Bicarbonate/CO2 is not required for zona pellucida- or progesterone-induced acrosomal exocytosis of mouse spermatozoa but is essential for capacitation

Sperm Capacitation and Kinematics in Phodopus Hamsters

This study was designed to analyze changes in the spermatozoa of three species of Phodopus hamsters incubated under different conditions. Cauda epididymal sperm were incubated for 4 h in modified Tyrode's medium containing albumin, lactate, pyruvate, and Hepes (mTALP-H), in the same medium with the addition of bicarbonate (mTALP-BH), or with bicarbonate and 20 ng/mL of progesterone (mTALP-BH+P4). Media with bicarbonate are believed to promote capacitation in rodent species. Sperm motility, viability, capacitation patterns, and kinematics were assessed at different times. Capacitation in live cells was quantified after staining with Hoechst 33258 and chlortetracycline. Patterns believed to correspond to non-capacitated cells (F pattern), capacitated, acrosome-intact cells (B pattern), and acrosome-reacted cells (AR pattern) were recognized. Kinematics were examined via computer-assisted sperm analysis (CASA). The results showed a decrease in total motility in all three species in different media, with a sharp decrease in progressive motility in bicarbonate-containing media (without or with progesterone), suggesting hyperactivated motion. However, none of the other signs of hyperactivation described in rodents (i.e., decrease in STR or LIN, together with an increase in ALH) were observed. F pattern cells diminished with time in all media and were generally lower in P. roborovskii and higher in P. campbelli. B pattern cells increased in mTALP-BH media in all species. Progesterone did not enhance the percentage of B pattern cells. Finally, AR pattern cells increased in all species incubated in different media, showing the highest percentage in P. roborovskii and the lowest in P. campbelli. Comparisons between media revealed that there were higher percentages of F pattern cells and lower percentages of B pattern cells over time in medium without bicarbonate (mTALP-H) in comparison to media containing bicarbonate (mTALP-BH; mTALP-BH+P4). Overall, changes consistent with the acquisition of capacitation and development of hyperactivated motility were found; however, further studies are required to better characterize media necessary to support the pathways involved in these processes in Phodopus species.

Evaluation of sperm and hormonal assessments in Wagyu, Nellore, and Angus bulls

Wagyu bulls are known to have a highly exacerbated libido, as shown by the intense sexual interest of young calves. Therefore we believe that Wagyu male animals have specialized Sertoli and Leydig cells that are directly involved with the sexual precocity in this breed as mature bulls have a small scrotal circumference. This study aimed to evaluate whether there were differences in the hormone and sperm characteristics of Wagyu bulls compared with the same characteristics of subspecies Bos indicus and Bos taurus sires. Frozen-thawed semen from Wagyu, Nellore, and Angus sires were analyzed for sperm kinetics (computer-assisted sperm analysis), plasma membrane integrity, chromatin integrity, acrosome status, mitochondrial activity, lipid peroxidation and hormone [luteinizing hormone (LH) and testosterone] serum concentration. The results showed that Wagyu had lower total motility and an increased number of sperm with no motility when compared with Nellore and Angus bulls. Wagyu breed did not differ from those breeds when considering plasma and acrosome membranes integrity, mitochondrial potential, chromatin resistance, sperm lipid peroxidation or hormone (LH and testosterone) concentrations. We concluded that Wagyu sires had lower total motility when compared with Nellore and Angus bulls. Wagyu breed did not differ from these breeds when considering plasma and acrosome membranes integrity, mitochondrial potential, chromatin resistance, sperm lipid peroxidation, or hormone (LH and testosterone) concentrations.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

Bioenergetic changes in response to sperm capacitation and two-way metabolic compensation in a new murine model

The acquisition of fertilizing ability by mammalian spermatozoa, known as "capacitation," includes processes that depend on particular metabolic pathways. This has led to the hypothesis that ATP demands might differ between capacitated and non-capacitated cells. Mouse sperm can produce ATP via OXPHOS and aerobic glycolysis, an advantageous characteristic considering that these cells have to function in the complex and variable environment of the female reproductive tract. Nonetheless, despite evidence showing that both metabolic pathways play a role in events associated with mouse sperm capacitation, there is contradictory evidence regarding changes promoted by capacitation in this species. In addition, the vast majority of studies regarding murine sperm metabolism use Mus musculus laboratory strains as model, thus neglecting the wide diversity of sperm traits of other species of Mus. Focus on closely related species with distinct evolutionary histories, which may be the result of different selective pressures, could shed light on diversity of metabolic processes. Here, we analyzed variations in sperm bioenergetics associated with capacitation in spermatozoa of the steppe mouse, Mus spicilegus, a species with high sperm performance. Furthermore, we compared sperm metabolic traits of this species with similar traits previously characterized in M. musculus. We found that the metabolism of M. spicilegus sperm responded to capacitation in a manner similar to that of M. musculus sperm. However, M. spicilegus sperm showed distinct metabolic features, including the ability to perform cross-pathway metabolic compensation in response to either respiratory or glycolytic inhibition, thus revealing a delicate fine-tuning of its metabolic capacities.

Effect of High Viscosity on Energy Metabolism and Kinematics of Spermatozoa from Three Mouse Species Incubated under Capacitating Conditions

In order to sustain motility and prepare for fertilization, sperm require energy. The characterization of sperm ATP production and usage in mouse species revealed substantial differences in metabolic pathways that can be differentially affected by capacitation. Moreover, spermatozoa encounter different environments with varying viscoelastic properties in the female reproductive tract. Here, we examine whether viscosity affects sperm ATP levels and kinematics during capacitation in vitro. Sperm from three mouse species (Mus musculus, M. spretus, M. spicilegus) were incubated under capacitating conditions in a modified Tyrode's medium containing bicarbonate, glucose, pyruvate, lactate, and bovine serum albumin (mT-BH) or in a bicarbonate-free medium as a non-capacitating control. Viscosity was increased with the inclusion of polyvinylpyrrolidone. ATP was measured with a bioluminescence kit, and kinematics were examined with a computer-aided sperm analysis system. In M. musculus sperm, ATP declined during capacitation, but no differences were found between non-capacitating and capacitating sperm. In contrast, in M. spretus and M. spicilegus, ATP levels decreased in capacitating sperm. Increasing viscosity in the medium did not modify the timing or proportion of cells undergoing capacitation but did result in additional time- and concentration-dependent decreases in ATP in M. spretus and M. spicilegus under capacitating conditions. Additionally, increased viscosity altered both velocity and trajectory descriptors. The limited impact of capacitation and higher viscosity on M. musculus sperm ATP and kinematics could be related to the low intensity of postcopulatory sexual selection in this species. Responses seen in the other two species could be linked to the ability of their sperm to perform better under enhanced selective pressures.

In Vitro versus Cryo-Induced Capacitation of Bovine Spermatozoa, Part 2: Changes in the Expression Patterns of Selected Transmembrane Channels and Protein Kinase A

Since the molecular similarities and differences among physiological capacitation and cryocapacitation have not been studied in detail, this study was designed to assess the gene and protein expression levels of the Cation channel of sperm (CatSper) 1 and 2, sodium bicarbonate (Na+/HCO3−) cotransporter (NBC) and protein kinase A (PKA) in un-capacitated (control), in vitro capacitated (CAP) and cryopreserved (CRYO) bovine spermatozoa. All samples were subjected to motility evaluation using the computer assisted sperm analysis and chlortetracycline (CTC) assay for the assessment of the capacitation patterns. Furthermore, quantitative reverse transcription PCR (qRT-PCR) and Western blots were used to monitor the expression patterns of the selected capacitation markers. The results showed a significant reduction in the gene and protein expression levels of CatSper1 and 2 in the CRYO group when compared to the CAP group (p < 0.0001). In the case of NBC, the results were not significantly different or were inconclusive. While a non-significant down-regulation of PKA was found in the CRYO group, a significant reduction in the expression of the PKA protein was found in frozen-thawed spermatozoa in comparison to the CAP group (p < 0.05). In conclusion, we may hypothesize that while in vitro capacitated and cryopreserved spermatozoa exhibit CTC-patterns consistent with capacitation events, the molecular machinery underlying CTC-positivity may be different.

Capacitation promotes a shift in energy metabolism in murine sperm

In mammals, sperm acquire fertilization ability after a series of physiological and biochemical changes, collectively known as capacitation, that occur inside the female reproductive tract. In addition to other requirements, sperm bioenergetic metabolism has been identified as a fundamental component in the acquisition of capacitation. Mammalian sperm produce ATP through two main metabolic processes, oxidative phosphorylation (OXPHOS) and aerobic glycolysis that are localized to two different flagellar compartments, the midpiece, and the principal piece, respectively. In mouse sperm, the occurrence of many events associated with capacitation relies on the activity of these two energy-producing pathways, leading to the hypothesis that some of these events may impose changes in sperm energetic demands. In the present study, we used extracellular flux analysis to evaluate changes in glycolytic and respiratory parameters of murine sperm that occur as a consequence of capacitation. Furthermore, we examined whether these variations affect sperm ATP sustainability. Our results show that capacitation promotes a shift in the usage ratio of the two main metabolic pathways, from oxidative to glycolytic. However, this metabolic rewiring does not seem to affect the rate at which the sperm consume ATP. We conclude that the probable function of the metabolic switch is to increase the ATP supply in the distal flagellar regions, thus sustaining the energetic demands that arise from capacitation.

Effect of Motility Factors D-Penicillamine, Hypotaurine and Epinephrine on the Performance of Spermatozoa from Five Hamster Species

Simple Summary

Analysis of sperm performance under in vitro conditions provides a good indication of fertilizing potential. Parameters such as motility, swimming kinetics, acrosome integrity, or ATP content are thus examined in efforts to characterize such potential. Hamster species are a good model to study sperm parameters that are key determinants of fertilizing capacity because these species are at the higher end of the diversity of mammalian sperm morphology and performance. In vitro functional studies demand that sperm remain viable during a long period of time under conditions that resemble those in the female tract. Sperm from certain species require supplementation of the incubation medium with factors that stimulate viability and swimming, or that promote acquisition of fertilizing capacity. Molecules important for sperm performance in hamsters have been identified, namely D-penicillamine, hypotaurine and epinephrine (PHE). In the present study, we investigated the effect of PHE on spermatozoa from five hamster species incubated for up to 4 h. Our results revealed that PHE maintains sperm performance in the golden hamster, whereas it improves sperm quality in the Chinese hamster. In contrast, it does not seem to have any effect on sperm from the Siberian (Djungarian), Roborovski and Campbell’s dwarf hamsters. These results are valuable to understand the different regulatory mechanisms of sperm motility and survival in different species.

Abstract

Assessments of sperm performance are valuable tools for the analysis of sperm fertilizing potential and to understand determinants of male fertility. Hamster species constitute important animal models because they produce sperm cells in high quantities and of high quality. Sexual selection over evolutionary time in these species seems to have resulted in the largest mammalian spermatozoa, and high swimming and bioenergetic performances. Earlier studies showed that golden hamster sperm requires motility factors such as D-penicillamine, hypotaurine and epinephrine (PHE) to sustain survival over time, but it is unknown how they affect swimming kinetics or ATP levels and if other hamster species also require them. The objective of the present study was to examine the effect of PHE on spermatozoa of five hamster species (Mesocricetus auratus, Cricetulus griseus, Phodopus campbelli, P. sungorus, P. roborovskii). In sperm incubated for up to 4 h without or with PHE, we assessed motility, viability, acrosome integrity, sperm velocity and trajectory, and ATP content. The results showed differences in the effect of PHE among species. They had a significant positive effect on the maintenance of sperm quality in M. auratus and C. griseus, whereas there was no consistent effect on spermatozoa of the Phodopus species. Differences between species may be the result of varying underlying regulatory mechanisms of sperm performance and may be important to understand how they relate to successful fertilization.

Establishment of a novel assessment of the quality of human spermatozoa measuring mitochondrial oxygen metabolism

Objective

We aimed to establish a novel sperm quality evaluation technology by measuring mitochondrial oxygen metabolism in human spermatozoa.

Results

Normozoospermic human sperm samples were used. After establishing the optimal parameters for measuring the oxygen metabolism of human sperm cells using the extracellular flux analyzer, we measured the oxygen consumption rate (OCR) of human spermatozoa exposed to different storage temperatures. Although sperm motility was significantly lower at 4 °C when compared with sperm motility at 37 °C, there were no significant differences in sperm vitality and the OCR under both conditions. The present study established a methodology for human sperm quality evaluation using extracellular flux analysis technology. The OCR evaluation could be a reliable measurement tool for assessing human sperm quality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-022-06012-4.

Energy Metabolism and Hyperactivation of Spermatozoa from Three Mouse Species under Capacitating Conditions

Mammalian sperm differ widely in sperm morphology, and several explanations have been presented to account for this diversity. Less is known about variation in sperm physiology and cellular processes that can give sperm cells an advantage when competing to fertilize oocytes. Capacitation of spermatozoa, a process essential for mammalian fertilization, correlates with changes in motility that result in a characteristic swimming pattern known as hyperactivation. Previous studies revealed that sperm motility and velocity depend on the amount of ATP available and, therefore, changes in sperm movement occurring during capacitation and hyperactivation may involve changes in sperm bioenergetics. Here, we examine differences in ATP levels of sperm from three mouse species (genus Mus), differing in sperm competition levels, incubated under non-capacitating and capacitating conditions, to analyse relationships between energetics, capacitation, and swimming patterns. We found that, in general terms, the amount of sperm ATP decreased more rapidly under capacitating conditions. This descent was related to the development of a hyperactivated pattern of movement in two species (M. musculus and M. spicilegus) but not in the other (M. spretus), suggesting that, in the latter, temporal dynamics and energetic demands of capacitation and hyperactivation may be decoupled or that the hyperactivation pattern differs. The decrease in ATP levels during capacitation was steeper in species with higher levels of sperm competition than in those with lower levels. Our results suggest that, during capacitation, sperm consume more ATP than under non-capacitating conditions. This higher ATP consumption may be linked to higher velocity and lateral head displacement, which are associated with hyperactivated motility.

Understanding sperm physiology: Proximate and evolutionary explanations of sperm diversity

Much can be gained from the comprehensive study of a biological system. Based on what is known as Mayr's proximate-ultimate causation and the subsequent expansion to Tinbergen's four questions, biological traits can be understood by taking into account different approximations that try to explain mechanisms, development, adaptive significance or phylogeny. These, in principle, separate areas, can be integrated crossing boundaries, but bearing in mind that answers to one question would not explain a different query. Studies of sperm biology have, until now, not benefited much from this framework and potential integration. Proximate causes (particularly mechanisms) have been the subject of interest for reproductive biologists, and evolutionary explanations have been the domain of behavioural ecologists with interest in adaptive significance of traits in the context of post-copulatory sexual selection. This review will summarize opportunities for research in the different areas, focusing on sperm preparation for fertilization and suggesting possible integration within and between proximate and evolutionary studies.

Methodological considerations for examining the relationship between sperm morphology and motility

Sperm cells of all taxa share a common goal to reach and fertilize an ovum, yet sperm are one of the most diverse cell types in nature. While the structural diversity of these cells is well recognized, the functional significance of variation in sperm design remains elusive. An important function of spermatozoa is a need to migrate toward the ova, often over long distances in a foreign environment, which may include a complex and hostile female reproductive tract. Several comparative and experimental studies have attempted to address the link between sperm morphology and motility, yet the conclusions drawn from these studies are often inconsistent, even within the same taxa. Much of what we know about the functional significance of sperm design in internally fertilizing species has been gleaned from in vitro studies, for which experimental parameters often vary among studies. We propose that discordant results from these studies are in part due to a lack of consistency of methods, conditions that do not replicate those of the female reproductive tract, and the overuse of simple linear measures of sperm shape. Within this review, we provide a toolkit for imaging, quantifying, and analyzing sperm morphology and movement patterns for in vitro studies and discuss emerging approaches. Results from studies linking morphology to motility enhance our understanding of the evolution of adaptive sperm traits and the mechanisms that regulate fertility, thus offering new insights into methods used in assisted reproductive technologies in animal science, conservation and public health.

Faster and more efficient swimming: energy consumption of murine spermatozoa under sperm competition†

ATP supply is essential for sperm performance and increases in ATP content coevolve with enhanced sperm swimming velocity as a response to sperm competition in rodents. ATP content is the balance between production and consumption but, although ATP production has received much attention, little is known about ATP consumption. The rate of ATP consumption is crucial for the propagation of the flagellar wave, becoming a main determinant of the time and distance sperm could move before exhausting their reserves. A high yield in distance per unit of ATP consumed (efficiency) could provide advantages in sperm competition. We characterized sperm ATP consumption rate in a group of mouse species with different sperm competition levels to understand its impact on swimming velocity, duration, and yield of sperm ATP reserves. Interspecific comparisons revealed that sperm of species with higher sperm competition levels had high ATP consumption rates and faster swimming velocity. Moreover, sperm that consumed ATP at a faster rate swam more efficiently, since they were able to cover more distance per unit of ATP consumed. Our results suggest that by coupling the advantages of higher ATP turnover rates to increased efficiency of ATP expenditure, sperm would respond to increasingly competitive environments while maintaining a positive ATP balance.

Fibronectin modulates the endocannabinoid system through the cAMP/PKA pathway during human sperm capacitation

Fibronectin (Fn) enhances human sperm capacitation via the cAMP/PKA pathway, and the endocannabinoid system participates in this process. Moreover, Fn has been linked to endocannabinoid system components in different cellular models, even though no evidence of such interactions in human sperm is available. Normal semen samples were evaluated over a 4-year period. Our findings suggest that (a) the capacitating effects of Fn were reversed by preincubating the sperm with a cannabinoid receptor 1 (CB1) or transient receptor potential cation channel subfamily V member 1 (TRPV1) antagonist ( p < 0.001 and p < 0.05, respectively); (b) cooperation between CB1 and TRPV1 may exist ( p < 0.01); (c) the activity of specific fatty acid amide hydroxylase (FAAH) decreased after 1 min ( p < 0.01) and increased after 60 min ( p < 0.01) of capacitation in the presence of Fn; (d) the effects of Fn on FAAH activity were prevented by preincubating spermatozoa with a protein kinase A (PKA) inhibitor ( p < 0.01); (e) Fn modulated both the cyclic adenosine monophosphate concentration and PKA activity ( p < 0.05) during early capacitation; and (f) FAAH was a PKA substrate modulated by phosphorylation. These findings indicate that Fn stimulates human sperm capacitation via the cAMP/PKA pathway through modulation of the endocannabinoid system. Understanding the functional competence of human spermatozoa is essential for facilitating clinical advances in infertility treatment and for developing novel contraceptive strategies.

mtDNA polymorphism and metabolic inhibition affect sperm performance in conplastic mice

Whereas a broad link exists between nucleotide substitutions in the mitochondrial genome (mtDNA) and a range of metabolic pathologies, exploration of the effect of specific mtDNA genotypes is on-going. Mitochondrial DNA mutations are of particular relevance for reproductive traits, since they are expected to have profound effects on male specific processes as a result of the strict maternal inheritance of mtDNA. Sperm motility is crucially dependent on ATP in most systems studied. However, the importance of mitochondrial function in the production of the ATP necessary for sperm function remains uncertain. In this study, we test the effect of mtDNA polymorphisms upon mouse sperm performance and bioenergetics by using five conplastic inbred strains that share the same nuclear background while differing in their mitochondrial genomes. We found that, while genetic polymorphisms across distinct mtDNA haplotypes are associated with modification in sperm progressive velocity, this effect is not related to ATP production. Furthermore, there is no association between the number of mtDNA polymorphisms and either (a) the magnitude of sperm performance decrease, or (b) performance response to specific inhibition of the main sperm metabolic pathways. The observed variability between strains may be explained in terms of additive effects of single nucleotide substitutions on mtDNA coding sequences, which have been stabilized through genetic drift in the different laboratory strains. Alternatively, the decreased sperm performance might have arisen from the disruption of the nuclear DNA/mtDNA interactions that have coevolved during the radiation of Mus musculus subspecies.

A cost for high levels of sperm competition in rodents: increased sperm DNA fragmentation

Sperm competition, a prevalent evolutionary process in which the spermatozoa of two or more males compete for the fertilization of the same ovum, leads to morphological and physiological adaptations, including increases in energetic metabolism that may serve to propel sperm faster but that may have negative effects on DNA integrity. Sperm DNA damage is associated with reduced rates of fertilization, embryo and fetal loss, offspring mortality, and mutations leading to genetic disease. We tested whether high levels of sperm competition affect sperm DNA integrity. We evaluated sperm DNA integrity in 18 species of rodents that differ in their levels of sperm competition using the sperm chromatin structure assay. DNA integrity was assessed upon sperm collection, in response to incubation under capacitating or non-capacitating conditions, and after exposure to physical and chemical stressors. Sperm DNA was very resistant to physical and chemical stressors, whereas incubation in non-capacitating and capacitating conditions resulted in only a small increase in sperm DNA damage. Importantly, levels of sperm competition were positively associated with sperm DNA fragmentation across rodent species. This is the first evidence showing that high levels of sperm competition lead to an important cost in the form of increased sperm DNA damage.

Focal adhesion kinase is required for actin polymerization and remodeling of the cytoskeleton during sperm capacitation

Several focal adhesion proteins are known to cooperate with integrins to link the extracellular matrix to the actin cytoskeleton; as a result, many intracellular signaling pathways are activated and several focal adhesion complexes are formed. However, how these proteins function in mammalian spermatozoa remains unknown. We confirm the presence of focal adhesion proteins in guinea pig spermatozoa, and we explore their role during capacitation and the acrosome reaction, and their relationship with the actin cytoskeleton. Our results suggest the presence of a focal adhesion complex formed by β1-integrin, focal adhesion kinase (FAK), paxillin, vinculin, talin, and α-actinin in the acrosomal region. Inhibition of FAK during capacitation affected the protein tyrosine phosphorylation associated with capacitation that occurs within the first few minutes of capacitation, which caused the acrosome reaction to become increasingly Ca²⁺ dependent and inhibited the polymerization of actin. The integration of vinculin and talin into the complex, and the activation of FAK and paxillin during capacitation, suggests that the complex assembles at this time. We identify that vinculin and α-actinin increase their interaction with F-actin while it remodels during capacitation, and that during capacitation focal adhesion complexes are structured. FAK contributes to acrosome integrity, likely by regulating the polymerization and the remodeling of the actin cytoskeleton.

Summary: We describe the role of FAK and focal adhesion proteins in capacitation, acrosome reaction, polymerization and remodeling of actin cytoskeleton, and how inhibition of FAK affects sperm physiology.

Characterization of an Alpha Type Carbonic Anhydrase from Paracentrotus lividus Sea Urchin Embryos

Carbonic anhydrases (CA) are zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide to bicarbonate. In the sea urchin, CA has a role in the formation of the calcitic skeleton during embryo development. Here, we report a newly identified mRNA sequence from embryos of the sea urchin Paracentrotus lividus, referred to as Pl-can. The complete coding sequence was identified with the aid of both EST databases and experimental procedures. Pl-CAN is a 447 aa-long protein, with an estimated molecular mass of 48.5 kDa and an isoelectric point of 6.83. The in silico study of functional domains showed, in addition to the alpha type CA-specific domain, the presence of an unexpected glycine-rich region at the N-terminal of the molecule. This is not found in any other species described so far, but probably it is restricted to the sea urchins. The phylogenetic analysis indicated that Pl-CAN is evolutionarily closer to human among chordates than to other species. The putative role(s) of the identified domains is discussed. The Pl-can temporal and spatial expression profiles, analyzed throughout embryo development by comparative qPCR and whole-mount in situ hybridization (WMISH), showed that Pl-can mRNA is specifically expressed in the primary mesenchyme cells (PMC) of the embryo and levels increase along with the growth of the embryonic skeleton, reaching a peak at the pluteus stage. A recombinant fusion protein was produced in E. coli and used to raise specific antibodies in mice recognized the endogenous Pl-CAN by Western blot in embryo extracts from gastrula and pluteus.

Performance of Rodent Spermatozoa Over Time Is Enhanced by Increased ATP Concentrations: The Role of Sperm Competition

Sperm viability, acrosome integrity, motility, and swimming velocity are determinants of male fertility and exhibit an extreme degree of variation among closely related species. Many of these sperm parameters are associated with sperm ATP content, which has led to predictions of trade-offs between ATP content and sperm motility and velocity. Selective pressures imposed by sperm competition have been proposed as evolutionary causes of this pattern of diversity in sperm traits. Here, we examine variation in sperm viability, acrosome integrity, motility, swimming velocity, and ATP content over time, among 18 species of closely related muroid rodents, to address the following questions: (a) Do sperm from closely related species vary in ATP content after a period of incubation? (b) Are these differences in ATP levels related to differences in other sperm traits? (c) Are differences in ATP content and sperm performance over time explained by the levels of sperm competition in these species? Our results revealed a high degree of interspecific variability in changes in sperm ATP content, acrosome integrity, sperm motility and swimming velocity over time. Additionally, species with high sperm competition levels were able to maintain higher levels of sperm motility and faster sperm swimming velocity when they were incubated under conditions that support sperm survival. Furthermore, we show that the maintenance of such levels of sperm performance is correlated with the ability of sperm to sustain high concentrations of intracellular ATP over time. Thus, sperm competition may have an important role maximizing sperm metabolism and performance and, ultimately, the fertilizing capacity of spermatozoa.

Differences in ATP Generation Via Glycolysis and Oxidative Phosphorylation and Relationships with Sperm Motility in Mouse Species

Mouse sperm produce enough ATP to sustain motility by anaerobic glycolysis and respiration. However, previous studies indicated that an active glycolytic pathway is required to achieve normal sperm function and identified glycolysis as the main source of ATP to fuel the motility of mouse sperm. All the available evidence has been gathered from the studies performed using the laboratory mouse. However, comparative studies of closely related mouse species have revealed a wide range of variation in sperm motility and ATP production and that the laboratory mouse has comparatively low values in these traits. In this study, we compared the relative reliance on the usage of glycolysis or oxidative phosphorylation as ATP sources for sperm motility between mouse species that exhibit significantly different sperm performance parameters. We found that the sperm of species with higher oxygen consumption/lactate excretion rate ratios were able to produce higher amounts of ATP, achieving higher swimming velocities. Additionally, we show that the species with higher respiration/glycolysis ratios have a higher degree of dependence upon active oxidative phosphorylation. Moreover, we characterize for the first time two mouse species in which sperm depend on functional oxidative phosphorylation to achieve normal performance. Finally, we discuss that sexual selection could promote adaptations in sperm energetic metabolism tending to increase the usage of a more efficient pathway for the generation of ATP (and faster sperm).

Differences in the fatty-acid composition of rodent spermatozoa are associated to levels of sperm competition

Sperm competition is a prevalent phenomenon that drives the evolution of sperm function. High levels of sperm competition lead to increased metabolism to fuel higher sperm velocities. This enhanced metabolism can result in oxidative damage (including lipid peroxidation) and damage to the membrane. We hypothesized that in those species experiencing high levels of sperm competition there are changes in the fatty-acid composition of the sperm membrane that makes the membrane more resistant to oxidative damage. Given that polyunsaturated fatty acids (PUFAs) are the most prone to lipid peroxidation, we predicted that higher sperm competition leads to a reduction in the proportion of sperm PUFAs. In contrast, we predicted that levels of sperm competition should not affect the proportion of PUFAs in somatic cells. To test these predictions, we quantified the fatty-acid composition of sperm, testis and liver cells in four mouse species (genus Mus) that differ in their levels of sperm competition. Fatty-acid composition in testis and liver cells was not associated to sperm competition levels. However, in sperm cells, as predicted, an increase in sperm competition levels was associated with an increase in the proportion of saturated fatty-acids (the most resistant to lipid peroxidation) and by a concomitant decrease in the proportion of PUFAs. Two particular fatty acids were most responsible for this pattern (arachidonic acid and palmitic acid). Our findings thus indicate that sperm competition has a pervasive influence in the composition of sperm cells that ultimately may have important effects in sperm function.

Central role of soluble adenylyl cyclase and cAMP in sperm physiology

Cyclic adenosine 3',5'-monophosphate (cAMP), the first second messenger to be described, plays a central role in cell signaling in a wide variety of cell types. Over the last decades, a wide body of literature addressed the different roles of cAMP in cell physiology, mainly in response to neurotransmitters and hormones. cAMP is synthesized by a wide variety of adenylyl cyclases that can generally be grouped in two types: transmembrane adenylyl cyclase and soluble adenylyl cyclases. In particular, several aspects of sperm physiology are regulated by cAMP produced by a single atypical adenylyl cyclase (Adcy10, aka sAC, SACY). The signature that identifies sAC among other ACs, is their direct stimulation by bicarbonate. The essential nature of cAMP in sperm function has been demonstrated using gain of function as well as loss of function approaches. This review unifies state of the art knowledge of the role of cAMP and those enzymes involved in cAMP signaling pathways required for the acquisition of fertilizing capacity of mammalian sperm. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Evolution of protamine genes and changes in sperm head phenotype in rodents

Little is known about the genetic basis of evolutionary changes in sperm phenotype. Postcopulatory sexual selection is associated with differences in protamine gene sequences and promoters and is a powerful force acting on sperm form and function, although links between protamine evolution and sperm phenotype are scarce. Protamines are involved in sperm chromatin condensation, and protamine deficiency negatively affects sperm morphology and male fertility, thus suggesting that they are important for sperm design and function. We examined changes in protamine genes and sperm phenotype in rodents to understand the role of sexual selection on protamine evolution and sperm design. We performed a genotype-phenotype association study using root-to-tip dN/dS (nonsynonymous/synonymous substitutions rate ratio) to account for evolutionary rates and phylogenetic generalized least squares analyses to compare genetic and morphometric data. Evolutionary rates of protamine 1 and the protamine 2 domain cleaved off during chromatin condensation correlated with head size and elongation. Protamine 1 exhibited restricted positive selection on some functional sites, which seemed sufficient to preserve its role in head design. The cleaved-protamine 2, whose relaxation is halted by sexual selection, seems to ensure small, elongated heads that would make sperm more competitive. No association existed between mature-protamine 2 and head phenotype, suggesting little involvement during chromatin condensation and a likely role maintaining the condensed state. Our results suggest that evolutionary changes in protamines could be related to complex developmental modifications in the sperm head. This represents an important step toward understanding the role of changes in gene coding sequences in the divergence of germ cell phenotype.

SLC26 anion exchangers in uterine epithelial cells and spermatozoa: clues from the past and hints to the future

The solute carrier 26 (SLC26) family emerges as a distinct class of anion transporters with its members SLC26A3 (Slc26a3) and SLC26A6 (Slc26a6) reported to be electrogenic Cl(-)/HCO3(-) exchangers. While it is known that uterine fluid has high HCO3(-) content and that HCO3(-) is essential for sperm capacitation, the molecular mechanisms underlying the transport of HCO3(-) across uterine epithelial cells and sperm have not been fully investigated. The present review re-examines the results from early reports studying anion transport, finding clues for the involvement of Cl(-)/HCO3(-) anion exchangers in electrogenic HCO3(-) transport across endometrial epithelium. We also summarise recent work on Slc26a3 and Slc26a6 in uterine epithelial cells and sperm, revealing their functional role in working closely with the cystic fibrosis transmembrane conductance regulator (CFTR) for HCO3(-) transport in these cells. The possible involvement of these anion exchangers in other HCO3(-) dependent reproductive processes and their implications for infertility are also discussed.

Postcopulatory sexual selection increases ATP content in rodent spermatozoa

Sperm competition often leads to increase in sperm numbers and sperm quality, and its effects on sperm function are now beginning to emerge. Rapid swimming speeds are crucial for mammalian spermatozoa, because they need to overcome physical barriers in the female tract, reach the ovum, and generate force to penetrate its vestments. Faster velocities associate with high sperm competition levels in many taxa and may be due to increases in sperm dimensions, but they may also relate to higher adenosine triphosphate (ATP) content. We examined if variation in sperm ATP levels relates to both sperm competition and sperm swimming speed in rodents. We found that sperm competition associates with variations in sperm ATP content and sperm-size adjusted ATP concentrations, which suggests proportionally higher ATP content in response to sperm competition. Moreover, both measures were associated with sperm swimming velocities. Our findings thus support the idea that sperm competition may select for higher ATP content leading to faster sperm swimming velocity.

Involvement of A1Adenosine Receptors in the Acquisition of Fertilizing Capacity

Ejaculated mammalian spermatozoa acquire competence to fertilize oocytes by a two-step process: capacitation followed by acrosome reaction. The biochemical and biophysical modifications occurring in vivo in the female reproductive tract can be reproduced in vitro, and previous studies have suggested a capacitative role for adenosine A(1) receptor (A(1)R). Mice with a targeted disruption of the Adora 1 gene (A(1)R-/- mice) provide a useful model for better understanding the role of the A(1)R in fertility. Murine spermatozoa express A(1)R in the head, neck, midpiece region, and tail. The number of capacitated spermatozoa incubated in human tubal fluid was significantly reduced in A(1)R-/- compared with A(1)R+/+ and A(1)R+/- spermatozoa. The difference between A(1) R+/+ and A(1)R-/- mouse spermatozoa was mainly in the time necessary to reach the maximum percentage of capacitation. A(1)R+/+ murine sperm obtained the full state of capacitation within 90 minutes whereas A(1)R-/- sperm required 240 minutes. Caffeine, a known antagonist of A(1) and A(2A) adenosine receptors, lowered the number of capacitated sperm and affected the time of capacitation in a dose-dependent manner, mimicking the effects of the lack of A(1) receptors. Although number, motility, and viability of A(1)R-/- murine sperm was not significantly different from A(1)R+/+ mouse spermatozoa, a significant reduction of the number of pups produced by A(1)R-/- male mice suggests that A(1) receptors must be fully operative to accomplish the optimal degree of capacitation and thereby fertilization.

Regulation of male fertility by CFTR and implications in male infertility

BACKGROUND

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-activated Cl(-) and HCO(3)(-) conducting channel, mutations of which are known to be associated with male infertility. However, the underlying mechanisms remain elusive.

METHODS

Literature databases were searched for papers on the topics related to CFTR and male fertility and infertility with relevant keywords. Unpublished data from authors' laboratory were also included for analysis.

RESULTS

Clinical evidence shows increased mutation frequency or reduced CFTR expression in men with congenital bilateral absence of vas deferens (CBAVD) or sperm abnormalities, such as azoospermia teratospermia and oligoasthenospermia. Studies on primary rodent Sertoli cells and germ cells, as well as testes from CFTR knockout mice or a cryptorchidism model, yield findings indicating the involvement of CFTR in spermatogensis through the HCO(3)(-)/sAC/cAMP/CREB(CREM) pathway and the NF-κB/COX-2/PGE(2) pathway. Evidence also reveals a critical role of CFTR in sperm capacitation by directly or indirectly mediating HCO(3)(-) entry that is essential for capacitation. CFTR is emerging as a versatile player with roles in mediating different signaling pathways pertinent to various reproductive processes, in addition to its long-recognized role in electrolyte and fluid transport that regulates the luminal microenvironment of the male reproductive tract.

CONCLUSIONS

CFTR is a key regulator of male fertility, a defect of which may result in different forms of male infertility other than CBAVD. It would be worthwhile to further investigate the potential of developing novel diagnostic and contraceptive methods targeting CFTR.

Identification of NO induced and capacitation associated tyrosine phosphoproteins in buffalo (Bubalus bubalis) spermatozoa

To acquire the fertilizing competence, spermatozoa must undergo a cascade of physiological and biochemical changes collectively defined as capacitation. Compelling evidence signifies that the global increase in protein tyrosine phosphorylation is the driving factor for capacitation. In our laboratory, we previously demonstrated that nitric oxide (NO) induces capacitation in buffalo sperm and is associated with an increase in protein tyrosine phosphorylation. The aim of the present study is to identify the proteins undergo tyrosine phosphorylation during NO induced buffalo sperm capacitation using 2-D immunoblotting and mass spectrometry. The percentage of progressively motile and capacitated sperm was more in presence of l-arginine. Along with known tyrosine phosphoproteins like ATP synthase subunit beta, pyruvate dehydrogenase E1 component subunit beta, GST mu 3, F-actin capping protein subunit beta 2, GPD2 and VDAC2, interestingly novel tyrosine phosphoprotein substrates such as actin, serine/threonine-protein phosphatase PP1-gamma catalytic subunit, and glutamine synthetase were also identified which might be specific to the NO induced signaling and also emphasizes the species specificity with respect to tyrosine phosphorylation of proteins during capacitation. In conclusion, this study forms an essential step in delineating the proteins undergo tyrosine phosphorylation in response to NO induced signaling pathways during capacitation of buffalo sperm.

Sperm competition differentially affects swimming velocity and size of spermatozoa from closely related muroid rodents: head first

Sperm competition favours an increase in sperm swimming velocity that maximises the chances that sperm will reach the ova before rival sperm and fertilise. Comparative studies have shown that the increase in sperm swimming speed is associated with an increase in total sperm size. However, it is not known which are the first evolutionary steps that lead to increases in sperm swimming velocity. Using a group of closely related muroid rodents that differ in levels of sperm competition, we here test the hypothesis that subtle changes in sperm design may represent early evolutionary changes that could make sperm swim faster. Our findings show that as sperm competition increases so does sperm swimming speed. Sperm swimming velocity is associated with the size of all sperm components. However, levels of sperm competition are only related to an increase in sperm head area. Such increase is a consequence of an increase in the length of the sperm head, and also of the presence of an apical hook in some of the species studied. These findings suggest that the presence of a hook may modify the sperm head in such a way that would help sperm swim faster and may also be advantageous if sperm with larger heads are better able to attach to the epithelial cells lining the lower isthmus of the oviduct where sperm remain quiescent before the final race to reach the site of fertilisation.

Sperm competition, sperm numbers and sperm quality in muroid rodents

Sperm competition favors increases in relative testes mass and production efficiency, and changes in sperm phenotype that result in faster swimming speeds. However, little is known about its effects on traits that contribute to determine the quality of a whole ejaculate (i.e., proportion of motile, viable, morphologically normal and acrosome intact sperm) and that are key determinants of fertilization success. Two competing hypotheses lead to alternative predictions: (a) sperm quantity and quality traits co-evolve under sperm competition because they play complementary roles in determining ejaculate's competitive ability, or (b) energetic constraints force trade-offs between traits depending on their relevance in providing a competitive advantage. We examined relationships between sperm competition levels, sperm quantity, and traits that determine ejaculate quality, in a comparative study of 18 rodent species using phylogenetically controlled analyses. Total sperm numbers were positively correlated to proportions of normal sperm, acrosome integrity and motile sperm; the latter three were also significantly related among themselves, suggesting no trade-offs between traits. In addition, testes mass corrected for body mass (i.e., relative testes mass), showed a strong association with sperm numbers, and positive significant associations with all sperm traits that determine ejaculate quality with the exception of live sperm. An "overall sperm quality" parameter obtained by principal component analysis (which explained 85% of the variance) was more strongly associated with relative testes mass than any individual quality trait. Overall sperm quality was as strongly associated with relative testes mass as sperm numbers. Thus, sperm quality traits improve under sperm competition in an integrated manner suggesting that a combination of all traits is what makes ejaculates more competitive. In evolutionary terms this implies that a complex network of genetic and developmental pathways underlying processes of sperm formation, maturation, transport in the female reproductive tract, and preparation for fertilization must all evolve in concert.

Differential involvement of rat sperm choline glycerophospholipids and sphingomyelin in capacitation and the acrosomal reaction

Rat spermatozoa main lipid classes and their fatty acids were studied to assess their possible changes in capacitation and the acrosomal reaction (AR), induced in vitro. Capacitation-associated protein tyrosine phosphorylation, and the efflux of 30% of the total cholesterol from gametes to the medium, took place concomitantly with the release of a similar percentage, i.e., a larger amount, of the total phospholipid, mostly after hydrolysis of the major choline glycerophospholipids (CGP). Main medium lipid metabolites after capacitation were lyso-CGP and polyenoic fatty acids typical of CGP (22:4n-9, 22:5n-6), as free fatty acids (FFA). The AR, induced by a calcium ionophore, resulted in further phospholipid loss, but the produced metabolites remained in the gametes. CGP decrease in AR accounted for some additional FFA and lyso-CGP, but mostly for (22:5n-6-rich) diglycerides. Hydrolysis of sphingomyelins (SM) to ceramides also occurred, mostly affecting species with very long chain polyenoic fatty acids. Quantitatively, CGP and SM were the lipid classes decreasing the most after capacitation and AR, respectively. The massive cholesterol and phospholipid loss from the gametes during capacitation is thus associated with protein phosphorylation, a function that has been located to the sperm tail. The lipid metabolites produced during AR, by accumulating in the gamete heads, could be implicated in sperm-oocyte interactions.

CFTR is essential for sperm fertilizing capacity and is correlated with sperm quality in humans

BACKGROUND

Our previous studies have demonstrated the cystic fibrosis transmembrane conductance regulator (CFTR) is important for capacitation and male fertility in mouse and guinea pig spermatozoa. However, the exact function of CFTR on human sperm fertilizing capacity, and correlation with sperm quality has not been established. The present study may shed light on some unexplained male infertility, and on a possible new method for diagnosis of male infertility and strategy for male contraception.

METHODS

To assess the effect of CFTR on human sperm fertilizing capacity, we examined sperm capacitation and the acrosome reaction using chlortetracycline staining, analyzed sperm hyperactivation by computer-assisted semen analysis (CASA), measured intracellular cAMP levels using ElA and evaluated sperm penetration of zona-free hamster eggs assay in fertile men. The percentage of spermatozoa expressing CFTR from fertile, healthy and infertile men (mainly teratospermic, asthenoteratospermic, asthenospermic and oligospermic) was conducted by indirect immunofluorescence staining.

RESULTS

Progesterone significantly facilitated human sperm capacitation and ZP3 triggered the acrosome reaction, both were significantly inhibited by CFTR inhibitor-172 (CFTRinh-172; 10 nM-1 microM) in a dose-dependent manner. The presence of 100 nM CFTRinh-172 markedly depressed intracellular cAMP levels, sperm hyperactivation and sperm penetration of zona-free hamster eggs. In addition, the percentage of spermatozoa expressing CFTR in the fertile men was significantly higher than healthy and infertile men categories (P < 0.01).

CONCLUSIONS

CFTR is essential for human sperm fertilizing capacity and the impairment of CFTR expression in spermatozoa is correlated with a reduction of sperm quality. These results suggest that defective expression of CFTR in human sperm may lead to the reduction of sperm fertilizing capacity.

Sexual selection drives weak positive selection in protamine genes and high promoter divergence, enhancing sperm competitiveness

Phenotypic adaptations may be the result of changes in gene structure or gene regulation, but little is known about the evolution of gene expression. In addition, it is unclear whether the same selective forces may operate at both levels simultaneously. Reproductive proteins evolve rapidly, but the underlying selective forces promoting such rapid changes are still a matter of debate. In particular, the role of sexual selection in driving positive selection among reproductive proteins remains controversial, whereas its potential influence on changes in promoter regions has not been explored. Protamines are responsible for maintaining DNA in a compacted form in chromosomes in sperm and the available evidence suggests that they evolve rapidly. Because protamines condense DNA within the sperm nucleus, they influence sperm head shape. Here, we examine the influence of sperm competition upon protamine 1 and protamine 2 genes and their promoters, by comparing closely related species of Mus that differ in relative testes size, a reliable indicator of levels of sperm competition. We find evidence of positive selection in the protamine 2 gene in the species with the highest inferred levels of sperm competition. In addition, sperm competition levels across all species are strongly associated with high divergence in protamine 2 promoters that, in turn, are associated with sperm swimming speed. We suggest that changes in protamine 2 promoters are likely to enhance sperm swimming speed by making sperm heads more hydrodynamic. Such phenotypic changes are adaptive because sperm swimming speed may be a major determinant of fertilization success under sperm competition. Thus, when species have diverged recently, few changes in gene-coding sequences are found, while high divergence in promoters seems to be associated with the intensity of sexual selection.

Capacitation-associated changes in protein tyrosine phosphorylation, hyperactivation and acrosome reaction in hamster spermatozoa

The aim of this study was to evaluate the effects of Ca2+, BSA, NaHCO3 and PVA on the capacitation-associated time-dependent increase in protein tyrosine phosphorylation, hyperactivation, and acrosome reaction in hamster spermatozoa. Hamster spermatozoa when incubated in TALP, a medium that assists capacitation, showed a time-dependent increase in protein tyrosine phosphorylation that correlated with the capacitated state of the spermatozoa. An absence of Ca2+ or NaHCO3 in the capacitation medium delayed the phosphorylation of the proteins, but without both there was a significant decrease in the phosphorylation of the proteins throughout the period of capacitation. An absence of bovine serum albumin also caused a decrease in the phosphorylation of the proteins but this did not occur if polyvinyl alcohol was substituted for it in the medium. The percentage hyperactivation was not affected in the absence of bovine serum albumin if the medium contained polyvinyl alcohol. However, it was delayed in the absence of NaHCO3 and inhibited in the absence of Ca2+. The absence of NaHCO3 or bovine serum albumin had no effect on the acrosome reaction. These results show that hamster spermatozoa undergo capacitation-associated protein tyrosine phosphorylation similar to that of the spermatozoa of other mammals. However, hamster spermatozoa are unique in that the capacitation-associated protein tyrosine phosphorylation is not absolutely dependent on the presence of Ca2+ and NaHCO3. As far as we know, this study is the first to provide evidence that capacitation-associated protein tyrosine phosphorylation is linked to hyperactivation in hamster spermatozoa.

Cl- is required for HCO3- entry necessary for sperm capacitation in guinea pig: involvement of a Cl-/HCO3- exchanger (SLC26A3) and CFTR

Our previous study demonstrated the involvement of cystic fibrosis transmembrane conductance regulator (CFTR) in transporting bicarbonate that is necessary for sperm capacitation; however, whether its involvement is direct or indirect remains unclear. The present study investigated the possibility of a Cl-/HCO3- exchanger (solute carrier family 26, number 3 [SLC26A3]) operating with CFTR during guinea pig sperm capacitation. Incubating sperm in media with various concentrations of Cl- resulted in varied percentages of capacitated sperm in a concentration-dependent manner. Depletion of Cl-, even in the presence of HCO3-, abolished sperm capacitation and vice versa, indicating the involvement of both anions in the process. Capacitation-associated HCO3--dependent events, including increased intracellular pH, cAMP production, and protein tyrosine phosphorylation, also depend on Cl- concentrations. Similar Cl- dependence and inhibitor sensitivity were observed for sperm-hyperactivated motility and for sperm-egg fusion. The expression and localization of CFTR and SLC26A3 were demonstrated using immunostaining and Western blot analysis. Taken together, our results indicate that Cl- is required for the entry of HCO3- that is necessary for sperm capacitation, implicating the involvement of SLC26A3 in transporting HCO3-, with CFTR providing the recycling pathway for Cl-.

Signal transduction mechanisms involved in in vitro ram sperm capacitation

We validate the chlortetracycline (CTC) technique for the evaluation of capacitation and acrosome reaction-like changes in ram sperm, carrying out a double estimation of the acrosome status after treatment with lysophosphatidylcholine, using fluorescein isocyanate (FITC)-RCA/ethidium homodimer 1 (EthD-1) and CTC/EthD-1. Highly consistent results and a positive correlation between the results of acrosome-reacted sperm evaluated with both techniques were obtained. In this study, we evaluate the effects of ram sperm capacitation of BSA, Ca(2+), NaHCO(3) and cAMP agonists and their influence on the associated protein tyrosine phosphorylation. We found a time-dependent increase in capacitation related to protein tyrosine phosphorylation, either in the absence or the presence of BSA. The addition of an increasing concentration of cholesterol to samples containing BSA did not influence results. The effect of bicarbonate was concentration-dependent, with a significantly lowered value of non-capacitated sperm in the presence 18 and 25 mM. The addition of extracellular calcium did not significantly increase either the proportion of capacitated sperm or the protein tyrosine phosphorylation signalling, although a significantly higher value of acrosome-reacted sperm was found in samples containing 4 mM Ca(2+). cAMP agonists increased capacitated sperm and protein tyrosine phosphorylation signalling. The inhibition of protein kinase A by H-89 caused a decrease in sperm capacitation. Addition of a calcium-entry blocker (Verapamil; Sigma) did not influence results, which suggests that the calcium entry blocker was unable to inhibit the calcium influx associated with capacitation in ram sperm. Our findings might benefit our understanding of the biochemical mechanisms involved in mammalian sperm capacitation and ultimately, fertility.

Effect of fructose on motility, acrosome reaction and in vitro fertilization capability of boar spermatozoa

Aim:  The present study was carried out to investigate the effects of fructose supplementation in glucose containing mTALP medium on motility, acrosome reaction and in vitro fertilization capability of boar spermatozoa. Methods:  Boar spermatozoa were preincubated, swum-up, resuspended and then incubated for 6 h in mTALP medium supplemented with 0, 0.5, or 1.0 mmol fructose in the presence of 5.0 mmol glucose. After completion of the specified incubation period, motility was determined subjectively on the basis of speed of progression and on the type of forward movement of spermatozoa; acrosome status was evaluated by applying a triple staining technique; and in vitro fertilization capability was assessed by acetic-orcein staining. Results:  The combination of fructose and glucose (0.5 + 5.0 mmol) supplements in mTALP medium improved sperm motility significantly (P < 0.05), more than glucose alone (5.0 mmol) at 2-6 h of incubation. Acrosome reaction (live spermatozoa) and the sperm penetration rate was increased significantly (P < 0.05) when the spermatozoa were treated with the combination of fructose and glucose compared with glucose alone, but the incidence of polyspermy was not significantly different between the treatments. Conclusion:  These results suggest that the combination of glucose and fructose as supplements in mTALP medium improve the progressive motility, acrosome reaction and fertilization capability of boar spermatozoa. (Reprod Med Biol 2006; 5: 255-261).

Identification of a tyrosine-phosphorylated CCCTC-binding nuclear factor in capacitated mouse spermatozoa

The molecular basis of mammalian sperm capacitation, either in vivo in the female reproductive tract, or in vitro, is poorly understood. It is well known that sperm capacitation is associated with an increase in tyrosine phosphorylation of a subset of proteins. We resolved the phosphoproteins in the cell lysate of mouse sperm after capacitation by 2-DE. One tyrosine-phosphorylated 130-kDa spot was trypsin-digested, and six oligopeptide sequences were established from the MS data. These were confirmed in a CCCTC-binding nuclear factor (CTCF), a widely expressed and highly conserved protein. Further, both an anti-phosphotyrosine antibody and an anti-CTCF antibody showed immunoreactivity to a 130-kDa component in the immunoprecipitates obtained after incubation of the cell lysate from the capacitated sperm using another anti-CTCF antibody. The data support the presence of a tyrosine-phosphorylated CTCF in the capacitated sperm. Immunolocalization of the CTCF revealed fluorescent staining in the acrosome region in both capacitated and incapacitated sperm. The electrophoretic mobility shift assay, using a CTCF target sequence 5'-GGCGGCGCCGCTAGGGGTCTCTCT-3' found in the promoter of the amyloid beta-protein precursor, manifested that, relative to CTCF in the incapacitated sperm, the tyrosine-phosphorylated protein in the capacitated sperm had stronger affinity to the CTCF target sequence.

Sperm competition enhances functional capacity of mammalian spermatozoa

When females mate promiscuously, sperm from rival males compete within the female reproductive tract to fertilize ova. Sperm competition is a powerful selective force that has shaped sexual behavior, sperm production, and sperm morphology. However, nothing is known about the influence of sperm competition on fertilization-related processes, because it has been assumed that sperm competition only involves a race to reach the site of fertilization. We compared four closely related rodent species with different levels of sperm competition to examine whether there are differences in the proportion of spermatozoa that become ready to interact with the ovum ("capacitated") and in the proportion of spermatozoa that experience the acrosome reaction in response to a natural stimulant. Our results show that differences between species in levels of sperm competition were associated with the proportion of spermatozoa that undergo capacitation and with the proportion of spermatozoa that respond to progesterone, an ovum-associated signal. Sperm competition thus favors a larger population of spermatozoa that are competent to fertilize, and spermatozoa that are more sensitive to the signals emitted by the ovum and that may penetrate the ova vestments more rapidly. These results suggest that, contrary to previous assumptions, competition between spermatozoa from rival males continues at the site of fertilization. These findings may have further evolutionary implications because the enhanced competitiveness of spermatozoa during fertilization may increase the risk of polyspermy to females. This could lead to antagonistic coevolution between the sexes and may contribute to the explanation of the rapid divergence observed in fertilization-related traits.

Critical role of CFTR in uterine bicarbonate secretion and the fertilizing capacity of sperm

Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-activated Cl- channel expressed in a wide variety of epithelial cells, mutations of which are responsible for hallmark defective Cl- and HCO3- secretion seen in cystic fibrosis (CF). However, the physiological role of CFTR in reproductive tracts is far from understood although infertility has been observed in CF patients of both sexes. Previously we have demonstrated the expression of CFTR in the female reproductive tract and the involvement of CFTR in mediating anion secretion by the endometrium. Our recent results show that endometrial epithelial cells possess a cAMP-activated HCO3- transport mechanism, which could be impaired with channel blockers known to block CFTR or antisense against CFTR. Co-culture of sperm with CFTR antisense-treated endometrial cells or HCO3- secretion-defective CF epithelial cells resulted in reduced sperm capacitation and egg-fertilizing ability. Addition of HCO3- to the culture media and transfection of wild-type CFTR into CF cells rescued the fertilizing capacity of sperm. Immunostaining and Western blot revealed that CFTR is expressed in rodent sperm and intracellular measurement of pH during sperm capacitation indicated that the entry of HCO3- into sperm could be inhibited by CFTR inhibitor. These results are consistent with a critical role of CFTR in controlling uterine HCO3- secretion and sperm fertilizing capacity, suggesting that CFTR may be a potential target for post-meiotic regulation of fertility.

A sodium bicarbonate transporter from sea urchin spermatozoa

Bicarbonate (HCO3-) transporters play crucial roles in cell-signaling pathways and are essential for cell viability. Here we describe the first cloning and localization of a HCO3- transporter from sperm of the sea urchin, Strongylocentrotus purpuratus. The deduced protein is 1214 amino acids and has a calculated molecular mass of 135 kDa. The annotated protein coding region of the transporter gene consists of 24 exons. The most similar human protein is the Na+/HCO3- cotransporter-2 (NBC2), which has 53% identity and 68% similarity to the sea urchin protein. The sea urchin protein shares the major structural features of HCO3- transporters, including 13 transmembrane segments, a DIDS (4,4-diiodothiocyanatostilbene-2, 2-disulfonic acid) binding motif and N-linked glycosylation sites. It has longer N- and C-terminal cytoplasmic domains compared to human HCO3- transporters. The sea urchin protein possesses a relatively long 3rd extracellular loop with four conserved cysteine residues. This is characteristic for Na+/HCO3- cotransporters, but not for anion exchangers, suggesting that the sea urchin protein is a Na+/HCO3- cotransporter. It is therefore designated as Sp-NBC. A neighbor-joining tree shows that Sp-NBC branches closer to the electroneutral type of HCO3- transporters. Western immunoblots and immunoflourescence show that Sp-NBC is concentrated in the flagellar plasma membrane, suggesting a role in motility regulation.

Inadvertent transgenesis by conventional ICSI in mice

BACKGROUND

ICSI is a relatively new treatment for human male-related infertility, as well as an efficient method for the production of transgenic animals by injecting into the oocyte sperm previously incubated with foreign DNA. As semen samples collected in human infertility clinics are frequently contaminated with bacteria, one risk associated with the ICSI procedure is the injection of foreign, sperm-associated exogenous DNA into the oocyte, and the generation of transgenic offspring.

METHODS

To analyse this possibility, ICSI was performed in mouse oocytes with frozen-thawed and Percoll-treated fresh sperm samples intentionally contaminated with plasmid EGFP-transformed E. coli bacteria or medium from which these bacteria were washed. Fertilized embryos were cultured in vitro until morula/blastocyst stage, transferred into pseudopregnant females, and at day 14, fetuses and reabsorptions were analysed by PCR for the genomic presence of integrated plasmid and/or bacterial DNA.

RESULTS

Independently of the sperm pretreatment tested, transgenesis was produced.

CONCLUSIONS

Inadvertent transgenesis by conventional ICSI is a possibility that should not be neglected. Particular precautions, such as full bacteriological semen examinations and effective antibiotic semen pretreatments, should be taken in human infertility clinics, in order to exclude the possibility of accidental transgenesis.