Characterization of recombinant murine binder of sperm protein homolog 1 and its role in capacitation

Genome-wide association and genomic prediction for scrotal circumference in Hereford and Braford bulls

Scrotal circumference (SC) is widely used as a selection criterion for bulls in breeding programs, since it is easily assessed and correlated with several desirable reproductive traits. The objectives of this study were: to perform a genome-wide association study (GWAS) to identify genomic regions associated with SC adjusted for age (SCa) and for both age and weight (SCaw); to select Tag SNPs from GWAS to construct low-density panel for genomic prediction; and to compare the prediction accuracy of the SC through different methods for Braford and Hereford bulls from the same genetic breeding program. Data of SC from 18,172 bulls (30.4 ± 3.7 cm) and of genotypes from 131 sires and 3,545 animals were used. From GWAS, the top 1% of 1-Mb windows were observed on chromosome (BTA) 2, 20, 7, 8, 15, 3, 16, 27, 6 and 8 for SCa and on BTA 8, 15, 16, 21, 19, 2, 6, 5 and 10 for SCaw, representing 17.4% and 18.8% of the additive genetic variance of SCa and SCaw, respectively. The MeSH analysis was able to translate genomic information providing biological meanings of more specific gene functions related to the SCa and SCaw. The genomic enhancement methods, especially single step GBLUP, that combined phenotype and pedigree data with direct genomic values generated gains in accuracy in relation to pedigree BLUP, suggesting that genomic predictions should be applied to improve genetic gain and to narrow the generation interval compared to traditional methods. The proposed Tag-SNP panels may be useful for lower-cost commercial genomic prediction applications in the future, when the number of bulls in the reference population increases for SC in Hereford and Braford breeds.

Assessment of binder of sperm protein 1 (BSP1) and heparin effects on in vitro capacitation and fertilization of bovine ejaculated and epididymal sperm

The present study evaluated the effect of binder of sperm protein 1 (BSP1) and/or heparin on in vitro bovine capacitation and fertilization rates using epididymal and ejaculated bovine sperm. Frozen-thawed sperm were selected and used in the following treatments. Control group: Fert-TALP medium without heparin; heparin (HEP) group: Fert-TALP with heparin (10 UI/ml); BSP1 group: Fert-TALP medium with BSP1 (10 µg/ml for ejaculated sperm; 40 µg/ml for epididymal sperm); HEP + BSP1 group: Fert-TALP medium with heparin (5 UI/ml) and BSP1 (5 µg/ml for ejaculated sperm; 20 µg/ml for epididymal sperm) and determined in vitro capacitation rates in different interval times (0, 15, 30 and 60 min) using the chlortetracycline fluorescence (CTC) method. Also, we evaluated the development rates of oocytes fertilized with ejaculated or epididymal sperm into the same treatments. Capacitation was greater and faster when ejaculated sperm were treated for 60 min with heparin compared with other treatments. However, developmental rates were similar in all treatments. For epididymal sperm, the treatments with BSP1 presented higher capacitation and fertilization rates compared with heparin (P < 0.05). The effects of heparin + BSP1 on capacitation and developmental rates did not cause any increase in capacitation or blastocyst rates compared with other groups for ejaculated or epididymal sperm. In conclusion, this study confirmed that either BSP1 and heparin can be used as capacitator agents for bovine ejaculated sperm during IVF. However, BSP1 seems to be more efficient compared with heparin for epididymal sperm. Furthermore, BSP1 and heparin have no synergic effects on sperm capacitation.

Role of Binder of SPerm homolog 1 (BSPH1) protein in mouse sperm-egg interaction and fertilization

In mice, the Binder of Sperm Homolog 1 protein is exclusively expressed in the epididymis. BSP proteins play a role in the membrane modification events that occur during sperm capacitation. In the current study, we investigated the role of mouse recombinant BSP homolog 1 (rec-BSPH1) in sperm-egg interaction. Mouse oocytes were co-incubated with different concentrations of rec-BSPH1 or control proteins and then inseminated with sperm. To establish whether rec-BSPH1 interfered with in vitro fertilization of mouse oocytes, rec-BSPH1 binding to egg and sperm was first tested using an immunodetection assay. In separate experiments, sperm were immuno-neutralized by anti-rec-BSPH1 antibodies to indirectly verify the implication of BSPH1 in sperm-egg interaction and fertilization. The study revealed a dose-dependent inhibition of fertilization when oocytes were pre-incubated with rec-BSPH1. Moreover, sperm immuno-neutralization with anti-rec-BSPH1 antibodies led to dramatic motility changes, followed by compromised fertilization. In view of these results, we conclude that BSPH1 could be a marker of sperm fertility and thus an eventual target for male contraceptive development.

Epididymal proteins Binder of SPerm Homologs 1 and 2 (BSPH1/2) are dispensable for male fertility and sperm motility in mice

The binder of sperm family of proteins has been reported to be indispensable for sperm maturation and capacitation. However, their physiological functions in fertility have only been studied in vitro. CRISPR/Cas9 genome editing was utilized to generate double knockout (DKO) mice by simultaneously targeting the two murine binder of sperm genes, Bsph1 and Bsph2. To confirm that the homologous genes and proteins were completely eliminated in the DKO mice, different methods such as reverse transcription polymerase chain reaction, digital droplet-polymerase chain reaction and liquid chromatography tandem mass spectrometry were applied. Bsph1/2 DKO male mice were bred by intercrossing. Compared to wild type counterparts, male Bsph1/2 null mice, lacking BSPH1/2 proteins, were fertile with no differences in sperm motility and sperm count. However, the weights of male pups were significantly increased in Bsph1/2 double knockout mice in a time dependent manner spanning days 6 and 21, as well as 6 weeks of age. No change was detected in the weights of female pups during the same period. Taken together, these data indicate that BSPH1/2 proteins are dispensable for male fertility in mice but may influence growth.

Recombinant peptide reverses cryo-capacitation in ram sperm and improves in vitro fertilization

Semen cryopreservation is a very important technique for assisted reproduction; however, the cryopreservation process is harmful because it results in a reduction in sperm motility and viability, and leads to premature signals of capacitation, resulting in lesser than desirable fertility rates after artificial insemination. A fraction of seminal plasma, enriched in proteins that contain type II fibronectin domains (FNII) can reverse molecular indicators of cryo-capacitation. The beneficial effects of these proteins, however, depend on the relative abundance in seminal plasma. To create a safe additive for improving frozen sperm functionality, in the present study there was cloning and expression of a recombinant peptide containing four FNII domains (named TrxA-FNIIx4-His6) and evaluation of its effect after addition to frozen/thawed ram sperm. The cDNA for this protein was expressed in E. coli and after denaturation and re-naturalization of the protein, toxicity and binding capacity were assessed. By fluorescent labelling assessment, there was binding of the protein to the thawed sperm. At the two doses used (0.15 and 0.3 μM), TrxA-FNIIx4-His6 had the capacity to reverse the molecular indicators of cryo-capacitation as indicated by the reduction on phosphorylated substrates of PKA. Furthermore, the supplementation with this protein resulted in a normal capacitation process as evidenced by the increase in the in vitro fertilization rate when the greatest concentration of the protein was evaluated (73.25 ± 2.95; 40.13 ± 11.82 for 0.3 μM and control, respectively). There was no effect of protein supplementation on sperm objective motility compared to untreated sperm. In conclusion, the use of TrxA-FNIIx4-His6 is a promising biotechnological approach for cryopreserving ram sperm and maintaining sperm viability.

Binder of Sperm Proteins 1 and 5 have contrasting effects on the capacitation of ram spermatozoa

Binder of Sperm Proteins (BSPs) are the most abundant seminal plasma protein family in the ram and bull. They have been extensively studied in the bull but less is known about their function in ovine seminal plasma and current knowledge suggests that BSPs may have different effects in these two species. In the bull, they facilitate capacitation and destabilize the sperm membrane during in vitro handling, whereas in the ram, they appear to stabilize the sperm membrane and prevent cryopreservation-induced capacitation-like changes. Further investigation into the effects of BSPs on ram spermatozoa under capacitating conditions is required to further clarify their physiological roles in the ram. We investigated the effects of Binder of Sperm Proteins 1 and 5 on epididymal ram spermatozoa in conditions of low, moderate, and high cAMP. BSPs had minimal effects on sperm function in low-cAMP conditions, but caused significant changes under cAMP upregulation. BSP1 stabilized the membrane and qualitatively reduced protein tyrosine phosphorylation, but significantly increased cholesterol efflux and induced spontaneous acrosome reactions. BSP5 slightly increased spontaneous acrosome reactions and caused sperm necrosis. However, BSP5 had minimal effects on membrane lipid order and cholesterol efflux and did not inhibit protein tyrosine phosphorylation. These findings demonstrate that under maximal cAMP upregulation, BSP1 affected ram spermatozoa in a manner comparable to bull spermatozoa, while BSP5 did not.

CRISPR-Cas9-mediated mutation revealed BSPH2 protein is dispensable for male fertility

Members of the Binder of SPerm (BSP) superfamily have been identified in both human and mouse epididymis. These proteins are known to bind sperm membrane and promote sperm capacitation. Studies suggest that BSPH2 might play a different role in sperm functions from its counterparts; however, the role of BSPH2 remains mainly unexplored. To investigate whether the absence of one member of the BSP family could affect fertility, mice lacking Bsph2 expression were generated using clustered regularly interspaced short palindromic repeats (CRISPR) associated 9 (Cas9) technology. Knockout (KO) male mice were mated with wild-type (WT) females, and the number and weight of the pups were determined. Sperm motility in WT and KO was assessed using sperm class analyzer (SCA). Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used for protein identification. Fertility analysis of null Bsph2 mice did not reveal any phenotype. No differences were noticed on average litter size or average pup weight. Normal testis weight and morphology were observed in Bsph2^+/- and Bsph2^-/- compared to the WT. Quantitative polymerase chain reaction analyses revealed that Bsph1 messenger RNA expression was increased in mutant mice, whereas LC-MS/MS analysis displayed no increase in protein expression level. Taken together, we show the existence of redundant function for murine BSPH2 and the lack of BSPH2 itself does not lead to sterility.

Gelatin Binding Proteins in Reproductive Physiology

In order to advance the assisted reproductive technologies used in animals and human beings, it is important to accumulate basic informations about underlying molecular mechanisms that shape the biological processes of reproduction. From within seminal plasma, proteins perform a wide variety of distinct functions that regulate major reproductive events such as fertilization. The ability of such proteins to bind and interact with different antagonistic ions and biomolecules such as polysaccharides, lipids, and other proteins present in the male and female reproductive tract define these capabilities. Over the last two decades, extensive work has been undertaken in an attempt to define the role of seminal plasma proteins, of which, Gelatin binding proteins (GBPs) represent a large family. GBPs comprise of known group of Bovine seminal plasma (BSP) protein family, matrix metallo proteinases (MMP 2 and MMP 9) and fibronectin, which have been widely studied. The presence of a type II repeat is a characteristic feature of GBPs, which is similar in structure to the fibronectin type II domain (fn2), which has ability to bind multiple ligands including gelatin, glycosaminoglycans, choline phospholipids, and lipoproteins. Two fn2 domains are present within the BSP protein family, while, three fn2 domains are found in gelatinases (MMP-2 and MMP9), and ELSPBP1 (Epididymosomes Transfer Epididymal Sperm Binding Protein 1) contains four long fn2 domains. For the most part BSP proteins are exclusively expressed in seminal vesicles although mBSPH1, mBSPH2 and hBSPH1 are all expressed in the epididymis. The expression of gelatinases has been demonstrated in several organs and tissues such as the prostate, testis, epididymis, ovary, human placenta, cervix and endometrial wall. This review intends to bring current updates on the role of GBPs in reproductive physiology to light, which may act as basis for future studies on GBPs.

Purification of binder of sperm protein 1 (BSP1) and its effects on bovine in vitro embryo development after fertilization with ejaculated and epididymal sperm

The present study evaluated functional aspects of binder of sperm 1 (BSP1) in the bovine species. In a first experiment, cumulus-oocyte complexes (n = 1274) were incubated with frozen-thawed ejaculated sperm (18 hours) in Fert-TALP medium containing: heparin, 10, 20, or 40 μg/mL BSP1. Heparin followed by gelatin affinity chromatography was used for purification of BSP1 from bovine seminal vesicle fluid. With ejaculated sperm, cleavage rates were similar when Fert-TALP medium was incubated with heparin (74.1 ± 2.7%), 10 μg/mL BSP1 (77.8 ± 3.1%), or 20 μg/mL BSP1 (74 ± 2.0%). Day-7 blastocyst rates were equivalent after incubations with heparin (40.8 ± 5.0%) and 10 μg/mL BSP1 (34.1 ± 4.4%), but reduced after 20 μg/mL BSP1 (22.4 ± 2.9%) and 40 μg/mL BSP1 (19.3 ± 4.1%; P < 0.05). In the second experiment, cumulus-oocyte complexes (n = 1213) were incubated with frozen-thawed cauda epididymal sperm (18 hours) in Fert-TALP medium containing: no heparin, heparin, 10, 20, or 40 μg/mL. Cleavage and blastocyst rates were similar after treatments with heparin (68.5 ± 1.3% and 24.7 ± 3.2%, respectively) or without heparin (65.5 ± 1.8% and 27.3 ± 1.6%, respectively). Cleavage was higher after treatment with any BSP1 concentrations (74.2 ± 2.7%-79.0 ± 1.1%) than without heparin (P < 0.05). Also, cleavage was better after Fert-TALP medium incubation with 40 μg/mL BSP1 (79.0 ± 1.1%) than with heparin (68.5 ± 1.3%; P < 0.05). Embryo development was higher (P < 0.05) after treatment with 20 μg/mL BSP1 (35.6 ± 2.5%) and 40 μg/mL (41.1 ± 2%) than after incubations with heparin (24.7 ± 3.2%) or without heparin (27.3 ± 1.6%). Interestingly, BSP1 did not cause reductions in blastocyst rates after fertilization with epididymal sperm, as observed with ejaculated sperm. On the basis of immunocytochemistry, there was BSP1 binding to frozen-thawed ejaculated but not to epididymal sperm. Also, anti-BSP1 reaction remained on ejaculated sperm (as expected) and appeared on epididymal sperm after incubation with purified BSP1. Acrosome reaction of ejaculated and epididymal sperm was induced after incubation with purified BSP1 as well, indicating an effect of BSP1 on capacitation. In conclusion, purified BSP1 from bull seminal vesicles was able to bind to and induce capacitation of ejaculated and epididymal sperm. Also, BSP1 added to fertilization media and allowed proper cleavage and embryo development, with the effects being modulated by previous exposure or not of spermatozoa to seminal plasma.

New Insights into the Phylogeny and Gene Context Analysis of Binder of Sperm Proteins (BSPs)

Seminal plasma (SP) proteins support the survival of spermatozoa acting not only at the plasma membrane but also by inhibition of capacitation, resulting in higher fertilizing ability. Among SP proteins, BSP (binder of sperm) proteins are the most studied, since they may be useful for the improvement of semen diluents, storage and subsequent fertilization results. However, an updated and detailed phylogenetic analysis of the BSP protein superfamily has not been carried out with all the sequences described in the main databases. The update view shows for the first time an equally distributed number of sequences between the three families: BSP, and their homologs 1 (BSPH1) and 2 (BSPH2). The BSP family is divided in four subfamilies, BSP1 subfamily being the predominant, followed by subfamilies BSP3, BSP5 and BSP2. BSPH proteins were found among placental mammals (Eutheria) belonging to the orders Proboscidea, Primates, Lagomorpha, Rodentia, Chiroptera, Perissodactyla and Cetartiodactyla. However, BSPH2 proteins were also found in the Scandentia order and Metatheria clade. This phylogenetic analysis, when combined with a gene context analysis, showed a completely new evolutionary scenario for the BSP superfamily of proteins with three defined different gene patterns, one for BSPs, one for BSPH1/BSPH2/ELSPBP1 and another one for BSPH1/BSPH2 without ELSPBP1. In addition, the study has permitted to define concise conserved blocks for each family (BSP, BSPH1 and BSPH2), which could be used for a more reliable assignment for the incoming sequences, for data curation of current databases, and for cloning new BSPs, as the one described in this paper, ram seminal vesicle 20 kDa protein (RSVP20, Ovis aries BSP5b).

Functional characterization of the domains of the bovine binder of SPerm 5 (BSP5) protein

BACKGROUND

Bovine BSP5 is a multifunctional protein primarily involved in sperm capacitation. BSP5 consists of long N-terminal part followed by two similar and highly conserved fibronectin type II domains designated A and B.

METHODS

In order to assess the role of these domains in the sperm binding and capacitation processes, we created recombinant individual domains (N, A, B), series of overlapping domains (NA and AB) and full-length BSP5 in an Escherichia coli expression system. The recombinant constructs were also tested for their ability to interact with ligands such as gelatine, heparin, chondroitin sulphate B and phosphatidylcholine liposomes by affinity chromatography and co-sedimentation studies.

RESULTS

With the exception of the N domain, all recombinant constructs retained gelatine, phosphatidylcholine, heparin and chondroitin sulphate B binding activities. Domain-wise studies showed clearly that AB domain is capable of performing its biological functions as well as the full-length protein, as it was able to potentiate heparin-mediated sperm capacitation.

CONCLUSIONS

These results indicate that the C-terminal domain composed of two Fn2 domains is sufficient and crucial to maintain the biological functions of BSP proteins. The N-terminal part of the protein did not bind to any of known BSP5-ligands including epididymal sperm and did not seem to be required for either sperm binding or sperm capacitation. This study also confirmed that glycosylation is not required for BSP-mediated sperm capacitation or any of the binding characteristics displayed by BSP5.