Variation of the genetic expression pattern after exposure to estradiol-17beta and 4-nonylphenol in male zebrafish (Danio rerio)

Multi-omic approach to evaluate the response of gilt-head sea bream (Sparus aurata) exposed to the UV filter sulisobenzone

Sulisobenzone (BP-4) is one of the benzophenone type UV filters most frequently detected in aquatic ecosystems. As a suspected endocrine disrupting compound, scarce information is available yet about other molecular effects and its mechanism of action. Here, we used an integrated transcriptomic and metabolomic approach to improve the current understanding on the toxicity of BP-4 towards aquatic species. Gilt-head sea bream individuals were exposed at environmentally relevant concentrations (10 μg L^-1) for 22 days. Transcriptomic analysis revealed 371 differentially expressed genes in liver while metabolomic analysis identified 123 differentially modulated features in plasma and 118 in liver. Integration of transcriptomic and metabolomic data showed disruption of the energy metabolism (>10 pathways related to the metabolism of amino acids and carbohydrates were impacted) and lipid metabolism (5 glycerophospholipids and the expression of 3 enzymes were affected), suggesting oxidative stress. We also observed, for the first time in vivo and at environmental relevant concentrations, the disruption of several enzymes involved in the steroid and thyroid hormones biosynthesis. DNA and RNA synthesis was also impacted by changes in the purine and pyrimidine metabolisms. Overall, the multiomic workflow presented here increases the evidence on suspected effects of BP-4 exposure and identifies additional modes of action of the compounds that could have been overlooked by using single omic approaches.

Chronic exposure to nonylphenol induces oxidative stress and liver damage in male zebrafish (Danio rerio): Mechanistic insight into cellular energy sensors, lipid accumulation and immune modulation

Nonylphenol (NP), an environmentally persistent and toxic endocrine-disrupting chemical with estrogenic properties, has severe implications on humans and wildlife. Accumulating evidence demonstrates the toxic response of NP on the developmental process, nervous system, and reproductive parameters. Although NP exposure has been implicated in chronic liver injury, the underlying events associated with hepatic pathophysiology remain less investigated. Using male zebrafish (Danio rerio) as the model, the present study investigates the impact of environmentally relevant concentrations of NP (50 and 100 μg/L, 21 days) on hepatic redox homeostasis vis-à-vis cellular energy sensors, inflammatory response, and cell death involving a mechanistic insight into estrogen receptor (ER) modulation. Our results demonstrate that congruent with significant alteration in transcript abundance of antioxidant enzymes (SOD1, SOD2, Catalase, GPx1a, GSTα1), chronic exposure to NP promotes ROS synthesis, more specifically superoxide anions and H₂O₂ levels, and lipid peroxidation potentially through elevated NOX4 expression. Importantly, NP perturbation of markers associated with fatty acid biosynthesis (srebf1/fasn) and cellular energy-sensing network (sirt1/ampkα/pgc1α) indicates dysregulated energy homeostasis, metabolic disruption, and macrovesicular steatosis, albeit with differential sensitivity at the dose level tested. Besides, elevated p38-MAPK phosphorylation (activation) together with loss of ER homeostasis at both mRNA (esr1, esr2a, esr2b) and protein (ERα, ERβ) levels suggest that NP modulation of ER abundance may have a significant influence on hepatic events. Elevated expression of inflammatory markers (TLR4, p-NF-κB, TNF-α, IL-6, IL-1β, and NOS2) and pro-apoptotic and necrotic regulators, e.g., Bax, caspase- 8, -9 and cleaved PARP1 (50 kDa), indicate chronic inflammation and hepatotoxicity in NP-exposed males. Collectively, elevated oxidative stress, metabolic dysregulation and immune modulation may lead to chronic liver injury in organisms exposed to metabolic disrupting chemicals.

Multigenerational reproduction and developmental toxicity, and HPG axis gene expression study on environmentally-relevant concentrations of nonylphenol in zebrafish

Nonylphenol (NP) is a toxic xenobiotic compound, which is persistent in the aquatic environment and is extremely toxic to aquatic organisms. Although the exact molecular mechanisms of its toxic effect are well understood, the multigenerational reproduction and multigenerational - gene expression changes caused by NP still remain unclear. The following work investigated the effect of NP on four consecutive generations of zebrafish by examining their growth and several reproductive parameters, the degree of gonad damage, and the expression of related reproduction related genes. The results showed that high concentrations (20 and 200 μg·L^-1) of NP could decrease growth and induce gonad damage in zebrafish. In addition, gnrh2 and gnrh3 genes were up-regulated, and fshβ and lhβ genes were downregulated in the hypothalamus in male zebrafish; while in female fish, the fshβ and lhβ were upregulated in P and F1 generations, and then down-regulated in the F2 generation. Meanwhile, the cyp19a1a gene was downregulated in the gonad of male fish, while the genes of fshr, lhr and esr showed a downward trend in females. Compared to P generation, F2 generation was more tolerant to higher NP concentrations (20 and 200 μg·L^-1), as was also more sensitive to lower concentrations of NP (2 μg·L^-1). Consequently, stress and damage caused by environmentally-relevant concentrations of aquatic pollutants in a vertebrate model were measured and predicted. Prevention and control measures can be actively and effectively proposed, which might be transversal to other exposed organisms, including humans. After several generations, typical transgenerational genetic phenomena might occur, which should be addressed by further studies.

Nonylphenol exposure affects mouse oocyte quality by inducing spindle defects and mitochondria dysfunction

Nonylphenol (NP) is a chemical raw material and intermediate which is mainly used in the production of surfactants, lubricating oil additives and pesticide emulsifiers. NP is reported to be toxic on the immune system, nervous system and reproductive system due to its binding to estrogen receptors. However, the toxicity of NP on mammalian oocyte quality remains unclear. In present study, we explored the effects of NP exposure on mouse oocyte maturation. Our results showed that 4 weeks of NP exposure increased the number of atresia follicles and decreased oocyte developmental competence. Transcriptomic analysis indicated that NP exposure altered the expression of more than 800 genes in oocytes, including multiple biological pathways. Subcellular structure examination indicated that NP exposure disrupted meiotic spindle organization and caused chromosome misalignment. Moreover, aberrant mitochondrial distribution and decreased membrane potential were also observed, indicating that NP exposure caused mitochondria dysfunction. Further analysis showed that NP exposure resulted in the accumulation of reactive oxygen species (ROS), which causes oxidative stress; and the NP-exposed oocytes showed positive Annexin-V signal, indicating the occurrence of early apoptosis. In summary, our results indicated that NP exposure reduced oocyte quality by affecting cytoskeletal dynamics and mitochondrial function, which further induced oxidative stress and apoptosis in mice.

Adrenal gland response to endocrine disrupting chemicals in fishes, amphibians and reptiles: A comparative overview

The adrenal gland is an essential component of the body stress response; it is formed by two portions: a steroidogenic and a chromaffin tissue. Despite the anatomy of adrenal gland is different among classes of vertebrates, the hormones produced are almost the same. During stress, these hormones contribute to body homeostasis and maintenance of ion balance. The adrenal gland is very sensitive to toxic compounds, many of which behave like endocrine-disruptor chemicals (EDCs). They contribute to alter the endocrine system in wildlife and humans and are considered as possible responsible of the decline of several vertebrate ectotherms. Considering that EDCs regularly can be found in all environmental matrices, the aim of this review is to collect information about the impact of these chemical compounds on the adrenal gland of fishes, amphibians and reptiles. In particular, this review shows the different behavior of these "sentinel species" when they are exposed to stress condition. The data supplied in this review can help to further elucidate the role of EDCs and their harmful impact on the survival of these vertebrates.

Impacts of bisphenol A analogues on zebrafish post-embryonic brain

Bisphenol A (BPA) is a widely studied and well-recognised endocrine-disrupting chemical, and one of the current issues is its safe replacement by various analogues. Using larva zebrafish as a model, the present study reveals that moderate and chronic exposure to BPA analogues such as bisphenol S, bisphenol F and bisphenol AF may also affect vertebrate neurodevelopment and locomotor activity. Several parameters of embryo-larval development were investigated, such as mortality, hatching, number of mitotically active cell, as defined by 5-bromo-2'-deoxyuridine incorporation and proliferative cell nuclear antigen labelling, aromatase B protein expression in radial glial cell and locomotor activity. Our results show that exposure to several bisphenol analogues induced an acceleration of embryo hatching rate. At the level of the developing brain, a strong up-regulation of the oestrogen-sensitive Aromatase B was also detected in the hypothalamic region. This up-regulation was not associated with effects on the numbers of mitotically active progenitors nor differentiated neurones in the preoptic area and in the nuclear recessus posterior of the hypothalamus zebrafish larvae. Furthermore, using a high-throughput video tracking system to monitor locomotor activity in zebrafish larvae, we show that some bisphenol analogues, such as bisphenol AF, significantly reduced locomotor activity following 6 days of exposure. Taken together, our study provides evidence that BPA analogues can also affect the neurobehavioural development of zebrafish.

Prioritizing selected PPCPs on the basis of environmental and toxicogenetic concerns: A toxicity estimation to confirmation approach

Pharmaceuticals and personal care products (PPCPs), the pollutants of emerging concerns, present potential risks to the ecological environment. This study focused on the prioritization of widely used selected PPCPs belonging to two categories:personal care products (PCPs) and non-steroidal anti-inflammatory drugs (NSAIDs). We predicted the toxicogenetic endpoints of PPCPs and then confirmed them using experimental approaches. Our results revealed a significant similarity in the findings obtained through both approaches, indicating NSAIDs with relatively high environmental impacts and in vitro/vivo toxicity. Experimental approach revealed that musk xylene (MX) from PCPs and DIC from NSAIDs as individual chemicals of priority concern showed elevated environmental impacts and significantly induced pi3k-akt-mTOR in vitro. Similarly, propyl paraben (PP) from PCPs and diclofenac (DIC) from NSAIDs caused significant cytotoxicity and DNA damage in vitro. Moreover, PP and MX from the PCPs group and naproxen (NAP) and DIC from the NSAIDs group induced developmental toxicity and perturbations to phases I, II, and III detoxification pathways in vivo. In addition, MX and DIC as priority PPCPs inhibited hematopoiesis and hepatogenesis in vivo. Apart from the specific effects, PPCPs can be ranked as: MX > PP > methylparaben (MP) for PCPs, and DIC > NAP > ibuprofen (IBU) for NSAIDs, regarding their toxic and environmental concerns.

Concentration-dependent effects of 17β-estradiol and bisphenol A on lipid deposition, inflammation and antioxidant response in male zebrafish (Danio rerio)

Environmental estrogenic compounds are important pollutants, which are widely distributed in natural water bodies. They produce various adverse effects on fish, but their concentration-dependent toxicities in fish metabolism and health are not fully understood. This study investigated the effects of 17β-estradiol (E2) and bisphenol A (BPA) at low and high concentrations on lipid deposition, inflammation and antioxidant response in male zebrafish. We measured fish growth parameters, gonad development, lipid contents and the activities of inflammatory and antioxidant enzymes, as well as their mRNA expressions. All E2 and BPA concentrations used increased body weight, damaged gonad structure and induced feminization in male zebrafish. The exposure of zebrafish to E2 and BPA promoted lipid accumulation by increasing total fat, liver triglycerides and free fatty acid contents, and also upregulated lipogenic genes expression, although they decreased total cholesterol content. Notably, zebrafish exposed to low concentrations of E2 (200 ng/L) and BPA (100 μg/L) had higher lipid synthesis and deposition compared to high concentrations (2000 ng/L and 2000 μg/L, respectively). However, the high concentrations of E2 and BPA increased inflammation and antioxidant response. Furthermore, BPA caused greater damage to fish gonad development and more severe lipid peroxidation compared to E2. Overall, the results suggest that the toxic effects of E2 and BPA on zebrafish are concentration-dependent such that, the relative low concentrations used induced lipid deposition, whereas the high ones caused adverse effects on inflammation and antioxidant response.

Gonadal, body color, and genotoxic alterations in Lithobates catesbeianus tadpoles exposed to nonylphenol

Endocrine disrupting chemicals are one of the most important factors contributing to worldwide amphibian decline. The 4-nonylphenol (NP) is a degradation product of several compounds, such as detergents and pesticides, affecting the aquatic environment. Here, we test whether treatment with NP has an effect on developing ovarian tissue, nuclear abnormalities in erythrocytes, and body darkness in pre-metamorphic tadpoles of the bullfrog Lithobates catesbeianus. Tadpoles were exposed for 14 days to three different concentrations of NP (1, 10, and 100 μg/L) besides the control group, which was maintained only with water. After determining body coloration, animals were euthanized and gonads and blood were collected and processed for histology and genotoxic analysis. Even though most animals were females, intersex tadpoles were observed in control and treated groups and there were no males in any group. The highest concentration of NP showed an increase in atretic oocytes, but the area corresponding to somatic compartment and early and late germ cells were not affected. Furthermore, all treated groups presented higher amount of nuclear abnormalities in erythrocytes and body darkening when compared with the control group. These results suggest that NP causes genetic damage and morphological alterations in L. catesbeianus tadpoles by disrupting oogenesis, inducing genotoxicity and increasing body coloration. Its effects on gonadal development could cause future impairments in reproduction, while its deleterious effects on genotoxicity and body pigmentation could be used as a biomarker of effect to this compound.

Immunotoxicity of estrogen and nonylphenol on apoptosis and expression of ERs in goldfish macrophage: Opening new avenue for discovering the role of experimental model systems and sexes

The expression of estrogen receptors (ERs) and their roles in important cell processes such as apoptosis in the macrophages exposed to estrogen/xenoestrogen have remained a complex secret. This study focused on the expression of estrogen receptors (ERs) and the stimulation of apoptosis in the macrophages from the two sexes of goldfish (Carassius auratus) exposed to 17-βestradiol (E2) and nonylphenol (NP) under in vivo and in vitro conditions. For the in vivo experiment, fish were exposed to NP (10^-6 M and 10^-7 M) and E2 (10^-6 M) for 24 days. Then, the head kidney macrophages from the male and the female goldfish were isolated and assayed. For the in vitro experiments, the macrophages derived from the two sexes were cultured in L-15 medium and exposed to E2 (150 nM) and NP (10 nM and 150 nM) for 3 days. The results showed that the three isoforms of ERs (ERα, ERβ₁, ERβ₂) were expressed in the goldfish macrophages. After the exposure of macrophages to NP and E2, sex-specific increase of ERs expression and apoptosis were observed (P < 0.05). The expression of ERα after NP treatment showed the highest alteration, with the response being concentration-dependent. The most alteration of ERs expression were observed in the in vivo experiment. This study provides insight to understand how exposure of the goldfish macrophages to E2 and NP can up-regulate the transcript levels of estrogen receptor subtypes and stimulate apoptosis.

Testicular transcriptome alterations in zebrafish (Danio rerio) exposure to 17β-estradiol

The hormone 17β-estradiol (E₂) can be found in rivers, effluents, and even drinking water. Researches have demonstrated that E₂ affects various metabolic pathways through gene activation and may cause reproductive toxicity in fish. Therefore, the aim of this study was to evaluate E₂-induced toxicity via testicular transcriptome of zebrafish (Danio rerio) exposed to different concentrations (10 ng L^-1, and 100 ng L^-1) of E₂. A total of >600 significant differentially expressed genes (DEGs) were enriched among the three treatments. Short time-series expression miner analysis revealed five KEGG pathways including drug metabolism, other enzymes, calcium signaling pathway, ECM-receptor interaction, gap junction, and cell adhesion molecules. Twenty genes were selected to verify the accuracy of RNA-Seq. Other reported genes related to sex differentiation, development, energy metabolism, and other processes were found. One set of genes significantly increased/decreased/fluctuated over time, especially 12 h after E₂ exposure. Genes associated with ovaries (zp3c), and development (bmp15, gdf9, and sycp2l) were significantly upregulated with increasing E₂ concentration. E₂ and testosterone was significantly decreased by 10 (except for T) and 100 ng L^-1 E₂ exposure at 12 h. The current study demonstrated that sex differentiation, development, energy metabolism, immunity, and ribosome biogenesis in male zebrafish were all significantly affected by 17β-estradiol exposure through transcriptional alterations.

Immunotoxic effects of 4-nonylphenol on Clarias gariepinus: Cytopathological changes in hepatic melanomacrophages

Melanomacrophage centres (MMCs) play a key role in the immune response in fish. They are considered sensitive bio-monitoring structures with roles in the assessment of toxicant impacts. The aim of this study was to examine the potential histopathological effect of 4-nonylphenol (4-NP) on hepatic MMCs in Clarias gariepinus. To achieve this objective, adult male fish were divided randomly and equally into two groups: a control group and a group that was exposed to 4-NP (dissolved in water at a dose of 0.1 mg/L) for 21 days. The 4-NP-intoxicated hepatic MMCs contained numerous necrotic macrophages. Superoxide dismutase 2 was immuno-expressed in the hepatic MMCs in both groups, with no significant difference. Histomorphometric examination revealed that the sizes and numbers of MMCs were dramatically higher in the livers of 4-NP-exposed C. gariepinus than in control fish. Following 4-NP challenge, in the liver, the abundance of lipofuscin and haemosiderin pigments increased, and single-pigmented macrophages, aggregated groups of deformed red blood cells (RBCs) and macrophages were present near blood vessels and hepatic sinusoids. These results reveal that 4-NP exerts immunological effects on hepatic MMCs in C. gariepinus and support the utility of MMCs as a cytological biomarker for aquatic exposure to 4-NP.

Systems analysis of the liver transcriptome in adult male zebrafish exposed to the non-ionic surfactant nonylphenol

Nonylphenol (NP) arises from the environmental degradation of nonylphenol ethoxylates. It is a ubiquitous environmental contaminant and has been detected at levels up to 167 nM in rivers in the United States. NP is an endocrine disruptor (ED) that can act as an agonist for estrogen receptors. The Adverse Outcome Pathway (AOP) framework defines an adverse outcome as the causal result of a series of molecular initiating events (MIEs) and key events (KEs) that lead to altered phenotypes. This study examined the liver transcriptome after a 21 day exposure to NP and 17β-estradiol (E2) by exploiting the zebrafish (Danio rerio) as a systems toxicology model. The goal of this study was to tease out non-estrogenic genomic signatures associated with NP exposure using DNA microarray and RNA sequencing. Our experimental design included E2 as a positive and potent estrogenic control in order to effectively compare and contrast the 2 compounds. This approach allowed us to identify hepatic transcriptomic perturbations that could serve as MIEs for adverse health outcomes in response to NP. Our results revealed that exposure to NP was associated with differential expression (DE) of genes associated with the development of steatosis, disruption of metabolism, altered immune response, and metabolism of reactive oxygen species, further highlighting NP as a chemical of emerging concern (CEC).

New toxicogenetic insights and ranking of the selected pharmaceuticals belong to the three different classes: A toxicity estimation to confirmation approach

Tetracycline hydrochloride (TH), indomethacin (IM), and bezafibrate (BF) belong to the three different important classes of pharmaceuticals, which are well known for their toxicity and environmental concerns. However, studies are still elusive to highlight the mechanistic toxicity of these pharmaceuticals and rank them using both, the toxicity prediction and confirmation approaches. Therefore, we employed the next generation toxicity testing in 21st century (TOX21) tools and estimated the in vitro/vivo toxic endpoints of mentioned pharmaceuticals, and then confirmed them using in vitro/vivo assays. We found significant resemblance in the results obtained via both approaches, especially in terms of in vivo LC50 s and developmental toxicity that ranked IM as most toxic among the studied pharmaceuticals. However, TH appeared most toxic with the lowest estimated AC50s, the highest experimental IC50s, and DNA damages in vitro. Contrarily, IM was found as congener with priority concern to activate the Pi3k-Akt-mTOR pathway in vitro at concentrations substantially lower than that of TH and BF. Further, IM exposure at lower doses (2.79-13.97 μM) depressed the pharmaceuticals detoxification phase I (CYP450 s), phase II (UGTs, SULTs), and phase III (TPs) pathways in zebrafish, whereas, at relatively higher doses, TH (2.08-33.27 μM) and BF (55.28-884.41 μM) partially activated these pathways, which ultimately caused the developmental toxicity in the following order: IM > TH > BF. In addition, we also ranked these pharmaceuticals in terms of their particular toxicity to myogenesis, hematopoiesis, and hepatogenesis in zebrafish embryos. Our results revealed that IM significantly affected myogenesis, hematopoiesis, and hepatogenesis, while TH and BF induced prominent effects on hematopoiesis via significant downregulation of associated genetic markers, such as drl, mpx, and gata2a. Overall, our findings confirmed that IM has higher toxicity than that of TH and BF, therefore, the consumption of these pharmaceuticals should be regulated in the same manner to ensure human and environmental safety.

Adverse stimulation of 4-nonylphenol in abnormal reproductive organs of female chickens

4-Nonylphenol (4-NP) is a known endocrine disrupting chemical and a persistent environmental contaminant. However, the 4-NP caused mechanism of reproductive toxicity still remains largely unknown in birds. In this study, female chickens (Hy-Line Variety White) were dosed via oral gavage in the early laying period with 0, 50, 100, and 200 mg 4-NP/kg/d for 60 days. Food intake and weight increase were monitored in this organism to investigate chicken growth and development. Moreover, pathological changes of reproductive organs, serum hormone, and mRNA changes on the HPOA were detected. The results showed that gonad development and maturity were retarded in female chickens, and the circulating concentrations of sex hormones were disordered in 4-NP-treated chicken. In 4-NP exposed animals, the mRNA expressions of GnRH and PRLH in hypothalamus and FSH and LH in pituitary were significantly unregulated by 4-NP. In addition, expressions of FSHR and LHR were down-regulated in ovaries of the 4-NP-treatment group, while the levels of stAR, P450scc, P450arom, 3β-HSD, and 17β-HSD were up-regulated in ovaries. Furthermore, expression of ERα in the ovaries of chicken was up-regulated, however, no significant change was observed for ERβ expression. Our results suggest that granulosa cells were an important target and severely disturbed by 4-NP.

Estrogen regulation of gene expression in the teleost fish immune system

Elucidating the mechanisms of estrogens-induced immunomodulation in teleost fish is of great importance due to the observed worldwide continuing decrease in pristine environments. However, little is know about the immunotoxicological consequences of exposure to these chemicals in fish, or of the mechanisms through which these effects are mediated. In this review, we summarize the results showing estrogens (natural or synthetic) acting through estrogen receptors and regulating specific target genes, also through microRNAs (miRNAs), leading to modulation of the immune functioning. The identification and characterization of miRNAs will provide new opportunities for functional genome research on teleost immune system and can also be useful when screening for novel molecule biomarkers for environmental pollution.

Ectopic synthesis of vitellogenin in testis and epididymis of estrogen-treated lizard Podarcis sicula

In oviparous vertebrates, vitellogenin (VTG) is the major yolk precursor synthesized in the liver of sexually mature females during the reproductive period. In males, the VTG gene is silent, but it may be activated by estradiol-17β (E2) or estrogen-like substances. Until now, extra-hepatic expression and synthesis of VTG after estrogen exposure has been reported only for aquatic vertebrates. This study demonstrates the ability of testis and epididymis of the terrestrial oviparous lacertid Podarcis sicula to synthesize VTG following E2 exposure. The results of in situ hybridization and immunohistochemistry analysis show the presence of both VTG mRNA and protein in these districts besides the known induction in the liver. The possible contemporaneous uptake of the E2-induced hepatic VTG by means of the specific vitellogenin receptor has been also evaluated. Finally, histological analysis shows that the E2-treatment during the mating season impairs spermatogenesis.

Estrogenic Effects of Several BPA Analogs in the Developing Zebrafish Brain

Important set of studies have demonstrated the endocrine disrupting activity of Bisphenol A (BPA). The present work aimed at defining estrogenic-like activity of several BPA structural analogs, including BPS, BPF, BPAF, and BPAP, on 4- or 7-day post-fertilization (dpf) zebrafish larva as an in vivo model. We measured the induction level of the estrogen-sensitive marker cyp19a1b gene (Aromatase B), expressed in the brain, using three different in situ/in vivo strategies: (1) Quantification of cyp19a1b transcripts using RT-qPCR in wild type 7-dpf larva brains exposed to bisphenols; (2) Detection and distribution of cyp19a1b transcripts using in situ hybridization on 7-dpf brain sections (hypothalamus); and (3) Quantification of the cyp19a1b promoter activity in live cyp19a1b-GFP transgenic zebrafish (EASZY assay) at 4-dpf larval stage. These three different experimental approaches demonstrated that BPS, BPF, or BPAF exposure, similarly to BPA, significantly activates the expression of the estrogenic marker in the brain of developing zebrafish. In vitro experiments using both reporter gene assay in a glial cell context and competitive ligand binding assays strongly suggested that up-regulation of cyp19a1b is largely mediated by the zebrafish estrogen nuclear receptor alpha (zfERα). Importantly, and in contrast to other tested bisphenol A analogs, the bisphenol AP (BPAP) did not show estrogenic activity in our model.

Disruption of endocrine function in H295R cell in vitro and in zebrafish in vivo by naphthenic acids

Oil sands process-affected water (OSPW) have been reported to exhibit endocrine disrupting effects on aquatic organisms. Although the responsible compounds are unknown, naphthenic acids (NAs) have been considered to be implicated. The current study was designed to investigate the endocrine disruption of OSPW extracted NAs (OS-NAs) and commercial NAs (C-NAs) using a combination of in vitro and in vivo assays. The effects of OS-NAs and C-NAs on steroidogenesis were assessed both at hormone levels and expression levels of hormone-related genes in the H295R cells. The transcriptions of biomarker genes involved in endocrine systems in zebrafish larvae were investigated to detect the effects of OS-NAs and C-NAs on endocrine function in vivo. Exposure to OS-NAs and C-NAs significantly increased production of 17β-estradiol (E2) and progesterone (P4), and decreased production of testosterone (T). Both OS-NAs and C-NAs significantly induced the expression of several genes involved in steroidogenesis. The abundances of transcripts of biomarker gene CYP19b, ERα, and VTG were significantly up-regulated in zebrafish larvae exposed to OS-NAs and C-NAs, which indicated that NAs had negative effects on estrogen-responsive gene transcription in vivo. These results indicated that NAs should be partly responsible for the endocrine disrupting effects of OSPW.

Meta-Analysis of Microarray Data of Rainbow Trout Fry Gonad Differentiation Modulated by Ethynylestradiol

Sex differentiation in fish is a highly labile process easily reversed by the use of exogenous hormonal treatment and has led to environmental concerns since low doses of estrogenic molecules can adversely impact fish reproduction. The goal of this study was to identify pathways altered by treatment with ethynylestradiol (EE2) in developing fish and to find new target genes to be tested further for their possible role in male-to-female sex transdifferentiation. To this end, we have successfully adapted a previously developed bioinformatics workflow to a meta-analysis of two datasets studying sex reversal following exposure to EE2 in juvenile rainbow trout. The meta-analysis consisted of retrieving the intersection of the top gene lists generated for both datasets, performed at different levels of stringency. The intersecting gene lists, enriched in true positive differentially expressed genes (DEGs), were subjected to over-representation analysis (ORA) which allowed identifying several statistically significant enriched pathways altered by EE2 treatment and several new candidate pathways, such as progesterone-mediated oocyte maturation and PPAR signalling. Moreover, several relevant key genes potentially implicated in the early transdifferentiation process were selected. Altogether, the results show that EE2 has a great effect on gene expression in juvenile rainbow trout. The feminization process seems to result from the altered transcription of genes implicated in normal female gonad differentiation, resulting in expression similar to that observed in normal females (i.e. the repression of key testicular markers cyp17a1, cyp11b, tbx1), as well as from other genes (including transcription factors) that respond specifically to the EE2 treatment. The results also showed that the bioinformatics workflow can be applied to different types of microarray platforms and could be generalized to (eco)toxicogenomics studies for environmental risk assessment purposes.

Identification of conserved hepatic transcriptomic responses to 17β-estradiol using high-throughput sequencing in brown trout

Estrogenic chemicals are major contaminants of surface waters and can threaten the sustainability of natural fish populations. Characterization of the global molecular mechanisms of toxicity of environmental contaminants has been conducted primarily in model species rather than species with limited existing transcriptomic or genomic sequence information. We aimed to investigate the global mechanisms of toxicity of an endocrine disrupting chemical of environmental concern [17β-estradiol (E2)] using high-throughput RNA sequencing (RNA-Seq) in an environmentally relevant species, brown trout (Salmo trutta). We exposed mature males to measured concentrations of 1.94, 18.06, and 34.38 ng E2/l for 4 days and sequenced three individual liver samples per treatment using an Illumina HiSeq 2500 platform. Exposure to 34.4 ng E2/L resulted in 2,113 differentially regulated transcripts (FDR < 0.05). Functional analysis revealed upregulation of processes associated with vitellogenesis, including lipid metabolism, cellular proliferation, and ribosome biogenesis, together with a downregulation of carbohydrate metabolism. Using real-time quantitative PCR, we validated the expression of eight target genes and identified significant differences in the regulation of several known estrogen-responsive transcripts in fish exposed to the lower treatment concentrations (including esr1 and zp2.5). We successfully used RNA-Seq to identify highly conserved responses to estrogen and also identified some estrogen-responsive transcripts that have been less well characterized, including nots and tgm2l. These results demonstrate the potential application of RNA-Seq as a valuable tool for assessing mechanistic effects of pollutants in ecologically relevant species for which little genomic information is available.

Developmental toxicity and endocrine disruption of naphthenic acids on the early life stage of zebrafish (Danio rerio)

Oil sands process-affected water (OSPW) has been reported to exhibit adverse effects on the environment and wildlife. Although the compounds responsible are unknown, naphthenic acids (NAs) have been considered to be implicated. The current study was designed to investigate whether NAs might cause developmental toxicity and endocrine disruption on the early life stage of zebrafish (Danio rerio). The success of embryo hatch was inhibited by 2.5 mg l(-1) oil sands NAs (OS-NAs) exposure, and both OSPW NAs and commercial NAs (C-NAs) exposure resulted in a variety of developmental lesions in the fish larvae, such as yolk sac edema, pericardial edema and spinal malformation. The transcription of genes involved cytochrome P450 aromatase (CYP19a and CYP19b), estrogen receptors (ERα, ERβ1 and ERβ2), and vitellogenin (VTG) was analyzed to evaluate the endocrine disrupting effects of NAs. Significant up-regulated gene expressions of CYP19b, ERα and VTG were observed in both OS-NAs and C-NAs groups, which indicated the deleteriously estrogenic potential of NAs. These results confirmed that NAs derived from crude petroleum could negatively impact the development and endocrine function of zebrafish, and be primarily responsible for the toxicity of OSPW.

Metabolite profiling of fish skin mucus: a novel approach for minimally-invasive environmental exposure monitoring and surveillance

The application of 'omics tools to biologically based monitoring and surveillance of aquatic environments shows considerable promise for complementing chemical monitoring in ecological risk assessments. However, few of the current approaches offer the ability to sample ecologically relevant species (e.g., fish) in a way that produces minimal impact on the health of the organism(s) under study. In the current study we employ liquid chromatography tandem mass spectrometry (LC-MS/MS) to assess the potential for skin mucus-based metabolomics for minimally invasive sampling of the fathead minnow (FHM; Pimephales promelas). Using this approach we were able to detect 204 distinct metabolites in the FHM skin mucus metabolome representing a large number of metabolite classes. An analysis of the sex specificity of the skin mucus metabolome showed it to be highly sexually dimorphic with 72 of the detected metabolites showing a statistically significant bias with regard to sex. Finally, in a proof-of-concept fashion we report on the use of skin mucus-based metabolomics to assess exposures in male and female fathead minnows to an environmentally relevant concentration of bisphenol A, a nearly ubiquitous environmental contaminant and an established endocrine active chemical.

Interferences of an environmental pollutant with estrogen-like action in the male reproductive system of the terrestrial vertebrate Podarcis sicula

Nonylphenol (NP) is classified among the endocrine disruptor chemicals with estrogen-like properties. It is widely used in many industries and to dilute pesticides in agriculture, and is known to affect the reproductive system of many aquatic and semi-aquatic organisms. This study aimed to verify how NP, administered via food and water, may interfere with the reproductive cycle of a terrestrial vertebrate. Our model was the male Italian wall lizard Podarcis sicula, a seasonal breeding species that may be naturally exposed to environmental pollution. From our findings it emerges that an NP-polluted diet administered during the mating period causes in this lizard a slowdown of spermatogenesis and affects the testicular and epididymal structure, making it similar to that of the non-reproductive period. The distribution in the testis and epididymis of mRNA for steroid hormone receptors, i.e., estrogen α and β and androgen receptors, was also investigated. NP treatment inhibits the expression of AR, ERα, and ERβ-mRNA in spermatogonia and primary spermatocytes and causes a switch-off of the secretory activity of the epididymal corpus by inducing the expression of ERα.

Complex effects of two presumably antagonistic endocrine disrupting compounds on the goldfish Carassius aumtus: a comprehensive study with multiple toxicological endpoints

We studied the effects of endocrine disrupting compounds nonylphenol (NP) and letrozole (LE) on the male goldfish Carassius aumtus. Exposure to NP (20 μg l(-1)) alone caused a significant up-regulation in the expression of aromatase, estrogen receptors and vitellogenin (VTG) genes, an increase in hepatic and plasma VTG concentration, but no obvious testicular impairment. Exposure to LE (1 mg kg(-1)) alone resulted in a significant decline in aromatase activity, reduced levels of plasma 17β-estradiol (E2), and enhanced sperm maturation. Co-exposure with LE (1 mg kg(-1)) could only partially affect some of the estrogenic effects caused by NP (20 μg l(-1)) (i.e. expression of hepatic and brain estrogen receptor genes, hepatic VTG concentration), but inhibit other estrogenic effects (i.e. brain and testicular aromatase activity, plasma E2). In addition, co-exposure resulted in impairment of liver mitochondria (i.e. detachment of ridges from the membrane, and uneven distribution of the cytoplasm with clusters of glycogen granules), but did not cause significant damage to the testes (i.e. the morphology, the spermatogonia and spermatozoa densities). Our results clearly showed that nonylphenol and letrozole co-exposure could induce profound effects on fish, and highlighted the importance of adopting multiple toxicological endpoints when evaluating the combined effects of endocrine disrupting compounds.

Expression profile of ribosomal protein L10a throughout gonadal development in rainbow trout (Oncorhynchus mykiss)

Ribosomal protein L10a (RpL10A) has been previously established as a stimulator during the early stages of ovarian development in both the banana prawn and the fruit fly. In order to develop a greater understanding of the role of this protein in vertebrates, the present study aimed to characterize the expression profile of rpl10a during gonadal development in fish. It was determined that the expression of rpl10a within genital ridges increased during embryonic development. Although rpl10a expression was observed in both gonadal somatic cells and primordial germ cells, higher levels of both transcript and protein expression were detected in somatic cells. rpl10a transcripts were observed in all of the adult tissues examined. Cellular level expression of rpl10a was subsequently characterized across various maturational stages using in situ hybridization and immunohistochemistry of both testes and ovaries. Analysis of tissue derived from the testis showed high levels of rpl10a expression within spermatogonia and the Sertoli cells attached to them. In ovarian tissue, rpl10a was strongly expressed in chromatin-nucleolus-stage and peri-nucleolus-stage oocytes. The relationship between rpl10a expression and regulation of gonadal development was confirmed using real-time PCR, which was performed in order to analyze rpl10a expression in testicular and ovarian tissues subsequent to incubation with salmon pituitary extract and various sex steroids for 24 h. Among them, 11-ketotestosterone at 100 ng/mL effectively up-regulated expression of rpl10a in testicular tissues, while 17β-estradiol down-regulated rpl10a expression in ovarian tissues. These results suggested that rpl10a played a role in the regulation of gonadal development in fish.

Nonylphenol effects on the HPA axis of the bioindicator vertebrate, Podarcis sicula lizard

Nonylphenol (NP) is an endocrine disruptor widely distributed in the environment. It accumulates in the lipids of living organisms and enters the human food chain. The main source of human exposure is expected to be food, drinking water and foodstuff contaminated through leaching from packaging or pesticide formulation applications. NP acts as an estrogenic compound and it is able to mimic the action of estradiol 17β (E2) by binding to the estrogen receptor (ER). The aim of the present study was to investigate the NP effects on the hypothalamic-pituitary-adrenal gland (HPA) axis of the bioindicator Podarcis sicula lizard. A time-dependent stimulation of the HPA axis and variations of both catecholamine plasma levels were showed. Moreover, NP effects on adrenal gland morphology were evaluated by light and transmission electron microscopy. Clear morphological signs of adrenal gland stimulation such as an increase of steroidogenic cord diameter and vascularization, a strong escalation of adrenaline cell number and a decrease of noradrenaline cells were observed. The notably elevated levels of adrenal hormones suggested a permanent turning on of hypothalamic corticotropin releasing factor (CRF) secretion together with a lack of the negative feedback of HPA axis, perturbing systemic responses of the organism. Our data may help to predict the biological alterations induced by NP and to extend its impact upon adrenal function.

A rapid screening test for endocrine disrupting chemicals using primary cell culture of the marine medaka

While endocrine disrupting chemicals (EDCs) pose a significant threat to wildlife worldwide, their diverse chemical structures present a major challenge to their detection, particularly since they are present at very low concentrations in the environment. We here report the development of an in vitro system for rapid screening of EDCs, using primary cell cultures (pituitary, ovarian follicular and testicular cells) of the marine medaka (Oryzias melastigma). Pituitary, testis and ovary cell cultures were developed and challenged by environmentally relevant concentrations of three well known EDCs (viz. estradiol, 2,2',4,4'-tetrabromodiphenyl ether, and 4-n-nonylphenol) as well as hypoxia (which has been shown to be a potent endocrine disruptor). In general, the mRNA expression levels of gonadotropins, their receptors and steroidogenic enzymes exhibited dose response relationships to the four endocrine disruptors in different tissues. The sensitivity and responses were also comparable to in vivo responses of whole fish and in vitro responses of the H295R human adrenocortical cell line. Our results suggest that the use of marine medaka primary cultured cells can serve as a cost effective tool for rapid screening of EDCs in the marine environment, and at the same time, sheds light on the underlying mechanisms of EDCs by deciphering their specific target sites along the hypothalamus-pituitary-gonad axis of vertebrates.

Identification of estrogen target genes during zebrafish embryonic development through transcriptomic analysis

Estrogen signaling is important for vertebrate embryonic development. Here we have used zebrafish (Danio rerio) as a vertebrate model to analyze estrogen signaling during development. Zebrafish embryos were exposed to 1 µM 17β-estradiol (E2) or vehicle from 3 hours to 4 days post fertilization (dpf), harvested at 1, 2, 3 and 4 dpf, and subjected to RNA extraction for transcriptome analysis using microarrays. Differentially expressed genes by E2-treatment were analyzed with hierarchical clustering followed by biological process and tissue enrichment analysis. Markedly distinct sets of genes were up and down-regulated by E2 at the four different time points. Among these genes, only the well-known estrogenic marker vtg1 was co-regulated at all time points. Despite this, the biological functional categories targeted by E2 were relatively similar throughout zebrafish development. According to knowledge-based tissue enrichment, estrogen responsive genes were clustered mainly in the liver, pancreas and brain. This was in line with the developmental dynamics of estrogen-target tissues that were visualized using transgenic zebrafish containing estrogen responsive elements driving the expression of GFP (Tg(5xERE:GFP)). Finally, the identified embryonic estrogen-responsive genes were compared to already published estrogen-responsive genes identified in male adult zebrafish (Gene Expression Omnibus database). The expressions of a few genes were co-regulated by E2 in both embryonic and adult zebrafish. These could potentially be used as estrogenic biomarkers for exposure to estrogens or estrogenic endocrine disruptors in zebrafish. In conclusion, our data suggests that estrogen effects on early embryonic zebrafish development are stage- and tissue- specific.

Transcriptomic analyses of sexual dimorphism of the zebrafish liver and the effect of sex hormones

The liver is one of the most sex-dimorphic organs in both oviparous and viviparous animals. In order to understand the molecular basis of the difference between male and female livers, high-throughput RNA-SAGE (serial analysis of gene expression) sequencing was performed for zebrafish livers of both sexes and their transcriptomes were compared. Both sexes had abundantly expressed genes involved in translation, coagulation and lipid metabolism, consistent with the general function of the liver. For sex-biased transcripts, from in addition to the high enrichment of vitellogenin transcripts in spawning female livers, which constituted nearly 80% of total mRNA, it is apparent that the female-biased genes were mostly involved in ribosome/translation, estrogen pathway, lipid transport, etc, while the male-biased genes were enriched for oxidation reduction, carbohydrate metabolism, coagulation, protein transport and localization, etc. Sexual dimorphism on xenobiotic metabolism and anti-oxidation was also noted and it is likely that retinol x receptor (RXR) and liver x receptor (LXR) play central roles in regulating the sexual differences of lipid and cholesterol metabolisms. Consistent with high ribosomal/translational activities in the female liver, female-biased genes were significantly regulated by two important transcription factors, Myc and Mycn. In contrast, Male livers showed activation of transcription factors Ppargc1b, Hnf4a, and Stat4, which regulate lipid and glucose metabolisms and various cellular activities. The transcriptomic responses to sex hormones, 17β-estradiol (E2) or 11-keto testosterone (KT11), were also investigated in both male and female livers and we found that female livers were relatively insensitive to sex hormone disturbance, while the male livers were readily affected. E2 feminized male liver by up-regulating female-biased transcripts and down-regulating male-biased transcripts. The information obtained in this study provides comprehensive insights into the sexual dimorphism of zebrafish liver transcriptome and will facilitate further development of the zebrafish as a human liver disease model.

Cortisol response to waterborne 4-nonylphenol exposure leads to increased brain POMC and HSP70 mRNA expressions and reduced total antioxidant capacity in juvenile sole (Solea solea)

4-Nonylphenol (4-NP) is a breakdown product of alkylphenolpolyethoxylates and can be found in almost all environmental water matrices. 4-NP can act as environmental stressor on fish, typically causing modulation of hypothalamic-pituitary-interrenal axis (HPI). To examine the effects of the xenoestrogen 4-NP or 17β-estradiol (E2) on induction of stress response mechanisms by evaluating the levels of proopiomelanocortin (POMC) mRNA, heat shock protein 70 (HSP70) mRNA and plasma cortisol, we exposed juvenile sole (Solea solea), under static condition for 7 day, to either 10(-6) or 10(-8) M 4-NP, or 10(-8) M E2. In addition, plasma cortisol titers were correlated to the total antioxidant capacity (TAC), one of the oxidative stress parameters. 4-NP treatments resulted in high levels of POMC mRNA, HSP70 mRNA and plasma cortisol. On the contrary, E2 basically down-regulated POMC expression. Moreover, elevated cortisol levels in fish exposed to the highest dose of 4-NP were accompanied by low TAC. These results suggest that 4-NP modulates the sole HPI axis inducing a cortisol-mediated stress response. Specifically, we suggest that 4-NP affects brain POMC mRNA levels via non-estrogen receptor (ER)-mediated mechanism further supporting the ability of 4-NP to target multiple receptor systems.

The effect of nonylphenol on gene expression in Atlantic salmon smolts

The parr-smolt transformation in Atlantic salmon (Salmo salar) is a complex developmental process that culminates in the ability to migrate to and live in seawater. Exposure to environmental contaminants like nonylphenol can disrupt smolt development and may be a contributing factor in salmon population declines. We used GRASP 16K cDNA microarrays to investigate the effects of nonylphenol on gene expression in Atlantic salmon smolts. Nonylphenol exposure reduced gill Na(+)/K(+)-ATPase activity and plasma cortisol and triiodothyronine levels. Transcriptional responses were examined in gill, liver, olfactory rosettes, hypothalamus, and pituitary. Expression of 124 features was significantly altered in the liver of fish exposed to nonylphenol; little to no transcriptional effects were observed in other tissues. mRNA abundance of genes involved in protein biosynthesis, folding, modification, transport and catabolism; nucleosome assembly, cell cycle, cell differentiation, microtubule-based movement, electron transport, and response to stress increased in nonylphenol-treated fish. This study expands our understanding of the effect of nonylphenol on smolting and provides potential targets for development of biomarkers.

Quantitative proteomics in teleost fish: insights and challenges for neuroendocrine and neurotoxicology research

Neuroendocrine systems integrate both extrinsic and intrinsic signals to regulate virtually all aspects of an animal's physiology. In aquatic toxicology, studies have shown that pollutants are capable of disrupting the neuroendocrine system of teleost fish, and many chemicals found in the environment can also have a neurotoxic mode of action. Omics approaches are now used to better understand cell signaling cascades underlying fish neurophysiology and the control of pituitary hormone release, in addition to identifying adverse effects of pollutants in the teleostean central nervous system. For example, both high throughput genomics and proteomic investigations of molecular signaling cascades for both neurotransmitter and nuclear receptor agonists/antagonists have been reported. This review highlights recent studies that have utilized quantitative proteomics methods such as 2D differential in-gel electrophoresis (DIGE) and isobaric tagging for relative and absolute quantitation (iTRAQ) in neuroendocrine regions and uses these examples to demonstrate the challenges of using proteomics in neuroendocrinology and neurotoxicology research. To begin to characterize the teleost neuroproteome, we functionally annotated 623 unique proteins found in the fish hypothalamus and telencephalon. These proteins have roles in biological processes that include synaptic transmission, ATP production, receptor activity, cell structure and integrity, and stress responses. The biological processes most represented by proteins detected in the teleost neuroendocrine brain included transport (8.4%), metabolic process (5.5%), and glycolysis (4.8%). We provide an example of using sub-network enrichment analysis (SNEA) to identify protein networks in the fish hypothalamus in response to dopamine receptor signaling. Dopamine signaling altered the abundance of proteins that are binding partners of microfilaments, integrins, and intermediate filaments, consistent with data suggesting dopaminergic regulation of neuronal stability and structure. Lastly, for fish neuroendocrine studies using both high-throughput genomics and proteomics, we compare gene and protein relationships in the hypothalamus and demonstrate that correlation is often poor for single time point experiments. These studies highlight the need for additional time course analyses to better understand gene-protein relationships and adverse outcome pathways. This is important if both transcriptomics and proteomics are to be used together to investigate neuroendocrine signaling pathways or as bio-monitoring tools in ecotoxicology.

Effects of nonylphenol on vitellogenin synthesis in adult males of the spotted ray Torpedo marmorata

The aim of this investigation was to assess the effects of nonylphenol (NP), an oestrogen-like environmental pollutant, on the vitellogenin (VTG) synthesis in adult males of the aplacental viviparous cartilaginous fish Torpedo marmorata. The VTG recovery in males is considered a biomarker of xeno-oestrogenic pollution as this lipophosphoglycoprotein is physiologically induced by oestrogens only in females of oviparous and ovoviparous vertebrates. Using in situ hybridization and immunohistochemistry, T. marmorata males injected with nonylphenol showed the presence of VTG in the liver and the kidney. In particular, vtg messenger (m)RNA and VTG protein were expressed in the liver, whereas in the kidney cells only the presence of VTG was recorded. By contrast, no expression for VTG was detected in the testis. These results demonstrate that in T. marmorata NP induces the expression of vtg only in the liver; the presence of VTG in the kidney and its absence in the testis are discussed.

Expression of vitellogenin in the testis and kidney of the spotted ray Torpedo marmorata exposed to 17β-estradiol

In vertebrates, the liver was long thought to be the only site of vitellogenin (Vtg) production, but recent studies demonstrated that Vtg is also expressed in extrahepatic districts. The aim of this paper is to assess, by in situ hybridization and immunohistochemistry, the expression of Vtg in the testis and kidney of Torpedo marmorata exposed to 17β-estradiol (E(2)). In treated samples vtg mRNA and Vtg were detected contemporaneously only in the testis; differently the kidney cells were positive to Vtg antibody, but negative to vtg mRNA. This is the first study to assess that male germ cells, after an exposure to E(2), synthesize Vtg in a stage-dependent manner. The presence of Vtg and the modifications observed in the kidney after E(2) treatment are discussed.

Developmental toxicity of the environmental pollutant 4-nonylphenol in zebrafish

4-Nonylphenol (4-NP), an estrogen mimicking compound is produced by biodegradation of alkylethoxylates. It is well established that 4-NP can affect the development of aquatic animals by disrupting the endocrine signals. Here we show for the first time in zebrafish that 4-NP does not only target the neuroendocrine system but also the notochord and the muscle. The notochord malformation was first evident as distortions at 24hourspostfertilization (hpf) which within 24h appeared as kinks and herniations. The notochord phenotype was accompanied by reduced motility and impaired swimming behavior. Whole-mount in situ hybridization using chordamesoderm markers and electron microscopic analysis showed failure in the notochord differentiation and disruption of the perinotochordal basement membrane. Late larval stages of 4-NP treated embryos displayed abnormal mineralization, vertebral curvature, fusion of vertebral bodies and abnormal extension of haemal arches. The muscle structure and the maximal active force in isolated muscle preparations were similar between 4-NP exposed and of control embryos, suggesting that 4-NP did not induce major changes in striated muscle function. However, repeated electrical stimulation (>40Hz) of the 4-NP exposed larvae revealed an impaired relaxation between stimuli, possibly reflecting an alteration in the relaxant mechanisms (e.g. in cellular Ca(2+) removal) which could explain the abnormal swimming pattern exhibited by 4-NP exposed larvae. Additionally, we demonstrate that the expression levels of the stress hormone, corticotropin releasing hormonewere elevated in the brain following 4-NP treatment. We also observed a significant decrease in the transcript levels of luteinizing hormone b at early larval stages. Collectively, our results show that 4-NP is able to disrupt the notochord morphogenesis, muscle function and the neuroendocrine system. These data suggest that 4-NP enduringly affects the embryonic development in zebrafish and that this compound might exert these deleterious effects through diverse signaling pathways.

Microarray analyses of shrimp immune responses

Shrimp aquaculture is one of the major foodproducing industries in the world. However, it is being impacted by several problems including diseases, antibiotic use, and environmental factors. The extent of the effects of these problems in the immune system of the shrimp at the molecular level is just beginning to be understood. Here, we review the gene expression profile of shrimp in response to some of these problems using the high-throughput microarray analysis, including white spot syndrome virus, yellow head virus, Vibrio spp., peptidoglycan, oxytetracycline, oxolinic acid, salinity, and temperature.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

Incorporating zebrafish omics into chemical biology and toxicology

In this communication, we describe the general aspects of omics approaches for analyses of transcriptome, proteome, and metabolome, and how they can be strategically incorporated into chemical screening and perturbation studies using the zebrafish system. Pharmacological efficacy and selectivity of chemicals can be evaluated based on chemical-induced phenotypic effects; however, phenotypic observation has limitations in identifying mechanistic action of chemicals. We suggest adapting gene-expression-based high-throughput screening as a complementary strategy to zebrafish-phenotype-based screening for mechanistic insights about the mode of action and toxicity of a chemical, large-scale predictive applications and comparative analysis of chemical-induced omics signatures, which are useful to identify conserved biological responses, signaling pathways, and biomarkers. The potential mechanistic, predictive, and comparative applications of omics approaches can be implemented in the zebrafish system. Examples of these using the omics approaches in zebrafish, including data of ours and others, are presented and discussed. Omics also facilitates the translatability of zebrafish studies across species through comparison of conserved chemical-induced responses. This review is intended to update interested readers with the current omics approaches that have been applied in chemical studies on zebrafish and their potential in enhancing discovery in chemical biology.

An integrated transcriptomic and proteomic approach characterizing estrogenic and metabolic effects of 17 alpha-ethinylestradiol in zebrafish (Danio rerio)

Nowadays there is much concern about the presence of endocrine disrupting compounds (EDCs) in the environment due to their ability to interfere with the endocrine system. In the presented study, adult zebrafish (Danio rerio) were exposed to 30 ng L(-1) 17alpha-ethinylestradiol (EE2) for 4 and 28 days. The underlying molecular mechanisms of EE2 were studied in the zebrafish liver by applying a combined transcriptomics and proteomics approach. In addition, we assessed the added value of such an integrated-omics approach. Oligo microarrays, spotted with 3479 zebrafish-specific oligos, were employed to generate differential gene expression levels. The proteomic responses were evaluated by means of differential in-gel electrophoresis (DiGE), combined with MALDI-tandem mass spectrometry. Assessment of the major biological functions of the differentially expressed transcripts and proteins illustrated that both individual platforms could profile a clear estrogenic interference, next to numerous metabolism-related effects and stress responses. Cross-comparison of both transcriptomics and proteomics datasets displayed limited concordance, though, thorough revision of the results illustrated that transcriptional effects were projected on protein level as downstream effects of affected signalling pathways. Overall, this study demonstrated that a proteomics approach can lift the biological interpretation of microarrays to a higher level, and moreover, opens a window for identification of possible new biomarkers.

Levels of 17beta-estradiol receptors expressed in embryonic and adult zebrafish following in vivo treatment of natural or synthetic ligands

The nuclear receptors encompass a group of regulatory proteins involved in a number of physiological processes. The estrogen receptors (ERs), of which one alpha and one beta form exist in mammals function as transcription factors in response to 17β-estradiol (E2). In zebrafish there are three gene products of estrogen receptors and they are denoted esr1 (ERalpha), esr2a (ERbeta2) and esr2b (ERbeta1). Total RNA of zebrafish early life stages (<3, 6, 12, 24, 48, 72, 96 and 120 hours post fertilization) and of adult fish (liver, intestine, eye, heart, brain, ovary, testis, gill, swim bladder and kidney) were isolated following in vivo exposures. Using specific primers for each of the three zebrafish ERs the expression levels were quantified using real time PCR methodology. It was shown that in absence of exposure all three estrogen receptors were expressed in adult fish. The levels of expression of two of these three ER genes, the esr1 and esr2a were altered in organs such as liver, intestine, brain and testis in response to ligand (E2, diethylstilbestrol or 4-nonylphenol). During embryogenesis two of the three receptor genes, esr1 and esr2b were expressed, and in presence of ligand the mRNA levels of these two genes increased. The conclusions are i) estrogen receptor genes are expressed during early development ii) altered expression of esr genes in response to ligand is dependent on the cellular context; iii) the estrogenic ligand 4-nonylphenol, a manufactured compound commonly found in sewage of water treatment plants, acts as an agonist of the estrogen receptor during development and has both agonist and antagonist properties in tissues of adult fish. This knowledge of esr gene function in development and in adult life will help to understand mechanisms of interfering mimicking endocrine chemicals in vivo.

Stimulation of growth and changes in the hepatic transcriptome by 17β-estradiol in the yellow perch (Perca flavescens)

The effects of dietary 17β-estradiol (E2) on growth and liver transcriptomics were investigated in the yellow perch ( Perca flavescens). After a 3-mo treatment, E2 significantly stimulated an increase in length and weight of juvenile male and female perch relative to control animals. The increase was significantly greater in females compared with males. Separate, unnormalized cDNA libraries were constructed from equal quantities of RNA from 6 male and 6 female livers of E2-treated and control perch, and 3,546 and 3,719 expressed sequence tags (ESTs) were obtained, respectively. To characterize E2-regulated transcripts, EST frequencies between libraries were calculated within contiguous sequences that were assembled from the combined ESTs of both libraries. Frequencies were also determined in EST transcript groupings produced by aligning all of the ESTs from both libraries at the nucleotide level. From these analyses, there were 28 annotated transcripts that were regulated by 75% between libraries and for which there were at least 5 ESTs of the same transcript between libraries. Regulation of a subset ( 14 ) of these transcripts was confirmed by quantitative reverse transcription-polymerase chain reaction (QPCR). Transcripts that were upregulated by E2 included reproduction-related proteins, binding proteins, and proteases and protease inhibitors. While not part of the transcript frequency analysis, QPCR showed significant upregulation of estrogen receptor esr1 and of insulin-like growth factor I (IGF-I) in E2 livers. E2-downregulated transcripts represented a variety of functional categories including components of the respiratory chain, lipid transport and metabolism, glycolysis, amino acid and nitrogen metabolism, binding proteins, a hydrolytic enzyme, and a transcriptional regulator. In perch it appears that exogenous estrogen drastically shifts liver metabolism toward the production of lipoproteins and carbohydrate binding proteins, and that the growth-promoting action may involve an increase in hepatic IGF-I production.