Sperm Binding to Oviductal Epithelial Cells in the Rat: Role of Sialic Acid Residues on the Epithelial Surface and Sialic Acid-Binding Sites on the Sperm Surface1

Mating Increases CHST10 Activity in Rat Oviductal Mucosa to Induce the Synthesis of HNK-1 Glycoproteins: Possible Role in Sperm-Oviduct Interactions

Previously, we reported that mating induces an early transcriptional response in the oviductal mucosa of rats. The functional category 'cell-to-cell signaling and interaction' was overrepresented in this gene list. Therefore, in the present study, we describe the role of one of these genes, carbohydrate sulfotransferase 10 (Chst10), in the oviductal mucosa. CHST10 participates in the synthesis of the carbohydrate moiety human natural killer-1 (HNK-1), which mediates cell-to-cell interactions. When using one-dimensional Western blot and sulfotransferase analyses, we found that mating increased the protein level and activity of CHST10 in the oviductal mucosa at 3 h after stimulation. A two-dimensional Western blot analysis and mass spectrometry were used to identify the novel HNK-1 glycoproteins aldehyde dehydrogenase 9 family, member A1 (ALDH9A1), fructose bisphosphate aldolase A (ALDOA), and four and a half LIM domains protein 1 (FHL1) in the oviductal mucosa, and we found that mating induces the synthesis of their acidic variants. Interestingly, in the utero-tubal junction (UTJ), acrosome-reacted sperm apparently were interacting with regions in which ALDH9A1 and HNK-1 signals overlap. Furthermore, vaginocervical stimulation applied to unmated rats increased the mRNA level of Chst10 in the oviductal mucosa. In conclusion, mating increases the activity of CHST10 in the oviductal mucosa, which in turn induces the synthesis of acidic variants of ALDH9A1 and FHL1 via HNK-1 glycosylation. ALDH9A1, HNK-1-ALDH9A1, and/or other HNK-1 glycoproteins could participate in the negative selection of sperm in the UTJ, since we detected acrosome-reacted sperm apparently interacting with regions where these proteins are located. Finally, the sensorial component of mating could regulate early events (e.g., sperm transport and selection) occurring in the oviductal mucosa after mating.

Sialylation: fate decision of mammalian sperm development, fertilization, and male fertility†

Sperm development, maturation, and successful fertilization within the female reproductive tract are intricate and orderly processes that involve protein translation and post-translational modifications. Among these modifications, sialylation plays a crucial role. Any disruptions occurring throughout the sperm's life cycle can result in male infertility, yet our current understanding of this process remains limited. Conventional semen analysis often fails to diagnose some infertility cases associated with sperm sialylation, emphasizing the need to comprehend and investigate the characteristics of sperm sialylation. This review reanalyzes the significance of sialylation in sperm development and fertilization and evaluates the impact of sialylation damage on male fertility under pathological conditions. Sialylation serves a vital role in the life journey of sperm, providing a negatively charged glycocalyx and enriching the molecular structure of the sperm surface, which is beneficial to sperm reversible recognition and immune interaction. These characteristics are particularly crucial during sperm maturation and fertilization within the female reproductive tract. Moreover, enhancing the understanding of the mechanism underlying sperm sialylation can promote the development of relevant clinical indicators for infertility detection and treatment.

Buffalo sperm membrane glycan-binding proteins reveal precise and preferential binding signatures with specific glycans targets on oviduct epithelium and zona pellucida-an implication in fertilization

Sperm membrane glycan-binding proteins (lectins) interact with the counterpart glycans in the oviduct, oocytes, and vice-versa. It has already been well known that specific glycans are present on oviductal epithelium and zona pellucida (ZP) in different mammalian species. Some of these glycans are necessary for oviductal sperm reservoir formation and gamete recognition. The specific binding phenomenon of lectin-glycans is one of the vital factors for successful fertilization in mammals. We hypothesized that buffalo sperm membrane glycan-binding proteins have specific glycan targets in the oviduct and ZP supporting the fertilization event. In the present investigation, sperm membrane proteins were extracted and assessed for their binding capacity with glycans using a high-throughput glycan microarray. The most promising glycan binding signals were evaluated to confirm the sperm putative receptors for glycan targets in the oviductal epithelial cells (OEC) and on ZP using an in-vitro competitive binding inhibition assay. Based on an array of 100 glycans, we found that N-acetyllactosamine (LacNAc), Lewis-a trisaccharide, 3'-sialyllactosamine and LacdiNAc were the most promising glycans and selected for further in-vitro validation. We established an inhibitory concentration of 12 mM Lewis-a trisaccharide and 10 μg/ml Lotus tetragonolobus (LTL) lectin for the sperm-OEC binding interaction, indicating its specificity and sensitivity. We observed that 3 mM 3'-sialyllactosamine, and LacdiNAc were the most competitive inhibitory concentration in sperm-ZP binding, suggesting a specific and abundance-dependent binding affinity. The competitive binding affinity of Maackia amurensis (MAA) lectin with Neu5Ac(α2-3)Gal(β1-4)GlcNAc further supports the abundance of 3'-sialyllactosamine on ZP responsible for sperm binding. Our findings develop the strong evidence on buffalo sperm putative receptors underlying their locking specificities with Lewis-a trisaccharide in oviduct and 3'-sialyllactosamine on ZP. The functional interaction of buffalo sperm lectins with the target glycans in OEC and ZP appears to be accomplished in an abundance-dependent manner, facilitating the fertilization event in buffaloes.

Molecules involved in the sperm interaction in the human uterine tube: a histochemical and immunohistochemical approach

In humans, even where millions of spermatozoa are deposited upon ejaculation in the vagina, only a few thousand enter the uterine tube (UT). Sperm transiently adhere to the epithelial cells lining the isthmus reservoir, and this interaction is essential in coordinating the availability of functional spermatozoa for fertilization. The binding of spermatozoa to the UT epithelium (mucosa) occurs due to interactions between cell-adhesion molecules on the cell surfaces of both the sperm and the epithelial cell. However, in humans, there is little information about the molecules involved. The aim of this study was to perform a histological characterization of the UT focused on determining the tissue distribution and deposition of some molecules associated with cell adhesion (F-spondin, galectin-9, osteopontin, integrin αV/β3) and UT's contractile activity (TNFα-R1, TNFα-R2) in the follicular and luteal phases. Our results showed the presence of galectin-9, F-spondin, osteopontin, integrin αV/β3, TNFα-R1, and TNFα-R2 in the epithelial cells in ampullar and isthmic segments during the menstrual cycle. Our results suggest that these molecules could form part of the sperm-UT interactions. Future studies will shed light on the specific role of each of the identified molecules.

Diversity of sialic acids and sialoglycoproteins in gametes and at fertilization

Sialic acids are a family of 9-carbon monosaccharides with particular physicochemical properties. They modulate the biological functions of the molecules that carry them and are involved in several steps of the reproductive process. Sialoglycoproteins participate in the balance between species recognition and specificity, and the mechanisms of these aspects remain an issue in gametes formation and binding in metazoan reproduction. Sialoglycoproteins form a specific coat at the gametes surface and specific polysialylated chains are present on marine species oocytes. Spermatozoa are submitted to critical sialic acid changes in the female reproductive tract facilitating their migration, their survival through the modulation of the female innate immune response, and the final oocyte-binding event. To decipher the role of sialic acids in gametes and at fertilization, the dynamical changes of enzymes involved in their synthesis and removal have to be further considered.

Role of Integrins in Sperm Activation and Fertilization

In mammals, integrins are heterodimeric transmembrane glycoproteins that represent a large group of cell adhesion receptors involved in cell-cell, cell-extracellular matrix, and cell-pathogen interactions. Integrin receptors are an important part of signalization pathways and have an ability to transmit signals into and out of cells and participate in cell activation. In addition to somatic cells, integrins have also been detected on germ cells and are known to play a crucial role in complex gamete-specific physiological events, resulting in sperm-oocyte fusion. The main aim of this review is to summarize the current knowledge on integrins in reproduction and deliver novel perspectives and graphical interpretations presenting integrin subunits localization and their dynamic relocation during sperm maturation in comparison to the oocyte. A significant part of this review is devoted to discussing the existing view of the role of integrins during sperm migration through the female reproductive tract; oviductal reservoir formation; sperm maturation processes ensuing capacitation and the acrosome reaction, and their direct and indirect involvement in gamete membrane adhesion and fusion leading to fertilization.

Porcine oocyte preincubation in oviductal fluid flush before in vitro fertilization in the presence of oviductal epithelial cells improves monospermic zygote production

The present study was designed to evaluate the effect of the combination of oviduct fluid flush (OFF) and oviduct epithelial cells (OEC) in modulating the incidence of polyspermy in pigs. Therefore, for in vitro fertilization (IVF), oocyte and sperm were co-cultured in Tris-buffered medium (TBM) either supplemented with 10% OFF (OFFD group), or in the presence of a bovine OEC monolayer (OEC group), or the oocytes were exposed to OFF for 30 min before IVF (OFFB group), or in the presence of an OEC monolayer (OFFB + OEC group). Regardless of sperm concentration used (0.5, 1.5, and 4.5 × 105 cells/ml), supplementation of IVF medium with 10% OFF led to an increased (P < 0.05) monospermy rate, without alteration (P > 0.05) of the penetration rate in comparison with the control and OEC groups. When the IVF medium was supplemented with heparin, an overall increase (P < 0.05) of the final output of the IVF system in terms of zygotes with two pronuclei (2PN) was observed in the OFFD group, compared with the control and OEC groups, at a sperm concentration of 4.5 × 105 cells/ml. At this concentration, OFFB improved the monospermy rate but decreased the penetration rate, resulting in low efficiency of monospermic zygotes production. Despite this, no major effect was observed in the developmental competence of the presumed zygotes up to the blastocyst stage. The combination of OFFB with OEC improved the penetration rate, while maintaining the high monospermic rate induced by OFFB. In conclusion, the combination of treatment of oocytes by diluted OFF 30 min before IVF, followed by IVF in the presence of OEC, improved monospermic zygote production without reducing the penetration rate, when the IVF medium was supplemented with heparin.

Postnatal cadmium administration affects the presence and distribution of carbohydrates in the sperm membrane during maturation in the epididymis in adult Wistar rats

Cadmium (Cd) is a heavy metal related to a decrease in sperm parameters. The transit of spermatozoa through the epididymis is necessary to generate changes in the sperm membrane, such as the assembly of various carbohydrates that are added to the spermatazoan's surface to prepare it for successful fertilisation of the oocyte. No studies have yet analysed whether Cd alters the presence and distribution of these carbohydrates. We aimed to evaluate the changes induced by Cd in the distribution pattern of N-acetylglucosamine, sialic acid, mannose and fucose on the sperm membrane in the epididymis (e.g. caput, corpus, cauda) and if it alters the epididymal epithelium. Male Wistar pups were treated with Cd doses (0.125, 0.25 and 0.5mg/kg) on postnatal days 1-49. At postnatal day 90, they were humanely killed, sperm samples were obtained from the epididymis and tissue samples were taken for histological analysis. Cd concentrations in the blood and epididymis increased in proportion to the dose administered and decreased the serum testosterone levels and sperm quality. Histological analysis revealed alterations in the epithelium in all Cd-treated groups. Cd altered the distribution patterns of carbohydrates and fluorescence indices. All these alterations affected the structure and functioning of sperm.

Sperm interactions with the female reproductive tract: A key for successful fertilization in mammals

Sperm migration through the female genital tract is not a quiet journey. Uterine contractions quickly operate a drastic selection, leading to a very restrictive number of sperm reaching the top of uterine horns and finally, provided the presence of key molecules on sperm, the oviduct, where fertilization takes place. During hours and sometimes days before fertilization, subpopulations of spermatozoa interact with dynamic and region-specific maternal components, including soluble proteins, extracellular vesicles and epithelial cells lining the lumen of the female tract. Interactions with uterine and oviductal cells play important roles for sperm survival as they modulate the maternal immune response and allow a transient storage before ovulation. The body of work reported here highlights the importance of sperm interactions with proteins originated from both the uterine and oviductal fluids, as well as hormonal signals around the time of ovulation for sperm acquisition of fertilizing competence.

Adhesion to oviduct glycans regulates porcine sperm Ca2+ influx and viability

Before fertilization, sperm bind to epithelial cells of the oviduct isthmus to form a reservoir that regulates sperm viability and capacitation. The sperm reservoir maintains optimum fertility in species, like swine, in which semen deposition and ovulation may not be well synchronized. We demonstrated previously that porcine sperm bind to two oviductal glycan motifs, a biantennary 6-sialylated N-acetyllactosamine (bi-SiaLN) oligosaccharide and 3-O-sulfated Lewis X trisaccharide (suLe^X). Here, we assessed the ability of these glycans to regulate sperm Ca²⁺ influx, capacitation and affect sperm lifespan. After 24 h, the viability of sperm bound to immobilized bi-SiaLN and suLe^X was higher (46% and 41% respectively) compared to viability of free-swimming sperm (10–12%). Ca²⁺ is a central regulator of sperm function so we assessed whether oviduct glycans could affect the Ca²⁺ influx that occurs during capacitation. Using a fluorescent intracellular Ca²⁺ probe, we observed that both oviduct glycans suppressed the Ca²⁺ increase that occurs during capacitation. Thus, specific oviduct glycans can regulate intracellular Ca²⁺. Because the increase in intracellular Ca²⁺ was suppressed by oviduct glycans, we examined whether glycans affected capacitation, as determined by protein tyrosine phosphorylation and the ability to undergo a Ca²⁺ ionophore-induced acrosome reaction. We found no discernable suppression of capacitation in sperm bound to oviduct glycans. We also detected no effect of oviduct glycans on sperm motility during capacitation. In summary, Le^X and bi-SiaLN glycan motifs found on oviduct oligosaccharides suppress the Ca²⁺ influx that occurs during capacitation and extend sperm lifespan but do not affect sperm capacitation or motility.

Siglec expression on the surface of human, bull and ram sperm

Sialic acid (Sia) is a major constituent of both the sperm glycocalyx and female reproductive mucosal surface and is involved in regulating sperm migration, uterotubal reservoir formation and oocyte binding. Siglecs (sialic acid-binding immunoglobulin - like lectins) commonly found on immune cells, bind to Sia in a linkage- and sugar-specific manner and often mediate cell-to-cell interactions and signalling. Proteomic and transcriptomic analysis of human and bovine sperm have listed Siglecs, but to date, their presence and/or localisation on sperm has not been studied. Therefore, the aim of this study was to characterise the presence of Siglecs on the surface of bovine, human and ovine sperm using both immunostaining and Western blotting. Siglec 1, 2, 5, 6, 10 and 14 were identified and displayed both species- and regional-specific expression on sperm. Almost universal expression across Siglecs and species was evident in the sperm neck and midpiece region while variable expression among Siglecs, similar among species, was detected in the head and tail regions of the sperm. The possible role for these proteins on sperm is discussed.

Review: The epic journey of sperm through the female reproductive tract

Millions or billions of sperm are deposited by artificial insemination or natural mating into the cow reproductive tract but only a few arrive at the site of fertilization and only one fertilizes an oocyte. The remarkable journey that successful sperm take to reach an oocyte is long and tortuous, and includes movement through viscous fluid, avoiding dead ends and hostile immune cells. The privileged collection of sperm that complete this journey must pass selection steps in the vagina, cervix, uterus, utero-tubal junction and oviduct. In many locations in the female reproductive tract, sperm interact with the epithelium and the luminal fluid, which can affect sperm motility and function. Sperm must also be tolerated by the immune system of the female for an adequate time to allow fertilization to occur. This review emphasizes literature about cattle but also includes work in other species that emphasizes critical broad concepts. Although all parts of the female reproductive tract are reviewed, particular attention is given to the sperm destination, the oviduct.

The role of mating in oviduct biology

The oviduct connects the ovary to the uterus, and is subject to changes that influence gamete transport, fertilization, and early embryo development. The ovarian steroids estradiol and progesterone are largely responsible for regulating oviduct function, although mating signals also affect the female reproductive tract, both indirectly, through sensory stimulation, and directly, through contact with seminal plasma or spermatozoa. The resulting alterations in gene and protein expression help establish a microenvironment that is appropriate for sperm storage and selection, embryo development, and gamete transport. Mating may also induce the switch from a non-genomic to a genomic pathway of estradiol-accelerated oviduct egg transport, reflecting a novel example of the functional plasticity in well-differentiated cells. This review highlights the physiological relevance of various aspects of mating to oviduct biology and reproductive success. Expanding our knowledge of the mating-associated molecular and cellular events in oviduct cells would undoubtedly facilitate new therapeutic strategies to treat infertility attributable to oviduct pathologies. Mol. Reprod. Dev. 83: 875-883, 2016 © 2016 Wiley Periodicals, Inc.

Glycan variation and evolution in the eukaryotes

In this review, we document the evolution of common glycan structures in the eukaryotes, and illustrate the considerable variety of oligosaccharides existing in these organisms. We focus on the families of N- and O-glycans, glycosphingolipids, glycosaminoglycans, glycosylphosphatidylinositol (GPI) anchors, sialic acids (Sias), and cytoplasmic and nuclear glycans. We also outline similar and divergent aspects of the glycans during evolution within the groups, which include inter- and intraspecies differences, molecular mimicry, viral glycosylation adaptations, glycosyltransferase specificity relating to function, and the natural dynamism powering these events. Finally, we present an overview of the patterns of glycosylation found within the groups comprising the Eukaryota, namely the Deuterostomia, Fungi, Viridiplantae, Nematoda, and Arthropoda.

LewisX-containing glycans on the porcine oviductal epithelium contribute to formation of the sperm reservoir

In many mammals, after semen deposition, a subpopulation of the sperm is transported to the lower oviduct, or isthmus, to form a functional sperm reservoir that provides sperm to fertilize oocytes. The precise molecular interactions that allow formation of this reservoir are unclear. It is proposed that binding of sperm receptors (lectins) to their oviductal cell ligands is accomplished by glycans. Previous results indicated that Lewis trisaccharides are present in glycosphingolipids and O- and N-linked glycans of the porcine isthmus and that Le(X)-containing molecules bind porcine sperm. Immunohistochemistry indicated that the Lewis structures identified by mass spectrometry were, in fact, Lewis X (Le(X)) trisaccharides. These motifs were localized to the luminal border of the isthmus. Assays using fluoresceinated glycans showed that 3-O-sulfated Le(X) (suLe(X)) bound to receptors localized on the head of nearly 60% of uncapacitated boar sperm but that the positional isomer 3-O-sulfo-Le(A) (suLe(A)) bound to <5% of sperm. Sperm also bound preferentially to suLe(X) made insoluble by coupling to beads. Capacitation reduced the ability of suLe(X) to bind sperm to <10%, perhaps helping to explain why sperm are released at capacitation. Pretreatment of oviduct cell aggregates with the Le(X) antibody blocked 57% of sperm binding to isthmic aggregates. Blocking putative receptors on sperm with soluble Le(X) and suLe(X) glycans specifically reduced sperm binding to oviduct cells up to 61%. These results demonstrate that the oviduct isthmus contains Le(X)-related moieties and that sperm binding to these oviduct glycans is necessary and sufficient for forming the sperm reservoir.

Occurrence of novel Cu(2+)-dependent sialic acid-specific lectin, on the outer surface of mature caprine spermatozoa

Effects of several bivalent metal ions on the autoagglutination event in mature caprine epididymal sperm cells have been investigated using a chemically defined medium. This study demonstrates for the first time that Copper (Cu(2+)) ion (300 μM) has high specificity for autoagglutination of mature cauda-epididymal sperm. Head-to-head interaction of the male gametes is responsible for this event. Studies on the effect of various sugars reveal that the autoagglutinated cells can be dissociated specifically with neutralized sialic acid (50 mM), which also inhibits the sperm cell autoagglutination phenomenon. Blood serum protein fetuin, that contains terminal sialic acid residue, showed high efficacy for inhibiting this autoagglutination event at 4 μM concentration. However, asialofetuin is not capable of inhibiting this Cu(2+)-dependent cellular event. Mature sperm cells bound with caprine erythrocytes at their head region in presence of Cu(2+) ion. The purified sperm membrane fraction isolated by aqueous two phase polymer method showed high efficacy to agglutinate erythrocytes. These sperm-erythrocyte interactions as well as sperm membrane induced haemagglutination were strongly blocked by neutralized sialic acid (50 mM). The results confirm the occurrence of unique Cu(2+) dependent, sialic acid-specific lectin on the outer surface of a mammalian cell using caprine sperm as the model. The observed Cu(2+)-mediated cellular autoagglutination is caused by the interaction of the cell surface lectin with the lectin receptor on the surface of the neighboring homologous cell.

A novel subclass of bovine β-defensins links reproduction and immunology

β-defensins are effector molecules of the innate immune system, found in many diverse species. Their presence in invertebrates as well as vertebrates suggests highly conserved functional roles. Most β-defensins are believed to act as antimicrobial agents at epithelial surfaces, although additional functions have also been described, including immune regulatory activity, wound repair and a role in coat-colour determination. High expression of β-defensins have been found in testis and epididymidal epithelium as well as in the seminal fluid of humans, macaque, rat, mouse and cow. Human and macaque β-defensins have recently been shown to affect sperm motility while a mutation in β-defensin 126 is associated with reduced fertility in men. Genetic variation in bovine defensin genes may explain the increased incidence of low fertility in cattle. Here, we present a summary of the known functions of β-defensins as well as their emerging role in reproduction and their potential to improve fertility in cattle.

Structural and histological characterization of oviductal magnum and lectin-binding patterns in Gallus domesticus

BACKGROUND

Although chicken oviduct is a useful model and target tissue for reproductive biology and transgenesis, little is known because of the highly specific hormonal regulation and the lack of fundamental researches, including lectin-binding activities and glycobiology. Because lectin is attached to secreted glycoproteins, we hypothesized that lectin could be bound to secretory egg-white proteins, and played a crucial role in the generation of egg-white protein in the oviduct. Hence, the purpose of this study was to investigate the structural, histological and lectin-binding characteristics of the chicken oviductal magnum from juvenile and adult hens.

METHODS

The oviductal magnums from juvenile and adult hens were prepared for ultrastructural analysis, qRT-PCR and immunostaining. Immunohistochemistry of anti-ovalbumin, anti-ESR1 and anti-PGR, and mRNA expression of egg-white genes and steroid hormone receptor genes were evaluated. Lectin histochemical staining was also conducted in juvenile and adult oviductal magnum tissues.

RESULTS

The ultrastructural analysis showed that ciliated cells were rarely developed on luminal surface in juvenile magnum, but not tubular gland cells. In adult magnum, two types of epithelium and three types of tubular gland cells were observed. qRT-PCR analysis showed that egg-white genes were highly expressed in adult oviduct compared with the juvenile. However, mRNA expressions of ESR1 and PGR were considerably higher in juvenile oviduct than adult (P < 0.05). The immunohistochemical analysis showed that anti-ovalbumin antibody was detected in adult oviduct not in juvenile, unlikely anti-ESR1 and anti-PGR antibodies that were stained in both oviducts. In histological analysis, Toluidine blue was stained in juvenile and adult oviductal epithelia, and adult tubular glands located in the outer layer of oviductal magnum. In contrast, PAS was positive only in adult oviductal tubular gland. Lectins were selectively bound to oviductal epithelium, stroma, and tubular gland cells. Particularly, lectin-ConA and WGA were bound to electron-dense secretory granules in tubular gland.

CONCLUSIONS

The observation of ultrastructural analysis, mRNA expression, immunohistochemistry and lectin staining showed structural and physiological characterization of juvenile and adult oviductal magnum. Consequently, oviduct study could be helped to in vitro culture of chicken oviductal cells, to develop epithelial or tubular gland cell-specific markers, and to understand female reproductive biology and endocrinology.

Ability of sulfated glycoconjugates and disulfide-reductants to release bovine epididymal sperm bound to the oviductal epithelium in vitro

In Bos taurus, at ejaculation, epididymal sperm acquire a number of proteins secreted in the seminal plasma that increase their ability to interact with the female reproductive tract. Sperm-oviduct interaction comprises a transient sperm adhesion to the isthmus, the lower portion of the oviduct, followed by sperm release around ovulation. Oviductal fluid molecules, such as sulfated glycoconjugates and disulfide-reductants, are able to release bovine ejaculated sperm bound to the oviductal epithelium in vitro through the reduction of sperm surface protein disulfides to sulfhydryls. To understand whether the sperm molecules sensitive to releasing signals are already exposed on the surface of epididymal sperm, we studied the ability of cauda epididymal sperm to adhere to the oviductal epithelium and to be released by sulfated glycoconjugates and the disulfide-reductant penicillamine. Surface protein sulfhydryls in cauda epididymal sperm were analyzed in the initial suspension, in sperm bound to the in vitro-cultured oviductal epithelium, and in released sperm. Results showed that epididymal sperm are able to bind the oviductal epithelium in vitro, although at a lower extent than frozen-thawed ejaculated sperm; the interaction is mediated by oviductal cell microvilli that closely bind to the plasma membrane of the sperm head rostral region, as previously shown for ejaculated sperm. The sulfated glycoconjugates heparin, fucoidan, and dextran sulfate, as well as the disulfide-reductant penicillamine, are all powerful inducers of sperm release. The level of sulfhydryls in sperm surface proteins was (1) high in the initial sperm suspension; (2) low in bound sperm; (3) markedly increased in sperm released by heparin or by penicillamine. In conclusion, epididymal sperm are already able to bind the oviductal epithelium and to respond to the inducers of release through the reduction of sperm surface protein disulfides to sulfhydryls.

Lectin binding patterns and carbohydrate mediation of sperm binding to llama oviductal cells in vitro

Sperm binding to oviductal epithelium would be involved in sperm reservoir formation in the utero tubal junction (UTJ). Although in other mammals sperm-oviduct interaction has been proved to be mediated by carbohydrate-recognition mechanisms, the factors implicated in the sperm adhesion to oviductal epithelium of llama are still unknown. In order to assess the role of carbohydrates present in the mucosa surface, we examined the distribution of glycoconjugates in the llama oviduct by confocal lectin-histochemistry. Mannosyl, glucosyl, N-acetylglucosaminyl, galactosyl, N-acetylgalactosaminyl and sialic acid residues were detected in the oviductal mucose glycocalyx. By incubation of UTJ oviductal explants with LCA, DBA, UEA-1 or PNA lectin previous to co-culture with sperm, we observed a significant decrease in sperm binding only with LCA lectin. In the mucosa surface there were numerous d-glucosyl and D-manosyl residues, which were spotted by this lectin. Probably, this fact promotes the whole covering of the oviduct luminal surface by the sugar-lectin complex, preventing sperm access and adhesion of further residues. However, sperm incubation with mannose or glucose does not significantly prevent binding, which means that glucose and mannose would not be involved in a specific sperm-oviduct interaction. On the other hand, we observed a high reduction in sperm binding to UTJ explants with N-acetylgalactosamine and galactose (p<0.001). Coincidentally, binding sites for N-acetylgalactosamine-PAA-FITC conjugate were observed on the whole surface of the sperm, supporting the concept that llama sperm have lectin-like molecules in their surface, as is the case in other mammals. Probably, these lectin-like molecules, by means of N-acetylgalactosamine and galactose recognition, could link the sperm to the oviductal mucosa with the purpose of forming storing sites in the UTJ. Our results support the idea that more than one carbohydrate could participate in sperm reservoir formation in the llama UTJ oviductal segment.

Redox control of surface protein sulphhydryls in bovine spermatozoa reversibly modulates sperm adhesion to the oviductal epithelium and capacitation

Oviductal fluid molecules, such as sulphated glycosaminoglycans and disulphide-reductants, may represent periovulatory signals for the release of spermatozoa from the oviductal reservoir in the bovine species. Disulphide-reductants release spermatozoa through the reduction of sperm-surface disulphides to sulphhydryls (SH). Herein, we studied sperm-surface protein SH through labelling with maleimidylpropionyl biocytin in the initial sperm suspension, in the subpopulations able and unable to adhere to the in vitro cultured oviductal epithelium, and in spermatozoa released either through the disulphide-reductant penicillamine (PEN) or the sulphated glycosaminoglycan heparin (HEP). Adhesion assays were performed to study the ability of released spermatozoa to readhere to the oviductal epithelium. Results showed that the level of SH in sperm-surface proteins was: 1) low in adhering spermatozoa; 2) high in spermatozoa unable to adhere; and 3) markedly increased in released spermatozoa. Adhesion assays showed that: 1) PEN-released spermatozoa promptly recovered adhesion after removal of the disulphide-reductant and could be released again in response to PEN; 2) conversely, a limited number of HEP-released spermatozoa was able to readhere to the oviductal epithelium and this ability was not affected by HEP removal. Recovery of adhesion was associated to reoxidation of sperm-surface protein SH and to the reversal of capacitation. In conclusion, redox modulation of sperm-surface protein SH is involved in the release of spermatozoa adhering to the oviduct in vitro; the reversible action of disulphide-reductants might be responsible for intermittent phases of adhesions and releases; and the irreversible action of HEP indicates that it may represent a terminal releasing signal.

The sialoglycoconjugates in the oviducts of fertile and postmenopausal women

OBJECTIVES

The aim of the study was to investigate the distribution of the sialoderivatives of the glycoconjugates in the oviduct of normally menstruating and postmenopausal women.

METHODS

Biopsies of ampullary and isthmic portions of the oviduct were obtained from fertile women, in proliferative and secretive phases, and from postmenopausal subjects. The study was carried out using digoxigenin-labelled lectins (MAA, SNA and PNA) in addition to the use of enzymatic and chemical treatments to characterize the different glycosidic linkages of the sialoderivatives and to obtain information on their structure.

RESULTS

No appreciable difference in sialoderivatives distribution was observed among the oviducts, particularly at the epithelium luminal surface, of the fertile women in the two menstrual cycle phases or among those of the fertile and some postmenopausal women, independently from age. Moreover, no appreciable difference of distribution was observed between the ampullary and the isthmic portions in both the study groups.

CONCLUSIONS

In the fertile women sialoderivatives present at the luminal surface of the epithelial cells could play a role in sperm capacitation and mobility, and facilitate the transit of the egg and of the early embryo along the oviducts. The similar distribution of sialoderivatives in the oviduct epithelium of some postmenopausal women of different age, compared to the fertile ones, suggests a maintaining of some functions of the organ, independently from the age of the woman. This could be due, in some cases, to the influence of remaining still sufficient sex hormonal levels.

Antigenic epitope for sperm-immobilizing antibody detected in infertile women

CD52 is a glycosylphosphatidylinositol (GPI) anchor protein occurring in lymphocytes, the epididymis, seminal plasma and on ejaculated sperm surface. The molecular structure of male reproductive tract CD52 (mrtCD52) is quite different from that of lymphocyte CD52 except for a peptide sequence comprising 12 amino acids. The carbohydrate molecule may thus provide antigenic epitopes to females. The repeated N-acetyllactosamine units of the N-linked carbohydrate present in the mrtCD52 were identified as a pathogenic antigen for infertility using a monoclonal antibody (MAb H6-3C4) generated from an infertile patient's peripheral blood lymphocyte. We suggested also the possible presence of O-linked carbohydrate in human mrtCD52, although it is not known whether this carbohydrate is immunogenic or not. This article gives an overview of the structure and function of mrtCD52 as well as the fertilization-blocking mechanism of the antibody against this molecule.

Spermadhesin AQN1 is a candidate receptor molecule involved in the formation of the oviductal sperm reservoir in the pig

Sperm are stored in the isthmic region of the oviduct under conditions that maintain viability and suppress early capacitation steps until ovulation occurs. The initial contact between sperm and oviductal epithelium is mediated by carbohydrate-protein interactions. In the pig, the carbohydrate recognition system has been shown to involve oligomannosyl structures. The spermadhesins AWN and AQN1 are the dominant porcine carbohydrate-binding sperm proteins. The objective of this study was to demonstrate that AQN1 contributes to sperm binding to the oviductal epithelium. AQN1 showed a broad carbohydrate-binding pattern as it recognizes both alpha- and beta-linked galactose as well as Manalpha1-3(Manalpha1-6)Man structures, whereas AWN bound only the galactose species. Binding of ejaculated sperm to oviductal epithelium was inhibited by addition of AQN1 but not by AWN. Mannose-binding sites were localized over the rostral region of the sperm head. Flow cytometry showed that, under capacitating conditions, the population of live sperm was shifted within 30 min toward an increase in the proportion of cells with low mannose- and high galactose-binding. The loss of mannose-binding sites was accompanied by the loss of AQN1 in sperm extracts and the significant reduction in the sperm-oviduct binding. The oviductal epithelium was shown by GNA-lectin histochemistry and by SDS-PAGE and lectin blotting of the apical membrane fraction to express mannose components that could be recognized by AQN1. These results demonstrate that the sperm lectin AQN1 fulfils the criteria for an oviduct receptor in the pig and may play a role in the formation of the oviductal sperm reservoir.