Ion channels, phosphorylation and mammalian sperm capacitation

Metabolic Shift in Porcine Spermatozoa during Sperm Capacitation-Induced Zinc Flux

Mammalian spermatozoa rely on glycolysis and mitochondrial oxidative phosphorylation for energy leading up to fertilization. Sperm capacitation involves a series of well-regulated biochemical steps that are necessary to give spermatozoa the ability to fertilize the oocyte. Additionally, zinc ion (Zn2+) fluxes have recently been shown to occur during mammalian sperm capacitation. Semen from seven commercial boars was collected and analyzed using image-based flow cytometry before, after, and with the inclusion of 2 mM Zn2+ containing in vitro capacitation (IVC) media. Metabolites were extracted and analyzed via Gas Chromatography-Mass Spectrometry (GC-MS), identifying 175 metabolites, with 79 differentially abundant across treatments (p < 0.05). Non-capacitated samples showed high levels of respiration-associated metabolites including glucose, fructose, citric acid, and pyruvic acid. After 4 h IVC, these metabolites significantly decreased, while phosphate, lactic acid, and glucitol increased (p < 0.05). With zinc inclusion, we observed an increase in metabolites such as lactic acid, glucitol, glucose, fructose, myo-inositol, citric acid, and succinic acid, while saturated fatty acids including palmitic, dodecanoic, and myristic acid decreased compared to 4 h IVC, indicating regulatory shifts in metabolic pathways and fatty acid composition during capacitation. These findings underscore the importance of metabolic changes in improving artificial insemination and fertility treatments in livestock and humans.

Influence of BMI, Cigarette Smoking and Cryopreservation on Tyrosine Phosphorylation during Sperm Capacitation

Capacitation involves tyrosine phosphorylation (TP) as a key marker. Lifestyle-related factors, such as obesity and smoking, are recognized for their adverse effects on semen quality and male fertility, yet the underlying mechanisms, including their potential impact on TP, remain unclear. Moreover, the effect of sperm cryopreservation on TP at the human sperm population level is unexplored. Flow cytometry analysis of global TP was performed on pre-capacitated, post-capacitated and 1- and 3-hours' incubated fresh and frozen-thawed samples from sperm donors (n = 40). Neither being overweight nor smoking (or both) significantly affected the percentage of sperm showing TP. However, elevated BMI and smoking intensity correlated with heightened basal TP levels (r = 0.226, p = 0.003) and heightened increase in TP after 3 h of incubation (r = 0.185, p = 0.017), respectively. Cryopreservation resulted in increased global TP levels after capacitation but not immediately after thawing. Nonetheless, most donors' thawed samples showed increased TP levels before and after capacitation as well as after incubation. Additionally, phosphorylation patterns in fresh and frozen-thawed samples were similar, indicating consistent sample response to capacitation stimuli despite differences in TP levels. Overall, this study sheds light on the potential impacts of lifestyle factors and cryopreservation on the dynamics of global TP levels during capacitation.

pH Homeodynamics and Male Fertility: A Coordinated Regulation of Acid-Based Balance during Sperm Journey to Fertilization

pH homeostasis is crucial for spermatogenesis, sperm maturation, sperm physiological function, and fertilization in mammals. HCO3- and H+ are the most significant factors involved in regulating pH homeostasis in the male reproductive system. Multiple pH-regulating transporters and ion channels localize in the testis, epididymis, and spermatozoa, such as HCO3- transporters (solute carrier family 4 and solute carrier family 26 transporters), carbonic anhydrases, and H+-transport channels and enzymes (e.g., Na+-H+ exchangers, monocarboxylate transporters, H+-ATPases, and voltage-gated proton channels). Hormone-mediated signals impose an influence on the production of some HCO3- or H+ transporters, such as NBCe1, SLC4A2, MCT4, etc. Additionally, ion channels including sperm-specific cationic channels for Ca2+ (CatSper) and K+ (SLO3) are directly or indirectly regulated by pH, exerting specific actions on spermatozoa. The slightly alkaline testicular pH is conducive to spermatogenesis, whereas the epididymis's low HCO3- concentration and acidic lumen are favorable for sperm maturation and storage. Spermatozoa pH increases substantially after being fused with seminal fluid to enhance motility. In the female reproductive tract, sperm are subjected to increasing concentrations of HCO3- in the uterine and fallopian tube, causing a rise in the intracellular pH (pHi) of spermatozoa, leading to hyperpolarization of sperm plasma membranes, capacitation, hyperactivation, acrosome reaction, and ultimately fertilization. The physiological regulation initiated by SLC26A3, SLC26A8, NHA1, sNHE, and CFTR localized in sperm is proven for certain to be involved in male fertility. This review intends to present the key factors and characteristics of pHi regulation in the testes, efferent duct, epididymis, seminal fluid, and female reproductive tract, as well as the associated mechanisms during the sperm journey to fertilization, proposing insights into outstanding subjects and future research trends.

The uniqueness of on-demand male contraception

Because nearly half of pregnancies worldwide are unintended, available contraceptive methods are inadequate. Moreover, due to the striking imbalance between contraceptive options available for men compared to the myriad of options available to women, there is an urgent need for new methods of contraception for men. This review summarizes ongoing efforts to develop male contraceptives highlighting the unique aspects particular to on-demand male contraception, where a man takes a contraceptive only when and as often as needed.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Flagellar pH homeostasis mediated by Na+/H+ exchangers regulates human sperm functions through coupling with CatSper and KSper activation

STUDY QUESTION

Whether and how do Na+/H+ exchangers (NHEs) regulate the physiological functions of human sperm?

SUMMARY ANSWER

NHE-mediated flagellar intracellular pH (pHi) homeostasis facilitates the activation of the pH-sensitive, sperm-specific Ca2+ channel (CatSper) and the sperm-specific K+ channel (KSper), which subsequently modulate sperm motility, hyperactivation, flagellar tyrosine phosphorylation, and the progesterone (P4)-induced acrosome reaction.

WHAT IS KNOWN ALREADY

Sperm pHi alkalization is an essential prerequisite for the acquisition of sperm-fertilizing capacity. Different sperm functions are strictly controlled by particular pHi regulatory mechanisms. NHEs are suggested to modulate sperm H+ efflux.

STUDY DESIGN, SIZE, DURATION

This was a laboratory study that used samples from >50 sperm donors over a period of 1 year. To evaluate NHE action on human sperm function, 5-(N,N-dimethyl)-amiloride (DMA), a highly selective inhibitor of NHEs, was utilized. All experiments were repeated at least five times using different individual sperm samples or cells.

PARTICIPANTS/MATERIALS, SETTING, METHODS

By utilizing the pH fluorescent indicator pHrodo Red-AM, we detected alterations in single-cell pHi value in human sperm. The currents of CatSper and KSper in human sperm were recorded by the whole-cell patch-clamp technique. Changes in population and single-cell Ca2+ concentrations ([Ca2+]i) of human sperm loaded with Fluo 4-AM were measured. Membrane potential (Vm) and population pHi were quantitatively examined by a multimode plate reader after sperm were loaded with 3,3'-dipropylthiadicarbocyanine iodide and 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester, respectively. Sperm motility parameters were assessed by a computer-assisted semen analysis system. Tyrosine phosphorylation was determined by immunofluorescence, and sperm acrosome reaction was evaluated by Pisum sativum agglutinin-FITC staining.

MAIN RESULTS AND THE ROLE OF CHANCE

DMA-induced NHEs inhibition severely acidified the human sperm flagellar pHi from 7.20 ± 0.04 to 6.38 ± 0.12 (mean ± SEM), while the effect of DMA on acrosomal pHi was less obvious (from 5.90 ± 0.13 to 5.57 ± 0.12, mean ± SEM). The whole-cell patch-clamp recordings revealed that NHE inhibition remarkably suppressed alkalization-induced activation of CatSper and KSper. As a consequence, impairment of [Ca2+]i homeostasis and Vm maintenance were detected in the presence of DMA. During the capacitation process, pre-treatment with DMA for 2 h potently decreased sperm pHi, which in turn decreased sperm motility and kinetic parameters. Sperm capacitation-associated functions, including hyperactivation, tyrosine phosphorylation, and P4-induced acrosome reaction, were also compromised by NHE inhibition.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This was an in vitro study. Caution should be taken when extrapolating these results to in vivo applications.

WIDER IMPLICATIONS OF THE FINDINGS

This study revealed that NHEs are important physiological regulators for human CatSper and KSper, which are indispensable for human sperm fertility, suggesting that malfunction of NHEs could be an underlying mechanism for the pathogenesis of male infertility.

FUNDING/COMPETING INTEREST(S)

This work was supported by the National Natural Science Foundation of China (32271167 and 81871202 to X.Z.), Jiangsu Innovation and Entrepreneurship Talent Plan (JSSCRC20211543 to X.Z.), the Social Development Project of Jiangsu Province (No. BE2022765 to X.Z.), the Society and livelihood Project of Nantong City (No. MS22022087 to X.Z.), and the Natural Science Foundation of Jiangsu Province (BK20220608 to H.K.). The authors have no competing interests to declare.

Inhibition of phospholipase C reduces the capacitation of cryopreserved ovine sperm

This study aimed to evaluate the effect of phospholipase C (PLC) on the capacitation of cryopreserved ovine semen. Sixteen semen samples were cryopreserved with diluent added by 0, 10, or 20 μM of U73122, a PLC inhibitor. The sperm kinetics of the thawed samples were evaluated using the "Computer-assisted Sperm Analysis" system, and the integrity of the plasma and mitochondrial membranes was evaluated using fluorescent probes. Additionally, sperm capacitation and the acrosome reaction with chlortetracycline hydrochloride were evaluated before and after capacitation induction. The results were analysed using analysis of variance and Tukey's test with a 95% probability. Concentrations of 10 or 20 μM of U73122 did not affect the kinetics or number of sperm with intact plasma and mitochondrial membranes. However, after thawing, 10 and 20 μM of the inhibitor reduced the percentage of capacitated and acrosome-reacted sperm. After induction of capacitation, there was a reduction in the number of non-capacitated sperm in all treatment groups, suggesting a reversible effect of U73122. In conclusion, U73122 at concentrations of 10 or 20 μM prevents premature capacitation and acrosome reaction induced by the freezing procedure, without affecting the kinetics and integrity of the sperm membranes.

Mechanisms That Protect Mammalian Sperm from the Spontaneous Acrosome Reaction

To acquire the capacity to fertilize the oocyte, mammalian spermatozoa must undergo a series of biochemical reactions in the female reproductive tract, which are collectively called capacitation. The capacitated spermatozoa subsequently interact with the oocyte zona-pellucida and undergo the acrosome reaction, which enables the penetration of the oocyte and subsequent fertilization. However, the spontaneous acrosome reaction (sAR) can occur prematurely in the sperm before reaching the oocyte cumulus oophorus, thereby jeopardizing fertilization. One of the main processes in capacitation involves actin polymerization, and the resulting F-actin is subsequently dispersed prior to the acrosome reaction. Several biochemical reactions that occur during sperm capacitation, including actin polymerization, protect sperm from sAR. In the present review, we describe the protective mechanisms that regulate sperm capacitation and prevent sAR.

Characterization of acrosin and acrosin binding protein as novel CRISP2 interacting proteins in boar spermatozoa

BACKGROUND

Previously, we reported that cysteine-rich secretory protein 2 is involved in high molecular weight complexes in boar spermatozoa. These cysteine-rich secretory protein 2protein complexes are formed at the last phase of sperm formation in the testis and play a role in sperm shaping and functioning.

OBJECTIVES

This study aimed to identify cysteine-rich secretory protein 2 interacting partners. These binding partner interactions were investigated under different conditions, namely, non-capacitating conditions, after the induction of in vitro sperm capacitation and subsequently during an ionophore A23187-induced acrosome reaction.

MATERIALS AND METHODS

The incubated pig sperm samples were subjected to protein extraction. Extracted proteins were subjected to blue native gel electrophoresis and native immunoblots. Immunoreactive gel bands were excised and subjected to liquid chromatography-mass spectrometry (LC-MS) analysis for protein identification. Protein extracts were also subjected to CRISP2 immunoprecipitation and analyzed by LC-MS for protein identification. The most prominent cystein-rich secretory protein 2 interacting proteins that appeared in both independent LC-MS analyses were studied with a functional in situ proximity interaction assay to validate their property to interact with cystein-rich secretory protein 2 in pig sperm.

RESULTS

Blue native gel electrophoresis and native immunoblots revealed that cystein-rich secretory protein 2 was present within a ∼150 kDa protein complex under all three conditions. Interrogation of cystein-rich secretory-protein 2-immunoreactive bands from blue native gels as well as cystein-rich secretory protein 2 immunoprecipitated products using mass spectrometry consistently revealed that, beyond cystein-rich secretory protein 2, acrosin and acrosin binding protein were among the most abundant interacting proteins and did interact under all three conditions. Co-immunoprecipitation and immunoblotting indicated that cystein-rich secretory protein 2 interacted with pro-acrosin (∼53 kDa) and Aacrosin binding protein under all three conditions and additionally to acrosin (∼35 kDa) after capacitation and the acrosome reaction. The colocalization of these interacting proteins with cystein-rich secretory protein 2 was assessed via in situ proximity ligation assays. The colocalization signal of cystein-rich secretory protein 2 and acrosin in the acrosome seemed dispersed after capacitation but was consistently present in the sperm tail under all conditions. The fluorescent foci of cystein-rich secretory protein 2 and acrsin binding protein colocalization appeared to be redistributed within the sperm head from the anterior acrosome to the post-acrosomal sheath region upon capacitation.

DISCUSSION AND CONCLUSION

These results suggest that CRISP2 may act as a scaffold for protein complex formation and dissociation to ensure the correct positioning of proteins required for the acrosome reaction and zona pellucida penetration.

Advances in non-hormonal male contraception targeting sperm motility

BACKGROUND

The high rates of unintended pregnancy and the ever-growing world population impose health, economic, social, and environmental threats to countries. Expanding contraceptive options, including male methods, are urgently needed to tackle these global challenges. Male contraception is limited to condoms and vasectomy, which are unsuitable for many couples. Thus, novel male contraceptive methods may reduce unintended pregnancies, meet the contraceptive needs of couples, and foster gender equality in carrying the contraceptive burden. In this regard, the spermatozoon emerges as a source of druggable targets for on-demand, non-hormonal male contraception based on disrupting sperm motility or fertilization.

OBJECTIVE AND RATIONALE

A better understanding of the molecules governing sperm motility can lead to innovative approaches toward safe and effective male contraceptives. This review discusses cutting-edge knowledge on sperm-specific targets for male contraception, focusing on those with crucial roles in sperm motility. We also highlight challenges and opportunities in male contraceptive drug development targeting spermatozoa.

SEARCH METHODS

We conducted a literature search in the PubMed database using the following keywords: 'spermatozoa', 'sperm motility', 'male contraception', and 'drug targets' in combination with other related terms to the field. Publications until January 2023 written in English were considered.

OUTCOMES

Efforts for developing non-hormonal strategies for male contraception resulted in the identification of candidates specifically expressed or enriched in spermatozoa, including enzymes (PP1γ2, GAPDHS, and sAC), ion channels (CatSper and KSper), transmembrane transporters (sNHE, SLC26A8, and ATP1A4), and surface proteins (EPPIN). These targets are usually located in the sperm flagellum. Their indispensable roles in sperm motility and male fertility were confirmed by genetic or immunological approaches using animal models and gene mutations associated with male infertility due to sperm defects in humans. Their druggability was demonstrated by the identification of drug-like small organic ligands displaying spermiostatic activity in preclinical trials.

WIDER IMPLICATIONS

A wide range of sperm-associated proteins has arisen as key regulators of sperm motility, providing compelling druggable candidates for male contraception. Nevertheless, no pharmacological agent has reached clinical developmental stages. One reason is the slow progress in translating the preclinical and drug discovery findings into a drug-like candidate adequate for clinical development. Thus, intense collaboration among academia, private sectors, governments, and regulatory agencies will be crucial to combine expertise for the development of male contraceptives targeting sperm function by (i) improving target structural characterization and the design of highly selective ligands, (ii) conducting long-term preclinical safety, efficacy, and reversibility evaluation, and (iii) establishing rigorous guidelines and endpoints for clinical trials and regulatory evaluation, thus allowing their testing in humans.

The Role of Sperm Membrane Potential and Ion Channels in Regulating Sperm Function

During the last seventy years, studies on mammalian sperm cells have demonstrated the essential role of capacitation, hyperactivation and the acrosome reaction in the acquisition of fertilization ability. These studies revealed the important biochemical and physiological changes that sperm undergo in their travel throughout the female genital tract, including changes in membrane fluidity, the activation of soluble adenylate cyclase, increases in intracellular pH and Ca2+ and the development of motility. Sperm are highly polarized cells, with a resting membrane potential of about -40 mV, which must rapidly adapt to the ionic changes occurring through the sperm membrane. This review summarizes the current knowledge about the relationship between variations in the sperm potential membrane, including depolarization and hyperpolarization, and their correlation with changes in sperm motility and capacitation to further lead to the acrosome reaction, a calcium-dependent exocytosis process. We also review the functionality of different ion channels that are present in spermatozoa in order to understand their association with human infertility.

Fer and FerT: A New Regulatory Link between Sperm and Cancer Cells

Fer and its sperm and cancer specific variant, FerT, are non-receptor tyrosine kinases which play roles in cancer progression and metastasis. Recent studies have shed light on the regulatory role of these kinases in ensuring proper sperm function. Comparison of the regulatory cascades in which Fer and FerT are engaged in sperm and cancer cells presents an interesting picture, in which similar regulatory interactions of these enzymes are integrated in a similar or different regulatory context in the two cell types. These diverse compositions extend from the involvement of Fer in modulation of actin cytoskeleton integrity and function, to the unique regulatory interactions of Fer with PARP-1 and the PP1 phosphatase. Furthermore, recent findings link the metabolic regulatory roles of Fer and FerT in sperm and cancer cells. In the current review, we discuss the above detailed aspects, which portray Fer and FerT as new regulatory links between sperm and malignant cells. This perspective view can endow us with new analytical and research tools that will deepen our understanding of the regulatory trajectories and networks that govern these two multi-layered systems.

Iberiotoxin and clofilium regulate hyperactivation, acrosome reaction, and ion homeostasis synergistically during human sperm capacitation

Potassium channels play essential roles in the regulation of male fertility. However, potassium channels mediating K⁺ currents in human sperm (I_KSper ) remain controversial. Besides SLO3, the SLO1 potassium channel is a potential candidate for human sperm KSper. This study intends to elucidate the function of SLO1 potassium channel during human sperm capacitation. Human sperm were treated with iberiotoxin (IbTX, a SLO1 specific inhibitor) and clofilium (SLO3 inhibitor) separately or simultaneously during in vitro capacitation. A computer-assisted sperm analyzer was used to assess sperm motility. The sperm acrosome reaction (AR) was analyzed using fluorescein isothiocyanate-conjugated Pisum sativum agglutinin staining. Sperm protein tyrosine phosphorylation was studied using western blotting. Intracellular Ca²⁺ , K⁺ , Cl^- , and pH were analyzed using ion fluorescence probes. Independent inhibition with IbTX or clofilium decreased the sperm hyperactivation, AR, and protein tyrosine phosphorylation, and was accompanied by an increase in [K⁺ ]_i , [Cl^- ]_i , and pH_i , but a decrease in [Ca²⁺ ]_i . Simultaneously inhibition with IbTX and clofilium lower sperm hyperactivation and AR more than independent inhibition. The increase in [K⁺ ]_i , [Cl^- ]_i , and pH_i , and the decrease in [Ca²⁺ ]_i were more pronounced. This study suggested that the SLO1 potassium channel may have synergic roles with SLO3 during human sperm capacitation.

Supplementation of Schisandrin B in Semen Extender Improves Quality and Oxidation Resistance of Boar Spermatozoa Stored at 4 °C

During cold storage, boar spermatozoa undergo oxidative stress, which can impair sperm function and fertilizing capacity. The objective of the present study was to assess the effects of Schisandrin B (Sch B) in semen extenders on the quality of boar semen stored at hypothermia. Semen was collected from twelve Duroc boars and diluted in extenders supplemented with different concentrations of Sch B (0 μmol/L, 2.5 μmol/L, 5 μmol/L, 10 μmol/L, 20 μmol/L, and 40 μmol/L). Here, we demonstrated that 10 μmol/L Sch B provided the best effects on motility, plasma membrane integrity, acrosome integrity, sperm normality rate, average movement velocity, wobbility, mitochondrial membrane potential (MMP), and DNA integrity of sperm. The results of Sch B effects on antioxidant factors in boar sperm showed that Sch B significantly elevated the total antioxidant capacity (T-AOC) and markedly decreased the reactive oxygen species (ROS) and malondialdehyde (MDA) content of sperm. The expression of catalase (CAT) and superoxide dismutase (SOD) mRNA was increased, while the expression of glutathione peroxidase (GPx) mRNA demonstrated no change compared to non-treated boar sperm. Compared to the non-treated group, Sch B triggered a decrease in Ca²⁺/protein kinase A (PKA) and lactic acid content in boar sperm. Similarly, Sch B led to a statistically higher quantitative expression of AWN mRNA and a lower quantitative expression of porcine seminal protein I (PSP-I) and porcine seminal protein II (PSP-II) mRNA. In a further reverse validation test, no significant difference was observed in any of the parameters, including adhesion protein mRNA, calcium content, lactic acid content, PKA, and protein kinase G (PKG) activity after sperm capacitation. In conclusion, the current study indicates the efficient use of Sch B with a 10 μmol/L concentration in the treatment of boar sperm through its anti-apoptosis, antioxidative, and decapacitative mechanisms, suggesting that Sch B is a novel candidate for improving antioxidation and decapacitation factors in sperm in liquid at 4 °C.

Bull spermatozoa selected by thermotaxis exhibit high DNA integrity, specific head morphometry, and improve ICSI outcome

BACKGROUND

Sperm migration by thermotaxis is a guidance mechanism that operates along the oviduct and it has proved to be a valid method for selecting spermatozoa with low DNA fragmentation (SDF) in mice, humans, and stallions. This study aimed to analyse if bull spermatozoa could be selected by thermotaxis and to assess their quality in terms of SDF as well as determine the presence of a specific sperm subpopulation based on sperm morphometry and assess their fertilizing capacity by ICSI.

METHODS

We used frozen-thawed sperm from 6 bulls and sperm selection by thermotaxis was performed with TALP medium supplemented with 25 mmol/L of HEPES and 5 mmol/L of caffeine. In these conditions, sperm selection was achieved, obtaining a net thermotaxis of 3.6%. Subsequently, we analysed the SDF of the migrated and not-migrated spermatozoa using the neutral COMET assay, and we evaluated the size of the sperm head using Hemacolor® staining with Motic Images Plus 3 software. Additionally, migrated and not-migrated spermatozoa by thermotaxis were used to fertilize bovine in vitro matured (IVM) oocytes by ICSI, a very inefficient procedure in cattle that is only successful when the oocyte is artificially activated.

RESULTS

The results showed lower SDF (χ², P < 0.001, 13.3% reduction, n = 8) and lower head size parameters (length and width, P < 0.01; and perimeter and area, P < 0.001; n = 4) in those spermatozoa migrated in comparison to those not-migrated. The distribution of sperm subpopulations structure varied between groups, highlighting cluster 2, characterized by spermatozoa with small head size, and high ellipticity and elongated heads, as the most abundant in the thermotaxis migrated group. When performed ICSI (without oocyte artificial activation) with the thermotactic sperm, the blastocyst rate was 32.2% ± 9.3% in the group microinjected with the thermotactic spermatozoa vs. 8.3% ± 7.8% in the group of not-migrated sperm (χ², P < 0.05).

CONCLUSION

Our results showed that bull sperm selection by thermotaxis has a much higher DNA integrity, small and elongated head size parameters, and different sperm subpopulation structure than the not-selected spermatozoa. Additionally, we evidenced that thermotactic spermatozoa improve ICSI success rates.

In vivo characterization of sAC null sperm

Targeted disruption of the soluble adenylyl cyclase (ADCY10; sAC) gene results in male-specific sterility without affecting spermatogenesis, mating behavior, or spermatozoa morphology and count; however, it dramatically impairs sperm motility and prevents capacitation. These phenotypes were identified in sperm from sAC null mice surgically extracted from the epididymis and studied in vitro. Epididymal sperm are dormant, and never exposed to physiological activators in semen or the female reproductive tract. To study sAC null sperm under conditions which more closely resemble natural fertilization, we explored phenotypes of ejaculated sAC null sperm in vivo post-coitally as well as ex vivo, collected from the female reproductive tract. Ex vivo ejaculated sAC null sperm behaved similarly to epididymal sAC null sperm, except with respect to the physiologically induced acrosome reaction. These studies suggest there is a sAC-independent regulation of acrosome responsiveness induced upon ejaculation or exposure to factors in the female reproductive tract. We also studied the behavior of sAC null sperm in vivo post-coitally by taking advantage of transgenes with fluorescently labelled sperm. Transgenes expressing GFP in the acrosome and DsRed2 in the mitochondria located in the midpiece of sperm (DsRed2/Acr3-EGFP) allow visualization of sperm migration through the female reproductive tract after copulation. As previously reported, sperm from wild type (WT) double transgenic mice migrated from the uterus through the uterotubular junction (UTJ) into the oviduct within an hour post-copulation. In contrast, sperm from sAC null double transgenic mice were only found in the uterus. There were no sAC null sperm in the oviduct, even 8 h after copulation. These results demonstrate that sAC KO males are infertile because their sperm do not migrate to the fertilization site.

Effect of High Viscosity on Energy Metabolism and Kinematics of Spermatozoa from Three Mouse Species Incubated under Capacitating Conditions

In order to sustain motility and prepare for fertilization, sperm require energy. The characterization of sperm ATP production and usage in mouse species revealed substantial differences in metabolic pathways that can be differentially affected by capacitation. Moreover, spermatozoa encounter different environments with varying viscoelastic properties in the female reproductive tract. Here, we examine whether viscosity affects sperm ATP levels and kinematics during capacitation in vitro. Sperm from three mouse species (Mus musculus, M. spretus, M. spicilegus) were incubated under capacitating conditions in a modified Tyrode's medium containing bicarbonate, glucose, pyruvate, lactate, and bovine serum albumin (mT-BH) or in a bicarbonate-free medium as a non-capacitating control. Viscosity was increased with the inclusion of polyvinylpyrrolidone. ATP was measured with a bioluminescence kit, and kinematics were examined with a computer-aided sperm analysis system. In M. musculus sperm, ATP declined during capacitation, but no differences were found between non-capacitating and capacitating sperm. In contrast, in M. spretus and M. spicilegus, ATP levels decreased in capacitating sperm. Increasing viscosity in the medium did not modify the timing or proportion of cells undergoing capacitation but did result in additional time- and concentration-dependent decreases in ATP in M. spretus and M. spicilegus under capacitating conditions. Additionally, increased viscosity altered both velocity and trajectory descriptors. The limited impact of capacitation and higher viscosity on M. musculus sperm ATP and kinematics could be related to the low intensity of postcopulatory sexual selection in this species. Responses seen in the other two species could be linked to the ability of their sperm to perform better under enhanced selective pressures.

Intra and intercellular signals governing sperm maturation

After their production in the testis, spermatozoa do not have the capacity to move progressively and are unable to fertilise an oocyte. They sequentially acquire these abilities following their maturation in the epididymis and their capacitation/hyperactivation in the female reproductive system. As gene transcription is silenced in spermatozoa, extracellular factors released from the epididymal epithelium and from secretory glands allow spermatozoa to acquire bioactive molecules and to undergo intrinsic modifications. These modifications include epigenetic changes and post-translational modifications of endogenous proteins, which are important processes in sperm maturation. This article emphasises the roles played by extracellular factors secreted by the epididymis and accessory glands in the control of sperm intercellular signallings and fertilising abilities.

A novel function for the sperm adhesion protein IZUMO1 in cell-cell fusion

Mammalian sperm-egg adhesion depends on the trans-interaction between the sperm-specific type I glycoprotein IZUMO1 and its oocyte-specific GPI-anchored receptor JUNO. However, the mechanisms and proteins (fusogens) that mediate the following step of gamete fusion remain unknown. Using live imaging and content mixing assays in a heterologous system and structure-guided mutagenesis, we unveil an unexpected function for IZUMO1 in cell-to-cell fusion. We show that IZUMO1 alone is sufficient to induce fusion, and that this ability is retained in a mutant unable to bind JUNO. On the other hand, a triple mutation in exposed aromatic residues prevents this fusogenic activity without impairing JUNO interaction. Our findings suggest a second function for IZUMO1 as a unilateral mouse gamete fusogen.

Role of Genital Tract Bacteria in Promoting Endometrial Health in Cattle

Microbiota regulate endometrial health in cattle. It is important to know what a ‘good’ microbiome is, in order to understand pathogeneses of uterine disease. Given that microbial influx into the genital tract of cows at calving is unavoidable, exploring the involvement of genital tract bacteria in promoting endometrial health is warranted. The dysbiosis of endometrial microbiota is associated with benign and malign uterine diseases. The present review discusses current knowledge about the altered endometrial microbiome and the implications of this modulation on endometrial inflammation, ovarian activity, fecundation, pregnancy, and postpartum complications. Intravaginal administration of symbiotic microbes in cattle is a realistic alternative to antibiotic and hormone therapy to treat uterine disease. Genital microbial diversity can be modeled by nutrition, as the energy balance would improve the growth of specific microbial populations. It may be that probiotics that alter the endometrial microbiome could provide viable alternatives to existing therapies for uterine disease in cattle.

Introduction to the pathways involved in the activation and regulation of sperm motility: A review of the relevance of ion channels

To participate in sperm-oocyte fusion, spermatozoa need to be motile. In the testes, spermatozoa are immotile, although these gametes acquire the capacity for motility during the transit through the epididymis. During the period of epididymal transport from the male genital tract to the female genital tract, spermatozoa exhibit various types of motility that are regulated by complex signalling and communication mechanisms. Because motility is very dynamic, it can be affected by small changes in the external or internal environment of spermatozoa within a very short time. This indicates that regulatory membrane proteins, known as sperm ion channels, are involved in the regulation of sperm motility. Research results from studies, where there was use of electrophysiological, pharmacological, molecular and knock-out approaches, indicate ion channels are possibly involved in the regulation of sperm membrane polarisation, intracellular pH, motility, energy homeostasis, membrane integrity, capacitation, hyperactivity, acrosome reaction and fertilisation processes. In this review, there is summarisation of the key functions that ion channels have in the regulation, initiation, maintenance, and modulation of sperm motility. In addition, in this review there is highlighting of novel insights about the pathways of ion channels that are activated in spermatozoa while these gametes are located in the oviduct leading to the fertilisation capacity of these cells.

Protein acetylation protects sperm from spontaneous acrosome reaction

In order to penetrate the egg, spermatozoa must undergo the acrosome reaction in close proximity to the egg. This process can take place only after a series of biochemical changes in the sperm, collectively termed capacitation, occur in the female reproductive tract. Sperm cells can undergo spontaneous-acrosome reaction(sAR) before reaching the vicinity of the egg, preventing successful fertilization. Several mechanisms were shown to protect sperm from undergoing sAR, and all of them are involved in proper capacitation. Here, we describe the involvement of protein acetylation in the mechanism that protects bovine spermatozoa from sAR. Incubation of bovine sperm under non-capacitation conditions revealed a strong increase in sAR that was significantly reduced in the presence of deacetylase inhibitors. Protein kinase A (PKA) is an essential key enzyme in sperm capacitation, and its inhibition results in high sAR. The reduction in sAR by hyperacetylation was independent of PKA activity. We previously demonstrated that calmodulin-kinase II (CaMKII) activity protects sperm from sAR, and here we show that its activity is essential for reduction in sAR by hyperacetylation. We further show that the 'exchange protein directly activated by Camp' (EPAC) mediates both protein lysine acetylation and the reduced rate of sAR caused by hyperacetylation. In conclusion, these results suggest a PKA-independent and EPAC-CaMKII dependent hyperacetylation mechanism that protects sperm from sAR.

The Stallion Spermatozoa: A Valuable Model to Help Understand the Interplay Between Metabolism and Redox (De)regulation in Sperm Cells

Significance: Proper functionality of the spermatozoa depends on the tight regulation of their redox status; at the same time these cells are highly energy demanding and in the energetic metabolism, principally in the electron transport chain in the mitochondria, reactive oxygen species are continuously produced, in addition to that observed in the Krebs cycle and during the β-oxidation of fatty acids. Recent Advances: In addition, in glycolysis, elimination of phosphate groups from glyceraldehyde 3-phosphate and dihydroxyacetone phosphate results in the byproducts glyoxal (G) and methylglyoxal (MG); these products are 2-oxoaldehydes. The presence of adjacent carbonyl groups makes them strong electrophiles that react with nucleophiles in proteins, lipids, and DNA, forming advanced glycation end products. Critical Issues: This mechanism is behind subfertility in diabetic patients; in the animal breeding industry, commercial extenders for stallion semen contain a supraphysiological concentration of glucose that promotes MG production, constituting a potential model of interest. Future Directions: Increasing our knowledge of sperm metabolism and its interactions with redox regulation may improve current sperm technologies in use, and shall provide new clues to understanding infertility in males. Moreover, stallion spermatozoa due to its accessibility, intense metabolism, and suitability for proteomics/metabolomic studies may constitute a suitable model for studying regulation of metabolism and interactions between metabolism and redox homeostasis. Antioxid. Redox Signal. 37, 521-537.

Functional significance of mouse seminal vesicle sulfhydryl oxidase on sperm capacitation in vitro

During ejaculation, cauda epididymal spermatozoa are suspended in a protein-rich solution of seminal plasma which is composed of proteins mostly secreted from the seminal vesicle. These seminal proteins interact with the sperm cells and bring about changes in their physiology, so that they can become capacitated in order for the fertilization to take place. Sulfhydryl oxidase (SOX) is a member of the QSOX family and its expression is found to be high in the seminal vesicle secretion of mouse. Previously, it has been reported to cross-link thiol containing amino acids among major seminal vesicle secretion (SVS) proteins. However, its role in male reproduction is unclear. In this study, we determined the role of SOX on epididymal sperm maturation and also disclosed the binding effect of SOX on the sperm fertilizing ability in vitro. In order to achieve the above two objectives, we constructed a Sox clone (1.7 kb) using a pET-30a vector. His-tagged recombinant Sox was over expressed in Shuffle Escherichia coli cells and purified using His-Trap column affinity chromatography along with hydrophobic interaction chromatography. The purified SOX was confirmed by Western blot analysis and by its activity with DTT as a substrate. Results obtained from immunocytochemical staining clearly indicated that SOX possesses a binding site on the sperm acrosome. The influence of SOX on oxidation of sperm sulfhydryl to disulfides during epididymal sperm maturation was evaluated by a thiol labelling agent, mBBr. The SOX protein binds on to the sperm cells and increases their progressive motility. The effect of SOX binding on reducing the [Ca2+]i concentration in sperm head, was determined using a calcium probe, Fluo-3 AM. The inhibitory influence of SOX on sperm acrosome reaction was shown by using calcium ionophore A32187 to induce the acrosome reaction. The acrosome-reacted sperm were examined by staining with FITC-conjugated Arachis hypogaea (peanut) lectin. Furthermore, immunocytochemical analysis revealed that SOX remains bound to the sperm cells in the uterus but disappears in the oviduct during their transit in the female reproductive tract. The results from the above experiment revealed that SOX binding on to the sperm acrosome prevents sperm capacitation by affecting the [Ca2+]i concentration in the sperm head and the ionophore-induced acrosome reaction. Thus, the binding of SOX on to the sperm acrosome may possibly serve as a decapacitation factor in the uterus to prevent premature capacitation and acrosome reaction, thus preserving their fertilizing ability.

Genetic Ablation of Na,K-ATPase α4 Results in Sperm Energetic Defects

The Na,K-ATPase alpha 4 isoform (NKAα4) is expressed specifically in the male germ cells of the testes and is particularly abundant in mature spermatozoa. Genetic deletion of NKAα4 in mice (NKAα4 KO mice) results in complete infertility of male, but not female mice. The reduced fecundity of NKAα4 KO male mice is due to a series of defects, including a severe impairment in total and hyperactive sperm motility. In this work, we show that deletion of NKAα4 also leads to major defects in sperm metabolism and energetics. Thus, compared to wild-type sperm, sperm from NKAα4 KO mice display a significant reduction in the extracellular acidification rate (ECAR), indicative of impaired glycolytic flux. In addition, mitochondrial function is disrupted in sperm lacking NKAα4, as indicated by a reduction in the mitochondrial membrane potential and lower oxygen consumption rate (OCR). Moreover, the ratio between the oxidized and reduced forms of nicotinamide adenine dinucleotide (NAD/NADH) is increased in NKAα4 KO sperm, indicating a shift in the cellular redox state. These metabolic changes are associated with augmented reactive oxygen species (ROS) production and increased lipid peroxidation in NKAα4 KO sperm. Altogether, these findings reveal a novel link between NKAα4 activity and sperm energetics, highlighting the essential role of this ion transporter in sperm physiology.

Ion Channels of Spermatozoa: Structure, Function, and Regulation Mechanisms

Ion transport is essential for sperm physiology, being involved in sperm-cell differentiation and maturation, motility activation, chemotaxis towards the oocyte, and fertilization, as well as in sperm adaptation to the surrounding medium [...].

Exploring the ovine sperm transcriptome by RNAseq techniques. I Effect of seasonal conditions on transcripts abundance

Understanding the cell molecular changes occurring as a results of climatic circumstances is crucial in the current days in which climate change and global warming are one of the most serious challenges that living organisms have to face. Sperm are one of the mammals’ cells most sensitive to heat, therefore evaluating the impact of seasonal changes in terms of its transcriptional activity can contribute to elucidate how these cells cope with heat stress events. We sequenced the total sperm RNA from 64 ejaculates, 28 collected in summer and 36 collected in autumn, from 40 Manchega rams. A highly rich transcriptome (11,896 different transcripts) with 90 protein coding genes that exceed an average number of 5000 counts were found. Comparing transcriptome in the summer and autumn ejaculates, 236 significant differential abundance genes were assessed, most of them (228) downregulated. The main functions that these genes are related to sexual reproduction and negative regulation of protein metabolic processes and kinase activity. Sperm response to heat stress supposes a drastic decrease of the transcriptional activity, and the upregulation of only a few genes related with the basic functions to maintain the organisms’ homeostasis and surviving. Rams’ spermatozoids carry remnant mRNAs which are retrospectively indicators of events occurring along the spermatogenesis process, including abiotic factors such as environmental temperature.

Sperm Phosphoproteome: Unraveling Male Infertility

Infertility affects approximately 15% of couples worldwide of childbearing age, and in many cases the etiology of male infertility is unknown. The current standard evaluation of semen is insufficient to establish an accurate diagnosis. Proteomics techniques, such as phosphoproteomics, applied in this field are a powerful tool to understand the mechanisms that regulate sperm functions such as motility, which is essential for successful fertilization. Among the post-translational modifications of sperm proteins, this review summarizes, from a proteomic perspective, the updated knowledge of protein phosphorylation, in human spermatozoa, as a relevant molecular mechanism involved in the regulation of sperm physiology. Specifically, the role of sperm protein phosphorylation in motility and, consequently, in sperm quality is highlighted. Additionally, through the analysis of published comparative phosphoproteomic studies, some candidate human sperm phosphoproteins associated with low sperm motility are proposed. Despite the remarkable advances in phosphoproteomics technologies, the relatively low number of studies performed in human spermatozoa suggests that phosphoproteomics has not been applied to its full potential in studying male infertility yet. Therefore, further studies will improve the application of this procedure and overcome the limitations, increasing the understanding of regulatory mechanisms underlying protein phosphorylation in sperm motility and, consequently, in male fertility.

A Sea Anemone Lebrunia neglecta Venom Fraction Decreases Boar Sperm Cells Capacitation: Possible Involvement of HVA Calcium Channels

Sea anemones produce venoms characterized by a complex mixture of low molecular weight compounds, proteins and peptides acting on voltage-gated ion channels. Mammal sperm cells, like neurons, are characterized by their ion channels. Calcium channels seem to be implicated in pivotal roles such as motility and capacitation. In this study, we evaluated the effect of a low molecular weight fraction from the venom of the sea anemone Lebrunia neglecta on boar sperm cells and in HVA calcium channels from rat chromaffin cells. Spermatozoa viability seemed unaffected by the fraction whereas motility and sperm capacitation were notoriously impaired. The sea anemone fraction inhibited the HVA calcium current with partial recovery and no changes in chromaffin cells’ current kinetics and current–voltage relationship. These findings might be relevant to the pharmacological characterization of cnidarian venoms and toxins on voltage-gated calcium channels.

Sperm Ion Transporters and Channels in Human Asthenozoospermia: Genetic Etiology, Lessons from Animal Models, and Clinical Perspectives

In mammals, sperm fertilization potential relies on efficient progression within the female genital tract to reach and fertilize the oocyte. This fundamental property is supported by the flagellum, an evolutionarily conserved organelle that provides the mechanical force for sperm propulsion and motility. Importantly several functional maturation events that occur during the journey of the sperm cells through the genital tracts are necessary for the activation of flagellar beating and the acquisition of fertilization potential. Ion transporters and channels located at the surface of the sperm cells have been demonstrated to be involved in these processes, in particular, through the activation of downstream signaling pathways and the promotion of novel biochemical and electrophysiological properties in the sperm cells. We performed a systematic literature review to describe the currently known genetic alterations in humans that affect sperm ion transporters and channels and result in asthenozoospermia, a pathophysiological condition defined by reduced or absent sperm motility and observed in nearly 80% of infertile men. We also present the physiological relevance and functional mechanisms of additional ion channels identified in the mouse. Finally, considering the state-of-the art, we discuss future perspectives in terms of therapeutics of asthenozoospermia and male contraception.

Mysteries and unsolved problems of mammalian fertilization and related topics

Mammalian fertilization is a fascinating process that leads to the formation of a new individual. Eggs and sperm are complex cells that must meet at the appropriate time and position within the female reproductive tract for successful fertilization. I have been studying various aspects of mammalian fertilization over 60 years. In this review, I discuss many different aspects of mammalian fertilization, some of my laboratory's contribution to the field, and discuss enigmas and mysteries that remain to be solved.

Acrosomal alkalinization occurs during human sperm capacitation

Mammalian sperm capacitation is a prerequisite for successful fertilization. Capacitation involves biochemical and physiological modifications of sperm as they travel through the female reproductive tract. These modifications prepare the sperm to undergo the acrosome reaction (AR), an acrosome vesicle exocytosis that is necessary for gamete fusion. Capacitation requires an increase in both intracellular calcium ([Ca2+]i) and pH (pHi). Mouse sperm capacitation is accompanied by acrosomal alkalinization and artificial elevation of the acrosome pH (pHa) is sufficient to trigger the AR in mouse and human sperm, but it is unknown if pHa increases naturally during human sperm capacitation. We used single-cell imaging and image-based flow cytometry to evaluate pHa during capacitation and its regulation. We found that pHa progressively increases during capacitation. The V-ATPase, which immunolocalized to the acrosome and equatorial segment, is mainly responsible for the acidity of the acrosome. It is likely that the regulation of V-ATPase is at least in part responsible for the progressive increase in pHa during capacitation. Acrosome alkalinization was dependent on extracellular HCO3- and Ca2+. Inhibition of the HCO3--dependent adenylyl cyclase and protein kinase A induced significant pHa changes. Overall, alkalinization of the acrosome may be a key step in the path towards the AR.

piR-121380 Is Involved in Cryo-Capacitation and Regulates Post-Thawed Boar Sperm Quality Through Phosphorylation of ERK2 via Targeting PTPN7

Cryopreservation induces capacitation-like (cryo-capacitation) changes, similar to natural capacitation, and affects the fertility potential of post-thawed sperm. The molecular mechanism of sperm cryo-capacitation during cryopreservation remains unknown. PIWI-interacting RNAs (piRNAs) have been reported to be involved in cryo-capacitation of post-thawed sperm and regulation of sperm motility, capacitation, and chemotaxis. In this study, protein tyrosine phosphatase nonreceptor type 7 (PTPN7) was positively targeted by piR-121380 after a dual luciferase assay. The mRNA expression of PTPN7 and piR-121380 was significantly decreased (p < 0.01); however, PTPN7 protein was significantly increased (p < 0.01) in post-thawed boar sperm. Furthermore, E1RK1/2 phosphorylation was reduced during cryopreservation. Six hours after transfection with piR-121380 mimic and inhibitor, the phosphorylation of ERK2 was significantly increased and decreased (p < 0.01), respectively. Furthermore, the highest and lowest total sperm motility, forward motility, and capacitation rate were observed after piR-121380 mimic and inhibitor treatments, respectively. The concentration of intracellular calcium ([Ca2+]i) showed no significant difference after transfection with either piR-121380 mimic or inhibitor at 1, 3, and 6 h. In conclusion, we demonstrated that piR-121380 modulates ERK2 phosphorylation by targeting PTPN7, which induces sperm cryo-capacitation, and eventually affects the motility and fertility potential of post-thawed sperm.

C2CD6 regulates targeting and organization of the CatSper calcium channel complex in sperm flagella

The CatSper cation channel is essential for sperm capacitation and male fertility. The multi-subunit CatSper complexes form highly organized calcium signaling nanodomains on flagellar membranes. Here, we report identification of an uncharacterized protein, C2CD6, as a subunit of the mouse CatSper complex. C2CD6 contains a calcium-dependent, membrane-targeting C2 domain. C2CD6 associates with the CatSper calcium-selective, core-forming subunits. Deficiency of C2CD6 depletes the CatSper nanodomains from the flagellum and results in male sterility. C2CD6-deficient sperm are defective in hyperactivation and fail to fertilize oocytes both in vitro and in vivo. CatSper currents are present but at a significantly lower level in C2CD6-deficient sperm. Transient treatments with either Ca2+ ionophore, starvation, or a combination of both restore the fertilization capacity of C2CD6-deficient sperm. C2CD6 interacts with EFCAB9, a pH-dependent calcium sensor in the CatSper complex. We postulate that C2CD6 facilitates incorporation of the CatSper complex into the flagellar plasma membrane and may function as a calcium sensor. The identification of C2CD6 may enable the long-sought reconstitution of the CatSper ion channel complex in a heterologous system for male contraceptive development.

Energy Metabolism and Hyperactivation of Spermatozoa from Three Mouse Species under Capacitating Conditions

Mammalian sperm differ widely in sperm morphology, and several explanations have been presented to account for this diversity. Less is known about variation in sperm physiology and cellular processes that can give sperm cells an advantage when competing to fertilize oocytes. Capacitation of spermatozoa, a process essential for mammalian fertilization, correlates with changes in motility that result in a characteristic swimming pattern known as hyperactivation. Previous studies revealed that sperm motility and velocity depend on the amount of ATP available and, therefore, changes in sperm movement occurring during capacitation and hyperactivation may involve changes in sperm bioenergetics. Here, we examine differences in ATP levels of sperm from three mouse species (genus Mus), differing in sperm competition levels, incubated under non-capacitating and capacitating conditions, to analyse relationships between energetics, capacitation, and swimming patterns. We found that, in general terms, the amount of sperm ATP decreased more rapidly under capacitating conditions. This descent was related to the development of a hyperactivated pattern of movement in two species (M. musculus and M. spicilegus) but not in the other (M. spretus), suggesting that, in the latter, temporal dynamics and energetic demands of capacitation and hyperactivation may be decoupled or that the hyperactivation pattern differs. The decrease in ATP levels during capacitation was steeper in species with higher levels of sperm competition than in those with lower levels. Our results suggest that, during capacitation, sperm consume more ATP than under non-capacitating conditions. This higher ATP consumption may be linked to higher velocity and lateral head displacement, which are associated with hyperactivated motility.

Effect of Milk Type Subjected to Different Heat Treatments on Cryo-Survivability and In Vivo Fertility of Buffalo (Bubalus bubalis) Spermatozoa in a Milk-Based Extender

Oxidative stress is a major contributory factor to cellular damage during semen cryopreservation and results in a decreased fertilizing capacity of cryopreserved bull sperm. The inclusion of exogenous antioxidants sometimes exerts deleterious effects on sperm quality. Thus, enhancing the endogenous production of antioxidants is a requirement. This study aimed to investigate the effect of milk type heated at different temperatures on the antioxidant potential of extenders, and the subsequent post-thaw quality parameters and in vivo fertility of buffalo bull semen. Cow (C) and buffalo whole milk (B) were used separately for semen extender preparation, heated at five different temperatures (T₁ = 90°C, T₂ = 100°C, T₃ = 110°C, T₄ = 120°C, T₅ = 130°C) for 10 minutes. Reactive sulfhydryl groups were measured in each subgroup by Ellman's reagents as CT₁ = 143.2 μM, CT₂ = 147.4 μM, CT₃ = 151.5 μM, CT₄ = 157.2 μM, CT₅ = 161.8 μM, BT₁ = 168.3 μM, BT₂ = 172.5 μM, BT₃ = 176.7 μM, BT₄ = 196.3 μM, and BT₅ = 205.7 μM. All semen samples were cryopreserved in milk-based extenders by using standard procedures. Post-thaw quality parameters including total and progressive motility, mitochondrial membrane potential, plasma membrane integrity, and acrosome integrity were found to be higher (p < 0.05) in the group (BT₃) containing buffalo milk heated at 110°C, whereas in the same group, lipid peroxidation was found to be lower (p < 0.05) as compared with other treatment groups and control group. In vivo fertility of cryopreserved buffalo sperm was compared among BT₃, CT₁ (conventionally used milk extender), and a Tris egg yolk extender group. The fertility rates [47% (54/114), 30% (33/108), and 36% (37/103)] were higher (p < 0.05) in BT₃ as compared with other groups. This study suggests that buffalo milk heated at 110°C has high antioxidant potential and improves post-thaw quality and in vivo fertility of cryopreserved buffalo bull semen.

Impact of Cryopreservation on Motile Subpopulations and Tyrosine-Phosphorylated Regions of Ram Spermatozoa during Capacitating Conditions

Simple Summary

Spermatozoa go through diverse changes to achieve their fertilizing potential (capacitation) and develop a specific motility pattern (hyperactivation). However, to ensure a greater reproductive success, not all the spermatozoa present in an ejaculate react equally or at the same time. Therefore, a comparative analysis was performed in the present study to improve our current understanding about how cryopreservation may affect the heterogeneous nature of fresh ejaculates during these two events. Among the four motile sperm subpopulations identified in fresh and frozen-thawed ram semen, one of them developed a hyperactivated-like movement and was the main group involve in those changes associated with sperm capacitation based on the marked increase and the positive correlation with mitochondrial activity and tyrosine phosphorylation, two relevant parameters that usually increase during capacitation. In addition, cryopreservation altered the distribution of the motile sperm subpopulations. Although the subpopulation with hyperactivated-like movement increased at the beginning of incubation in frozen-thawed samples, this subpopulation together with the subpopulation of rapid and progressive spermatozoa were replaced after a prolonged incubation by the subpopulation of slow spermatozoa with the lowest mitochondrial activity, which clearly indicate the reduction in sperm quality. These findings will aid to optimize the current cryopreservation and in vitro fertilization protocols.

Abstract

The heterogeneous nature of ejaculates highlights the relevance of studying the behavior of different sperm subpopulations. Changes in sperm motility and the increase in tyrosine phosphorylation are key events that usually occur during capacitation and can be modified by the cryopreservation process. However, the relationship between both events remains poorly defined throughout capacitation in the different sperm subpopulations. Fresh and frozen-thawed spermatozoa were incubated in capacitating (CAP) and non-capacitating (NC) media up to 240 min. Sperm kinematics, tyrosine phosphorylation and mitochondrial activity were measured by the CASA system and imaging flow cytometry. Four motile sperm subpopulations (SP) were identified in fresh and frozen-thawed ram semen after the cluster analysis. Incubation under CAP conditions over time led to greater changes in the percentage of spermatozoa included in each subpopulation compared to NC conditions, being different between fresh and frozen-thawed spermatozoa. The SP1, characterized by slow spermatozoa, progressively increased after 15 min in frozen-thawed samples incubated in both media but not in fresh ones. The SP4, characterized by fast and non-linear spermatozoa, showed a marked increase during CAP, but not under NC conditions, occurring more rapidly in frozen-thawed spermatozoa. This subpopulation (SP4) was also the only one positively and strongly correlated with mitochondrial activity and all phosphorylated sperm regions during capacitation, either in fresh or frozen-thawed samples. Our results indicated that in vitro capacitation induced significant changes in the distribution of motile sperm subpopulations, being affected by cryopreservation. Notwithstanding, the subpopulation which probably represents hyperactivated-like spermatozoa (SP4) also increased in frozen-thawed samples, occurring faster and simultaneously to the increment of mitochondrial activity and tyrosine phosphorylation of different sperm regions.

Bovine Follicular Fluid Derived Extracellular Vesicles Modulate the Viability, Capacitation and Acrosome Reaction of Bull Spermatozoa

Simple Summary

Before the union of an egg and spermatozoon, several vital processes occur for fertilization in the female reproductive system. One of these processes is the maturation of spermatozoa which occurs in the female reproductive tract. Spermatozoa not undergoing maturation in the female reproductive tract are unable to penetrate the egg. Many reports have suggested the involvement of different factors in mediating the functional maturation of spermatozoa. Follicular fluid (FF) is named as one of those factors. FF is an ovarian fluid that plays an essential role in egg maturation and sources extracellular vesicles (EVs). EVs are nano-containers that are released from different cells and are present in all body fluids. Several studies have reported that FF supports the functional maturation of spermatozoa. Therefore, we hypothesized that FF EVs might have a role in inducing functional maturation in spermatozoa. Surprisingly, the FF-derived EVs were able to aid vital functional parameters of spermatozoa and the effects from EVs were species- and source-specific. Therefore, deciphering the cargo of FF EVs responsible for modulating spermatozoa’s functions can potentially prove beneficial in diagnosing and treating male infertility and improving the current assisted reproductive technology protocols.

Abstract

While follicular fluid (FF) is known to enhance the functional properties of spermatozoa, the role of FF-derived extracellular vesicles (EVs) in this respect is unknown. We hypothesized that bovine FF EVs convey signals to spermatozoa supporting sperm viability, inducing sperm capacitation and acrosome reaction. In this study, the effects of bovine FF EVs on sperm functions are evaluated. Irrespective of the size of the follicles which FF EVs had originated from, they were capable of supporting sperm viability, inducing capacitation and acrosome reaction. These effects were specific to the source of bovine FF EVs, as human-cell-line-derived or porcine FF EVs did not affect spermatozoa viability or induced capacitation and acrosome reaction. A minimum of 5 × 10⁵ EVs/mL was adequate to maintain sperm viability and induce capacitation and acrosome reaction in spermatozoa. Interestingly, with FF EV trypsin treatment, FF EVs lost their ability to support sperm functions. In conclusion, this study demonstrates that bovine FF EVs can support spermatozoa function and may contribute to a favorable periconceptional microenvironment. This is an important aspect of the interactions between different sexes at the earliest stages of reproduction and helps to understand molecular mechanisms modulating processes such as sperm competition and female cryptic choice.

KCNQ1 Potassium Channel Expressed in Human Sperm Is Involved in Sperm Motility, Acrosome Reaction, Protein Tyrosine Phosphorylation, and Ion Homeostasis During Capacitation

Potassium channels are involved in membrane hyperpolarization and ion homeostasis regulation during human sperm capacitation. However, the types of potassium channels in human sperm remain controversial. The voltage-gated ion channel KCNQ1 is ubiquitously expressed and regulates key physiological processes in the human body. In the present study, we investigated whether KCNQ1 is expressed in human sperm and what role it might have in sperm function. The expression and localization of KCNQ1 in human sperm were evaluated using Western blotting and indirect immunofluorescence. During capacitation incubation, human sperm were treated with KCNQ1- specific inhibitor chromanol 293B. Sperm motility was analyzed using a computer-assisted sperm analyzer. The acrosome reaction was studied using fluorescein isothiocyanate-conjugated Pisum sativum agglutinin staining. Protein tyrosine phosphorylation levels and localization after capacitation were determined using Western blotting and immunofluorescence. Intracellular K⁺, Ca²⁺, Cl⁻, pH, and membrane potential were analyzed using fluorescent probes. The results demonstrate that KCNQ1 is expressed and localized in the head and tail regions of human sperm. KCNQ1 inhibition reduced sperm motility, acrosome reaction rates, and protein tyrosine phosphorylation but had no effect on hyperactivation. KCNQ1 inhibition also increased intracellular K⁺, membrane potential, and intracellular Cl⁻, while decreasing intracellular Ca²⁺ and pH. In conclusion, the KCNQ1 channel plays a crucial role during human sperm capacitation.

Mitoquinone does not improve sperm cryo-resistance in bulls

Oxidative stress is associated with impaired post‐thaw sperm quality. As mitochondria are the main source of reactive oxygen species (ROS) in sperm, the goal of this study was to evaluate effects of the mitochondria‐targeting antioxidant Mitoquinone (MitoQ) during cryopreservation of bull sperm. Semen was collected from 11 Simmental bulls (two ejaculates per bull) and diluted in Triladyl^® supplemented with various concentrations of MitoQ (0, 0.2, 2, and 20 nM) to a final concentration of 65 × 10⁶ sperm/ml. After thawing (0 and 3 hr), we assessed the following sperm traits: sperm motility by computer‐assisted sperm analysis (CASA), DNA fragmentation index by SCSA^® and plasma and acrosome membrane integrity, intracellular calcium concentration, esterase activity, mitochondrial membrane potential and synthesis of ROS using two multicolour flow cytometric assays. After 3 hr of incubation, 20 nM MitoQ increased (p < .05) sperm ROS synthesis compared to Control, whereas none of the other quality parameters were altered (p > .05). Therefore, we concluded that addition of MitoQ to semen extender before cryopreservation of bull sperm was unable to improve post‐thaw sperm quality. Furthermore, 20 nM of MitoQ increased frozen‐thawed sperm ROS synthesis, without apparent negative effects on the evaluated sperm traits.

Contribution of epididymal epithelial cell functions to sperm epigenetic changes and the health of progeny

BACKGROUND

Spermatozoa acquire their motility and fertilizing abilities during their maturation through the epididymis. This process is controlled by epididymal epithelial cells that possess features adapted to sense and respond to their surrounding environment and to communicate with spermatozoa. During the past decade, new intercellular communication processes have been discovered, including the secretion and transport of molecules from the epithelium to spermatozoa via extracellular vesicles (EVs), as well as sensing of the intraluminal milieu by cellular extensions.

OBJECTIVE AND RATIONALE

This review addresses recent findings regarding epididymal epithelial cell features and interactions between spermatozoa and the epididymal epithelium as well as epigenetic modifications undergone by spermatozoa during transit through the epididymal microenvironment.

SEARCH METHODS

A systematic search was conducted in Pubmed with the keyword 'epididymis'. Results were filtered on original research articles published from 2009 to 2021 and written in the English language. One hundred fifteen original articles presenting recent advancements on the epididymis contribution to sperm maturation were selected. Some additional papers cited in the primary reference were also included. A special focus was given to higher mammalian species, particularly rodents, bovines and humans, that are the most studied in this field.

OUTCOMES

This review provides novel insights into the contribution of epididymal epithelium and EVs to post-testicular sperm maturation. First, new immune cell populations have been described in the epididymis, where they are proposed to play a role in protecting the environment surrounding sperm against infections or autoimmune responses. Second, novel epididymal cell extensions, including dendrites, axopodia and primary cilia, have been identified as sensors of the environment surrounding sperm. Third, new functions have been outlined for epididymal EVs, which modify the sperm epigenetic profile and participate in transgenerational epigenetic inheritance of paternal traits.

WIDER IMPLICATIONS

Although the majority of these findings result from studies in rodents, this fundamental research will ultimately improve our knowledge of human reproductive physiopathologies. Recent discoveries linking sperm epigenetic modifications with paternal environmental exposure and progeny outcome further stress the importance of advancing fundamental research on the epididymis. From this, new therapeutic options for infertile couples and better counseling strategies may arise to increase positive health outcomes in children conceived either naturally or with ART.

Parkinson Disease Protein 7 (PARK7) Is Related to the Ability of Mammalian Sperm to Undergo In Vitro Capacitation

Parkinson disease protein 7 (PARK7) is a multifunctional protein known to be involved in the regulation of sperm motility, mitochondrial function, and oxidative stress response in mammalian sperm. While ROS generation is needed to activate the downstream signaling pathways required for sperm to undergo capacitation, oxidative stress has detrimental effects for sperm cells and a precise balance between ROS levels and antioxidant activity is needed. Considering the putative antioxidant role of PARK7, the present work sought to determine whether this protein is related to the sperm ability to withstand in vitro capacitation. To this end, and using the pig as a model, semen samples were incubated in capacitation medium for 300 min; the acrosomal exocytosis was triggered by the addition of progesterone after 240 min of incubation. At each relevant time point (0, 120, 240, 250, and 300 min), sperm motility, acrosome and plasma membrane integrity, membrane lipid disorder, mitochondrial membrane potential, intracellular calcium and ROS were evaluated. In addition, localization and protein levels of PARK7 were also assessed through immunofluorescence and immunoblotting. Based on the relative content of PARK7, two groups of samples were set. As early as 120 min of incubation, sperm samples with larger PARK7 content showed higher percentages of viable and acrosome-intact sperm, lipid disorder and superoxide levels, and lower intracellular calcium levels when compared to sperm samples with lower PARK7. These data suggest that PARK7 could play a role in preventing sperm from undergoing premature capacitation, maintaining sperm viability and providing a better ability to keep ROS homeostasis, which is needed to elicit sperm capacitation. Further studies are required to elucidate the antioxidant properties of PARK7 during in vitro capacitation and acrosomal exocytosis of mammalian sperm, and the relationship between PARK7 and sperm motility.

Curcumin in a tris-based semen extender improves cryosurvival of Hariana bull spermatozoa

In this study, the cryoprotective potential of natural antioxidant curcumin in Hariana bull semen was evaluated as an additive in a tris-based extender with the assessment of motility and motion parameters of spermatozoa, membrane intactness, progesterone-receptor binding, protein carbonyl content, cervical mucus penetration, cryocapacitation-associated and apoptotic-like changes. The collected ejaculates were divided into five groups in the tris-based extender (control without curcumin-I, 10 µM-II, 25 µM-III, 50 µM-IV and 75µM-V) and were cryopreserved. Groups II and III containing 10 and 25 µM curcumin substantially (p < .05) improved the post-thaw sperm parameters like viability, motility, and velocity parameters; intact acrosome and membrane; lowered protein carbonyl content; DNA fragmentation and cryocapacitation-associated changes in comparison to control. It was interesting to note that early apoptotic-like changes in sperm cells were significantly (p < .05) decreased in Group II along with an increase in a higher population of sperm cells having high mitochondrial transmembrane potential. Higher progesterone-receptor binding, Vanguard distance and in vitro capacitation response were observed only in Group II (10µM) compared to other groups. In conclusion, curcumin in a semen extender manifests cryoprotective effects and may be incorporated at 10 µM concentration in a Hariana bull semen extender for better post-thaw sperm quality.

Physiologically detectable bisphenol A impairs human sperm functions by reducing protein-tyrosine phosphorylation

BACKGROUND

Bisphenol A (BPA), a widely used plastic monomer and plasticizer, is detectable in blood, urine and semen of a healthy people, with concentrations ranging from 0.1 nM to 10 nM. It has been shown that in vitro exposure of BPA as low as 0.001 nM could significantly inhibited mouse sperm motility and acrosome reaction. However, it is still unclear whether BPA at those physiologically detectable concentration affects human sperm.

METHODS

The effects of different concentrations of BPA (0, 10^-3, 10^-2, 10^-1, 10, 10³ nM) on sperm functions were examined, including human sperm viability, kinematic parameters, hyperactivation and capacitation.

RESULTS

BPA caused a remarkable decline in human sperm viability, motility and progressive motility, hyperactivation, capacitation and progesterone-induced acrosome reaction. Mechanism studies showed that BPA could suppress the protein tyrosine phosphorylation level of human sperm, but had no effect on sperm calcium signaling.

CONCLUSIONS

Physiologically detectable concentrations of BPA may impair human sperm functions via suppressing protein tyrosine phosphorylation of human sperm, implying that environmental pollution of BPA might be a factor contributing to male infertility.

F4-Neuroprostanes: A Role in Sperm Capacitation

F₄-neuroprostanes (F₄-NeuroPs), derived from the oxidative metabolization of docosahexaenoic acid (DHA), are considered biomarkers of oxidative stress in neurodegenerative diseases. Neurons and spermatozoa display a high DHA content. NeuroPs might possess biological activities. The aim of this in vitro study was to investigate the biological effects of chemically synthetized 4-F_4t-NeuroP and 10-F_4t-NeuroP in human sperm. Total progressive sperm motility (p < 0.05) and linearity (p = 0.016), evaluated by a computer-assisted sperm analyzer, were significantly increased in samples incubated with 7 ng F₄-NeuroPs compared to non-supplemented controls. Sperm capacitation was tested in rabbit and swim-up-selected human sperm by chlortetracycline fluorescence assay. A higher percentage of capacitated sperm (p < 0.01) was observed in samples incubated in F₄-NeuroPs than in the controls. However, the percentage of capacitated sperm was not different in F₄-NeuroPs and calcium ionophore treatments at 2 h incubation. The phosphorylated form of AMPKα was detected by immunofluorescence analysis; after 2 h F₄-NeuroP incubation, a dotted signal appeared in the entire sperm tail, and in controls, sperm were labeled in the mid-piece. A defined level of seminal F₄-NeuroPs (7 ng) showed a biological activity in sperm function; its addition in sperm suspensions stimulated capacitation, increasing the number of sperm able to fertilize.

ACRBP (Sp32) is involved in priming sperm for the acrosome reaction and the binding of sperm to the zona pellucida in a porcine model

In boar sperm, we have previously shown that capacitation is associated with the appearance of the p32 tyrosine phosphoprotein complex. The principal tyrosine phosphoprotein involved in this complex is the acrosin-binding protein (ACRBP), which regulates the autoconversion of proacrosin to intermediate forms of acrosin in both boar and mouse sperm. However, the complete biological role of ACRBP has not yet been elucidated. In this study, we tested the hypothesis that tyrosine phophorylation and the presence of the ACRBP in the sperm head are largely necessary to induce capacitation, the acrosome reaction (AR) and sperm-zona pellucida (ZP) binding, all of which are necessary steps for fertilization. In vitro fertilization (IVF) was performed using matured porcine oocytes and pre-capacitated boar sperm cultured with anti-phosphotyrosine antibodies or antibodies against ACRBP. Anti-ACRBP antibodies reduced capacitation and spontaneous AR (P<0.05). Sperm-ZP binding declined in the presence of anti-phosphotyrosine or anti-ACRBP antibodies. The localisation of anti-ACRBP antibodies on the sperm head, reduced the ability of the sperm to undergo the AR in response to solubilized ZP or by inhibiting the sarco/endoplasmic reticulum Ca2+-ATPase. These results support our hypothesis that tyrosine phosphorylated proteins and ACRBP are present upon the sperm surface in order to participate in sperm-ZP binding, and that ACRBP upon the surface of the sperm head facilitates capacitation and the AR in the porcine.

Kcnj16 (Kir5.1) Gene Ablation Causes Subfertility and Increases the Prevalence of Morphologically Abnormal Spermatozoa

The ability of spermatozoa to swim towards an oocyte and fertilize it depends on precise K+ permeability changes. Kir5.1 is an inwardly-rectifying potassium (Kir) channel with high sensitivity to intracellular H+ (pHi) and extracellular K+ concentration [K+]o, and hence provides a link between pHi and [K+]o changes and membrane potential. The intrinsic pHi sensitivity of Kir5.1 suggests a possible role for this channel in the pHi-dependent processes that take place during fertilization. However, despite the localization of Kir5.1 in murine spermatozoa, and its increased expression with age and sexual maturity, the role of the channel in sperm morphology, maturity, motility, and fertility is unknown. Here, we confirmed the presence of Kir5.1 in spermatozoa and showed strong expression of Kir4.1 channels in smooth muscle and epithelial cells lining the epididymal ducts. In contrast, Kir4.2 expression was not detected in testes. To examine the possible role of Kir5.1 in sperm physiology, we bred mice with a deletion of the Kcnj16 (Kir5.1) gene and observed that 20% of Kir5.1 knock-out male mice were infertile. Furthermore, 50% of knock-out mice older than 3 months were unable to breed. By contrast, 100% of wild-type (WT) mice were fertile. The genetic inactivation of Kcnj16 also resulted in smaller testes and a greater percentage of sperm with folded flagellum compared to WT littermates. Nevertheless, the abnormal sperm from mutant animals displayed increased progressive motility. Thus, ablation of the Kcnj16 gene identifies Kir5.1 channel as an important element contributing to testis development, sperm flagellar morphology, motility, and fertility. These findings are potentially relevant to the understanding of the complex pHi- and [K+]o-dependent interplay between different sperm ion channels, and provide insight into their role in fertilization and infertility.

Network Analyses Predict Small RNAs That Might Modulate Gene Expression in the Testis and Epididymis of Bos indicus Bulls

Spermatogenesis relies on complex molecular mechanisms, essential for the genesis and differentiation of the male gamete. Germ cell differentiation starts at the testicular parenchyma and finishes in the epididymis, which has three main regions: head, body, and tail. RNA-sequencing data of the testicular parenchyma (TP), head epididymis (HE), and tail epididymis (TE) from four bulls (three biopsies per bull: 12 samples) were subjected to differential expression analyses, functional enrichment analyses, and co-expression analyses. The aim was to investigate the co-expression and infer possible regulatory roles for transcripts involved in the spermatogenesis of Bos indicus bulls. Across the three pairwise comparisons, 3,826 differentially expressed (DE) transcripts were identified, of which 384 are small RNAs. Functional enrichment analysis pointed to gene ontology (GO) terms related to ion channel activity, detoxification of copper, neuroactive receptors, and spermatogenesis. Using the regulatory impact factor (RIF) algorithm, we detected 70 DE small RNAs likely to regulate the DE transcripts considering all pairwise comparisons among tissues. The pattern of small RNA co-expression suggested that these elements are involved in spermatogenesis regulation. The 3,826 DE transcripts (mRNAs and small RNAs) were further subjected to co-expression analyses using the partial correlation and information theory (PCIT) algorithm for network prediction. Significant correlations underpinned the co-expression network, which had 2,216 transcripts connected by 158,807 predicted interactions. The larger network cluster was enriched for male gamete generation and had 15 miRNAs with significant RIF. The miRNA bta-mir-2886 showed the highest number of connections (601) and was predicted to down-regulate ELOVL3, FEZF2, and HOXA13 (negative co-expression correlations and confirmed with TargetScan). In short, we suggest that bta-mir-2886 and other small RNAs might modulate gene expression in the testis and epididymis, in Bos indicus cattle.