Cytofluorescent assay to quantify adhesion of equine spermatozoa to oviduct epithelial cells in vitro

Fluorescent labelling of boar spermatozoa for quantitative studies on competitive sperm-oviduct binding

Invitro sperm-oviduct binding assays enable assessment of the capacity of spermatozoa to form a 'reservoir' in the oviduct. Competitive approaches, such as experimental set-ups that test multiple males or semen samples simultaneously on the same tissue explants, are desirable because they reduce the likelihood of bias when using material from different females. Therefore, we established a fluorescent labelling technique that allows tagging and storage of spermatozoa before competitive studies of sperm-oviduct binding invitro. Fluorescent markers were tested for reliability and compatibility with parameters of boar spermatozoa viability. The addition of seminal plasma after density gradient centrifugation was essential to counteract centrifugation stress during the labelling procedure. It was demonstrated that sperm tagged with MitoTracker Green FM or MitoTracker Red FM can be successfully used in competitive sperm-oviduct binding studies. The assay was sensitive enough to indicate subtle effects of semen storage temperature on the ability of the spermatozoa to contribute to the female sperm reservoir.

Fertilisation in the horse and paracrine signalling in the oviduct

The mammalian oviduct plays a crucial role in the preparation of gametes for fertilisation (transport and final maturation) and fertilisation itself. An increasing number of studies offers a comprehensive overview of the functions of the oviduct and its secretions, but this topic has had limited investigation in the horse. Limited data are available on the final oocyte maturation in the equine oviduct. However, in vitro and in vivo systems have been established to analyse the influence of equine oviduct epithelial cells (OEC) during maturation on the potential of oocytes for fertilisation and development. Most studies focus on the role of the oviduct in equine sperm function, such as spermatozoa transport, attachment to oviduct epithelium, viability, motility and capacitation. Moreover, some possible candidate molecules for sperm-oviducal interactions have been identified in the horse. Finally, the low efficiency of conventional in vitro fertilisation and the in vivo fertilisation of equine oocytes transferred into the oviduct of an inseminated mare predicted an influence of oviduct in equine fertilisation. Actually, in vivo and in vitro experiments demonstrated a role of the oviduct in equine fertilisation. Moreover, recent studies showed a beneficial effect of homologous and heterologous OEC on equine in vitro fertilisation, and some candidate molecules have been studied.

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.

Sperm binding to epithelial oviduct explants in bulls with different nonreturn rates investigated with a new in vitro model

A new in vitro method was developed for analyzing the capacity of sperm to bind to oviductal epithelium to determine whether this binding capacity could be used to predict nonreturn rates (NRR). Sperm binding was evaluated by counting 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1)-labeled spermatozoa attached to oviductal epithelium and by measuring the surface area of the oviduct explants by means of an image analysis program. Hepes + Tyrode albumin lactate pyruvate (TALP) was a more useful medium than in vitro fertilization (IVF)-TALP, TCM-199 medium + 10% fetal calf serum, and TCM-199 medium alone for the investigation of sperm binding to oviductal explants. Oviduct explants with a surface area of < 20 000 micro m(2) provided more consistent results than did explants with a surface area of >100 000 micro m(2). A positive association was found between the log(e) transformed number of spermatozoa bound to 0.1 mm(2) oviductal epithelium and the NRR of the respective sires after 24 h of coincubation, provided that the membrane integrity of the sperm sample was >60%. Determination of the capacity of sperm to bind to oviductal explants could become a reliable in vitro method for predicting the NRR of a given sire.

In vitro-cultured bovine oviductal cells bind acrosome-intact sperm and retain this ability upon sperm release

The mammalian oviduct plays a key role in sperm storage, capacitation, and selection. Specific oviduct secretions and/or binding to oviductal cells are thought to be responsible for the extension of the fertile life span of sperm. In this in vitro study, a quantitative assay for sperm binding was developed to analyze the mechanisms of sperm-oviductal cell adhesion and release in the bovine species. Distribution and acrosomal status of sperm bound to in vitro-cultured ampullary and isthmic cell monolayers were followed until the time of sperm release by means of fluorescence labeling techniques. In order to understand whether release is due to surface changes of sperm or oviductal cells, double incubation experiments with unlabeled and Hoechst-labeled sperm have been performed. Main findings demonstrate that (1) only acrosome-intact sperm bind specific bovine oviductal epithelial cells; (2) acrosomes of bound sperm are preserved intact over time; and (3) release of unreacted sperm is likely to be due to changes of the sperm surface, probably triggered by capacitation. These findings support the hypothesis that binding to oviductal cells is essential for preserving the sperm fertilization competence during the interval from the onset of estrus to ovulation.

Generation of an equine oviductal epithelial cell line for the study of sperm-oviduct interactions

Equine oviductal epithelial cells (OEC) were transformed with simian virus 40 large T antigen (SV 40 T-ag) to create a cell line for the study of the interaction of equine spermatozoa with oviductal epithelium. One cell line was established based on the expression of the SV 40 T-ag and extended lifespan in culture. Immortalized equine OEC retained the characteristics of differentiated OEC such as the formation of monolayers with characteristic epithelial morphology and cell polarization as well as expression of cytokeratin and equine major histocompatibility complex I. Monolayers of immortalized equine OEC retained their functional competence to bind equine spermatozoa in a dose-dependent manner comparable to that of primary equine OEC cultures. This immortalized cell line of equine OEC provides a uniform, readily available system for sperm-OEC co-cultures, and may be a useful model for the study of sperm-oviduct interactions in the horse.

Isolation and characterization of a protein with homology to angiotensin converting enzyme from the periacrosomal plasma membrane of equine spermatozoa

The periacrosomal plasma membrane of spermatozoa is involved in sperm binding to oviductal epithelial cells and to the zona pellucida. A protein of 68-70 kD molecular mass was purified biochemically from the isolated periacrosomal plasma membrane of equine spermatozoa as a possible receptor for adhesion of spermatozoa to oviductal epithelial cells. A polyclonal antibody raised in rabbits against the purified equine sperm membrane protein recognized the 70 kD and an antigenically related to 32 kD protein in preparations of isolated periacrosomal sperm plasma membrane and in detergent extracted ejaculated and epididymal spermatozoa. A larger protein (approximately 110 kD) was detected in equine testis. Two antigenically related proteins (64 and 45 kD) were recognized on the plasma membrane of cynomolgus macaque spermatozoa. In vitro sperm-binding assays were performed in the presence of antigen-binding fragments or IgG purified from the polyclonal antiserum to investigate a possible function to the isolated protein in binding of equine spermatozoa to homologous oviductal epithelial cells or zona pellucida. Incubation with antigen-binding fragments or IgG purified from the antiserum did not inhibit binding of equine spermatozoa either to oviductal epithelial cells or the zona pellucida. On ultrastructural examination, the antibody bound exclusively to the cytoplasmic side of the periacrosomal plasma membrane of equine and macaque spermatozoa. Microsequence analysis of 13 residues of sequence showed strong homology with a number of angiotensin converting enzymes: An 84% identity was identified with testis specific and somatic forms of human and mouse angiotensin-converting enzyme. Immunocytochemistry and immunoblot analysis established that the protein is specific for the periacrosomal membrane of ejaculated, epididymal, and testicular stallion spermatozoa.