Roles of extracellular ions and pH in 5-HT-induced sperm motility in marine bivalve

pH Homeodynamics and Male Fertility: A Coordinated Regulation of Acid-Based Balance during Sperm Journey to Fertilization

pH homeostasis is crucial for spermatogenesis, sperm maturation, sperm physiological function, and fertilization in mammals. HCO3- and H+ are the most significant factors involved in regulating pH homeostasis in the male reproductive system. Multiple pH-regulating transporters and ion channels localize in the testis, epididymis, and spermatozoa, such as HCO3- transporters (solute carrier family 4 and solute carrier family 26 transporters), carbonic anhydrases, and H+-transport channels and enzymes (e.g., Na+-H+ exchangers, monocarboxylate transporters, H+-ATPases, and voltage-gated proton channels). Hormone-mediated signals impose an influence on the production of some HCO3- or H+ transporters, such as NBCe1, SLC4A2, MCT4, etc. Additionally, ion channels including sperm-specific cationic channels for Ca2+ (CatSper) and K+ (SLO3) are directly or indirectly regulated by pH, exerting specific actions on spermatozoa. The slightly alkaline testicular pH is conducive to spermatogenesis, whereas the epididymis's low HCO3- concentration and acidic lumen are favorable for sperm maturation and storage. Spermatozoa pH increases substantially after being fused with seminal fluid to enhance motility. In the female reproductive tract, sperm are subjected to increasing concentrations of HCO3- in the uterine and fallopian tube, causing a rise in the intracellular pH (pHi) of spermatozoa, leading to hyperpolarization of sperm plasma membranes, capacitation, hyperactivation, acrosome reaction, and ultimately fertilization. The physiological regulation initiated by SLC26A3, SLC26A8, NHA1, sNHE, and CFTR localized in sperm is proven for certain to be involved in male fertility. This review intends to present the key factors and characteristics of pHi regulation in the testes, efferent duct, epididymis, seminal fluid, and female reproductive tract, as well as the associated mechanisms during the sperm journey to fertilization, proposing insights into outstanding subjects and future research trends.

Effects of salinity on pre- and post-fertilization developmental events in the mangrove oyster Crassostrea rhizophorae (GUILDING, 1828)

The mangrove oyster Crassostrea rhizophorae is identified as a potentially valuable species for tropical aquaculture, however, information on the physiological mechanisms of reproduction under laboratory conditions for this species is limited. This study investigated the effects of salinity at different concentrations (15, 20, 25, 30, 35, and 40 g/L) on the induction of germinal vesicle breakdown (GVBD) of oocytes obtained through stripping, the release of polar bodies (PB1 and PB2), and the larval development of the mangrove oyster. The results revealed a relationship between salinity and the percentage of GVBD, with the most effective range being 30-40 g/L within the hydration time frame between 70 and 120 min. The release of 50 % of PB1 was detected within this salinity range, while for the release of 50 % of PB2, the saline treatments of 35 and 40 g/L showed the best results. Overall, the salinity range of 30-40 g/L is suggested as the most suitable of polyploidy induction methodologies through the retention of PB1 or PB2. Regarding larval hatching, while salinities between 25 and 40 g/L presented similar percentages, at 15 g/L no hatching was observed. This study demonstrated that salinity is a key factor in early pre- and post-fertilization stages for the successful reproduction of mangrove oyster in hatcheries and that the percentages of oocyte maturation and artificial fertilization can be optimized by adjusting salinity.

Physiological evaluation of seasonal sperm quality in a biannual spawner, Pacific abalone: Effects on in-vitro fertilization and cryotolerance

Pacific abalone, Haliotis discus hannai, is a highly valuable gastropod mollusk commonly found in Southeast Asia. The present study aims to analyze the seminal plasma quality, sperm quality, and cryotolerance of the Pacific abalone sperm during its reproductive season. The seminal plasma quality was evaluated by analyzing biochemical and metabolite composition, enzymatic activity (superoxide dismutase, catalase, and glutathione), and lipid peroxidation (LPO) activity. The sperm quality was evaluated by analyzing motility, concentration, volume, ATP content, acrosome integrity (AI), plasma membrane integrity (PMI), mitochondrial membrane potential (MMP), DNA integrity, and fertilization potential. The cryotolerance capacity was evaluated by analyzing post-thaw motility, AI, PMI, MMP, and DNA integrity. Seminal plasma osmolarity was significantly higher (1123.3 ± 1.5 mOsmL-1) in May compared to other reproductive periods, with Cl- (516.8 ± 0.5 mM) and Na+ (460.2 ± 0.4 mM) as the dominant ions. The seminal plasma pH remained constant at 6.8 throughout the reproductive season. Improved enzymatic activity and lower LPO were detected in May or June. Sperm quality indicators were similar in May and June, except for sperm production. The fertilization potential (May: 93.0 ± 4.4%, June: 86.0 ± 7.2%) and hatching rate (May: 86.6 ± 5.78%, June: 82.3 ± 3.2%) of Pacific abalone were significantly higher in May or June than they were in other reproductive seasons. The motility (May: 50.19 ± 2.35%, June: 49.96 ± 1.60%), AI (May: 44.02 ± 3.46%, June: 42.16 ± 3.61%), PMI (May: 54.12 ± 3.29%, June: 52.82 ± 2.58%), and MMP (May: 44.02 ± 3.46%, June: 42.16 ± 3.61%) of the cryopreserved sperm were similar in May and June compared with those preserved in other reproductive seasons. The DNA integrity of the cryopreserved sperm was similar in May (80.3 ± 6.7%) or June (78.9 ± 7.4%) and had a higher cryotolerance than in other reproductive seasons. Hence, it can be suggested that May and/or June are suitable periods for sperm physiology experiments, artificial reproduction, and sperm cryopreservation of Pacific abalone.

Polystyrene Nanoplastics in Aquatic Microenvironments Affect Sperm Metabolism and Fertilization of Mytilus galloprovincialis (Lamark, 1819)

The continuous and unregulated discharge of wastes and pollutants into the aquatic environment has required constant monitoring of the risks incurred by aquatic ecosystems. Alarmism arises from plastic pollution as larger artifacts release nanoscale fragments that can contact free-living stages such as gametes, embryos, and larvae. Specifically, the interaction between spermatozoa, released in water in externally fertilizing species, and the surrounding microenvironment is essential for successful fertilization. Activation and kinematics of movement, proper maintenance of ionic balance, and chemotactism are processes highly sensitive to even minimal perturbations caused by pollutants such as polystyrene nanoplastics. Spermatozoa of Mytilus galloprovincialis (M. galloprovincialis), an excellent ecotoxicological model, undergo structural (plasma membrane ruptures, DNA damage) and metabolic (reduced motility, fertilizing capacity) damage upon exposure to 50 nm amino-modified polystyrene nanoplastics (nPS-NH2). Nanoplastics of larger diameter (100 nm) did not affect sperm parameters. The findings highlighted the negative impact that plastic pollution, related to nanoparticle diameter and concentration, could have on sperm quality and reproductive potential of organisms, altering the equilibrium of aquatic ecosystems.

Deleterious effect of gestagens from wastewater effluent on fish reproduction in aquatic environment: A review

Gestagens are common pollutants accumulated in the aquatic ecosystem. Gestagens are comprised of natural gestagens (i.e. progesterone) and synthetic gestagens (i.e. progestins). The major contributors of gestagens in the environment are paper plant mill effluent, wastewater treatment plants, discharge from pharmaceutical manufacturing, and livestock farming. Gestagens present in the aquatic environment interact with progesterone receptors and other steroid hormone receptors, negatively influencing fish reproduction, development, and behavior. In fish, the gonadotropin induces 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) production, an important steroid hormone involved in gametogenesis. DHP interacts with the membrane progestin receptor (mPR), which regulates sperm motility and oocyte maturation. Gestagens also interfere with the hypothalamic-pituitary-gonadal (HPG) axis, which results in altered hormone levels in fish. Moreover, recent studies showed that even at low concentrations exposure to gestagens can have detrimental effects on fish reproduction, including reduced egg production, masculinization, feminization in males, and altered sex ratio, raising concerns about their impact on the fish population. This review highlights the hormonal regulation of sperm motility, oocyte maturation, the concentration of environmental gestagens in the aquatic environment, and their detrimental effects on fish reproduction. However, the long-term and combined impacts of multiple gestagens, including their interactions with other pollutants on fish populations and ecosystems are not well understood. The lack of standardized regulations and monitoring protocols for gestagens pollution in wastewater effluent hampers effective control and management. Nonetheless, advancements in analytical techniques and biomonitoring methods provide potential solutions by enabling better detection and quantification of gestagens in aquatic ecosystems.

Genome-Wide Identification of 5-HT Receptor Gene Family in Razor Clam Sinonovacula constricta and Their Circadian Rhythm Expression Analysis

Serotonin (5-HT) is primarily distributed in the gastrointestinal and central nervous systems, where it plays a crucial role in regulating various physiological functions such as digestion, reproduction and establishing animal emotions. 5-HT is an effective oxytocin widely used in molluscan aquaculture, and its physiological functions are performed by binding to corresponding 5-HT receptors (5-HTRs). In this study, seven 5-HTR genes of Sinonovacula constricta (Sc5-HTRs) were identified and analyzed, and they were designated as Sc5-HT1A, Sc5-HT1D, Sc5-HT2-1, Sc5-HT2-2, Sc5-HT2-3, Sc5-HT4 and Sc5-HT6. Phylogenetic analysis showed that the seven Sc5-HTRs were conserved among mollusks, and the Sc5-HTRs were all transmembrane proteins. The seven Sc5-HTR genes were distributed on chromosome 1, 2, 13 and 14. After injecting 5-HT, there was a significant increase in mRNA expression levels of Sc5-HT1A (p < 0.05) and Sc5-HT2-3 (p < 0.01), while Sc5-HT4 decreased significantly (p < 0.01) compared to control groups which might be effective 5-HT receptors. Furthermore, two of the receptors (Sc5-HT2-3 and Sc5-HT4) were expressed in the circadian rhythm patterns, indicating their potential influence on the nocturnal spawning of S. constricta. Overall, these findings provide a theoretical basis for understanding the structures and functions of 5-HTR gene family members, and may facilitate the artificial propagation of mollusks.

A novel peptide identified from visceral ganglia induces oocyte maturation, spermatozoa active motility, and spawning in the pen shell Atrinapectinata

The identification of novel peptides that regulate reproduction is essential for studying reproductive physiology in bivalves. Therefore, we aimed to identify peptides that affect the reproductive physiology of bivalves. We identified an oocyte maturation-, sperm motility-, and spawning-inducing peptide from the visceral ganglia of the pen shell, Atrina pectinata. The peptide consisted of 26 amino acid residues (GFDSINFPGTIDGFKDYSSNKKERLL). This peptide induced oocyte maturation and sperm motility activation at less than 1 nM upon the treatment of gonad fragments and induced spawning at 1 nmol when injected into mature individuals. Mature eggs and sperms artificially spawned by peptide administration were fertilized, and we confirmed that the development proceeded normally to veliger (D-shape) larvae. These results indicated that GFDSINFPGTIDGFKDYSSNKKERLL stimulated the gonads of pen shells and induced oocyte maturation, sperm motility activation, and spawning.

Osmoregulation in fish sperm

In most fish exhibiting external fertilization, spermatozoa become motile after release into water, triggered by differences between intracellular and extracellular conditions such as osmotic pressure, ion composition, and pH. The rapid change in osmolarity initiating spermatozoon motility induces osmotic pressure, resulting in active water movement across the cell membrane. Mechanisms of ion and water transport across the plasma membrane and cell volume regulation are important in maintaining structure and functional integrity of the cell. The capacity of the fish spermatozoon plasma membrane to adapt to dramatic environmental changes is an essential prerequisite for motility and successful fertilization. Adaptation to change in external osmolality may be the basis of spermatozoon function and an indicator of sperm quality. The involvement of specific water channels (aquaporins) in cell volume regulation and motility is highly likely. The goal of this review is to describe basic mechanisms of water transport and their role in fish spermatozoon physiology, focusing on osmoresistance, cell volume regulation, motility, and survival.

Sex- and sexual maturation-related aspects of the element accumulation in soft tissues of the bivalve Mytilus galloprovincialis Lam. collected off coasts of Sevastopol (southwestern Crimea, Black Sea)

Mussels are widely used to monitor trace element pollution, but the role of their sex and sexual maturation in the element accumulation was not comprehensively studied and the number of elements under consideration never exceeded three dozen. In this work, concentrations of 67 elements in different tissues of females and males of the Mediterranean mussel are determined. Statistically significant differences are obtained in the element composition of analogous tissues of mussel males and females and in gonads of the same sex at different sexual maturation stages. The significantly higher concentrations of some elements found in gonads of females (Mn, Zn, As) and males (P) at most of the sexual maturation stages suggest essentiality of these elements in the reproduction. Elements exhibit several accumulation patterns in gonads during the ripening, with the most general one being the accumulation after spawning. Indications of a new phenomenon of circulation of most elements in gonads over the reproductive cycle are obtained, with the element concentrations decreasing at the first two stages and increasing at the posterior stages. Principal component analysis shows that the differences in the element accumulation are mainly due to the element uptake pathways and sexual differentiation. The most important identified factors determining the decrease in concentrations of tissue elements are their redistribution over mussel's body, biomass dilution, sequestration, and release with gametes. Five detected non-overlapping clusters of the non-normalized element concentrations in the pooled mussel tissues are associated with macroelements, two groups of trace elements, and two groups of ultratrace elements.

Regulation of sperm motility in Eastern oyster (Crassostrea virginica) spawning naturally in seawater with low salinity

Oyster aquaculture is expanding worldwide, where many farms rely on seed produced by artificial spawning. As sperm motility and velocity are key determinants for fertilization success, understanding the regulation of sperm motility and identifying optimal environmental conditions can increase fertility and seed production. In the present study, we investigated the physiological mechanisms regulating sperm motility in Eastern oyster, Crassostrea virginica. Sperm motility was activated in ambient seawater with salinity 4-32 PSU with highest motility and velocity observed at 12-24 PSU. In artificial seawater (ASW) with salinity of 20 PSU, sperm motility was activated at pH 6.5-10.5 with the highest motility and velocity recorded at pH 7.5-10.0. Sperm motility was inhibited or totally suppressed in Na+, K+, Ca2+, and Mg2+-free ASW at 20 PSU. Applications of K+ (500 μM glybenclamide and 10-50 mM 4-aminopyridine), Ca2+ (1-50 μM mibefradil and 10-200 μM verapamil), or Na+ (0.2-2.0 mM amiloride) channel blockers into ASW at 20 PSU inhibited or suppressed sperm motility and velocity. Chelating extracellular Ca2+ ions by 3.0 and 3.5 mM EGTA resulted in a significant reduction and full suppression of sperm motility by 4 to 6 min post-activation. These results suggest that extracellular K+, Ca2+, and Na+ ions are involved in regulation of ionic-dependent sperm motility in Eastern oyster. A comparison with other bivalve species typically spawning at higher salinities or in full-strength seawater shows that ionic regulation of sperm motility is physiologically conserved in bivalves. Elucidating sperm regulation in C. virginica has implications to develop artificial reproduction, sperm short-term storage, or cryopreservation protocols, and to better predict how changes in the ocean will impact oyster spawning dynamics.

The voltage-gated T-type Ca2+ channel is key to the sperm motility of Atlantic salmon (Salmo salar)

Ca²⁺ is a key element in the sperm activation process of Salmo salar. However, the molecular mechanisms by which this ion enters the sperm cell have been poorly studied. In this study, we examined, for the first time, the role of the voltage-gated T-type Ca²⁺ channel in the activation of sperm motility of Salmo salar. Using an in vitro inhibition assay, a significant decrease in total and progressive motility (P < 0.0001) was observed in Salmo salar sperm when they were treated with NNC-55-0396, a highly selective blocker. The in silico analysis showed that this blocker is docked with a strong affinity for the pore of the voltage-gated T-type calcium channel suggesting the blocking of Ca²⁺ ions. The results show that the T-type voltage-gated Ca²⁺ channel is key to sperm motility in Salmo salar.

Distribution of Molecules Related to Neurotransmission in the Nervous System of the Mussel Crenomytilus grayanus

In bivalves neurotransmitters are involved in a variety of behaviors, but their diversity and distribution in the nervous system of these organisms remains somewhat unclear. Here, we first examined immunohistochemically the distributions of neurons containing different neurotransmitters, neuropeptides, and related enzymes, as well as the proliferative status of neurons in the ganglia of the mussel Crenomytilus grayanus. H-Phe-Met-Arg-Phe-NH2 (FMRFamide), choline acetyltransferase (ChAT), γ-aminobutyric acid (GABA) and tyrosine hydroxylase (TH) were found to be expressed by neurons in all the ganglia, whereas serotonin (5-HT) neurons were found only in the cerebropleural and pedal, but not visceral ganglia. Moreover, incubation of living mussels in the presence of a 5-HT precursor (5-HTP) confirmed the absence of 5-HT-containing neurons from the visceral ganglia, indicating that the "serotonin center" of the visceral nervous system is located in the cerebral ganglia. Furthermore, immunostaining of molecules related to neurotransmission together with α-acetylated tubulin demonstrated that this cytoskeletal protein may be a potential pan-neuronal marker in bivalves. Adult mussel neurons do not proliferate, but a population of proliferating PCNA-LIP cells which do not express any of the neurotransmitters examined, perhaps glia cells, was detected in the ganglia. These novel findings suggest that the nervous system of bivalves contains a broad variety of signal molecules most likely involved in the regulation of different physiological and behavioral processes. In addition, proliferating cells may maintain and renew glial cells and neurons throughout the lives of bivalves.

Role of voltage-gated L-type calcium channel in the spermatozoa motility of Atlantic salmon (Salmo salar)

Ca²⁺ cations play a key role in the initiation of spermatozoa motility in Atlantic salmon (Salmo salar). In this study we assess the importance of the voltage-gated L-type calcium channels in the spermatozoa motility of Atlantic salmon by combined in vitro and in silico approaches. The results of this study showed that as in other fish species, voltage-gated L-type calcium channels are significant in the spermatozoa motility of Salmo salar. The in vitro assays showed that total and progressive motilities decrease significantly (****p < .001) when Salmo salar spermatozoa are treated with verapamil, which has its binding site in the pore of the voltage-gated L-type calcium channel according to the in silico analysis.

The relationship between semen seminal plasma ions and sperm cell velocities of wild-caught longspine scraper, Capoeta trutta

In this study, semen seminal plasma contents and the motility of sperm cells were determined in Capoeta trutta via a computer-assisted sperm analysis system. In addition, we evaluated the relationship between semen seminal plasma ions and the velocities of sperm cells. Although the predominant ions were K ( 206.84 ± 20.61  mg L- 1 ) and Na ( 128.06 ± 23.82  mg L- 1 ) in the semen seminal plasma, Ca ( 14.05 ± 4.13  mg L- 1 ) and Mg ( 3.35 ± 0.44  mg L- 1 ) were not predominate according to our results. However, partially strong relationships between the curvilinear velocity value (VCL) and K (R 2 = 0.67 ; p < 0.05 ) were found, while it was moderate with Mg (R 2 = 0.48 ; p < 0.05 ). There was a weak relationship with Na (R 2 = 0.17 ; p < 0.05 ) and Ca (R 2 = 0.34 ; p < 0.05 ). In our results, while the trace metals were determined as Zn > Al > B > Li > Cu in semen seminal plasma, they are not correlated with sperm cell velocities. Finally, we hope that the present information on the motility parameters of Capoeta trutta in this paper will eventually help artificial insemination in reproduction practices.

Zinc pyrithione induces immobilization of human spermatozoa and suppresses the response of the cAMP/PKA signaling pathway

Zinc pyrithione (ZPT), a zinc coordination complex, is used as an antimicrobial agent. This study investigated the molecular mechanisms underlying ZPT-induced spermatozoa immobilization by examining plasma membrane integrity, mitochondrial dysfunction, and the cAMP/PKA signaling pathway response. ZPT inhibited spermatozoa motility and movement patterns in a concentration-dependent manner. The 100% effective concentration (EC₁₀₀) and median effective concentration (EC₅₀) at which ZPT-induced spermatozoa immobilization at 20 s were 40 μmol/L and 16.19 μmol/L, respectively. ZPT did not significantly disrupt spermatozoa plasma membranes, but it exerted a strong and significant effect on the depolarization of mitochondria. In addition, ZPT exposure induced intracellular H⁺ accumulation and Ca²⁺ dissipation in spermatozoa, accompanied by suppression of the cAMP/PKA signaling pathway. Thus, ZPT induces spermatozoa immobilization without significant plasma membrane injury and so could be a candidate microbicidal spermicide.

Spermatozoa motility in bivalves: Signaling, flagellar beating behavior, and energetics

Though bivalve mollusks are keystone species and major species groups in aquaculture production worldwide, gamete biology is still largely unknown. This review aims to provide a synthesis of current knowledge in the field of sperm biology, including spermatozoa motility, flagellar beating, and energy metabolism; and to illustrate cellular signaling controlling spermatozoa motility initiation in bivalves. Serotonin (5-HT) induces hyper-motility in spermatozoa via a 5-HT receptor, suggesting a serotoninergic system in the male reproductive tract that might regulate sperm physiology. Acidic pH and high concentration of K⁺ are inhibitory factors of spermatozoa motility in the testis. Motility is initiated at spawning by a Na⁺-dependent alkalization of intracellular pH mediated by a Na⁺/H⁺ exchanger. Increase of 5-HT in the testis and decrease of extracellular K⁺ when sperm is released in seawater induce hyperpolarization of spermatozoa membrane potential mediated by K⁺ efflux and associated with an increase in intracellular Ca²⁺ via opening of voltage-dependent Ca²⁺ channels under alkaline conditions. These events activate dynein ATPases and Ca²⁺/calmodulin-dependent proteins resulting in flagellar beating. It may be possible that 5-HT is also involved in intracellular cAMP rise controlling cAMP-dependent protein kinase phosphorylation in the flagellum. Once motility is triggered, flagellum beats in asymmetric wave pattern leading to circular trajectories of spermatozoa. Three different flagellar wave characteristics are reported, including "full", "twitching", and "declining" propagation of wave, which are described and illustrated in the present review. Mitochondrial respiration, ATP content, and metabolic pathways producing ATP in bivalve spermatozoa are discussed. Energy metabolism of Pacific oyster spermatozoa differs from previously studied marine species since oxidative phosphorylation synthetizes a stable level of ATP throughout 24-h motility period and the end of movement is not explained by a low intracellular ATP content, revealing different strategy to improve oocyte fertilization success. Finally, our review highlights physiological mechanisms that require further researches and points out some advantages of bivalve spermatozoa to extend knowledge on mechanisms of motility.

Sperm handling in aquatic animals for artificial reproduction

Artificial reproduction involves collection and handling of gametes in a way that secures their quality and maximizes the fertilization outcome. In addition to initial sperm quality, numerous steps can affect the final result of fertilization, from the sperm collection process until gamete mixing (or co-incubation) when the spermatozoon enters or fuses with the oocyte. In this review, we summarize the whole process of sperm handling, from collection until fertilization for fish, penaeid shrimp, bivalve mollusks and marine mammals. To obtain sperm from captive animals, techniques vary widely across taxa, and include stripping by abdominal massage or testis surgical removal in fish, spermatophore collection in penaeid shrimps, gonadal scarification or temperature shock in bivalve mollusks, and voluntary collection via positive reinforcement in mammals. In most cases, special care is needed to avoid contamination by mucus, seawater, urine, or feces that can either activate sperm motility and/or decrease its quality. We also review techniques and extender solutions used for refrigerated storage of sperm across the aforementioned taxa. Finally, we give an overview of the different protocols for in vivo and in vitro fertilization including activation of sperm motility and methods for gamete co-incubation. The present study provides valuable information regarding breeder management either for animal production or species conservation.

The dinoflagellate Alexandrium minutum affects development of the oyster Crassostrea gigas, through parental or direct exposure

Harmful algal blooms are a threat to aquatic organisms and coastal ecosystems. Among harmful species, the widespread distributed genus Alexandrium is of global importance. This genus is well-known for the synthesis of paralytic shellfish toxins which are toxic for humans through the consumption of contaminated shellfish. While the effects of Alexandrium species upon the physiology of bivalves are now well documented, consequences on reproduction remain poorly studied. In France, Alexandrium minutum blooms have been recurrent for the last decades, generally appearing during the reproduction season of most bivalves including the oyster Crassostrea gigas. These blooms could not only affect gametogenesis but also spawning, larval development or juvenile recruitment. This study assesses the effect of toxic A. minutum blooms on C. gigas reproduction. Adult oysters were experimentally exposed to A. minutum, at environmentally realistic concentrations (10² to 10³ cells mL^-1) for two months during their gametogenesis and a control group, not exposed to A. minutum was fed with a non-toxic dinoflagellate. To determine both consequences to next generation and direct effects of A. minutum exposure on larvae, the embryo-larval development of subsequent offspring was conducted with and without A. minutum exposure at 10² cells mL^-1. Effects at each stage of the reproduction were investigated on ecophysiological parameters, cellular responses, and offspring development. Broodstock exposed to A. minutum produced spermatozoa with decreased motility and larvae of smaller size which showed higher mortalities during settlement. Embryo-larval exposure to A. minutum significantly reduced growth and settlement of larvae compared to non-exposed offspring. This detrimental consequence on larval growth was stronger in larvae derived from control parents compared to offspring from exposed parents. This study provides evidence that A. minutum blooms, whether they occur during gametogenesis, spawning or larval development, can either affect gamete quality and/or larval development of C. gigas, thus potentially impacting oyster recruitment.

Pattern formation of stains from dried drops to identify spermatozoa motility

We study how cell motility affects the stains left by the evaporation of droplets of a biofluid suspension containing mouse spermatozoa. The suspension, which contains also a high concentration of salts usually needed by motile cells, forms, upon drying, a crystallized pattern. We examine the structural characteristics of such patterns by optical microscopy. The analysis reveals that cell motility affects the formation of elongated crystals with lateral tips, as well as the creation of interlocked aggregates. We prove that a lacunarity algorithm based on polar symmetry, distinguishes among deposits generated by motile and non-motile cells with an accuracy greater than 95%.

pH controls spermatozoa motility in the Pacific oyster (Crassostrea gigas)

Investigating the roles of chemical factors stimulating and inhibiting sperm motility is required to understand the mechanisms of spermatozoa movement. In this study, we described the composition of the seminal fluid (osmotic pressure, pH, and ions) and investigated the roles of these factors and salinity in initiating spermatozoa movement in the Pacific oyster, Crassostrea gigas The acidic pH of the gonad (5.82±0.22) maintained sperm in the quiescent stage and initiation of flagellar movement was triggered by a sudden increase of spermatozoa external pH (pHe) when released in seawater (SW). At pH 6.4, percentage of motile spermatozoa was three times higher when they were activated in SW containing 30 mM NH4Cl, which alkalinizes internal pH (pHi) of spermatozoa, compared to NH4Cl-free SW, revealing the role of pHi in triggering sperm movement. Percentage of motile spermatozoa activated in Na+-free artificial seawater (ASW) was highly reduced compared to ASW, suggesting that change of pHi triggering sperm motility was mediated by a Na+/H+ exchanger. Motility and swimming speed were highest in salinities between 33.8 and 42.7‰ (within a range of 0 to 50 ‰), and pH values above 7.5 (within a range of 4.5 to 9.5).

Transcriptomics Analysis of Crassostrea hongkongensis for the Discovery of Reproduction-Related Genes

BACKGROUND

The reproductive mechanisms of mollusk species have been interesting targets in biological research because of the diverse reproductive strategies observed in this phylum. These species have also been studied for the development of fishery technologies in molluscan aquaculture. Although the molecular mechanisms underlying the reproductive process have been well studied in animal models, the relevant information from mollusks remains limited, particularly in species of great commercial interest. Crassostrea hongkongensis is the dominant oyster species that is distributed along the coast of the South China Sea and little genomic information on this species is available. Currently, high-throughput sequencing techniques have been widely used for investigating the basis of physiological processes and facilitating the establishment of adequate genetic selection programs.

RESULTS

The C.hongkongensis transcriptome included a total of 1,595,855 reads, which were generated by 454 sequencing and were assembled into 41,472 contigs using de novo methods. Contigs were clustered into 33,920 isotigs and further grouped into 22,829 isogroups. Approximately 77.6% of the isogroups were successfully annotated by the Nr database. More than 1,910 genes were identified as being related to reproduction. Some key genes involved in germline development, sex determination and differentiation were identified for the first time in C.hongkongensis (nanos, piwi, ATRX, FoxL2, β-catenin, etc.). Gene expression analysis indicated that vasa, nanos, piwi, ATRX, FoxL2, β-catenin and SRD5A1 were highly or specifically expressed in C.hongkongensis gonads. Additionally, 94,056 single nucleotide polymorphisms (SNPs) and 1,699 simple sequence repeats (SSRs) were compiled.

CONCLUSIONS

Our study significantly increased C.hongkongensis genomic information based on transcriptomics analysis. The group of reproduction-related genes identified in the present study constitutes a new tool for research on bivalve reproduction processes. The large group of molecular markers discovered in this study will be useful for population screening and marker assisted selection programs in C.hongkongensis aquaculture.