc (lacdiNAc analogue of Lewisx). It is possible that the oligosaccharides bearing sialylated lacNAc or lacdiNAc antennae may manifest immunosuppressive effects by specifically blocking adhesive and activation-related events mediated by CD22, the human B cell associated receptor. Oligosaccharides with fucosylated lacdiNAc antennae have previously been shown to potently block selectin-mediated adhesions and may perform the same function in glycodelin. The potent inhibitory effect of glycodelin on initial human sperm-zona pellucida binding is consistent with our previous suggestion that this cell adhesion event requires a selectin-like adhesion process. This result also raises the possibility that a convergence between immune and gamete recognition processes may have occurred in the types of carbohydrate ligands recognized in the human.

Dose-dependent effect of heparin on fertilizing ability of goat spermatozoa

Intact bovine oocytes were used to study the effect of heparin on goat IVF. Oocytes were matured in Medium 199 plus estrous sheep serum. Fresh semen was incubated for 4 h at room temperature, and spermatozoa were then resuspended in medium Talp plus serum and incubated further for 1 h at 39 degrees C in 5% CO(2) in air. Later, spermatozoa were resuspended in Talp plus serum and heparin and were then incubated in microdrops until the oocytes were matured. In Experiment 1, the effect of heparin on spermatozoa from individual males was studied by a dose-response curve. In Experiment 2, the timing of sperm penetration in matured oocytes was studied to assess the stage at which the action of heparin could be expressed in the fertilization process. In Experiment 3, heparin from the same source but at different grades of bioactivity was adjusted for bioactivity and its effect on spermatozoa was compared in terms of penetration rates in order to identify heparin-dependent variations on goat IVF. In Experiment 4, the influence of calcium on the effect of heparin at different levels of bioactivity on the fertilizing ability spermatozoa was assessed as in Experiment 3. In Experiment 5, different batches of heparin from the same source and grade of bioactivity were compared as above. The results suggest that 1) heparin stimulates fertilization rates following a comparable pattern between males; 2) the most probable site of action is at the stage of sperm capacitation; and 3) provided that the source and grade of bioactivity is preserved, heparin maintains the efficiency of sperm penetration into matured oocytes.

Monoclonal antibody against a 52 K sperm surface protein inhibits sperm-zona pellucida interactions in the rat

A major regulatory site for species specificity of fertilization in mammals lies at the level of sperm binding to the zona pellucida. This implies a high degree of complementarity between gamete and receptor molecules. These molecules support species-specific interactions between sperm and oocyte that lead to gamete fusion (fertilization). We identified a rat sperm head surface antigen using an IgG1 monoclonal antibody (HD1) against rat sperm of epididymis cauda. By electron microscopy the antigen was shown to be present on the plasma membrane surface of the sperm dorsal head. One- and two-dimensional immunoblotting analysis of sperm proteins demonstrated that HD1 reacted only with a 52 K molecule with a pI ranging from 6.6 to 7.2. The 52 K protein was first detected in situ by indirect immunofluorescence and showed to be underlining few elongated spermatids in testis. However, when the sperm reached the epididymis caput, the antigen was seen to be expressed on the dorsal surface of spermatozoa head. A similar fluorescence reaction was detected on sperms in the epididymis corpus and cauda. The specific spermatozoa-zona pellucida interaction was inhibited in the presence of monoclonal antibody HD1 in a sperm binding assay of in vitro fertilization.

Boar spermadhesin AWN-1. Oligosaccharide and zona pellucida binding characteristics

We have analyzed the oligosaccharide recognition ability of boar spermadhesin AWN-1 using biotinylated glycoproteins with defined carbohydrate chains as probes. Our results show that AWN-1 bound to proteins containing O-linked NeuAc alpha(2-3/6)-Gal beta(1-3)-GalNAc (PDC-109 and fetuin) with a Kd = 0.7 microM. AWN-1 also bound to NeuAc alpha(2-3/6)-Gal beta(1-4)-GlcNAc sequences in N-linked triantennary structures of fetuin, but not to the same oligosaccharide in the diantennary structures of IgG or fibrinogen. The absence of terminal sialic acid decreased fivefold the binding affinity. By competitive ELISA, peptides containing the N-linked oligosaccharide sequence inhibited the binding of the parent glycoprotein to immobilized AWN-1 5-45 times less effectively than those carrying O-linked NeuAc alpha(2-3/6)-Gal beta(1-3)-GalNAc structures. In addition, AWN-1 bound with a Kd = 0.3 microM to solubilized, biotinylated porcine zona pellucida glycoproteins. PDC-109 competed effectively with zona pellucida glycoproteins for AWN binding, whereas fetuin was a poor competitor. On the other hand, AWN epitopes were demonstrated on in vitro capacitated boar spermatozoa which were able to bind to, and penetrate, zona-encased oocytes. These data indicate that spermadhesin AWN-1 may play a role in pig fertilization as a sperm-associated lectin of broad specificity though preferential affinity for certain O-linked oligosaccharide structures of the oocyte's zona pellucida.

Use of lectins as diagnostic and therapeutic tools for cancer

Within the past few years, lectins have become a well-established means for understanding varied aspects of cancer and metastasis. Evidence is now emerging that lectins are dynamic contributors to tumor cell recognition (surface markers), cell adhesion and localization, signal transduction across membranes, mitogenic stimulation, augmentation of host immune defense, cytotoxicity, and apoptosis. To advance understanding of these lectin-dependent processes, attempts are being made to discover new lectins that have one or more of these functions and to develop lectin- (or glycoconjugate-) based tools that could be used to home in on tumor cells. This review will summarize current research on the lectins and recent advances in the development of lectin-based diagnostic and therapeutic tools for cancer. Additionally, the future potential of lectin-based diagnosis and therapy is discussed.

Sperm-binding proteins

Gamete recognition and binding are mediated by specific proteins on the surface of the sperm and egg. Identification and characterization of some of these proteins from several model systems, particularly mouse and sea urchin, have focused interest on the general properties and functions of gamete recognition proteins. Sperm-binding proteins located in egg extracellular coats as well as sperm-binding proteins that are localized to the egg plasma membrane are presented in the context of their structure and function in gamete binding. Unifying and disparate characteristics are discussed in light of the diverse biology of fertilization among species. Outstanding questions, alternative mechanisms and models, and strategies for future work are presented.