Relationship of protein tyrosine phosphorylation state with tolerance to frozen storage and the potential to undergo cyclic AMP-dependent hyperactivation in the spermatozoa of Japanese Black bulls

Characterization of expression patterns and dynamic relocation of Notch proteins during acrosome reaction of bull spermatozoa

Notch is a conserved cell-signaling pathway involved in spermatogenesis regulation. This study firstly evaluated the presence, localization patterns, acquisition origin and relation to acrosome reaction of Notch proteins in bull sperm. Western Blot analysis detected all Notch proteins in ejaculated bull sperm, and immunostaining described their specific sperm localization. Recovery of sperm from different segments showed that Notch proteins have testicular origin (NOTCH1, NOTCH2, DLL4), are sequentially acquired during sperm maturation along epididymal transit (NOTCH3, DLL3, JAGGED1-2), or post-ejaculation (DLL1, NOTCH4). Testis NOTCH2 is ubiquitously expressed in all germ-cell lines, whereas DLL4 is expressed in round and elongated spermatids during the Golgi, Cap, Acrosome and Maturation phases. In vitro spontaneous and induced sperm acrosome reaction induce consistent sperm regional relocation of NOTCH2, DLL4 and JAGGED1, and these relocation patterns are significantly associated to sperm acrosome status. NOTCH2 and JAGGED1 are relocated from the head apical to the post-equatorial regions, whereas DLL4 is lost along with the acrosome, evidencing that sperm spatial redistribution of NOTCH2 and JAGGED1 is linked to acrosome reaction onset, whereas DLL4 loss is linked to AR completion. Overall, results prompt for a relevant Notch role in bull sperm acrosome testicular development, epididymal maturation and acrosome reaction.

Recent advances in cryotolerance biomarkers for semen preservation in frozen form-A systematic review

Spermatozoa cryopreservation has been practiced for decades and is a very useful technique for long-term preservation of sperm fertility. The capability for semen cryopreservation varies across species, seasons, latitudes, and even for different ejaculates from the same animal. This article summarizes research results on sperm cryotolerance biomarkers in several species, focusing on three areas: spermatozoa cryotolerance biomarkers, seminal plasma proteins cryotolerance biomarkers, and other cryotolerance biomarkers. We discovered that sperm cryoresistance biomarkers are primarily related to sperm plasma membrane stability, the presence of antioxidant substances in sperm or seminal plasma, sperm cell energy metabolism, water and small molecule transport channels in the sperm plasma membrane, and antistress substances in sperm or seminal plasma. The research conducted using diverse livestock models can be employed to enhance the basic and applied reproduction of other mammals through the study of sperm cryotolerance biomarkers, as well as the substantial similarities between livestock and other organisms, including endangered species.

CpG DNA methylation changes during epididymal sperm maturation in bulls

BACKGROUND

During epididymal transit spermatozoa acquire specific morphological features which enhance their ability to swim in a progressive manner and interact with the oocytes. At the same time, sperm cells undergo specific molecular rearrangements essential for the fertilizing sperm to drive a correct embryo development. To assess epigenetic sperm changes during epididymal maturation, the caput, corpus and cauda epididymis sperm tracts were isolated from eight bulls and characterized for different sperm quality parameters and for CpG DNA methylation using Reduced Representation Bisulfite Sequencing (RRBS) able to identify differentially methylated regions (DMRs) in higher CpG density regions.

RESULTS

Caput sperm showed significant variation in motility and sperm kinetics variables, whereas spermatozoa collected from the corpus presented morphology variation and significant alterations in variables related to acrosome integrity. A total of 57,583 methylated regions were identified across the eight bulls, showing a significantly diverse distribution for sperm collected in the three epididymal regions. Differential methylation was observed between caput vs corpus (n = 11,434), corpus vs cauda (n = 12,372) and caput vs cauda (n = 2790). During epididymal transit a high proportion of the epigenome was remodeled, showing several regions in which methylation decreases from caput to corpus and increases from corpus to cauda.

CONCLUSIONS

Specific CpG DNA methylation changes in sperm isolated from the caput, corpus, and cauda epididymis tracts are likely to refine the sperm epigenome during sperm maturation, potentially impacting sperm fertilization ability and spatial organization of the genome during early embryo development.

The cryopreservation process induces alterations in proteins associated with bull sperm quality: The equilibration process could be a probable critical control point

The present study quantitatively characterized the proteomic changes in bull spermatozoa induced by the cryopreservation process. We performed high-throughput comparative global proteomic profiling of freshly ejaculated (before cryopreservation), equilibrated (refrigerated storage; during cryopreservation), and frozen (ultralow temperature; after cryopreservation) bull spermatozoa. Using the liquid chromatography-mass spectrometry (LC-MS/MS) technique, a total of 1,692, 1,415, and 1,286 proteins were identified in fresh, equilibrated, and cryopreserved spermatozoa, respectively. When the proteome of fresh spermatozoa was compared with equilibrated spermatozoa, we found that 166 proteins were differentially expressed. When equilibrated spermatozoa were compared with cryopreserved spermatozoa, we found that 147 proteins were differentially expressed between them. Similarly, we found that 156 proteins were differentially expressed between fresh and cryopreserved spermatozoa. Among these proteins, the abundance of 105 proteins was lowered during the equilibration process itself, while the abundance of 43 proteins was lowered during ultralow temperature preservation. Remarkably, the equilibration process lowered the abundance of sperm proteins involved in energy metabolism, structural integrity, and DNA repair and increased the abundance of proteins associated with proteolysis and protein degradation. The abundance of sperm proteins associated with metabolism, cGMP-PKG (cyclic guanosine 3',5'-monophosphate-dependent protein kinase G) signaling, and regulation of the actin cytoskeleton was also altered during the equilibration process. Collectively, the present study showed that the equilibration step in the bull sperm cryopreservation process was the critical point for sperm proteome, during which a majority of proteomic alterations in sperm occurred. These findings are valuable for developing efficient protocols to minimize protein damage and to improve the quality and fertility of cryopreserved bull spermatozoa.

Effects of reduced glutathione supplementation in semen freezing extender on frozen-thawed bull semen and in vitro fertilization

During cryopreservation, spermatozoa may suffer cold and cryo-induced injuries -associated with alterations in cell defense systems- that are detrimental to their function and subsequent fertility. This study aimed to determine the efficacy of supplementing the semen freezing extender with the antioxidant reduced glutathione (GSH) in cattle. Semen was collected from four bulls and diluted in a freezing extender supplemented with or without GSH (0, 1, 5, and 10 mM) before the cooling step of the cryopreservation process. After thawing, the quality of the frozen-thawed semen was investigated for motility, viability, acrosomal and DNA integrity, and subsequent embryo development after in vitro fertilization of bovine oocytes. Additionally, semen from one of the bulls was used to analyze semen antioxidative potential, sperm penetration into oocytes, male pronucleus formation rate, and embryo DNA integrity. The sperm quality varied among bulls after GSH supplementation. One bull had decreased sperm total motility, and two bulls had decreased sperm DNA integrity. GSH supplementation had positive effects on embryo development for three bulls. Two of them showed both improved cleavage and blastocyst formation rates, while the other one only showed an improved cleavage rate. We observed positive effects on early male pronucleus formation and no negative effects on DNA integrity and cell number in blastocyst stage embryos. Although the effect varies depending on individual bulls and GSH concentration, GSH supplementation in semen may improve in vitro embryo production from frozen semen.

Cyclic AMP efflux through MRP4 regulates actin dynamics signalling pathway and sperm motility in bovines

Previously we demonstrated that multidrug resistance-associated protein 4 transporter (MRP4) mediates cAMP efflux in bovine spermatozoa and that extracellular cAMP (ecAMP) triggers events associated to capacitation. Here, we deepen the study of the role of MRP4 in bovine sperm function by using MK571, an MRP4 inhibitor. The incubation of spermatozoa with MK571 during 45 min inhibited capacitation-associated events. MRP4 was localized in post-acrosomal region and mid-piece at 15 min capacitation, while at 45 min it was mainly located in the acrosome. After 15 min, MK571 decreased total sperm motility (TM), progressive motility (PM) and several kinematic parameters. The addition of ecAMP rescued MK571 effect and ecAMP alone increased the percentage of motile sperm and kinematics parameters. Since actin cytoskeleton plays essential roles in the regulation of sperm motility, we investigated if MRP4 activity might affect actin polymerization. After 15 min capacitation, an increase in F-actin was observed, which was inhibited by MK571. This effect was reverted by the addition of ecAMP. Furthermore, ecAMP alone increased F-actin levels while no F-actin was detected with ecAMP in the presence of PKA inhibitors. Our results support the importance of cAMP efflux through MRP4 in sperm capacitation and suggest its involvement in the regulation of actin polymerization and motility.

Effects of digoxin on full-type hyperactivation in bovine ejaculated spermatozoa with relatively lower survivability for incubation with stimulators of cAMP signaling cascades

Previous researches of our laboratory reported that addition of cAMP analog cBiMPS and protein phosphatase inhibitor calyculin A (stimulators of cAMP signaling cascades) improved the capacity of incubation medium to induce full-type hyperactivation in bovine ejaculated spermatozoa. However, this modified medium was valid only for samples with relatively good survivability for incubation with stimulators of cAMP signaling cascades. Thus, it is necessary to make further modified medium for evaluation of potentials to exhibit full-type hyperactivation in bovine sperm samples with relatively lower survivability. Na⁺/K⁺-ATPase is an integral membrane protein and involved with the regulation of rodent sperm motility. To make further modification of the medium, we examined effects of Na⁺/K⁺-ATPase inhibition with digoxin on motility, full-type hyperactivation and protein tyrosine phosphorylation in bovine ejaculated spermatozoa with relatively lower survivability for incubation with stimulators of cAMP signaling cascades and also performed the immunodetection of bovine sperm Na⁺/K⁺-ATPase. The addition of Na⁺/K⁺-ATPase inhibitor digoxin to the incubation medium containing cBiMPS and calyculin A had the tendency to lessen the decreases in the percentages of motile spermatozoa in all of 12 samples after the incubation for 1-3 h and significantly increased the percentages of full-type hyperactivation in one group of 4 samples (Sample-A1) and another group of 4 samples (Sample-A2) after 1 and 2 h respectively, though it had no significant effects on full-type hyperactivation in the other group of 4 samples (Sample-B). In addition, incubation time-related changes in the sperm protein tyrosine phosphorylation (a good marker for sperm capacitation) were correlated with those in the percentages of full-type hyperactivation in Sample-A1 containing digoxin. Immunodetection showed that Na⁺/K⁺-ATPase is present in the middle and principal pieces of the flagella, indicating that Na⁺/K⁺-ATPase has possible relations with sperm motility. These results obtained with bull ejaculated spermatozoa with relatively lower survivability indicate that incubation method using digoxin is useful to evaluate potentials of sperm samples to exhibit full-type hyperactivation, that digoxin has effects on suppressing reduction of sperm motility, and that prolonged incubation with digoxin induces reduction of capacitation state which may suppress the maintenance of full-type hyperactivation.

Characteristics of bull sperm acrosome associated 1 proteins

An atypical distribution of sperm acrosomal tyrosine-phosphorylated proteins [which include sperm acrosome associated 1 (SPACA1) proteins] may be related to the relatively lesser pregnancy rates when semen of some bulls are used for artificial insemination (AI). There may also be these associations with bull SPACA1 proteins that are translocated from the equatorial segment to the anterior part in the acrosomes during sperm maturation in the normally functioning epididymis. The aim of the present study, therefore, was assessment of the characteristics of bull SPACA1 proteins. Results from immunocytochemical evaluations indicate there were large variations in sperm percentages with typically distributed SPACA1 proteins in acrosomes of cauda epididymal sperm samples (7%-95%). These values were positively correlated with percentages of epididymal spermatozoa with typically distributed acrosomal tyrosine-phosphorylated proteins (r=0.8564, P<0.001). Results indicate there are individual differences in translocation of SPACA1 proteins in the epididymis during sperm maturation, and that SPACA1 protein is one of the main determinants for the typical distribution of acrosomal tyrosine-phosphorylated proteins. In addition, conception rates as a result of AI using cryopreserved spermatozoa tended to be associated with percentages of epididymal spermatozoa with typically distributed SPACA1 proteins. Results from sucrose gradient centrifugation fractionation experiments indicate SPACA1 proteins are sperm membrane raft-associated proteins. Based on these results, it is hypothesized that there is an association between bull subfertility when semen is used for AI and epididymal dysfunctions in the arrangement of membrane lipid rafts during sperm maturation.

Necessity of exact examination of sperm characteristics to assess artificial insemination-subfertile bulls

Conception rates of artificial insemination (AI) have gradually been decreasing in the cattle. In order to overcome this problem, AI centers need supply high-quality frozen semen whose insemination makes cow pregnant efficiently. Semen quality is conventionally assessed under the light microscope with cell biological methods, and only high-quality frozen semen straws are used for AI. However, lower conception rates are occasionally recorded in AI with frozen semen straws from some bulls (AI-subfertile bulls). In this paper, we introduce new methods to assess sperm molecular characteristics to find AI-subfertile bulls.

The proportion of tyrosine phosphorylated spermatozoa in cryopreserved semen is negatively related to crossbred bull fertility

Sub-fertility is a major problem in crossbred bulls. Identification of subtle differences in the quality of cryopreserved spermatozoa among bulls belonging to different fertility rankings would help determine the latent fertility of semen before their use at field conditions. In the present study, we assessed the status of tyrosine phosphorylation, membrane integrity and acrosome reaction of cryopreserved spermatozoa in crossbred bulls (n = 22) with different levels of field fertility and assessed their relationship with fertility. Bulls were categorized into above-average (n = 4), average (n = 14) and below-average (n = 4) based on their different field fertility rates. The progressive sperm motility was significantly (P < 0.05) higher in above-average fertile bulls compared to either average or below-average fertile bulls whereas sperm membrane integrity and acrosomal reaction status did not differ among the three groups. The proportion of live tyrosine-phosphorylated spermatozoa were significantly (P < 0.05) higher in below-average and average fertile bulls compared to above-average bulls. Immunolocalization of protein tyrosine phosphorylation in spermatozoa revealed that the proportion of spermatozoa showing tyrosine phosphorylation at acrosome and post-acrosomal area (APA) and at acrosome, post-acrosome and tail (APAT) were significantly (P < 0.05) higher in below-average fertile bulls than other groups. The APA pattern (r = -0.605; P < 0.01) and APAT (r = 0.507; P < 0.05) pattern were significantly and negatively correlated with bull fertility. It was concluded that the proportion of live tyrosine-phosphorylated spermatozoa in cryopreserved semen was negatively related to bull fertility.

Plasma estradiol-17β, cortisol, and insulin concentrations and serum biochemical parameters surrounding puberty in Japanese Black beef bulls with normal and abnormal semen

The associations of semen abnormalities with circulating hormones (estrogens, glucocorticoid, insulin) and common biochemical parameters are unclear in beef bulls. We compared plasma concentrations of estradiol-17β, cortisol, and insulin and serum biochemical parameters surrounding puberty in Japanese Black beef bulls (n = 96) with normal post-thaw or abnormal semen (fresh and frozen). Blood samples were collected monthly from 4 to 24 months of age (n = 50) for the assays of plasma estradiol, cortisol, and insulin and every 3 months from 6 to 21 months of age (n = 92) for the serum biochemical analyses. Semen was collected weekly from 12 months until at least 18 months of age. Fresh semen was evaluated for semen volume, sperm progressive motility, concentrations, and morphological defects. The normal fresh semen was frozen by a standard method and examined for post-thaw sperm motility and fertility, which were evaluated for rates of transferable embryos. Bulls were classified as having either normal fresh semen or abnormal fresh semen (when at least one of the above test items was abnormal for 6 months). The normal fresh semen was categorized as having either normal post-thaw semen or low fertility post-thaw semen. The abnormal fresh semen was categorized as having sperm morphological defects, low motility, or morphological defects plus low motility. Plasma cortisol concentrations in the abnormal fresh semen group were higher than those of the normal fresh semen group (p < 0.0001). Plasma estradiol-17β and insulin concentrations in the low-fertility post-thaw semen group were lower than those of the normal post-thaw semen group (p < 0.0001). Serum aspartate aminotransferase and magnesium concentrations were greater for the abnormal fresh semen group vs. the normal fresh semen group (p < 0.005). These results suggest that fresh semen abnormality in pubertal beef bulls might be associated with increased circulating aspartate aminotransferase, magnesium and cortisol. Low-fertility post-thaw semen could have been involved with the lower peripheral estradiol and insulin levels in beef bulls.

Methodological improvement of fluorescein isothiocyanate peanut agglutinin (FITC-PNA) acrosomal integrity staining for frozen-thawed Japanese Black bull spermatozoa

This study aimed to improve the staining of frozen-thawed Japanese Black bull sperm acrosomes with fluorescein isothiocyanate-conjugated peanut agglutinin (FITC-PNA). Spermatozoa were washed, fixed with 1–3% paraformaldehyde (PFA) in suspension for 10, 20, and 30 min, permeabilized with 0–2% Triton X-100 for 5 min, stained with FITC-PNA, and mounted with different antifade agents (0.22 M 1,4-diazabicyclo [2,2,2] octane (DABCO), SlowFade®, and ProLong®) in suspension (In-suspension) or on a smear (On-smear). The spermatozoa were categorized into seven pattern types either immediately or after storage for 24 hr. Experiment 1 showed that 1) the In-suspension method was better than the On-smear method; 2) if spermatozoa were stained using the In-suspension method and examined immediately, the best antifade agent was SlowFade®; 3) if samples were to be stored after staining using the On-smear method, DABCO should be avoided; 4) if spermatozoa were stained using the In-suspension method, storage of the stained samples was not recommended; and 5) if samples were to be stored after staining using the In-suspension method, ProLong® might be the best antifade agent. The results of experiment 2 showed that the concentration of Triton X-100 could be reduced to 0.1 from 1%. The results of experiment 3 showed that the paraformaldehyde concentration used for a 30 min fixation could be reduced from 3 to 2%. It is expected that the improved staining protocol will be useful to determine bull sperm acrosomal integrity.

Sperm functional attributes and oviduct explant binding capacity differs between bulls with different fertility ratings in the water buffalo (Bubalus bubalis)

We report here the differences in sperm functional attributes and sperm–oviduct binding index in bulls with different field fertility ratings. Cryopreserved spermatozoa from Murrah buffalo bulls (n=9) with different fertility ratings were evaluated for membrane integrity, capacitation status, acrosome intactness and protein tyrosine phosphorylation status. Frozen­–thawed spermatozoa were incubated with oviduct explants for 1h under 5% CO2, 38.5°C with 95% relative humidity and the number of spermatozoa bound to the unit area of oviduct explants (binding index; BI) was assessed using 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1) fluorescent staining. The proportion of membrane-intact and acrosome-intact spermatozoa was significantly (P&lt;0.05) higher and the proportion of capacitated spermatozoa was significantly (P&lt;0.05) lower in high-fertile bulls compared with medium- and low-fertile bulls. The relationship between BI and bull fertility was significant and positive (r=0.69; P=0.04). BI was negatively and significantly (r=−0.83; P=0.01) related to membrane-compromised spermatozoa. It was concluded that the sperm–oviduct explant binding index was positively related to (1) the proportion of membrane-intact spermatozoa in a given semen sample and (2) invivo fertility of the buffalo bull, indicating the possibility of developing a fertility prediction tool using a sperm–oviduct explant binding model, once validated on a greater number of bulls.

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

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

Plasma IGF-I, INSL3, testosterone, inhibin concentrations and scrotal circumferences surrounding puberty in Japanese Black beef bulls with normal and abnormal semen

The relationships between semen abnormalities and peripheral concentrations of testicular and metabolic hormones in beef bulls are unclear. Here we compared plasma insulin-like growth factor I (IGF-I), insulin-like peptide 3 (INSL3), testosterone, inhibin concentrations, and scrotal circumferences surrounding puberty in Japanese Black beef bulls (n = 66) with normal or abnormal semen. We collected blood samples and measured scrotal circumferences monthly from 4 to 24 months of age. Semen was collected weekly from 12 months until at least 18 months of age. Fresh semen was evaluated for semen volume, sperm motility, concentrations, and morphological defects. The normal fresh semen was frozen by a standard method and examined for post-thaw sperm motility and fertility. Bulls were classified as having either normal post-thaw semen (n = 45) or abnormal semen (n = 21, when at least one of the above test items was abnormal for 6 months). Abnormal semen was classified into abnormal fresh or low-fertility post-thaw which evaluated for rates of transferable embryos. The abnormal fresh was categorized as having sperm morphological defects, low motility, and morphological defects plus low motility. Scrotal circumferences were smaller for the abnormal-semen group vs. the normal-semen group at 20 and 24 months (p < 0.05). Plasma IGF-I, INSL3, and inhibin concentrations in the abnormal-semen group were lower than those of the normal-semen group (p < 0.05) surrounding puberty (4-6, 8, 18-22, and 24 months for IGF-I; 6, 9, 11-14, 17, and 20-21 months for INSL3; 5, 8-13, 16, 17, 19, and 20 months for inhibin). The plasma testosterone concentrations were lower in the abnormal-semen bulls vs. normal-semen bulls only at 22 months (p < 0.05). Analyses of the classified abnormal semen showed lower plasma INSL3 concentrations for morphological defects plus low motility in fresh semen (p < 0.05) and lower IGF-I and inhibin concentrations for low-fertility post-thaw semen (p < 0.05) compared to the normal semen. Our results suggest that reduced secretions of IGF-I, INSL3, and inhibin surrounding puberty may be associated with semen aberration in beef bulls. Notably, the combined sperm abnormality of morphological defects and low motility in fresh semen could involve lowered INSL3, whereas the low-fertility post-thaw semen might be related to decreases of IGF-I and/or inhibin. Pre-puberty blood IGF-I, INSL3 and inhibin concentrations could be used as indicators to predict aberrant semen in beef bulls.

Protein biomarkers for male artificial insemination subfertility in bovine spermatozoa

Background

Although artificial insemination (AI) technique is an established biotechnology for bovine reproduction, the results of AI (conception rates) have a tendency to decline gradually. To our annoyance, moreover, AI‐subfertile bulls have been occasionally found in the AI centers. To resolve these serious problems, it is necessary to control the sperm quality more strictly by the examinations of sperm molecules.

Methods

We reviewed a number of recent articles regarding potentials of bovine sperm proteins as the biomarkers for bull AI‐subfertility and also showed our unpublished supplemental data on the bull AI‐subfertility associated proteins.

Main findings

Bull AI‐subfertility is caused by the deficiency or dysfunctions of various molecules including regulatory proteins of ATP synthesis, acrosomal proteins, nuclear proteins, capacitation‐related proteins and seminal plasma proteins.

Conclusion

In order to control the bovine sperm quality more strictly by the molecular examinations, it is necessary to select suitable sperm protein biomarkers for the male reproductive problems which happen in the AI centers.

Variation among individual bulls in the distribution of acrosomal tyrosine-phosphorylated proteins in epididymal and ejaculated spermatozoa

In Japanese black cattle, AI severely subfertile males have occasionally been found. In order to solve this problem, we previously asserted the need for exact examinations of acrosomal tyrosine-phosphorylated proteins and acrosome morphology in cryopreserved spermatozoa. In the present study, we further investigated acrosomal tyrosine-phosphorylated proteins in spermatozoa before cryopreservation and examined possible relationships between these phosphoproteins and acrosome stability. Ejaculated, epididymal and cryopreserved spermatozoa were subjected to examinations of general characteristics (motility, shape and acrosome morphology) and indirect immunofluorescence of acrosomal phosphoproteins. Unlike all general characteristic parameters, the distribution of acrosomal tyrosine-phosphorylated proteins in ejaculated and cauda epididymal spermatozoa varied considerably among bulls and was linked to the maintenance of morphologically normal acrosomes in cryopreserved spermatozoa or ejaculated spermatozoa after 270 min incubation. Moreover, the distribution of these phosphoproteins was arranged in the spermatozoa of the proximal epididymides. These findings indicate that acrosomal tyrosine-phosphorylated proteins are distributionally arranged during early process of sperm maturation, that their distribution of cauda epididymal and ejaculated spermatozoa are largely different among bulls, and that varied states of acrosomal phosphoproteins may result in individual differences in acrosome stability among bulls.

Translocation of Tektin 3 to the equatorial segment of heads in bull spermatozoa exposed to dibutyryl cAMP and calyculin A

Tektins (TEKTs) are filamentous proteins associated with microtubules in cilia, flagella, basal bodies, and centrioles. Five TEKTs (TEKT1, -2, -3, -4, and -5) have been identified as components of mammalian sperm flagella. We previously reported that TKET1 and -3 are also present in the heads of rodent spermatozoa. The present study clearly demonstrates that TEKT2 is present at the acrosome cap whereas TEKT3 resides just beneath the plasma membrane of the post-acrosomal region of sperm heads in unactivated bull spermatozoa, and builds on the distributional differences of TEKT1, -2, and -3 on sperm heads. We also discovered that hyperactivation of bull spermatozoa by cell-permeable cAMP and calyculin A, a protein phosphatase inhibitor, promoted translocation of TEKT3 from the post-acrosomal region to the equatorial segment in sperm heads, and that TEKT3 accumulated at the equatorial segment is lost upon acrosome reaction. Thus, translocation of TEKT3 to the equatorial segment may be a capacitation- or hyperactivation-associated phenomenon in bull spermatozoa. Mol. Reprod. Dev. 84: 30-43, 2017. © 2016 Wiley Periodicals, Inc.

Individual differences in the distribution of sperm acrosome-associated 1 proteins among male patients of infertile couples; their possible impact on outcomes of conventional in vitro fertilization

The aims of this study were to show the existence of individual differences in the distribution of sperm acrosome-associated 1 (SPACA1) among male patients of infertile couples and to examine their possible impact on the outcomes of conventional in vitro fertilization (IVF). The spermatozoa were collected from male patients of infertile couples, washed by centrifugation, collected by the swim-up method, and then used for clinical treatments of conventional IVF. The surplus sperm samples were fixed and stained with an anti-SPACA1 polyclonal antibody for the immunocytochemistry. In the clinical IVF treatments, fertilization rates and blastocyst development rates were evaluated. The immunocytochemical observations revealed that SPACA1 were localized definitely in the acrosomal equatorial segment and variedly in the acrosomal principal segment. Specifically, the detection patterns of SPACA1 in the acrosomal principal segment could be classified into three categories: (A) strong, (B) intermediate or faint, and (C) almost no immunofluorescence. The SPACA1 indexes were largely different among male patients with the wide range from 13 to 199 points. The SPACA1 indexes were significantly correlated with developmental rates of embryos to blastocysts (r = 0.829, P = 0.00162), although they were barely associated with fertilization rates at 19 h after insemination (r = 0.289, P = 0.389). These results suggest that the distribution of SPACA1 in sperm affects the outcomes of conventional IVF. In conclusion, this study provides initial data to promote large-scale clinical investigation to demonstrate that the SPACA1 indexes are valid as molecular biomarkers that can predict the effectiveness of conventional IVF of infertile couples.

Effect of cooling (4°C) and cryopreservation on cytoskeleton actin and protein tyrosine phosphorylation in buffalo spermatozoa

Semen cryopreservation is broadly utilized as a part of the bovine reproducing industry, a large portion of the spermatozoa does not survive and the majority of those that do survive experience various molecular and physiological changes that influence their fertilizing capacity. The main aim of this study is to determine the effect of cooling (4 °C) and cryopreservation on cytoskeleton actin, tyrosine phosphorylation and quality of buffalo spermatozoa, and to determine the similarity between in vitro capacitation and cryopreservation induced capacitation like changes. To achieve this, Western blot was used to examine the changes in actin expression and protein tyrosine phosphorylation, whereas changes in actin polymerization, localization of actin and protein tyrosine phosphorylation during capacitation and cryopreservation were evaluated by indirect immunofluorescence technique. Localization studies revealed that the actin localized to flagella and acrosome membrane regions and following, capacitation it migrated towards the acrosome region of sperm. Time dependent increase in actin polymerization and protein tyrosine phosphorylation was observed during in vitro capacitation. The cooling phase (4 °C) and cryopreservation processes resulted in the loss/damage of cytoskeleton actin. In addition, we performed the actin polymerization and protein tyrosine phosphorylation in cooled and cryopreserved buffalo spermatozoa. Interestingly, cooling and cryopreservation induces actin polymerization and protein tyrosine phosphorylation, which were similar to in vitro capacitation (cryo-capacitation). These changes showed 1.3 folds reduction in the sperm quality parameters which includes motility, viability and plasma membrane integrity. Furthermore, our findings indicate that cooling and cryopreservation damages the cytoskeleton actin and also induces capacitation like changes such as protein tyrosine phosphorylation and actin polymerization. This could be one of the main reasons for reduced sperm quality and fertility failure of cryopreserved spermatozoa.

Effects of acrosomal conditions of frozen-thawed spermatozoa on the results of artificial insemination in Japanese Black cattle

The purposes of this study were to examine the relationship between male artificial insemination (AI) fertility and sperm acrosomal conditions assessed by new and conventional staining techniques and to identify possible reproductive dysfunctions causing low conception rates in AI using frozen-thawed spermatozoa with poor acrosomal conditions in Japanese Black bulls. We investigated individual differences among bulls in the results concerning (1) acrosomal conditions of frozen-thawed spermatozoa as assessed by not merely peanut agglutinin-lectin staining (a conventional staining technique) but also immunostaining of acrosomal tyrosine-phosphorylated proteins (a new staining technique), (2) routine AI using frozen-thawed spermatozoa as assessed by pregnancy diagnosis, (3) in vivo fertilization of frozen-thawed spermatozoa and early development of fertilized eggs as assessed by superovulation/AI-embryo collection tests and (4) in vitro fertilization of frozen-thawed spermatozoa with oocytes. The percentages of frozen-thawed spermatozoa with normal acrosomal conditions assessed by the abovementioned staining techniques were significantly correlated with the conception rates of routine AI, rates of transferable embryos in superovulation/AI-embryo collection tests and in vitro fertilization rates. These results are consistent with new suggestions that the distribution of acrosomal tyrosine-phosphorylated proteins as well as the acrosomal morphology of frozen-thawed spermatozoa are AI fertility-associated markers that are valid for the prediction of AI results and that low conception rates in AI using frozen-thawed spermatozoa with poor acrosomal conditions result from reproductive dysfunctions in the processes between sperm insemination into females and early embryo development, probably failed fertilization of frozen-thawed spermatozoa with oocytes.

The protein tyrosine phosphorylation during in vitro capacitation and cryopreservation of mammalian spermatozoa

Before the process of fertilization, spermatozoa necessitate a period of residence in the female reproductive environment, and undergo a sequence of physiological and biochemical changes collectively referred to as capacitation. Accumulated evidences from several laboratories indicated that the protein tyrosine phosphorylation (PTP) is one of the most important intracellular signaling events regulating sperm function, and is a meaningful indicator of capacitation. Different factors that affect PTP are cholesterol efflux, influx of HCO3(-), increased intracellular Ca(2+), cAMP and reactive oxygen species (ROS). cAMP/PKA and extracellular signal regulated kinases (ERKs) are the known important signaling pathways primarily involved in PTP. Advanced proteomics approaches have revealed several proteins that undergo tyrosine phosphorylation during capacitation. Semen cryopreservation subjects spermatozoa to frequent stressors, which result in capacitation like changes (cryo-capacitation). The cryo-capacitated spermatozoa usually show different patterns of PTP than the normal in vitro capacitated spermatozoa. In the current manuscript, we have summarized some information about the proteins undergoing tyrosine phosphorylation during capacitation and the effect of cryopreservation on PTP as well as the possibilities to reduce the changes associated with cryopreservation process.

Roles of intracellular cyclic AMP signal transduction in the capacitation and subsequent hyperactivation of mouse and boar spermatozoa

It is not until accomplishment of a variety of molecular changes during the transit through the female reproductive tract that mammalian spermatozoa are capable of exhibiting highly activated motility with asymmetric whiplash beating of the flagella (hyperactivation) and undergoing acrosomal exocytosis in the head (acrosome reaction). These molecular changes of the spermatozoa are collectively termed capacitation and promoted by bicarbonate, calcium and cholesterol acceptors. Such capacitation-promoting factors can stimulate intracellular cyclic AMP (cAMP) signal transduction in the spermatozoa. Meanwhile, hyperactivation and the acrosome reaction are essential to sperm fertilization with oocytes and are apparently triggered by a sufficient increase of intracellular Ca²⁺ in the sperm flagellum and head, respectively. Thus, it is necessary to investigate the relationship between cAMP signal transduction and calcium signaling cascades in the spermatozoa for the purpose of understanding the molecular basis of capacitation. In this review, I cover updated insights regarding intracellular cAMP signal transduction, the acrosome reaction and flagellar motility in mammalian spermatozoa and then account for possible roles of intracellular cAMP signal transduction in the capacitation and subsequent hyperactivation of mouse and boar spermatozoa.

Novel approach for the detection of the vestiges of testicular mRNA splicing errors in mature spermatozoa of Japanese Black bulls

There is a serious problem with the reduction of male reproductive performance of the livestock in the world. We have a hypothesis that the splicing error-caused derivation of aberrant sperm motility-related proteins may be one of its causal factors. It is thought that fresh testicular tissues are necessary for the detection of splicing errors of the mRNA. However, it is difficult to obtain testicular tissues from a number of agriculturally important bulls by surgical methods, because such procedures may have deleterious effects on bulls’ reproductive performance. The aim of this study was to examine the usefulness of mRNA fragments collected from ejaculated spermatozoa as alternative analytical samples for detection of the splicing errors. In the first experiment, we characterized the alternative splicing and splicing error of bull testicular ADCY10 mRNA which coded the synthase of the regulatory molecule for sperm motility “cAMP”. In testes, the exon 11-lacking variant coding the truncated ADCY10 was derived by alternative splicing. However, splicing errors, which accompanied the frame shift in the second cyclase domain, were occasionally observed in the exon 11-lacking variant. This aberrant variant retained intronic nucleotides (4 bases, CCAG) connecting the initial part of exon 10 due to splicing errors and consequently yielded the cleavage site for a restriction enzyme (Cac8I) which recognized the nucleotide sequences (GCNNGC). In the second experiment, we recovered residual testicular mRNA fragments from ejaculated spermatozoa and observed the splicing error-caused derivation of the aberrant variant of ADCY 10. Ejaculated spermatozoa conserved mRNA fragments of the exon 11-lacking variant coding exons 9, 10, 12 and 13. Moreover, the above-mentioned aberrant variant of ADCY10 mRNA fragment was detectable by Cac8I digestion treatment using the sperm mRNAs. These results indicate the utility of sperm mRNA fragments for the detection of splicing errors in bull testicular mRNAs.

Relationship between cyclic AMP-dependent protein tyrosine phosphorylation and extracellular calcium during hyperactivation of boar spermatozoa

In mammalian spermatozoa, the state of protein tyrosine phosphorylation is modulated by protein tyrosine kinases and protein tyrosine phosphatases that are controlled via cyclic AMP (cAMP)-protein kinase A (PKA) signaling cascades. The aims of this study were to examine the involvement of cAMP-induced protein tyrosine phosphorylation in response to extracellular calcium and to characterize effects of pharmacological modulation of the cAMP-induced protein phosphorylation state and calmodulin activity during hyperactivation in boar spermatozoa. Ejaculated spermatozoa were incubated with cBiMPS (a cell-permeable cAMP analog) and CaCl(2) at 38.5°C to induce hyperactivation, and then used for Western blotting and indirect immunofluorescence of phosphorylated proteins and for the assessment of motility. Both cBiMPS and CaCl(2) were necessary for hyperactivation. The increase in hyperactivated spermatozoa exhibited a dependence on the state of cBiMPS-induced protein tyrosine phosphorylation in the connecting and principal pieces. The addition of calyculin A (an inhibitor for protein phosphatases 1/2A (PP1/PP2A), 50-100 nM) coincidently promoted hyperactivation and cAMP-induced protein tyrosine phosphorylation in the presence of cBiMPS and CaCl(2). Moreover, the addition of W-7 (a calmodulin antagonist, 2-4 µM) enhanced the percentages of hyperactivated spermatozoa after incubation with cBiMPS and CaCl(2), independently of protein tyrosine phosphorylation. These findings indicate that cAMP-induced protein tyrosine phosphorylation in the connecting and principal pieces is involved in hyperactivation in response to extracellular calcium, and that calmodulin may suppress hyperactivation via the signaling cascades that are independent of cAMP-induced protein tyrosine phosphorylation.

Quantification of kinetic changes in protein tyrosine phosphorylation and cytosolic Ca2+ concentration in boar spermatozoa during cryopreservation

Protein tyrosine phosphorylation in sperm is associated with capacitation in several mammalian species. Although tyrosine phosphorylated proteins have been demonstrated in cryopreserved sperm, indicating capacitation-like changes during cryopreservation, these changes have not yet been quantified objectively. We monitored tyrosine phosphorylation, intracellular calcium and sperm kinematics throughout the cryopreservation process, and studied the relationships among them in boar spermatozoa. Sperm kinetics changed significantly during cryopreservation: curvilinear velocity, average path velocity and straight line velocity all decreased significantly (P < 0.05). While the percentage of sperm with high intracellular calcium declined (P < 0.05), global phosphorylation increased significantly (P < 0.01). Specifically, cooling to 5°C induced phosphorylation in the spermatozoa. After cooling, a 32-kDa protein not observed in fresh semen appeared and was consistently present throughout the cryopreservation process. While the level of expression of this phosphoprotein decreased after addition of the second extender, frozen–thawed spermatozoa showed an increased expression. The proportion of sperm cells with phosphorylation in the acrosomal area also increased significantly (P < 0.05) during cryopreservation, indicating that phosphorylation might be associated with capacitation-like changes. These results provide the first quantitative evidence of dynamic changes in the subpopulation of boar spermatozoa undergoing tyrosine phosphorylation during cryopreservation.