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

The role of reproductive tract extracellular vesicles on boar sperm function

Extracellular vesicles (EVs) are abundant in reproductive tract fluids and serve as important mediators of paracrine communication, influencing the function of gametes. Sperm undergo development in the male reproductive tract and exert their function within the female reproductive tract, engaging in interactions with various types of EVs present throughout the reproductive system. Previous studies have demonstrated that both male and female reproductive tract EVs can impact sperm function by transferring regulatory cargoes to them. Nevertheless, inconsistencies of previous research regarding the effects of EVs on sperm function, coupled with a lack of investigation into the influence of female reproductive tract EVs on sperm fertilization, have left the true role and underlying mechanisms of reproductive tract EVs on sperm function largely unexplored. Given that pigs represent significant economic livestock and serve as an ideal biomedical model for human diseases, this review aims to provide a comprehensive summary of the current knowledge regarding reproductive tract EVs and their influence on boar sperm function, while highlighting their potential roles. We anticipate that this review will facilitate future research on reproductive tract EVs and their impact on sperm function, contributing to improved animal reproductive efficiency and advancements in the treatment of male infertility.

Thawing of cryopreserved sperm from domestic animals: Impact of temperature, time, and addition of molecules to thawing/insemination medium

In recent decades, there has been a growing interest in optimizing the protocols intended to sperm cryopreservation in domestic animals. These protocols include initial cooling, freezing, and thawing. While different attempts have been devised to improve sperm cryopreservation, the efficiency of this reproductive biotechnology is still far from being optimal. Furthermore, while much attention in improving cooling/freezing, less emphasis has been made in how thawing can be ameliorated. Despite this, the conditions through which, upon thawing, sperm return to physiological temperatures are much relevant, given that these cells must travel throughout the female genital tract until they reach the utero-tubal junction. Moreover, the composition of the media used for artificial insemination (AI) may also affect sperm survival, which is again something that one should bear because of the long journey that sperm must make. Furthermore, sperm quality and functionality decrease dramatically during post-thawing incubation time. Added to that, the deposition of the thawed sperm suspension devoid of seminal plasma in some species during an AI is accompanied by a leukocyte migration to the uterine lumen and with it the activation of immune mechanisms. Because few reviews have focused on the evidence gathered after sperm thawing, the present one aims to compile and discuss the available information concerning ruminants, pigs and horses.

The effects of boar seminal plasma extracellular vesicles on sperm fertility

Extracellular vesicles (EVs) are abundant in body fluid and are critical in cell interaction. Seminal plasma contains numerous EVs which affecting sperm function via transferring regulatory cargoes to the sperm. However, the mechanism of seminal plasma extracellular vesicles (SP-EVs) is still not clear. The present study aimed to isolate the boar SP-EVs and explore its potential function, then identify the key protein involved in SP-EVs and sperms interaction, and elucidate mechanism of SP-EVs protein on sperms. Here, we successfully isolated and concentrated boar SP-EVs, the SP-EVs showed a typical vesicle structure under transmission electron microscopy, most of their diameters range between 50 and 200 nm and express EVs biomarkers CD9 and CD63. We proved that SP-EVs could inhibit sperm acrosome reaction and in vitro fertility. Through a data-independent acquisition analysis of protein profiles of noncapacitated sperms, normal capacitated sperms and SP-EVs treated capacitated sperms, we identified that EZRIN was one of the active proteins that participated in SP-EVs and sperms interaction. Furthermore, we tested that the inhibition of EZRIN could promote boar sperm fertility, which is in consistence with the function of SP-EVs. The results may facilitate future research of SP-EVs on sperm function and male infertility.

Sperm induce macrophage extracellular trap formation via phagocytosis-dependent mechanism

Infertility is a public health concern worldwide. Asthenozoospermia is a common cause of male infertility and is characterized by decreased motility. Sperm motility ensures that sperm migrate to complete fertilization. Macrophages are an essential component of innate immunity in the female reproductive tract. Macrophage extracellular traps are induced by various microorganisms to capture and mediate the clearance of microorganisms. The relationship between sperm and macrophage extracellular traps is unclear. The human monocyte leukemia (THP-1) cells differentiated by phorbol myristate acetate (PMA) are widely used as surrogate of human macrophages. This study investigated sperm-induced macrophage extracellular trap formation and clarified some of the mechanisms affecting macrophage extracellular trap production. Sperm-induced macrophage extracellular traps were visualized and components of macrophage extracellular traps were identified by immunofluorescence analyses and scanning electron microscopy. By inhibiting macrophage extracellular trap production and macrophage phagocytosis, the relationship between macrophage phagocytosis and macrophage extracellular trap production was analyzed. Sperm could trigger PMA-differentiated THP-1 macrophages to produce extracellular traps. Sperm-triggered macrophage extracellular traps are dependent on phagocytosis and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Sperm from asthenozoospermia donors are more likely to be phagocytosed by macrophages than sperm from healthy donors, which induce more macrophage extracellular trap release. These data confirm the phenomenon and partial mechanism of sperm-induced macrophage extracellular trap formation in vitro. These may partly provide evidence to explain the mechanisms of clearing abnormally morphological or hypomotile sperm in the female reproductive tract and the rationale for the decreased probability of successful fertilization in asthenozoospermia.

Buffalo sperm membrane glycan-binding proteins reveal precise and preferential binding signatures with specific glycans targets on oviduct epithelium and zona pellucida-an implication in fertilization

Sperm membrane glycan-binding proteins (lectins) interact with the counterpart glycans in the oviduct, oocytes, and vice-versa. It has already been well known that specific glycans are present on oviductal epithelium and zona pellucida (ZP) in different mammalian species. Some of these glycans are necessary for oviductal sperm reservoir formation and gamete recognition. The specific binding phenomenon of lectin-glycans is one of the vital factors for successful fertilization in mammals. We hypothesized that buffalo sperm membrane glycan-binding proteins have specific glycan targets in the oviduct and ZP supporting the fertilization event. In the present investigation, sperm membrane proteins were extracted and assessed for their binding capacity with glycans using a high-throughput glycan microarray. The most promising glycan binding signals were evaluated to confirm the sperm putative receptors for glycan targets in the oviductal epithelial cells (OEC) and on ZP using an in-vitro competitive binding inhibition assay. Based on an array of 100 glycans, we found that N-acetyllactosamine (LacNAc), Lewis-a trisaccharide, 3'-sialyllactosamine and LacdiNAc were the most promising glycans and selected for further in-vitro validation. We established an inhibitory concentration of 12 mM Lewis-a trisaccharide and 10 μg/ml Lotus tetragonolobus (LTL) lectin for the sperm-OEC binding interaction, indicating its specificity and sensitivity. We observed that 3 mM 3'-sialyllactosamine, and LacdiNAc were the most competitive inhibitory concentration in sperm-ZP binding, suggesting a specific and abundance-dependent binding affinity. The competitive binding affinity of Maackia amurensis (MAA) lectin with Neu5Ac(α2-3)Gal(β1-4)GlcNAc further supports the abundance of 3'-sialyllactosamine on ZP responsible for sperm binding. Our findings develop the strong evidence on buffalo sperm putative receptors underlying their locking specificities with Lewis-a trisaccharide in oviduct and 3'-sialyllactosamine on ZP. The functional interaction of buffalo sperm lectins with the target glycans in OEC and ZP appears to be accomplished in an abundance-dependent manner, facilitating the fertilization event in buffaloes.

Exosomes: New regulators of reproductive development

Exosomes are a subtype of extracellular vesicles (EVs) with a size range between 30 and 150 ​nm, which can be released by the majority of cell types and circulate in body fluid. They function as a long-distance cell-to-cell communication mechanism that modulates the gene expression profile and fate of target cells. Increasing evidence has indicated exosomes' central role in regulating various complex reproductive processes. However, to our knowledge, a review that focally and vividly describes the role of exosomes in reproductive development is still lacking. This review highlights our knowledge about the contribution of exosomes to early mammalian reproduction, such as gametogenesis, fertilization, early embryonic development, implantation, placentation and pregnancy. The discussion is primarily drawn from literature pertaining to the mammalian lineage with emphasis on the roles of exosomes in human reproduction and laboratory and livestock models.

Epigenetics Role in Spermatozoa Function: Implications in Health and Evolution-An Overview

The unique properties of spermatozoa are established through the spermatogenesis and maturation processes concurrently with its epigenome. It is known that damage to epigenetic mechanisms can lead to reproductive problems. However, scientific reviews addressing the role of the spermatozoa epigenome during the reproductive process are scarce. Therefore, the aim of this review was to offer a detailed overview of current knowledge in the field of spermatozoa epigenetics and its consequent implications. A full search was performed through three databases by combining five keywords. Inclusion criteria were implemented to grant accessibility, relevance, and concretion. Besides, some articles were manually removed or added to obtain an adequate and complete collection of 485 scientific publications. This compilation was used to conduct the bibliometric analysis and the data review separately. Bibliometric results displayed that spermatozoa epigenetics is an active and growing research area. The bibliographic overview showed that sperm epigenome correlates with the development of its function, explaining the environmental influence on reproductive pathologies or abnormal inheritance. The main conclusions were that the normal performance of sperm is heavily reliant on its epigenetics and that this study area is burgeoning, with the potential ability to provide society with clinical innovations in a short-term period.

Beta-defensins as marker for male fertility: a comprehensive review†

Bovine male fertility in animals has a direct impact on the productivity of dairy herds. The epididymal sperm maturations involve extensive sperm surface modifications to gain the fertilizing ability, especially by absorptions of the plethora of biomolecules, including glycoprotein beta-defensins (BDs), enzymes, organic ions, protein, and phospholipids. Defensins are broad-range nonspecific antimicrobial peptides that exhibit strong relations with innate and adaptive immunity, but their roles in male fertility are relatively recently identified. In the course of evolution, BD genes give rise to different clusters with specific functions, especially reproductive functions, by undergoing duplications and nonsynonymous mutations. BD polymorphisms have been reported with milk compositions, disease resistance, and antimicrobial activities. However, in recent decades, the link of BD polymorphisms with fertility has emerged as an appealing improvement of reproductive performance such as sperm motility, membrane integrity, cervical mucus penetration, evading of uterus immunosurveillance, oviduct cell attachment, and egg recognition. The reproductive-specific glycosylated BD class-A BDs (CA-BDs) have shown age- and sex-specific expressions in male reproductive organs, signifying their physiological pleiotropism, especially in the sperm maturation and sperm transport in the female reproductive tract. By considering adult male reproductive organ-specific BD expressions, importance in sperm functionalities, and bioinformatic analysis, we have selected two bovine BBD126 and BBD129 genes as novel potential biomarkers of bovine male fertility. Despite the importance of BDs, however, genomic characterization of most BD genes across most livestock and nonmodel organisms remains predictive/incomplete. The current review discusses our understanding of BD pleiotropic functions, polymorphism, and genomic structural attributes concerning the fertilizability of the male gamete in dairy animals.

Sexual selection drives the coevolution of male and female reproductive traits in Peromyscus mice

When females mate with multiple partners within a single reproductive cycle, sperm from rival males may compete for fertilization of a limited number of ova, and females may bias the fertilization of their ova by particular sperm. Over evolutionary timescales, these two forms of selection shape both male and female reproductive physiology when females mate multiply, yet in monogamous systems, post-copulatory sexual selection is weak or absent. Here, we examine how divergent mating strategies within a genus of closely related mice, Peromyscus, have shaped the evolution of reproductive traits. We show that in promiscuous species, males exhibit traits associated with increased sperm production and sperm swimming performance, and females exhibit traits that are predicted to limit sperm access to their ova including increased oviduct length and a larger cumulus cell mass surrounding the ova, compared to monogamous species. Importantly, we found that across species, oviduct length and cumulus cell density are significantly correlated with sperm velocity, but not sperm count or relative testes size, suggesting that these female traits may have coevolved with increased sperm quality rather than quantity. Taken together, our results highlight how male and female traits evolve in concert and respond to changes in the level of post-copulatory sexual selection.

Bacterial killing activity and lysozymes: A stable defence mechanism in stallion seminal plasma?

During insemination, bacterial contamination of the ejaculate can lead to reduced sperm quality and transmission of pathogens to the female, thus should be avoided. The semen of a variety of animal taxa possess antimicrobial properties against a wide range of bacterial species through antimicrobial molecules, such as lysozyme, but their variance and the factors influencing it are unknown for most species. In this study, the antibacterial defence (bacterial killing activity (BKA) against Escherichia (E.) coli and Staphylococcus (S.) aureus as well as lysozyme concentration) was studied in seminal fluid from two consecutive ejaculates of 18 stallions. All ejaculates showed BKA against the tested bacteria, which correlated between the two consecutive ejaculates (r_S  = 0.526, p = .025 for E. coli and r_S  = 0.656, p = .003 for S. aureus) and appeared to be stable over the tested period. The lysozyme concentration (LC) showed no significant correlation between the consecutive ejaculates (r_S  = 0.161, p = .681). However, LC had a positive correlation to the ratio of apoptotic spermatozoa within the ejaculates (r_S  = 0.426, p = .019). In contrast to other livestock (e.g., boar, bull), the BKA in stallion semen did not correlate significantly with the age of the animal nor sperm quality characteristics.

Analysis of amplification and association polymorphisms in the bovine beta-defensin 129 (BBD129) gene revealed its function in bull fertility

β-defensins are adsorbable on the sperm surface in the male reproductive tract (MRT) and enhance sperm functional characteristics. The beta-defensin 129 (DEFB129) antimicrobial peptide is involved in sperm maturation, motility, and fertilization. However, its role in bovine fertility has not been well investigated. This study examines the relationship between the bovine BBD129 gene and Bos indicus x Bos taurus bull fertility. The complete coding sequence of BBD129 mRNA was identified by RNA Ligase Mediated-Rapid Amplification of cDNA End (RLM-RACE) and Sanger sequencing methodologies. It consisted of 582 nucleotides (nts) including 5' untranslated region (UTR) (46nts) and 3'UTR (23nts). It conserves all beta-defensin-like features. The expression level of BBD129 was checked by RT-qPCR and maximal expression was detected in the corpus-epididymis region compared to other parts of MRT. Polymorphism in BBD129 was also confirmed by Sanger sequencing of 254 clones from 5 high fertile (HF) and 6 low fertile (LF) bulls at two positions, 169 T > G and 329A > G, which change the S57A and N110S in the protein sequence respectively. These two mutations give rise to four types of BBD129 haplotypes. The non-mutated TA-BBD129 (169 T/329A) haplotype was substantially more prevalent among high-fertile bulls (P < 0.005), while the double-site mutated GG-BBD129 (169 T > G/329A > G) haplotype was significantly more prevalent among low-fertile bulls (P < 0.005). The in silico analysis confirmed that the polymorphism in BBD129 results in changes in mRNA secondary structure, protein conformations, protein stability, extracellular-surface availability, post-translational modifications (O-glycosylation and phosphorylation), and affects antibacterial and immunomodulatory capabilities. In conclusion, the mRNA expression of BBD129 in the MRT indicates its region-specific dynamics in sperm maturation. BBD129 polymorphisms were identified as the deciding elements accountable for the changed proteins with impaired functionality, contributing to cross-bred bulls' poor fertility.

What is the relevance of seminal plasma from a functional and preservation perspective?

When preserving sperm in the liquid or cryopreserved state, seminal plasma (SP) components within ejaculates can alter fertilizing capacity of these gametes. Depending on the species or how semen is collected, volume and concentration of SP components varies considerably. The SP contains substances essential for maintenance of sperm viability and fertility; however, these components can be deleterious depending on quantity, or duration of time before there is removal of SP from sperm in semen processing. Substances that impair (e.g., BSP - bull; HSP-1 - stallion; Major seminal plasma protein PSPI - boar) or improve (e.g., spermadhesin PSP-I - boar) spermatozoa fertilizing capacity have been identified. Depending on individual males, species, and semen collection procedures, SP removal may be beneficial before preservation in the liquid or cryopreserved state. In some cases, SP that is removed can be added back to thawing extender with there being positive effects in thawed sperm and for sperm viability in the female reproductive tract. In this review article, there is a focus on different effects of SP in samples of cooled and cryopreserved semen from four domestic species (pigs, horses, cattle, and sheep) with there being emphasis on how SP modulates the function and morphology of sperm cells before, during, and after preservation in the refrigerated or cryopreserved state. The present review is part of the Festschrift in honor of Dr. Duane Garner who made major contributions to the area of focus in this manuscript as evidenced by the many times his research is cited in this manuscript.

Evaluation of sperm integrin α5β1 as a potential marker of fertility in humans

Sperm selection for assisted reproduction techniques is generally based on basic parameters, while key aspects of sperm competence and its journey from the deposition site to the fertilization site are overlooked. Consequently, identifying molecular markers in spermatozoa that can efficiently predict the fertility of a semen sample could be of great interest, particularly in cases of idiopathic male infertility. When spermatozoa reach the female reproductive tract, it provides to them the cellular and molecular microenvironment needed to acquire fertilizing ability. In this sense, considering the role that integrin α5β1 of spermatozoa plays in reproduction-related events, we investigated the correlation between the subcellular localization of sperm integrin α5β1 and early embryo development outcome after in vitro fertilization (IVF) procedures in human. Twenty-four semen samples from normozoospermic men and metaphase II (MII) oocytes from healthy women aged under 38 years, from couples who underwent IVF cycles, were used in this work. Sperm α5β1 localization was evaluated by immunofluorescence assay using an antibody against integrin α5 subunit. Integrin α5β1 was mainly localized in the sperm acrosomal region (45.33±7.89%) or the equatorial segment (30.12±7.43%). The early embryo development rate (data obtained from the Fertility Center) correlated positively with the localization of α5β1 in the acrosomal region (number of usable embryos / inseminated oocytes: ρ = 0.75; p<0.01 and number of usable embryos/total number of two pronuclear zygotes: ρ = 0.80; p<0.01). However, this correlation was not significant when the equatorial segment mark was evaluated. In addition, human sperm released from co-culture with bovine oviductal epithelial cells (BOEC) showed a significant enrichment in the acrosomal localization pattern of α5β1 compared to those sperm that were not co-cultured with BOEC (85.20±5.35% vs 35.00±17.09%, respectively, p<0.05). In conclusion, the evaluation of sperm integrin α5β1 immunolocalization could be a useful tool to select sperm with fertilizing ability from human semen samples before IVF procedures.

Seminal lipid profiling and antioxidant capacity: A species comparison

On their way to the oocyte, sperm cells are subjected to oxidative stress, which may trigger the oxidation of phospholipids (PL). Applying MALDI-TOF MS, HPTLC and ESI-IT MS, we comparatively analyzed the PL compositions of semen and blood of species differing in their reproductive systems and types of nutrition (bull, boar, stallion, lion and man) with regard to the sensitivity to oxidation as well as the accumulation of harmful lyso-PL (LPL), transient products of lipid oxidation. In addition, the protective capacity of seminal fluid (SF) was also examined. The PL composition of erythrocytes and blood plasma is similar across the species, while pronounced differences exist for sperm and SF. Since the blood function is largely conserved across mammalian species, but the reproductive systems may vary in many aspects, the obtained results suggest that the PL composition is not determined by the type of nutrition, but by the relatedness of species and by functional requirements of cell membranes such as fluidity. Sperm motion and fertilization of oocytes require a rather flexible membrane, which is accomplished by significant moieties of unsaturated fatty acyl residues in sperm lipids of most species, but implies a higher risk of oxidation. Due to a high content of plasmalogens (alkenyl ether lipids), bull sperm are most susceptible to oxidation. Our data indicate that bull sperm possess the most effective protective power in SF. Obviously, a co-evolution of PL composition and protective mechanisms has occurred in semen and is related to the reproductive characteristics. Although the protective capacity in human SF seems well developed, we recorded the most pronounced individual contaminations with LPL in human semen. Probably, massive oxidative challenges related to lifestyle factors interfere with natural conditions.

The Design of a New Catheter for Transcervical Artificial Insemination in Ewes

In ovine species, transcervical artificial insemination (TCAI) is limited by the poor quality of frozen-thawed semen and by the convoluted cervical lumen hampering the passage of inseminating devices. The aim of the study was to test the efficiency of three newly designed catheters with bent tips of 3.5 mm, 5.0 mm or 8.0 mm in terms of reproductive performances (experiment 1) and to compare the results of TCAI with the best performing catheter of experiment 1 to those obtained in ewes submitted to surgical incision of cervical folds (SICF) prior to insemination (experiment 2). The following parameters were assessed: time to pass the cervix; depth of cervical penetration; site of deposition of semen; pregnancy (PR); and lambing rates (LR). The results of experiment 1 indicated that the 5.0 mm tip catheter resulted in deeper and faster TCAI and higher PR and LR compared to 3.5 mm and 8.0 mm tip catheters (p < 0.05). In experiment 2, TCAI with the 5.0 mm catheter did not differ from TCAI after SICF in terms of depth of semen deposition, time to pass the cervix, PR and LR (p < 0.05). In conclusion, the use of a catheter that allowed transcervical uterine deposition of semen without excessive manipulation led to satisfactory pregnancy rates.

Evolutionary consequences of environmental effects on gamete performance

Variation in pre- and post-release gamete environments can influence evolutionary processes by altering fertilization outcomes and offspring traits. It is now widely accepted that offspring inherit epigenetic information from both their mothers and fathers. Genetic and epigenetic alterations to eggs and sperm-acquired post-release may also persist post-fertilization with consequences for offspring developmental success and later-life fitness. In externally fertilizing species, gametes are directly exposed to anthropogenically induced environmental impacts including pollution, ocean acidification and climate change. When fertilization occurs within the female reproductive tract, although gametes are at least partially protected from external environmental variation, the selective environment is likely to vary among females. In both scenarios, gamete traits and selection on gametes can be influenced by environmental conditions such as temperature and pollution as well as intrinsic factors such as male and female reproductive fluids, which may be altered by changes in male and female health and physiology. Here, we highlight some of the pathways through which changes in gamete environments can affect fertilization dynamics, gamete interactions and ultimately offspring fitness. We hope that by drawing attention to this important yet often overlooked source of variation, we will inspire future research into the evolutionary implications of anthropogenic interference of gamete environments including the use of assisted reproductive technologies. This article is part of the theme issue 'How does epigenetics influence the course of evolution?'

In vitro performance and in vivo fertility of antibiotic-free preserved boar semen stored at 5 °C

BACKGROUND

Hypothermic preservation of boar semen is considered a potential method for omitting antibiotics from insemination doses, thereby contributing to the global antibiotic resistance defence strategy. The main challenges are chilling injury to spermatozoa and bacterial growth during semen storage leading to reduced fertility.

OBJECTIVES

To examine chilling injury and the number and type of bacteria in boar semen stored at 5 °C in the absence of antibiotics, and to assess the applicability of hypothermic semen storage under field conditions.

MATERIAL AND METHODS

Boar ejaculates were extended with AndroStar® Premium, stored at 17 °C with and at 5 °C without antibiotics and tested for functional sperm parameters by flow cytometry. Raw semen and extended samples were investigated bacteriologically. Fertility was evaluated after once-daily inseminations of 194 sows in a field study.

RESULTS

Lethal sperm damage assessed by motility and membrane integrity was low throughout storage in both experimental groups. Sublethal chilling effects based on the decrease of viable spermatozoa with low membrane fluidity were higher (P < 0.05) up until 72 h in sperm stored at 5 °C compared to 17 °C but did not differ after 144 h. After 72 h, incubation in capacitating medium for 60 min induced a similar decrease in viable sperm with high mitochondria membrane potential and low cytosolic calcium in both groups. In semen stored at 5 °C, bacteria counts were below 10³ CFU/mL and the bacteria spectrum was similar to that of raw semen. In 88% of 34 boars, cooled semen fulfilled the requirements for insemination. Fertility was high and did not differ (P > 0.05) between sow groups inseminated with semen stored antibiotic-free at 5 °C and semen stored at 17 °C with antibiotics.

CONCLUSION

Despite subtle chilling effects and low bacterial numbers, antibiotic-free hypothermic storage of boar semen offers the possibility to reduce the use of antibiotics in pig insemination. However, strict sanitary guidelines must be maintained and further evidence of efficiency under field conditions is considered desirable.

Normal and abnormal response to sperm deposition in female dogs: A review and new hypotheses for endometritis

In mammalian species there are significant physiological responses of the female reproductive tract to the deposition of sperm. These are particularly notable in species where sperm are deposited directly into the uterus, and function both to facilitate sperm transport to the sperm reservoir, and to eliminate introduced contaminants. In the bitch, sperm are deposited into the vagina and are rapidly transported through the open cervix. Sperm are then distributed around the uterus by uterine contractions such that transportation to the tip of the uterine horns occurs within 1 min of the start of mating. The main sperm reservoir appears to be the distal part of the utero-tubal junction which forms a pre-uterine tube reservoir. Sperm remain attached here by their heads to uterine epithelium and remain viable. In non-capacitating conditions sperm slowly detach from this site and this seems important to replenish the uterine tube reservoir, where sperm may re-attach to the epithelium. Post-ovulatory signals trigger capacitation changes and subsequent hyperactivated motility that is associated with detachment of sperm from both reservoirs; thus facilitating fertilization. After mating, a physiological post-mating uterine inflammatory response occurs, evidenced by an influx of polymorphonuclear neutrophils, increased uterine contractions, an increased uterine artery blood flow and a decrease of the resistance index indicating a short-duration vasodilation. Disturbance of this tightly regulated system has the potential to impact fertility by a failure of elimination of the introduced contaminants (such that a clinically-significant post-breeding endometritis ensues) but also by impairing sperm transport.

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.

Sperm Proteome after Interaction with Reproductive Fluids in Porcine: From the Ejaculation to the Fertilization Site

Ejaculated sperm are exposed to different environments before encountering the oocyte. However, how the sperm proteome changes during this transit remains unsolved. This study aimed to identify proteomic changes in boar sperm after incubation with male (seminal plasma, SP) and/or female (uterine fluid, UF; and oviductal fluid, OF) reproductive fluids. The following experimental groups were analyzed: (1) SP: sperm + 20% SP; (2) UF: sperm + 20% UF; (3) OF: sperm + 20% OF; (4) SP + UF: sperm + 20% SP + 20% UF; and (5) SP+OF: sperm + 20% SP + 20% OF. The proteome analysis, performed by HPLC-MS/MS, allowed the identification of 265 proteins. A total of 69 proteins were detected in the UF, SP, and SP + UF groups, and 102 proteins in the OF, SP, and SP + OF groups. Our results showed a higher number of proteins when sperm were incubated with only one fluid than when they were co-incubated with two fluids. Additionally, the number of sperm-interacting proteins from the UF group was lower than the OF group. In conclusion, the interaction of sperm with reproductive fluids alters its proteome. The description of sperm-interacting proteins in porcine species after co-incubation with male and/or female reproductive fluids may be useful to understand sperm transport, selection, capacitation, or fertilization phenomena.

Sex Manipulation Technologies Progress in Livestock: A Review

Sex manipulation technologies allow predetermination of the sex of animal offspring by altering the normal reproductive process. In livestock production, the difference in type and gender can translate into significant economic benefits, including alleviation of severe food shortages. In livestock, however, the commercial application of sex manipulation technologies is currently available for cattle only. In this review, we described the brief history of sex manipulation, and the research progresses of common methods used in sex manipulation thus far. Information presented in this review can inform future studies on expanding the scope and use of sex manipulation technologies in livestock.

Antibacterial defense in bull and boar semen: A putative link to the microbiome and reproductive strategy?

Several domestic and wildlife species have been shown to possess antibacterial defenses in their ejaculate most probably in order to increase the fertilization success and protect against sexually transmitted pathogens. However, very little is known about the consequences and factors influencing the differences within and between species as far as ejaculate-associated immunity. In the present study, we have analyzed bacterial killing activity (BKA) against Escherichia (E.) coli and Staphylococcus (S.) aureus as well as lysozyme concentrations (LC) in seminal plasma from 60 Fleckvieh bulls. Further, sperm quality and its association with BKA and LC were determined. Twenty percent of the individuals displayed BKA against both bacteria, 78.3% against S. aureus only and 1.7% of the bulls did not indicate any BKA in seminal plasma. No bulls with seminal plasma BKA only against E. coli were identified; implying that 80.0% of the tested bulls had no ejaculate associated defense mechanisms against this gram-negative bacterial species in place. This is in striking contrast to results of Pietrain boars within our previous study, in which 42.8% of the 119 boars expressed an antibacterial activity against E. coli in seminal plasma, 10.9% amongst them with BKA against E. coli only. LC was higher in the bull group with BKA against both bacteria (1.2 ± 0.6 μg/mL) compared to the group with BKA against S. aureus only (0.7 ± 0.3 μg/mL), but - if calculated over all individuals - LC in bulls (0.8 ± 0.4 μg/mL) was lower compared to boars (2.4 ± 1.2 μg/mL). LC showed positive correlations to the age of the bulls and sperm quality as well as a negative relation to bacterial load in raw semen although the highest bacterial contamination was found in animals with seminal plasma BKA against both strains. We discuss the obtained results with regards to possible differences within the microbiome of female and male genital tracts and the reproductive strategies (vaginal vs. uterine depositors) in these two livestock species. Besides identifying the responsible molecules, future phylogenetically controlled comparative studies are needed for a better understanding of the evolution of species differences in ejaculate-associated antibacterial defenses.

Sperm surface changes and their consequences for sperm transit through the female reproductive tract

Spermatozoa are faced with considerable challenges during their passage through the female reproductive tract. Following deposition, they must deal with several physical and biochemical barriers as well as an aggressive immune defence system before they reach the site of fertilisation. While many factors are at play, the surface characteristics of spermatozoa are central to communication with the female and successful transit. The surface proteome of spermatozoa has been extensively studied and shown to vary considerably between species that deposit semen in the vagina (ram and bull) and uterus (boar and stallion), likely due to major differences in accessory sex gland anatomy. Comparing the surface characteristics of spermatozoa from these domestic species and how individual components may equip spermatozoa to interact with different features of the female tract could help understand how spermatozoa navigate from vagina or uterus to oviduct ampulla. Furthermore, we can begin to explain why use of high quality preserved spermatozoa in artificial insemination programs may still result in reduced fertility due to altered interaction with the female. In this review, we describe the sperm surface characteristics of the ram, bull, boar and stallion and compare changes as a result of mixture with seminal plasma and/or in vitro processing. The role of these seminal components in facilitating sperm survival and transit within the female reproductive tract is summarised, drawing attention to potential implications for applied reproductive technologies.