Induction of bovine sperm capacitation by TEST-yolk semen extender

Microenvironment of the male and female reproductive tracts regulate sperm fertility: Impact of viscosity, pH, and osmolality

BACKGROUND

Terminally differentiated mammalian sperm are exposed to gradients of viscosity, pH, and osmolality both in the male and female reproductive tract during their perilous journey to quest the ovum. The complex physicochemical factors play an integral role in preparing sperm for the fertilization process.

OBJECTIVES

To elucidate the influence of the reproductive tract microenvironment especially viscosity, pH, and osmolality in regulating sperm functional and fertilization competence.

MATERIALS AND METHODS

The data used in this review were collected from the research papers and online databases focusing on the influence of viscosity, pH, and osmolality on sperm function.

DISCUSSION

The gradients of viscosity, pH, and osmolality exist across various segments of the male and female reproductive tract. The changes in the viscosity create a physical barrier, pH aid in capacitation and hyperactivation, and the osmotic stress selects a progressive sperm subpopulation for accomplishing fertilization. The sperm function tests are developed based on the concept that the male genotype is the major contributor to the reproductive outcome. However, recent studies demonstrate the significance of sperm genotype-environment interactions that are essentially contributing to reproductive success. Hence, it is imperative to assess the impact of physicochemical stresses and the adaptive ability of the terminally differentiated sperm, which in turn would improve the outcome of the assisted reproductive technologies and male fertility assessment.

CONCLUSION

Elucidating the influence of the reproductive tract microenvironment on sperm function provides newer insights into the procedures that need to be adopted for selecting fertile males for breeding, and ejaculates for the assisted reproductive technologies.

Effects of egg yolk during the freezing step of cryopreservation on the viability of goat spermatozoa

Four experiments were conducted to investigate the effects of egg yolk during the freezing step of cryopreservation (namely, the process except for the cooling step), on the viability of goat spermatozoa. The effects of egg yolk on sperm motility and acrosome integrity during the freezing step were investigated in Experiment 1. Spermatozoa diluted with Tris-citric acid-glucose (TCG) solution containing 20% (v/v) egg yolk were cooled to 5 degrees C, washed, and then frozen in TCG with egg yolk (TCG-Y), TCG without egg yolk (TGG-NY), 0.370 M trehalose with egg yolk (TH-Y), or trehalose without egg yolk (TH-NY). All extenders contained glycerol. In frozen-thawed spermatozoa, the inclusion of egg yolk in the freezing extenders increased (P<0.05) percentages of motile sperm, progressively motile sperm, and the recovery rate (ratio of post-thaw to pre-freeze values), but decreased (P<0.05) acrosomal integrity. Moreover, extenders with trehalose had better (P<0.05) post-thaw sperm viability. In Experiment 2, the effects of egg yolk on acrosome status before and after freezing were studied. Egg yolk significantly decreased the proportion of intact acrosomes before freezing, leading to fewer (P<0.05) intact acrosomes post-thaw and lower (P<0.05) recovery rates for intact acrosomes. In Experiment 3, including sodium dodecyl sulfate (SDS) in a diluent containing egg yolk tended to preserve the acrosome compared with the egg yolk containing diluent free of SDS, however, spermatozoa had a lower (P<0.05) proportion of intact acrosomes than those in a yolk-free diluent. However, after cooling, spermatozoa were diluted with a glycerolated extender containing egg yolk. Therefore, the objective of Experiment 4 was to explore whether the egg yolk or glycerol was responsible for the reduced intact acrosome percentage. In this experiment, after cooling and washing the spermatozoa were diluted in TCG with glycerol and/or egg yolk. The combination of glycerol and egg yolk in the extender reduced (P<0.05) the proportion of intact acrosomes compared with egg yolk or glycerol alone. In conclusion, the inclusion of egg yolk significantly improved sperm motility, indicating its beneficial effects during the freezing step of cryopreservation; trehalose appeared to synergistically increase its cryoprotective effects. Furthermore, although neither glycerol nor egg yolk per se affected the proportion of intact acrosomes, the combination of the two significantly reduced the proportion of acrosome-intact spermatozoa.

Acrosomal integrity and capacitation are not influenced by sperm cryopreservation in the giant panda

Sperm cryopreservation and artificial insemination are important management tools for giant panda breeding and the preservation of extant genetic diversity. This study examined the influence of freeze-thawing on sperm function, specifically capacitation. Sperm from nine giant pandas were assessed before and after rapid (- 40 and - 100 degrees C/min) cryopreservation by incubation in HEPES-buffered Ham's F10 medium with and without the capacitation accelerators, 3-isobutyl-1-methylxanthine (IBMX) and dibutyryl cyclic AMP (dbcAMP). At 0, 3 and 6 h of exposure, aliquots were assessed for sperm motility traits and capacitation, defined as the proportion of sperm with intact acrosomes following exposure to solubilised zonae pellucidae (ursid or felid) or calcium ionophore subtracted from the proportion of sperm with intact acrosomes before exposure. Although mean+/-S.E.M. sperm motility post-thaw (56.1 +/- 3.9% at 0 h) was less (P < 0.05) than pre-freeze (71.7 +/- 6.0%), there was no difference (P > 0.05) in the proportion of acrosome-intact sperm (fresh, 93.0 +/- 1.7% versus cryopreserved-thawed, 81.7 +/- 4.7% at 0 h). Incidence of capacitation was greater (P < 0.05) in fresh sperm incubated with capacitation accelerators IBMX and dbcAMP (9 h: 50.9 +/- 1.1) compared with fresh sperm incubated without accelerators (9 h: 41.2 +/- 1.1%). Frozen-thawed sperm preincubated without accelerators underwent capacitation (49.6 +/- 1.1%) to a greater extent (P < 0.05) compared with these fresh counterparts. Thawed samples with (9 h: 45.9 +/- 1.4%) and without accelerators (9 h: 41.2 +/- 1.1%) did not differ (P > 0.05) during the 9-h incubation. We conclude that giant panda spermatozoa (1) undergo capacitation in vitro with or without chemical accelerators and (2) withstand a rapid cryopreservation protocol, including retaining normal acrosomal integrity and functional capacitation ability.

Low-Density Lipoprotein Fraction from Hen’s Egg Yolk Decreases the Binding of the Major Proteins of Bovine Seminal Plasma to Sperm and Prevents Lipid Efflux from the Sperm Membrane1

For sperm preservation, semen is generally diluted with extender containing egg yolk (EY), but the mechanisms of sperm protection by EY are unclear. The major proteins of bull seminal plasma (BSP proteins: BSP-A1/A2, BSP-A3, and BSP-30-kDa) bind to sperm surface at ejaculation and stimulate cholesterol and phospholipid efflux from the sperm membrane. Since EY low-density lipoprotein fraction (LDF) interacts specifically with BSP proteins, it is proposed that the sequestration of BSP proteins in seminal plasma by EY-LDF represents the major mechanism of sperm protection by EY. In order to gain further insight into this mechanism, we investigated the effect of seminal plasma, EY, and EY-LDF on the binding of BSP proteins to sperm and the lipid efflux from the sperm membrane. As shown by immunodetection, radioimmunoassays, and lipid analysis, when semen was incubated undiluted or diluted with control extender (without EY or EY-LDF), BSP proteins bound to sperm in a time-dependent manner, and there is a continuous cholesterol and phospholipid efflux from the sperm membrane. In contrast, when semen was diluted with extender containing EY or EY-LDF, there was 50%-80% fewer BSP proteins associated with sperm and a significant amount of lipid added to sperm membrane during incubation. In addition, sperm function analysis showed that the presence of EY or EY-LDF in the extender preserved sperm motility. These results show that LDF is the constituent of EY that prevents binding of the BSP proteins to sperm and lipid efflux from the sperm membrane and is beneficial to sperm functions during sperm preservation.

Sperm capacitation in vitro in the eld's deer

Sperm capacitation was examined in the endangered Eld's deer (Cervus eldi thamin). Sperm motility and viability (percentage of sperm cells with intact membranes) were assessed in vitro over time after attempting to induce capacitation in TALP alone and TALP supplemented with calcium (10 mM CaCl2), dibutyryl cAMP (1 mM dbcAMP), or fetal calf serum (20% FCS). Sperm aliquots were evaluated at 0, 3, 6, 9, and 12 h for motility, viability, and ability to acrosome react after exposure to calcium ionophore (A23187, CI; 10 microM) or lysophosphatidylcholine (LC; 100 microg/mL). Fresh sperm aliquots in TALP + 10 mM CaCl2 exposed to CI had fewer (P < 0.05) intact acrosomes than the TALP control (TALP alone) or dbcAMP and FCS treatments after 9 h. Mean (+/- SEM) percentage of intact acrosomes of spermatozoa incubated in medium with increased CaCl2 declined (P < 0.05) from 80.2 +/- 2.6% (0 h) to 49.7 +/- 7.3% after prolonged incubation (9 h). The proportion of capacitated fresh spermatozoa was not influenced by LC treatment. Capacitation was not induced (P > 0.05) by any of the presumptive sperm capacitators after freeze-thawing. Likewise, neither CI nor LC induced the acrosome reaction (AR) in these spermatozoa, suggesting that the freeze-thawing process may have caused membrane damage. Results revealed that the supplementation of medium with CaCl2 evokes capacitation in some spermatozoa. However, Eld's deer spermatozoa appear remarkably resistant to conventional stimulators of capacitation and the AR.

Comparison of bovine sperm capacitation systems for ability of sperm to penetrate zona-free hamster oocytes and bovine oocytes matured in vitro

Sperm from the same ejaculate were capacitated in calcium-free Tyrode's, modified Tyrode's with bovine follicular fluid or heparin, and TEST-yolk. Capacitated sperm were coincubated with zona-free hamster oocytes at 37 degrees C for 3 h or with bovine cumulus-enclosed oocytes matured in vitro for 8 h at 37 or 39 degrees C. Bovine oocytes were transferred to fertilization medium and incubated for 72 h at 37 or 39 degrees C. Penetration of zona-free hamster oocytes was highest in calcium-free Tyrode's (53.7%), followed by Tyrode's with follicular fluid (50.6%), TEST-yolk (48.6%), and Tyrode's with heparin (34.2%). Penetration of bovine cumulus-enclosed oocytes matured in vitro at 37 degrees C was highest with heparin (48.1%), followed by TEST-yolk (35.0%), calcium-free Tyrode's (32.5%), and follicular fluid (26.4%). Sperm capacitation with heparin, assayed by penetration of bovine oocytes at 39 degrees C, was better at 39 degrees C (77.1%) than at 37 degrees C (46.1%). However, penetration rates in calcium-free Tyrode's and TEST-yolk were higher at 37 degrees C. The capacitation system with heparin at 39 degrees C and bovine oocytes was best followed by the systems using TEST-yolk and calcium-free Tyrode's at 37 degrees C.

Effect of various capacitation systems on bovine sperm motion characteristics, acrosome integrity, and induction of hyperactivation

Sperm from the same ejaculate were capacitated in TEST-yolk, calcium-free Tyrode's, modified Tyrode's containing follicular fluid or heparin, and analyzed at 0, 4, 8, and 12 h for motility characteristics and acrosomal integrity. Percentage of motility, progressive motility, progressive velocity, path velocity, curvilinear velocity, linearity, and amplitude of lateral head displacement differed with media and decreased with time. Calcium-free Tyrode's ranked first in maintaining most motility parameters. However, TEST-yolk sperm ranked first for lateral head displacement but last for linearity at each time. Acrosome-reacted sperm increased over time but were not different between TEST-yolk, calcium-free Tyrode's, and heparin at 4 h. The TEST-yolk sperm at 4 h had about twice the hyperactivation (62.3%) of the other sperm capacitation media. Capacitation of bovine sperm was not associated with a specific change in any measured motility parameter. Differences among the efficacies of capacitation systems were unrelated to parameters of sperm motion, hyperactivation, or acrosomal integrity.

Comparison of various bovine sperm capacitation systems for their ability to alter the net negative surface charge of spermatozoa

Semen was divided into five aliquots and capacitated for 4 or 6 h in calcium-free Tyrode's (37 degrees C), modified Tyrode's bovine follicular fluid (39 degrees C), modified Tyrode's heparin (39 degrees C), and TEST-yolk buffer (4 degrees C) or incubated in BSA-saline (39 degrees C). Sperm before and after capacitation were electrophoresed at 100 V of constant current for 3 and 6 min. Samples were collected, sperm were counted, and percentages of sperm migrating toward the anode at 0 h and 4 or 6 h were calculated. At 0 h, 61 to 80% of the sperm migrated with a net negative charge. After 4 or 6 h, the percentage of sperm migrating toward the anode significantly decreased in all capacitation media but not in the control. The percentage of sperm migrating toward anode was lowest in calcium-free Tyrode's (22.1%) followed by TEST (28.4%), Tyrode's follicular fluid (29.5%), and Tyrode's heparin (42.5%); these values were less than those for the control (56.0%). The movement of live sperm without the influence of current or freeze-killed sperm under the influence of electrical current (control trials) was negligible. Capacitation reduced the net negative surface charge of sperm, the magnitude of which depended on capacitation system. Net negative charge of sperm was inversely associated with efficiency in penetration of zona-free hamster oocytes.

Ram spermatozoa cocultured with epithelial cell monolayers: an in vitro model for the study of capacitation and the acrosome reaction

The effects of different epithelial cells, namely, hamster oviduct, sheep oviduct, and pig kidney epithelial cells (IBRS-2), on the viability, percentage of progressive motility (PPM), and acrosome reactions of ejaculated ram spermatozoa were investigated. Sperm aliquots were cultured on cells, cell-conditioned medium 199, or control medium 199. The PPM of unattached spermatozoa was estimated after 0, 3, 6, 9, 12, and 24 hr of incubation at 37 degrees C under 5% CO2 in air. Viability and the occurrence of true acrosome reactions were assessed using a triple-stain technique. Spermatozoa started to attach within 1 hr of coculture with the hamster or sheep oviductal epithelial cell (OEC) monolayers, and these spermatozoa showed vigorous tail motion. No spermatozoa were found to attach to the IBRS-2 monolayer. The PPM of unattached spermatozoa cocultured with the various types of epithelial cell monolayers for 12 hr was significantly higher than that of spermatozoa incubated in conditioned media or medium 199 alone (54% in hamster OEC vs. 40% in conditioned; 68% in sheep OEC vs. 38% in conditioned; 36% in control medium). On the other hand, after 24 hr of incubation, there were no differences in the PPM of spermatozoa cocultured with epithelial cells or incubated in conditioned media. The percentages of cells undergoing a true acrosome reaction reached maximum values (P < 0.05) in spermatozoa incubated for 9 hr in the presence of hamster OEC (22.5%) or for 12 hr on sheep OEC (20.5%) monolayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of a TEST-yolk sperm capacitation system for use in bovine in vitro fertilization

Bovine sperm acquire the ability to penetrate zona-free hamster oocytes (capacitation) after incubation in TEST-yolk buffer. Our objective was to determine whether such sperm could penetrate zona-intact bovine oocytes in vitro. Bovine cumulus enclosed oocytes from 2- to 5-mm follicles were incubated in maturation medium for 24 h at 37 degrees C. Ejaculated bovine semen was diluted 1: 10 in TEST-yolk buffer, cooled to 4 degrees C, and stored for 8 h to induce capacitation. Sperm were then washed thrice in pH 7.6, .15 M NaCl containing .1% bovine serum albumin V (37 degrees C) and diluted to 2 x 10(6) sperm/ml in fertilization medium. Droplets of fertilization medium containing capacitated sperm, killed sperm, or no sperm were made under paraffin oil. Oocytes (matured 24 h) were added and cocultured with sperm for 8 h and then transferred to fresh fertilization medium for 40 h. After 24 h, 53% of the oocytes had matured (metaphase II). The fertilization rate of the metaphase II oocytes (203) with TEST-yolk capacitated sperm was 87%, whereas the parthenogenetic controls were 2 and 0%, respectively. Therefore, TEST-yolk buffer can be used to capacitate bull sperm for in vitro fertilization.

Behavior of bull spermatozoa in bovine uterine tube epithelial cell co-culture: An in vitro model for studying the cell interactions of reproduction

Freshly ejaculated bull semen was centrifuged and spermatozoa were resuspended in modified sperm TALP. Bovine uterine tube epithelial cell monolayers (BUTC) were obtained from cows in the periovulatory phase of estrus. In Experiment 1, sperm aliquots were assigned to culture wells containing either BUTC, BUTC-conditioned TALP, or control TALP. Sperm heads attached to the monolayers within 1 h of co-culture. Attached spermatozoa showed vigorous tail motion. At 5, 8 and 11 h of incubation at 39 degrees C, the percentage of unattached sperm cells with intact acrosome membranes and percentage of motility of these cells was measured. Sperm-BUTC co-cultures were also fixed in situ for electron microscopy. Unattached spermatozoa in co-culture had more (P<0.05) acrosomal membrane loss, showed hyperactive motion and had an overall decrease in motility as compared to sperm cells in control or conditioned medium. Evaluation by electron microscopy showed BUTC attached spermatozoa to behave in the co-culture system similar to reports for spermatozoa found in uterine tubes in vivo. Microvilli of the BUTC appeared to actively entrap the spermatozoa. Mucus-type granules could be seen on acrosomal regions and vesiculation of acrosomal membranes was seen in some cells. In Experiment 2, 43% of the 12 x 10(6) sperm cells added to 2-cm(2) BUTC bound within 4 h of co-culture. By 7 h of co-culture 19% of the previously bound sperm cells had been released from the BUTC. Released cells had limited motility and were mostly dead (73%). Sperm cells remaining on the monolayer at 7 h showed vigorous tail motion and were gradually released from the BUTC over 48 h. Spermatozoa in co-culture interacted with the BUTC in a manner much like that seen in vivo, and sperm capacitation changes were stimulated by this interaction.

Identification of the capacitating agent for bovine sperm in egg yolk-TEST semen extender

Bovine sperm can be capacitated in egg yolk-TEST buffer. To determine what constituent of the buffer was responsible, ejaculated semen was diluted 1:10 at 37 degrees C with the following 20% egg yolk (vol/vol)-containing buffers: TES-Tris, TES-tetramethylammonium hydroxide, taurine-Tris, citric acid-Tris, citrate, egg yolk salts, egg yolk proteins Tris, and citrate-taurine. Buffers were pH 7.6 and 321 to 325 mOsmol/kg. Extended semen was cooled slowly to 4 degrees C and stored 8 h. Sperm taken at 0 and 8 h were washed in pH 7.6 bovine serum albumin-saline and assessed for motility and capacitation using zona-free hamster eggs. Sperm motilities at 0 and 8 h were similar (60 to 73%) in all extenders except citric acid-Tris (54%) and egg yolk proteins Tris (15%). Bull sperm, stored 8 h in egg yolk-TEST, became capacitated. Because sperm storage in egg yolk-citrate did not result in penetration, both egg yolk and citrate were ruled out as capacitating agents. Capacitating activity resided in the TES and Tris molecules. The TES molecule contains a Tris component and this capacitated bull sperm. The TES molecule also contains a taurine component. However, taurine was not a capacitating agent for bull sperm. In conclusion, both TES- and Tris-containing buffers, alone or together (TEST), were equally effective in capacitating bull sperm.

Effect of washing and capacitating media pH on bull sperm motility, acrosome integrity, and ability to penetrate zona-free hamster oocytes

Bovine-ejaculated sperm were washed thrice in bovine serum albumin-saline media, pH 7.2 to 8.4, and incubated at 37 degrees C in Ca++-free Tyrode's media. pH 7.2 to 8.4, for 0, 2, 4, 6, and 8 h. Motility was highest when sperm were washed in pH 7.2 medium and incubated in pH 8.0 or 8.4 media. Motility remained above 50% until 8 h. Washing in pH 7.6, 8.0, or 8.4 media induced more acrosome reactions after incubation than washing at pH 7.2. Percentage of acrosome-reacted sperm increased at each successive time period. Sperm penetrated more oocytes at 4, 6, and 8 h when wash medium pH was fixed at 7.2 and capacitating media pH was raised at .4 unit increments from 7.2 to 8.4. When sperm were washed in pH 7.2 medium, the postincubation penetration rates peaked at 8 h. With wash media of pH 7.6, 8.0, or 8.4, the postincubation penetration rates peaked at 4 h and then gradually declined. In conclusion, the most effective system for capacitating bull sperm was a pH 7.6 wash followed by capacitation in pH 7.6 medium for 4 to 8 h and this system resulted in the highest penetration rates. Wash media pH hastened capacitation but was not a capacitating agent.