Sperm binding glycoprotein is differentially present surrounding the lumen of isthmus and ampulla of the pig’s oviduct

Assessment of Sperm Binding Capacity in the Tubal Reservoir Using a Bovine Ex Vivo Oviduct Culture and Fluorescence Microscopy

Sperm binding within the oviductal sperm reservoir plays an important role for reproductive success by enabling sperm survival and maintaining fertilizing capacity. To date, numerous in vitro technologies have been established to measure sperm binding capacity to cultured oviductal cells or oviductal explants. However, these methods do not accurately represent the microenvironment and complex multi-molecular nature of the oviduct. In this paper, we describe a novel protocol for assessing sperm binding capacity in the tubal sperm reservoir using an ex vivo oviduct culture in the bovine model. This protocol includes the staining of frozen-thawed bovine spermatozoa with the DNA-binding dye Hoechst 33342, the co-incubation of stained sperm in closed segments of the oviduct and the visualization and quantification of bound spermatozoa by fluorescence microscopy. By generating overlays of multiple Z-stacks of randomly selected regions of interest (ROIs), spermatozoa bound in the sperm reservoir can be visualized and quantified within the 3D arrangement of the oviductal folds. This method, which is applicable to multiple species, can be used to assess individual sperm binding capacity in males for prognostic purposes as well as to assess the impact of diseases and medications on the formation of the sperm reservoir in the oviduct in humans and animals.

Microenvironment of the male and female reproductive tracts regulate sperm fertility: Impact of viscosity, pH, and osmolality

BACKGROUND

Terminally differentiated mammalian sperm are exposed to gradients of viscosity, pH, and osmolality both in the male and female reproductive tract during their perilous journey to quest the ovum. The complex physicochemical factors play an integral role in preparing sperm for the fertilization process.

OBJECTIVES

To elucidate the influence of the reproductive tract microenvironment especially viscosity, pH, and osmolality in regulating sperm functional and fertilization competence.

MATERIALS AND METHODS

The data used in this review were collected from the research papers and online databases focusing on the influence of viscosity, pH, and osmolality on sperm function.

DISCUSSION

The gradients of viscosity, pH, and osmolality exist across various segments of the male and female reproductive tract. The changes in the viscosity create a physical barrier, pH aid in capacitation and hyperactivation, and the osmotic stress selects a progressive sperm subpopulation for accomplishing fertilization. The sperm function tests are developed based on the concept that the male genotype is the major contributor to the reproductive outcome. However, recent studies demonstrate the significance of sperm genotype-environment interactions that are essentially contributing to reproductive success. Hence, it is imperative to assess the impact of physicochemical stresses and the adaptive ability of the terminally differentiated sperm, which in turn would improve the outcome of the assisted reproductive technologies and male fertility assessment.

CONCLUSION

Elucidating the influence of the reproductive tract microenvironment on sperm function provides newer insights into the procedures that need to be adopted for selecting fertile males for breeding, and ejaculates for the assisted reproductive technologies.

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

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

Sperm binding to porcine oviductal cells is mediated by SRCR domains contained in DMBT1

The oviduct is an organ in which a subpopulation of sperm is stored in a reservoir, preserving its fertilizing potential. In porcine, two oviductal proteins have been identified in relation to sperm binding, Annexin A2 and Deleted in Malignant Brain Tumor 1 (DMBT1). DMBT1 is a multifunctional, multidomain glycoprotein, and the characteristics of all of its domains, as well as its carbohydrates, make them candidates for sperm binding. In this work, we challenge sperm for binding to pig oviductal cells on primary culture, after treatment with antibodies specific for the different domains present in DMBT1. Only anti-SRCR antibodies produced inhibition of sperm binding to cells. Thus, SRCR is the main domain in DMBT1 promoted sperm binding to form the reservoir in the oviduct, and this function is probably elicited through the polypeptide itself.

S100A7 in the Fallopian tube: a comparative study

The oviduct is a dynamic organ in which final gamete maturation, fertilization and early embryo development take place. It is considered to be a sterile site; however the mechanism for sterility maintenance is still unknown. S100A7 is an anti-microbial peptide that has been reported in human reproductive tissues such as prostate, testicle, ovary, normal cervical epithelium and sperm. The current work reports the presence of S100A7 in the Fallopian tube and its localization at the apical surface of epithelial cells. For comparison, porcine S100A7 was used for antibody development and search for peptide in reproductive tissues. Although present in boar seminal vesicles and seminal plasma, S100A7 was not detected on female porcine organs. Also, in contrast with the human protein, porcine S100A7 did not show anti-microbial activity under the conditions tested. Phylogenetic analyses showed high divergence of porcine S100A7 from human, primate, bovine, ovine and equine sequences, being the murine sequence at a most distant branch. The differences in sequence homology, Escherichia coli-cidal activity, detectable presence and localization of S100A7 from human and pig, suggest that there are possible different functions in each organism.

First evidence of the interaction between deleted in malignant brain tumor 1 and galectin-3 in the mammalian oviduct

The oviduct supports the transport and final maturation of gametes, and harbors fertilization and early embryo development. The oviductal epithelium is responsible for providing the correct environment for these processes. Deleted in malignant brain tumor 1 (DMBT1) is expressed by multiple organisms and several cell types, and the interaction of the rabbit ortholog of DMBT1 with galectin-3 (gal-3) modulates the polarity of epithelial cells. This interaction has not yet been shown in locations other than rabbit kidney and human-cultured endothelial cells. DMBT1 and gal-3 also protect epithelial layers from pathogens and trauma, and are innate immunity components. DMBT1 has been detected in the porcine oviduct, and gal-3 has been reported in the Fallopian tube and in the cow oviduct. Interaction between both proteins would show a probable physiological function in the female reproductive tract. This work describes the presence and co-localization of DMBT1 and gal-3 mainly in the apical region of the epithelial cells of the Fallopian tube and the porcine oviduct, and co-immunoprecipitation in membrane-enriched epithelial cell extracts from the porcine oviduct. The findings strongly support a functional interaction in the mammalian oviduct, suggestive of a role on epithelial protection and homeostasis, which might be related to epithelium-gamete interaction.

Deleted in malignant brain tumor 1 is secreted in the oviduct and involved in the mechanism of fertilization in equine and porcine species

Oviductal environment affects preparation of gametes for fertilization, fertilization itself, and subsequent embryonic development. The aim of this study was to evaluate the effect of oviductal fluid and the possible involvement of deleted in malignant brain tumor 1 (DMBT1) on IVF in porcine and equine species that represent divergent IVF models. We first performed IVF after pre-incubation of oocytes with or without oviductal fluid supplemented or not with antibodies directed against DMBT1. We showed that oviductal fluid induces an increase in the monospermic fertilization rate and that this effect is canceled by the addition of antibodies, in both porcine and equine species. Moreover, pre-incubation of oocytes with recombinant DMBT1 induces an increase in the monospermic fertilization rate in the pig, confirming an involvement of DMBT1 in the fertilization process. The presence of DMBT1 in the oviduct at different stages of the estrus cycle was shown by western blot and confirmed by immunohistochemical analysis of ampulla and isthmus regions. The presence of DMBT1 in cumulus–oocyte complexes was shown by western blot analysis, and the localization of DMBT1 in the zona pellucida and cytoplasm of equine and porcine oocytes was observed using immunofluorescence analysis and confocal microscopy. Moreover, we showed an interaction between DMBT1 and porcine spermatozoa using surface plasmon resonance studies. Finally, a bioinformatic and phylogenetic analysis allowed us to identify the DMBT1 protein as well as a DMBT1-like protein in several mammals. Our results strongly suggest an important role of DMBT1 in the process of fertilization.

The effect of oviductal deleted in malignant brain tumor 1 over porcine sperm is mediated by a signal transduction pathway that involves pro-AKAP4 phosphorylation

The interaction between sperm and oviduct results in the selection of sperm with certain qualities. Porcine oviductal deleted in malignant brain tumor 1, DMBT1 (previously called sperm-binding glycoprotein, SBG), has been proposed to be implicated in sperm selection through acrosome alteration and suppression of motility of a subpopulation of sperm that have begun capacitation prematurely. It producesin vitroacrosome alteration and decrease of motility of boar sperm, concomitant with tyrosine phosphorylation of a 97 kDa sperm protein (p97). We hypothesized that the phosphorylation of p97 may be a link between DMBT1 sensing by a subpopulation of boar sperm and its biological effect. In this work, p97 was identified by mass spectrometry and immunoprecipitation as a porcine homologue of AKAP4. Pro-AKAP4 was localized by immunofluorescence and subcellular fractionation to the periacrosomal membranes and was shown to be tyrosine phosphorylated by DMBT1 regardless of the presence of calcium or bicarbonate, and of cAMP analogs, protein kinase A inhibitors, or a protein kinase C inductor. A processed ∼80 kDa form of AKAP4 was also detected at the tail of boar sperm, which was not tyrosine phosphorylated by DMBT1 under the conditions tested. Immunohistochemistry of testis showed presence of AKAP4 in boar sperm precursor cells. The evidence presented here supports the involvement of AKAP4 in the formation of the fibrous sheath on boar precursor sperm cells and implicates the phosphorylation of pro-AKAP4 as an early step in the signal transduction pathway gated by DMBT1 that leads to sperm selection through acrosome alteration.

Determination of glycosidase activity in porcine oviductal fluid at the different phases of the estrous cycle

Sperm-oocyte binding and gamete-oviductal epithelium interactions are carbohydrate-mediated events occurring in the oviductal fluid (OF). Thus, knowledge about the activities of glycosidases (enzymes catalyzing hydrolytic cleavage of terminal sugar residues) in this milieu would help us understand the molecular mechanisms involved in these events. This work was carried out to investigate the glycosidase activity, protein content, and volume of OF collected from gilts and sows. Oviducts were classified into four phases of the estrous cycle (early follicular, late follicular, early luteal, and late luteal) based on the appearance of the ovaries. OF was aspirated, centrifuged, measured for volume, and frozen until assay. Substrates conjugated to 4-methylumbelliferyl were used to screen the activities of seven different glycosidases at physiological pH (7.2). alpha-L-Fucosidase and beta-N-acetyl-glucosaminidase activities increased at the late follicular phase to decrease after ovulation. beta-D-Galactosidase, alpha-D-mannosidase, and beta-N-acetyl-galactosaminidase showed higher activities at the early follicular phase, which decreased after ovulation. N-Acetyl-neuraminidase and alpha-D-galactosidase did not show activity at any phase of estrous cycle neither in sows nor in gilts at pH 7.2, although it did at acidic pH (4.4) in the follicular and luteal phase samples. Total protein also changed during the cycle showing the maximum secretion at the late follicular phase (2118.6+/-200.7 microg/oviduct). The highest volumes of OF were collected from the oviducts at the late follicular phase (50.7+/-1.3 microl/oviduct). These results indicate that OF from sows and gilts shows glycosidase activity varying throughout the estrous cycle suggesting a role of these enzymes in carbohydrate-mediated events.

Sperm binding glycoprotein (SBG) produces calcium and bicarbonate dependent alteration of acrosome morphology and protein tyrosine phosphorylation on boar sperm

The oviduct is a dynamic organ which modulates gamete physiology. Two subpopulations of sperm have been described in the oviduct of sows, a majority with normal appearance in the deep furrows and a minority, centrally located, and showing damaged membranes. Sperm-oviduct interaction provides the formation of a sperm storage and allows the selection of sperm with certain qualities. Pig (Sus scrofa) oviductal sperm binding glycoprotein (SBG) binds to sperm and exposes Gal beta1-3GalNAc. This disaccharide may be recognized by boar spermadhesin AQN1, which seems to be involved in sperm interaction with the oviduct. SBG is present at the apical surface of the epithelial cells that surround the lumen of the oviduct rather than at the bottom of the crypts. These characteristics imply it could be involved in sperm interaction with this organ. In this study, we evaluate the effect of SBG over boar sperm. We show that the presence of SBG produces alterations of the acrosome morphology of sperm only when they are incubated in capacitating conditions. SBG binds to the periacrosomal region of sperm undergoing capacitation. Its presence induces an increase on the tyrosine-phosphorylation of a polypeptide of apparent molecular mass 97 kDa, as occurs with a 95 kDa protein in other mammalian sperm upon acrosomic reaction. Altogether, these results suggest that SBG might be involved in sperm selection by alteration of the acrosome of sperm that have already begun the capacitation process when they arrive to the oviduct.