K+-independent initiation of motility in chum salmon sperm treated with an organic alcohol, glycerol

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.

Diploid and aneuploid sperm in tetraploid ginbuna, Carassius auratus langsdorfii

Ginbuna (Carassius auratus langsdorfii (Teleostei: Cyprinidae)) occur in diploid, triploid, and tetraploid forms in wild populations. Diploid females reproduce bisexually, whereas polyploid (triploid and tetraploid) females reproduce gynogenetically with no contribution from sperm nuclei. However, tetraploid males produce diploid sperm. The mechanism responsible for the differences in egg and sperm ploidy has not been elucidated as tetraploid males are rare in wild populations. Here, we aimed to characterize the types of sperm and elucidate the mechanism of spermatogenesis in ginbuna. In the present study, we artificially produced tetraploid males by crossbreeding triploid ginbuna females with diploid goldfish (Carassius auratusauratus) males via accidental incorporation of sperm nuclei. We then examined spermatogenesis to reveal the process by which reduced diploid sperm are generated from tetraploid germ cells. DNA fingerprinting by random amplified polymorphic DNA (RAPD)-PCR indicated that the tetraploid progeny had a paternally derived genome. For the tetraploid male sperm, there were narrow (N-type) and broad (B-type) flow cytometrical histograms. The N-type were determined to be diploid with a low coefficient of variation (CV) by flow cytometry. The B-type were found to be aneuploid (hypodiploid to hexaploid) with a high CV. The head sizes of B-type sperm were variable, whereas those of the N-type sperm were uniform. Computer-assisted sperm analysis (CASA) revealed that both the haploid and diploid B-type sperm were weakly motile compared with the haploid sperm of goldfish and the diploid N-type sperm of tetraploid males. Bivalents and various multivalents were observed in the meiotic configurations of diploid spermatogenesis. In aneuploid spermatogenesis, most of the chromosomes were unpaired univalents and there were very few bivalents. Our findings provide empirical evidence for two different types of spermatogenesis in tetraploid C. a. langsdorfii males. Meiotic synapses might explain the observed differences in the ploidy status of the two sperm types.

Effects of cryopreservation on cAMP-dependent protein kinase and AMP-activated protein kinase in Atlantic salmon (Salmo salar) spermatozoa: Relation with post-thaw motility

Sperm motility in fish with external fertilization is critical for reproductive efficiency in aquaculture, especially in salmonids. Gamete preservation techniques, such as cryopreservation, however, reduce sperm motility and fertilizing capacity. Very few studies have addressed cryodamage from energetic and cell signalling approaches. In this study, cAMP-dependent protein kinase (PKA) and AMP-activated kinase (AMPK) activities were quantified in fresh and cryopreserved spermatozoa of Atlantic salmon (Salmo salar); and the relation with motility was analysed. Results indicate there was a decrease in membrane integrity and motility in post-thawed spermatozoa compared to fresh samples, however, there was about 30% of cells with intact plasma membrane but incapable of motility. The PKA and AMPK activities were less after cryopreservation, indicating that loss of motility may be related to alteration of these key enzymes. Furthermore, PKA and AMPK activities were positively correlated with each other and with motility; and inhibition decreased motility, indicating there is a functional relationship between PKA and AMPK. The PKA inhibition also decreased AMPK activity, but results from protein-protein docking analyses indicated AMPK activation directly by PKA is unlikely, thus an indirect mechanism may exist. There have been no previous reports of these kinase actions in fish spermatozoa, making these findings worthy of assessment when there are future studies being planned, and may serve as base knowledge for optimization of cryopreservation procedures and development of biotechnologies to improve reproduction efficiency in the aquaculture industry.

Sperm motility in fishes: (III) diversity of regulatory signals from membrane to the axoneme

Fish spermatozoa acquire potential for motility in the sperm duct where they are immotile. Osmolality of the seminal plasma is a key factor to maintain spermatozoa in the quiescent state in either freshwater or marine fishes. However, potassium (K⁺) ions prevent spermatozoa motility in salmonid and sturgeon fishes, while CO₂ inhibits spermatozoa motility in flatfishes. Once, spermatozoa are released at spawning, their motility is initiated in hypo-osmotic and hyper-osmotic environments in freshwater and marine fishes, respectively. Some substances produced by the testes (a progestin), or released from oocytes (peptides) induce spermatozoa hypermotility in some marine fishes including the Atlantic croaker and Pacific herrings, respectively. Duration of spermatozoa motility is short, lasting for a few seconds to few minutes in most fishes due to rapid depletion of energy required for the beating of the motility apparatus called axoneme. In the osmotic-activated spermatozoa, K⁺ and water effluxes occur in freshwater and marine fishes, respectively, which trigger spermatozoa motility signaling. In general, initiation of axonemal beating is associated with an increase in intracellular calcium (Ca²⁺) ions in spermatozoa of both freshwater and marine fishes and a post- or pre-increase in intracellular pH, while cyclic adenosine monophosphate (cAMP) remains unchanged. However, axonemal beating is cAMP-dependent in demembranated spermatozoa of salmonid and sturgeon fishes. Calcium from extracellular environment or intracellular stores supply required Ca²⁺ concentration for axonemal beating. Several axonemal proteins have been so far identified in fishes that are activated by Ca²⁺ and cAMP, directly or mediated by protein kinase C and protein kinase A, respectively. The present study reviews differences and similarities in complex regulatory signals controlling spermatozoa motility initiation in fishes, and notes physiological mechanisms that await elucidation.

Role of Ca2+ in the IVM of spermatozoa from the sterlet Acipenser ruthenus

The role of Ca2+ in sturgeon sperm maturation and motility was investigated. Sperm from mature male sterlets (Acipenser ruthenus) were collected from the Wolffian duct and testis 24 h after hormone induction. Testicular spermatozoa (TS) were incubated in Wolffian duct seminal fluid (WDSF) for 5 min at 20°C and were designated ‘TS after IVM’ (TSM). Sperm motility was activated in media with different ion compositions, with motility parameters analysed from standard video microscopy records. To investigate the role of calcium transport in the IVM process, IVM was performed (5 min at 20°C) in the presence of 2 mM EGTA, 100 µM Verapamil or 100 µM Tetracaine. No motility was observed in the case of TS (10 mM Tris, 25 mM NaCl, 50 mM Sucr with or without the addition of 2 mM EGTA). Both incubation of TS in WDSF and supplementation of the activation medium with Ca2+ led to sperm motility. The minimal Ca2+ concentration required for motility activation of Wolffian duct spermatozoa, TS and TSM was determined (1–2 nM for Wolffian duct spermatozoa and TSM; approximately 0.6 mM for TS). Motility was obtained after the addition of verapamil to the incubation medium during IVM, whereas the addition of EGTA completely suppressed motility, implying Ca2+ involvement in sturgeon sperm maturation. Further studies into the roles of Ca2+ transport in sturgeon sperm maturation and motility are required.

Control of sturgeon sperm motility: Antagonism between K+ ions concentration and osmolality

Spermatozoa are stored in a quiescent state in the male reproductive tract and motility is induced in response to various environmental stimuli, such as change of osmolality (general case) and a decrease of extracellular K+ in fish from Acipenseridae family. This study was aimed to investigate the relationship between osmolality and extracellular K+ concentration in controlling sperm motility in sturgeon. Pre-incubation of sturgeon sperm for 5s in hypertonic solutions of glycerol, NaCl, or sucrose (each of 335 mOsm/kg osmolality) prepares sturgeon spermatozoa to become fully motile in presence of high concentration of K+ ions (15 mM), which has previously been demonstrated to fully repress motility. Furthermore, presence of 0.5mM KCl during the high osmolality pre-incubation exposure completely prevented subsequent spermatozoa activation in a K+-rich media. Manipulating the transport of K+ ions by the presence of K+ ionophore (valinomycin), it was concluded that once an efflux of K+ ions, the precursor of sturgeon sperm motility activation, is taking place, spermatozoa then become insensitive to a large extracellular K+ concentration.

Regulation of salmonid fish sperm motility by osmotic shock-induced water influx across the plasma membrane

The motility of salmonid fish sperm is initiated by a decrease in the extracellular K(+) concentration. However, our previous studies revealed that salmonid fish sperm motility could be initiated in the presence of an inhibitory concentration of K(+) by drastic osmotic shock induced by suspension in a hypertonic glycerol solution and subsequent dilution in a hypotonic solution (glycerol-treatment). In the present study, we examined if an osmotic shock-induced water influx is involved in the regulation of salmonid fish sperm motility. HgCl2, a common inhibitor of aquaporins (AQPs), decreased the duration of salmonid fish sperm motility. Dilution of sperm cells in a hypotonic solution increased the cellular volume, whereas HgCl2 inhibited such an increase in cellular volume. Furthermore, the expression of AQP 1a and 10 in rainbow trout testes was confirmed. In contrast, HgCl2 did not affect glycerol-treated sperm motility, indicating that AQPs are not involved in glycerol-treated sperm motility. We also explored the possibility of aquaporin-independent water influx in glycerol-treated sperm by assessing the sperm membrane permeability using propidium iodide. The plasma membrane of glycerol-treated sperm was considerably permeabilized. The cellular volume was decreased in a hypertonic glycerol solution and increased upon subsequent hypoosmotic shock, indicating an AQP-independent water flux across the plasma membrane upon glycerol-treatment. Taken together, these results showed that water influx across the plasma membrane via AQP is crucial for the maintenance of salmonid fish sperm motility under normal conditions, whereas water influx by osmotic shock-induced membrane permeation is critical for the initiation of glycerol-treated sperm motility.

The role of Ca(2+) and Na (+) membrane transport in brook trout (Salvelinus fontinalis) spermatozoa motility

The role of environmental ion composition and osmolality in Ca(2+) signaled activation was assessed in spermatozoa of brook trout Salvelinus fontinalis. Milt from ten mature males was obtained by abdominal massage. Spermatozoa motility was evaluated in 0, 100, and 300 mOsm/kg NaCl or sucrose solutions, buffered by 10 mM Tris-HCl pH 8.5. For investigation of spermatozoa reaction to external Ca(2+) concentration, 2 mM ethylene glycol tetraacetic acid (EGTA) was added to the activation media as a calcium ions chelator. For investigation of the effect of external Na(+) concentration in conditions of low external Ca(2+), 100 µM amiloride was added to the EGTA-containing solutions as a Na(+) transport blocker. Low motility was observed in sucrose (Na(+) free) solutions containing 2 mM EGTA but not in Na(+) solutions containing 2 mM EGTA. Addition of amiloride led to significantly increased motility (P < 0.05) compared with sucrose (Na(+) free) solutions containing 2 mM EGTA. We conclude that Na(+) transport in Ca(2+)-free solutions plays a regulatory role in brook trout spermatozoa activation. The influence of competitive Na(+) and Ca(2+) transport on the control of spermatozoa activation requires further study with respect to its application for improvement of artificial activation and storage media.

Motility of fish spermatozoa: from external signaling to flagella response

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

Transient Ca2+ mobilization caused by osmotic shock initiates salmonid fish sperm motility

Salmonid fish sperm motility is known to be suppressed in millimolar concentrations of extracellular K+, and dilution of K+ upon spawning triggers cAMP-dependent signaling for motility initiation. In a previous study, however, we demonstrated that suspending sperm in a 10% glycerol solution and subsequent dilution into a low-osmotic solution induced motility independently of extracellular K+ and cAMP. In the present study, we further investigated the glycerol-induced motility mechanism. We found that treatment with solutions consisting of organic or inorganic ions, as well as glycerol, induced sperm motility in an osmolarity-dependent manner. Elimination of intracellular Ca2+ by BAPTA-AM significantly inhibited glycerol-treated sperm motility, whereas removal of extracellular Ca2+ by EGTA did not. Monitoring intracellular Ca2+, using fluo-4, revealed that intracellular Ca2+ increased when sperm were suspended in hypertonic solutions, and a subsequent dilution into a hypotonic solution led to a decrease in intracellular Ca2+ concomitant with motility initiation. In addition, upon dilution of sperm into a hypertonic glycerol solution prior to demembranation, the motility of demembranated sperm was reactivated in the absence of cAMP. The motility recovery suggests that completion of axonemal maturation occurred during exposure to a hypertonic environment. As a result, it is likely that glycerol treatment of sperm undergoing hypertonic shock causes mobilization of intracellular Ca2+ from the intracellular Ca2+ store and also causes maturation of axonemal proteins for motility initiation. The subsequent dilution into a hypotonic solution induces a decrease in intracellular Ca2+ and flagellar movement. This novel mechanism of sperm motility initiation seems to act in a salvaging manner for the well-known K+-dependent pathway.

Development of a novel CASA system based on open source software for characterization of zebrafish sperm motility parameters

Although computer-assisted sperm analysis (CASA) outperforms manual techniques, many investigators rely on non-automated analysis due to the high cost of commercial options. In this study, we have written and validated a free CASA software primarily for analysis of fish sperm. This software is a plugin for the free National Institutes of Health software ImageJ and is available with documentation at . That it is open source makes possible external validation, should improve quality control and enhance the comparative value of data obtained among laboratories. In addition, we have improved upon the traditional velocity straight line (VSL) algorithm, eliminating inaccurate characterization of highly curved fish sperm paths. Using this system, the motion of zebrafish (Danio rerio) sperm was characterized relative to time post-activation and the impact of acquisition conditions upon data analysis determined. There were decreases in velocity and path straightness (STR), but not linearity (LIN), relative to time. From 30 to 300 frames/s, frame rate significantly affected curvilinear velocity (VCL) and STR measurements. Sperm density in the field of view did not affect any measured parameter. There was significant inter-male variation for VCL, VSL, velocity average path (VAP), percent motility, path character (STR, LIN), and duration of motility. Furthermore, relative sperm output (a measure reflecting both semen volume and concentration) was positively correlated to percent motility. For all motion parameters measured (except duration), the average CV was < or =10%, comparable to values obtained using commercial systems.