Affinity binding of hamster oviductin to spermatozoa and its influence on in vitro fertilization

Proteins from male and female reproductive tracts involved in sperm function regulation

Spermatogenesis is a dynamic process that culminates in the production of mature spermatozoa in the seminiferous tubules of sexually mature animals. Although sperm leaving the testis are fully differentiated, they must further undergo two additional maturation steps before acquiring the capability to fertilize the egg. Such processes take place during the epididymal residency and transport in the seminal fluid during ejaculation and, after delivery into the female reproductive tract, during the journey aiming the encountering the egg in the oviduct. Throughout this trip, spermatozoa are exposed to different reproductive fluids whose molecular compositions regulate the progress towards obtaining a fertilized competent cell. This review summarizes the evidence obtained so far supporting the participation of male and female reproductive tract-derived proteins in the modulation of sperm fertilizing ability and discusses the mechanisms by which such regulation may be accomplished.

Dicalcin, a zona pellucida protein that regulates fertilization competence of the egg coat in Xenopus laevis

Fertilization is a highly coordinated process whereby sperm interact with the egg-coating envelope (called the zona pellucida, ZP) in a taxon-restricted manner, Fertilization triggers the resumption of the cell cycle of the egg, ultimately leading to generation of a new organism that contains hereditary information of the parents. The complete sperm-ZP interaction comprises sperm recognition of the ZP, the acrosome reaction, penetration of the ZP, and fusion with the egg. Recent evidence suggests that these processes involve oligosaccharides associated with a ZP constituent (termed ZP protein), the polypeptide backbone of a ZP protein, and/or the proper three-dimensional filamentous structure of the ZP. However, a detailed description of the molecular mechanisms involved in sperm-ZP interaction remains elusive. Recently, I found that dicalcin, a novel ZP protein-associated protein, suppresses fertilization through its association with gp41, the frog counterpart of the mammalian ZPC protein. This review focuses on molecular aspects of sperm-ZP interaction and describes the fertilization-suppressive function of dicalcin and associated molecular mechanisms. The amount of dicalcin in the ZP significantly correlates with alteration of the lectin-staining pattern within the ZP and the orientation pattern of ZP filaments, which may assist in elucidating the complex molecular mechanisms that underlie sperm-ZP interaction.

Protein-Carbohydrate Interaction between Sperm and the Egg-Coating Envelope and Its Regulation by Dicalcin, a Xenopus laevis Zona Pellucida Protein-Associated Protein

Protein-carbohydrate interaction regulates multiple important processes during fertilization, an essential biological event where individual gametes undergo intercellular recognition to fuse and generate a zygote. In the mammalian female reproductive tract, sperm temporarily adhere to the oviductal epithelium via the complementary interaction between carbohydrate-binding proteins on the sperm membrane and carbohydrates on the oviductal cells. After detachment from the oviductal epithelium at the appropriate time point following ovulation, sperm migrate and occasionally bind to the extracellular matrix, called the zona pellucida (ZP), which surrounds the egg, thereafter undergoing the exocytotic acrosomal reaction to penetrate the envelope and to reach the egg plasma membrane. This sperm-ZP interaction also involves the direct interaction between sperm carbohydrate-binding proteins and carbohydrates within the ZP, most of which have been conserved across divergent species from mammals to amphibians and echinoderms. This review focuses on the carbohydrate-mediated interaction of sperm with the female reproductive tract, mainly the interaction between sperm and the ZP, and introduces the fertilization-suppressive action of dicalcin, a Xenopus laevis ZP protein-associated protein. The action of dicalcin correlates significantly with a dicalcin-dependent change in the lectin-staining pattern within the ZP, suggesting a unique role of dicalcin as an inherent protein that is capable of regulating the affinity between the lectin and oligosaccharides attached on its target glycoprotein.

Modifications of carbohydrate residues in the sheep oviductal ampulla after superovulation

Epithelium of oviductal ampulla was studied in normal and in superovulated sheep using morphologic analysis and lectin glycohistochemistry. The lining epithelium consisted of two types of cells, ciliated and nonciliated cells. Unlike superovulated samples, the nonciliated cells from control ewes showed apical protrusions indicating an apocrine secretory activity. The ciliated cells showed lectin-binding sites mainly at the level of the cilia which bound all the used lectins except Peanut agglutinin, suggesting the lack of glycans terminating with Galβ1,3GalNAc. In superovulated specimens, the ciliated cells with high mannosylated glycans Concanavalin A (Con A) and GlcNAc and GalNac termini Griffonia simplicifolia agglutinin II (GSA II) and Dolicurus biflorus agglutinin (DBA) decreased. The luminal surface of nonciliated cells showed all investigated sugar residues in controls, whereas it was lacking in high mannosylated (Con A) and terminal GalNAcα1,3(LFucα1,2)Galβ1,3/4GlcNAcβ1 sequence (DBA) in superovulated ewes. Apical protrusions from control ampullae nonciliated cells showed glycans containing mannose, GlcNac, GalNAc, galactose, and α2,3-linked sialic acid (Con A, KOH-sialidase- Wheat germ agglutnin [WGA], GSA II, SBA, Griffonia simplicifolia agglutinin-isolectin B4 [GSA I-B4], Maackia amurensis agglutinin II [MAL II]). The supranuclear cytoplasm of nonciliated cells expressed terminal GlcNAc (GSA II) in all specimens, also O-linked glycans (mucin-type glycans) with GalNAc and sialic acid termini (Helix pomatia agglutinin [HPA] and MAL II) in control animals, and also N-linked glycans with fucose, galactose, lactosamine, and α2,3-linked sialic acid termini (Ulex europaeus agglutinin I [UEA I], GSA I-B4, Ricinus communis agglutinin120 [RCA120], and Sambucus nigra agglutinin [SNA] ) in superovulated ewes. These results report for the first time that the superovulation treatment affects the secretory activity and the glycan pattern of the epithelium lining the sheep oviductal ampulla.

Oviductal secretion and gamete interaction

Experimental evidence from the last 30 years supports the fact that the oviduct is involved in the modulation of the reproductive process in eutherian mammals. Oviductal secretion contains molecules that contribute to regulation of gamete function, gamete interaction, and the early stages of embryo development. The oviductal environment would act as a sperm reservoir, maintaining sperm viability, and modulating the subpopulation of spermatozoa that initiates the capacitation process. It could also contribute to prevent the premature acrosome reaction and to reduce polyspermy. Many studies have reported the beneficial effects of the oviductal environment on fertilization and on the first stages of embryo development. Some oviductal factors have been identified in different mammalian species. The effects of oviductal secretion on the reproductive process could be thought to result from the dynamic combined action (inhibitory or stimulatory) of multiple factors present in the oviductal lumen at different stages of the ovulatory cycle and in the presence of gametes or embryos. It could be hypothesized that the absence of a given molecule would not affect fertility as its action could be compensated by another factor with similar functions. However, any alteration in this balance could affect certain events of the reproductive process and could perhaps impair fertility. Thus, the complexity of the reproductive process warrants a continuous research effort to unveil the mechanisms and factors behind its regulation in the oviductal microenvironment.

Localization of immunoreactive gonadotropin-releasing hormone and relative expression of its mRNA in the oviduct during pregnancy in rats

This study was designed to determine the cellular and ultrastructural distribution of the gonadotropin-releasing hormone (GnRH) and the relative expression of its mRNA in the oviduct of rats during different time points (days 7, 9, 16, and 20) of pregnancy. Immunofluorescent localization and confocal microscopic techniques were used to determine the cellular distribution of GnRH in the oviduct. Immunogold electron microscopy indicated its localization at the ultrastructural level, and real-time PCR was used to study the expression pattern of GnRH mRNA in the oviduct during pregnancy. In general, GnRH was localized within the epithelial cells lining the oviductal lumen at each selected time point. A strong correlation between the fluorescence intensity of GnRH-immunoreactive cells and the relative expression of GnRH mRNA was noted on days 7 and 16, followed by a plateau by day 20. At the ultrastructural level, uniform labeling of colloidal gold particles was observed in secretory vesicles and lamella of the luminal epithelium as well as the lumen of the oviduct. Collectively, these results demonstrate for the first time that the oviductal epithelium synthesizes and secretes the decapeptide GnRH during pregnancy in rats, which may have a possible role in postimplantation embryonic development and the maintenance of pregnancy.

Surface mapping of binding of oviductin to the plasma membrane of golden hamster spermatozoa during in vitro capacitation and acrosome reaction

Oviductins are high-molecular-weight glycoproteins synthesized and secreted by nonciliated oviductal epithelial cells and have been shown to play a role in fertilization and early embryo development. The present study was carried out to examine the in vitro binding capacity of hamster oviductin to homologous sperm and to determine the sites of its localization in untreated, capacitated, and acrosome-reacted spermatozoa. Freshly prepared epididymal and capacitated sperm as well as acrosome-reacted sperm were incubated with oviductal fluid prepared from isolated hamster oviducts, fixed and then probed with a monoclonal antibody against hamster oviductin. Results obtained with pre-embedding immunolabeling experiments revealed binding of oviductin to the acrosomal cap and the apical aspect of the postacrosomal region. Immunolabeling of both regions appeared to be more intense in capacitated spermatozoa. Acrosome-reacted sperm showed an immunoreaction of moderate intensity over the postacrosomal region. The plasma membrane overlying the equatorial segment also exhibited a weak labeling. Quantitative analysis obtained with the surface replica technique indicated that oviductin had a higher binding affinity for the acrosomal cap than the postacrosomal region and that the binding of oviductin to the latter plasma membrane domain was enhanced during capacitation. Binding of oviductin to the postacrosomal region, however, was attenuated after acrosome reaction. Immunolabeling for oviductin was found to be the weakest over the equatorial segment regardless of the experimental conditions. The binding of hamster oviductin to specific membrane domains of the homologous sperm and the changes in its distribution during capacitation and acrosome reaction may be important for the function of hamster oviductin preceding and during fertilization.

Effect of a null mutation of the oviduct-specific glycoprotein gene on mouse fertilization

The mammalian fertilization process takes place in a complex microenvironment within the female genital tract. A member of the chitinase protein family, oviduct-specific glycoprotein (OGP), has been identified in oviductal fluid from various mammalian species, including humans. Although OGP is widely believed to be involved in the process of mammalian fertilization, including spermatozoon function and gamete interactions, based on experimental results obtained in vitro, its physiological significance remains controversial. The present study established OGP gene-null ( ogp (-/-)) mice, and primarily characterized their reproductive properties to study the physiological function(s) of OGP. Results obtained from studies using an in vivo or in vitro system showed that the fertility of ogp (-/-) females was within normal limits. These results indicate that OGP is not essential for the process of in vivo fertilization, at least in mice.

Antibodies against the C-terminal peptide of rabbit oviductin inhibit mouse early embryo development to pass 2-cell stage

A full-length rabbit oviductin cDNA(1909bp) was cloned. It consists of a 5'-UTR of 52bp, an open reading frame (ORF) of 1374bp and a 3'-UTR of 483bp and has more than 80% homology with that of other mammal oviductins. N-terminal peptide (NTP) (384 residues) and C-terminal peptide (CTP) (73 residues) of deduced protein precursor has about 80% and 50% identity with that of other mammals respectively. Fusion proteins GST-NTP 368(1R-368N)and GST-CTP73 (369F-441A) were expressed and purified. NH2-terminal of CTP sequencing reveals that the purified protein is consistent with the deduced one. In order to study the function of NTP and CTP the mouse anti-NTP and rabbit anti-CTP antisera were prepared. Tissue-specific (skeleton muscle, oviduct, uterus, ovary, liver, heart and brain) analysis indicated that rabbit oviductin was only found in oviduct. The conditioned medium derived from the rabbit oviduct mucosa epithelial cells has a function of overcoming the early embryonic development block of Kunming mouse cultured in vitro. Anti-CTP antiserum could totally inhibit the early embryo development at 2-cell stage cultured in the conditioned culture medium, but anti-NTP antiserum couldn't. There was a positive relationship between the ratio of early embryos at development block and the dosage of anti-CTP antiserum added in the conditioned culture medium. These results suggest that oviductin has a function not only on fertilization, but also on the release of early embryonic development block, and the later function domain of rabbit oviductin may be situate in its C-terminal.

Contact of dog spermatozoa with homologous uterine tube epithelium prolongs flagellar activity in relation to the stage of the estrous cycle

There is scant information about the storage of spermatozoa within the reproductive tract of the bitch. In several species the uterine tube plays a significant role in sperm storage. The present study was performed to investigate the interaction between spermatozoa and the epithelium of the uterine tube, in particular how this interaction might influence the flagellar activity of spermatozoa in relation to the stage of the estrous cycle. Epithelium was harvested from uterine tubes of 24 bitches at various stages of the estrous cycle (estrus, luteal phase or anestrus), and cultured with pooled spermatozoa collected from 6 dogs. Spermatozoa rapidly bound to the epithelial surface by their heads and the majority of attached spermatozoa were motile. The intimate association between spermatozoa and the uterine tube epithelium maintained motility in a manner that was related to the stage of the estrous cycle. Flagellar activity was significantly greater for spermatozoa bound to estrous epithelium than epithelium from the luteal phase or anestrus. On average, approximately 10% of spermatozoa that were attached to the uterine tube epithelium of estrous bitches retained their flagellar activity for 48 h after innoculation. There was no apparent influence of the region of the uterine tube on this effect. These findings suggest that the uterine tube may form a functional spermatozoal reservoir in the bitch.

Effects of the porcine oviduct-specific glycoprotein on fertilization, polyspermy, and embryonic development in vitro

This study evaluated the effects of porcine oviduct-specific glycoprotein (pOSP) on in vitro fertilization (IVF), polyspermy, and development to blastocyst. Experiment 1 evaluated the effects of various concentrations (0-100 microgram/ml) of purified pOSP on fertilization parameters, including penetration, polyspermy, male pronuclear formation, and mean number of sperm penetrated per oocyte. Experiment 2 examined the ability of an anti-pOSP immunoglobulin G to inhibit the observed effects of pOSP on fertilization parameters. Experiments 3 and 4 examined various concentrations of pOSP (0-100 microgram/ml) on zona pellucida solubility and sperm binding, respectively. Lastly, experiment 5 assessed the effects of various concentrations of pOSP (0-100 microgram/ml) on the in vitro embryo cleavage rate and development to blastocyst. Pig oocytes matured and fertilized in vitro were used for all experiments. An effect of treatment (P < 0.05) was detected for pOSP on penetration, polyspermy, and mean number of sperm per oocyte. Concentrations for pOSP of 0-50 microgram/ml had no effect on sperm penetration rates; however, compared with the control, 100 microgram/ml significantly decreased the penetration rate (74% vs. 41%). Addition of 10-100 microgram/ml significantly reduced the polyspermy rate compared with the control (61% vs. 24-29%). The decrease in polyspermy achieved by addition of pOSP during preincubation and IVF was blocked with a specific antibody to pOSP. No effect of treatment was observed on zona digestion time relative to the control; however, the number of sperm bound to the zona pellucida was significantly decreased by treatment (P < 0.05). Compared with the control, all concentrations of pOSP examined reduced the number of sperm bound per oocyte (45 vs. 19-34). A treatment effect (P < 0.05) was observed for pOSP on embryo development to blastocyst but not on cleavage rates. Addition of pOSP during preincubation and fertilization significantly increased postcleavage development to blastocyst, but a synergistic stimulation on development was not detected when pOSP was included during in vitro culture. These results indicate that exposure to pOSP before and during fertilization reduces the incidence of polyspermy in pig oocytes, reduces the number of bound sperm, and increases postcleavage development to blastocyst.

Effects of human oviductal cell coculture on various functional parameters of human spermatozoa

OBJECTIVE

To investigate the effect of human oviductal cells on various sperm functions in vitro.

DESIGN

Controlled experimental laboratory study.

SETTING

University gynecology unit.

PATIENT(S)

Women undergoing tubal ligation or hysterectomy and men who were visiting our subfertility clinics.

INTERVENTION(S)

Coculture of oviductal cells with human spermatozoa in vitro; sperm functions were determined after coculture.

MAIN OUTCOME MEASURE(S)

Capacitation, acrosome reaction, zona binding, and oocyte fusion.

RESULT(S)

Oviductal cells and conditioned medium induced more spermatozoa to capacitate than did control medium. Although there was no difference in the spontaneous acrosome reaction between any of the groups, the coculture group had a lower percentage of acrosome-reacted spermatozoa after calcium ionophore challenge than did the control and conditioned medium groups. Coculture and conditioned medium treatment reduced the number of spermatozoa bound to the zona pellucida. The penetration rate and penetration index of the control spermatozoa in the zona-free hamster oocyte penetration test were significantly higher than that of the cocultured or conditioned medium-treated spermatozoa.

CONCLUSION(S)

Human oviductal cells promoted capacitation, stabilized the acrosome, and suppressed binding to the zona pellucida and fusion with the oocyte in vitro.

Species-specific effect of oviductal glycoproteins on hamster sperm binding to hamster oocytes

The secretory cells of the oviductal epithelium secrete a high-molecular-weight glycoprotein (OGP). OGPs from different mammalian species show similar immunological characteristics, their cDNAs show high homologies, and they associate with the zona pellucida of oviductal oocytes in vivo. The purpose of this study was to determine the effect of OGP obtained from different species on the binding of hamster sperm to hamster oocytes. Hamster oocytes were inseminated (30 min) in the presence or absence of homologous or heterologous OGPs, and sperm bound/oocyte were counted after removing loosely attached sperm. Ovarian oocytes had an average of 2.9 +/- 0.6 sperm bound/oocyte, whereas oviductal oocytes had 36.3 +/- 2.7. Hamster OGP (0.1 mg/ml) significantly increased sperm binding to ovarian oocytes twofold and had no effect on sperm bound/oviductal oocytes. Human OGP (0.5 mg/ml) significantly decreased sperm binding to ovarian oocytes (0.9 +/- 0.3 sperm bound/oocyte). This effect was dose dependent for oviductal oocytes and could be blocked by preincubating human OGP with a specific antibody to human OGP. The presence of baboon and cow OGP during the insemination of hamster oviductal oocytes also resulted in a significant decrease in sperm bound/oocyte, whereas the addition of hamster OGP to hamster oviductal oocytes had no effect. These results show that homologous OGP enhances sperm binding to the ZP, whereas heterologous OGP inhibits that effect. Thus, our results suggest that OGP plays a role in the species-specific characteristics of sperm/ZP interaction, and that one must use a homologous system (OGP and gametes from the same species) to study the biological effect of OGP.