Effects of semen preservation on boar spermatozoa head membranes

Existence and importance of Na+K+-ATPase in the plasma membrane of boar spermatozoa

Sodium-potassium-ATPase (Na+K+-ATPase), a target to treat congestive heart failure, is the only known receptor for cardiac glycosides implicated in intracellular signaling and additionally functions enzymatically in ion transport. Spermatozoa need transmembrane ion transport and signaling to fertilize, and Na+K+-ATPase is identified here for the first time in boar spermatozoa. Head plasma membrane (HPM) isolated from boar spermatozoa was confirmed pure by marker enzymes acid and alkaline phosphatase (218 ± 23% and 245 ± 38% enrichment, respectively, versus whole spermatozoa). Western immunoblotting detected α and β subunits (isoforms α1, α3, β1, β2, and β3) in different concentrations in whole spermatozoa and HPM. Immunofluorescence of intact sperm only detected α3 on the post-equatorial exterior membrane; methanol-permeabilized sperm also had α3 post-equatorially and other isoforms on the acrosomal ridge and cap. Mass spectrometry confirmed the presence of all isoforms in HPM. Incubating boar sperm in capacitating media to induce the physiological changes preceding fertilization significantly increased the percentage of capacitated sperm compared to 0 h control (33.0 ± 2.6% vs. 19.2 ± 2.6% capacitated sperm, respectively; p = 0.014) and altered the β2 immunofluorescence pattern. These results demonstrate the presence of Na+K+-ATPase in boar sperm HPM and that it changes during capacitation.

Differential seminal plasma proteome signatures of boars with high and low resistance to hypothermic semen preservation at 5°C

BACKGROUND

Hypothermic storage at 5°C has been investigated as an alternative to promote the prudent use of antibiotics for boar artificial insemination doses. However, this temperature is challenging for some ejaculates or boars.

OBJECTIVE

The present study aimed to identify putative biomarkers for semen resistance to hypothermic storage at 5°C by comparing the seminal plasma proteomes of boars with high and low seminal resistance to preservation at 5°C.

MATERIALS AND METHODS

From an initial group of 34 boars, 15 were selected based on the following criteria: ejaculate with ≤20% abnormal spermatozoa and at least 70% progressive motility at 120 hours of storage at 17°C. Then, based on the response to semen hypothermic storage at 5°C, boars were classified into two categories: high resistance-progressive motility of >75% in the three collections (n = 3); and low resistance-progressive motility of <75% in the three collections (n = 3). Seminal plasma proteins were analyzed in pools, and differential proteomics was performed using Multidimensional Protein Identification Technology.

RESULTS

Progressive motility was lower at 120 hours of storage in low resistance, compared to high resistance boars (P < .05). Acrosome and plasma membrane integrity were not affected by the boar category, storage time, or their interaction (P ≥ .104). Sixty-five proteins were considered for differential proteomics. Among the differentially expressed and exclusive proteins, the identification of proteins such cathepsin B, legumain, and cystatin B suggests significant changes in key enzymes (eg, metalloproteinases) involved in spermatogenesis, sperm integrity, and fertilizing potential.

DISCUSSION AND CONCLUSION

Differences in the seminal plasma suggest that proteins involved in the proteolytic activation of metalloproteinases and proteins related to immune response modulation could disrupt key cellular pathways during spermatogenesis and epididymal maturation, resulting in altered resistance to chilling injury. Further in vivo studies focusing on the immunological crosstalk between epithelial cells and gametes might explain how the immune regulators influence sperm resistance to hipothermic storage.

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.

Effect of cholesterol-loaded-cyclodextrin on sperm viability and acrosome reaction in boar semen cryopreservation

This study was undertaken to examine the effect of cholesterol-loaded-cyclodextrin (CLC) on boar sperm viability and spermatozoa cryosurvival during boar semen cryopreservation, and methyl-β-cyclodextrin (MBCD) was treated for comparing with CLC. Boar semen treated with CLC and MBCD before freezing process to monitor the effect on survival and capacitation status by flow cytometry with appropriate fluorescent probes. Sperm viability was higher in 1.5mg CLC-treated sperm (76.9±1.01%, P<0.05) than un-treated and MBCD-treated sperm before cryopreservation (58.7±1.31% and 60.3±0.31%, respectively). For CTC patterns, F-pattern was higher in CLC treated sperm than MBCD-treated sperm, for B-pattern was higher in CLC-treated sperm than fresh sperm (P<0.05). For AR pattern (an acrosome-reacted sperm) was lower in CLC-treated sperm than MBCD-treated sperm (P<0.05). Moreover, we examined in vitro development of porcine oocytes after in vitro fertilization using CLC-treated frozen-thawed semen, in which CLC treatment prior to freezing and thawing increased the development of oocytes to blastocyst stage in vitro. In conclusion, CLC could protect the viability of spermatozoa from cryodamage prior to cryopreservation in boar semen.

Effects of hypothermic storage on intracellular calcium, reactive oxygen species formation, mitochondrial function, motility, and plasma membrane integrity in striped bass (Morone saxatilis) sperm

Experiments were conducted to determine the effect of hypothermic 24 h storage on striped bass sperm cell plasma membrane integrity, free intracellular Ca(2+) ([Ca(2+)](i)), mitochondrial membrane potential (ΔΨ(m)), and reactive oxygen species (ROS) formation (oxidation of hydroethidine to ethidium) as determined by flow cytometry; motion activation and ATP concentration as determined by Luciferin-Luciferase bioluminescence assay. Semen was stored for 1 or 24 h at 4 °C in an O(2) atmosphere undiluted or diluted (one volume semen with 3 volumes diluent) with T350 (20 mM TRIS base-NaCl, 350 mOsm/mL, pH 8) or with seminal plasma in the presence of various treatments. Viability (% cells excluding propidium iodide) approached 100% after 1 h storage in undiluted or diluted semen. After 1 h of storage the [Ca(2+)](i) marker, Fluo-3, was detected in only 3% of sperm cells in undiluted or diluted semen. In contrast to storage for 1 h, after 24 h the incidence Fluo-3 fluorescence intensity was increased (P < 0.05) in > 50% of the viable cells in undiluted and diluted semen along with increased cell death; the presence of 1 mM ethylene glycol tetraacetic acid (EGTA) blocked CaCl(2)-induced Fluo-3 fluorescence and cell death. Activation of sperm motility was 82% after 1 h in T350 and decreased (P < 0.05) to 30% after 24 h. However, motility activation failed in the presence of EGTA at 1 or 24 h. During storage ΔΨ(m) was not affected by storage time or treatment. In contrast, sperm ATP was greater (P < 0.05) at 1 h than at 24 h and was greater in sperm stored in diluted than undiluted form. While ROS formation was induced by menadione treatment, there was no evidence of storage-induced ROS formation in the absence of menadione. The increased [Ca(2+)](i) found after 24 h indicates a storage induced defect in the maintenance of cellular calcium homeostasis which may be detrimental to sperm activation.

Effect of thawing temperature on the motility recovery of cryopreserved human spermatozoa

OBJECTIVE

To investigate the effects of thawing temperature on sperm function after cryopreservation. The technical aspects of sperm cryopreservation have significantly improved over the last few decades. However, a standard protocol designed to optimize sperm motility recovery after thawing has not yet been established.

DESIGN

Prospective study.

SETTING

Private infertility institute and university-based research laboratory.

PATIENT(S)

Eighty consenting normozoospermic patients consulting for infertility.

INTERVENTION(S)

Spermatozoa from donor semen samples were thawed at different temperatures.

MAIN OUTCOME MEASURE(S)

Sperm motility, viability, adenosine-5'-triphosphate (ATP) content, acrosomal status, and DNA integrity were evaluated as a function of thawing temperature in cryopreserved human sperm samples.

RESULT(S)

Thawing at 40 degrees C resulted in a statistically significant increase in sperm motility recovery compared with thawing at temperatures between 20 degrees C and 37 degrees C. There were no statistically significant differences in sperm viability, acrosomal status, ATP content, and DNA integrity after thawing at 40 degrees C compared with thawing at temperatures between 20 degrees C and 37 degrees C.

CONCLUSION(S)

Sperm thawing at 40 degrees C could be safely used to improve motility recovery after sperm cryopreservation.

Resistance to osmotic stress of horse spermatozoa: the role of ionic pumps and their relationship to cryopreservation success

To study the resistance of horse spermatozoa against hyperosmotic stress, cells were incubated in solutions of 600 to 4000 mOsm(undisturbed media). Then, semen was immediately placed into an iso-osmotic solution (disrupted media). Incubation in undisturbed media decreased sperm viability in an osmolarity- and temperature-dependent manner. Viability was further decreased in disrupted media, with the effect dependent upon the initial osmolarity of the media and on the temperature. Treatment with ouabain or amiloride impaired the resistance of horse spermatozoa to hyperosmotic stress. Very few correlations were strong between viability after hyperosomotic stress and quality parameters of fresh and frozen-thawed horse semen. The results indicate that the usefulness of resistance to hyperosmotic stress in assessing frozen-thawed semen quality is compromised, since other factors are involved in the resistance to freezing-thawing. Both Na (+)K (+) ATP-ase and the Na (+)H (+) antiporter act in the resistance to hyperosmotic stress in horse spermatozoa.

Spontaneous uptake of exogenous DNA by bull spermatozoa

Sperm-mediated DNA transfer can be used to transfer exogenous DNA into the oocyte for the production of transgenic animals. In spite of controversy in the literature, sperm-mediated DNA transfer is a simple and quick technique that can be used in routine breeding programs (AI, embryo transfer and IVF). The main objective of this study was to determine the factors affecting the spontaneous uptake of exogenous DNA by bull spermatozoa. For this purpose, fresh and frozen spermatozoa (0.25 x 10(6)), from the same ejaculate from each of four bulls were co-incubated with fluorescent-labeled green fluorescent protein (GFP) and chloremphenicol acetyltransferase (CAT) plasmids at 37 degrees C for 30 min. Neither bull nor plasmid significantly affected the uptake of exogenous DNA. However, transfection efficiency was higher in frozen-thawed versus fresh spermatozoa (P<0.001). Regardless of whether transfected spermatozoa were alive or dead, all transfected spermatozoa were immotile. It can be concluded that a population of spermatozoa is present in bull semen which has the ability to uptake exogenous DNA spontaneously. There is tremendous scope to improve transfection efficiency of spermatozoa while maintaining motility; this needs to be achieved in order to more easily use this technique in transgenesis. However, live-transfected bull spermatozoa clearly can incorporate exogenous DNA and should be usable in intracytoplasmic sperm injection protocols.

Cryopreservation and Thawing Is Associated with Varying Extent of Activation of Apoptotic Machinery in Subsets of Ejaculated Human Spermatozoa1

We investigated the impact of cryopreservation and thawing on levels of caspases-3, -8, and -9 activity, intact mitochondrial membrane potential (Deltapsim), and DNA fragmentation in human spermatozoa. Eleven pools of cryopreserved and eight pools of fresh semen samples were examined. Mature and immature fractions were separated on a two-layer density gradient (47% and 90%) and further subdivided based on the externalization of phosphatidylserine and its binding to annexin V-labeled superparamagnetic microbeads (ANMB). Levels of activated caspases were assessed using fluorescein-labeled inhibitors of caspases (FLICA), Deltapsim using a lipophilic cationic dye, and DNA fragmentation by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay. Cryopreservation was significantly associated with activation of caspases-3, -8, and -9, as well as disruption of the mitochondrial membrane potential but no significant changes were observed in DNA fragmentation. In mature sperm, caspase activation was only detected in the ANMB+ fraction, whereas in immature sperm, both ANMB+ and ANMB- fractions showed activated caspase levels. In ANMB+ immature sperm, apoptosis seemed to be triggered by a surface ligand-receptor mechanism as well as by disruption of mitochondria, whereas in ANMB- immature sperm, apoptosis was induced by activation of caspase-9 following loss of intact Deltapsim. These results demonstrate that selection of annexin V-negative mature spermatozoa might be of clinical relevance for fertility preservation, as this sperm fraction shows no activated apoptosis during the cryopreservation process.

Effect of cholesterol-loaded cyclodextrin on the cryosurvival of bull sperm

Bull sperm were treated with several levels of cholesterol-loaded cyclodextrin (CLC) and frozen in egg yolk diluents containing either Tris or sodium citrate, to determine the CLC concentration that best benefits bull sperm cryosurvival. After thawing, higher percentages of motile (60%) and viable (55%) sperm were obtained when 1.5mg/ml CLC was added to sperm prior to freezing, than for sperm frozen in egg yolk Tris alone (42 and 46%, respectively; P < 0.05). Increasing concentration of CLCs, maintained higher percentages of viable sperm up to addition of 6.0mg/ml CLC when the percentages of viable sperm began to decline (50%; P < 0.05). Addition of 1.5mg/ml CLC to sperm frozen in sodium citrate diluent resulted in 53% motile sperm compared to 37% for control, although these were not different (P > 0.05). The beneficial effects of CLC addition were observed regardless of whether sperm incubated with CLC at 22 or 37 degrees C (P > 0.05) and maximum effects were observed when sperm incubated with CLC for 15min. Longer incubation times, up to 60min, resulted in similar results (P > 0.05). The amount of cholesterol that incorporated into sperm, increased with increasing CLC concentration, in a linear fashion, and each sperm incorporates a similar amount of cholesterol (coefficient of variation=12.9+/-0.7%). In addition, the cholesterol incorporates into all sperm membranes. Increasing membrane cholesterol levels, by adding CLCs to cells, prior to freezing, is a simple technology that increases the cryosurvival of bull sperm, and may benefit the cryosurvival of many cell types.

A differential mechanism is involved during heparin- and cryopreservation-induced capacitation of bovine spermatozoa

After ejaculation, mammalian spermatozoa must undergo capacitation to fertilize. Capacitation of bovine spermatozoa occurs in vitro in medium supplemented with heparin. Semen cryopreservation is an important tool for assisted reproduction, although the fertility of frozen-thawed spermatozoa is reduced, possibly due to precocious capacitation-like changes that are known to occur. Our purpose was to clarify the mechanisms involved in bull sperm cryocapacitation induced by cryopreservation. Our general hypothesis is that the signaling pathways that lead to capacitation are triggered by the cryopreservation procedure. Ejaculated bovine semen was divided into two aliquots and diluted in extender; one was then kept fresh, whereas the second was cryopreserved. Western blots of extracted sperm proteins with anti-phosphotyrosine antibody showed that capacitation, induced by either heparin in fresh sperm or cryopreservation (cryocapacitation), is associated with a differential profile of phosphotyrosine-containing proteins. Immunolocalization of phosphotyrosine-containing proteins in the fresh and cryopreserved spermatozoa showed that, after thawing, cryocapacitated sperm displayed labeling over the acrosomal region, whereas for fresh sperm, this labeling appeared after 5-h incubation with heparin. The chlortetracycline assay and the ability of the sperm to undergo the lysophosphatidylcholine-induced acrosome reaction were used to confirm that a subpopulation of cryopreserved sperm is capacitated at thawing, irrespective of heparin inclusion. Since glucose is known to inhibit heparin-induced capacitation, the semen extender was modified to include glucose as a means of inhibiting cryocapacitation; however, cryocapacitation was not prevented according to the chlortetracycline assay and profile of phosphotyrosine-containing sperm proteins.

Optimizing and quantifying fusion of liposomes to mammalian sperm using resonance energy transfer and flow cytometric methods

BACKGROUND

Liposomes are used to carry pharmaceutical agents and to alter the lipid composition of cell membranes. This study compared resonance energy transfer (RET), fluorescence dequenching, and flow cytometry as monitors and quantifiers of fusion between liposomes and mammalian spermatozoa.

METHODS

Preliminary experiments used RET to determine the optimum sperm concentration for fusion of DL-alpha-phosphatidylcholine dipalmitoyl (PC)/DL-alpha-phosphatidylethanolamine dipalmitoyl (PE) liposomes at 35 degrees C +/- 5 mM Ca2+. Microscopy confirmed the fusion of liposomes, not just adhesion (n = 3). Dequenching tested the time-dependent fusion of liposomes of two different lipid compositions to sperm, both, (n = 3) +/- 1 mM Ca2+ and (n = 3) without Ca2+ at two sperm concentrations. Finally, flow cytometry absolutely quantified the percentage of sperm fusing to liposomes at different liposome-to-sperm ratios (n = 4) and with sperm from different donors (n = 3).

RESULTS

RET detected fusion of liposomes with sperm and microscopy confirmed the interaction to be true fusion. Dequenching detected more fusion of liposomes with sperm at 100 x 10(6) sperm per milliliter than at lower concentrations (P < 0.05). Fusion dynamics differed with lipid composition but Ca2+ had no effect. Flow cytometry reliably quantified the percentage of sperm fusing with liposomes, which varied from bull to bull (P < 0.05).

CONCLUSION

Liposome fusion with mammalian sperm membranes can be quantified cytometrically and varies with lipid composition, sperm-to-liposome ratio, and individual animals.

Sperm apoptosis in fresh and cryopreserved bull semen detected by flow cytometry and its relationship with fertility

The present study was conducted to detect sperm apoptosis in fresh and frozen semen and to determine its relationship with bull fertility. Three ejaculates were collected from five breeding bulls with different fertility levels and were cryopreserved using standard methods. Two flow cytometric methods were employed to measure apoptosis: an assay for phosphatidylserine (PS) translocation across the plasma membranes using fluorescein-labeled Annexin V and propidium iodide (PI), and an assay for nicked DNA using bromodeoxyuridine (BrdU), terminal deoxynucleotidyl transferase, and fluorescein-labeled anti-BrdU monoclonal antibody. Both assays showed that fresh sperm contained 10%-20% apoptotic sperm. Significant differences in the percentage of apoptotic sperm were observed among the bulls. Cryopreservation induced translocation of PS to the outer leaflet of the plasma membrane and caused most of the necrotic cells in fresh sperm to disintegrate. Bull fertility was significantly related to the percentage of necrotic or viable sperm in fresh semen as detected by the Annexin V/PI assay, to the number of apoptotic sperm in fresh semen as detected by the TUNEL assay, and to the level of chromatin or DNA condensation as detected by PI staining. The present study suggests that the presence of apoptotic spermatozoa in fresh semen could be one of the reasons for poor fertility in breeding bulls.

Cryopreservation in different concentrations of glycerol alters boar sperm and their membranes

To test the hypothesis that glycerol would concomitantly affect sperm membrane structure and the function of the intact cells, boar semen (4 ejaculates from 4 boars) was cryopreserved in an egg yolk extender with 0%, 2%, 4%, or 8% glycerol in 0.5-mL straws using previously derived optimal cooling and thawing rates. Increasing glycerol concentrations increased spermatozoal progressive motility immediately after thawing and after 2 hours at 43 degrees C, but decreased the percentage of sperm with normal acrosomal morphology. The mathematical products of the motility and acrosomal integrity scores (MOT x NAR index) were low in 0% and 8% glycerol, and significantly higher in 2% and 4% glycerol. The fluidity of sperm-head plasma membranes, a measure of molecular interaction, was assessed with the lipid probes trans-parinaric acid and cisparinaric acid (tPNA, cPNA), during a 2.5-hour incubation with or without 1 mM Ca2+. Membrane fluidity detected by each probe differed significantly, indicating the presence of at least 2 domains whose constituent molecules had unique dynamics. Behavior of each domain was radically altered by cryopreservation. Increasing glycerol concentration caused a variably faster loss of fluidity in the cPNA domain, and had highly variable effects on fluidity change over time in the tPNA domain. Normal acrosomal ridge (NAR) and the MOT x NAR index correlated significantly with the fluidity of the more mobile cPNA domain (+/- 1 mM Ca2+), supporting the hypothesis of an interrelationship of glycerol concentration during cryopreservation with sperm membrane structure and cell function. The MOT x NAR index may be a useful guide in choosing optimal cryoprotectant concentrations.

Incorporating lipids into boar sperm decreases chilling sensitivity but not capacitation potential

Fresh boar sperm were incubated with small unilamellar liposomes composed of either the total lipids extracted from head plasma membranes (HPM) of fresh boar sperm or selected lipids (SL) of five defined phospholipids with specific acyl chains. To optimize fusion, liposomes with 2 mol% octadecyl rhodamine fluorophore in Beltsville Thawing Solution +/- 1 mM CaCl(2) were incubated at 35 degrees C with 1;ts 10(7) or 10(8) spermatozoa/ml and monitored over 60 min, using flow cytometry and fluorescence microscopy. The HPM fused to both sperm concentrations faster than SL but was equivalent by 30 min (10(8) sperm/ml) or 60 min (10(7) sperm/ml; 57.5 +/- 3% and 67.1 +/- 8% sperm fused to HPM and SL, respectively) +/- Ca(2+). Neither HPM nor SL affected onset of capacitation or spontaneous or ionophore-induced acrosome reactions at 0 or 3 h (chlortetracycline and fluorescein isothiocyanate-Pisum sativum agglutinin; n = 3). During cooling and after cryopreservation (n = 4 ejaculates), SL but not HPM significantly improved sperm motility and viability (Sybr14/propidium iodide staining) +/- 20% egg yolk, but egg yolk alone was more effective than SL alone. Liposomes of complex composition can fuse to boar sperm without harming in vitro capacitation or acrosome reaction and reduce sperm chilling sensitivity.

Viability, susceptibility to peroxidation and fatty acid composition of boar semen during liquid storage

The changes in viability, susceptibility to peroxidation and fatty acid composition of total phospholipid were studied in boar spermatozoa during 5 day liquid storage in a standard or alpha-tocopherol (alphaT) enriched diluent. The sperm rich fraction of the ejaculates was collected from 6-month old boars. Sperm viability progressively decreased during storage and alphaT inclusion into the diluent significantly inhibited this trend. alphaT inclusion also decreased significantly peroxidation (TBARS production of spermatozoa). Spermatozoa stored in the treatment diluent became rapidly enriched in alphaT with a concomitant decrease of alphaT content in the medium. The proportion of polyunsaturates, mainly 22:6n-3, decreased with a complementary increase in the content of the saturates, mainly 18:0. The inclusion of alphaT into the diluent was effective in totally preventing the significant decrease of 22:6n-3 observed in sperm phospholipid in the control samples during the storage period. It is concluded that the alphaT inclusion in the boar semen diluent increased cell viability through its prevention of an oxidative reduction in the levels of the major polyunsaturated fatty acids, namely 22:6n-3.

Relationship between the proportion of capacitated spermatozoa present in frozen-thawed bull semen and fertility with artificial insemination

The objective of the present study was to confirm the presence of prematurely capacitated spermatozoa in frozen-thawed bull semen and to investigate the relationship of premature capacitation to the fertility of the respective semen. Twenty batches of frozen semen from young AI bulls of the Swedish Red and White breed with known fertility (expressed as 56-day non-return rates; 56 d-NRR) were tested using a Chlortetracycline (CTC) assay to assess capacitation status in frozen-thawed spermatozoa. The status of capacitation, as evidenced in this experiment, was further tested based on the hypothesis that capacitated spermatozoa present in frozen-thawed semen should undergo the acrosome reaction (AR) on co-incubation with homologous zona pellucida (ZP) glycoproteins. The percentage (mean +/- SEM) of uncapacitated, capacitated and acrosome-reacted spermatozoa in the frozen-thawed semen (n = 20) were 49.3 +/- 11.9, 36.3 +/- 8.3 and 14.2 +/- 11.9, respectively. On co-incubation with ZP, there was a significant increase (p = 0.001) in the proportion of spermatozoa undergoing the AR compared to the control with a concurrent decrease in the proportion of capacitated spermatozoa, suggesting that a proportion of capacitated spermatozoa were undergoing the AR. The proportion of viable, uncapacitated spermatozoa present in the frozen-thawed semen was correlated to the 56 d-NRR (n = 20, r = 0.5, p = 0.03). In conclusion, a proportion of spermatozoa in frozen-thawed semen was capacitated and the proportion of viable, uncapacitated spermatozoa present in semen was positively correlated to fertility.

Use of lectins to characterize plasma membrane preparations from boar spermatozoa: a novel technique for monitoring membrane purity and quantity

The object of this study was to develop a method to quantify the amount of outer acrosomal membrane material in isolated plasma membranes from boar sperm cells. The cells were fractionated by nitrogen cavitation, and plasma membranes were isolated by subsequent differential centrifugation steps. Marker enzyme measurement showed that the plasma membrane isolates were enriched in plasma membrane markers and did not contain nuclei, inner acrosomal membranes, or mitochondria. Since there is no marker enzyme known for the outer acrosomal membrane, lectins were used for the detection of this membrane. The membrane specificity of a number of lectin conjugates was tested with fluorescence microscopy and transmission electron microscopy. Membrane binding of these lectin conjugates was quantified with flow-cytometry and an enzyme-linked lectin binding assay. Wheat germ agglutinin was specific for the plasma membrane while peanut agglutinin was specific for the outer acrosomal membrane. The use of these lectins made it possible for the first time to discriminate between these two membranes. The isolated plasma membrane fraction was enriched more than 10-fold (17-fold after further purification by a sucrose gradient) in plasma membrane material compared to outer acrosomal membrane material. Highly purified sperm plasma membranes should prove to be useful for research on primary sperm-zona interactions.

Visualization and quantification of glycolipid polarity dynamics in the plasma membrane of the mammalian spermatozoon

Seminolipid (sulphogalactosylalkylacylglycerol), the glycolipid that is specific for mammalian germ cells, is located exclusively in the outer leaflet of the sperm plasma membrane. In this study the lateral distribution of seminolipid on sperm heads has been investigated by indirect immunofluorescence labelling and detection with digital imaging fluorescence microscopy. In freshly ejaculated sperm cells this glycolipid was present primarily at the apical ridge subdomain of the plasma membrane of the sperm head. After binding the sperm cells to zona-coated coverslips seminolipid migrated, in 40 minutes, from the apical ridge to the equatorial subdomain of the plasma membrane. A similar redistribution of seminolipid was observed during capacitation of sperm cells in vitro induced by Ca2+ or bovine serum albumin. Comparable migration of seminolipid was also found after prolonged storage of ejaculated sperm cells, albeit at a much slower rate. Addition of arylsulphatase A, an enzyme present in seminal plasma that desulphates seminolipid, significantly enhanced the migration of seminolipid during storage of sperm cells. Its breakdown product desulphoseminolipid (galactosylalkylacylglycerol) appeared highly specifically at the equatorial segment. The measured fluorescence intensity over the sperm head surface correlated linearly with the spatial probe distribution as was checked by fluorescence lifetime imaging microscopy. This paper demonstrates and quantifies for the first time the polarity of seminolipid on the surface of the sperm cell and the dynamic alterations that occur in this polarity during post-ejaculatory events.

Diet and breed influence the sperm membranes of beef bulls

Semen was collected from 12 Hereford and 10 Simmental bulls at the conclusion of a 119-day Record of Performance growth trial. Within each breed, the bulls were fed a standard test ration (Diet 1) or an experimental diet consisting entirely of a pelleted concentrate with ground corn cobs as the primary fibre source (Diet 2). Semen was analyzed for motility and morphology while testicular tissue obtained at slaughter the day after semen collection was assessed for seminiferous tubule integrity; none of these parameters varied significantly with breed or diet. The fluidity of head plasma membranes from the spermatozoa was assessed with fluorescence polarization using tPNA. Fluidity decreased over the 160 minute observation period, indicating molecular rearrangments within the head membranes which may reflect sperm changes preceding fertilization. The fluidization displayed a breed-by-diet interaction since membrane fluidity differed significantly between breeds on Diet 1 and between diets for Simmental bulls. Fluidities of some samples were also analyzed with cPNA, and these differed significantly from those obtained with tPNA, indicating the presence of domains in sperm head membranes. Neither diet nor breed affected traditionally measured semen characteristics of Hereford and Simmental bulls, but the membrane dynamics differed between the 2 breeds, and diet affected the sperm membrane dynamics of Simmental bulls.

Effects of cold shock and phospholipase A2 on intact boar spermatozoa and sperm head plasma membranes

Head plasma membranes (HPM) isolated from cryopreserved boar spermatozoa show an excessive fluidization, which might be involved in the loss of fertility. The current study assessed the ability of cold shock (5 degrees C) and phospholipase A2 (PA2) to duplicate these effects on membrane structure and to affect 45Ca2+ uptake and gross morphological characteristics of whole, fresh boar-sperm. The HPM from cold-shocked sperm showed a significantly greater rate of fluidization over time than did HPM from control sperm. Addition of PA2 (bee or snake venom, 0.1 or 10.0 ng/ml) to HPM from control sperm caused fluidization similar to cold shocking, but to a lesser degree (P less than 0.05). Cold-shocked intact sperm exhibited severe acrosomal disruption, loss of motility, and increased 45Ca2+ uptake relative to control sperm. Addition of PA2 (bee or snake venom, 0.1, 1.0., 10.0, and 1,000 ng/ml) to control sperm had no effect on gross morphology or motility while maintaining or increasing sperm extrusion of 45Ca2+. Therefore, although PA2 can, to some extent, duplicate the effects of cold shock on HPM molecular organization, its lipid hydrolytic action is insufficient to cause all the gross disruptions of severe thermal shock. Both PA2 and cold shock disrupted HPM structure, but only cold shock increased 45Ca2+ uptake, suggesting that cold shock may be increasing 45Ca2+ uptake in areas other than the head. Cold shock disrupts sperm on three levels; membrane molecular organization, intracellular Ca2+ regulation, and gross morphology/motility.