The mechanism of fertilization remains largely enigmatic in mammals. Most studies exploring the molecular mechanism underlying fertilization have been restricted to a single species, generally the mouse, without a comparative approach. However, the identification of divergences between species could allow us to highlight key components in the mechanism of fertilization. In the pig, in vitro fertilization (IVF) and polyspermy rates are high, and spermatozoa penetrate easily through the zona pellucida (ZP). In contrast, IVF rates are low in the horse, and polyspermy is scarce. Our objective was to develop a comparative strategy between these two divergent models. First, we compared the role of equine and porcine gametes in the following five functions using intraspecific and interspecific IVF: ZP binding, acrosome reaction, penetration through the ZP, gamete fusion, and pronucleus formation. Under in vitro conditions, we showed that the ZP is a determining element in sperm-ZP attachment and penetration, whereas the capacity of the spermatozoa is of less importance. In contrast, the capacity of the spermatozoa is a key component of the acrosome reaction step. Second, we compared the composition and structure of the equine and porcine ZP. We observed differences in the number and localization of the ZP glycoproteins and in the mesh-like structure of the ZP between equine and porcine species. These differences might correlate with the differences in spermatozoal attachment and penetration rates. In conclusion, our comparative approach allows us to identify determining elements in the mechanism of fertilization.

Twenty-two boar ejaculates were frozen in 0.25 ml straws using a controlled cooling rate, then evaluated in vitro in order to assess: (i) the extent to which a range of semen evaluation parameters accurately characterize sperm quality, (ii) the value of quality assessment in the characterization of long-term sperm survival and fertility and (iii) the suitability of the cryopreservation protocol used for yielding semen with good quality and fertilizing capacity. Motility with or without caffeine, plasma membrane integrity (PMI) evaluated with both propidium iodide (PI) and Hoechst 33258, and acrosome morphology were studied, the ejaculates being then classified into five quality groups. A thermoresistance test and a homologous in vitro fertilization test were applied to selected ejaculates of these groups. Caffeine-stimulated motility and PMI evaluated with PI provided better estimations of semen quality than the other tests of motility, PMI, or acrosome morphology, but this quality assessment could not reveal differences in fertilizing capacity or thermoresistance among ejaculates. Over 43% spermatozoa survived cryopreservation in 19 of the 22 ejaculates, with inter-boar and inter-ejaculate variability in the freezing success being observed. The fertilizing capacity, however, was seriously affected by the process regardless of the semen quality. It is concluded that caffeine-stimulated motility and PMI evaluated with PI give accurate information on sperm quality, but important aspects to the valuation of semen such as thermoresistance and fertilizing capacity are not revealed by this quality study. Moreover, the approach of selecting suitable protocols of cryopreservation does not appear to be sufficient for guaranteeing systematically good quality and fertilizing capacity in the frozen-thawed semen.

The fertility rates of cryopreserved poultry semen are highly variable and not reliable for use in preservation of commercial genetic stocks. Our objective was to evaluate the cryosurvival of semen from 8 pedigreed layer lines at 2 different ages: the onset and end of commercial production. Semen from 160 roosters (20/line) was frozen individually with 11% glycerol at 6 and 12 mo of age. Glycerol was removed from thawed semen by Accudenz gradient centrifugation. The viability of thawed sperm from each male was determined using fluorescent live-dead staining and flow cytometry; sperm velocity parameters were measured using computerized motion analysis. The fertilizing ability of thawed sperm was evaluated in vitro by assessing hydrolysis of the inner perivitelline membrane. The postthaw function of sperm from the elite lines varied widely, despite the fact that fresh semen from all of these lines typically yielded high fertility rates. The percentage of thawed sperm with intact plasma membranes ranged from 27.8 + or - 2.1 to 49.6 + or - 1.9 and varied among lines and between age groups. Thawed sperm from 2 lines consistently demonstrated the highest and lowest motility parameters, whereas the velocity parameters of the remaining 6 lines varied widely. The mean number of hydrolysis points per square millimeter of inner perivitelline membrane ranged from 12.5 + or - 4.1 (line 2) to 103.3 + or - 30.2 (line 6). Age effects were observed for 4 out of 8 lines; however, improved postthaw sperm function at 12 mo of age was not consistent for all 3 assays. These results demonstrate variability among pedigreed lines in withstanding glycerol-based semen cryopreservation and provide a model for delineating genotypic and phenotypic factors affecting sperm cryosurvival.

The carbohydrate-rich zone on the sperm surface is essential for inmunoprotection in the female tract and early gamete interactions. We recently have shown the glycocalyx of chicken sperm to be extensively sialylated and to contain residues of mannose, glucose, galactose, fucose, N-acetyl-galactosamine, N-acetyl-glucosamine, and N-acetyl-lactosamine. Our objective here was to evaluate the effects of 3 different cryopreservation methods on the sperm glycocalyx. Semen from roosters was pooled, diluted, cooled to 5°C, and aliquoted for cryopreservation using 6% dimethylacetamide (DMA), 11% dimethylsulfoxide (DMSO), or 11% glycerol (GOH). For the DMA method, semen was equilibrated for 1 min with cryoprotectant and rapidly frozen by dropping 25-µL aliquots into liquid nitrogen. For the other methods, semen was equilibrated for either 1 min (DMSO) or 20 min (GOH), loaded into straws, and frozen with a programmable freezer. Thawing rates mimicked the freezing rates (e.g., rapid for DMA; moderate for DMSO and GOH). Aliquots of thawed and fresh, unfrozen semen were incubated with 1 of 12 fluorescein isothiocyanate-conjugated lectins and counterstained with propidium iodide, and mean fluorescence intensity (MFI) was assessed by flow cytometry. For each lectin, the MFI of propidium iodide-negative (viable sperm) was compared among the fresh and frozen-thawed treatments (n = 5). For sperm frozen with GOH and DMA, the MFI of most lectins was similar (P > 0.05) to that of fresh sperm, whereas only 5 of 12 lectins were similar between fresh and DMSO-frozen sperm. Sperm from all 3 methods had higher (P < 0.05) MFI for lectins specific for N-acetyl-glucosamine and β-galactose than did fresh sperm. Fewer sperm were damaged (P < 0.001) with GOH than with DMA or DMSO, and membrane integrity was correlated with MFI for 9 of 12 lectins (P < 0.05). These data indicate that surface carbohydrates are altered during cryopreservation, and that cryoprotectant type and freezing-thawing rates affect the degree of modification. Although the glycoconjugates have not yet been identified, it is likely that these cryopreservation-induced changes contribute to the reduced fertility of frozen-thawed chicken semen.

The aim of the present work was to use a battery of lectins to 1) delineate the carbohydrate content of sperm glycocalyx in the turkey and chicken using flow cytometry analysis, and 2) evaluate the distribution of existing sugars over the sperm plasma membrane surface with epifluorescent microscopy. Carbohydrate groups (corresponding lectins) that were investigated included galactose (GS-I, Jacalin, RCA-I, PNA), glucose and/or mannose (Con A, PSA, GNA), N-acetyl-glucosamine (GS-II, s-WGA, STA), Nacetyl-galactosamine (SBA, WFA), fucose (Lotus, UEA-I), sialic acid (LFA, LPA), and N-acetyl-lactosamine (ECA). Spermatozoa were assessed before and after treatment with neuraminidase to remove sialic acid. Mean fluorescence intensity (MnFI) was used as indicator of lectin binding for flow cytometry analysis. Nontreated spermatozoa from both species showed high MnFI when incubated with RCA-I, Con A, LFA, and LPA, as did chicken spermatozoa incubated with s-WGA. Neuraminidase treatment increased the MnFI for most lectins except LFA and LPA, as expected. Differences in MnFI between species included higher values for s-WGA and ECA in chicken spermatozoa and for WFA in turkey spermatozoa. Microscopy revealed segregation of some sugar residues into membranespecific domains; however, the 2 staining techniques (cell suspension vs fixed preparation) differed in identifying lectin binding patterns, with fixed preparations yielding a high degree of nonspecific binding. We conclude that 1) the glycocalyx of turkey and chicken spermatozoa contains a diversity of carbohydrate groups, 2) these residues are extensively masked by sialic acid, 3) the glycocalyx composition is species-specific, and 4) some glycoconjugates appear to be segregated into membrane-specific domains. Characterization of the poultry sperm glycocalyx is the first step in identifying the physiological impact of semen storage on sperm fucntion.

No abstract

The turkey sperm glycocalyx is known to contain residues of sialic acid, a-mannose/a-glucose, a-and b-galactose, afucose, a-and b-N-acetyl-galactosamine, monomers and dimers of N-acetyl-glucosamine, and N-acetyl-lactosamine. Potential changes in these carbohydrates during in vitro semen storage at 4uC were evaluated using males of both high-and low-sperm-mobility phenotypes. Changes in carbohydrate residues were quantified by flow cytometry analysis using a battery of 14 fluorescein isothiocyanate-labeled lectins in combination with control (sialylated) or neuraminidase-treated ( ). For nonsialylated sperm, increased binding of ECA, GS-II, SBA, and WFA was observed at variable time points; only Canavalia ensiformis lectin (Con A) and PSA remained unchanged during storage. Differences between mobility phenotypes existed for lectins Con A, GS-II, LFA, PSA, SBA, and sWGA, with sperm from lowmobility males exhibiting higher MnFI than high-mobility males throughout 24 hours of storage. We concluded that the observed increases in lectin binding during semen storage indicate an augmentation of nonsialylated terminal residues, which could alter sperm antigenicity and negatively impact fertility. Further, spermatozoa from low-mobility males may have higher antigenicity even before semen storage. Other possible functional implications are discussed.

No abstract