DNA repair genes play a variety of roles in the development of fish embryos.

Embryogenesis is one of the most important life stages because it determines an organism's healthy growth. However, embryos of externally fertilizing species, such as most fish, are directly exposed to the environment during development and may be threatened by DNA damaging factors (pollutants, UV, reactive oxygen species). To counteract the negative effects of DNA fragmentation, fish embryos evolved complex damage response pathways. DNA repair pathways have been extensively studied in some fish species, such as zebrafish (Danio rerio). Our literature review, on the other hand, revealed a paucity of knowledge about DNA damage response and repair in non-model aquaculture fish species. Further, several pieces of evidence underlie the additional role of DNA repair genes and proteins in organogenesis, spatiotemporal localization in different tissue, and its indispensability for normal embryo development. In this review, we will summarize features of different DNA repair pathways in course of fish embryo development. We describe how the expression of DNA repair genes and proteins is regulated during development, their organogenetic roles, and how the expression of DNA repair genes changes in response to genotoxic stress. This will aid in addressing the link between genotoxic stress and embryo phenotype. Furthermore, available data indicate that embryos can repair damaged DNA, but the effects of early-life stress may manifest later in life as behavioral changes, neoplasia, or neurodegeneration. Overall, we conclude that more research on DNA repair in fish embryos is needed.

Transcriptome and Proteome Analyses Reveal Stage-Specific DNA Damage Response in Embryos of Sturgeon (Acipenser ruthenus).

DNA damage during early life stages may have a negative effect on embryo development, inducing mortality and malformations that have long-lasting effects during adult life. Therefore, in the current study, we analyzed the effect of DNA damage induced by genotoxicants (camptothecin (CPT) and olaparib) at different stages of embryo development. The survival, DNA fragmentation, transcriptome, and proteome of the endangered sturgeon Acipenser ruthenus were analyzed. Sturgeons are non-model fish species that can provide new insights into the DNA damage response and embryo development. The transcriptomic and proteomic patterns changed significantly after exposure to genotoxicants in a stage-dependent manner. The results of this study indicate a correlation between phenotype formation and changes in transcriptomic and proteomic profiles. CPT and olaparib downregulated oxidative phosphorylation and metabolic pathways, and upregulated pathways involved in nucleotide excision repair, base excision repair, and homologous recombination. We observed the upregulated expression of zona pellucida sperm-binding proteins in all treatment groups, as well as the upregulation of several glycolytic enzymes. The analysis of gene expression revealed several markers of DNA damage response and adaptive stress response, which could be applied in toxicological studies on fish embryos. This study is the first complex analysis of the DNA damage response in endangered sturgeons.

High-content analysis of larval phenotypes for the screening of xenobiotic toxicity using Phallusia mammillata embryos.

In recent years, pollution of surface waters with xenobiotic compounds became an issue of concern in society and has been the object of numerous studies. Most of these xenobiotic compounds are man-made molecules and some of them are qualified as endocrine disrupting chemicals (EDCs) when they interfere with hormones actions. Several studies have investigated the teratogenic impacts of EDCs in vertebrates (including marine vertebrates). However, the impact of such EDCs on marine invertebrates is much debated and still largely obscure. In addition, DNA-altering genotoxicants can induce embryonic malformations. The goal of this study is to develop a reliable and effective test for assessing toxicity of chemicals using embryos of the ascidian (Phallusia mammillata) in order to find phenotypic signatures associated with xenobiotics. We evaluated embryonic malformations with high-content analysis of larval phenotypes by scoring several quantitative and qualitative morphometric endpoints on a single image of Phallusia tadpole larvae with semi-automated image analysis. Using this approach we screened different classes of toxicants including genotoxicants, known or suspected EDCs and nuclear receptors (NRs) ligands. The screen presented here reveals a specific phenotypic signature for ligands of retinoic acid receptor/retinoid X receptor. Analysis of larval morphology combined with DNA staining revealed that embryos with DNA aberrations displayed severe malformations affecting multiple aspects of embryonic development. In contrast EDCs exposure induced no or little DNA aberrations and affected mainly neural development. Therefore the ascidian embryo/larval assay presented here can allow to distinguish the type of teratogenicity induced by different classes of toxicants.

Ancient Sturgeons Possess Effective DNA Repair Mechanisms: Influence of Model Genotoxicants on Embryo Development of Sterlet, Acipenser ruthenus.

DNA damage caused by exogenous or endogenous factors is a common challenge for developing fish embryos. DNA damage repair (DDR) pathways help organisms minimize adverse effects of DNA alterations. In terms of DNA repair mechanisms, sturgeons represent a particularly interesting model due to their exceptional genome plasticity. Sterlet (Acipenser ruthenus) is a relatively small species of sturgeon. The goal of this study was to assess the sensitivity of sterlet embryos to model genotoxicants (camptothecin, etoposide, and benzo[a]pyrene), and to assess DDR responses. We assessed the effects of genotoxicants on embryo survival, hatching rate, DNA fragmentation, gene expression, and phosphorylation of H2AX and ATM kinase. Exposure of sterlet embryos to 1 µM benzo[a]pyrene induced low levels of DNA damage accompanied by ATM phosphorylation and xpc gene expression. Conversely, 20 µM etoposide exposure induced DNA damage without activation of known DDR pathways. Effects of 10 nM camptothecin on embryo development were stage-specific, with early stages, before gastrulation, being most sensitive. Overall, this study provides foundational information for future investigation of sterlet DDR pathways.

Bisphenols disrupt differentiation of the pigmented cells during larval brain formation in the ascidian.

The endocrine disruptor Bisphenol A (BPA), a widely employed molecule in plastics, has been shown to affect several biological processes in vertebrates, mostly via binding to nuclear receptors. Neurodevelopmental effects of BPA have been documented in vertebrates and linked to neurodevelopmental disorders, probably because some nuclear receptors are present in the vertebrate brain. Similarly, endocrine disruptors have been shown to affect neurodevelopment in marine invertebrates such as ascidians, mollusks or echinoderms, but whether invertebrate nuclear receptors are involved in the mode-of-action is largely unknown. In this study, we assessed the effect of BPA on larval brain development of the ascidian Phallusia mammillata. We found that BPA is toxic to P. mammillata embryos in a dose-dependent manner (EC50: 11.8µM; LC50: 21µM). Furthermore, micromolar doses of BPA impaired differentiation of the ascidian pigmented cells, by inhibiting otolith movement within the sensory vesicle. We further show that this phenotype is specific to other two bisphenols (BPE and BPF) over a bisphenyl (2,2 DPP). Because in vertebrates the estrogen-related receptor gamma (ERRγ) can bind bisphenols with high affinity but not bisphenyls, we tested whether the ascidian ERR participates in the neurodevelopmental phenotype induced by BPA. Interestingly, P. mammillata ERR is expressed in the larval brain, adjacent to the differentiating otolith. Furthermore, antagonists of vertebrate ERRs also inhibited the otolith movement but not pigmentation. Together our observations suggest that BPA may affect ascidian otolith differentiation by altering Pm-ERR activity whereas otolith pigmentation defects might be due to the known inhibitory effect of bisphenols on tyrosinase enzymatic activity.

Potential roles of nuclear receptors in mediating neurodevelopmental toxicity of known endocrine-disrupting chemicals in ascidian embryos.

Endocrine Disrupting Chemicals (EDCs) are molecules able to interfere with the vertebrate hormonal system in different ways, a major one being the modification of the activity of nuclear receptors (NRs). Several NRs are expressed in the vertebrate brain during embryonic development and these NRs are suspected to be responsible for the neurodevelopmental defects induced by exposure to EDCs in fishes or amphibians and to participate in several neurodevelopmental disorders observed in humans. Known EDCs exert toxicity not only on vertebrate forms of marine life but also on marine invertebrates. However, because hormonal systems of invertebrates are poorly understood, it is not clear whether the teratogenic effects of known EDCs are because of endocrine disruption. The most conserved actors of endocrine systems are the NRs which are present in all metazoan genomes but their functions in invertebrate organisms are still insufficiently characterized. EDCs like bisphenol A have recently been shown to affect neurodevelopment in marine invertebrate chordates called ascidians. Because such phenotypes can be mediated by NRs expressed in the ascidian embryo, we review all the information available about NRs expression during ascidian embryogenesis and discuss their possible involvement in the neurodevelopmental phenotypes induced by EDCs.

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.

The in vitro effect of nonylphenol, propranolol, and diethylstilbestrol on quality parameters and oxidative stress in sterlet (Acipenser ruthenus) spermatozoa.

The sturgeon is a highly endangered fish mostly due to over-fishing, habitat destruction, and water pollution. Nonylphenol (NP), propranolol (PN), and diethylstilbestrol (DES) are multifunctional xenobiotic compounds used in a variety of commercial and industrial products. The mechanism by which these xenobiotic compounds interfere with fish reproduction is not fully elucidated. This study assessed the effect of NP, PN, and DES on motility parameters, membrane integrity, and oxidative/antioxidant status in sterlet Acispenser ruthenus spermatozoa. Spermatozoa were incubated with several concentrations of target substances for 1h. Motility rate and velocity of spermatozoa decreased in the presence of xenobiotics in a dose-dependent manner compared with controls. A significant decrease in membrane integrity was recorded with exposure to 5µM of NP, 25µM of PN, and 50µM of DES. After 1h exposure at higher tested concentrations NP (5-25µM), PN (25-100µM), and DES (50-200µM), oxidative stress was apparent, as reflected by significantly higher levels of protein and lipid oxidation and significantly greater superoxide dismutase activity. The results demonstrated that NP, PN, and DES can induce reactive oxygen species stress in fish spermatozoa, which could impair sperm quality and the antioxidant defence system and decrease the percentage of intact sperm cells.

Ascidians: An Emerging Marine Model for Drug Discovery and Screening.

Ascidians (tunicates; sea squirts) are marine animals which provide a source of diverse, bioactive natural products, and a model for toxicity screenings. Compounds isolated from ascidians comprise an approved anti-tumor drug and many others are potent drug leads. Furthermore, the use of invertebrate embryos for toxicological screening tests or analysis offers the possibility to image a large number of samples for high throughput screens. Ascidians are members of a sister clade to the vertebrates and make a vertebrate-like tadpole larva composed of less than 3000 cells in 18 hours. The neural complex of the ascidian larva is made of only 350 cells (of which 100 are neurons) and functional genomic studies have now uncovered numerous GRNs underpinning neural specification and differentiation. Numerous studies showed that brain formation in ascidians is sensitive to toxic insults especially from endocrine disruptors making them a suitable model to study neurodevelopmental defects. Modern techniques available for ascidians, including transgenic embryos where 3D time lapse imaging of GFPexpressing reporter constructs can be analyzed, now permit numerous end-points to be evaluated in order to test the specific mode of action of many compounds. This review summarizes the key evidence suggesting that ascidian embryos are a favorable embryological model to study neurodevelopmental toxicity of different compounds with molecular and cellular end-points. We predict that ascidians may become a significant source of marine blue biotechnologies in the 21st century.

The effect of reactive oxygen species on motility parameters, DNA integrity, tyrosine phosphorylation and phosphatase activity of common carp (Cyprinus carpio L.) spermatozoa.

The effect of reactive oxygen species production on the motility parameters, DNA integrity, acid phosphatase activity, and protein tyrosine phosphorylation in spermatozoa of the common carp (Cyprinus carpio) was investigated. Spermatozoa were exposed to different concentrations of xanthine and xanthine oxidase (X-XO) either in the presence or absence of antioxidants for 15 and 60 min. A dose- and time-dependent reduction in spermatozoa motility and velocity was observed. Comet assays showed a dramatic increase in DNA fragmentation after 15 min. Changes in tyrosine phosphorylation of spermatozoa proteins were observed by Western blotting with anti-phosphotyrosine antibodies, and proteins of interest were identified by mass spectrometry. After a 60 min exposure to X-XO, O-linked N-acetylglucosamine transferase, isoform 4 was phosphorylated and septin-8-A was dephosphorylated. Acid phosphatase activity also decreased in a dose-dependent manner after a 60 min exposure to oxidative stress. The results demonstrate that oxidative stress impaired functional variables (sperm motility, velocity, DNA integrity) of carp spermatozoa, and altered intracellular signalling pathways through changes in tyrosine phosphorylation and acid phosphatase activity.

Isolation and transplantation of sturgeon early-stage germ cells.

We report, for the first time, a series of baseline techniques comprising isolation and transplantation of female and male early-stage germ cells in sturgeon to generate a germline chimera as a potential tool for surrogate reproduction and gene banking. Cells were dissociated from testis, characterized by mostly spermatogonia, and from ovary, exclusively comprising oogonia and previtellogenic oocytes, of Acipenser baerii, using 0.3% trypsin (2 hours, 23 °C) dissolved in PBS, isotonic with blood plasma. The dissociated germ cells were sorted by Percoll gradient centrifugation followed by immunolabeling with germ cell-specific vasa antibody DDX4, while 10% to 30% Percoll solution contained 79.4% and 70.8% labeled testicular and ovarian cells. Sorted germ cells were transplanted into a cavity close to a presumptive genital ridge of newly hatched heterospecific Acipenser ruthenus larvae with fluorescein isothiocyanate-labeled endogenous primordial germ cells. The transplanted germ cells were randomly distributed in the body cavity through 30-day posttransplantation (dpt). Subsequently, the cells were organized into genital ridges 50 dpt and proliferated 90 dpt. The number of both transplanted and endogenous germ cells significantly increased from 18.1, 22.2, and 29.1 (30 dpt) to 108.5, 90.8, and 118.5 (90 dpt) in ovarian, testicular, and endogenous germ cells, respectively (P < 0.05). The efficiency of transplantation was 60% (counted 90 dpt).

Effects of tetrabrombisphenol A on DNA integrity, oxidative stress, and sterlet (Acipenser ruthenus) spermatozoa quality variables.

The sperm of sterlet (Acispenser ruthenus) was used to investigate the effect of the xenobiotic tetrabrombisphenol A (TBBPA) on sperm quality variables (ATP content, spermatozoa motility, and velocity), DNA integrity, and oxidative stress indices. Sperm was diluted to obtain a spermatozoa density of 5 × 10(8) cells/mL and exposed for 2 h to final concentrations of TBBPA (0.5, 1.75, 2.5, 5, and 10 µg/L). The oxidative stress indices, including lipid peroxidation, carbonyl derivatives of proteins, and antioxidant activity were significantly higher with increased concentrations of TBBPA. There was significantly less intracellular ATP in sperm samples at TBBPA concentrations of 2.5 µg/L and above. Spermatozoa velocity and percent motile sperm were significantly lower at each sampling time post-activation compared to controls. DNA damage expressed as percent DNA in Tail and Olive Tail moment was significantly higher with exposures ≥2.5 µg/L TBBPA. The results demonstrated that TBBPA and other xenobiotics can induce reactive oxygen species stress in fish spermatozoa, which could impair the sperm quality, DNA integrity, ATP content, and the antioxidant defense system. This study confirmed that fish spermatozoa can be used in in vitro assays for monitoring residual pollution in aquatic environments.

In vitro sperm maturation in sterlet, Acipenser ruthenus.

The aim of the study was to examine sperm maturation in sturgeon and to establish the localization of the maturation. We demonstrated that sperm maturation occurs in sturgeon outside the testes via dilution of sperm by urine. The process involves the participation of high molecular weight (>10kDa) substances and calcium ions.

In vitro effects of bisphenol A on the quality parameters, oxidative stress, DNA integrity and adenosine triphosphate content in sterlet (Acipenser ruthenus) spermatozoa.

Among endocrine disruptors, the xenoestrogen bisphenol A (BPA) deserves particular attention due to widespread human exposure. Besides hormonal effects, BPA has been suspected to be responsible for adverse effect on reproductive ability of various species. In the present study the effect of BPA on the quality parameters, oxidative stress, the DNA integrity and intracellular ATP content of sterlet (Acipenser ruthenus) spermatozoa were investigated in vitro. Fish spermatozoa were exposed to concentrations of BPA possibly occurring in nature (0.5, 1.75, 2.5, 5 and 10µg/L) for 2h. Results revealed that BPA significantly decreased spermatozoa motility and velocity of spermatozoa at concentration of BPA 2.5-10µg/L. Significant positive correlation (r=0.713, P<0.05) was found between percent motile spermatozoa and ATP content. Oxidative stress was observed at concentrations 1.75-10µg/L, as reflected by significantly higher levels of protein and lipid oxidation and superoxide dismutase activity. Intracellular ATP content of spermatozoa decreased with increasing concentrations of BPA. A dramatic increase in DNA fragmentation expressed as percent tail DNA (2.2%±0.46) and Olive tail moment (0.37±0.09 arbitrary units) was recorded at concentrations of 1.75µg/L and above. The present study confirms that concentrations of BPA that can be encountered in nature are capable to induce oxidative stress, leading to impaired sperm quality, DNA fragmentation and intracellular ATP content.

The in vitro effect of duroquinone on functional competence, genomic integrity, and oxidative stress indices of sterlet (Acipenser ruthenus) spermatozoa.

The sturgeon is a highly endangered fish species mostly due to over-fishing, habitat destruction, and water pollution. Duroquinone (derivative of 1,4-benzoquinone) is a xenobiotic compound widespread in the environment. The effect of duroquinone on motility, DNA integrity, and oxidative stress indices in sterlet, Acispenser ruthenus, spermatozoa was investigated. Sterlet sperm was exposed for 2h to duroquinone at concentrations of 25, 50, 100, and 150 µM. Spermatozoa motility, velocity, and ATP content were significantly decreased with exposure to duroquinone. The level of DNA damage significantly increased at concentrations of 50 µM and above. Oxidative stress indices (lipid peroxidation and content of carbonyl proteins) and superoxide dismutase (SOD) activity increased significantly with increasing concentrations of duroquinone. Oxidative stress in sterlet spermatozoa induced by duroquinone was shown to impair spermatozoa DNA integrity, motility parameters, and the antioxidant defense system. Spermatozoa motility, content of carbonyl proteins, and SOD activity were shown to be sensitive biomarkers, exhibiting strong responses to low concentrations of the xenobiotic. Results also suggested that fish spermatozoa in vitro assays may provide a simple and efficient means of monitoring residual pollutants in the aquatic environment.

Influence of environmentally relevant concentrations of vinclozolin on quality, DNA integrity, and antioxidant responses of sterlet Acipenser ruthenus spermatozoa.

The effects of vinclozolin (VIN), an anti-androgenic fungicide, on quality, oxidative stress, DNA integrity, and ATP level of sterlet (Acipenser ruthenus) spermatozoa were investigated in vitro. Fish spermatozoa were incubated with different concentrations of vinclozolin (0.5, 2, 10, 15, 20 and 50 µg/l) for 2 h. A dose-dependent reduction in spermatozoa motility and velocity was observed at concentrations of 2-50 µg/l. A dramatic increase in DNA fragmentation was recorded at concentrations 10 µg/l and above. After 2 h exposure at higher test concentrations (10-50 µg/l), oxidative stress was apparent, as reflected by significantly higher levels of protein and lipid oxidation and significantly greater superoxide dismutase activity. Intracellular ATP content of spermatozoa decreased with increasing concentrations of VIN. The results demonstrated that VIN can induce reactive oxygen species stress in fish spermatozoa, which could impair the sperm quality, DNA integrity, ATP content, and the antioxidant defense system.