Physiology and endocrinology symposium: a proteome-based model for sperm mobility phenotype.

Sperm mobility is defined as sperm movement against resistance at body temperature. Although all mobile sperm are motile, not all motile sperm are mobile. Sperm mobility is a primary determinant of male fertility in the chicken. Previous work explained phenotypic variation at the level of the sperm cell and the mitochondrion. The present work was conducted to determine if phenotypic variation could be explained at the level of the proteome using semen donors from lines of chickens selected for low or high sperm mobility. We began by testing the hypothesis that premature mitochondrial failure, and hence sperm immobility, arose from Ca(2+) overloading. The hypothesis was rejected because staining with a cell permeant Ca(2+)-specific dye was not enhanced in the case of low mobility sperm. The likelihood that sperm require little energy before ejaculation and the realization that the mitochondrial permeability transition can be induced by oxidative stress arising from inadequate NADH led to the hypothesis that glycolytic enzymes might differ between lines. This possibility was confirmed by 2-dimensional electrophoresis for aldolase and phosphoglycerate kinase 1. This outcome warranted evaluation of the whole cell proteome by differential detergent fractionation and mass spectrometry. Bioinformatics evaluation of proteins with different expression levels confirmed the likelihood that ATP metabolism and glycolysis differ between lines. This experimental outcome corroborated differences observed between lines in previous work, which include mitochondrial ultrastructure, sperm cell oxygen consumption, and straight line velocity. Although glycolytic proteins were more abundant within highly mobile sperm, quantitative PCR of representative testis RNA, which included mRNA for phosphoglycerate kinase 1, found no difference between lines. In summary, we propose a proteome-based model for sperm mobility phenotype in which a genetic predisposition puts sperm cells at risk of premature mitochondrial failure as they pass through the excurrent ducts of the testis. In other words, we attribute mitochondrial failure to sperm cell and reproductive tract attributes that interact to affect sperm in a stochastic manner before ejaculation. In conclusion, our work provides a starting point for understanding chicken semen quality in terms of gene networks.

A new approach to sperm preservation based on bioenergetic theory.

To date, attempts to preserve chicken sperm have been based on a trial-and-error experimental approach. The present work outlines the development of an alternative approach based on empiricism and bioenergetic theory. In previous work, we found fowl sperm motility to be dependent on mitochondrial calcium cycling, phospholipase A(2), and long-chain fatty acids as an endogenous energy source. It is noteworthy that fowl sperm reside within the sperm storage tubules (SST) of the oviduct over an interval of days to weeks after insemination. In this regard, a model for in vivo sperm storage was developed and tested in additional previous research. Sperm penetration of the SST, sperm residence within the SST, and sperm egress from the SST can be explained in terms mitochondrial function. Understanding sperm function and longevity in terms of bioenergetics presented the possibility that sperm could be inactivated by disrupting mitochondrial calcium cycling and could thereby be preserved. However, this possibility also posed a problem: maintenance of the inner membrane potential of the mitochondrion within inactivated sperm. This report describes a series of experiments in which fowl sperm were inactivated by treatment with the calcium chelator tetrasodium 1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, and then reactivated by treatment with calcium ions. The effect of tetrasodium 1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid on mitochondrial calcium cycling was confirmed by flow cytometry and confocal microscopy. When treated sperm were cooled to 10 degrees C, inactivated sperm could be reactivated throughout a 5-h storage interval. When stored sperm were held for 3 h before reactivation and insemination, fertility was 88% of the control. Storage did not affect hatchability. In summary, short-term storage was realized by manipulating mitochondrial function. We propose that 1) complex V consumes ATP within inactivated sperm and, by doing so, maintains the inner membrane potential of the mitochondrion, 2) ATP is regenerated within inactivated sperm by the action of creatine kinase on phosphocreatine, and 3) necrosis follows depletion of intracellular phosphocreatine. Therefore, future attempts to preserve chicken sperm can be based on a theory that encompasses regulation of energy production, a biological context in which sperm cells are motile, and the consequences of mitochondrial failure.

Sperm mobility: deduction of a model explaining phenotypic variation in roosters (Gallus domesticus).

In previous work, variation in sperm mobility phenotype was attributed to the proportion of ejaculated fowl sperm containing dysfunctional mitochondria. In the present work, latent mitochondrial dysfunction was inferred from patterns of sperm egress from the oviduct's sperm-storage tubules. In addition, experiments were performed to help explain how mitochondrial function could be compromised in viable sperm cells. Confocal microscopy demonstrated that sperm Ca2+ content differed between low and high sperm-mobility phenotypes when sperm were stained with rhod-2 AM, a Ca2+ -specific dye. Fluorescence was associated with the nuclear envelope, a variant of the endoplasmic reticulum, and greater fluorescence was observed in sperm from low sperm-mobility males. Fluorescence was reduced by 50% when motile sperm were rendered immotile by incubation with a Ca2+ chelator. Thus, a relationship was established between a dynamic intracellular Ca2+ pool and sperm motility. Sperm N-methy-D-aspartic acid (NMDA) receptors were inferred by the action of D-homocysteinesulfinic acid, a potent NMDA receptor agonist. Seminal plasma from low sperm mobility males was characterized by an elevated glutamate concentration. Thapsigargin, which inhibits the smooth endoplasmic reticulum Ca2+ pump and thereby promotes Ca2+ efflux, rendered sperm immotile. This effect was blocked by cyclosporin A, which prevents the formation of the mitochondrial permeability transition pore (PTP) in response to elevated mitochondrial Ca2+ content. In summary, we propose that 1) glutamate enables Ca2+ uptake into sperm before ejaculation, 2) excessive Ca2+ uptake triggers formation of the PTP in a subpopulation of sperm, and 3) sperm mobility is decreased in proportion.

Fowl (Gallus domesticus) sperm motility depends upon mitochondrial calcium cycling driven by extracellular sodium.

A relationship between extracellular Ca(+2), fowl sperm phospholipase A2 activity, long-chain acylcarnitine content, and motility was demonstrated in previous work. Sperm motility appeared to depend upon Na+-dependent Ca(+2) cycling when sperm were incubated at body temperature without glucose. In the present work, motility decreased as a function of time when sperm were incubated in 2 mM Ca(+2) prepared with either buffered isotonic sucrose or LiCl. However, this effect was less pronounced in the case of LiCl. The sparing effect of Li+ was attributed to the mitochondrial Na+/Ca(+2) exchanger. Motile concentration decreased exponentially in response to micromolar concentrations of CGP 37157, a specific inhibitor of the mitochondrial Na+/Ca(+2) exchanger. KB-R7943 mesylate, an inhibitor of the reverse mode of the Na+/Ca(+2) exchanger, prevented re-initiation of motility when exogenous Ca(+2) was added to sperm rendered immotile by incubation with 1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, a high-affinity Ca(+2) chelator. The presence of voltage-gated Ca(+2) channels was confirmed by the effect of nifedipine on motile concentration. Neither motile concentration nor straight line velocity was affected by either ouabain or orthovanadate, which inhibit Na+-K+ ATPase and Ca(+2)-ATPase, respectively. In summary, we infer that 1) fowl sperm motility is dependent upon extracellular Ca(+2) cycling through mitochondria; 2) such cycling is dependent upon extracellular Na+; and 3) fowl sperm conserve ATP by moving neither Na+ nor Ca(+2) by active transport. Understanding the relationship between mitochondrial Ca(+2) cycling and ATP production may be applicable to long-term semen storage.

Sperm mobility: phenotype in roosters (Gallus domesticus) determinedby concentration of motile sperm and straight line velocity.

Previous research demonstrated that sperm mobility, i.e., the net movement of a sperm population, is a quantitative trait of the domestic fowl. However, the cellular basis for this trait was unknown. In the present work, individual motile sperm were evaluated with a Hobson SpermTracker in order to identify one or more properties of motile sperm that could account for variation in sperm mobility observed among males. A method was validated for assessing sperm motion over an erythrocyte monolayer at body temperature. A small-scale experiment with roosters from the tails and center of a normal distribution of sperm mobility phenotypes (n = 33 roosters) demonstrated that straight line velocity (VSL) and motile concentration were critical to expression of phenotype. The importance of these variables was confirmed with a large-scale experiment using a representative subpopulation (n = 100 roosters). VSL of individual sperm at 41 degrees C ranged between 5 and 100 microm/sec. VSL averaged 32, 39, and 40 microm/sec for low, average, and high sperm mobility phenotypes. Sperm were diluted to 1.2 x 10(6)/ml for motion analysis. Mean motile concentrations were 0.52, 0.84, and 0.95 x 10(6)/ml for low, average, and high sperm mobility phenotypes. Motile concentration was correlated with sperm mobility (r = 0.71). VSL appeared to have an additive effect as it was correlated with straightness of sperm cell trajectory (r = 0.79).

Sperm mobility: A primary determinant of fertility in the domestic fowl (Gallus domesticus).

Previous research demonstrated that sperm mobility is a quantitative trait of the domestic fowl. The trait is quantified by measuring the absorbance of an Accudenz solution after overlay with a sperm suspension and brief incubation at body temperature. In the present work, average and high sperm mobility phenotypes (n = 30 males per phenotype) were selected from a base population. Differences were found between sperm oxygen consumption (p < 0.0001), acylcarnitine content (p < 0.05), linear velocity (p < 0.001), and straightness (p < 0.001), a trajectory variable measured with the Hobson SpermTracker. Oxygen consumption and stearoylcarnitine content of sperm from the high-mobility phenotype were twice those observed with sperm from average males, implying a pivotal role for mitochondria. On the basis of these results, a graded relationship was predicted between fertility and sperm mobility. Males (n = 48) were chosen at random from another base population, sperm mobility was measured per male, and each ejaculate was used to inseminate 8-12 hens (8 x 10(7) viable sperm per hen). When fertility was plotted as a function of sperm mobility, data points approximated a skewed logistic function. The hypothesis that vaginal immunoglobulins constitute an immunological barrier to sperm transport was tested and rejected. Therefore, we concluded that sperm mobility is a primary determinant of fertility in the fowl.

Transfer of sperm into a chemically defined environment by centrifugation through 12% (wt/vol) Accudenz.

Centrifugation is commonly used to wash sperm; however, most washing techniques do not put sperm in a chemically defined environment. Rather, washing by centrifugation, in effect, dilutes seminal plasma components. A 0.5-mL volume of 30% (wt/vol) Accudenz was layered beneath 5 mL of 12% (wt/vol) Accudenz in a 15-mL polypropylene centrifuge tube. Diluted semen from individual males (n = 10) was overlaid upon the 12% (wt/vol) Accudenz. After centrifugation at 1,250 x g at 4 C for 25 min, washed sperm were present at the interface of the Accudenz layers. Based upon hemacytometer counts, sperm recovery was 83% (CV = 12%). Neither sperm viability nor morphology was affected by washing. Efficacy of the washing procedure was evaluated by using extracellular glucose, glutamic acid, Ca+2, and protein as markers. Washing eliminated 99% of the glutamic acid and glucose associated with sperm. Likewise, washing removed 98.5% of the extracellular Ca+2 associated with sperm. As evidenced by total protein analysis and SDS-PAGE, washing removed 98% of soluble seminal plasma proteins from sperm. In addition, washing did not affect sperm mobility or fertilizing ability. This procedure returns extended sperm to a physiological concentration in a chemically defined environment. By suspending washed sperm in distinct media, we induced differential sperm mobility. Therefore, this procedure is suitable for the study of the effect of specific substances upon sperm cell function.

Sperm mobility: a quantitative trait of the domestic fowl (Gallus domesticus).

Sperm from each rooster within a base population (n = 271) were evaluated with a mobility assay validated in previous work. Frequency analysis confirmed a normal distribution for the variable of sperm mobility. Repeated-measure analysis of males categorized by phenotype demonstrated that average and high sperm mobility phenotypes were distinct and independent of time. Sperm morphology, fertilizing ability, and ATP content were compared between phenotypes. Fertility and sperm ATP content differed (p < 0.001) between phenotypes, whereas sperm morphology did not (p > 0.05). Experimentation with washed sperm demonstrated that phenotype was fully expressed when mitochondrial respiration was the only source of ATP. Sperm mobility increased (p < 0.001) when sperm from average males were exposed to calyculin A, a protein phosphatase inhibitor. Correlation analyses were performed with data from a subpopulation (n = 46) whose range, mean, and variance were equivalent to those of the base population. Neither body weight nor the combined weight of the testes was correlated with sperm mobility (r = -0.02 and 0.01, respectively). In contrast, sperm ATP content was correlated with sperm mobility (r = 0.80). We attribute phenotypic differences in sperm mobility to differential rates of mitochondrial ATP synthesis.

Increased fecundity resulting from semen donor selection based upon in vitro sperm motility.

Semen donors were selected from a population of 100 roosters based upon the extent to which sperm penetrated 6% (wt/vol) Accudenz from an overlay of extended semen. Semen donors categorized by average or high sperm motility (n = 5 per phenotype) were ejaculated weekly, their ejaculates pooled by phenotype, and pooled semen extended. A subsample of each sperm suspension was overlaid on 6% (wt/vol) Accudenz in a cuvette, the cuvette was placed in a 41 C water bath, and the absorbance of the Accudenz layer was measured after a 5-min incubation. The remainder of the sperm suspension was inseminated (n = 55 hens per phenotype). Each hen was inseminated weekly with 50 x 10(6) sperm for 14 wk. The hatchability of eggs laid by hens inseminated with sperm from the high motility phenotype was 10% greater (P < or = 0.001) than that of hens inseminated with sperm from the average phenotype. The difference in fecundity was explicable in terms of fertility (P < or = 0.001). A replicate experiment tested the effect of sperm motility as well as insemination dose on fertility. Roosters were treated as above, and hens (n = 41 to 45 per phenotype) were inseminated weekly with 25, 50, or 100 x 10(6) sperm per hen for 3 wk. Two-way ANOVA detected a sperm motility effect (P < or = 0.0001) but did not detect a dose effect (P > or = 0.05) or a motility by dose interaction (P > or = 0.05). A posteriori comparison among means revealed that the maximal fertility obtained with sperm from average roosters was 9% less (P < or = 0.05) than that obtained with only 25% as many sperm from the high motility phenotype. These experiments demonstrated that the fecundity of artificially inseminated hens can be increased when sperm penetration of Accudenz is used as a selection criterion for semen donors.