Stallion Sperm Cryopreservation Using Various Permeating Agents: Interplay Between Concentration and Cooling Rate.

In this study, modeling and experimental approaches were used to investigate the interplay between cooling rate and protectant concentration for cryopreservation of stallion sperm. Glycerol (GLY), ethylene glycol (EG), dimethylformamide (DMF), propylene glycol (PG), and dimethyl sulfoxide (DMSO) were tested as cryoprotective agents (CPAs), using concentrations up to 1500 mM and cooling rates ranging from 5°C to 55°C min-1. Modeling of the extent of sperm dehydration during freezing was done using previously determined values of the sperm membrane permeability to water to predict optimal cooling rates for cryopreservation. Sperm cryosurvival was experimentally determined through flow cytometric assessments on membrane intactness and using computer-assisted analysis of motility. Sperm could withstand exposure to 1500 mM concentrations prefreeze for all CPAs tested. The overall highest cryosurvival rates were obtained with DMF, followed by GLY and EG, whereas the use of PG and DMSO resulted in poor cryosurvival rates. Cryosurvival with DMF increased with increasing concentration, reaching a plateau at 500 mM, whereas for GLY and EG, an optimum concentration between 250 and 500 mM resulted in maximal survival. An optimal cooling rate was only observed at low CPA concentrations, whereas at higher concentrations, cryosurvival rates were not affected by the cooling rate. In the case of DMF, survival remained relatively high in the investigated range of concentrations and cooling rates, whereas with GLY and EG, a much narrower combination of CPA concentration and cooling rate resulted in optimal cryosurvival. Sperm cryopreserved with DMF showed altered motility characteristics indicating hyperactivation, which was not observed with GLY and EG. Optimal cooling rates that were predicted from calculated dehydration curves did not match experimentally determined optimal cooling rates.

Fibronectin type II-module proteins in the bovine genital tract and their putative role in cell volume control during sperm maturation.

The male reproductive tract of ungulates contains two protein families bearing tandemly arranged fibronectin II (Fn2) modules; one (small Fn2 proteins) bears two modules (e.g. BSP-A1/2), the other (long Fn2 proteins) bears four (e.g. epididymal sperm-binding protein 1 (ELSPBP1)). While it is well known that small Fn2 proteins are present in bull semen, nothing is known about long Fn2 proteins. In the present study, the presence of ELSPBP1 proteins in the bull epididymis and their association with maturing spermatozoa were investigated using a specific antibody against canine ELSPBP1. Analysis of western blots showed ELSPBP1 to be present in the caput, corpus and cauda regions of the epididymis. The protein, which bound phosphorylcholine (PC) strongly, appeared to associate with the spermatozoa during maturation because it was absent from caput spermatozoa but present on cauda spermatozoa. Immunocytochemistry of cauda spermatozoa showed the protein to be bound to the post-acrosomal and midpiece regions. ELSPBP1 could not be detected on freshly ejaculated spermatozoa but was revealed after a capacitating treatment. Our previous studies have shown differences between bovine caput and cauda spermatozoa in terms of their ability to control cell volume. Because of the close homology of BSP-A1/2 PC binding regions with Fn2 regions in ELSPBP1, BSP-A1/2 was used as a model to investigate the effect of a PC-binding Fn2 protein on cell volume control. While the protein had no effect on cauda spermatozoa, it caused caput spermatozoa to swell more in response to hypotonic stress, similarly to untreated cauda spermatozoa.

Point mutations abolishing the mannose-binding capability of boar spermadhesin AQN-1.

The mannose-binding capability of recombinant wild-type boar spermadhesin AQN-1 and of its site-directed mutants in the highly-conserved region around of the single glycosylation site (asparagine 50) of some spermadhesins, where the carbohydrate binding site has been proposed to be located, was checked using a solid-phase assay and a biotinylated mannose ligand. Substitution of glycine 54 by amino acids bearing an unipolar side chain did not cause significant decrease in the mannose-binding activity. However, amino acids with uncharged polar side chains or having a charged polar side chain abolished the binding of biotinylated mannose to the corresponding AQN-1 mutants. The results suggest that the higher surface accessibility of amino acids possessing polar side chains compared to those bearing nonpolar groups may sterically interfere with monosaccharide binding. The location of the mannose-binding site in AQN-1 appears to be topologically conserved in other heparin-binding boar spermadhesins, i.e., AQN-3 and AWN, but departs from the location of the mannose-6-phosphate-recognition site of PSP-II. This indicates that different spermadhesin molecules have evolved non-equivalent carbohydrate-binding capabilities, which may underlie their distinct patterns of biological activities.

Carbohydrate-based interactions of oviductal sperm reservoir formation-studies in the pig.

Competitive inhibition of sperm to explants of the oviductal epithelium was used to study the complementary receptor system that may be involved in the establishment of the oviductal sperm reservoir in the pig. Sperm binding to the oviductal explants is expressed as Binding Index (BI = sperm cells/0.01 mm(2)). From a set of glycoproteins with known oligosaccharide structures, only asialofetuin and ovalbumin showed inhibitory activity, indicating that ovalbumin may block high affinity binding sites (IC(50) congruent with 1.3 microM) and asialofetuin low affinity sites (IC(50) congruent with 18 microM) of the complementary receptor systems, whereas fetuin carrying terminal sialic acid has no effect. Ovalbumin glycopeptides were isolated by Con A affinity chromatography and reverse-phase HPLC following tryptic digestion. Glycopeptides and enzymatically released glycans were analyzed by MS, and were shown to represent preferentially the two high mannose type glycans (Man)(5)(GlcNAc)(2) and (Man)(6)(GlcNAc)(2), and as a minor component the hybrid type glycan (Hex)(4)(GlcNAc)(5). Glycopeptides (84% inhibition) and glycans (81% inhibition) significantly reduced sperm-oviduct binding at a concentration of 3 microM, whereas the deglycosylated peptides showed no inhibitory activity. Mannopentaose (IC(50) congruent with 0.8 microM) representing the oligomannose residue of the high mannose glycans of ovalbumin was as effective as ovalbumin. These data indicate that the carbohydrate-based mechanisms underlying the formation of the oviductal sperm reservoir in the pig is the result of the concerted action of at least the high-affinity binding sites for oligomannose or nonreducing terminal mannose residues and low-affinity binding of galactose.