Physiological state of bull sperm affects fucose- and mannose-binding properties

The fate of spermatozoa in the female reproductive tract: A comparative review

The journey that spermatozoa take following deposition in the female tract is a long and perilous one. The barriers they face within the female tract differ depending on whether they are deposited in the vagina or uterus, like spermatozoa of the ram or boar respectively. Comparative studies on the transit of spermatozoa through the ewe and sow tracts serves to highlight similarities, or differences, in the way their sperm-surface properties enable them to overcome these barriers, progress through the tract and fertilise the oocyte. The female environment contributes towards this successful transit by providing a vehicle for sperm transport, aiding the removal of dead spermatozoa and other pathogens and applying strict selection pressures to ensure only those cells with the highest quality reach the site of fertilisation. Understanding the criteria behind these natural barriers helps an understanding of the limitations to fertility associated with preserved spermatozoa, and how in vitro manipulation can alter this complex interaction between spermatozoa and the female environment. Similar mechanisms or surface coat interactions exist in both species, but each has evolved to be used for physiologically disparate functions. Here we briefly describe the sperm surface characteristics of both fresh and frozen-thawed boar and ram spermatozoa and compare how these properties equip them to survive the physical, biochemical and immune interactions within the female reproductive tract.

Cumulus cell gene expression associated with pre-ovulatory acquisition of developmental competence in bovine oocytes

The final days before ovulation impact significantly on follicular function and oocyte quality. This study investigated the cumulus cell (CC) transcriptomic changes during the oocyte developmental competence acquisition period. Six dairy cows were used for 24 oocyte collections and received FSH twice daily over 3 days, followed by FSH withdrawal for 20, 44, 68 and 92 h in four different oestrous cycles for each of the six cows. Half of the cumulus-oocyte complexes were subjected to in vitro maturation, fertilisation and culture to assess blastocyst rate. The other half of the CC underwent microarray analysis (n=3 cows, 12 oocyte collections) and qRT-PCR (n=3 other cows, 12 oocyte collections). According to blastocyst rates, 20 h of FSH withdrawal led to under-differentiated follicles (49%), 44 and 68 h to the most competent follicles (71% and 61%) and 92 h to over-differentiated ones (51%). Ten genes, from the gene lists corresponding to the three different follicular states, were subjected to qRT-PCR. Interestingly, CYP11A1 and NSDHL gene expression profiles reflected the blastocyst rate. However most genes were associated with the over-differentiated status: GATM, MAN1A1, VNN1 and NRP1. The early period of FSH withdrawal has a minimal effect on cumulus gene expression, whereas the longest period has a very significant one and indicates the beginning of the atresia process.

Mammalian sperm interactions with the female reproductive tract

The mammalian female reproductive tract interacts with sperm in various ways in order to facilitate sperm migration to the egg while impeding migrations of pathogens into the tract, to keep sperm alive during the time between mating and ovulation, and to select the fittest sperm for fertilization. The two main types of interactions are physical and molecular. Physical interactions include the swimming responses of sperm to the microarchitecture of walls, to fluid flows, and to fluid viscoelasticity. When sperm encounter walls, they have a strong tendency to remain swimming along them. Sperm will also orient their swimming into gentle fluid flows. The female tract seems to use these tendencies of sperm to guide them to the site of fertilization. When sperm hyperactivate, they are better able to penetrate highly viscoelastic media, such as the cumulus matrix surrounding eggs. Molecular interactions include communications of sperm surface molecules with receptors on the epithelial lining of the tract. There is evidence that specific sperm surface molecules are required to enable sperm to pass through the uterotubal junction into the oviduct. When sperm reach the oviduct, most bind to the oviductal epithelium. This interaction holds sperm in a storage reservoir until ovulation and serves to maintain the fertilization competence of stored sperm. When sperm are released from the reservoir, they detach from and re-attach to the epithelium repeatedly while ascending to the site of fertilization. We are only beginning to understand the communications that may pass between sperm and epithelium during these interactions.

Anandamide induces sperm release from oviductal epithelia through nitric oxide pathway in bovines

Mammalian spermatozoa are not able to fertilize an egg immediately upon ejaculation. They acquire this ability during their transit through the female genital tract in a process known as capacitation. The mammalian oviduct acts as a functional sperm reservoir providing a suitable environment that allows the maintenance of sperm fertilization competence until ovulation occurs. After ovulation, spermatozoa are gradually released from the oviductal reservoir in the caudal isthmus and ascend to the site of fertilization. Capacitating-related changes in sperm plasma membrane seem to be responsible for sperm release from oviductal epithelium. Anandamide is a lipid mediator that participates in the regulation of several female and male reproductive functions. Previously we have demonstrated that anandamide was capable to release spermatozoa from oviductal epithelia by induction of sperm capacitation in bovines. In the present work we studied whether anandamide might exert its effect by activating the nitric oxide (NO) pathway since this molecule has been described as a capacitating agent in spermatozoa from different species. First, we demonstrated that 1 µM NOC-18, a NO donor, and 10 mM L-Arginine, NO synthase substrate, induced the release of spermatozoa from the oviductal epithelia. Then, we observed that the anandamide effect on sperm oviduct interaction was reversed by the addition of 1 µM L-NAME, a NO synthase inhibitor, or 30 µg/ml Hemoglobin, a NO scavenger. We also demonstrated that the induction of bull sperm capacitation by nanomolar concentrations of R(+)-methanandamide or anandamide was inhibited by adding L-NAME or Hemoglobin. To study whether anandamide is able to produce NO, we measured this compound in both sperm and oviductal cells. We observed that anandamide increased the levels of NO in spermatozoa, but not in oviductal cells. These findings suggest that anandamide regulates the sperm release from oviductal epithelia probably by activating the NO pathway during sperm capacitation.

Effect of tubal explants and their secretions on bovine spermatozoa: modulation of ROS production and DNA damage

Although low levels of reactive oxygen species (ROS) play a physiological role in maintaining sperm function, an increase in ROS generation above these levels may result in the induction of sperm membrane and DNA damage. The main objective of this study was to determine whether bovine oviducal explants (TU) and their conditioned media (CM) have a modulatory effect on the production of ROS, and consequently, on sperm DNA integrity. Thawed sperm were exposed to bovine TU and to CM obtained from the ampullar and isthmal regions after 4 and 12 h, and DNA damage and intracellular ROS production was assessed by TUNEL and DHE and SYTOX Green, respectively. Co-incubation of spermatozoa with oviducal explants from the ampullar region (TUa) for 4 h resulted in a statistically significant increase in the percentage of spermatozoa with DNA damage compared with controls (P = 0.0106), and this increase was positively correlated with ROS levels. Conversely, although the incubation of spermatozoa with explants and conditioned media from the isthmal region (TUi and CMi, respectively) for 12 h resulted in an increase of spermatozoa with DNA damage compared with controls (P < 0.0001), this increase was not correlated with ROS levels. In conclusion, significant oxidative stress may take place in the oviduct, particularly during short-term incubation, and this may be related to changes in the antioxidant factors present in the oviducal cells and secretions. A redox imbalance in pro-oxidants and antioxidants in the oviduct may lead to oxidative stress and sperm DNA damage.

Isothermal titration calorimetric studies on the interaction of the major bovine seminal plasma protein, PDC-109 with phospholipid membranes

The interaction of the major bovine seminal plasma protein, PDC-109 with lipid membranes was investigated by isothermal titration calorimetry. Binding of the protein to model membranes made up of diacyl phospholipids was found to be endothermic, with positive values of binding enthalpy and entropy, and could be analyzed in terms of a single type of binding sites on the protein. Enthalpies and entropies for binding to diacylphosphatidylcholine membranes increased with increase in temperature, although a clear-cut linear dependence was not observed. The entropically driven binding process indicates that hydrophobic interactions play a major role in the overall binding process. Binding of PDC-109 with dimyristoylphosphatidylcholine membranes containing 25 mol% cholesterol showed an initial increase in the association constant as well as enthalpy and entropy of binding with increase in temperature, whereas the values decreased with further increase in temperature. The affinity of PDC-109 for phosphatidylcholine increased at higher pH, which is physiologically relevant in view of the basic nature of the seminal plasma. Binding of PDC-109 to Lyso-PC could be best analysed in terms of two types of binding interactions, a high affinity interaction with Lyso-PC micelles and a low-affinity interaction with the monomeric lipid. Enthalpy-entropy compensation was observed for the interaction of PDC-109 with phospholipid membranes, suggesting that water structure plays an important role in the binding process.

Expression and putative function of fibronectin and its receptor (integrin alpha(5)beta(1)) in male and female gametes during bovine fertilization in vitro

Fibronectin (Fn) is a 440 kDa glycoprotein assumed to participate in sperm-egg interaction in human. Recently, it has been demonstrated that Fn--when present during bovine IVF--strongly inhibits sperm penetration. The present study was conducted firstly to evaluate the expression of Fn and its integrin receptor (alpha(5)beta(1)) on male and female bovine gametes using indirect immunofluorescence and secondly, to determine the function of Fn during bovine IVF. Endogenous Fn was detected underneath the zona pellucida (ZP) and integrin alpha(5) on the oolemma of cumulus-denuded oocytes. Bovine spermatozoa displayed integrin alpha(5) at their equatorial segment after acrosome reaction. We established that the main inhibitory effect of exogenously supplemented Fn was located at the sperm-oolemma binding, with a (concurrent) effect on fusion, and this can probably be attributed to the binding of Fn to spermatozoa at the equatorial segment, as shown by means of Alexa Fluor 488-conjugated Fn. Combining these results, the inhibitory effect of exogenously supplemented Fn seemed to be exerted on the male gamete by binding to the exposed integrin alpha(5)beta(1) receptor after acrosome reaction. The presence of endogenous Fn underneath the ZP together with integrin alpha(5) expression on oolemma and acrosome-reacted (AR) sperm cell surface suggests a 'velcro' interaction between the endogenous Fn ligand and corresponding receptors on both (AR) sperm cell and oolemma, initiating sperm-egg binding.

Beta-defensin 126 on the surface of macaque sperm mediates attachment of sperm to oviductal epithelia

Beta-defensin 126 (DEFB126) coats the entire surface of macaque sperm until sperm become capacitated, and the removal of DEFB126 from over the head of sperm is required for sperm-zona recognition. Viable sperm collected from cervix and the uterine lumen of mated female macaques had DEFB126 coating the entire surface, suggesting that DEFB126 is retained on sperm en route to the oviduct. DEFB126 plays a major role in attachment of sperm to oviductal epithelial cells (OECs). Following treatment to either remove or alter DEFB126, sperm were coincubated with explants of OECs, which were assessed for sperm binding following rinsing to remove superficially attached sperm. Sperm treated with either 1 mM caffeine + 1 mM dibutyryl cyclic adenosine monophosphate (dbcAMP) (induces capacitation and complete release of DEFB126 from sperm), 2 mM caffeine (removes DEFB126 from over the head and midpiece but does not induce capacitation), anti-DEFB126 immunoglobulin, or neuraminidase (cleaves sialic acid from terminal positions on glycosylation sites of DEFB126) resulted in similar and significant levels of inhibition of sperm-OEC binding. Preincubation of OECs with soluble DEFB126 also resulted in significantly reduced sperm-OEC binding. Furthermore, reduced OEC binding capability of sperm lacking DEFB126 could be restored by addition of soluble DEFB126 to the sperm surface prior to incubation with OECs. Finally, purified DEFB126, infused into oviducts in situ, associated primarily with the apical membranes of secretory-type epithelial cells. In summary, treatments of macaque sperm that result in either removal, masking, or alteration of DEFB126 result in loss of sperm-OEC binding that is independent of changes in sperm motility. DEFB126 may be directly involved in the formation of a reservoir of sperm in the oviduct of macaques.

Sperm release from oviduct epithelial binding is controlled hormonally by peri-ovulatory graafian follicles

To avoid inappropriate conclusions being drawn from the extensive use of in vitro preparations of sperm-oviduct epithelial binding, it is recalled that events in the genital tract of mammals are regulated by the gonads, primarily by their changing secretion of steroid hormones. Key observations from in vivo models are used to emphasise the dynamic interactions between viable sperm cells and the caudal (distal) portion of the oviduct isthmus, the site of the functional sperm reservoir. These include (1) pre-ovulatory arrest and epithelial binding of intact sperm cells and thereby suppression of completion of capacitation, (2) peri-ovulatory activation and release from binding of discrete sub-populations of competent spermatozoa, and (3) post-ovulatory liberation of large numbers of spermatozoa. These observations underline the influence of endocrine regulation of sperm binding and release by peri-ovulatory Graafian follicles, a point brought out by the enhanced sperm release prompted by diverse treatments with solutions of progesterone. In the light of this evidence, the suitability of in vitro preparations for clarifying physiological events should be questioned, especially if myosalpingeal catecholamines diffusing out of the autonomic nervous system contribute to sperm activation and/or release. None of this is to infer that sperm cells themselves are without influence on their epithelial binding reaction(s). Nor is it to suggest that in vitro models of sperm-oviduct binding are without relevance to the development of sperm evaluation technologies. However, pre-ovulatory sperm-epithelial binding and a regulated peri-ovulatory release should be seen as vital tactics in the overall strategy of achieving successful monospermic fertilisation.

Modifications of surface carbohydrates on bovine spermatozoa mediated by oviductal fluid: a flow cytometric study using lectins

The objective of the present study was to characterize and quantify changes in exposed saccharide residues of bovine sperm during capacitation in oviductal fluid (ODF) using flow cytometry (FC). Bovine sperm were incubated with 0% or 50% non-luteal ODF for 30 min or 3.5 h. After incubation, sperm were labelled with 11 fluorescein isothiocyanate-labelled lectins and evaluated for lectin binding with FC. Furthermore, inhibiting sugars were used to determine specificity of lectin binding to oligosaccharides on the sperm surface. After 30 min incubation, there was a 91% decrease in fluorescence intensity of labelled sperm incubated in WGA, a 76% decline for Con A, 75% decline for BS-I and a 36% decline for DBA. These differences remained approximately the same over the 3.5-h incubation. Interestingly, although there was no reduction in UEA-I binding at 30 min, a significant reduction (23%) was observed at 3.5 h. Con A fluorescence was mostly inhibited with either alpha-d-glucose or alpha-d-mannose (86% and 90% respectively). BS-I fluorescence was reduced after prior incubation of the control samples with N-acetyl-galactosamine and galactose by 74% and 80% respectively. After prior incubation with N-acetyl-galactosamine DBA fluorescence reduced by 18% in the control samples. With UEA-I no fluorescence reduction was observed after prior incubation with l-fucose. We have demonstrated that capacitation of bovine sperm in ODF is accompanied by a quantitative reduction in individual lectin binding sites. These modifications may be crucial to the subsequent signalling events involved with sperm-zona binding, zona penetration or interaction with the oolema.

Role of sialic acid in bovine sperm–zona pellucida binding

Sperm binding activity has been detected in zona pellucida (ZP) glycoproteins and it is generally accepted that this activity resides in the carbohydrate moieties. In the present study we aim to identify some of the specific carbohydrate molecules involved in the bovine sperm-ZP interaction. We performed sperm binding competition assays, in vitro fecundation (IVF) in combination with different lectins, antibodies and neuraminidase digestion, and chemical and cytochemical analysis of the bovine ZP. Both MAA lectin recognising alpha-2,3-linked sialic acid and neuraminidase from Salmonella typhimurium with catalytic activity for alpha-2,3-linked sialic acid, demonstrated a high inhibitory effect on the sperm-ZP binding and oocyte penetration. These results suggest that bovine sperm-ZP binding is mediated by alpha-2,3-linked sialic acid. Experiments with trisaccharides (sialyllactose, 3'-sialyllactosamine and 6'-sialyllactosamine) and glycoproteins (fetuin and asialofetuin) corroborated this and suggest that at least the sequence Neu5Ac(alpha2-3)Gal(beta1-4)GlcNAc is involved in the sperm-ZP interaction. Moreover, these results indicate the presence of a sperm plasma membrane specific protein for the sialic acid. Chemical analysis revealed that bovine ZP glycoproteins contain mainly Neu5Ac (84.5%) and Neu5GC (15.5%). These two types of sialic acid residues are probably linked to Galbeta1,4GlcNAc and GalNAc by alpha-2,3- and alpha-2,6-linkages, respectively, as demonstrated by lectin cytochemical analysis. The use of a neuraminidase inhibitor resulted in an increased number of spermatozoa bound to the ZP and penetrating the oocyte. From this last result we hypothesize that a neuraminidase from cortical granules would probably participate in the block to polyspermy by removing sialic acid from the ZP.

Interactions of spermatozoa with the female reproductive tract: inspiration for assisted reproduction

Artificial insemination with sexed semen, in vitro fertilisation and intracytoplasmic sperm injection have been used to reproduce animals, but often not as successfully as natural mating. Learning more about how spermatozoa normally interact with the female tract can provide inspiration for developing improvements in assisted reproduction. The present review focuses on Bos taurus, because more is known about this species than others. At coitus, bull spermatozoa are deposited into the anterior vagina, where they rapidly enter the cervix. Cervical mucus quickly filters out seminal plasma from spermatozoa, unlike most assisted reproduction protocols. Spermatozoa that reach the uterus may require certain cell surface proteins to swim through the uterotubal junction. Shortly after passing through the junction, most spermatozoa are trapped in a storage reservoir by binding to oviducal epithelium, in the case of cattle via bovine seminal plasma (BSP) proteins coating the sperm head. As ovulation approaches, spermatozoa capacitate and shed BSP proteins. This reduces sperm binding to the epithelium and releases them from storage. Motility hyperactivation assists spermatozoa in leaving the storage reservoir, swimming through oviducal mucus and the cumulus oophorus, and penetrating the oocyte zona pellucida. Chemotactically regulated switching between asymmetrical (i.e. hyperactivated) and symmetrical flagellar beating may also guide spermatozoa to the oocyte.

Separation, characterization and identification of boar seminal plasma proteins

Methods used for the isolation, separation and characterization of boar seminal plasma proteins are discussed, as well as techniques applied to study their binding properties. Attention is paid to interactions of these proteins with different types of saccharides and glycoconjugates, with membrane phospholipids, and to interactions between proteins. Boar seminal plasma contains different types of proteins: spermadhesins of the AQN and AWN families; DQH and PSP proteins belong to the most abundant. Some of these proteins are bound to the sperm surface during ejaculation and thus protein-coating layers of sperm are formed. Sperms coated with proteins participate in different types of interactions occurring in the course of the reproduction process, e.g. formation of the oviductal sperm reservoir, sperm capacitation, oocyte recognition and sperm binding to the oocyte.

Bovine Seminal Plasma Proteins PDC-109, BSP-A3, and BSP-30-kDa Share Functional Roles in Storing Sperm in the Oviduct1

On ejaculation, sperm become coated with proteins secreted by the male accessory sex glands. In the bull, these proteins consist predominantly of the bovine seminal plasma family of proteins (BSPs): PDC-109 (BSP-A1/-A2), BSP-A3, and BSP-30-kDa. PDC-109 plays a role in forming an oviductal sperm reservoir by enabling sperm to bind to oviductal epithelium. Because PDC-109 has high sequence identity with the other BSPs, we tested BSP-A3 and BSP-30-kDa for the capacity to bind sperm to oviductal epithelium. BSP-A3 and BSP-30-kDa each increased binding of epididymal sperm to epithelium and were as effective as PDC-109 in competitively inhibiting binding of ejaculated sperm. Because binding extends the motile life of sperm, BSPs were tested for the ability to maintain sperm motility. BSP-treated epididymal sperm incubated with plasma membrane vesicles from bovine oviductal epithelium maintained progressive motility longer than untreated sperm. To our knowledge, this is the first report of this protective effect of BSPs. Similarities in function among the BSPs were reflected in their three-dimensional structure, whereas surface maps of electrostatic potential indicated differences in binding affinities and kinetics. Such differences may provide sperm with greater adaptability to variations among females. Altogether, these results indicate that BSPs play a crucial role in fertilization by maintaining sperm motility during storage.

Saccharide-mediated interactions of boar sperm surface proteins with components of the porcine oviduct

The role of boar seminal plasma proteins attached to the sperm plasma membrane during ejaculation has been studied in saccharide-mediated events in the female reproductive tract. Heparin-binding (Hep(+)) proteins (DQH sperm surface protein, and AQN and AWN spermadhesins) and their aggregated forms (fractions II and III) interacted more strongly with both oviductal epithelium cells and fluid than non-heparin-binding (Hep(-)) proteins (PSP I and PSP II spermadhesins) and their heterodimer (fraction IV), and interactions correlate with affinity of these proteins to yeast mannan. Indirect immunofluorescence (IMF) showed that the AQN 1 spermadhesin and fraction II bind to the apical glycocalyx of the ampulla, as well as the isthmic and uterine tubal junction regions of the oviductal sections. IMF demonstrated the recognition of AQN 1 and fraction II and mannosyl components of oviductal epithelium. We suggest that Hep(+) proteins (especially AQN 1, fraction II) on sperm could enable sperm binding to oviductal epithelium and thus participate in formation of the sperm oviductal reservoir. Interactions of Hep(+) proteins to oviductal epithelium were inhibited by mannan, hyaluronic acid and sialylated O-glycoproteins. No or slight inhibition was observed with sulphated polysaccharides (heparin, chondroitin sulphate) and simple monosaccharides. Besides that, attachment of boar seminal plasma proteins to oviductal epithelium cells was affected by oviductal fluid, the natural environment in the oviduct. Moreover, the ability of hyaluronic acid to inhibit the interaction of sperm surface proteins to the oviduct might play a role in sperm release from the oviductal reservoir and in the capacitation process.

Sperm transport in the female reproductive tract

At coitus, human sperm are deposited into the anterior vagina, where, to avoid vaginal acid and immune responses, they quickly contact cervical mucus and enter the cervix. Cervical mucus filters out sperm with poor morphology and motility and as such only a minority of ejaculated sperm actually enter the cervix. In the uterus, muscular contractions may enhance passage of sperm through the uterine cavity. A few thousand sperm swim through the uterotubal junctions to reach the Fallopian tubes (uterine tubes, oviducts) where sperm are stored in a reservoir, or at least maintained in a fertile state, by interacting with endosalpingeal (oviductal) epithelium. As the time of ovulation approaches, sperm become capacitated and hyperactivated, which enables them to proceed towards the tubal ampulla. Sperm may be guided to the oocyte by a combination of thermotaxis and chemotaxis. Motility hyperactivation assists sperm in penetrating mucus in the tubes and the cumulus oophorus and zona pellucida of the oocyte, so that they may finally fuse with the oocyte plasma membrane. Knowledge of the biology of sperm transport can inspire improvements in artificial insemination, IVF, the diagnosis of infertility and the development of contraceptives.

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.

Dynamics of Carbohydrate Affinities at the Cell Surface of Capacitating Bovine Sperm Cells

In vivo capacitation of eutherian sperm cells coincides with changes in carbohydrate-dependent interaction with the oviduct epithelia (fucose-dependent for bovine). Heparin-like glycosaminoglycans (GAG) secreted by the oviduct compete for sperm-oviduct binding and are believed to release capacitated sperm cells from oviduct epithelia. A biochemical assay to quantify the specificity and dynamics of carbohydrate-mediated bovine sperm-oviduct binding is developed. Sperm apical plasma membranes (SPM) were purified by a factor eight and biotinylated carbohydrate probes were used for quantitative evaluation of carbohydrate binding. SPM of fresh sperm showed >12 times higher binding capacity for biotinylated fucose than for LewisA. SPM from fresh sperm also efficiently bound biotinylated fucoidan and mannan. Binding of biotinylated fucose could be inhibited by various mono- and oligosaccharides such as fucoidan, mannan, heparin, maltose, and, to a lesser extent, glucose (50% binding at 0.2 mM, 2 mM, 0.3 microg/ml, 15 mM, 50 mM, respectively). SPM from sperm cells that were in vitro capacitated for 4 h in bicarbonate-enriched media (either with or without 10 microg/ml heparin) showed a 70-85% reduction in fucose binding. This was also achieved by follicular fluid or by GAG, both obtained from dominant follicles. Total follicular fluid was much more potent in competing with fucose for sperm binding than the isolated GAG moieties (50% competition at 0.02 microg/ml, 20 microg/ml based on number of GAG moieties, respectively). These results support the hypothesis that in vivo capacitation of sperm cells is regulated by carbohydrate moieties similar to those regulating sperm-oviduct adhesion.

Mannan-binding proteins from boar seminal plasma

The interaction of boar seminal plasma proteins and sperm with yeast mannan was investigated by the enzyme-linked binding assay (ELBA) and specific detection of proteins after SDS electrophoresis and blotting using biotinylated derivative of the polysaccharide. Heparin-binding proteins (especially AQN 1 and DQH proteins) and their aggregated forms showed affinity to yeast mannan. Besides that, these proteins were shown to bind to oviductal epithelium. The mannan-binding activity of boar proteins and sperm was inhibited most efficiently by ovomucoid, ovalbumin and N-glycans released from ovalbumin, but not with d-glucose, d-mannose and their phosphates. On the other hand, yeast mannan inhibited both the interaction of boar seminal plasma and sperm with heparin and the binding of these proteins to porcine oviductal epithelium. Yeast mannan immobilized to divinyl sulfone-activated Sepharose was used for the isolation of mannan-binding proteins. Proteins adsorbed to the immobilized polysaccharide were analyzed by RP-HPLC, SDS electrophoresis and N-terminal amino acid sequencing. AQN and AWN spermadhesins and DQH protein (names are derived from the N-terminal amino acid sequence) were identified as components of the isolated fraction. The results suggest an involvement of mannan-binding proteins in the formation of the sperm oviductal reservoir in pig. The ability of these proteins to interact both the complex d-mannose-containing saccharide structures and the heparin may also play an important role in sperm release from the oviductal reservoir or the capacitation process.

Inhibition of bovine sperm-oocyte fusion by the p-aminophenyl derivative of D-mannose

Several steps in the process of mammalian fertilization are mediated by carbohydrates. This study investigated the role of the p-aminophenyl derivative of d-mannose (APMP) during bovine fertilization. Inseminating cumulus-oocyte complexes (COCs) in the presence of increasing APMP concentrations resulted in a significant dose-dependent decrease of the fertilization rate (P < 0.05). No negative effect of 50 mM APMP on total sperm motility and progressive motility was found. Subsequently, the fertilization steps at which this blocking effect could be exerted were investigated, i.e., sperm penetration of the cumulus oophorus, sperm-zona binding, acrosome reaction, sperm-oolemma binding, and/or sperm-oocyte fusion. Inseminating cumulus-enclosed and cumulus-denuded oocytes in the presence of 50 mM APMP significantly decreased the fertilization rate to a comparable minimum level (P < 0.05). There was no significant relationship between the number of spermatozoa bound to the zona pellucida and the APMP concentration, and APMP nor d-mannosylated bovine serum albumin (BSA) suppressed or stimulated sperm acrosomal status. Inseminating zona-free oocytes in the presence of 50 mM APMP did not influence sperm-oolemma binding, but significantly inhibited sperm-oocyte fusion (P < 0.05). Preincubating zona-free oocytes with 200 microg/ml Con A but not with 50 mM APMP inhibited the sperm-oocyte fusion rate to the same extent as when the gametes were simultaneously exposed to 50 mM APMP. These data indicate that the blocking effect of APMP on bovine fertilization is mainly due to an inhibition of sperm-oocyte fusion, probably by specific obstruction of the sperm receptor sites that are responsible for the fusion process.

Bicarbonate and its role in mammalian sperm function

This paper deals with the effects of bicarbonate induced signaling pathways on plasma membrane lipid organization and downstream protein signaling, and their role in sperm-egg interactions. It also provides an overview of results that indicate that bicarbonate responses are not related to cell death or apoptosis. The information presented shows that only those sperm cells that have functionally completed maturation in the epididymis are sensitive to bicarbonate whereas immature sperm fail to respond to this physiological challenge. Therefore, it is important to selectively analyze the responsive sperm subpopulations when studying sperm capacitation. Moreover, bicarbonate induced signaling responses differ within the diverse sperm structures (e.g. the tail versus the head). Consequently, dissecting sperm structures and signaling areas from each other deserves more attention in sperm capacitation research. The information discussed was obtained from a variety of mammalian species but the basic bicarbonate-mediated sperm responses are similar in most Eutherian species despite some species to species variations (most notably in kinetics rather than the sequence of events). The objective of the paper is to provide a comparative experimental overview of bicarbonate mediated sperm capacitation in the hope that this information will lead to a better understanding of the complex biochemical nature of the involvement of bicarbonate in mammalian sperm capacitation.

Kinetics of protein tyrosine phosphorylation in sperm selected by binding to homologous and heterologous oviductal explants: how specific is the regulation by the oviduct?

Essential steps of the capacitation process take place in the oviductal isthmus. A crucial step in the process of capacitation is the phosphorylation of membrane proteins. The aims of this work were (1) to study the effect of dog sperm binding to oviductal epithelium on tyrosine phosphorylation and (2) to investigate the specificity of regulation of molecular changes by the oviduct of different species by comparing the numbers of canine sperm bound to heterologous (porcine) and homologous epithelium, and the kinetics of tyrosine phosphorylation. Semen was collected from four healthy dogs and washed through a Percoll gradient. Explants, small pieces of epithelium, were cut from porcine and estrous bitch oviducts. During 6 h of coincubation in Tyrode medium, the numbers of bound sperm were counted by microvideographic observation, and the state of tyrosine phosphorylation was determined immunocytochemically after 3, 30, 90, 180 and 360 min. Canine sperm bound in similar numbers to homologous and heterologous explants. Increasing tyrosine phosphorylation of tail proteins and subsequent phosphorylation of sperm head proteins were observed. Binding occurred mainly in sperm with non-phosphorylated heads (approximately 2% phosphorylated), while higher proportions of head-phosphorylated cells were found in unbound populations (approximately 40-60%;P<0.05). The head phosphorylation progressed significantly during incubation in unbound spermatozoa (P<0.05), while it was suppressed in bound suspensions. The rate of tyrosine phosphorylation of sperm tail proteins was higher in cells bound to explants than in unbound cells or in those incubated in control medium. There were no significant differences with respect to the kinetics of tyrosine phosphorylation between the two coincubation systems. These observations support the hypothesis that spermatozoa with non-phosphorylated heads preferentially attach to epithelial cells. Tyrosine phosphorylation of sperm head proteins and capacitation are delayed in spermatozoa in close contact with oviductal epithelium. This mechanism appears to be species-independent, as sperm bound similarly to pig and dog oviduct explants, and similar phosphorylation kinetics were observed in both types of tissue.

Aggregated Forms of Bull Seminal Plasma Proteins and Their Heparin-Binding Activity

Heparin-binding activity of bull seminal plasma proteins was shown to be dependent on their aggregation state. The protein fraction interacting with immobilized heparin was characterized by large polydispersity in the region of molecular weight of 60 000-10 000, while that not retained on the affinity carrier was present as aggregates with molecular weight >100 000. Components of heparin-binding and non-heparin-binding fractions were separated by RP HPLC (reversed-phase HPLC) and analyzed by SDS (sodium dodecyl sulfate) electrophoresis and N-terminal sequencing. Size exclusion chromatography of whole seminal plasma and heparin-binding proteins in the presence of D-fructose (as a component of seminal plasma) showed that the region of molecular weights of protein-associated forms was shifted to lower values. An increase of heparin-binding activity of bull proteins, as determined by ELBA (Enzyme-Linked Binding Assay), correlates with a decrease of their aggregation state. The modulation of the aggregation state of bull proteins by seminal plasma components and, in this way, also of their heparin-binding properties suggests possible mechanisms for capacitation mediated by these proteins.

Carbohydrates and glycoproteins involved in bovine fertilization in vitro

In the present study, efforts were made towards identifying carbohydrates and glycoproteins involved in bovine in vitro fertilization (IVF). In vitro matured cumulus-oocyte complexes (COCs) were inseminated in the presence of a variety of carbohydrates and glycoproteins to determine which glycoconjugates act as competitive inhibitors of oocyte penetration. Among the carbohydrates and glycoproteins tested, D-mannose, fucoidan, dextran sulfate, and fibronectin were the most potent inhibitors of oocyte penetration (90% or more inhibition), while L-fucose and vitronectin inhibited the penetration rate to a lesser extent (around 50% inhibition). Other carbohydrates caused less than 40% inhibition (i.e., D-galactose, N-acetyl-D-galactosamine, D-fucose, and sialic acid) or were not effective as inhibitors of oocyte penetration (i.e., mannan, N-acetyl-D-glucosamine, dextran, and heparan sulfate). Heparin was the only carbohydrate that significantly increased the penetration rate. To exclude a possible toxic effect on spermatozoa, sperm motility was evaluated over time by means of computer-assisted sperm analysis in the presence of carbohydrates and/or glycoproteins that inhibited the penetration rate with 40% or more. L-fucose, dextran sulfate, and vitronectin did not significantly influence total and progressive sperm motility, whereas D-mannose, fucoidan, and fibronectin caused a significant, but slight reduction in both motility parameters. These results are indicative for the involvement of D-mannose, L-fucose, fucoidan, dextran sulfate, fibronectin, and vitronectin in bovine IVF.

Advances in deep uterine insemination: a fruitful way forward to exploit new sperm technologies in cattle

After clarifying regions of the female tract wherein spermatozoa are stored and the egg is fertilised, proposals are made for a modified site of sperm deposition in cattle. A deep pre-ovulatory insemination into the ipsilateral horn of the uterus-the side of the ovulatory follicle-should improve establishment of viable spermatozoa in the caudal region of the oviduct isthmus, the so-called functional sperm reservoir. Suppressed motility within viscous secretions and binding of sperm heads to endosalpingeal microvilli are features of this phase of storage. Activation and release of such spermatozoa would be prompted by imminent ovulation and associated ovarian endocrine programming by both local and systemic routes. Potential advantages of deep insemination include: (1) raising the fertility of genetically valuable bulls whose non-return rates are sub-optimal; (2) reducing the number of spermatozoa in each insemination dose; (3) exploiting the limited numbers of sex-selected sperm cells (X- and Y-chromosome-bearing spermatozoa) available from flow cytometry; (4) breeding from valuable but oligospermic bulls. Putative disadvantages might include: (1) rectal palpation of the ovaries to identify the pre-ovulatory follicle; (2) damage to or even perforation of the uterine wall by the insemination device; (3) the risk of polyspermic fertilisation; (4) specific training in the technique for non-clinically qualified inseminators. Each of these reservations receives comment. In conclusion, a modified technique of insemination should be feasible under commercial conditions, could be coupled with new sperm technologies, and would give a boost to the artificial insemination industry.

PDC-109 (BSP-A1/A2) promotes bull sperm binding to oviductal epithelium in vitro and may be involved in forming the oviductal sperm reservoir

Sperm reservoirs have been found in the oviducts of several species of mammals. In cattle, the reservoir is formed by the binding of sperm to fucose-containing glycoconjugates on the surface of oviductal epithelial cells. A fucose-binding molecule was purified from sperm extracts and identified as PDC-109 (BSP-A1/A2), a protein that is secreted by the seminal vesicles and associates with the plasma membrane of sperm upon ejaculation. The objective of this study was to demonstrate that PDC-109 promotes bull sperm binding to oviductal epithelium. PDC-109 was purified from bovine seminal plasma, and polyclonal antibodies were produced in rabbits. The antibodies detected PDC-109 on ejaculated sperm by indirect immunofluorescence and Western blots of extracts, but PDC-109 was not detected on epididymal sperm. When added to epididymal sperm, purified PDC-109 was absorbed onto the plasma membrane overlying the acrosome, as demonstrated by indirect immunofluorescence and by labeling sperm directly with fluorescein-conjugated PDC-109. When added to explants of oviductal epithelium, significantly fewer epididymal sperm than ejaculated sperm became bound. Addition of PDC-109 to epididymal sperm increased epithelial binding to the level observed for ejaculated sperm. In addition, binding of ejaculated sperm to oviductal epithelium was inhibited by addition of excess soluble PDC-109. Ejaculated sperm lost the ability to bind to oviductal epithelium after heparin-induced capacitation, but treatment with PDC-109 restored binding. These results demonstrate that PDC-109 enables sperm to bind to oviductal epithelium and plays a major role in formation of the bovine oviductal sperm reservoir.

Reflections upon sperm-endosalpingeal and sperm-zona pellucida interactions in vivo and in vitro

In terms of experimental studies of the process of fertilization in mammals, this essay attempts to give a balanced assessment of current interpretations and to raise questions of direct relevance to two fields of research. First, the nature of pre-ovulatory sperm-endosalpingeal binding is set in a physiological perspective, and examination of this dynamic process in vitro is shown to suffer from serious shortcomings. In particular, sperm-epithelial binding reactions demonstrated in cultures of endosalpingeal cells may represent only a portion of the binding reaction in vivo or, as revealed by sperm binding to the tracheal epithelium, could be largely non-specific. Second, concerning the subsequent phase of binding of a fertilizing spermatozoon to the zona pellucida, the nature of the initial contact arrest of the sperm head is evaluated, especially in the light of the highly uneven or 'pitted' surface of this outer coating of the oocyte. Bearing in mind the active phase of oviduct macromolecular secretion that continues after ovulation, the question is posed as to how functional sperm binding sites are preserved on the surface of the zona pellucida rather than masked by epithelial and cumulus cell secretions. Finally, it is recalled that initial sperm : egg ratios at the site of fertilization in the ampullary-isthmic region of the oviduct are close to unity in diverse species of mammal, such fertilizing spermatozoa being released from prominent reserves in the caudal isthmus shortly before the time of ovulation. On strictly quantitative grounds, therefore, the extent to which biochemical or molecular studies portray changes in the vanguard of fertilizing spermatozoa needs to be questioned. Such studies are more likely to be descriptive of overall changes in very large numbers of sperm cells at diverse stages of maturation.

Fertility estimation: a review of past experience and future prospects

Fertility has many components and stages which require that males and females be functionally capable of carrying out all critical stages if each generational reproductive cycle is to be completed. To accomplish this, the male must produce and ejaculate normal fertile sperm. The female must produce, store and ovulate normal fertilizable oocytes. Furthermore, the female must provide a reproductive system compatible with sperm transport, capacitation, and fertilization of the oocytes, embryo and fetal development, and finally birth of healthy young. Reproductive success or failure at several of these points can be estimated quantitatively on a population basis, and in a few situations on an individual basis. It is important that fertility estimates be determined accurately and with precision to be most useful to researchers and managers of animal enterprises. Many studies have underestimated the biological relationship of fertility to other traits because the estimates lacked precision. Many in vitro manipulations of sperm in artificial insemination, of gametes in various assisted reproductive technologies, and of embryos in embryo transfer are utilized in animal breeding programs. Accurate estimation of reproductive efficiency of these in vitro procedures also is important. Conditions surrounding different sets of fertility estimates almost certainly will be different. These conditions should be described as precisely as possible, and appropriate controls included in all experiments. When possible, experiments should be replicated over time and place to determine the repeatability of the various criteria used to estimate fertility and reproductive efficiency. Advances in genomic information and molecular biology should facilitate characterizing more fully inherent potential fertility of animals at birth. In vitro tests will improve, and automated techniques will facilitate making multiple determinations possible on a large scale. Reliability of fertility estimates will increase, with the potential for enhanced animal reproductive performance through more accurate selection, genetic engineering, and enlightened animal care. Simultaneously, it is important to recognize that prediction of future fertility is more hazardous than estimating fertility, as a completely new set of circumstances may occur which are not predictable. Because fertility estimation may be applied under a myriad of conditions, principles and factors affecting fertility will be emphasized in this review as being more useful than a compilation of numerical examples.

Affinity chromatography of bull seminal proteins on mannan-Sepharose

The interaction of bull seminal plasma proteins and sperm with mannan was investigated using an enzyme-linked binding assay (ELBA). A high mannan-binding activity was found in the protein fraction interacting with heparin. Mannan binding to seminal plasma proteins was inhibited by D-mannose and D-fructose, but not by D-mannose-6-phosphate, D-glucose-6-phosphate, ovalbumin and ovomucoid. Mannan inhibited the binding of bovine zona pellucida glycoproteins both to bull sperm and seminal plasma proteins. Yeast mannan immobilized to divinyl sulfone-activated Sepharose was used for the isolation of mannan-binding proteins. The protein components of this fraction were identified on the basis of relative molecular mass determination and N-terminal amino acid sequencing: RNAase dimer, PDC-109 and a protein homologous to BSP-30K (relative molecular mass 14,500). The isolated proteins were characterized by a high zona pellucida binding activity.

Effect of Bovine Oviduct Epithelial Cell Apical Plasma Membranes on Sperm Function Assessed by a Novel Flow Cytometric Approach1

In the bovine, as in many mammalian species, sperm are temporarily stored in the oviduct before fertilization by binding to the oviduct epithelial cell apical plasma membranes. As the oviduct is able to maintain motility and viability of sperm and modulate capacitation, we propose that proteins present on the apical plasma membrane of oviduct epithelial cells contribute to these effects. To verify this hypothesis, the motility of frozen-thawed sperm was determined after incubation for 6 h with purified apical plasma membranes from fresh or cultured oviduct epithelial cells or from bovine mammary gland cells as a control. Analysis of intracellular calcium levels was performed by flow cytometry on sperm incubated with fresh membranes using Indo-1 to assess the membrane effect on intracellular calcium concentration. The coculture of sperm with fresh and cultured apical membranes maintained initial motility for 6 h (65% and 84%, respectively). This effect was significantly different from control sperm incubated without oviduct epithelial cell apical membranes (23%), with mammary gland cell apical membranes (23%), or with boiled epithelial cell apical membranes (21%). Apical membranes from oviduct epithelial cells diminished the percentage of sperm that reached a lethal calcium concentration over a 4-h period (18.7%) compared with the control (53.8%) and maintained lower intracellular calcium levels in viable sperm. These results show that the apical plasma membrane of bovine oviduct epithelial cells contains anchored proteinic factors that contribute to maintaining motility and viability and possibly to modulating capacitation of bovine sperm.

Formation of a reservoir of sperm in the oviduct

A reservoir of sperm in the initial segment of the oviduct has been found in several species of domestic and laboratory mammals. Evidently, the reservoir serves to ensure successful fertilization by providing the appropriate number of sperm in the appropriate physiological state for fertilizing oocytes soon after they enter the oviduct. Recent evidence indicates that sperm are trapped in the reservoir by binding to specific carbohydrate moieties on the surface of the mucosal epithelium of the oviduct. A bovine seminal plasma protein has been identified that associates with sperm and confers on them the capacity to bind to the carbohydrate moiety.

Physiology of gamete and embryo transport through the fallopian tube

A great deal is now known about the migration of spermatozoa within the female reproductive tract, and how they interact with the oocyte and achieve fertilization in a variety of species. The process involves a series of complex features. It is a mixture of active and passive transport and active migration, with drastic jumps in the numbers of spermatozoa that migrate beyond specific physiological checkpoints, and with interactions occurring between spermatozoa, epithelium and luminal fluid. A reservoir of spermatozoa forms, at a discrete location, to hold and liberate spermatozoa in a gradual fashion. After fertilization has occurred, zygotes are passively transported to the uterus by a series of closely coordinated mechanical events where activities of cilia and smooth muscle predominate. Passage of the embryo from oviduct to uterus is regulated and timed by ovarian hormones, signals associated with mating, and zygotic substances. The diverse and exquisite patterns and regulatory signals typical of sperm migration and ovum transport across many species provide fascinating examples of adaptations according with differing reproductive strategies in various mammals.

Carbohydrate-based interactions of oviductal sperm reservoir formation-studies in the pig

Competitive inhibition of sperm to explants of the oviductal epithelium was used to study the complementary receptor system that may be involved in the establishment of the oviductal sperm reservoir in the pig. Sperm binding to the oviductal explants is expressed as Binding Index (BI = sperm cells/0.01 mm(2)). From a set of glycoproteins with known oligosaccharide structures, only asialofetuin and ovalbumin showed inhibitory activity, indicating that ovalbumin may block high affinity binding sites (IC(50) congruent with 1.3 microM) and asialofetuin low affinity sites (IC(50) congruent with 18 microM) of the complementary receptor systems, whereas fetuin carrying terminal sialic acid has no effect. Ovalbumin glycopeptides were isolated by Con A affinity chromatography and reverse-phase HPLC following tryptic digestion. Glycopeptides and enzymatically released glycans were analyzed by MS, and were shown to represent preferentially the two high mannose type glycans (Man)(5)(GlcNAc)(2) and (Man)(6)(GlcNAc)(2), and as a minor component the hybrid type glycan (Hex)(4)(GlcNAc)(5). Glycopeptides (84% inhibition) and glycans (81% inhibition) significantly reduced sperm-oviduct binding at a concentration of 3 microM, whereas the deglycosylated peptides showed no inhibitory activity. Mannopentaose (IC(50) congruent with 0.8 microM) representing the oligomannose residue of the high mannose glycans of ovalbumin was as effective as ovalbumin. These data indicate that the carbohydrate-based mechanisms underlying the formation of the oviductal sperm reservoir in the pig is the result of the concerted action of at least the high-affinity binding sites for oligomannose or nonreducing terminal mannose residues and low-affinity binding of galactose.

Capacitation and the acrosome reaction in equine sperm

During sexual reproduction, the sperm and oocyte must fuse before the production of a diploid zygote can proceed. In mammals such as equids, fusion depends critically on complex changes in the plasma membrane of the sperm and, not surprisingly, this membrane differs markedly from that of somatic cells. After leaving the testes, sperm cease to synthesize plasma membrane lipids or proteins, and vesicle-mediated transport stops. When the sperm reaches the female reproductive tract, it is activated by so-called capacitation factors that initiate a delicate reorientation and modification of molecules within the plasma membrane. These surface changes enable the sperm to bind to the extracellular matrix of the egg (zona pellucida ZP) and the zona then primes the sperm to initiate the acrosome reaction, an exocytotic event required for the sperm to penetrate the zona. This paper will review the processes that occur at the sperm plasma membrane before and during successful penetration of the equine ZP. It is noted that while several methods have been described for detecting changes that occur during capacitation and the acrosome reaction in bovine and porcine sperm, relatively little has been documented for equine sperm. Special attention will therefore be dedicated to recent attempts to develop and implement new assays for the detection of the capacitation status of live, acrosome-intact and motile equine sperm.

Characterization of a fucose-binding protein from bull sperm and seminal plasma that may be responsible for formation of the oviductal sperm reservoir

Oviductal sperm reservoirs have been found in cattle, mice, hamsters, pigs, and horses. In cattle (Bos taurus), the reservoir is evidently formed when sperm bind to fucosylated ligands resembling Le(a) trisaccharide on the surface of oviductal epithelium. The aim of this study was to characterize the fucose-binding protein on bull sperm. Fresh ejaculated sperm were extracted with 0.5 M KCl in Hepes-balanced salts. Extracts were subjected to affinity chromatography using immobilized Le(a) trisaccharide (alpha-L-Fuc[1,4]-beta-D-Gal[1,3]-D-GlcNAc). Two-dimensional PAGE of the affinity chromatography eluates revealed a prominent protein of approximately 16.5 kDa and a pI of 5.8. This protein inhibited binding of sperm to oviductal explants. A similar analysis of proteins extracted from capacitated sperm (which do not bind to oviductal epithelium) showed a reduction in the amount of the 16.5-kDa protein. When examined by epifluorescence microscopy, live uncapacitated sperm labeled over the acrosome with a fucose-BSA-fluorescein isothiocyanate (FITC) conjugate, while capacitated sperm did not. When capacitated sperm were treated with 16.5-kDa protein, labeling with fucose-BSA-FITC was partially restored. The comparative ease with which the protein was removed from sperm and its apparent reassociation with sperm suggested that it could be a peripheral protein derived from epididymal or accessory gland fluids. Blots of SDS-PAGE gels of seminal plasma proteins revealed the presence of a Le(a)-binding protein with an apparent mass of 16.5 kDA: Amino acid sequencing of two tryptic fragments of the protein purified from sperm extracts identified it as PDC-109 (BSP-A1/A2), a product of the seminal vesicles.

Heparin and Ca2+-free medium can enhance release of bull sperm attached to oviductal epithelial cell monolayers

The success of assisted reproductive techniques, such as IVF, could be enhanced by being able to select the most competent spermatozoa in a sample. Attachment and subsequent release of spermatozoa from oviductal epithelial cells (OEC) could provide populations of functionally superior spermatozoa for use in these protocols. The objective of the present study was to investigate the ability of heparin and Ca2+-free medium to induce spermatozoa release from bovine OEC. Epithelial cells were grown to confluence in 24-well plates and pooled frozen bull semen was added to a final concentration of 1 x 10(6) spermatozoa/well. Spermatozoa were allowed to bind to OEC for 2 h. Medium with unbound spermatozoa was removed and replaced by Sperm-TALP, only (control), with heparin (5, 10, or 15 IU/mL), or Ca2+-free with 2 mM EGTA. Treatments were left on sperm-OEC co-cultures for 0.5, 1, 2, 3, or 5 h. At each time, the media were recovered and spermatozoa from each treatment were counted and evaluated for acrosome integrity and motility. The total number of spermatozoa attached to OEC after 2 h of co-culture was considered 100%. Spermatozoa release is expressed as percentage of the total number of sperm cells bound to OEC after 2 h of co-culture. Data were analyzed by ANOVA and results are expressed as mean +/- SEM from three independent replicates. Beginning at 0.5 h, more sperm cells (P < 0.05) were released from OEC in the heparin groups (10 and 15 IU/mL, 77.3 +/- 6.2% and 84.0 +/- 6.2%, respectively) as compared to the control (46.4 +/- 6.2%). The Ca2+-free medium also induced spermatozoa release when compared with the control, but the effect was not significant until 3 h (38.2 +/- 1.9% vs 59.5 +/- 6.9%; P < 0.05). The percentage of acrosome reacted spermatozoa was not affected by heparin treatment. Heparin at 10 IU/mL increased (P < 0.05) the percentage of motile spermatozoa, whereas Ca2+-free medium caused the opposite effect at 0.5 h after addition of treatments. We conclude that both heparin and Ca2+-free medium are able to promote spermatozoa displacement from OEC attachment. Based on motility and acrosome status data, we predict that released sperm cells may be used for IVF and other assisted reproductive techniques.

Essential role of the nonreducing terminal alpha-mannosyl residues of the N-linked carbohydrate chain of bovine zona pellucida glycoproteins in sperm-egg binding

It has been proposed that mammalian sperm bind species-specifically to carbohydrate chains of zona pellucida glycoproteins at fertilization. Although the sperm ligand carbohydrate chains have been characterized in mice and pigs, the existence of the ligands of other mammals remains unclear. In order to explore the bovine sperm ligand, two in vitro competition assay methods were applied. As a result, a high-mannose-type carbohydrate chain, Manalpha1-6(Manalpha1-3)Manalpha1-6(Manalpha1-3)Manbeta1-4GlcNAcbeta1-4GlcNAc, which is the major neutral chain in bovine egg zona glycoproteins, was shown to possess bovine sperm ligand activity. When nonreducing terminal alpha-mannosyl residues were eliminated from the zona glycoproteins by alpha-mannosidase digestion, the ligand activity was reduced, indicating that the alpha-mannosyl residues play an essential role in bovine sperm-egg binding. The number of sperm binding to eggs was reduced to about one-half after fertilization. The ligand-active high-mannose-type chain may be buried after fertilization, since its amount remains unchanged. Pretreatment of bovine sperm with the sperm ligand-carbohydrate chain significantly inhibited penetration of the sperm into oocyte and the male pronucleus formation. Thus, a correlation between the sperm ligand activity and in vitro fertilization rate was observed.

Sperm-Attracting Activity in Follicular Fluid Associated to an 8.6-kDa Protein

Follicular fluid is made of both follicular cell-secreted molecules as well as blood infiltration into the follicle. Sperm-attracting activity has been associated to column-filtered proteins as well as to progesterone. Here we report the initial characterization of a protein with this activity. Follicular fluid was collected from preovulatory follicles in freshly obtained ovaries from a local slaughterhouse. Fluid was cleared from cells and fractionated by size exclusion chromatography and polyacrylamide gel electrophoresis. For gamete interaction, sperm were allowed to swim in an agarose-covered slide designed to separate two wells by a rod in a fixed pattern. At each well, a semisolid agarose solution containing either the attractant with oocytes or control solution in one end, whereas capacitated boar sperm was at the opposite well. Sperm bound to oocytes were evaluated under phase contrast microscopy. Results show that fluid from preovulatory follicles have a sperm attracting activity and that this activity can be associated with an 8600 Dalton protein that at the N-terminal end exhibit close relation to Apoliprotein B2.

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.