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

Protein expression patterns and metal metabolites in a protogynous hermaphrodite fish, the ricefield eel (Monopterus albus)

BACKGROUND

The ricefield eel Monopterus albus undergoes a natural sex change from female to male during its life cycle, and previous studies have shown the potential mechanisms of this transition at the transcriptional and protein levels. However, the changes in protein levels have not been fully explored, especially in the intersexual stage.

RESULTS

In the present study, the protein expression patterns in the gonadal tissues from five different periods, the ovary (OV), early intersexual stage gonad (IE), middle intersexual stage gonad (IM), late intersexual stage gonad (IL), and testis (TE), were determined by untargeted proteomics sequencing. A total of 5125 proteins and 394 differentially expressed proteins (DEPs) were detected in the gonadal tissues. Of the 394 DEPs, there were 136 between the OV and IE groups, 20 between the IM and IE groups, 179 between the IL and IM groups, and 59 between the TE and IL groups. Three candidate proteins, insulin-like growth factor 2 mRNA-binding protein 3 isoform X1 (Igf2bp3), triosephosphate isomerase (Tpi), and Cu-Zn superoxide dismutase isoform X1 [(Cu-Zn) Sod1], were validated by western blotting to verify the reliability of the data. Furthermore, metal metabolite-related proteins were enriched in the IL vs. IM groups and TE vs. IL groups, which had close relationships with sex change, including Cu2+-, Ca2+-, Zn2+- and Fe2+/Fe3+-related proteins. Analysis of the combined transcriptome data revealed consistent protein/mRNA expression trends for two metal metabolite-related proteins/genes [LOC109953912 and calcium Binding Protein 39 Like (cab39l)]. Notably, we detected significantly higher levels of Cu2+ during the sex change process, suggesting that Cu2+ is a male-related metal metabolite that may have an important function in male reproductive development.

CONCLUSIONS

In summary, we analyzed the protein profiles of ricefield eel gonadal tissues in five sexual stages (OV, IE, IM, IL, and TE) and verified the plausibility of the data. After preforming the functional enrichment of metal metabolite-related DEPs, we detected the contents of the metal metabolites Zn2+, Cu2+, Ca2+, and Fe2+/Fe3+ at these five stages and screened for (Cu-Zn) Sod1 and Mmp-9 as possible key proteins in the sex reversal process.

Differential metabolites screening in yak (Bos grunniens) seminal plasma after cryopreservation and the evaluation of the effect of galactose on post-thaw sperm motility

Sperm survival and activity depend on the provision of energy and nutrients from seminal plasma (SP). This study aimed to investigate the variations of metabolites within SP before and after freezing and subsequently explore the potential regulatory mechanisms affecting yak sperm cryodamage due to changes in metabolites in the SP. Untargeted metabolomics analysis was performed to screen for differential metabolites, followed by KEGG analysis to identify enriched signaling pathways. The combinatorial analysis of metabolomics and sperm proteomics revealed the influence of key SP metabolites on sperm proteins. Subsequently, the relevant differentially expressed proteins were verified by Western blot analysis. Finally, the mechanism underlying the positive effect of galactose on sperm motility was determined by assessing the change in ATP content in sperm before and after freezing and thawing. The data showed that a total of 425 and 269 metabolites were identified in the positive and negative ion modes, respectively. Freezing and thawing resulted in the up-regulation of 70 metabolites and the down-regulation of 29 metabolites in SP. The primary impact of freezing and thawing was observed in carbohydrate metabolism, including pyruvate metabolism, pentose phosphate pathway, galactose metabolism, the TCA cycle, and butanoate metabolism. In the combined analysis and Western blot results, a significant positive correlation was observed between galactose and Aldo-keto reductase family 1 member B1 (AKR1B1) (P < 0.05), which has the ability to convert galactose into galactol. Furthermore, the addition of galactose to thawed semen improved sperm motility by increasing AKR1B1 protein in sperm and was associated with the content of ATP. These data identify differential metabolites between fresh and frozen-thawed SP and suggest that galactose is a valuable additive for cryopreserved sperm, providing a theoretical basis for further exploration of the refrigerant formula for yak sperm cryopreservation.

Oxidative stress and cryoresistance of sturgeon sperm: A review

Currently, the majority of sturgeons are relict fishes of high economic value yet endangered with extinction. Cryopreservation of sperm has great potential in fish farming and conservation, but the problem of low cryoresistance of sturgeon sperm has not yet been solved. The goal of this work was to review current literature data on the causes of low tolerance of sturgeon sperm to cryodamage. The influence of cryopreservation on the parameters of physiology and metabolism of sturgeon sperm (morphology and fine ultrastructure, mobility and fertilization ability, integrity of the plasma membrane, protein, lipid and metabolite profiles, antioxidant status, DNA damage), as well as on biomarkers of oxidative stress (lipids peroxidation levels and carbonyl derivatives of proteins) is discussed. Since the development of oxidative stress is an important mechanism of sperm cryodamage induction, the review presents the literature on the role of oxygen-derived species in damage of sturgeon reproductive cells caused by cryopreservation. Particular attention is paid to the system of antioxidant protection of sturgeon seminal plasma and spermatozoa, represented by antioxidant enzymes and low molecular weight antioxidants capable of utilizing various reactive forms of oxygen and nitrogen. The review discusses the results of lipidomic and proteomic studies of sturgeon sperm, which made it possible to obtain new data on the lipid composition of cell membranes, to detect proteins involved in the protection of sturgeon spermatozoa from oxidative damage during cryopreservation. This review presents the use of «omics» technology to elucidate the mechanism of cryodamage in sturgeon sperm. Additionally, the review summarizes information on the unique anatomical, morphological, biochemical, and physiological features of sturgeon sperm, which may be associated with low cryoresistance of sturgeon, in order to establish prospects for further research on improving the methods of the conservation of sperm of these threatened species.

DIGE Analysis of Fish Tissues

Two-dimensional difference gel electrophoresis (2D-DIGE) appears to be especially useful in quantitative approaches, allowing the co-separation of proteins of control samples and proteins of treated/disease samples on the same gel, eliminating gel-to-gel variability. The principle of 2D-DIGE is to label proteins prior to isoelectric focusing and use three spectrally resolvable fluorescent dyes, allowing the independent labeling of control and experimental samples. This procedure makes it possible to reduce the number of gels in an experiment, allowing the accurate and reproducible quantification of multiple samples. 2D-DIGE has been found to be an excellent methodical tool in several areas of fish research, including environmental pollution and toxicology, the mechanisms of development and disorders, reproduction, nutrition, evolution, and ecology.

Protein profiling of testicular tissue from boars with different levels of hyperactive sperm motility

Hyperactive sperm motility is important for successful fertilization. In the present study, a proteome profiling approach was performed to identify the differences between Landrace boars with different levels of hyperactive sperm motility in liquid extended semen. Two contrasts were studied: (i) high versus low levels of sperm hyperactivity at semen collection day and (ii) high versus low change in levels of sperm hyperactivity after 96 h semen storage. Testicular samples were analyzed on a Q Exactive mass spectrometer and more than 6000 proteins were identified in the 13 samples. The most significant differentially expressed proteins were mediator complex subunit 28 (MED28), cell division cycle 37 like 1 (CDC37L1), ubiquitin specific peptidase 10 (USP10), zinc finger FYVE-type containing 26 (ZFYVE26), protein kinase C delta (PRKCD), actinin alpha 4 (ACTN4), N(alpha)-acetyltransferase 30 (NAA30), C1q domain-containing (LOC110258309) and uncharacterized LOC100512926. Of the differentially expressed proteins, 11 have previously been identified as differentially expressed at the corresponding mRNA transcript level using the same samples and contrasts. These include sphingosine kinase 1 isoform 2 (SPHK1), serine and arginine rich splicing factor 1 (SRSF1), and tubulin gamma-1 (TUBG1) which are involved in the acrosome reaction and sperm motility. A mass spectrometry approach was applied to investigate the protein profiles of boars with different levels of hyperactive sperm motility. This study identified several proteins previously shown to be involved in sperm motility and quality, but also proteins with no known function for sperm motility. Candidates that are differentially expressed on both mRNA and protein levels are especially relevant as biological markers of semen quality.

Proteomic Changes Associated With Sperm Fertilizing Ability in Meat-Type Roosters

The molecular basis of male fertility remains unclear, especially in chickens, where decades of genetic selection increased male fertility variability as a side effect. As transcription and translation are highly limited in sperm, proteins are key molecules defining their functionality, making proteomic approaches one of the most adequate methods to investigate sperm capacity. In this context, it is interesting to combine complementary proteomic approaches to maximize the identification of proteins related to sperm-fertilizing ability. In the present study, we aimed at identifying proteins related to fertility in meat-type roosters, showing fertility variability. Fertile roosters (fertility rates higher than 70% after artificial insemination) differed from subfertile roosters (fertility rates lower than 40%) in their sperm mass motility. Fertile and subfertile sperm protein contents were compared using two complementary label-free quantitative proteomic methods: Intact Cell MALDI-TOF-Mass Spectrometry and GeLC-MS/MS. Combining the two strategies, 57 proteins were identified as differentially abundant. Most of them were described for the first time as differentially abundant according to fertility in this species. These proteins were involved in various molecular pathways including flagellum integrity and movement, mitochondrial functions, sperm maturation, and storage in female tract as well as oocyte–sperm interaction. Collectively, our data improved our understanding of chicken sperm biology by revealing new actors involved in the complexity of male fertility that depends on multiple cell functions to reach optimal rates. This explains the inability of reductionist in vitro fertility testing in predicting male fertility and suggests that the use of a combination of markers is a promising approach.

Bioenergetics of fish spermatozoa with focus on some herring (Clupea harengus) enzymes

Herring (Clupea harengus) shows the unique behavior of reproductive biology in which spermatozoa remains in the surrounding media for extended periods. It is an excellent model for studying the malic enzyme (ME) and creatine kinase (CK) biochemical properties because of their high activity and variability of molecular isoforms. The specific activity of NAD-preferring ME in herring spermatozoa is the highest among other fish spermatozoa and is localized in its large mitochondrion. Two different CK isoforms, dimer and octamer, were detected in herring spermatozoa. It has already been shown that CK isoforms play an important role in energy homeostasis by catalyzing a reversible transfer of the phosphate of ATP to creatine to yield ADP and creatine phosphate (CP) (creatine/CP circuit). Two lactate dehydrogenase (LDH) isoenzymes were also shown in herring spermatozoa, LDH-B4 and LDH-A2B2. In this mini-review, the role of ME and energy transport system with easily diffusible creatine and CP in herring spermatozoa is discussed.

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.

Maladaptation of trout spermatozoa to fresh water is related to oxidative stress and proteome changes

Rainbow trout sperm are 'maladapted' to freshwater spawning, resulting in shorter duration of sperm motility in fresh water compared to buffered saline solution. We hypothesized that different sperm motility-activating media have various effects on sperm motility characteristics and oxidative stress, as well as on the protein profiles of rainbow trout sperm. We designed an experimental model for activation of rainbow trout sperm motility in different osmotic conditions: (i) isosmotic and (ii) hypoosmotic. Spermatozoa activation with hypoosmotic solution was associated with lower values for sperm motility parameters (52%) and an induced increase in ROS level (19.4%) in comparison to isosmotic activation with isosmotic solution (67 and 9.5% for sperm motility and ROS, respectively). Hypoosmotic activation resulted in a higher number of differentially abundant sperm proteins (out of which 50 were identified) compared to isosmotic conditions, where only two spots of protein disulfide-isomerase 6 were changed in abundance. The proteins are mainly involved in the TCA cycle, tight and gap junction signaling, Sertoli cell-Sertoli cell junction signaling and asparagine degradation. Our results, for the first time, indicate that during hypoosmotic activation of sperm motility, osmotic stress triggers oxidative stress and disturbances mostly to structural proteins and metabolic enzymes. Our results strongly suggest that comparative physiological and biochemical analysis of rainbow trout sperm characteristics in isosmotic and hypoosmotic conditions could be a useful model for studying the mechanism of sperm activation in salmonid fish.

Proteomic and metabolomic insights into the functions of the male reproductive system in fishes

Proteomics and metabolomics are emerging and powerful tools to unravel the complex molecular mechanisms regulating reproduction in male fish. So far, numerous proteins and metabolites have been identified that provide us with valuable information to conduct a comprehensive analysis on seminal plasma and spermatozoa components and their functions. These analyses have allowed a better understanding of the blood-testis barrier functions, the molecular mechanisms underlying spermatogenesis, spermatozoa maturation, motility signaling, and competition as well as the mechanism of cryodamage to sperm structure and functions. To extend, proteins that undergo posttranslational modification, such as phosphorylation and oxidation in response to spermatozoa motility activation and cryopreservation, respectively, have been identified. Proteomic studies resulted in identification of potential proteins that can be used as biomarkers for sperm quality and freezability to enable the control of artificial reproduction, and to improve methods for long-term preservation (cryopreservation) of sperm. The different proteins expressed in the spermatozoa of neomales and normal males can also provide new insights into development of methods for separating X and Y fish sperm, and changes in the protein profiles in haploid and diploid spermatozoa will provide new perspectives to better understand the mechanism of male polyploidy. Overall, the knowledge gained by proteomic and metabolomic studies is important from basic to applied sciences for the development and/or optimisation of techniques in controlled fish reproduction.

Comparative proteomic analysis of high- and low-fertile buffalo bull spermatozoa for identification of fertility-associated proteins

The present study identified few potential proteins in the spermatozoa of buffalo bulls that can be used as an aid in fertility determination through comparative proteomics. The sperm proteome of high-fertile buffalo bulls was compared with that of low-fertile buffalo bulls using two-dimensional difference gel electrophoresis (2D-DIGE), and the differentially expressed proteins were identified through mass spectrometric method. The protein interaction network and the functional bioinformatics analysis of differentially expressed proteins were also carried out. In the spermatozoa of high-fertile bulls, 10 proteins were found overexpressed and 15 proteins were underexpressed at the level of twofold or more (p ≤ 0.05). The proteins overexpressed in high-fertile spermatozoa were PDZD8, GTF2F2, ZNF397, KIZ, LOH12CR1, ACRBP, PRSS37, CYP11B2, F13A1 and SPO11, whereas those overexpressed in low-fertile spermatozoa were MT1A, ATP5F1, CS, TCRB, PRODH2, HARS, IDH3A, SRPK3, Uncharacterized protein C9orf9 homolog isoform X4, TUBB2B, GPR4, PMP2, CTSL1, TPPP2 and EGFL6. The differential expression ranged from 2.0- to 6.1-fold between the two groups, where CYP11B2 was high abundant in high-fertile spermatozoa and MT1A was highly abundant in low-fertile spermatozoa. Most of the proteins overexpressed in low-fertile spermatozoa were related to energy metabolism and capacitation factors, pointing out the possible role of pre-mature capacitation and cryo-damages in reducing the fertility of cryopreserved buffalo spermatozoa.

Identification of oxidatively modified proteins due to cryopreservation of carp semen

During semen cryopreservation, spermatozoa are exposed to physical and chemical stressors that result in their functional and structural damage. Growing evidence suggests that most cryoinjuries result from oxidative stress accompanying sperm cryopreservation. Elevated amounts of reactive oxygen species (ROS) generated during cryopreservation can react with sperm macromolecules, including proteins. The goal of this study was to investigate the oxidative modifications (measured as carbonylation level changes) of carp spermatozoa proteins triggered by the cryopreservation process. Flow cytometry and computer-assisted sperm analysis were used to evaluate changes in viability, ROS level, and motility of spermatozoa. The spermatozoa proteins that were specifically carbonylated were identified and quantified by Western blotting, in conjunction with 2-dimensional electrophoresis (2D-oxyblot) and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry. Cryopreservation decreased spermatozoa motility (P < 0.01) and viability (P < 0.0001) and significantly increased (P < 0.0001) the number of ROS-positive cells. We identified 25 protein spots, corresponding to 19 proteins, with increases (P < 0.05) in carbonylation level due to freezing/thawing. The identified proteins are involved in motility, metabolism, calcium-ion binding, signal transduction, protein folding, and intracellular transport. The results suggest that carbonylation of flagellar proteins can result in motility disorders and may contribute to the reduced percentage of motile spermatozoa and disturbances in movement trajectory after sperm cryopreservation. Moreover, cryopreservation may contribute to impaired cellular respiration, ATP regeneration, disturbances of Ca2+ turnover, unfolding of cytoplasmic or histone proteins, disturbances of cell signaling and intracellular transport, and reduced membrane stability. Our results contribute to the knowledge concerning cryoinjury and to further development of a modified cryopreservation procedure aimed at minimizing oxidative damage of carp sperm proteins.

Cryopreservation effects on a viable sperm sterlet (Acipenser ruthenus) subpopulation obtained by a Percoll density gradient method

In many fish species, sperm cryopreservation has deleterious effects and leads to a significant decrease in spermatozoa viability. However, the effect of cryopreservation on sperm cells that survive this process and are still viable is not fully understood. The objective of this study was to compare the viability and proteomes of fresh and cryopreserved sterlet (Acipenser ruthenus) sperm samples before and after live-dead cell separation using Percoll density gradient centrifugation. Both fresh and cryopreserved sperm samples were divided into two groups (with or without application of Percoll separation). At each step of the experiment, sperm quality was evaluated by video microscopy combined with integrated computer-assisted sperm analysis software and flow cytometry for live-dead sperm viability analysis. Sperm motility and the percentage of live cells were reduced in the cryopreserved group compared to the fresh group from 89% to 33% for percentage of motility and from 96% to 70% for live cells. Straight line velocity and linearity of track were significantly lower in cryopreserved samples than in those separated by Percoll before and after cryopreservation. However, the percentages of motile and live spermatozoa were higher than 90% in samples subjected to Percoll separation. Proteomic analysis of spermatozoa by two-dimensional differences in-gel electrophoresis coupled with matrix-assisted laser-desorption/ionization time-of-flight/time-of-flight mass spectrometry revealed that 20 protein spot abundances underwent significant changes in cryopreserved samples compared to fresh ones. However, only one protein spot was significantly altered when samples before and after cryopreservation followed by Percoll separation were compared. Thus, the results of this study show that cryopreservation leads to minimal proteomic changes in the spermatozoa population, retaining high motility and viability parameters. The results also suggest that global differences in protein profiles between unselected fresh and cryopreserved samples are mainly due to protein loss or changes in the lethal and sublethal damaged cell subpopulations.

Identification of a complex population of chromatin-associated proteins in the European sea bass (Dicentrarchus labrax) sperm

A very common conception about the function of the spermatozoon is that its unique role is to transmit the paternal genome to the next generation. Most of the sperm genome is known to be condensed in many species by protamines, which are small and extremely positively charged proteins (50-70% arginine) with the functions of streamlining the sperm cell and protecting its DNA. However, more recently, it has been shown in mammals that 2-10% of its mature sperm chromatin is also associated to a complex population of histones and chromatin-associated proteins differentially distributed in the genome. These proteins are transferred to the oocyte upon fertilization and may be involved in the epigenetic marking of the paternal genome. However, little information is so far available on the additional potential sperm chromatin proteins present in other protamine-containing non-mammalian vertebrates detected through high-throughput mass spectrometry. Thus, we started the present work with the goal of characterizing the mature sperm proteome of the European sea bass, with a particular focus on the sperm chromatin, chosen as a representative of non-mammalian vertebrate protamine-containing species. Proteins were isolated by acidic extraction from purified sperm cells and from purified sperm nuclei, digested with trypsin, and subsequently the peptides were separated using liquid chromatography and identified through tandem mass spectrometry. A total of 296 proteins were identified. Of interest, the presence of 94 histones and other chromatin-associated proteins was detected, in addition to the protamines. These results provide phylogenetically strategic information, indicating that the coexistence of histones, additional chromatin proteins, and protamines in sperm is not exclusive of mammals, but is also present in other protamine-containing vertebrates. Thus, it indicates that the epigenetic marking of the sperm chromatin, first demonstrated in mammals, could be more fundamental and conserved than previously thought. Abbreviations: AU-PAGE: acetic acid-urea polyacrylamide gel electrophoresis; CPC: chromosomal passenger complex; DTT: dithiothreitol; EGA: embryonic genome activation; FDR: false discovery rate; GO: Gene Ontology; IAA: iodoacetamide; LC: liquid chromatography; LC-MS/MS: liquid chromatography coupled to tandem mass spectrometry; MS: mass spectrometry; MS/MS: tandem mass spectrometry; MW: molecular weight; PAGE: polyacrylamide gel electrophoresis; PBS: phosphate buffered saline; SDS: sodium dodecyl sulfate; SDS-PAGE: sodium dodecyl sulfate polyacrylamide gel electrophoresis; TCA: trichloroacetic acid.

DIGE Analysis of Fish Tissues

Two-dimensional difference gel electrophoresis (2D-DIGE) appears to be especially useful in quantitative approaches, allowing the co-separation of proteins of control samples from proteins of treatment/disease samples on the same gel, eliminating gel-to-gel variability. The principle of 2D-DIGE is to label proteins prior to isoelectric focusing and use three spectrally resolvable fluorescent dyes, allowing the independent labeling of control and experimental samples. This procedure makes it possible to reduce the number of gels in an experiment, allowing the accurate and reproducible quantification of multiple samples. 2D-DIGE has been found to be an excellent methodical tool in several areas of fish research, including environmental pollution and toxicology, the mechanisms of development and disorders, reproduction, nutrition, evolution, and ecology.

Proteomic characterization of fresh spermatozoa and supernatant after cryopreservation in relation to freezability of carp (Cyprinus carpio L) semen

Our recent studies suggested that the freezability of carp semen is related to seminal plasma protein profiles. Here, we aimed to compare the spermatozoa proteomes of good (GF) and poor (PF) freezability semen of carp. To achieve this, we used two-dimensional difference in gel electrophoresis followed by MALDI-TOF/TOF mass spectrometry. The semen was classified as GF or PF based on sperm motility after freeze/thawing. We identified proteins enriched in spermatozoa of GF (22 proteins) and PF (18 proteins) semen. We also identified 12 proteins enriched in the supernatant after cryopreservation of PF semen. Good freezability is related to high concentrations of proteins involved in the maintenance of flagella structure, membrane fluidity, efficient control of Ca²⁺ and sperm motility, energy production, and antioxidative protection, which likely reflects the full maturation status of spermatozoa of GF semen. On the other hand poor freezability seems to be related to the presence of proteins identified as released in high quantities from cryopreserved sperm of PF. Thus, the identified proteins might be useful bioindicators of freezing resilience and could be used to screen carp males before cryopreservation, thus improve long-term sperm preservation in carp. Data are available via ProteomeXchange with identifier PXD008187.

Different expression patterns of sperm motility-related genes in testis of diploid and tetraploid cyprinid fish†

Sperm motility is an important standard to measure the fertility of male. In our previous study, we found that the diploid spermatozoa from allotetraploid hybrid (4nAT) had longer durations of rapid and slow progressive motility than haploid spermatozoa from common carp (COC). In this study, to explore sperm motility-related molecular mechanisms, we compared the testis tissues transcriptomes from 2-year-old male COC and 4nAT. The RNA-seq data revealed that 2985 genes were differentially expressed between COC and 4nAT, including 2216 upregulated and 769 downregulated genes in 4nAT. Some differentially expressed genes, such as tubulin genes, dynein, axonemal, heavy chain(dnah) genes, mitogen-activated protein kinase(mapk) genes, tektin 4, FOX transcription factors, proteasome genes, and ubiquitin carboxyl-terminal hydrolase(uchl) genes, are involved in the regulation of cell division, flagellar and ciliary motility, gene transcription, cytoskeleton, energy metabolism, and the ubiquitin–proteasome system, suggesting that these genes were related to sperm motility of the 4nAT. We confirmed the differential expression of 12 such genes in 4nAT by quantitative PCR. By western blotting, we also confirmed increased expression of Uchl3 in 4nAT testis. In addition, we identified 1915 and 2551 predicted long noncoding RNA (lncRNA) transcripts from testis tissue transcriptomes of COC and 4nAT, respectively. Of these, 1575 lncRNAs were specifically expressed in 4nAT and 939 were specifically expressed in COC. This study provides insights into the transcriptome profile of testis tissues from diploid and tetraploid, which are useful for research on regulatory mechanisms behind sperm motility in male polyploidy.

Variability in the protein profiles in spermatozoa of two sturgeon species

Conventional sperm analysis (i.e., motility and fertility) has been used to evaluate sperm quality. Understanding the quality of sperm on the molecular level in the sturgeons, Acipenser baerii and A. schrenckii, is essential for the improvement of the conservation of genetic resources and farming performance. In this study, we used the iTRAQ proteomics approach to perform proteomic profiling of spermatozoa associated with sperm quality in sturgeons (Data are available via ProteomeXchange with identifier PXD006108). The results showed 291 and 359 differentially expressed proteins in A. baerii and A. schrenckii, respectively, of which 72 were common to both species and all were upregulated in high quality compared with low quality samples. The differentially expressed proteins were mainly categorized into the generation of precursor metabolites and energy and oxidation, and they were localized to the mitochondria. Three distinguishing pathways, Arginine and proline metabolism, Pyruvate metabolism and the Citrate cycle (TCA cycle) were found to play an important role in energy metabolism, and some substrates could be used in the sperm medium for storage and cryopreservation. The quantity levels of two proteins, CKMT1 and LDHB, were verified by western blot analysis. Moreover, other potential biomarkers involved in oxidation reduction, ubiquitin-proteasome-dependent proteolysis, chaperones and binding activity were also discussed. Our study is the first to use the iTRAQ-based proteomics approach to analyse the sturgeon spermatozoa proteome, and the results that we obtained are valuable for the prediction of sperm quality and reproduction management in these threatened species.

Protein phosphorylation in spermatozoa motility of Acipenser ruthenus and Cyprinus carpio

Spermatozoa of externally fertilizing freshwater fish possess several different modes of motility activation. Spermatozoa of common carp (Cyprinus carpio L.) are activated by hypoosmolality, whereas spermatozoa of sterlet (Acipenser ruthenus) require Ca2+ and low concentration of K+ for motility activation. Intracellular signaling differs between these two species as well, particularly in terms of utilization of secondary messengers (cAMP and Ca2+), and kinase activities. The current study was performed in order to determine the importance of protein phosphorylation and protein kinases for activation of sperm motility in carp and sterlet. Treatment with kinase inhibitors indicates that protein kinases A and C (PKA and PKC) participate in spermatozoa motility of both species. Immunodetection of phospho-(Ser/Thr) PKA substrates shows that phosphorylated proteins are localized differently in spermatozoa of carp and sterlet. Strong phosphorylation of PKC substrate was observed in flagella of sterlet spermatozoa, whereas in carp sperm, PKC substrates were lightly phosphorylated in the midpiece and flagella. Motility activation induced either phosphorylation or dephosphorylation on serine, threonine and tyrosine residues of numerous proteins in carp and sterlet spermatozoa. Proteomic methods were used to identify proteins whose phosphorylation state changes upon the initiation of sperm motility. Numerous mitochondrial and glycolytic enzymes were identified in spermatozoa of both species, as well as axonemal proteins, heat shock proteins, septins and calcium-binding proteins. Our results contribute to an understanding of the roles of signaling molecules, protein kinases and protein phosphorylation in motility activation and regulation of two valuable fish species, C. carpio and A. ruthenus.