Functional significance of responsiveness to capacitating conditions in boar spermatozoa

Odorant Receptor OR2C1 Is an Essential Modulator of Boar Sperm Capacitation by Binding with Heparin

Heparin, a class of glycosaminoglycans (GAGs), is widely used to induce sperm capacitation and fertilization. How heparin induces sperm capacitation remains unclear. Olfactory receptors (ORs) which are G protein-coupled receptors, have been proposed to be involved in sperm capacitation. However, the interaction between ORs and odor molecules and the molecular mechanism of ORs mediating sperm capacitation are still unclear. The present study aimed to explore the underlying interaction and mechanism between heparin and ORs in carrying out the boar sperm capacitation. The results showed that olfactory receptor 2C1 (OR2C1) is a compulsory unit which regulates the sperm capacitation by recognizing and binding with heparin, as determined by Dual-Glo Luciferase Assay and molecular docking. In addition, molecular dynamics (MD) simulation indicated that OR2C1 binds with heparin via a hydrophobic cavity comprises of Arg3, Ala6, Thr7, Asn171, Arg172, Arg173, and Pro287. Furthermore, we demonstrated that knocking down OR2C1 significantly inhibits sperm capacitation. In conclusion, we highlighted a novel olfactory receptor, OR2C1, in boar sperm and disclosed the potential binding of heparin to Pro287, a conserved residue in the transmembrane helices region 7 (TMH7). Our findings will benefit the further understanding of ORs involved in sperm capacitation and fertilization.

A High Incidence of Sperm with Cytoplasmic Droplets Affects the Response to Bicarbonate in Preserved Boar Semen

Retained cytoplasmic droplets (CD) are the most frequent sperm abnormality in boar semen. A high incidence of CD is associated with subfertility, but the underlaying reasons are not well understood. The storage of extended semen might augment the adverse effects of CD on essential steps towards fertilization, such as capacitation. The aim of this study was to examine whether the enhanced presence of CD in boar semen influences sperm's response to the capacitation stimulus bicarbonate during long-term semen storage. Extended semen samples (n = 78) from 13 artificial insemination centers were analyzed using a flow cytometric calcium influx assay. Samples with >15% of CD showed a reduced specific response to bicarbonate and a higher non-specific destabilization after storage for 96 h and subsequent incubation at 38 °C in three variants of Tyrode's medium (p < 0.05). The size of the bicarbonate-responsive sperm population was inversely correlated with the presence of CD-bearing sperm (r = -0.61, p < 0.01). Samples with ≤15% and samples with >15% of CD did not differ in motility or viability and acrosome integrity during semen storage. In conclusion, incomplete epididymal sperm maturation impairs the in vitro capacitation ability and promotes sperm destabilization in stored boar semen.

Assessment of chilling injury in hypothermic stored boar spermatozoa by multicolor flow cytometry

Hypothermic storage of boar semen may allow antibiotic-free semen preservation but is limited due to chilling sensitivity of boar spermatozoa. Progress in this area requires sensitive tools to detect chilling injury. Therefore, multiparameter flow cytometry panels were evaluated to ascertain whether they are useful tools for identifying sublethal damage of sperm function at a single cell level, thus considering the high intrinsic sperm heterogeneity in a sample. The first fluorochrome panel consisted of Hoechst 33342 to identify DNA-containing events, Yo-Pro 1 to detect viability, merocyanine 540 to describe membrane fluidity, and PNA-Alexa Fluor™ 647 to identify acrosomic integrity. The second fluorochrome panel consisted of SiR700-DNA to identify DNA-containing events, JC-1 to characterize the mitochondrial transmembrane potential (MMP), and Calbryte 630 to assess the intracellular calcium level. Extended boar semen was stored either at 17°C (control) or 5°C (chilled). It is shown that chilling increased membrane fluidity in the viable (Yo-Pro 1 negative) sperm population at 24 h (p < 0.05). At 144 h, the viable, acrosomic intact sperm population with low membrane fluidity was similar for both storage temperatures. Moreover, chilling reduced the main sperm population with high MMP, medium fluorescence for JC-1 monomer and low intracellular calcium level (p < 0.05). However, after in vitro sperm capacitation, this population did not differ between the two storage temperatures. Exemplary computational data visualization in t-distributed stochastic neighbor embedding (t-SNE) maps and moving radar plots revealed similar subpopulations as identified by three-dimensional stacked bar charts. In conclusion, sperm surviving an initial chilling injury withstand long-term storage and respond in a similar manner to capacitation conditions as sperm stored conventionally at 17°C. Multicolor flow cytometry is a valuable tool for detecting chilling-induced alterations of cell function in sperm subpopulations.

Determination of a cooling-rate frame for antibiotic-free preservation of boar semen at 5°C

Hypothermic storage of boar semen provides the possibility to omit antibiotics from semen extenders so long as sperm quality is maintained and bacterial growth prevented. The objective of this study was to determine an optimal cooling-rate frame for boar semen preserved at 5°C in an antibiotic-free extender. Semen from eight boars extended in AndroStar^® Premium was cooled from 30°C to 5°C using seven different cooling rates, ranging initially from 0.01 to 0.36°C min^–1 and reaching 5°C between 2 h and 24 h after dilution. Sperm motility, membrane integrity, membrane fluidity, mitochondrial membrane potential and the response to the capacitation stimulus bicarbonate remained at a high level for 144 h at 5°C when the semen was initially cooled in a cooling-rate frame ranging from 0.01 to 0.09°C min^‑1 in the temperature zone from 30 to 25°C, followed by 0.02 to 0.06°C min^–1 to 10°C and 0.01 to 0.02°C min^‑1 to the final storage temperature. A cooling rate of 0.07°C min^–1 in the temperature zone from 30 to 10°C led to a reduced response to bicarbonate (P < 0.01) and fast cooling to 5°C within 1 h with a cooling rate of 0.31°C min^–1 resulted in lower values (P > 0.05) of all sperm parameters. In a further experiment, slow cooling with a holding time of 6 h at 22°C induced after 6 h storage a temporary increase in Escherichia coli of 0.5 × 10³ to 2.4 × 10³ CFU mL^–1 in the sperm-free inoculated extender. Overall, the load of mesophilic bacteria in the stored semen was below 6 × 10³ CFU mL^–1, a level that is not regarded as critical for sperm quality. In conclusion, appropriate cooling protocols were established for the antibiotic-free storage of boar semen at 5°C, allowing the application of hypothermic preservation in research and in artificial insemination.

Effects of exposure to triphenyltin (TPT) contaminant on sperm activity in adulthood of Calomys laucha exposed through breastfeeding

Triphenyltin (TPT) is an organotin compound (OT), primarily used in agriculture and in the composition of antifouling paints for ships worldwide. Studies have showed its effects as an endocrine disrupter in several organisms by preventing enzymatic expression and causing reproductive toxicity. This study aimed to evaluate the effects of exposure to TPT, via breastfeeding, on reproductive physiology in the Calomys laucha species. The experimental design was compound of five groups, two controls and three with different doses of TPT. Moreover, females were exposed by gavage to the TPT for 20 days, from the 1st day postpartum to the 21st postnatal day (PND). Then, the pups were euthanized and the kinetics, organelles, and biochemistry of the sperm were evaluated. The results presented a reduction in total motility in the groups exposed to TPT. Regarding cellular organelles analysis, a loss in membrane integrity was evidenced; the functionality of mitochondria showed diminution followed by increased acrosome reaction. In conclusion, the TPT causes alteration of the reproductive parameters, decreasing the activity and sperm quality in individuals exposed in the breastfeeding phase.

Triphenyltin exposition induces spermatic parameter alters of Calomys laucha species

The present study aims to evaluate the influence of triphenyltin (TPT) exposure on reproductive physiology on Calomys laucha species, since this species inhabits regions susceptible to exposure to this contaminant. Animals exposed to the highest dose (10.0 mg/kg) presented signs of severe intoxication in only 7 days of exposure, demonstrating a higher sensitivity of this species to triphenyltin. The 10.0 mg TPT/kg dose was analyzed separately for short-term exposure and results suggest that exposure to this dose was severely detrimental to sperm activity. Among the main results obtained in the evaluation of sperm kinetics, a reduction in total motility was observed from the 0.5 mg TPT/kg group, accentuated according to the increase in the doses of TPT. In progressive motility, there was a decrease from the dose of 0.5 mg TPT/kg and maintained the plateau until the dose of 5.0 mg TPT/kg. It was also observed an increase in the distances and velocities average path, rectilinear and curvilinear in doses of 2.5 and 5.0 mg/kg. From the flow cytometry, evaluation a decrease in mitochondrial functionality was observed as the dose increased. Increased membrane fluidity was also observed from the 5.0 mg TPT/kg dose and the acrosome reaction presented higher values at doses of 0.5 and 5.0 mg TPT/kg. We can conclude that TPT causes impairment of the sperm activity, reducing it in individuals exposed in the adult phase.

Suitability of the hemi-zona assay for the evaluation of the effect of the length of the equilibration period before cryopreservation

The aim of this study was to test the suitability of the interspecific hemizona assay (HZA) to predict the fertilizing capacity of bovine sperm after modifying the length of the equilibration period before freezing and thawing. Ejaculates from 10 proven fertile bulls were split after dilution, equilibrated at 4 °C for either 24 h (control sperm = CS) or 6, 48, 72 or 96 h (test sperm = TS) and cryopreserved. Hemizona (HZ) pairs from in vitro matured pig oocytes were used for the heterologous HZA: After thawing and swim-up (1 h) CS and TS were co-incubated with matching HZ (125,000 S/HZ in 25 μL Fert-TALP) for 4 h. Spermatological analyses (progressive motile sperm (PMS), plasma membrane- and acrosome-intact sperm (PMAI), sperm showing a high degree of DNA fragmentation (%DFI)) were performed after 0 and 3 h of incubation after thawing. After an equilibration time of 48 h and 72 h values for PMAI0h were higher (P < 0.05) compared to PMAI0h values of sperm equilibrated for 6 h, and %DFI3h values were higher after 96 h (P < 0.05) compared to 6 h equilibration. Between 12 and 90 TS and 13-97 CS were tightly bound to each HZ, respectively. The mean Hemizona Index (HZI) after a sperm equilibration for 48 h (HZI = 92.3 ± 12.7) or 72 h (HZI = 98.9 ± 16.23) was higher (P < 0.01) than after an equilibration for 6 h (HZI = 73.3 ± 13.93) or 96 h (HZI = 81.3 ± 11.41). The HZI for 96 h equilibration was moderately negatively related to PMS0h and PMS3h (r < -0.35, P < 0.05). Furthermore the HZI for 6 h equilibration was highly negatively correlated with DFI0h (r = -0,46, P < 0.01). On the basis of these results it can be concluded that the hemi-zona assay is a suitable test to detect alterations in the fertilizing capacity of bovine sperm after modifying the equilibration period.

The specific response to capacitating stimuli is a sensitive indicator of chilling injury in hypothermically stored boar spermatozoa

Boar spermatozoa are sensitive to storage temperatures below 15 °C. Chilling injury causes loss of motility and membrane integrity in a minority of cells, whereas the main population displays sublethal changes compromising fertility. In this study, changes of the response to capacitation conditions in hypothermically stored boar spermatozoa have been examined using a kinetic approach with well-defined test and control media. Ejaculates of seven boars were diluted in Beltsville Thawing Solution kept for 3 h at 22 °C or cooled to 17, 10 and 5 °C and stored for 24 and 96 h. At each time point, the standard sperm parameters motility and membrane integrity were evaluated. Subsequently, washed subsamples were incubated in capacitating and control medium before flow cytometric analysis of intracellular calcium content using the Fluo-3 probe and changes in phospholipid disorder using merocyanine. Kinetic changes of response parameters were monitored in viable (plasma membrane intact) cells. Chilling led to a loss of standard sperm quality traits in a minor subpopulation of cells, whereas storage length had no effect on these parameters. However, responses to incubation as determined by the loss of live cells with low intracellular calcium content showed marked changes in relation to storage conditions. The specific responsiveness to capacitation conditions decreased in close relation to storage temperature and length. In contrast, the merocyanine probe revealed to be limited to detect effects of hypothermic storage. Using Fourier transform infrared spectroscopy, no influence of chilling on membrane phase behaviour was found that might implicate decreased sperm function. In conclusion, assessment of response to capacitating media by monitoring intracellular calcium levels provides a sensitive measure for chilling injury in extended boar semen, and therefore, deserves implementation in hypothermic storage tests.

Bivalent response to long-term storage in liquid-preserved boar semen: a flow cytometric analysis

The fertility of liquid-preserved boar semen declines during storage at 17°C, insemination trials even indicating early losses in fertilizing ability within the first 24-48 h of storage. Standard semen parameters barely reflect these changes in semen quality, and new approaches for assessment of functional changes in stored spermatozoa are needed. Capacitation, the essential prefertilization step for spermatozoa in the female genital tract, is specifically induced in vitro by bicarbonate. Therefore, we have investigated changes in responsiveness of boar spermatozoa to bicarbonate during storage. Ejaculates of 14 boars were diluted in Beltsville thawing solution, cooled to 17°C and stored for 12, 24, 72, 120, and 168 h before investigation. At each time, basic semen quality was characterized by sperm motility and viability. Subsequently, washed subsamples were incubated in variants of an in vitro fertilization (IVF) medium and assessed for kinetic changes of viability (plasma membrane integrity) and intracellular calcium concentration using flow cytometry in combination with propidium iodide and Fluo-3. By this means, it was possible to determine specific effects of bicarbonate and calcium on sperm subpopulations over incubation time. During storage, standard semen parameters remained on a high level. However, flow cytometric analysis of sperm responses to capacitating and control media revealed two opposing effects of storage. There was a loss of response to bicarbonate in part of the live sperm population but an increasing degree of instability in the rest. Assessment of response to capacitating media by flow cytometry appears a markedly more sensitive way of monitoring sperm functionality during storage than the standard semen parameters of motility and viability.

Ubiquitin-activating enzyme (UBA1) is required for sperm capacitation, acrosomal exocytosis and sperm-egg coat penetration during porcine fertilization

Protein ubiquitination is a stable, covalent post-translational modification that alters protein activity and/or targets proteins for proteolysis by the 26S proteasome. The E1-type ubiquitin-activating enzyme (UBA1) is responsible for ubiquitin activation, the initial step of ubiquitin-protein ligation. Proteasomal proteolysis of ubiquitinated spermatozoa and oocyte proteins occurs during mammalian fertilization, particularly at the site of sperm acrosome contact with oocyte zona pellucida. However, it is not clear whether the substrates are solely proteins ubiquitinated during gametogenesis or if de novo ubiquitination also occurs during fertilization supported by ubiquitin-activating and -conjugating enzymes present in the sperm acrosome. Along this line of inquiry, UBA1 was detected in boar sperm-acrosomal extracts by Western blotting (WB). Immunofluorescence revealed accumulation of UBA1 in the nuclei of spermatogonia, spermatocytes and spermatids, and in the acrosomal caps of round and elongating spermatids. Thiol ester assays utilizing biotinylated ubiquitin and isolated sperm acrosomes confirmed the enzymatic activity of the resident UBA1. A specific UBA1 inhibitor, PYR-41, altered the remodelling of the outer acrosomal membrane (OAM) during sperm capacitation, monitored using flow cytometry of fluorescein isothiocyanate-conjugated peanut agglutinin (FITC-PNA). Although viable and motile, the spermatozoa capacitated in the presence of PYR-41, showed significantly reduced fertilization rates during in vitro fertilization (IVF; p < 0.05). Similarly, the fertilization rate was lowered by the addition of PYR-41 directly into fertilization medium during IVF. In WB, high Mr bands, suggestive of protein ubiquitination, were detected in non-capacitated spermatozoa by antibodies against ubiquitin; WB with anti-phosphotyrosine antibodies and antibodies against acrosomal proteins SPINK2 (acrosin inhibitor) and AQN1 (spermadhesin) revealed that the capacitation-induced modification of those proteins was altered by PYR-41. In summary, it appears that de novo protein ubiquitination involving UBA1 contributes to sperm capacitation and acrosomal function during fertilization.

Dynamics of the induced acrosome reaction in boar sperm evaluated by flow cytometry

The present study investigated the dynamics of the in vitro induced acrosome reaction (AR) in boar sperm in response to medium composition, incubation time and ionophore concentration. The AR is a prerequisite for normal sperm fertilizing capability and can be studied in vitro following induction by various agents. The ability of a sperm population to undergo the AR in vivo is expected to influence male fertilizing potential, and attempts to relate the in vitro induced AR to fertility has been reported. However, to relate the induced AR to fertility one should be aware of the dynamics of the in vitro induced AR. A detailed description of the dynamics of sperm viability and acrosomal status of boar sperm following in vitro induction of the AR has to our knowledge not previously been conducted. In the present study, a triple color flow cytometric detection technique was used, which gave simultaneous information on sperm viability and acrosomal status. The ionophore induced AR was dependent on extracellular Ca(2+), but could be easily induced in boar sperm without capacitation. Capacitation-associated plasma membrane phospholipid scrambling was assessed and a medium specific ability to induce these membrane changes was observed. Both sperm viability and the induced AR were significantly affected by sperm capacitation, incubation time and ionophore concentration. The results lead to suggestions for an optimized AR induction protocol that takes both sperm viability and the effectiveness of AR induction into consideration.

Identifying useable semen

The "predictors of useable semen" used in most commercial AI centers provide a very conservative estimate of the relative fertility of individual boars. Furthermore, the relatively high sperm numbers used in commercial AI practice (usually >3 x10(9) total sperm per dose of extended semen) usually compensate for reduced fertility, as can be demonstrated in some boars when lower numbers of sperm are used for AI. Differences in relative boar fertility are also masked by the widespread use of pooled semen for commercial AI in many countries. However, the need to continually improve the efficiency of pork production, suggests that commercial AI practice should involve increased use of boars with the highest genetic merit for important production traits. Necessarily, this must be linked to the use of fewer sperm per AI dose, fewer inseminations per sow bred, and hence more sows bred by these superior sires. In turn, this requires improved techniques for evaluating semen characteristics directly related to the fertilization process, such as IVM-IVF assays, analysis of seminal plasma protein markers, more discriminatory tests of sperm motility and morphology, with the goal of identifying high-index boars whose fertility is sustained when low numbers of sperm are used for AI. This paper reviews the current status of laboratory-based boar semen evaluation techniques that meet these criteria.

Zinc alpha 2-glycoprotein: a multidisciplinary protein

Zinc alpha 2-glycoprotein (ZAG) is a protein of interest because of its ability to play many important functions in the human body, including fertilization and lipid mobilization. After the discovery of this molecule, during the last 5 decades, various studies have been documented on its structure and functions, but still, it is considered as a protein with an unknown function. Its expression is regulated by glucocorticoids. Due to its high sequence homology with lipid-mobilizing factor and high expression in cancer cachexia, it is considered as a novel adipokine. On the other hand, structural organization and fold is similar to MHC class I antigen-presenting molecule; hence, ZAG may have a role in the expression of the immune response. The function of ZAG under physiologic and cancerous conditions remains mysterious but is considered as a tumor biomarker for various carcinomas. There are several unrelated functions that are attributed to ZAG, such as RNase activity, regulation of melanin production, hindering tumor proliferation, and transport of nephritic by-products. This article deals with the discussion of the major aspects of ZAG from its gene structure to function and metabolism.

PSP-I/PSP-II spermadhesin exert a decapacitation effect on highly extended boar spermatozoa

PSP-I/PSP-II heterodimer is a major protein of boar seminal plasma that is able to preserve, in vitro, the viability, motility and mitochondrial activity of highly-extended boar spermatozoa. However, a relationship between the protective effects of the heterodimer and sperm capacitation is still unclear. The present study investigated the effect of the PSP-I/PSP-II (1.5 mg/mL) on membrane stability, intracellular calcium concentration ([Ca(2+)](I)) and plasma membrane and acrosome integrity of highly extended boar spermatozoa. Boar spermatozoa were diluted to 1 x 10(6) spermatozoa/mL and incubated at 38 degrees C in Phosphate-buffered saline (PBS) for 10, 30, 60, 120 and 300 min or in modified Tris-buffered medium (mTBM) for 10, 20, 30, 60 and 120 min. After each incubation time, the membrane stability (using Merocyanine-540/Yo-Pro-1), elevation of [Ca(2+)](I) (using Fluo-3-AM/PI) and the sperm plasma membrane and acrosome integrity (using SYBR-14/PI/PE-PNA) were evaluated by flow cytometry. As expected, exposure of the spermatozoa to the PSP-I/PSP-II preserved the plasma membrane and acrosome integrity compared to non-exposed spermatozoa in both media PBS and mTBM (p < .01). The evaluation of membrane stability showed no differences in the percentages of viable sperm with instable plasma membrane in the presence of the PSP-I/PSP-II compared to controls irrespective of the dilution media. The evaluation of the [Ca(2+)](I) levels showed that while spermatozoa incubated in mTBM and exposed to PSP-I/PSP-II had lower [Ca(2+)](I) than controls (39.08% vs. 47.97%, respectively; p < .05), no differences were observed in those samples incubated in PBS. However, a temporal evaluation of the samples showed that a similar proportion of live spermatozoa were able to achieve high levels of [Ca(2+)](I) and membrane instability independent of the presence of PSP-I/PSP-II. In conclusion, PSP-I/PSP-II exert a non-permanent decapacitation effect on highly extended boar spermatozoa that is related with a delay in the increase of [Ca(2+)](I) levels.

α-Tocopherol modifies tyrosine phosphorylation and capacitation-like state of cryopreserved porcine sperm

Sperm cryopreservation is associated with the production of reactive oxygen species (ROS) leading to membrane destabilization, which induces capacitation-like changes, increases protein tyrosine phosphorylation, and decreases their fertilizing ability. alpha-Tocopherol, a lipid peroxidation inhibitor, preserves the functionality of cryopreserved porcine sperm. Our aim was to evaluate the effect of alpha-tocopherol on sperm quality parameters as well as capacitation-like changes and modifications in protein tyrosine phosphorylation. Boar sperm frozen with or without 200 microg/mL of alpha-tocopherol were thawed and maintained at 37 degrees C for 10 min in BTS. Routine parameters of semen quality were evaluated by optical microscopy and membrane changes were determined by the epifluorescence chlortetracycline technique. Changes in protein tyrosine phosphorylation were examined using a specific anti-phosphotyrosine monoclonal antibody. Motility was higher (18%, P<0.05) in semen with alpha-tocopherol. Viability did not differ (P>0.05) between treatments. However, there was less (P<0.05) capacitation-like changes in semen with alpha-tocopherol compared to control samples. A MW 32 kDa tyrosine-phosphorylated protein was detected in extracts of cryopreserved sperm; the intensity of immunostaining was lower in semen containing alpha-tocopherol compared to the control (0.211+/-0.030 versus 0.441+/-0.034 arbitrary units). Additionally, this band was not detected in fresh sperm. The addition of alpha-tocopherol to the extender prior to cryopreservation of boar semen protected sperm membranes against oxidative damage and reduced both tyrosine phosphorylation and the capacitation-like state.

Sperm-binding fibronectin type II-module proteins are genetically linked and functionally related

Fibronectin type II (Fn2) module-containing proteins in the male genital tract are characterized by different numbers of Fn2 modules. Predominantly two classes exist which are distinct by having either two or four Fn2 modules. Minor variants with three Fn2 modules were also found in the human and the porcine epididymis. To reveal their relationship, mRNAs and proteins of representatives of these classes were studied in human, in Sus scrofa, and in rodents. Adult boars expressed members of both classes, i.e. ELSPBP1 and pB1, in subsequent regions of the epididymis, and both were under androgenic control. Human and rodent epididymides, on the other hand, alternatively contained only representatives of one of these two classes, i.e. ELSPBP1 in the human and two different pB1-related counterparts in rodents. ELSPBP1 and pB1-related genomic sequences were closely linked in chromosomal regions HSA 19q and SSC 6 q11-q21; conserved synteny between these regions is well established. On the other hand, in a syntenic region on mouse chromosome 7, ELSPBP1-related sequences were lacking. Tight binding to the sperm membrane via a choline-mediated mechanism was a common feature of the two classes of Fn2-module proteins, suggesting related function(s). However, differences in their regionalized expression patterns along the male genital tract as well as in association sites on the sperm surface suggested a species-specific sequential order in sperm binding.

Identification of sperm forward motility-related proteins in human seminal plasma

Seminal plasma, an amorphous material that exists in semen, contains proteins related to sperm forward motility. Employing affinity chromatography with ConA beads and protein ultrafiltration, we isolated and concentrated proteins from heated human seminal plasma. Results of computer-assisted semen analyses (CASA) demonstrated that the forward motility index of bovine spermatozoa from the epididymal caput, incubated with proteins and theophylline, was significantly different from that of spermatozoa incubated with theophylline alone (P < 0.01). The electrophoreses revealed that the protein bands with high molecular weights in the gel of PAGE changed into low molecular weights in the gel of SDS-PAGE. Furthermore, proteins from a separated portion of the PAGE gel were still able to stimulate spermatozoa from the epididymal caput to gain forward motility. Two-dimensional (2D)-gel electrophoresis and mass spectrometry indicated that spots focused on the portion seemed, according to their amino acid sequences, to be like human alpha-1-antitrypsin and zinc-alpha-2-glycoprotein (ZAG) precursors. Western blot analysis showed the presence of these two proteins in seminal plasma. These proteins, related to the forward motility of spermatozoa in human seminal plasma, may play important roles during maturation of spermatozoa, from the epididymis through fertilization in the female reproductive tract.

Dynamic quantification of the tyrosine phosphorylation of the sperm surface proteins during capacitation

BACKGROUND

Spermatozoa acquire active fertilizing competence only after deposition in the female tract and subsequent capacitation. Recent studies on the cellular location of major sperm phosphoproteins suggest that capacitation is associated with tyrosine phosphorylation of proteins exposed on the sperm surface. However, these changes have not yet been quantified objectively. A calcium influx seems to be required for the completion of tyrosine phosphorylation in some species; however, the exact temporal coordination between these processes is still poorly understood.

METHODS

Flow cytometry was used to quantify the degree of phosphorylation of the sperm surface proteins by probing with fluorescein isothiocyanate-conjugated anti-phosphotyrosine (pY) antibody raised in mouse. Dynamic changes in other sperm parameters (calcium influx, membrane integrity, and spontaneous acrosome reaction) were assessed to analyze their temporal coordination.

RESULTS

: The changes in specific phosphotyrosine (pY) fluorescence signal detected in live, nonpermeabilized boar cell suspensions were biphasic during incubation under capacitating conditions. After 120 min of incubation, the degree of pY fluorescence increased threefold, indicating the changes in proteins exposed on sperm surface. At the same time there was a gradual increase in cytosolic calcium ion levels with the maximal rate at 60 min of incubation. This rate slowed immediately before the onset of the massive rise in tyrosine phosphorylation and decreased by 90% after its completion. The integrity of plasma and acrosome membranes decreased only slowly, illustrating that the changes observed were not due to the process of spontaneous acrosome reaction.

CONCLUSIONS

These data provide quantitative evidence for the appearance of tyrosine-phosphorylated proteins on the surface of live boar spermatozoa during capacitation. An exact temporal coordination exists between cytosolic calcium ion content and protein tyrosine phosphorylation under these conditions. This novel approach has the advantage of making possible a precise quantification and kinetic comparison of molecular processes in different cell subpopulations.