In vitro adverse effects of amitraz on semen quality: Consequences in bovine embryo development

Veterinary drugs are potential environmental pollutants that interfere with male reproductive function. Infertility has increased, and it is known that environmental toxins contribute to declining sperm parameters. Amitraz {N,N-[(methylamino) dimeth-ylidyne] di-2,4-xylidine} (AMZ) is a formamidine pesticide widely used as an insecticide and an acaricide. The aim of this study was to evaluate the toxicity of AMZ in bovine sperm. Three experiments using frozen-thawed bovine semen incubated with AMZ for 2 h were carried out. Negative and solvent (dimethyl sulfoxide) controls were run simultaneously with treatments. In experiment 1, the AMZ concentrations used were 10, 15 and 25 μg AMZ/ml and the sperm parameters evaluated were viability, mitochondrial activity, acrosomal status, functional membrane integrity and apoptosis. In experiments 2 and 3, 25 μg AMZ/ml was used to evaluate fertilizing capacity, embryo development and blastocyst DNA damage. In experiment 1, 25 μg AMZ/ml decreased sperm viability (P = 0.01), reduced mitochondrial activity (P = 0.03) and induced apoptosis (P < 0.01). Also, 15 and 25 μg AMZ/ml affected functional membrane integrity (P < 0.01). In experiment 2, AMZ did not alter sperm-zona binding (P = 0.40) and pronucleus formation (P = 0.36). In experiment 3, 25 μg AMZ/ml decreased the rate of embryo development (P < 0.01) and increased apoptosis (P = 0.03). These results suggest that AMZ induced alterations in bovine sperm, probably affecting male fertility at concentrations that could be present in the environment.

Cooled storage of semen from livestock animals (part I): boar, bull, and stallion

This review is part of the Festschrift in honor of Dr. Duane Garner and provides an overview of current techniques for cooled storage of semen from livestock animals. The first part describes the current state of the art of liquid semen preservation in boars, bulls, and stallions, including the diluents, use of additives, processing, temperature, and cooling of semen. The species-specific physiology and varying extents of cold shock sensitivity are taken into consideration. In addition, factors influencing the quality of cooled-stored semen are discussed. Methods, trends, and the most recent advances for improving sperm quality during cold-temperature storage are highlighted and their respective advantages and disadvantages are contrasted. There has been much progress in recent years regarding cold-temperature storage of boar sperm and there is great potential for a large-scale use to replace the current 17 °C temperature storage regime and the associated use of antibiotics in the future. For stallion sperm, there is an opposite trend away from previous low-temperature storage towards storage at higher temperatures to increase sperm viability and longevity. In bulls, liquid storage of sperm is mostly used in the seasonal dairy production systems of New Zealand and Ireland, but with further research focusing on shelf-live elongation of liquid preserved sperm, there is potential for an application in breeding programs worldwide.

TMT-based quantitative N-glycoproteomic analysis reveals glycoprotein protection can improve the quality of frozen bovine sperm

Cryopreservation of bovine semen plays a vital role in accelerating genetic improvement and elite breeding, but it has a detrimental effect on sperm quality, resulting in the decline of the reproductive efficiency. The glycosylation modification of protein has irreplaceable roles in spermatozoa. Herein, the effect of cryopreservation on glycoproteins of bovine spermatozoa has been studied for the first time using a tandem mass tag (TMT)-labeled quantitative glycoproteome. A total of 2598 proteins and 492 glycoproteins were identified, including 83 different expression proteins (DEPs) and 44 different expression glycosylated proteins (DEGPs) between fresh and frozen spermatozoa. Thirty-three DEPs are glycoproteins, which demonstrates that glycoproteins of bovine sperm were seriously affected by cryopreservation. Moreover, the effects include glycoprotein expression, glycosylation modification, and substructure localization for proteins such as glycoproteins TEX101, ACRBP, and IZOMU4. The biologic functions of the 115 changed proteins are mainly involved in sperm capacitation, migration in female genitalia, and sperm-egg interaction. Mostly key regulators were identified to be glycoproteins, which confirms that glycosylated proteins played important roles in bovine sperm. This comprehensive study of sperm glycoproteins helps to unravel the cryoinjury mechanisms, thus implying that glycoprotein protection should be an effective way to improve the quality of frozen sperm.

Semen extender and seminal plasma alter the extent of neutrophil extracellular traps (NET) formation in cattle

During artificial insemination in bovine, the deposition of semen into the uterus results in an immune reaction which is based on polymorphonuclear neutrophils activity, including the formation of neutrophil extracellular traps. The formation of neutrophil extracellular traps as a reaction of neutrophils to spermatozoa was recently described. However, it is not completely clear which components of the semen are responsible for this reaction. The objective of this study was to quantify and compare the formation of neutrophil extracellular traps following in vitro incubation of bovine polymorphonuclear neutrophils with semen and extenders of different origins and conditions. We investigated the interactions between bovine polymorphonuclear neutrophils and different semen extenders, various seminal plasma concentrations from young and old bulls as well as sexed and non-sexed semen and their corresponding extenders. Three different semen extenders from two companies in fresh and frozen-thawed conditions were compared. Fresh semen extenders showed higher neutrophil extracellular traps induction than did frozen-thawed ones. The formation of neutrophil extracellular traps were also dependent on the presence of seminal plasma. We could show that seminal plasma alone, without any sperm cells, induced the reaction and that the addition of at least 1% seminal plasma already resulted in the formation of neutrophil extracellular traps. Furthermore, seminal plasma from young bulls led to significant higher neutrophil extracellular traps induction. No difference between non-sex-sorted and sex-sorted sperm and its extenders was observed. Taken together, different semen extenders as well as the amount and origin of seminal plasma influence neutrophil extracellular traps formation, whereas sex-sorted sperm did not affect the reaction.

Improvement in blastocyst quality by neurotensin signaling via its receptors in bovine spermatozoa during in vitro fertilization

Previously, we reported that neurotensin (NT), which is expressed in the uterus and oviduct, enhanced bovine sperm capacitation and acrosome reactions. As NT mRNA expression in bovine oviducts increases dramatically in the follicular phase, we hypothesized that NT modulates fertilization and subsequent conception in cattle. The objective of this study was to evaluate the effect of NT on embryo development and blastocyst quality. The rate of embryo cleavage was significantly increased by the addition of NT to the fertilization medium. Furthermore, the total number of cells and numbers of cells in the inner cell mass of blastocysts were significantly increased by NT during in vitro fertilization (IVF). These results suggested that NT enhanced the efficiency of early bovine embryo development and blastocyst quality. The expression of NT receptors (NTRs) in sperm, testes, oocytes, and cumulus cells was evaluated to determine whether NT acted via NTRs in sperm alone or in both male and female reproductive cells during IVF. Immunocytochemistry and reverse transcription polymerase chain reaction revealed that NTR1 and NTR2 were expressed in sperm and testes, but not in oocytes and cumulus cells. We propose that NT selectively acts upon sperm via NTR1 and NTR2 during IVF to improve the cleavage rate and quality of blastocysts, which are important determinants of sperm quality for successful conception. This research supports our hypothesis that NT acts as a key modulator of fertilization and conception in cattle. Further studies are necessary to apply our findings to the industrial framework of bovine reproduction.

Improved bovine in vitro embryo production with sexed and unsexed sperm selected by chemotaxis

Assisted reproductive techniques (ART) have been widely used in farm animals in the last decades. Sexed cryopreserved spermatozoa, ovum pick up, in vitro embryo production and transfer constitute the ART that have revolutionized the dairy industry. However, the efficiency of some of these techniques is still low due in part to sperm quality, which influences fertilization, embryo development and implantation. The Sperm Selection Assay (SSA), based on sperm chemotaxis towards progesterone, provides a sperm subpopulation enriched with spermatozoa that are capacitated, with intact DNA and low level of oxidative stress. Since the SSA selects a sperm subpopulation at optimum physiological state, the application of the SSA may improve the efficiency of the current ART. The aim of this study was to adapt the SSA for unsexed and sexed bovine frozen-thawed semen samples, and then to test whether sperm selection by the SSA improves the cleavage rate of bovine embryos in vitro. The optimal SSA conditions to obtain the higher sperm accumulation percentage given by chemotaxis were the same for both unsexed and sexed semen samples. Thus, sperm accumulation in W2 was significantly higher when: 2 million sperm per mL were placed in W1 (unsexed samples: 12 ± 1%, p = 0.002; sexed samples: 14 ± 3%, p = 0.02); 1 pM progesterone was placed in W2 (unsexed sample: 9 ± 1%, p = 0.009; sexed samples: 11 ± 2%, p = 0.02); and to incubate the SSA device for 10 min (unsexed samples: 17 ± 2%, p = 0.007; sexed samples: 10 ± 1%, p = 0.004). We found that the quality of spermatozoa recovered from W2 in unsexed and sexed semen was enhanced. Thus, the capacitation index was significantly increased (unsexed samples: 1.75 ± 0.1, p = 0.0001; sexed samples: 1.76 ± 0.2, p = 0.004), while DNA fragmentation index was significantly decreased (unsexed samples: 0.33 ± 0.07, p = 0.0003; sexed samples: 0.32 ± 0.04, p = 0.002). Moreover, the cleavage index of oocytes fertilized with either unsexed or sexed SSA-selected sperm was significantly improved (unsexed samples: 3.2 ± 0.4, p = 0.0001; sexed samples: 2.3 ± 0.33, p = 0.03). Thus, we show that the SSA can be used to recruit a bovine sperm subpopulation at optimal functional state regardless of whether the sample is previously sexed, and that this optimal state improves bovine embryo cleavage rate.

The addition of docosahexaenoic acid (DHA) and antioxidants (glutathione peroxidase and superoxide dismutase) in extenders to epididymal sperm cryopreservation in bulls

SummaryThe cryopreservation of epididymal sperm is an important technique that allows genetic material to be preserved, even post mortem. However, cryopreservation leads to increased oxidative stress and impaired sperm viability. Polyunsaturated fatty acid (PUFA) supplementation may improve certain sperm characteristics, but it also makes sperm more susceptible to oxidative stress, therefore adding antioxidants that counteract oxidative stress has become an option. In this context, this study aimed to evaluate the effect of the interaction between docosahexaenoic acid (DHA) and antioxidants on the quality after the cryopreservation of epididymal bull sperm. Twenty epididymides were collected after slaughter, and epididymal sperm was cryopreserved with bovine extender supplemented with docosahexaenoic acid (DHA), glutathione peroxidase (GPx) and superoxide dismutase (SOD). We verified an improvement in motility in the group that was treated only with DHA 5 µM and a concentration-dependent effect on susceptibility to lipid peroxidation that was associated with DHA concentration (1 µM, 5 µM or 10 µM). Moreover, treatment with DHA (5 µM) and SOD (20 IU/ml) resulted in higher sperm motility. Thus, the association between DHA (5 µM) and SOD (20 IU/ml) appears to be an option for increased epididymal sperm features in bulls.

Whole-genome scan reveals significant non-additive effects for sire conception rate in Holstein cattle

Background

Service sire has a considerable impact on reproductive success in dairy cattle. Most gene mapping studies for bull fertility have focused on additive effects, while non-additive effects have been largely ignored. The main goal of this study was to assess the relevance of non-additive effects on Sire Conception Rate (SCR) in Holstein dairy cattle. The analysis included 7.5 k Holstein bulls with both SCR records and 57.8 k single nucleotide polymorphism (SNP) markers spanning the entire genome.

Results

The importance of non-additive effects was evaluated using an efficient two-step mixed model-based approach. Four genomic regions located on chromosomes BTA8, BTA9, BTA13 and BTA17 showed marked dominance and/or recessive effects. Most of these regions harbor genes, such as ADAM28, DNAJA1, TBC1D20, SPO11, PIWIL3 and TMEM119, that are directly implicated in testis development, male germ line maintenance, and sperm maturation.

Conclusions

This study provides further evidence for the relevance of non-additive effects in fitness-related traits, such as male fertility. In addition, these findings may point out new strategies for improving service sire fertility in dairy cattle via marker-assisted selection.

Effects of surrounding fluid on motility of hyperactivated bovine sperm

Mammalian spermatozoa in organisms with internal fertilization are required to swim in the cervical and oviductal mucus, whose rheological properties differ substantially from those of water. Moreover, on the way to the oviduct, a change in sperm motility called hyperactivation may occur. In the present study, we focused on the motion characteristics of hyperactivated bovine sperm and investigated the effect of the surrounding fluid on motility. We prepared two kinds of polyacrylamide with high-viscosity non-Newtonian fluid properties, similar to the actual cervical and oviductal mucus. Using semen from Japanese cattle, we evaluated curvilinear velocity (VCL), straight-line velocity (VSL), and average path velocity (VAP). Additionally, we estimated linearity (LIN), straightness (STR), and wobble (WOB) as sperm motility parameters for several surrounding fluids. We successfully induced hyperactivation of bovine sperm in high-viscosity non-Newtonian fluid. Hyperactivation resulted in an increase in VCL and a decrease in VSL. In the high-viscosity non-Newtonian fluid, the hyperactivated sperm moved in a zig-zag pattern with regularity, different from the movement observed in a diluted solution. The increase in WOB in the non-Newtonian fluid suggests that hyperactivated sperm efficiently progress along the groove that exists on the oviductal mucus wall. These results improve our understanding of the motility of bovine sperm when they undergo hyperactivation in the actual cervical and oviductal mucus.

Effects on glycocalyx structures of frozen-thawed bovine sperm induced by flow cytometry and artificial capacitation

Sperm sorting by flow cytometry is a useful technology in the bovine industry, but the conception rates after artificial insemination using sex-sorted sperm are lower than when using the un-sorted sperm. In this study, we have investigated the causes for these low conception rates. We have focused on changes caused by flow cytometry to the glycocalyx, which forms the outermost surface of the sperm membrane. We have also evaluated the effects of capacitation on the glycocalyx since capacitation involves a redistribution of the sperm membrane that is vital for successful fertilization and conception. Lectin histochemistry was used to visualize the structure of the sperm glycocalyx. Lectin-staining sites were examined in non-treated sperm, sex-sorted sperm, and capacitated sperm. We have detected six different staining patterns related to different labeling regions of the sperm. Phaseolus vulgaris–erythroagglutinin (PHA-E) lectin-staining patterns of non-treated sperm were very different from those observed for sex-sorted sperm or capacitated sperm, suggesting that both, sex sorting by flow cytometry and the capacitation process affected the glycocalyx structures in the sperm. In addition, the total tyrosine-phosphorylation level in sex-sorted sperm was significantly higher than that in the non-treated sperm. Therefore, we concluded that the unexpected capacitation of bovine sperm during flow cytometry is associated with changes in the glycocalyx. Since premature capacitation leads to low conception rates, this unexpected capacitation could be a cause of low conception rates after artificial insemination using sex-sorted sperm.

Unravelling the genomic architecture of bull fertility in Holstein cattle

BACKGROUND

Fertility is considered an important economic trait in dairy cattle. Most studies have investigated cow fertility while bull fertility has received much less consideration. The main objective of this study was to perform a comprehensive genomic analysis in order to unravel the genomic architecture underlying sire fertility in Holstein dairy cattle. The analysis included the application of alternative genome-wide association mapping approaches and the subsequent use of diverse gene set enrichment tools.

RESULTS

The association analyses identified at least eight genomic regions strongly associated with bull fertility. Most of these regions harbor genes, such as KAT8, CKB, TDRD9 and IGF1R, with functions related to sperm biology, including sperm development, motility and sperm-egg interaction. Moreover, the gene set analyses revealed many significant functional terms, including fertilization, sperm motility, calcium channel regulation, and SNARE proteins. Most of these terms are directly implicated in sperm physiology and male fertility.

CONCLUSIONS

This study contributes to the identification of genetic variants and biological processes underlying sire fertility. These findings can provide opportunities for improving bull fertility via marker-assisted selection.

Identification of bovine sperm acrosomal proteins that interact with a 32-kDa acrosomal matrix protein

Mammalian fertilization is accomplished by the interaction between sperm and egg. Previous studies from this laboratory have identified a stable acrosomal matrix assembly from the bovine sperm acrosome termed the outer acrosomal membrane-matrix complex (OMC). This stable matrix assembly exhibits precise binding activity for acrosin and N-acetylglucosaminidase. A highly purified OMC fraction comprises three major (54, 50, and 45 kDa) and several minor (38-19 kDa) polypeptides. The set of minor polypeptides (38-19 kDa) termed "OMCrpf polypeptides" is selectively solubilized by high-pH extraction (pH 10.5), while the three major polypeptides (55, 50, and 45 kDa) remain insoluble. Proteomic identification of the OMC32 polypeptide (32 kDa polypeptide isolated from high-pH soluble fraction of OMC) yielded two peptides that matched the NCBI database sequence of acrosin-binding protein. Anti-OMC32 recognized an antigenically related family of polypeptides (OMCrpf polypeptides) in the 38-19-kDa range with isoelectric points ranging between 4.0 and 5.1. Other than glycohydrolases, OMC32 may also be complexed to other acrosomal proteins. The present study was undertaken to identify and localize the OMC32 binding polypeptides and to elucidate the potential role of the acrosomal protein complex in sperm function. OMC32 affinity chromatography of a detergent-soluble fraction of bovine cauda sperm acrosome followed by mass spectrometry-based identification of bound proteins identified acrosin, lactadherin, SPACA3, and IZUMO1. Co-immunoprecipitation analysis also demonstrated the interaction of OMC32 with acrosin, lactadherin, SPACA3, and IZUMO1. Our immunofluorescence studies revealed the presence of SPACA3 and lactadherin over the apical segment, whereas IZUMO1 is localized over the equatorial segment of Triton X-100 permeabilized cauda sperm. Immunoblot analysis showed that a significant portion of SPACA3 was released after the lysophosphatidylcholine (LPC)-induced acrosome reaction, whereas the IZUMO1 and lactadherin polypeptides remain associated to the particulate fraction. Almost entire population of bovine sperm IZUMO1 relocates to the equatorial segment during the LPC-induced acrosome reaction. We propose that the interaction of OMC32 matrix polypeptide with detergent-soluble acrosomal proteins regulates the release of hydrolases/other acrosomal protein(s) during the acrosome reaction.

Identification and characterization of a bovine sperm acrosomal matrix protein and its mechanism of interaction with acrosomal hydrolases

Fertilization, the union of male and female gametes to create offspring, is an intricate biological process dependent upon several biochemical and physiological events. Our understanding of the functions of protein constituents of the outer acrosomal membrane-associated matrix complex (OMC) is limited. A highly purified OMC fraction isolated from bovine cauda sperm heads comprised 54, 50, 45, and 38-19 kDa polypeptides. The objective of this study is to identify and characterize the 45 kDa (OMC45) polypeptide, to define its role in binding acrosomal hydrolases, and to examine the fate of OMC45 polypeptide during the acrosome reaction. We isolated OMC45 polypeptide from the high-pH insoluble fraction of OMC. Proteomic analysis of OMC45 by MALDI-TOF-TOF yielded eight peptides that matched the NCBI database sequence of Tektin 3 (TEKT3). Triton X-100-permeabilized cauda sperm exhibited intense staining of the acrosomal segment with anti-OMC45 and anti-TEKT3. The OMC45 polypeptide was solubilized by radio-immunoprecipitation assay buffer extraction. The solubilized fraction was subjected to immunoprecipitation analysis. The OMC45 polypeptide was recovered in the anti-OMC45 immunoprecipitation pellet. An identical blot stained with anti-TEKT3 exhibited the presence of TEKT3 polypeptide in the anti-OMC45 pellet. Our immunofluorescence and biochemical studies confirm the proteomics identification of OMC45 polypeptide and that it exhibits a sequence similarity to TEKT3. OMC45 glycoprotein possesses both N-linked and O-linked oligosaccharides. Deglycosylated OMC45 revealed a significant reduction in both acrosin and N-acetylglucosaminidase (NAGA) binding in comparison with acrosin and NAGA binding to a native OMC45 polypeptide, demonstrating the important role of oligosaccharides in hydrolase binding. OMC45 polypeptide is not released during the acrosome reaction but remains in the particulate cell subfraction, associated with the hybrid membrane complex.

Effect of non-Newtonian fluid properties on bovine sperm motility

The swimming process by which mammal spermatozoa progress towards an egg within the reproductive organs is important in achieving successful internal fertilization. The viscosity of oviductal mucus is more than two orders of magnitude greater than that of water, and oviductal mucus also has non-Newtonian properties. In this study, we experimentally observed sperm motion in fluids with various fluid rheological properties and investigated the influence of varying the viscosity and whether the fluid was Newtonian or non-Newtonian on the sperm motility. We selected polyvinylpyrrolidone and methylcellulose as solutes to create solutions with different rheological properties. We used the semen of Japanese cattle and investigated the following parameters: the sperm velocity, the straight-line velocity and the amplitude from the trajectory, and the beat frequency from the fragellar movement. In a Newtonian fluid environment, as the viscosity increased, the motility of the sperm decreased. However, in a non-Newtonian fluid, the straight-line velocity and beat frequency were significantly higher than in a Newtonian fluid with comparable viscosity. As a result, the linearity of the sperm movement increased. Additionally, increasing the viscosity brought about large changes in the sperm flagellar shape. At low viscosities, the entire flagellum moved in a curved flapping motion, whereas in the high-viscosity, only the tip of the flagellum flapped. These results suggest that the bovine sperm has evolved to swim toward the egg as quickly as possible in the actual oviduct fluid, which is a high-viscosity non-Newtonian fluid.