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

Sperm-Particle Interactions and Their Prospects for Charge Mapping

In this article, a procedure to investigate sperm charge distribution by electrostatic sperm-particle interactions is demonstrated. Differently chargedparticles are fabricated and their attachment distribution on the bovine sperm membrane is investigated. The sperm-particle attachment sites are observed using bright field and cryo-scanning electron microscopy combined with energy-dispersive X-ray analysis. The findings suggest that the charge distribution of the sperm membrane is not uniform, and although the overall net charge of the sperm cell is negative, positively charged areas are especially found on the sperm heads. The newly developed method is used to investigate the dynamic charge distribution of the sperm cell membrane upon maturation induced by heparin, as a representation of the multitude of changes during the development of a sperm.

Macaque sperm coating protein DEFB126 facilitates sperm penetration of cervical mucus

BACKGROUND

Sperm coating protein beta-defensin 126 (DEFB126) is adsorbed onto the entire surface of macaque sperm in the caudal epididymis and is retained on viable sperm collected from the cervix and the uterine lumen of mated female macaques. We investigated the role of sperm coating protein DEFB126 in cervical mucus penetration (CMP).

METHODS

Cervical mucus (CM) was collected from peri-ovulatory female macaques and loaded into CMP chambers. Sperm were introduced to CMP chambers following treatment with either polyclonal antibodies raised to DEFB126 or seminal plasma proteins (SPPs), 1 mM caffeine+1 mM dibutyryl cyclic adenosine monophosphate (dbcAMP) (induces release of DEFB126 from sperm surface), neuraminidase (NMase) or poly-L-lysine (PLP). Following removal of DEFB126 or SPPs from the sperm surface, sperm were treated with concentrated DEFB126 or concentrated SPPs prior to being introduced to CMP chambers. The numbers of sperm that penetrated and traversed CM were scored over 6 min.

RESULTS

Treatment of sperm with anti-DEFB126 antibodies, 1 mM caffeine+1 mM dbcAMP, NMase, and PLP resulted in similar and significant levels of inhibition of sperm CMP, whereas addition of anti-SPPs antibodies had no effect. In experiments where DEFB126 and SPPs were removed, CMP capability of sperm was restored by addition of DEFB126 back to the sperm surface, whereas treatment of sperm with concentrated SPPs slightly inhibited sperm penetration.

CONCLUSIONS

DEFB126 and its high negative charge appears to be critical for the movement of sperm through CM in the macaque, while SPPs adhered to the sperm surface offer no advantage in CMP.

In vitro penetration into bovine oocytes and zona-free hamster oocytes by bull spermatozoa treated with liposomes

The objectives of this study were 1) to determine whether in vitro penetration of bovine and zona-free hamster oocytes, using spermatozoa treated with the lipid dilauroylphosphatidylcholine, was correlated with the fertility of bulls and 2) to determine whether utilizing results from several laboratory assays could effectively evaluate fertility. Cryopreserved semen was used from 12 bulls having lifetime nonreturn rates ranging from 66 to 81%. The lipid concentration that maximized penetration of hamster oocytes was determined as well as the number of spermatozoa entering all hamster oocytes, number of spermatozoa in each penetrated hamster oocyte, fertilization of bovine oocytes, blastocyst development of bovine oocytes, and the percentage of motile spermatozoa of each sample. Correlations were low between the lipid concentration that maximized each individual parameter and nonreturn rate (r < or = 0.34). The six-parameter regression equation accounted for 71% of the variation in bull fertility, and a four-parameter equation accounted for 61% of the variation in fertility. Pooling data for pairs of bulls into six fertility groups to increase information per data point still resulted in poor predictions of fertility for individual parameters. However, a four-variable model, including the penetration rates for hamster and bovine oocytes, the number of spermatozoa that penetrated hamster oocytes, and the percentage of motile spermatozoa, accounted for 98% of the variability in bull fertility.

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.