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

An association weight matrix identified biological pathways associated with bull fertility traits in a multi-breed population

Using seven indicator traits, we investigated the genetic basis of bull fertility and predicted gene interactions from SNP associations. We used percent normal sperm as the key phenotype for the association weight matrix-partial correlation information theory (AWM-PCIT) approach. Beyond a simple list of candidate genes, AWM-PCIT predicts significant gene interactions and associations for the selected traits. These interactions formed a network of 537 genes: 38 genes were transcription cofactors, and 41 genes were transcription factors. The network displayed two distinct clusters, one with 294 genes and another with 243 genes. The network is enriched in fertility-associated pathways: steroid biosynthesis, p53 signalling, and the pentose phosphate pathway. Enrichment analysis also highlighted gene ontology terms associated with 'regulation of neurotransmitter secretion' and 'chromatin formation'. Our network recapitulates some genes previously implicated in another network built with lower-density genotypes. Sequence-level data also highlights additional candidate genes relevant to bull fertility, such as FOXO4, FOXP3, GATA1, CYP27B1, and EBP. A trio of regulatory genes-KDM5C, LRRK2, and PME-was deemed core to the network because of their overarching connections. This trio probably influences bull fertility through their interaction with genes, both known and unknown as to their role in male fertility. Future studies may target the trio and their target genes to enrich our understanding of male fertility further.

Effect of bicarbonate and polyvinyl alcohol on in vitro capacitation and fertilization ability of cryopreserved equine spermatozoa

BACKGROUND

Factors contributing to the limited success of in vitro fertilization in horses remain to be studied. In this work, we elucidated the effect of different essential capacitation media components, bicarbonate, and bovine serum albumin or polyvinyl-alcohol, and the incubation microenvironment on sperm parameters associated with capacitation, acrosome reaction, and their ability to activate oocytes via heterologous intracytoplasmic spermatozoa injection in equine cryopreserved spermatozoa.

METHODS

Frozen-thawed spermatozoa underwent incubation at different time intervals in either Tyrode's albumin lactate pyruvate medium (non-capacitating; NC) or Tyrode's albumin lactate pyruvate supplemented with bicarbonate, bicarbonate and polyvinyl-alcohol, bicarbonate and bovine serum albumin, polyvinyl-alcohol and bovine serum albumin alone. Protein kinase A-phosphorylated substrates and tyrosine phosphorylation levels, sperm motility, and acrosome reaction percentages were evaluated. After determining the best condition media (capacitating; CAP), heterologous intracytoplasmic spermatozoa injection on pig oocytes was performed and the phospholipase C zeta sperm localization pattern was evaluated.

RESULTS

Incubation of frozen-thawed equine spermatozoa with bicarbonate and polyvinyl-alcohol in atmospheric air for 45 min induced an increase in protein kinase A-phosphorylated substrates and tyrosine phosphorylation levels compared to NC condition. Sperm incubation in bicarbonate and polyvinyl-alcohol medium showed an increase in total motility and progressive motility with respect to NC (p ≤ 0.05). Interestingly, three parameters associated with sperm hyperactivation were modulated under bicarbonate and polyvinyl-alcohol conditions. The kinematic parameters curvilinear velocity and amplitude of lateral head displacement significantly increased, while straightness significantly diminished (curvilinear velocity: bicarbonate and polyvinyl-alcohol = 120.9 ± 2.9 vs. NC = 76.91 ± 6.9 µm/s) (amplitude of lateral head displacement: bicarbonate and polyvinyl-alcohol = 1.15 ± 0.02 vs. NC = 0.77 ± 0.03 µm) (straightness: bicarbonate and polyvinyl-alcohol = 0.76 ± 0.01 vs. NC = 0.87 ± 0.02) (p ≤ 0.05). Moreover, the spontaneous acrosome reaction significantly increased in spermatozoa incubated in this condition. Finally, bicarbonate and polyvinyl-alcohol medium was established as CAP medium. Although no differences were found in phospholipase C zeta localization pattern in spermatozoa incubated under CAP, equine spermatozoa pre-incubated in CAP condition for 45 min showed higher fertilization rates when injected into matured pig oocytes (NC: 47.6% vs. CAP 76.5%; p ≤ 0.05).

CONCLUSION

These findings underscore the importance of bicarbonate and polyvinyl-alcohol in supporting critical events associated with in vitro sperm capacitation in the horse, resulting in higher oocyte activation percentages following heterologous intracytoplasmic spermatozoa injection. This protocol could have an impact on reproductive efficiency in the equine breeding industry.

Sperm proteostasis: Can-nabinoids be chaperone's partners?

The male gamete is a highly differentiated cell that aims to fuse with the oocyte in fertilization. Sperm have silenced the transcription and translational processes, maintaining proteostasis to guarantee male reproductive health. Despite the information about the implication of molecular chaperones as orchestrators of protein folding or aggregation, and the handling of body homeostasis by the endocannabinoid system, there is still a lack of basic investigation and random controlled clinical trials that deliver more evidence on the involvement of cannabinoids in reproductive function. Besides, we noticed that the information regarding whether recreational marijuana affects male fertility is controversial and requires further investigation. In other cell models, it has recently been evidenced that chaperones and cannabinoids are intimately intertwined. Through a literature review, we aim to explore the interaction between chaperones and cannabinoid signaling in sperm development and function. To untangle how or whether this dialogue happens within the sperm proteostasis. We discuss the action of chaperones, the endocannabinoid system and phytocannabinoids in sperm proteostasis. Reports of some heat shock and lipid proteins interacting with cannabinoid receptors prove that chaperones and the endocannabinoid system are in an intimate dialogue. Meanwhile, advancing the evidence to decipher these mechanisms for introducing innovative interventions into routine clinical settings becomes crucial. We highlight the potential interaction between chaperones and cannabinoid signaling in regulating proteostasis in male reproductive health.

TRPV1 channel in spermatozoa is a molecular target for ROS-mediated sperm dysfunction and differentially expressed in both natural and ART pregnancy failure

Bi-directional crosstalk between Ca2+ signaling and ROS modulates physiological processes as a part of a regulatory circuit including sperm function. The role of transient receptor potential vanilloid 1 (TRPV1) in this regard cannot be undermined. This is the first report demonstrating the Ca2+-sensitive TRPV1 channel to be under-expressed in spermatozoa of subfertile men, idiopathic infertile men, and normozoospermic infertile males with high ROS (idiopathic infertility and unilateral varicocele). To study the effect of TRPV1 in determining the fertility outcome, we compared the expression profile of TRPV1 in spermatozoa of male partners who achieved pregnancy by natural conception (NC+, n = 10), IVF (IVF+, n = 23), or ICSI (ICSI +, n = 9) and their respective counterparts with failed pregnancy NC (n = 7), IVF (n = 23), or ICSI (n = 10), by both immunocytochemistry and flow-cytometry. Reduced expression of TRPV1 in sperm of IVF ± and ICSI ± men with respect to that NC+ men imply its role in mediating successful fertilization. Unsuccessful pregnancy outcome with an underexpression of TRPV1 in sperm of NC-/IVF-/ICSI-men suggests its role in conception and maintenance of pregnancy. Since ROS is regarded as one of the major contributors to sperm dysfunction, the effect of H2O2 +/- TRPV1 modulators (RTX/iRTX) on acrosomal reaction and calcium influx was evaluated to confirm TRPV1 as a redox sensor in human sperm. A significant increment in the percentage of acrosome reacted spermatozoa along with augmented Ca2+-influx was observed after H2O2 treatment, both in the presence or absence of TRPV1 agonist resiniferatoxin (RTX). The effect was attenuated by the TRPV1 antagonist iodoresiniferatoxin (iRTX), indicating the involvement of TRPV1 in mediating H2O2 response. Enhancement of motility and triggering of acrosomal reaction post TRPV1 activation suggested that disruption of these signaling cascades in vivo, possibly due to down-regulation of TRPV1 in these subfertile males. Bioinformatic analysis of the crosstalk between TRPV1 with fertility candidate proteins (reported to influence IVF outcome) revealed cell death and survival, cellular compromise, and embryonic development to be the primary networks affected by anomalous TRPV1 expression. We therefore postulate that TRPV1 can act as a redox sensor, and its expression in spermatozoa may serve as a fertility marker.

Long-term exposure to environmental relevant triclosan induces reproductive toxicity on adult zebrafish and its potential mechanism

Triclosan (TCS) is widely used in personal care products and has become a contaminant ubiquitously found in the aquatic environment. It is reported exposure to triclosan can cause serious toxic effects on aquatic animals. However, the molecular mechanisms about long-term exposure to TCS-induced reproductive toxicity are not well elucidated. In the present study, adult zebrafish were exposed to TCS (2, 20 and 200 μg/L) for 150 days, and then the reproductive capacity assessment, steroid hormone and VTG quantitative measurement, histopathology observation and RNA sequencing analysis were performed to investigate the effects of TCS on its reproduction. The results indicated that long-term exposure to TCS causes the regulation disorder of the endocrine system, resulting in a reduction of the number of normal germ cells, and ultimately a decrease in the hatching rate and survival rate of offspring. This study revealed the toxic effects and contributed to our deep understanding about the potential disease of TCS exposure in the aquatic environment.

TRPV1 in male reproductive system: focus on sperm function

The transient receptor potential vanilloid 1 (TRPV1) is a receptor used to perceive external noxious stimuli and participates in the regulation of various pathophysiological mechanisms in vivo by integrating multiple signals. The explosive growth in knowledge of TRPV1 stemmed from research on neuronal pain and heat sensation over the last decades and is being expanded tremendously in peripheral tissue research. The discovery that TRPV1 is functionally active in male animal and human reproductive tissues have attracted increasing attention in recent years. Indeed, many studies have indicated that TRPV1 is an endocannabinoid receptor that mediates Anandamide's regulation of sperm function. Other characteristics of the TRPV1 channel itself, such as calcium penetration and temperature sensitivity, have also been investigated, especially the possibility that TRPV1 could act as a mediator for sperm thermotaxis. In addition, some reproductive diseases appear to be related to the protective effects of TRPV1 on oxidative stress and heat stress. A better understanding of TRPV1 in these areas should provide strategies for tackling male infertility. This paper is the first to review the expression and mechanism of TRPV1 in the male reproductive system from molecular and cellular perspectives. A focus is given on sperm function, including calcium homeostasis, crosstalk with endocannabinoid system, participation in cholesterol-related sperm maturation, and thermotaxis, hoping to capture the current situation of this rapidly developing field.

Roles of Nitric Oxide in the Regulation of Reproduction: A Review

Nitric oxide (NO) has attracted significant attention as a stellar molecule. Presently, the study of NO has penetrated every field of life science, and NO is widely distributed in various tissues and organs. This review demonstrates the importance of NO in both male and female reproductive processes in numerous ways, such as in neuromodulation, follicular and oocyte maturation, ovulation, corpus luteum degeneration, fertilization, implantation, pregnancy maintenance, labor and menstrual cycle regulation, spermatogenesis, sperm maturation, and reproduction. However, the mechanism of action of some NO is still unknown, and understanding its mechanism may contribute to the clinical treatment of some reproductive diseases.

Evaluation of α5β1 integrin as a candidate marker for fertility in bull sperm samples

With the progressive increase in the use of reproductive biotechnologies in the cattle industry, like artificial insemination and in vitro embryo production, the accurate determination of fertilizing competence of cryopreserved sperm samples is an essential issue. The routine methodology to assess bull sperm quality relies primarily on count, viability and motility of spermatozoa. However, these parameters do not tightly predict the reproductive success of samples. Therefore, identification of complementary markers of sperm functionality to strengthen the predictability of traditional spermogram is desirable to improve livestock reproduction practices. Previous results from our laboratory indicated that α5β1 integrin plays a key role in bovine sperm function and mediates their interaction with the female reproductive tract. Thus, this study aimed to investigate whether the localization of α5β1 held a correlation with fertilizing ability of bovine cryopreserved semen samples. Firstly, we assessed the quality of samples from six different bulls (A-F). We determined motility and viability of sperm samples after thawing and selection. Additionally, we measured the capacitation state of the samples by chlortetracycline (CTC) assay in the presence or absence of heparin, as an indicator of their responsiveness to a capacitating stimulus. Based on these assays, samples were classified being A the bull with the lowest quality and F the bull with the highest quality. Then, we studied the presence and localization of α5β1 integrin. This protein showed a distribution pattern in the acrosomal (A), post-acrosomal (P) and acrosomal + post-acrosomal (A + P) regions with different localization percentages among the studied samples. Next, we determined the fertilizing ability of the samples in in vitro fertilization (IVF) assays and performed correlation analyses between IVF outcome and the routine spermogram parameters or α5β1 integrin localization patterns. When the percentage of cells showing α5β1 integrin was compared to fertilization rate, no correlation was observed. However, the presence of α5β1 integrin in P and A + P regions (PA pattern), positively correlated with IVF rate (p < 0.05). These results suggest that while routine semen analyses failed to predict sperm reproductive competence, integrin localization in post-acrosomal region (PA pattern) showed a positive correlation with IVF outcome, thus posing an attractive marker to predict more accurately the reproductive performance of an individual.

Effects of In Vitro Interactions of Oviduct Epithelial Cells with Frozen-Thawed Stallion Spermatozoa on Their Motility, Viability and Capacitation Status

Simple Summary

The use of assisted reproductive techniques, which involve the manipulation of sperm and oocytes in the laboratory, support owner production of valuable animals’ offspring. However, several limitations remain underlining the need to further optimize existing protocols as well as to develop new strategies. For example, the required conditions to make equine spermatozoa competent to fertilize an oocyte in vitro (IVF) have not been established. Therefore, our initial goal was to optimize different conditions associated with frozen equine sperm manipulations in order to improve their quality. We observed that simple factors such as sample concentration, incubation period and centrifugation time affect the sperm motility. Since in vivo fertilization involves the interaction between spermatozoa and epithelial cells in the mare’s oviductal tract, our next goal was to mimic this environment by establishing primary cultures of oviductal cells. Using this in vitro system, we were able to select a sperm population capable of fertilization. In short, this study provides a novel protocol that improves the yield of fertilization-capable sperm obtained from equine frozen spermatozoa.

Abstract

Cryopreservation by negatively affecting sperm quality decreases the efficiency of assisted reproduction techniques (ARTs). Thus, we first evaluated sperm motility at different conditions for the manipulation of equine cryopreserved spermatozoa. Higher motility was observed when spermatozoa were incubated for 30 min at 30 × 10⁶/mL compared to lower concentrations (p < 0.05) and when a short centrifugation at 200× g was performed (p < 0.05). Moreover, because sperm suitable for oocyte fertilization is released from oviduct epithelial cells (OECs), in response to the capacitation process, we established an in vitro OEC culture model to select a sperm population with potential fertilizing capacity in this species. We demonstrated E-cadherin and cytokeratin expression in cultures of OECs obtained. When sperm–OEC cocultures were performed, the attached spermatozoa were motile and presented an intact acrosome, suggesting a selection by the oviductal model. When co-cultures were incubated in capacitating conditions a greater number of alive (p < 0.05), capacitated (p < 0.05), with progressive motility (p < 0.05) and with the intact acrosome sperm population was observed (p < 0.05) suggesting that the sperm population released from OECs in vitro presents potential fertilizing capacity. Improvements in handling and selection of cryopreserved sperm would improve efficiencies in ARTs allowing the use of a population of higher-quality 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.

Cyclic AMP efflux through MRP4 regulates actin dynamics signalling pathway and sperm motility in bovines

Previously we demonstrated that multidrug resistance-associated protein 4 transporter (MRP4) mediates cAMP efflux in bovine spermatozoa and that extracellular cAMP (ecAMP) triggers events associated to capacitation. Here, we deepen the study of the role of MRP4 in bovine sperm function by using MK571, an MRP4 inhibitor. The incubation of spermatozoa with MK571 during 45 min inhibited capacitation-associated events. MRP4 was localized in post-acrosomal region and mid-piece at 15 min capacitation, while at 45 min it was mainly located in the acrosome. After 15 min, MK571 decreased total sperm motility (TM), progressive motility (PM) and several kinematic parameters. The addition of ecAMP rescued MK571 effect and ecAMP alone increased the percentage of motile sperm and kinematics parameters. Since actin cytoskeleton plays essential roles in the regulation of sperm motility, we investigated if MRP4 activity might affect actin polymerization. After 15 min capacitation, an increase in F-actin was observed, which was inhibited by MK571. This effect was reverted by the addition of ecAMP. Furthermore, ecAMP alone increased F-actin levels while no F-actin was detected with ecAMP in the presence of PKA inhibitors. Our results support the importance of cAMP efflux through MRP4 in sperm capacitation and suggest its involvement in the regulation of actin polymerization and motility.

Sub-fertility in crossbred bulls: deciphering testicular level transcriptomic alterations between zebu (Bos indicus) and crossbred (Bos taurus x Bos indicus) bulls

BACKGROUND

The incidence of poor semen quality and sub-fertility/infertility is higher in crossbred as compared to Zebu males. Several attempts have been made to understand the possible reasons for higher incidence of fertility problems in crossbred males, at sperm phenotype, proteome and genome level but with variable results. Since the quality of the ejaculated spermatozoa is determined by the testicular environment, assessing the testicular transcriptome between these breeds would help in identifying the possible mechanisms associated with infertility in crossbred bulls. However, such information is not available. We performed global transcriptomic profiling of testicular tissue from crossbred and Zebu bulls using Agilent Bos taurus GXP 8X60k AMADID: 29411 array. To the best of our knowledge, this is the first study comparing the testicular mRNAs between crossbred and Zebu bulls.

RESULTS

Out of the 14,419 transcripts detected in bovine testis, 1466 were differentially expressed between crossbred and Zebu bulls, in which 1038 were upregulated and 428 were downregulated in crossbred bulls. PI4KB and DPY19L2 genes, reported to be involved in sperm capacitation and acrosome formation respectively, were among the top 10 downregulated transcripts in crossbred testis. Genes involved in ubiquitination and proteolysis were upregulated, while genes involved in cell proliferation, stem cell differentiation, stem cell population maintenance, steroidogenesis, WNT signalling, protein localization to plasma membrane, endocannabinoid signalling, heparin binding, cAMP metabolism and GABA receptor activity were downregulated in crossbred testis. Among the 10 genes validated using qPCR, expression of CCNYL, SOX2, MSMB, SPATA7, TNP1, TNP2 and CRISP2 followed the same trend as observed in microarray analysis with SPATA7 being significantly downregulated and transition proteins (TNP1, TNP2) being significantly upregulated in crossbred bulls.

CONCLUSIONS

Abundant proteolysis by ubiquitination and downregulation of WNT signaling, cell proliferation, differentiation and steroidogenesis might be associated with higher incidence of poor semen quality and/or sub-fertility/infertility in crossbred bulls as compared to Zebu bulls. Downregulation of SPATA7 (Spermatogenesis Associated 7) and upregulation of transition proteins (TNP1 and TNP2) in crossbred bull testis might be associated with impaired spermatogenesis processes including improper chromatin compaction in crossbred bulls.

The (endo)cannabinoid signaling in female reproduction: What are the latest advances?

Cannabis extracts like marijuana have the highest consumption rate worldwide. Yet, their societal acceptance as recreational and therapeutic drugs could represent a serious hazard to female human reproduction, because cannabis ingredients [termed (phyto)cannabinoids] can perturb an endogenous system of lipid signals known as endocannabinoids. Accumulated evidence on animal models and humans has demonstrated a crucial role of these endogenous signals on different aspects of female reproduction, where they act through an ensamble of proteins that synthesize, transport, degrade and traffic them. Several reports have recently evidenced the potential role of endocannabinoids as biomarkers of female infertility for disease treatment and prevention, as well as their possible epigenetic effects on pregnancy. The purpose of this review is to provide an update of data collected in the last decade on the effects of cannabinoids and endocannabinoids on female reproductive events, from development and maturation of follicles and oocytes, to fertilization, oviductal transport, implantation and labor. In this context, a particular attention has been devoted to the ovary and the production of fertilizable oocytes, because recent studies have addressed this hot topic with conflicting results among species.

Fibronectin modulates the endocannabinoid system through the cAMP/PKA pathway during human sperm capacitation

Fibronectin (Fn) enhances human sperm capacitation via the cAMP/PKA pathway, and the endocannabinoid system participates in this process. Moreover, Fn has been linked to endocannabinoid system components in different cellular models, even though no evidence of such interactions in human sperm is available. Normal semen samples were evaluated over a 4-year period. Our findings suggest that (a) the capacitating effects of Fn were reversed by preincubating the sperm with a cannabinoid receptor 1 (CB1) or transient receptor potential cation channel subfamily V member 1 (TRPV1) antagonist ( p < 0.001 and p < 0.05, respectively); (b) cooperation between CB1 and TRPV1 may exist ( p < 0.01); (c) the activity of specific fatty acid amide hydroxylase (FAAH) decreased after 1 min ( p < 0.01) and increased after 60 min ( p < 0.01) of capacitation in the presence of Fn; (d) the effects of Fn on FAAH activity were prevented by preincubating spermatozoa with a protein kinase A (PKA) inhibitor ( p < 0.01); (e) Fn modulated both the cyclic adenosine monophosphate concentration and PKA activity ( p < 0.05) during early capacitation; and (f) FAAH was a PKA substrate modulated by phosphorylation. These findings indicate that Fn stimulates human sperm capacitation via the cAMP/PKA pathway through modulation of the endocannabinoid system. Understanding the functional competence of human spermatozoa is essential for facilitating clinical advances in infertility treatment and for developing novel contraceptive strategies.

Crosstalk Between Nitric Oxide and Endocannabinoid Signaling Pathways in Normal and Pathological Placentation

Endocannabinoids are a group of endogenous lipid mediators that act as ligands of cannabinoid and vanilloid receptors, activating multiple signal transduction pathways. Together with enzymes responsible for their synthesis and degradation, these compounds constitute the endocannabinoid system (ECS), which is involved in different physiological processes in reproduction. The placenta, which is essential for the success of gestation and optimal fetal growth, undergoes constant tissue remodeling. ECS members are expressed in trophoblast cells, and current evidence suggests that this system is involved in placental development, apoptosis, and syncytialization. Impairment of endocannabinoid signaling has been associated with several pathological conditions such as intrauterine growth restriction and preeclampsia. Both clinical entities are characterized by dysregulation on vascular perfusion where nitrergic system performs a pivotal role. Nitric oxide (NO) is a potent local vasodepressor that exerts a critical role in the regulation of hemodynamic flow, contributing to the maintenance of low vascular resistance in the feto-placental circulation. NO production could be affected by different factors and growing evidence suggests that the endocannabinoid mediators may regulate nitrergic signaling. Herein, we review emerging knowledge supporting ECS-mediated regulation of NO production in normal placentation. Finally, we discuss how alterations in these systems could affect homoeostasis and contribute to the occurrence of placental-mediated pregnancy complications. Given the impact on women and perinatal heath, we will focus on current knowledge regarding the effects of ECS on nitrergic system in normal and pathological placentation.

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.

Factors and pathways involved in capacitation: how are they regulated?

In mammals, fertilization occurs via a comprehensive progression of events. Freshly ejaculated sperm have yet to acquire progressive motility or fertilization ability. They must first undergo a series of biochemical and physiological changes, collectively known as capacitation. Capacitation is a significant prerequisite to fertilization. During the process of capacitation, changes in membrane properties, intracellular ion concentration and the activities of enzymes, together with other protein modifications, induce multiple signaling events and pathways in defined media in vitro or in the female reproductive tract in vivo. These, in turn, stimulate the acrosome reaction and prepare spermatozoa for penetration of the egg zona pellucida prior to fertilization. In the present review, we conclude all mainstream factors and pathways regulate capacitation and highlight their crosstalk. We also summarize the relationship between capacitation and assisted reproductive technology or human disease. In the end, we sum up the open questions and future avenues in this field.

Chang's meaning of capacitation: A molecular perspective

Dr. Min Chue Chang's contributions to the field of reproductive biology set the stage for the development of the contraceptive pill and in vitro fertilization. Throughout his publications, Dr. Chang was also able to transmit his view of the fertilization process in ways that organized research for newer generations of reproductive biologists. Particularly relevant for the achievement of in vitro fertilization in mammals was the discovery that the sperm required a period of residence in the female tract to become fertilization-competent; Dr. Chang and Dr. Austin, in Australia, independently reported this process, now known as sperm capacitation. This review discusses Dr. Chang's views on capacitation, and puts them in the context of recent advances in the understanding of the molecular basis of this process. Mol. Reprod. Dev. 83: 860-874, 2016 © 2016 Wiley Periodicals, Inc.

Neuronal signaling repertoire in the mammalian sperm functionality

The common embryonic origin has been a recurrent explanation to understand the presence of "neural receptors" in sperm. However, this designation has conditioned a bias marked by the classical neurotransmission model, dismissing the possibility that neurotransmitters can play specific roles in the sperm function by themselves. For instance, the launching of acrosome reaction, a fundamental sperm function, includes several steps that recall the process of presynaptic secretion. Unlike of postsynaptic neuron, whose activation is mediated by molecular interaction between neurotransmitter and postsynaptic receptors, the oocyte activation is not mediated by receptors, but by cytosolic translocation of sperm phospholipase (PLCζ). Thus, the sperm has a cellular design to access and activate the oocyte and restore the ploidy of the species by an "allogenic pronuclear fusion." At subcellular level, the events controlling sperm function, particularly the capacitation process, are activated by chemical signals that trigger ion fluxes, sterol oxidation, synthesis of cyclic adenosine monophosphate, protein kinase A activation, tyrosine phosphorylations and calcium signaling, which correspond to second messengers similar to those associated with exocytosis and growth cone guidance in neurons. Classically, the sperm function associated with neural signals has been analyzed as a unidimensional approach (single ligand-receptor effect). However, the in vivo sperm are exposed to multidimensional signaling context, for example, the GABAergic, monoaminergic, purinergic, cholinergic, and melatoninergic, to name a few. The aim of this review is to present an overview of sperm functionality associated with "neuronal signaling" and possible cellular and molecular mechanisms involved in their regulation.

Enhanced in vitro maturation of canine oocytes by oviduct epithelial cell co-culture

Canine-assisted reproductive techniques have been successful for several years; however, the lack of an oocyte in vitro maturation system has limited their application. The aim of this study was to evaluate the effect of canine oviduct epithelial cells (cOECs) on canine oocyte maturation in vitro. Specifically, the method used for isolation of cOECs did not affect the expression of epithelial markers, E-cadherin and cytokeratin, on fresh, cultured and cryopreserved cells. Moreover, BrdU analysis showed that cOECs cultured in Medium 171 supplemented with mammary epithelial growth supplement were more proliferative than counterparts in advanced Dulbecco's modified Eagle medium or Medium 199. Maturation rate of canine oocytes collected from bitches at diestrus was significantly increased when oocytes were co-cultured with either fresh, cultured or frozen/thawed cOECs (13.23 ± 1.15%, 10.38 ± 4.89%, or 10.54 ± 2.96%, respectively) than that of control oocytes cultured without cOECs (2.48 ± 2.16%, p < 0.05). Additionally, the number of oocytes collected from bitches at estrus the reached metaphase II was increased ∼4 fold in co-culture with fresh, cultured, or frozen/thawed cOECs (47.2 ± 3.82%, 45.4 ± 7.34%, and 46.9 ± 1.51%, respectively) as compared with oocytes cultured without cOECs (11.9 ± 3.18%, p < 0.05). Nuclear maturation was further confirmed by assessing the formation of normal metaphase-II spindles, whereas cytoplasmic maturation was confirmed by inducing parthenogenetic oocyte activation. Embryonic development to the 8-cell stage was similar between in vivo and in vitro matured oocytes. These results suggested that co-culturing immature canine oocytes with cOECs facilitated canine oocyte maturation and early stages of embryonic development.

Expression and distribution of key proteins of the endocannabinoid system in the human seminal vesicles

The endocannabinoid system (ECS), comprising the cannabinoid receptors (CBR), their ligands, and enzymes controlling the turnover of endocannabinoids, has been suggested to be involved in male reproductive function. As information is scarce on the expression of the ECS in human male reproductive tissues, this study aimed to investigate by means of molecular biology (RT-PCR) and immunohistochemistry/immunofluorescence the expression and distribution of CB1 and CB2, GPR55 (an orphan G protein-coupled receptor that recognises cannabinoid ligands) and FAAH (isoforms 1 and 2) in the human seminal vesicles (SV). The specimens expressed PCR products corresponding to CB1 (66 bp), CB2 (141 bp), GPR55 (112 bp), FAAH1 (260 bp) and FAAH2 (387 bp). Immumohistochemistry revealed dense expression of CB1, CB2 and GPR55 located to the pseudo-stratified columnar epithelium and varicose nerves (also characterised by the expression of vasoactive intestinal polypeptide and calcitonin gene-related peptide). Cytosolic staining for FAAH1 and FAAH2 was seen in cuboidal cells of all layers of the epithelium. No immunoreactivity was detected in the smooth musculature or nerve fibres. CB1, CB2, GPR55, FAAH1 and FAAH2 are highly expressed in the human SV. Considering their localisation, the ECS may be involved in epithelial homeostasis, secretory function or autonomic mechano-afferent signalling.

Spatial distribution of cannabinoid receptor 1 and fatty acid amide hydrolase in the cat ovary and oviduct

Involvement of the endocannabinoid system in female reproduction has been extensively described in humans with the cognate receptors and ligands being found in the ovaries and genital tract. In human, an imbalance of the endocannabinoid system is linked with both ectopic pregnancy and infertility. In bovine species anandamide levels regulate aspects of sperm-oviduct interaction. Here we report the immunohistochemical distribution of cannabinoid receptor 1 (CB1R) and fatty acid amide hydrolase (FAAH) in cat ovary and oviduct, using paraffin-embedded tissue samples and commercially available antibodies. We found a differential expression of both CB1R and FAAH during different stages of ovarian function and in the oviduct. CB1R was detected only in tertiary follicle granulosa cells while more immature follicles were negative. FAAH was instead found in ovarian pre-antral follicles, the oocyte cytoplasm, and in granulosa cells of primary, secondary and tertiary follicles. Secondary and tertiary follicles were also FAAH immunoreactive. Luteal cells were immunopositive for both CB1R and FAAH. Because CBR1 in oviduct was found only in ciliated cells, it might represent a specific marker at least in cats. In contrast, FAAH immunoreactivity was observed in both ciliated and non-ciliated cells. The present study may thus serve as the starting point for further investigations on the role of the endocannabinoid system in cat reproduction. Additional work will be needed to assess whether the morphological distribution of CB1R and FAAH changes in different conditions such as pre-pubertal age, follicular phase of the sexual cycle and pregnancy.

Potential use and perspectives of nitric oxide donors in agriculture

Nitric oxide (NO) has emerged in the last 30 years as a key molecule involved in many physiological processes in plants, animals and bacteria. Current research has shown that NO can be delivered via donor molecules. In such cases, the NO release rate is dependent on the chemical structure of the donor itself and on the chemical environment. Despite NO's powerful signaling effect in plants and animals, the application of NO donors in agriculture is currently not implemented and research remains mainly at the experimental level. Technological development in the field of NO donors is rapidly expanding in scope to include controlling seed germination, plant development, ripening and increasing shelf-life of produce. Potential applications in animal production have also been identified. This concise review focuses on the use of donors that have shown potential biotechnological applications in agriculture. Insights are provided into (i) the role of donors in plant production, (ii) the potential use of donors in animal production and (iii) future approaches to explore the use and applications of donors for the benefit of agriculture. © 2016 Society of Chemical Industry.

Oviduct: roles in fertilization and early embryo development

Animal oviducts and human Fallopian tubes are a part of the female reproductive tract that hosts fertilization and pre-implantation development of the embryo. With an increasing understanding of roles of the oviduct at the cellular and molecular levels, current research signifies the importance of the oviduct on naturally conceived fertilization and pre-implantation embryo development. This review highlights the physiological conditions within the oviduct during fertilization, environmental regulation, oviductal fluid composition and its role in protecting embryos and supplying nutrients. Finally, the review compares different aspects of naturally occurring fertilization and assisted reproductive technology (ART)-achieved fertilization and embryo development, giving insight into potential areas for improvement in this technology.

Sperm Release From the Oviductal Epithelium Depends on Ca(2+) Influx Upon Activation of CB1 and TRPV1 by Anandamide

The oviduct acts as a functional sperm reservoir in many mammalian species. Both binding and release of spermatozoa from the oviductal epithelium are mainly modulated by sperm capacitation. Several molecules from oviductal fluid are involved in the regulation of sperm function. Anandamide is a lipid mediator involved in reproductive physiology. Previously, we demonstrated that anandamide, through activation of the cannabinoid receptor type 1 (CB1), promotes sperm release from bovine oviductal epithelial cells, and through CB1 and the transient receptor potential vanilloid 1 (TRPV1), induces sperm capacitation. Herein we investigate co-activation between CB1 and TRPV1, and Ca(2+) influx as part of the mechanism of action of anandamide during sperm release from oviductal cells. Our results indicate that in the absence of Ca(2+) anandamide failed to release spermatozoa from oviductal epithelial cells. Additionally, sperm release promoted by cannabinoid and vanilloid agonists was abolished when the spermatozoa were preloaded with BAPTA-AM, a Ca(2+) chelator. We also determined Ca(2+) levels in spermatozoa preloaded with FURA2-AM co-cultured with oviductal cells and incubated with different cannabinoid and vanilloid agonists. The incubation with different agonists induced Ca(2+) influx, which was abolished by CB1 or TRPV1 antagonists. Our results also suggest that a phospholypase C (PLC) might mediate the activation of CB1 and TRPV1 in sperm release from the bovine oviduct. Therefore, our findings indicate that anandamide, through CB1 and TRPV1 activation, is involved in sperm release from the oviductal reservoir. An increase of sperm Ca(2+) levels and the PLC activation might be involved in anandamide signaling pathway.

Age-dependent changes in inflammation and extracellular matrix in bovine oviduct epithelial cells during the post-ovulatory phase

The mammalian oviduct is an essential site for sperm storage, the transport of gametes, fertilization, and embryo development-functions that are aided by cytokines secreted from oviduct epithelial cells (OECs). Aging leads to cellular and organ dysfunction, with infertility associated with advanced maternal age. Few studies have investigated age-dependent changes in the oviduct as a possible cause of infertility, so we compared OECs from young (30-50 months) versus aged (more than 120 months) cattle. Next-generation sequencing was first used to identify age-related differences in gene expression. Several proinflammatory-related genes (including IL1B, IL1A, IL17C, IL8, S100A8, S100A9, and TNFA) were activated in OECs from aged (more than 120 months) compare to young (30-50 months) individuals, whereas genes associated with extracellular matrix-related factors (COLs, POSTN, BGN, and LUM) were down-regulation in aged OECs. Indeed, IL1 B and IL8 abundance was higher in aged OECs than in young OECs. Young OECs also tended to proliferate faster, and the revolution frequency of young, ciliated OECs was higher than that of their aged counterparts. In contrast, aged OECs possessed more F-actin, an actin cytoskeleton marker associated with reduced elasticity, and contained high levels of reactive oxygen species, which are mediators of inflammation and senescence. These different functional characteristics of bovine OECs during the post-ovulatory phase support the emerging concept of "inflammaging," that is, age-dependent inflammation. Mol. Reprod. Dev. 83: 815-826, 2016 © 2016 Wiley Periodicals, Inc.

Fibronectin stimulates human sperm capacitation through the cyclic AMP/protein kinase A pathway

STUDY QUESTION

Does fibronectin (Fn) stimulate the sperm capacitation process in humans?

SUMMARY ANSWER

Fibronectin stimulates human sperm capacitation.

WHAT IS KNOWN ALREADY

Capacitation is a process that occurs in the oviduct. It has been suggested that some molecules present in the oviductal fluid and cells as well as proteins present in the cumulus oophorus could be involved in the modulation of sperm function and their acquisition of fertilizing capacity. Fibronectin is a glycoprotein that is present in the fluid and the oviduct epithelium, and its receptor (alpha 5 beta 1 integrin) is present in human sperm. When alpha 5 beta 1 (α5β1) integrin binds to fibronectin, intracellular signals similar to the process of sperm capacitation are activated.

STUDY DESIGN, SIZE, DURATION

Human sperm were selected via a percoll gradient and were then incubated in non-capacitated medium (NCM) or reconstituted capacitated medium (RCM), in the presence or absence of fibronectin for different time periods. A total of 39 donors were used during the study, which lasted 3 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Freshly ejaculated sperm from healthy volunteers were obtained by masturbation. All semen samples were normal according to the World Health Organization parameters. Six approaches were used to determine the effects of fibronectin on sperm capacitation: chlortetracycline (CTC) assay, heterologous co-culture of human sperm with bovine oviductal epithelial cells (BOEC), measurement of cyclic (c) AMP levels, activity of protein kinase A (PKA), phosphorylation of proteins in tyrosine (Tyr) residues, and induction of acrosome reaction with progesterone.

MAIN RESULTS AND THE ROLE OF CHANCE

When sperm were incubated in RCM in the presence of Fn, we observed differences with respect to sperm incubated in RCM without Fn (control): (i) a 10% increase in the percentage of sperm with the B pattern (capacitated sperm) of CTC fluorescence from the beginning of capacitation (P < 0.001); (ii) an effect on both the concentration of cAMP (P < 0.05) and PKA activity (P < 0.05) during early capacitation; (iii) an increase in the degree of phosphorylation of proteins on tyrosine residues after 60 min of capacitation (P < 0.01); (iv) an increase in the percentage of acrosome-reacted sperm in response to progesterone (P < 0.05); and (v) a decrease in the percentage of sperm attached to BOEC (P < 0.05). Moreover, we noted that the effect of Fn was specific and mediated by alpha 5 beta 1 integrin (P < 0.001). Fn by itself had no effect on sperm capacitation.

LIMITATIONS, REASONS FOR CAUTION

This study was carried out with sperm from young adult men. Men with abnormal semen samples were excluded. The results cannot be directly extrapolated to other mammalian species.

WIDER IMPLICATIONS OF THE FINDINGS

Currently, male subfertility has become a huge public health problem, which makes it imperative to develop new treatments. This is a novel discovery that extends our current knowledge concerning normal and pathological sperm physiology as well as events that regulate the process of fertilization.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by grants from FONDECYT (1130341, E.S.D. and 1120056, P.M.) and FONCYT (PIP 2011-0496, S.P.-M). The authors have no conflicts of interest.

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.

Relationship between seminal plasma levels of anandamide congeners palmitoylethanolamide and oleoylethanolamide and semen quality

OBJECTIVE

To determine whether changes in seminal plasma concentrations of the endogenous lipid signaling molecules palmitoylethanolamide (PEA) and oleoylethanolamide (OEA) have significant effects on sperm quality.

DESIGN

Biochemical and physiological studies of human seminal plasma and spermatozoa.

SETTING

Academic tertiary care medical center.

PATIENT(S)

Ninety men attending an infertility clinic for semen analysis.

INTERVENTION(S)

Palmitoylethanolamide and OEA extracted from seminal plasma were quantified by ultra high-performance liquid chromatography (HPLC)-tandem mass spectrometry. Patient sperm from semen with normal parameters were exposed in vitro to PEA or OEA to determine effects on sperm motility, viability, and mitochondrial activity.

MAIN OUTCOME MEASURE(S)

The relationship between seminal plasma concentrations of PEA and OEA and sperm quality and the effect of these compounds on sperm motility, viability, and mitochondria activity in vitro.

RESULT(S)

Palmitoylethanolamide and OEA concentrations in seminal plasma were lower in men with asthenozoospermia and oligoasthenoteratozospermia compared with men with normal semen parameters. Palmitoylethanolamide and OEA rapidly and significantly improved sperm motility and maintained viability without affecting mitochondria activity in vitro.

CONCLUSION(S)

Maintenance of normal PEA and OEA tone in human seminal plasma may be necessary for the preservation of normal sperm function and male fertility. Exocannabinoids found in Cannabis, such as delta-9-tetrahydrocannabinol and cannabidiol, could compete with these endocannabinoids upsetting their finely balanced, normal functioning and resulting in male reproductive failure.

Anandamide levels fluctuate in the bovine oviduct during the oestrous cycle

Mammalian oviduct acts as a reservoir for spermatozoa and provides an environment in which they may compete for the opportunity to fertilize the oocyte. Whilst in the oviduct spermatozoa undergo capacitation essential for fertilization. Sperm-oviduct interaction is essential for sperm capacitation and is a tightly regulated process influenced by the local microenvironment. Previously we reported that the endocannabinoid anandamide (AEA) regulates sperm release from epithelial oviductal cells by promoting sperm capacitation. The aims of this work were to measure the AEA content and to characterize the main AEA metabolic pathway in the bovine oviduct and determine how these change through the oestrous cycle. In this study, the levels of AEA and two other N-acylethanolamines, N-oleoylethanolamine and N-palmitoylethanolamine, were measured in bovine oviduct collected during different stages of oestrous cycle by ultra high performance liquid chromatography tandem mass spectrometry. Results indicated that intracellular oviductal epithelial levels of all three N-acylethanolamines fluctuate during oestrous cycle. Anandamide from oviductal fluid also varied during oestrous cycle, with the highest values detected during the periovulatory period. Endocannabinoid levels from ipsilateral oviduct to ovulation were higher than those detected in the contralateral one, suggesting that levels of oviductal AEA may be regulated by ovarian hormones. The expression and localization of N-acylethanolamines metabolizing enzymes in bovine oviduct were also determined by RT-PCR, Western blot, and immunohistochemistry but no change was found during the oestrous cycle. Furthermore, nanomolar levels of AEA were detected in follicular fluids, suggesting that during ovulation the mature follicle may contribute to oviductal AEA levels to create an endocannabinoid gradient conducive to the regulation of sperm function for successful fertilization.

Cyclic AMP efflux, via MRPs and A1 adenosine receptors, is critical for bovine sperm capacitation

Sperm capacitation has been largely associated with an increase in cAMP, although its relevance in the underlying mechanisms of this maturation process remains elusive. Increasing evidence shows that the extrusion of cAMP through multidrug resistance associated protein 4 (MRP4) regulates cell homeostasis not only in physiological but also in pathophysiological situations and studies from our laboratory strongly support this assumption. In the present work we sought to establish the role of cAMP efflux in the regulation of sperm capacitation. Sperm capacitation was performed in vitro by exposing bovine spermatozoa to bicarbonate 40 and 70 mM; cAMP; probenecid (a MRPs general inhibitor) and an adenosine type 1 receptor (A1 adenosine receptor) selective antagonist (DPCPX). Capacitation was assessed by chlortetracycline assay and lysophosphatidylcholine-induced acrosome reaction assessed by PSA-FITC staining. Intracellular and extracellular cAMP was measured by radiobinding the regulatory subunit of PKA under the same experimental conditions. MRP4 was detected by western blot and immunohistochemistry assays. Results showed that the inhibition of soluble adenylyl cyclase significantly inhibited bicarbonate-induced sperm capacitation. Furthermore, in the presence of 40 and 70 mM bicarbonate bovine spermatozoa synthesized and extruded cAMP. Interestingly, in the absence of IBMX (a PDEs inhibitor) cAMP efflux still operated in sperm cells, suggesting that cAMP extrusion would be a physiological process in the spermatozoa complementary to the action of PDE. Blockade of MRPs by probenecid abolished the efflux of the cyclic nucleotide resulting not only in the accumulation of intracellular cAMP but also in the inhibition of bicarbonate-induced sperm capacitation. The effect of probenecid was abolished by exposing sperm cells to cAMP. The high-affinity efflux pump for cAMP, MRP4 was expressed in bovine spermatozoa and localized to the midpiece of the tail as previously reported for soluble adenylyl cyclase and A1 adenosine receptor. Additionally, blockade of A1 adenosine receptor abolished not only bicarbonate-induced sperm capacitation but also that stimulated by cAMP. Present findings strongly support that cAMP efflux, presumably through MRP4, and the activation of A1 adenosine receptor regulate some events associated with bicarbonate-induced sperm capacitation, and further suggest a paracrine and/or autocrine role for cAMP.

Storage and release of spermatozoa from the pre-uterine tube reservoir

In mammals, after coitus a small number of spermatozoa enter the uterine tube and following attachment to uterine tube epithelium are arrested in a non-capacitated state until peri-ovulatory signalling induces their detachment. Whilst awaiting release low numbers of spermatozoa continually detach from the epithelium and the uterine tube reservoir risks depletion. There is evidence of attachment of spermatozoa to uterine epithelium in several species which might form a potential pre-uterine tube reservoir. In this study we demonstrate that: (1) dog spermatozoa attach to uterine epithelium and maintain flagellar activity, (2) in non-capacitating conditions spermatozoa progressively detach with a variety of motility characteristics, (3) attachment is not influenced by epithelial changes occurring around ovulation, (4) attachment to uterine epithelium slows capacitation, (5) capacitated spermatozoa have reduced ability to attach to uterine epithelium, (6) under capacitating conditions increased numbers of spermatozoa detach and exhibit transitional and hyperactive motility which differ to those seen in non-capacitating conditions, (7) detachment of spermatozoa and motility changes can be induced by post-ovulation but not pre-ovulation uterine tube flush fluid and by components of follicular fluid and solubilised zona pellucida, (8) prolonged culture does not change the nature of the progressive detachment seen in non-capacitating conditions nor the potential for increased detachment in capacitating conditions. We postulate that in some species binding of spermatozoa to uterine epithelium is an important component of the transport of spermatozoa. Before ovulation low numbers of spermatozoa continually detach, including those which are non-capacitated with fast forward progressive motility allowing the re-population of the uterine tube, whilst around the time of ovulation, signalling from as-yet unknown factors associated with follicular fluid, oocytes and uterine tube secretion promotes the detachment of large numbers of capacitated spermatozoa with hyperactive motility that may contribute to the fertilising pool.

Porcine sperm bind to specific 6-sialylated biantennary glycans to form the oviduct reservoir

After mating, many female mammals store a subpopulation of sperm in the lower portion of the oviduct, forming a reservoir. The reservoir lengthens sperm lifespan, regulates sperm capacitation, controls polyspermy, and selects normal sperm. It is believed that sperm bind to glycans on the oviduct epithelium to form the reservoir, but the specific adhesion molecules that retain sperm are unclear. Herein, using a glycan array to test 377 glycans for their ability to bind porcine sperm, we found two glycan motifs in common among all glycans with sperm-binding ability: the Lewis X trisaccharide and biantennary structures containing a mannose core with 6-sialylated lactosamine at one or more termini. Binding to both motifs was specific; isomers of each motif did not bind sperm. Further work focused on sialylated lactosamine. Sialylated lactosamine was found abundantly on the apical side of epithelial cells collected from the oviduct isthmus, among N-linked and O-linked glycans. Sialylated lactosamine bound to the head of sperm, the region that interacts with the oviduct epithelium. After capacitation, sperm lost affinity for sialylated lactosamine. Receptor modification may contribute to release from the reservoir so that sperm can move to the site of fertilization. Sialylated lactosamine was required for sperm to bind oviduct cells. Simbucus nigra agglutinin or an antibody specific to sialylated lactosamine with a preference for Neu5Acalpha2-6Gal rather than Neu5Acalpha2-3Gal reduced sperm binding to oviduct isthmic cells, as did occupying putative receptors on sperm with sialylated biantennary glycans. These results demonstrate that sperm binding to oviduct 6-sialylated biantennary glycans is necessary for normal adhesion to the oviduct.