Isolation and properties of a protein complex containing flagellar movement-initiating phosphoprotein from testes of a white salmon

Motility of carp spermatozoa is associated with profound changes in the sperm proteome

In freshwater cyprinids, spermatozoa are quiescent in seminal plasma and sperm motility is initiated by a decrease in osmolality (hypo-osmotic shock) after discharge into the aqueous environment. However, it is unknown at present if and to what extent changes in proteins are involved in carp sperm motility. Therefore, the aim of our study was to identify proteins related to carp sperm motility through a comparison of immobilized and activated carp spermatozoa using a 2D-DIGE approach. Our results, for the first time indicated that carp sperm motility is associated with changes in protein content. Seventy-two differentially expressed proteins were identified. These proteins are mainly involved in ubiquitin-proteasome pathways, glycolysis, the TCA cycle, remodeling and are putatively related to sperm energy metabolism and motility. Moreover proteins associated with oxidative stress responses, signal transduction by Ca(2+)-dependent MAPK cascades, and PKC and protein folding have been identified. The proteins involved in carp sperm motility were localized to the cytoplasm, mitochondria, cytoskeleton, nucleus and sperm membrane. The identification of a high number of proteins involved in carp sperm motility would contribute to current knowledge about the molecular mechanisms of sperm motility in freshwater fish.

BIOLOGICAL SIGNIFICANCE

To the best of our knowledge, few changes in proteins involved in the initiation of fish sperm motility have been identified. This is a limited number of proteins compared with the 80 recently identified proteins involved in human sperm motility. However, no proteomic studies of sperm motility have yet been performed on freshwater fish. Our present study allowed for the first time a comprehensive characterization of the proteins associated with carp sperm motility and a better understanding of the molecular mechanisms underlying sperm motility activation and maintenance. The application of 2D-DIGE facilitated the identification proteins crucial for sperm structural organization and motility. The identification of a high number of proteins involved in carp sperm motility would contribute appreciably to the presently limited information available on the mechanisms of sperm motility in freshwater fish. Moreover the identified list of proteins will create a platform for future studies designed to assess the functional significance of specific proteins in sperm motility.

Motility of fish spermatozoa: from external signaling to flagella response

For successful fertilization, spermatozoa must access, bind, and penetrate an egg, processes for which activation of spermatozoa motility is a prerequisite. Fish spermatozoa are stored in seminal plasma where they are immotile during transit through the genital tract of most externally fertilizing teleosts and chondrosteans. Under natural conditions, motility is induced immediately following release of spermatozoa from the male genital tract into the aqueous environment. The nature of an external trigger for the initiation of motility is highly dependent on the aquatic environment (fresh or salt water) and the species' reproductive behavior. Triggering signals include osmotic pressure, ionic and gaseous components of external media and, in some cases, egg-derived substances. Extensive study of environmental factors influencing fish spermatozoa motility has led to the proposal of several mechanisms of activation in freshwater and marine fish. However, the signal transduction pathways initiated by these mechanisms remain clear. This review presents the current knowledge with respect to (1) membrane reception of the activation signal and its transduction through the spermatozoa plasma membrane via the external membrane components, ion channels, and aquaporins; (2) cytoplasmic trafficking of the activation signal; (3) final steps of the signaling, including signal transduction to the axonemal machinery, and activation of axonemal dyneins and regulation of their activity; and (4) pathways supplying energy for flagellar motility.

Egg and sperm quality in fish

Fish egg quality can be defined as the ability of the egg to be fertilized and subsequently develop into a normal embryo. Similarly, sperm quality can be defined as its ability to successfully fertilize an egg and subsequently allow the development of a normal embryo. In the wild or under aquaculture conditions, the quality of fish gametes can be highly variable and is under the influence of a significant number of external factors or broodstock management practices. For these reasons, the topic of gamete quality has received increasing attention. Despite the significant efforts made towards a better understanding of the factors involved in the control of gamete quality, the picture is far from being complete and the control of gamete quality remains an issue in the aquaculture industry. Some of the factors responsible for the observed variability of gamete quality remain largely unknown or poorly understood. In addition very little is known about the cellular and molecular mechanisms involved in the control of egg and sperm quality. In the present review, the molecular and cellular characteristics of fish gametes are presented with a special interest for the mechanisms that could participate in the regulation of gamete quality. Then, after defining egg and sperm quality, and how can it can be accurately estimated or predicted, we provide an overview of the main factors that can impact gamete quality in teleosts.

Reactivation of motility of demembranated hamster spermatozoa: role of protein tyrosine kinase and protein phosphatases

Demembranated cauda epididymidal spermatozoa of hamster, following reactivation with 1 mm ATP, exhibited either a loop or planar type of motility. The spermatozoa with planar motility exhibited increased progressive velocity (VSL), straightness (STR), linearity (LIN) and beat cross frequency (BCF) compared to the spermatozoa with loop type motility. cAMP was observed to have differential effects on the motility parameters of the demembranated spermatozoa depending on the type of motility. For instance, in the loop type, average path velocity (VAP), curvilinear velocity (VCL) and VSL were increased in the presence of cAMP unlike in the planar type. Furthermore, in an attempt to understand the role of protein kinases and protein phosphatases in regulation of sperm motility, the effects of various inhibitors of these enzymes on the motility and phosphorylation of proteins of reactivated demembranated spermatozoa were studied. Inhibitors of PTKase (protein tyrosine kinase) and protein phosphatases inhibited the motility of reactivated demembranated hamster spermatozoa. The activity of the respective enzymes associated with demembranated spermatozoa was concurrently inhibited, thus providing evidence that the effect of the inhibitors on motility was mediated through their inhibitory effects on the activities of the enzymes. The results also demonstrated that two phosphotyrosinylated proteins of molecular weight 65 and 80 kDa showed reduced phosphorylation in the presence of PTKase inhibitors, thus indicating their possible role in reactivation of motility of demembranated hamster spermatozoa.

Membrane hyperpolarization by sperm-activating and -attracting factor increases cAMP level and activates sperm motility in the ascidian Ciona intestinalis

In the ascidian Ciona intestinalis (and C. savignyi), sperm-activating and -attracting factor (SAAF) is released from the egg at fertilization and stimulates both Ca(2+) influx and a transient increase in cAMP level of the sperm, leading to the activation of sperm motility (M. Yoshida et al., 1994, Dev. Growth Differ. 36, 589-595). In this paper we show in C. intestinalis that valinomycin, a potassium-selective ionophore, as well as SAAF, activated sperm motility, and this activation was suppressed by extracellular high K(+). Membrane potential measurements showed that both SAAF and valinomycin increase K(+) permeability of sperm and induce membrane hyperpolarization, the amplitude of which depends on the external K(+) concentration. The membrane potential and intracellular K(+) concentration of Ciona sperm without SAAF were estimated to be about -50 mV and 560 +/- 40 mM, respectively. After treatment with SAAF or valinomycin the membrane potential became almost equal to the equilibrium potential of K(+) (-100 mV), and the cAMP level increased in artificial seawater. A potent voltage-dependent K(+) channel blocker, MCD peptide, at the concentration of 10 microM blocked SAAF-induced hyperpolarization of the cells, increase in cAMP, and sperm motility. These results suggest that membrane hyperpolarization produced by the opening of K(+) channels elevates cAMP synthesis and leads to the activation of sperm motility in Ciona.

Effects of tyrosine kinase inhibitor on the motility and ATP concentrations of fowl spermatozoa

The possible role of tyrosine kinase in the regulation of fowl sperm motility was investigated by using a stable analogue of erbstatin, methyl 2,5-dihydroxycinnamate (2,5-MeC), a specific inhibitor of tyrosine kinase. This inhibited the motility of intact spermatozoa at 30 degrees C in a dose-dependent manner. In contrast, the motility of demembranated spermatozoa was not inhibited by the same concentrations of 2,5-MeC. At 40 degrees C, both intact and demembranated spermatozoa were almost immotile with or without 2,5-MeC. Additionally, intact spermatozoa, stimulated by the addition of Ca2+ or calyculin A, a specific inhibitor of protein phosphatases, lost their motility with the subsequent addition of 2,5-MeC at 40 degrees C. However, unlike the motility, the ATP concentrations of spermatozoa were maintained in about 30-35 nmol ATP/10(9) cells during these incubation periods. The activity of tyrosine kinase of spermatozoa at 30 degrees C, estimated by measuring the phosphorylation of a synthetic peptide substrate, RR-SRC, was 0.17 pmol/min per milligram of protein. This activity was lower than that of fowl testes or chick brain but higher than that of chick liver. These results suggest that tyrosine kinase activity, which is not retained in the axoneme and/or accessory cytoskeletal components, may be involved in the maintenance of flagellar movement of fowl spermatozoa at 30 degrees C.

sp42, the boar sperm tyrosine kinase, is a male germ cell-specific product with a highly conserved tissue expression extending to other mammalian species

sp42, a tyrosine kinase of 42 kDa originally found in ejaculated boar spermatozoa, is so far the only tyrosine protein kinase to have been purified from mature male germ cells. We have developed and characterized rabbit polyclonal antibodies specifically directed against the boar sperm enzyme, which has been here purified to homogeneity. Anti-sp42 serum and sp42 affinity-purified antibodies work very well in western blot, immunoprecipitation and immunocytochemistry, and do not inhibit sp42 catalytic activity. Immunoblotting analyses reveal the presence of sp42 both in maturing boar epididymal (caput, corpus and cauda segment) spermatozoa and in testicular spermatogenic cells, thus establishing that the protein is effectively expressed in the germ cells and is not a sperm-associated protein secreted by the epididymal epithelium or male accessory glands. This finding is further strengthened by the fact that sp42 is not glycosylated, since different lectins fail to bind to sp42 and treatment of sp42 with different deglycosylation enzymes does not result in a reduction of the molecular mass of sp42. When different boar tissues are immunoscreened in western blot analysis, the results are all sp42-negative. The extension of the study to other mammalian species (human, mouse and rat) demonstrates that proteins immunologically related to boar sp42, which share the same molecular mass and tyrosine kinase activity, are both expressed in spermatogenic cells and maintained in mature sperm cells. Intriguingly, when a wide spectrum of somatic mouse and rat tissues is probed with sp42-antiserum, no tissue presents anti-sp42 immunoreactivity. Immunocytochemistry shows that in boar spermatozoa sp42 is confined to the tail mid-piece, while by immunohistochemistry carried out on sections of adult rat testis the appearance time of the kinase appears to be consistent with a post-meiotic synthesis in haploid spermatids. Altogether, these results demonstrate that boar sp42 is a new male germ cell-specific gene product, with highly conserved tissue expression extended to other mammalian species, and suggest a possible role played by the cytoplasmic tyrosine kinase in the cell signalling network specific to haploid male germ cells.

cAMP/ATP relationship in the activation of trout sperm motility: their interaction in membrane-deprived models and in live spermatozoa

Live trout spermatozoa initiate flagellar motility for only a short period (30 sec at 18 degrees C) during which their mean beat frequency decreases steadily from 60 to 20 Hz. Motility then stops abruptly. Investigations of the activation of movement in demembranated sperm points to cyclic-AMP being necessary for reactivation (half effect at 0.5 microM) in some conditions. cAMP acts mainly by increasing the percentage of motile cells and not the beat frequency (BF) of the flagellar axoneme. Dibutyryl cAMP does not initiate movement or prolong motility of live sperm. The initiation of movement of demembranated trout sperm was investigated in various incubation conditions relative to previous phases of in vivo movement and to ATP concentration. In the absence of cAMP and in the presence of ATP lower than 25 microM, all sperm cell models were active with BF up to 15-20 Hz whatever their previous physiological conditions. In contrast, at ATP concentrations above 100 microM, the fraction of active spermatozoa decreased proportionally but the BF of the active ones increased so that, at 1 mM ATP, only 5% were active but with a BF of 65 Hz: the addition of cAMP up to 20 microM restored activity to 100% sperm models with a similar BF of 65 Hz. At ATP concentrations higher than 25 microM, cAMP was necessary in a concentration dependent manner in the reactivation, but not in the demembranation medium. This dependence was found to be unrelated to a previous in vivo phase of movement. The antagonistic effects of ATP vs. cAMP were tested at various concentrations of both nucleotides: the apparent affinity for cAMP, measured as the concentration restoring movement of 50% cell models, was decreased from 15 nM at 0.1 mM ATP to 0.5 microM at 1 mM ATP; conversely, the affinity for ATP, measured as the concentration giving rise to the half maximal beat frequency, was not significantly affected when the concentration of cAMP was raised to 0.5 mM. Preincubation with phosphodiesterase (PDE) resulted in motility of 100% of sperm models even at low ATP concentration. This tends to show that cAMP must be constantly present to sustain motility.