In vitrocapacitation of bull spermatozoa by oviductal fluid and its components

The Cation/Calcium Channel of Sperm (CatSper): A Common Role Played Despite Inter-Species Variation?

The main cation/calcium channel of spermatozoa (CatSper), first identified in 2001, has been thoroughly studied to elucidate its composition and function, while its distribution among species and sperm sources is yet incomplete. CatSper is composed of several subunits that build a pore-forming calcium channel, mainly activated in vivo in ejaculated sperm cells by intracellular alkalinization and progesterone, as suggested by the in vitro examinations. The CatSper channel relevance is dual: to maintain sperm homeostasis (alongside the plethora of membrane channels present) as well as being involved in pre-fertilization events, such as sperm capacitation, hyperactivation of sperm motility and the acrosome reaction, with remarkable species differences. Interestingly, the observed variations in CatSper localization in the plasma membrane seem to depend on the source of the sperm cells explored (i.e., epididymal or ejaculated, immature or mature, processed or not), the method used for examination and, particularly, on the specificity of the antibodies employed. In addition, despite multiple findings showing the relevance of CatSper in fertilization, few studies have studied CatSper as a biomarker to fine-tune diagnosis of sub-fertility in livestock or even consider its potential to control fertilization in plague animals, a more ethically defensible strategy than implicating CatSper to pharmacologically modify male-related fertility control in humans, pets or wild animals. This review describes inter- and intra-species differences in the localization, structure and function of the CatSper channel, calling for caution when considering its potential manipulation for fertility control or improvement.

New insights into posttranslational modifications of proteins during bull sperm capacitation

BACKGROUND

Due to the unique nature of spermatozoa, which are transcriptionally and translationally silent, the regulation of capacitation is based on the formation of posttranslational modifications of proteins (PTMs). However, the interactions between different types of PTMs during the capacitation remain unclear. Therefore, we aimed to unravel the PTM-based regulation of sperm capacitation by considering the relationship between tyrosine phosphorylation and reversible oxidative PTMs (oxPTMs), i.e., S-nitrosylation and S-glutathionylation. Since reversible oxPTMs may be closely related to peroxyredoxin (PRDX) activity, the second aim was to verify the role of PRDXs in the PTM-based regulation of capacitation.

METHODS

Cryopreserved bull sperm were capacitated in vitro with or without PRDX inhibitor. Qualitative parameters of sperm and symptoms characteristic of capacitation were analyzed. Posttranslational protein modifications (S-nitrosylation, S-glutathionylation, tyrosine phosphorylation) were investigated at the cellular level (flow cytometry, fluorescence microscopy) and at the proteomic level (fluorescent gel-based proteomic approach).

RESULTS

Zona-pellucida binding proteins (ACRBP, SPAM1, ZAN, ZPBP1 and IZUMO4) were particularly rich in reversible oxPTMs. Moreover, numerous flagellar proteins were associated with all analyzed types of PTMs, which indicates that the direction of posttranslational modifications was integrated. Inhibition of PRDX activity during capacitation caused an increase in S-nitrosylation and S-glutathionylation and a decrease in tyrosine phosphorylation. Inhibition of PRDXs caused GAPDHS to undergo S-glutathionylation and the GSTO2 and SOD2 enzymes to undergo denitrosylation. Moreover, PRDX inhibition caused the AKAP proteins to be dephosphorylated.

CONCLUSIONS

Our research provides evidence that crosstalk occurs between tyrosine phosphorylation and reversible oxPTMs during bull sperm capacitation. This study demonstrates that capacitation triggers S-nitrosylation and S-glutathionylation (and reverse reactions) of zona-pellucida binding proteins, which may be a new important mechanism that determines the interaction between sperms and oocytes. Moreover, TCA-related and flagellar proteins, which are particularly rich in PTMs, may play a key role in sperm capacitation. We propose that the deglutathionylation of ODFs and IZUMO4 proteins is a new hallmark of bull sperm capacitation. The obtained results indicate a relationship between PRDX activity and protein phosphorylation, S-glutathionylation and S-nitrosylation. The activity of PRDXs may be crucial for maintaining redox balance and for providing proper PKA-mediated protein phosphorylation during capacitation. Video Abstract.

A stallion spermatozoon's journey through the mare's genital tract: In vivo and in vitro aspects of sperm capacitation

Conventional in vitro fertilization is not efficacious when working with equine gametes. Although stallion spermatozoa bind to the zona pellucida in vitro, these gametes fail to initiate the acrosome reaction in the vicinity of the oocyte and cannot, therefore, penetrate into the perivitelline space. Failure of sperm penetration most likely relates to the absence of optimized in vitro fertilization media containing molecules essential to support stallion sperm capacitation. In vivo, the female reproductive tract, especially the oviductal lumen, provides an environmental milieu that appropriately regulates interactions between the gametes and promotes fertilization. Identifying these 'fertilization supporting factors' would be a great contribution for development of equine in vitro fertilization media. In this review, a description of the current understanding of the interactions stallion spermatozoa undergo during passage through the female genital tract, and related specific molecular changes that occur at the sperm plasma membrane is provided. Understanding these molecular changes may hold essential clues to achieving successful in vitro fertilization with equine gametes.

Bull Sperm Capacitation Is Accompanied by Redox Modifications of Proteins

The ability to fertilise an egg is acquired by the mammalian sperm during the complex biochemical process called capacitation. Capacitation is accompanied by the production of reactive oxygen species (ROS), but the mechanism of redox regulation during capacitation has not been elucidated. This study aimed to verify whether capacitation coincides with reversible oxidative post-translational modifications of proteins (oxPTMs). Flow cytometry, fluorescence microscopy and Western blot analyses were used to verify the sperm capacitation process. A fluorescent gel-based redox proteomic approach allowed us to observe changes in the level of reversible oxPTMs manifested by the reduction or oxidation of susceptible cysteines in sperm proteins. Sperm capacitation was accompanied with redox modifications of 48 protein spots corresponding to 22 proteins involved in the production of ROS (SOD, DLD), playing a role in downstream redox signal transfer (GAPDHS and GST) related to the cAMP/PKA pathway (ROPN1L, SPA17), acrosome exocytosis (ACRB, sperm acrosome associated protein 9, IZUMO4), actin polymerisation (CAPZB) and hyperactivation (TUBB4B, TUB1A). The results demonstrated that sperm capacitation is accompanied by altered levels of oxPTMs of a group of redox responsive proteins, filling gaps in our knowledge concerning sperm capacitation.

Short communication: Bull sperm selection by attachment to hyaluronic acid semi-interpenetrated hydrogels

We report the development of a hydrogel-based approach to select bull spermatozoa, a crucial step for successful assisted reproductive techniques (ARTs). Hyaluronic acid (HA) semi-interpenetrated N-isopropylacrylamide (PNIPAM) co-20% N-Tris (hydroxymethyl) methyl acrylamide (HMA) hydrogels were synthetized on glass surfaces and cultured in presence of frozen-thawed bull spermatozoa. A fraction of motile bull spermatozoa population strongly attached to hydrogels and was partially released by treatment with hyaluronidase. Fifty-nine (59 ± 7.24) per cent of sperm cells attached to PNIPAM-HMA-HA hydrogels and 31.16 ± 4.81% of them were released upon treatment with medium containing hyaluronidase. This attached-released sperm fraction has acceptable characteristics of progressive motility (50.0 ± 5.0%), vigour (4), high viability (58.7 ± 11.7%) and low percentage of acrosome reacted spermatozoa (23.36 ± 4.1%). Our findings indicate that PNIPAM-HMA-HA hydrogels are non-toxic and allow the selection of high-quality sperm cells for ART.

Porcine oocyte preincubation in oviductal fluid flush before in vitro fertilization in the presence of oviductal epithelial cells improves monospermic zygote production

The present study was designed to evaluate the effect of the combination of oviduct fluid flush (OFF) and oviduct epithelial cells (OEC) in modulating the incidence of polyspermy in pigs. Therefore, for in vitro fertilization (IVF), oocyte and sperm were co-cultured in Tris-buffered medium (TBM) either supplemented with 10% OFF (OFFD group), or in the presence of a bovine OEC monolayer (OEC group), or the oocytes were exposed to OFF for 30 min before IVF (OFFB group), or in the presence of an OEC monolayer (OFFB + OEC group). Regardless of sperm concentration used (0.5, 1.5, and 4.5 × 105 cells/ml), supplementation of IVF medium with 10% OFF led to an increased (P < 0.05) monospermy rate, without alteration (P > 0.05) of the penetration rate in comparison with the control and OEC groups. When the IVF medium was supplemented with heparin, an overall increase (P < 0.05) of the final output of the IVF system in terms of zygotes with two pronuclei (2PN) was observed in the OFFD group, compared with the control and OEC groups, at a sperm concentration of 4.5 × 105 cells/ml. At this concentration, OFFB improved the monospermy rate but decreased the penetration rate, resulting in low efficiency of monospermic zygotes production. Despite this, no major effect was observed in the developmental competence of the presumed zygotes up to the blastocyst stage. The combination of OFFB with OEC improved the penetration rate, while maintaining the high monospermic rate induced by OFFB. In conclusion, the combination of treatment of oocytes by diluted OFF 30 min before IVF, followed by IVF in the presence of OEC, improved monospermic zygote production without reducing the penetration rate, when the IVF medium was supplemented with heparin.

Bovine seminal plasma osteopontin: Structural modelling, recombinant expression and its relationship with semen quality

Osteopontin (OPN) is a multifunctional phosphoprotein that has been linked to fertility in bulls. However, the exact mechanism by which OPN contributes to fertilisation is yet unknown. The biotechnological use of OPN in bovine reproduction is promising but some gaps remain unfilled. The present work aimed: (a) to verify whether the seminal plasma OPN is associated with seminal traits and a standard breeding soundness exam; (b) to predict OPN interactions with integrins, CD44 and glycosaminoglycans through molecular docking; and (c) to develop a protocol for recombinant expression of OPN from vesicular gland cDNA. Ejaculates from top ranked bulls had higher amounts of seminal plasma OPN in comparison with bulls classified as questionable (p < .01). The structural modelling and molecular docking predictions indicated that bovine OPN binds to heparin disaccharide, hyaluronic acid and hyaluronan. In addition, docking studies described the binding complexes of OPN with CD44 and the integrin heterodimers α5β1 and αVβ3. Finally, expression of rOPN-6His was successfully obtained after 3 hr of induction with 0.5 mM IPTG at 37°C and a denaturing purification protocol resulted in efficiently purified recombinant OPN. The present results contribute to the development of biotechnological uses of OPN as a biomarker in bovine reproduction.

Effect of oviductal fluid on bull sperm functionality and fertility under non-capacitating and capacitating incubation conditions

This study investigated the effect of bovine oviductal fluid from late follicular (LF) and early luteal (EL) phases on bull sperm functionality under non-capacitating (NCAP) and capacitating (CAP) conditions. Frozen-thawed semen samples from five bulls were thawed and incubated (0, 1 or 2 h) in NCAP and CAP media supplemented with 1% bovine oviductal fluid (LF and EL groups) and in absence of fluid (C group). Motion parameters were assessed by CASA; sperm viability, acrosomal integrity and membrane lipid disorder parameters were evaluated by flow cytometry; and sperm DNA fragmentation was evaluated by the Comet assay. Finally, in vitro fertilization with sperm treated under CAP conditions was performed and further embryo culture results evaluated. In NCAP medium, addition of LF and EL fluid increased the total and progressive motility, and LF fluid improved the stability of sperm DNA. However, under CAP conditions addition of LF and EL fluid decreased some sperm motion parameters and some parameters of sperm DNA stability. Proportion of viable sperm cells with low lipid disorder was higher in NCAP than CAP medium and addition of LF fluid markedly increased the proportion of viable spermatozoa with high lipid disorder and acrosome alteration (spontaneous acrosome reaction). Under current conditions, incubation of bull sperm with oviductal fluid before insemination did not affect detrimentally the IVF results nor embryo development, being blastocyst rate similar between CAP-LF, CAP-EL and control groups. In conclusion, oviductal fluid positively influences sperm functionality and modulate in vitro capacitation.

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.

Does the Pre-Ovulatory Pig Oviduct Rule Sperm Capacitation In Vivo Mediating Transcriptomics of Catsper Channels?

Spermatozoa need to conduct a series of biochemical changes termed capacitation in order to fertilize. In vivo, capacitation is sequentially achieved during sperm transport and interaction with the female genital tract, by mechanisms yet undisclosed in detail. However, when boar spermatozoa are stored in the tubal reservoir pre-ovulation, most appear to be in a non-capacitated state. This study aimed at deciphering the transcriptomics of capacitation-related genes in the pig pre-ovulatory oviduct, following the entry of semen or of sperm-free seminal plasma (SP). Ex-vivo samples of the utero-tubal junction (UTJ) and isthmus were examined with a microarray chip (GeneChip^® Porcine Gene 1.0 ST Array, Thermo Fisher Scientific) followed by bioinformatics for enriched analysis of functional categories (GO terms) and restrictive statistics. The results confirmed that entry of semen or of relative amounts of sperm-free SP modifies gene expression of these segments, pre-ovulation. It further shows that enriched genes are differentially associated with pathways relating to sperm motility, acrosome reaction, single fertilization, and the regulation of signal transduction GO terms. In particular, the pre-ovulation oviduct stimulates the Catsper channels for sperm Ca²⁺ influx, with AKAPs, CATSPERs, and CABYR genes being positive regulators while PKIs and CRISP1 genes appear to be inhibitors of the process. We postulate that the stimulation of PKIs and CRISP1 genes in the pre-ovulation sperm reservoir/adjacent isthmus, mediated by SP, act to prevent premature massive capacitation prior to ovulation.

Hyaluronic acid capacitation induces intracellular signals modulated by membrane-associated adenylate cyclase and tyrosine kinase involved in bovine in vitro fertilization

Heparin is the most commonly used in vitro capacitation inducer in the bovine. However, hyaluronic acid (HA) has been recently used for capacitation induction as well as for other reproductive biotechnologies, such as sperm selection and in vitro fertilization (IVF). Our aim was to induce sperm capacitation with heparin or HA in order to study mAC and TK intracellular signals and their relation with cleavage and blastocyst rates after IVF as well as with the oxidative status of the potential bovine embryos. 2,5-dideoxyadenosine and genistein were used as mAC and TK inhibitors, respectively. Sperm capacitation was analyzed using CTC technique, sperm plasma membrane and acrosome integrity were determined using trypan blue stain and differential interference contrast, and mitochondrial activity was evaluated using fluorochrome JC-1. Cleavage rate was analyzed 48h and blastocyst production 7-8 days after IVF, while cytosolic oxidative activity was determined using RedoxSensor Red CC-1 fluorochrome 7h after IVF. When mAC and TK inhibitors were added to sperm samples, only capacitation decreased significantly both in HA and heparin treated samples (P < 0.05), but plasma membrane and acrosome integrity percentages were not affected in any of these groups (P > 0.05). Sperm mitochondrial membrane potential only decreased in heparin treated samples in the presence of both inhibitors (P < 0.05). Oocytes activated with HA sperm treated samples with the addition of 2,5-dideoxyadenosine and genistein presented a lower cytosolic oxidative status than those activated with sperm treated with HA alone (P < 0.05). On the other hand, oocytes activated with heparin treated sperm samples presented a lower cytosolic oxidative status only in the presence of 2,5-dideoxyadenosine (P < 0.05). Therefore, mAC and TK present a differential participation in heparin and HA sperm induced capacitation and mitochondrial function as well as in IVF.

Bovine oviductal fluid (bOF) collected in the follicular or luteal phase of the estrous cycle exerts similar effects on ram sperm kinematics and acrosome reactivity in vitro

This study examined the effects of bovine oviductal fluid (bOF) obtained during the follicular or luteal phase of the estrous cycle on ram sperm kinematics, capacitation status and plasma membrane (PM) integrity at various time points during the 24-h incubation period. Fresh ram spermatozoa were selected using the swim-up technique and then incubated separately with either follicular phase (FbOF) or luteal phase (LbOF) bovine oviductal fluid added to Fert-TALP medium (positive control - POSControl) or in Fert-TALP medium without capacitating agents (negative control - NEGControl) at 38 °C under 5% CO₂. Incubation with FbOF or LbOF for 2 h and 4 h promoted an increase (P <  0.05) in most of the sperm motility parameters as compared with the NEGControl group, and bOF-induced changes in sperm kinematics were similar (P >  0.05) to those seen in the POSControl group. After 6 h of incubation, the stimulatory effect of FbOF or LbOF on ram sperm kinematics was no longer observed (P >  0.05). Sperm PM integrity was not affected (P >  0.05) by incubation in bOF-supplemented media or in absence of capacitating factors (NEGControl). Although neither FbOF nor LbOF had any effect on sperm capacitation rates, the proportion of acrosome-reacted spermatozoa was greater (P < 0.05) for bOF-containing media compared with the NEGControl group during the long incubation periods (18 h and 24 h). In conclusion, bOF from either follicular or luteal phase of the estrous cycle enhances ram sperm motility for up to 4 h and the rate of acrosome reaction after long (18-24 h) incubation periods without affecting sperm viability.

Identification of Rabbit Oviductal Fluid Proteins Involved in Pre-Fertilization Processes by Quantitative Proteomics

Oviductal fluid (ODF) proteins modulate and support reproductive processes in the oviduct. In the present study, proteins involved in the biological events that precede fertilization have been identified in the rabbit ODF proteome, isolated from the ampulla and isthmus of the oviduct at different time points within 8 h after intrauterine insemination. A workflow is used that integrates lectin affinity capture with stable-isotope dimethyl labeling prior to nanoLC-MS/MS analysis. In total, over 400 ODF proteins, including 214 lectin enriched glycoproteins, are identified and quantified. Selected data are validated by Western blot analysis. Spatiotemporal alterations in the abundance of ODF proteins in response to insemination are detected by global analysis. A subset of 63 potentially biologically relevant ODF proteins is identified, including extracellular matrix components, chaperones, oxidoreductases, and immunity proteins. Functional enrichment analysis reveals an altered peptidase regulator activity upon insemination. In addition to protein identification and abundance changes, N-glycopeptide analysis further identifies 281 glycosites on 199 proteins. Taken together, these results show, for the first time, the evolving oviductal milieu early upon insemination. The identified proteins are likely those that modulate in vitro processes, including spermatozoa function.

Effect of bovine oviductal fluid on motility, tyrosine phosphorylation, and acrosome reaction in cryopreserved bull spermatozoa

This study was conducted to investigate the complex interactions between oviducts and cryopreserved spermatozoa. Herein we report the dynamic changes in bull sperm functions during in vitro incubation with bovine estrus and luteal oviductal fluid. Frozen-thawed bull spermatozoa was incubated either in non-capacitating medium, capacitating medium, non-capacitating medium containing 20% v/v estrus oviductal fluid or non-capacitating medium containing 20% v/v luteal oviductal fluid for 6 h at 38 °C under 5% CO₂. At hourly interval spermatozoa were evaluated for kinematics, tyrosine phosphorylation and acrosome reaction. The sperm velocity parameters were higher (P < 0.05) in capacitating medium compared to the other treatments. At 4 and 5 h of incubation, the proportion of live tyrosine phosphorylated spermatozoa was higher (P < 0.05) in estrus oviductal fluid compared to all other treatments. From 4 to 6 h of incubation the proportion of live acrosome reacted spermatozoa was higher (P < 0.05) in estrus oviductal fluid compared to the other treatments. We conclude that estrus oviductal fluid induced tyrosine phosphorylation and acrosome reaction in a higher proportion of frozen-thawed bull spermatozoa compared to luteal oviductal fluid, although sperm kinematics were not significantly influenced by oviductal during incubation.

Sperm function during incubation with oestrus oviductal fluid differs in bulls with different fertility

Spermatozoa undergo several modifications in the oviduct before acquiring fertilising capacity. Although spermatozoa are exposed to similar conditions in the oviduct, the speed of the response varies with the male and the state of the spermatozoa. We hypothesised that spermatozoa from bulls with different fertility may differ in their ability to respond to oviductal fluid (ODF). Frozen-thawed spermatozoa from four bulls were incubated with oestrus oviductal fluid (OODF) for 6h. Sperm kinematics, tyrosine phosphorylation, phosphorylation patterns, capacitation and acrosome reaction were analysed at hourly intervals. The amplitude of lateral head displacement (ALH) and straightness coefficient (STR) were higher (P<0.05) in bulls with higher fertility compared with those with lower fertility, at 1-4h of incubation. At 4h of incubation and onwards, spermatozoa from bulls with higher fertility showed a lower degree (P<0.05) of tyrosine phosphorylation and higher degree of capacitation and acrosome reaction. At least five tyrosine-phosphorylated sperm proteins were detected in all bulls. However, the expression of two phosphorylated sperm proteins (183 and 109 kDa) was upregulated in bulls with lower fertility. It may be concluded that cryopreserved spermatozoa from high- and low- fertile bulls differ in their ability to respond to OODF. This may help in developing tools for assessing fertility of bulls, once validated in more animals.

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.

Identification by proteomics of oviductal sperm-interacting proteins

The interactions between oviductal fluid (OF) proteins and spermatozoa play major roles in sperm selection, storage and capacitation before fertilization. However, only a few sperm-interacting proteins in the OF has been identified and very little is known about the regulation of sperm-oviduct interactions across the estrous cycle. Samples of bovine frozen-thawed sperm from three bulls were incubated with OF at pre-, post-ovulatory stages (Pre-/Post-ov) or luteal phase (LP) of the estrous cycle (7 mg/mL proteins, treated groups) or with a protein-free media (control). The proteomes of sperm cells were assessed by nanoLC-MS/MS and quantified by label-free methods. A total of 27 sperm-interacting proteins originating in the OF were identified. Among those, 14 were detected at all stages, eight at Post-ov and LP and five only at LP. The sperm-interacting proteins detected at all stages or at LP and Post-ov were on average more abundant at LP than at other stages (P < 0.05). At Pre-ov, OVGP1 was the most abundant sperm-interacting protein while at Post-ov, ACTB, HSP27, MYH9, MYH14 and OVGP1 were predominant. Different patterns of abundance of sperm-interacting proteins related to the stage were evidenced, which greatly differed from those previously reported in the bovine OF. In conclusion, this study highlights the important regulations of sperm-oviduct interactions across the estrous cycle and provides new protein candidates that may modulate sperm functions.

The ubiquitous hyaluronan: Functionally implicated in the oviduct?

Hyaluronan (hyaluronic acid) is a simple, nonantigenic, nonsulfated glycosaminoglycan present everywhere in the extracellular compartments of the body. Noteworthy, it is highly conserved phylogenetically, from sauropsida to mammals; and plays a plethora of roles from embryonic/fetal development to adult physiological and pathological events, including tumor development. In reproduction, hyaluronan has proven related to initial events as sperm survival, buildup of the sperm reservoir in the oviduct, regulation of sperm capacitation, and prefertilization to later participate in embryo, fetal, and placental development. Synthesis, binding (via the CD44 membrane receptor), and degradation of hyaluronan occur in male and female genital organs, the oviduct being no exception. This review discusses our current knowledge on roles of this ubiquitous glycosaminoglycan on the survival of immunologically foreign spermatozoa in the pig oviduct, a relevant event for fertility. During preovulatory storage in the functional tubal sperm reservoir, spermatozoa are entrapped in a mucus-like tubal fluid. This fluid contains fluctuating levels of hyaluronan, which is synthesized by the lining epithelium by hyaluronan synthase 3. Both hyaluronan and its CD44 receptor are particularly evident in the deep mucosal furrows of the sperm reservoir, in which most spermatozoa are embedded in; kept alive, uncapacitated but also undetected by the immune system of the female. Hyaluronan is also present in the seminal plasma, and evidence points toward an involvement of hyaluronan and its receptor in the local (tubal and possibly uterine) production of antiinflammatory cytokines, such as interleukin-10, pertaining maternal immune tolerance of these foreign cells.

Cryopreservation of ram semen in extenders containing soybean lecithin as cryoprotectant and hyaluronic acid as antioxidant

A soybean lecithin-based extender supplemented with hyaluronic acid (HA) was assayed for effectiveness to improve the quality of frozen-thawed ram semen. HA has not been tested yet in an extender containing soybean lecithin for freezing ram semen. Thus, the aim of this study was to analyse the effects of soybean lecithin at 1% or 1.5% along with HA at 0, 0.5 and 1 mg ml(-1) in a Tris-based extender on the motion characteristics, membrane integrity (HOST), viability, GSH peroxidase (GSH-PX) activity, lipid peroxidation and acrosomal status after freezing-thawing. Semen was collected from four Mehraban rams during the breeding season and frozen in the six lecithin×HA extenders. The extender containing 1.5% lecithin supplemented with no HA yielded higher total motility (52.5%±1.6), viability (55.8%±1.6) and membrane integrity (44.5%±1.7), but the effects of the lecithin concentration did not reach signification. Linearity-related parameters, ALH, BCF, lipid peroxidation, GSH-PX activity, morphology and acrosomal status were not affected by the extender composition. In general, adding HA significantly decreased sperm velocity (1 mg ml(-1) HA), total motility (only with 1.5% lecithin), viability (1 mg ml(-1) HA for 1% lecithin; both concentrations for 1.5% lecithin) and membrane integrity. In conclusion, adding HA to the freezing extender supplemented with soybean lecithin failed to improve quality-related variables in ram semen. Increasing the lecithin content could have a positive effect, but further studies are needed.

Effect of Glycosaminoglycans on In vitro Fertilizing Ability and In vitro Developmental Potential of Bovine Embryos

The glycosaminoglycans (GAGs) present in the female reproductive tract promote sperm capacitation. When bovine sperm were exposed to 10 μg/ml of one of four GAGs (Chondroitin sulfate, CS; Dermatan sulfate, DS; Hyaluronic acid, HA; Heparin, HP) for 5 h, the total motility (TM), straight-line velocity (VSL), and curvilinear velocity (VCL) were higher in the HP- or HA-treated sperm, relative to control and CS- or DS-treated sperm. HP and HA treatments increased the levels of capacitated and acrosome-reacted sperm over time, compared to other treatment groups (p<0.05). In addition, sperm exposed to HP or HA for 1 h before IVF exhibited significantly improved fertilizing ability, as assessed by 2 pronucleus (PN) formation and cleavage rates at d 2. Exposure to these GAGs also enhanced in vitro embryo development rates and embryo quality, and increased the ICM and total blastocyst cell numbers at d 8 after IVF (p<0.05). A real-time PCR analysis showed that the expression levels of pluripotency (Oct 4), cell growth (Glut 5), and anti-apoptosis (Bax inhibitor) genes were significantly higher in embryos derived from HA- or HP-treated sperm than in control or other treatment groups, while pro-apoptotic gene expression (caspase-3) was significantly lower in all GAG treatment groups (p<0.05). These results demonstrated that exposure of bovine sperm to HP or HA positively correlates with in vitro fertilizing ability, in vitro embryo developmental potential, and embryonic gene expression.

Bovine oviductal monolayers cultured under three-dimension conditions secrete factors able to release spermatozoa adhering to the tubal reservoir in vitro

Different in vitro models have been developed to understand the interaction of gametes and embryos with the maternal reproductive tract. We recently showed that bovine oviductal monolayers three-dimensionally cultured in Gray's medium on collagen-coated microporous polycarbonate inserts under liquid-air interface conditions are well polarized, develop cilia, remain viable for at least 3 weeks postconfluence, and mantain the viability of bound spermatozoa significantly better than bidimensionally cultured monolayers. Herein, we used these culture conditions to understand whether: (1) spermatozoa adhering to three-dimensionally cultured oviductal monolayers can be released by heparin or penicillamine as previously shown with bidimensionally cultured oviductal monolayers and explants; and (2) media conditioned by three-dimensionally cultured oviductal monolayers were able to release spermatozoa adhering to oviductal explants. Findings demonstrated that (1) spermatozoa adhering to three-dimensionally cultured oviductal monolayers are readily released by heparin and penicillamine, (2) media conditioned by three-dimensionally cultured oviductal monolayers are able to release spermatozoa bound to oviductal explants, (3) do not depress sperm motility and viability, (4) they improve sperm kinetics, and (5) promote binding to the zona pellucida. In conclusion, in vitro data suggest that the release of spermatozoa adhering to the oviductal reservoir in vivo can be triggered by factors secreted by the oviduct itself that induce sperm capacitation.

Proteins from human oviductal tissue-conditioned medium modulate sperm capacitation

BACKGROUND

Spermatozoa acquire the ability to fertilize an oocyte when they become capacitated. Capacitation takes place when sperm pass through the female reproductive tract, interacting with female fluids. Both tyrosine phosphorylation of sperm proteins and the ability to respond to acrosome reaction (AR) inducers have been associated with sperm capacitation. Recent data indicate that conditioned media (CM) from human oviductal tissue culture decrease sperm affinity for the zona pellucida in vitro. Since capacitation enables the sperm-oocyte interaction, the aim of the present study was to investigate the effect of CM on events related to sperm capacitation and to assess whether these effects were permanent.

METHODS

Oviductal tissue was obtained from premenopausal patients (scheduled for hysterectomies because of uterine fibromyoma). The tissues were cultured as explants and CM were collected. Explant viability was assessed as tissue DNA integrity. Normozoospermic semen samples were obtained from healthy donors. Motile spermatozoa were incubated under capacitating conditions with or without increasing protein concentrations of CM for 6 or 22 h. Human follicular fluid-induced AR was detected by the Pisum sativum technique. Tyrosine phosphorylated proteins were detected with a monoclonal anti-phosphotyrosine antibody.

RESULTS

The incubation of spermatozoa in the presence of increasing concentrations of conditioned medium (CM) proteins caused a dose-dependent decrease in both tyrosine phosphorylation of sperm proteins and in the level of AR induction. When CM was removed from the sperm incubation media, the effects were reversed. Heat-inactivated CM did not affect either tyrosine phosphorylation or the induction of AR.

CONCLUSIONS

The present data suggest that proteins secreted from human oviductal tissue are able to inhibit events associated with sperm capacitation in vitro.

Effect of type of semen, time of insemination relative to ovulation and embryo transfer on early equine embryonic vesicle growth as determined by ultrasound

Embryonic vesicle growth in the mare is easily monitored by ultrasound. Apart from pregnancy diagnosis, assessment of the embryonic vesicle in practice is also useful to evaluate its viability. Although subject to individual variation, embryo growth rate follows a constant pattern in the early stages of development in relation to embryonic age. Previous studies have shown a significant effect of some factors routinely used in practice, such as post-ovulation insemination and embryo transfer, on embryonic growth and the time in which the vesicle is first detected. This study attempts to confirm previous results in different settings and characterise the causes for this delay in growth. A total of 159 pregnancies from different mating protocols: (1) pre-ovulation natural mating, (2) pre-ovulation natural mating and transfer into recipient mares, (3) post-ovulation natural mating, and (4) post-ovulation AI with frozen/thaw spermatozoa were evaluated ultrasonographically from day 12 to 19 of pregnancy and vesicle diameters recorded. Regression analysis between embryonic vesicle diameters and embryonic ages was performed for each group and mean vesicle diameter at different age periods among groups were tested for statistical difference with a general linear model of variance. There was no significant difference between groups 1 and 2 (P=0.73) or between groups 3 and 4 (P=0.71). However both pre-ovulation groups (1 and 2) had larger vesicle diameters (P<0.000) at any embryonic age analysed than either of the post-ovulation groups (3 and 4). In conclusion, post-ovulation inseminations produced pregnancies with smaller vesicle diameters equivalent to approximately 1 day's growth.

Fertilization and early embryonic development in the porcine fallopian tube

Fertilization and early embryo development relies on a complex interplay between the Fallopian tube and the gametes before and after fertilization. Thereby the oviduct, as a dynamic reproductive organ, enables reception, transport and maturation of male and female gametes, their fusion, and supports early embryo development. This paper reviews current knowledge regarding physiological processes behind the transport of boar spermatozoa, their storage in and release from the functional sperm reservoir (SR), and of the interactions that newly ovulated oocytes play within the tube during their transport to the site of fertilization. Experimental evidence of an ovarian control on sperm release from the SR is highlighted. Furthermore, the impact of oviductal secretion on sperm capacitation, oocyte maturation, fertilization and early embryo development is stressed.

Biofluid mechanics of the human reproductive process: modelling of the complex interaction and pathway to the oocytes

Recent revelations in the human reproductive process have fuelled much interest in this field of study. In particular, the once prevailing view of large numbers of ejaculated sperms racing towards the egg has been refuted recently. This is opposed to the current views derived from numerous clinical findings that state that only a very small number of sperms will ever enter the oviduct. It is believed that these few sperms must have been guided to make the long, tedious and obstructed journey to the egg. For a mature spermatozoon, its hyperactivated swimming motility upon capacitation plays an important role in the fertilization of a mature egg. Likewise, the female genital tract also provides guiding mechanisms to complement the survival of normal hydrodynamic profile sperms and thus promotes an eventual sperm–egg interaction. Understanding these mechanisms can be essential for the derivation of assisted conception techniques especially those in vitro. With the aid of computational models and simulation, suitability and effectiveness of novel assisted conception methodology can be assessed, particularly for those yet to be ready for clinical trials. This review discusses the possible bioengineering models and the mechanisms by which human spermatozoa are guided to the egg.

Effect of chondroitin sulfate C on sperm capacitation and fertilization parameters in vitro in pigs

The objective of this study was to determine the effects of chondroitin sulfate C (CS-C) on sperm capacitation and fertilization parameters in vitro in pigs. Frozen-thawed ejaculated pig sperm (semen S-484) were incubated with fertilization medium containing CS-C (0-2mg/ml) for 1h and the capacitation rate with chlorotetracycline (CTC) assay was examined, which showed that CS-C increased the rate of incapacitation F pattern spermatozoa converted to capacitation B pattern sperm cell in concentration-dependent manner and mostly increased capacitation B pattern sperm cell and decreased acrosome reaction AR pattern sperm cell in 1mg/ml concentration. When sperm was incubated for 1, 2 and 4h in fertilization medium containing 1mg/ml CS-C, it showed that the capacitated B pattern sperm cell was significantly (p<0.01) increased and the AR pattern sperm cell was significantly decreased at each time point in the presence than in the absence of CS-C. For identifying the validity of CS-C in sperm capacitation, sperm-oocyte was inseminated in fertilization medium containing CS-C (0-2mg/ml) and the rate of fertilized oocytes was examined, which showed that the penetration rates significantly (p<0.05) increased from 0.5 to 1.0mg/ml concentrations (87.4-96.3%) compared with control (74.9%). For identifying the universality of CS-C in sperm capacitation, four different semens (boar S-484, S-454, D-815 and D-748) were incubated in fertilization medium containing CS-C (1mg/ml) for 2h, respectively, which showed that CS-C increased the rate of capacitation B pattern sperm cell and decreased acrosome reaction AR pattern sperm cell in each semen. And it showed that CS-C yielded a higher promote effect (93.9%, 83.9%, 60.7% and 44.9%, respectively) on sperm penetration compared to unaddition control (63.4%, 22.0%, 3.3% and 3.3%, respectively). Sperm-oocyte binding analysis showed that CS-C increased the number of sperm bound to oocyte compared unaddition control in each semen. These results suggested that CS-C is the efficient factor on sperm capacitation in pigs, CS-C may promote sperm from the incapacitated to capacitated state and sequentially prevent sperm from spontaneous acrosome reaction, and thus facilitate the sperm-zona binding and sperm penetration to oocyte.

Controlled cooling during semen cryopreservation does not induce capacitation of spermatozoa from two portions of the boar ejaculate

Cryopreservation imposes dramatic changes in boar sperm survivability but it is as yet unclear which part of the process affects the spermatozoa the most. The present study monitored, along the entire process of cryopreservation, the stability (PMS) of the architecture of the lipid plasma membrane and its integrity (PMI), as well as the kinetics of the processed spermatozoa using two portions from the boar ejaculate (P1 = the first 10 mL of the sperm-rich fraction, SRF; P2 = the rest of the ejaculate), frozen in a recently developed package, the MiniFlatPack (MFPs, 0.5 x 10(9) sperm/dose). Evaluation was made at four specific stages, viz. S1 = after collection (suspended in Beltsville thawing solution, BTS); S2 = at 15 degrees C (suspended in lactose-egg yolk, LEY); S3 = at 5 degrees C (suspended in LEY plus glycerol); and S4 = post-thaw. Both sperm kinetics (using computer-assisted sperm analysis, CASA) and PMS [i.e. the degree of lipid disorder and of the exteriorization of phosphatidylserine (PS) in the plasma membrane, measured by flow cytometry using Merocyanine-540 (M-540), and Annexin-V (AV) respectively], as well as plasma membrane integrity [PMI, i.e. the degree of membrane damage, measured using Yo-Pro-1 or propidium iodide (PI)] were assessed after incubation in BTS at 38 degrees C. Moreover, spermatozoa were challenged by incubation in modified Brackett-Oliphant medium (mBO+) with 37 mm of bicarbonate at 38 degrees C for 30 min, and their PMS and PMI further explored. Total sperm motility was significantly higher in P1 than in P2 along the entire process (S1-S4; p < 0.01), decreasing significantly at S4 for both fractions (p < 0.0001). The proportion of spermatozoa showing linear motility (LinM) was similar between ejaculate portions (P1 and P2), with a significant increase post-thaw (S4; p < 0.0001). During cooling (S1-S3) but not post-thaw (S4), lateral head displacement (LHD) differed between portions and changed along the stages (p < 0.01). Sperm velocity differed between portions in S1 (p < 0.01), but remained similar, independently of the portion, thereafter (S2-S4). Both PMS and the total number of live spermatozoa remained similar between S1 and S3 while incubated in BTS for both ejaculate portions. Sperm mortality increased post-thaw (S4) in both portions but the degree of lipid disorder remained low in the live cells (1.28% for P1; 1.55% for P2). Exposure to mBO+, on the other hand, significantly increased membrane lipid disorder along cooling (S1-S3; p < 0.0001), increasing the percentages of dead spermatozoa, especially post-thaw (around 70%, both portions). PS-exteriorization (AV) was not evident along the cryopreservation process in control (BTS) samples and exposure to mBO+ only induced minor variations. The data showed that kinetics, PMS and PMI of boar spermatozoa suspended in BTS (S1), LEY (S2) or LEY plus glycerol (S3) were maintained during controlled cooling but were altered by thawing, showing more characteristics of cell injury than of sperm capacitation. The spermatozoa were able to capacitate but the bicarbonate challenge destabilized the plasma membrane during initial cooling and accelerated membrane changes post-thaw. We conclude that capacitation of boar spermatozoa does not occur during controlled cooling.

Role of the oviduct in sperm capacitation

Following insemination of spermatozoa pre-ovulation, the mammalian oviduct ensures, by the formation of a functional sperm reservoir (SR), that suitable (low) numbers of viable and potentially fertile spermatozoa are available for fertilization at the ampullary isthmic junction (AIJ). As ovulation approaches, a proportion of the SR-stored spermatozoa is continuously distributed towards the AIJ and individually activated leading to step-wise capacitation and the attainment of hyperactivated motility. This paper reviews in vivo changes in the intra-luminal milieu of the oviduct of pigs and cows, in particular the SR and the AIJ which relate to the modulation of sperm capacitation around spontaneous ovulation. In vivo, most viable spermatozoa in the pre-ovulatory SR are uncapacitated. Capacitation rates significantly increase after ovulation, apparently not massively but concurrent with the individual, continuous sperm dislocation from the SR. Bicarbonate, whose levels differ between the SR and the AIJ, appears as the common primary effector of the membrane destabilizing changes that encompasses the first stages of capacitation. Sperm activation can be delayed or even reversed by co-incubation with membrane proteins of the tubal lining, isthmic fluid or specific tubal glycosaminoglycans, such as hyaluronan. Although the pattern of response to in vitro induction of sperm activation - capacitation in particular - is similar for all spermatozoa, the capacity and speed of the response is very individual. Such diversity in responsiveness among spermatozoa insures full sperm viability before ovulation and the presence of spermatozoa at different stages of capacitation at the AIJ, thus maximizing the chances of normal fertilization.

Heparin and dermatan sulphate induced capacitation of frozen-thawed bull spermatozoa measured by merocyanine-540

Glycosaminoglycans (GAGs) are present in the oviduct in which the major part of sperm capacitation occurs. In this study we have tested how capacitation of frozen-thawed bull spermatozoa is effected by exposure to different GAGs detectable or possibly present in oviductal fluid; i.e. heparin, hyaluronan, heparan sulphate, dermatan sulphate and chondroitin sulphate. Following exposure of different duration, the spermatozoa were stained with either Chlortetracycline (CTC) or merocyanine-540 and evaluated with epifluorescent light microscopy or flow cytometry, respectively. Heparin elicited a significant increase in the number of alive, capacitated spermatozoa, either expressed as higher merocyanine-540 fluorescence (p < 0.0001) or as B-pattern (p = 0.0021) in the CTC assay, during 4 h of incubation. When comparing the different GAG treatments one by one to the negative control in the flow cytometric study, only heparin and dermatan sulphate were significant (p < 0.0001) higher than the control at 0–30 min of incubation. Duration of incubation did not affect the proportion of capacitated spermatozoa when measured as merocyanine-540 fluorescence or CTC B-pattern, but the length of the incubation did affect the number of dead (Yo-PRO 1 positive) spermatozoa (p < 0.0001). Exposure to zona pellucida proteins significantly increased the proportion of acrosome reacted spermatozoa (p = 0.016). Both heparin and dermatan sulphate induce capacitation of frozen-thawed bull spermatozoa in vitro.

Determinants of sperm quality and fertility in domestic species

Fertilization success cannot be attributed solely to the absolute number of vital, motile, morphologically normal spermatozoa inseminated into the female but more especially to their functional competence. A range ofin vitrotests has therefore been developed to monitor crucial aspects of sperm function: their ability to adapt to changing osmotic conditions, to bind to the oviductal epithelium, and to undergo capacitation in an appropriate and timely manner. The tests employ flow cytometry in conjunction with fluorescent techniques, electronic cell counting, and computer-assisted image area analysis. The highly quantitative analysis provided by electronic sizing and flow cytometry enables assessment of representative cell numbers in a very short time with high reproducibility. More importantly, it allows the detection of physiological heterogeneity within an ejaculate in terms of the development of cell subpopulations and enables the kinetic analysis of changes in living cell suspensions. The tests offer a promising strategy for evaluating fertility in domestic animals. The capability for volume regulation ensures that sperm recover from the tonic shocks experienced at ejaculation and during cryopreservation. Assessment of capacitationin vitroprovides valuable information on both the sperm’s ability to respond to fertilizing conditions and the sequence and rates of ongoing capacitation/destabilization processes. The monitoring of response to capacitating conditions in kinetic terms allows the sensitive and adequate detection of sperm populations expressing fertilization attributes and their ability to respond to external stimuli in a timely manner. However, subfertility is likely to be associated with a suboptimal response (i.e. too high or too low) rather than a minimal response.

State of the art in farm animal sperm evaluation

Our ability to screen the structural and functional integrity of the spermatozoon in vitro has increased markedly over the past decades, but our capacity to estimate the fertility of a semen sample or of the sire from which it has been collected, especially in selected farm animal breeders, has not. The estimation of fertility is constrained by several factors (e.g. type of cell, analysis strength, sperm deposition strategies, recordings of fertility), including the fact that the ejaculate is composed of a diverse sperm population. Such cell heterogeneity is reflected not only in differences in the intactness of attributes needed for fertilisation, such as motility or morphology, but also in the relative ability of the spermatozoa to remain fertile over time, to sustain selection steps and responses to exogenous stimuli similar to those during sperm transport in the female genital tract, all of which account for innate variations in the fertilising ability among doses, ejaculates and sires. Determination of how large such a sperm population with competence for fertilisation and in-built ability to display these attributes under physiological signalling is would allow for a better estimation o f fertility, provided that th e particular s ire produces this sub-population in a repeatable manner. The value of these analyses is discussed in the present paper.

Can we increase the estimated value of semen assessment?

Estimating the fertility of a semen sample or of the male from where it has been collected by simple assessment of in vitro sperm characteristics is still difficult, owing to the variable correlations that laboratory results achieve with in vivo fertility. A major reason behind these variations is the fact that the ejaculate and the artificial insemination (AI)-doses it generates are composed of a diverse sperm population. Such heterogeneity is reflected both in differences of intactness of attributes needed for fertilization, such as motility or morphology, but also in the relative ability of spermatozoa to prevail fertile over time, handling and exposure to different stimuli, all of which account for innate variations in fertilizing ability among doses, ejaculates and sires. However, methods are already available to select sub-populations of intact spermatozoa which can be tested for their degree of competence for fertilization and whose estimated power is promising, allowing the elimination of cases of sub-fertility, particularly in bovine. Examples of these methods are the separation of viable spermatozoa by swim-up or discontinuous gradient centrifugation, followed by testing the ability of the selected spermatozoa to dose-response/time sustain capacitation and acrosome reaction induction. Finding how large a sperm population with non-compensated attributes for fertilization and ability to display and sustain stimuli is, perhaps by a quick screening of membrane integrity and stability by multi-parametric methods, would allow, provided the particular male produces this sub-population in a repeatable manner, for a better estimation of fertility.