Genome and transcriptome of Chinese medaka (Oryzias sinensis) and its uses as a model fish for evaluating estrogenicity of surface water

Ecological toxicity assessments of contaminants in aquatic environments are of great concern. However, a dilemma in ecological toxicity assessments often arises when linking the effects found in model animals in the laboratory and the phenomena observed in wild fishes in the field due to species differences. Chinese medaka (Oryzias sinensis), widely distributed in East Asia, is a satisfactory model animal to assess aquatic environment in China. Here, we domesticated this species and assembled its genome (814 Mb) using next-generation sequencing (NGS). A total of 21,922 high-confidence genes with 41,306 transcripts were obtained and annotated, and their expression patterns in tissues were determined by RNA-sequencing. Six mostly sensitive biomarker genes, including vtg1, vtg3, vtg6, zp3a.2, zp2l1, and zp2.3 to estrogen exposure were screened and validated in the fish exposed to concentrations of estrone (E₁), 17β-estradiol (E₂), and estriol (E₃) under laboratory condition. Field investigations were then performed to evaluating the gene expression of biomarkers in wild Chinese medaka and levels of E₁, E₂, and E₃ in the fish habitats. It was found that in 40 sampling sites, the biomarker genes were obviously highly expressed in the wild fish from about half sites, and the detection frequencies of E₁, E₂, and E₃, were 97.5%, 42.5%, and 45% with mean concentrations of 82.48, 43.17, 52.69 ng/L, respectively. Correlation analyses of the biomarker gene expressions in the fish with the estrogens levels which were converted to EEQs showed good correlation, indicating that the environmental estrogens and estrogenicity of the surface water might adversely affect wild fishes. Finally, histologic examination of gonads in male wild Chinese medaka was performed and found the presence of intersex in the fish. This study facilitated the uses of Chinese medaka as a model animal for ecotoxicological studies.

Endocrine disruption in the sub Antarctic fish Patagonotothen tessellata (Perciformes, Notothenidae) from Beagle Channel associated to anthropogenic impact

Situated in the sub-Antarctic region, Beagle Channel represents a unique marine ecosystem due to the connection between the Pacific and the Atlantic Oceans, and its proximity to the Antarctic Peninsula. Ushuaia city, the biggest settlement on the channel, exerts an increasing anthropogenic pressure by discharges of urban and industrial effluents. In the present work, we use Patagonotothen tessellata, one of the most abundant and widespread species in the channel, as a bioindicator species in order to evidence anthropic impact from Ushuaia Bay and surrounding areas. We first analyzed and characterized real time gene expression of androgen receptor, estrogen receptor and different forms of vitellogenin (VTG), under laboratory conditions. This was achieved by induction with estradiol of P. tessellata males. Then, the selected genes were used as biomarkers for an environmental biomonitoring study. Morphometric indices and circulating sex steroids (estradiol and testosterone) were also quantified in male fish collected from different sites. The qPCR analysis showed that vtgAb form is more inducible than vtgAa or vtgC forms after estrogen induction. The field survey revealed the up-regulation of vtgAb and the androgen receptor in fish from sites with higher anthropogenic influence. Sex steroids followed seasonal variations according to their reproductive cycle, with higher levels of estradiol and testosterone in winter and summer seasons. The use of biomarkers such as gene expression of VTG demonstrates that fish from Ushuaia Bay are likely to be exposed to endocrine disrupting compounds. To our knowledge, this research is the first attempt to assess the endocrine disruption associated to anthropic impact in a widespread fish of the Beagle Channel and contributes to a better understanding of the reproductive physiology of sub Antarctic ichthyofauna.

Combined endocrine disruptive toxicity of malathion and cypermethrin to gene transcription and hormones of the HPG axis of male zebrafish (Danio rerio)

Cypermethrin (CYP) and malathion (MAT) have been widely used and are frequently detected in surface waters. The purpose of the present study was to investigate the endocrine disrupting toxicity of CYP, MAT, and CYP + MAT to 5-month-old male zebrafish (Danio rerio). After exposure, the hepatosomatic index (HSI) and gonadosomatic index (GSI) did not change significantly. Following exposure to the combination of 0.1 μg/L CYP +25 μg/L MAT, the E2 and VTG levels of male zebrafish were significantly increased compared to those after individual pesticide treatments. The molecular level of the hypothalamic-pituitary-gonadal (HPG) axis in zebrafish was studied; it was found that the expression of the estrogen-related genes, especially the vtg1 gene, was significantly altered in 0.1 μg/L CYP + 25 μg/L MAT. Overall, our observation indicated that CYP or MAT could disturb the hormonal balance, and their combination of 0.1 μg/L CYP +25 μg/L MAT could significantly enhance the estrogenic effect.

Ovary removal modifies liver message RNA profiles in single Comb White Leghorn chickens

Ovaries produce sex hormones, and ovariectomized animals are often used as models for ovarian dysfunction. The liver is a vital organ involved in metabolism and immunity. In the present study, we conducted experiments to investigate the effects of ovariectomy on transcription and metabolic processes in the liver in chicken. Eight Single Comb White Leghorn (SCWL) female chickens were ovariectomized at 17 wk of age, and 8 intact SCWL females served as controls. At 100 wk of age, all chickens were euthanized. High-throughput transcriptome sequencing was performed on liver RNA obtained from ovariectomized and intact females. A total of 267 differentially expressed genes (DEG) were identified in our study. After analysis using DAVID functional annotation tool, one significant Kyoto Encyclopedia of Genes and Genomes pathway, the phosphatidylinositol signaling pathway, was clustered. Gene Ontology enrichment analysis yielded 46 significant Gene Ontology terms. Among terms describing biological processes, the glycerolipid metabolic and lipid localization processes were dominant. The anabolic genes, PEPCK and GK5, and the catabolic genes, VTG1; VTG2; PLD5; DGKQ; DGKE; and FABP3, were detected in ovariectomized chickens. Differentially expressed genes such as ENSGALG00000000162, IL-1Β, SVOPL, and CA12 implied that livers in ovariectomized chickens were subjected to strong inflammatory reactions, whereas defenses against endogenous materials were compromised. A comprehensive view of gene expression in the liver of ovariectomized chickens would advance our understanding of lipid metabolism, glycometabolism, and their relationships to pathologies induced by absence of the ovary. The identified DEG indicated that ovariectomy disturbed lipid metabolism in the liver and was accompanied by an increase in hepatic gluconeogenesis and reductions in phosphatidic acid synthesis and lipid carrier capacity.

Chronic toxicity and endocrine disruption of naproxen in freshwater waterfleas and fish, and steroidogenic alteration using H295R cell assay

Naproxen is a non-steroidal anti-inflammatory drug (NSAID) and has been frequently detected in surface waters around the world. Although endocrine disruption and reproduction related effects of NSAIDs are of increasing concern, the ecotoxicity of naproxen in aquatic organisms is limited primarily to acute lethal effects. In this study, chronic toxicity of naproxen was evaluated employing two daphnids (Daphnia magna and Moina macrocopa) and a fish (Oryzias latipes). The effects of naproxen on sex steroid hormones and gene transcription related to steroidogenesis were also evaluated in H295R cells. The chronic no observed effect concentrations (NOECs) of naproxen for reproduction were determined to be 10 mg L^-1 in D. magna and 0.3 mg L^-1 in M. macrocopa. At concentrations of 0.5 mg L^-1, the survival of juvenile medaka fish was significantly decreased and transcription of erβ2 gene was significantly increased. Concentration of 17β-estradiol (E2) and the ratio of E2 and testosterone were significantly increased in H295R cells at 10 mg L^-1, suggesting that naproxen could modulate sex hormone production. The current detected levels of naproxen in ambient Korean rivers are far lower than the effective levels, however potential adverse effects cannot be ignored in some highly polluted areas. Endocrine disruption effects in fish warrant further investigation particularly for their ecological implications.

In silico prediction and in vivo analysis of antiestrogenic potential of 2-isopropylthioxanthone (2-ITX) in juvenile goldfish (Carassius auratus)

Previous studies have shown both anti-estrogenic and anti-androgenic activities of 2-isopropylthioxanthone (2-ITX), a well known food contaminant, in in vitro assays. However, no data are available on the anti-estrogenic potentials and risks of 2-ITX in aquatic organisms. This work evaluated the potential endocrine disrupting effects of 2-ITX at the level of estrogen receptor (ER) signaling cascade using juvenile goldfish (Carassius auratus) as model. Firstly, we investigated the ligand binding efficiency of 2-ITX to the ligand binding domains (LBD) of goldfish ER subtypes using a molecular docking approach. Secondly, we assessed the effects of 2-ITX on E2-induced hepatic expression of ERα1, ERβ1, ERβ2, and vitellogenin (VTG) in vivo. Crosstalk between ER-VTG and aryl hydrocarbon receptor 2 (AhR2)-cytochrome P4501A (CYP1A) was also investigated. Fish were injected with increasing doses of 2-ITX ranging from 2 to 10µg/g BW, and results were compared to the effect of tamoxifen, a well-known ER modulator. We observed that compared to ERβ, the interaction potentials of 2-ITX to goldfish ERα1 LBD was more stable in the inactive receptor conformation. The in silico docking simulation analysis also revealed that 2-ITX acted as agonist for the goldfish AhR2 LBDs suggesting the ability of this compound to activate the cross-talk between the ERα- and AhR-signaling pathways. In vivo experiments confirm in silico simulation predictions demonstrating that 2-ITX reduced the estrogenicity of E2 at both transcriptional and post-transcriptional levels, indicating a clear anti-estrogenic effect. Co-exposure of E2 and 2-ITX also resulted in a significant decrease of CYP1A gene expression with respect to 2-ITX alone. Results from these studies collectively revealed that the antiestrogenic property of 2-ITX can be ascribed to a combination of effects on multiple signaling pathways suggesting the potential for this environmental contaminant to affect the hormonal control of reproductive processes in fish.

Sharing the Roles: An Assessment of Japanese Medaka Estrogen Receptors in Vitellogenin Induction

Teleost fish express at least three estrogen receptor (ER) subtypes. To date, however, the individual role of these ER subtypes in regulating expression of estrogen responsive genes remains ambiguous. Here, we investigate putative roles of three ER subtypes in Japanese medaka (Oryzias latipes), using vitellogenin (VTG) I and II as model genes. We identify specific ligand/receptor/promoter dynamics, using transient transactivation assays that incorporate luciferase reporters comprising 3kb promoter/enhancer regions of medaka VTGI and VTGII genes. Four steroidal estrogens (17β-estradiol, estrone, estriol, and 17α-estradiol) were tested in these assays. Results indicate that all three medaka ERs (mERs) are capable of initiating transactivation of both VTG I and II, with ERβ2 exhibiting greatest activity. Promoter deletion analysis suggests that ligand-specific receptor transactivation and utilization of regional-specific estrogen response elements may be associated with differential activities of each medaka ER. Further, cluster analysis of in vivo gene expression and in vitro transactivation suggests that all three ER subtypes putatively play a role in up-regulation of VTG. Results illustrate that preferential ligand/receptor/promoter interactions may have direct implications for VTG gene expression and other ER-mediated regulatory functions that are relevant to the risk assessment of estrogenic compounds.

Developmental exposures to an azole fungicide triadimenol at environmentally relevant concentrations cause reproductive dysfunction in females of medaka fish

Triadimenol is an effective meatabolite derived from the triazole fungicide triadimenfon. It is an agriculturally important reagent of environmentally emerging concern because of its broad use, persistent occurrence in the environment and greater fungicidal or toxic potency than the parent compound. However, the ecotoxicological impact of triadimenol on fish populations remains unclear. In this study, we investigated developmental toxicity and endocrine disruption effects in medaka fish (Oryzias latipes) exposed at an early life stage to triadimenol. First, mortality, gross development and oxidative stress responses were assessed with triadimenol exposure (3-3000 μg/L) during the embryonic stage. Then, medaka at a sensitive stage of early sexual development underwent 35-day continuous chronic exposure to triadimenol, and the endocrine disruption effects were assessed in adulthood and the next generation. Embryonic exposure to triadimenol did not induce significant teratogenic effects or oxidative stress in embryos or hatchlings. However, early-life exposure to triadimenol under environmentally relevant concentrations (3-30 μg/L) and 300 μg/L persistently altered ovary development and reproduction in female adults and skewed the sex ratio in progeny. As well, triadimenol exposure interrupted the hormone balance, as seen by the expression of genes responsible for estrogen metabolism and egg reproduction. Environmentally relevant triadimenol exposure in medaka fish at early life stages may have ecotoxicological impact in aquatic environments. Along with previous studies, we suggest that conazoles share similar modes of action in disrupting hormone homeostasis and reproduction in fish and mammals.

Accumulation of di(2-ethylhexyl) phthalate causes endocrine-disruptive effects in marine medaka (Oryzias melastigma) embryos

Di (2-ethylhexyl) phthalate (DEHP) is extensively distributed in marine environments. However, limited research on the toxicological and molecular effects of DEHP on marine organisms has been conducted. Our study investigated the accumulation, elimination, and endocrine-disruptive effects of DEHP on embryonic marine medaka (Oryzias melastigma). The medaka embryos were continuously exposed to DEHP (0.01, 0.1, and 1 mg/L) or 17β-estradiol (E2, 0.01 mg/L) until hatching, and the newly hatched larvae were then transferred to clean sea water for 12 days of depuration. DEHP and E2 appeared to have no significant effects on the mortality and hatching rates of medaka embryos, but E2 exposure significantly delayed the hatching. Significantly higher DEHP embryonic burdens were detected in the group treated with higher DEHP (0.1 and 1 mg/L) at 10 dpf (days post fertilization). The recovered larvae showed an elimination tendency of DEHP during the recovery period. DEHP had no significant effects on the transcriptional responses of endocrine-disrupting biomarker genes in the 3-dpf embryos. Treatment with 0.1 and 1 mg/L DEHP elicited a significant induction of transcriptional responses of ER, PPAR, and the CYP19 genes in a concentration-dependent manner at 10 dpf, indicating endocrine disruption may be due to bioaccumulation of DEHP. With the elimination of DEHP during the depuration period, all of the effects on these genes showed no significant effects. However, 0.1 mg/L E2 significantly affected the expression of ER, PPAR, and the CYP19 genes in the exposed embryos at both 3 and 10 dpf and recovered larvae. Therefore, these results demonstrate that accumulation of DEHP caused endocrine disruption in medaka embryos and that recovery in clean sea water may weaken the endocrine-disrupting effects.

In vivo and in silico analyses of estrogenic potential of bisphenol analogs in medaka (Oryzias latipes) and common carp (Cyprinus carpio)

Various studies have demonstrated the estrogenic effect of bisphenol A (BPA), a member of bisphenol analogs (BPs), in in vitro and in vivo assays. However, limited data are available on the estrogenic potentials and risks of other BPs in aquatic organisms. In addition, the estrogenic effect of chemicals is known to have species-specific responses in teleost fish. The objective of this study was to evaluate the potential estrogenic effects of BPs on the medaka (Oryzias latipes) and common carp (Cyprinus carpio) using in vivo and in silico assays. Our quantitative real-time PCR analyses revealed that the expression levels of several hepatic estrogen-responsive biomarker genes in male medaka responded to various types and concentrations of BPs in a dose-response manner. The order of in vivo estrogenic potencies of BPs was as follows: BPC≈BPAF>BPB>BPA⋙BPP. To further investigate the interaction potential of BPs with medaka estrogen receptor α (ERα) in silico, a three-dimensional model of the ERα ligand-binding domain (LBD) was built and docking simulations were performed. The docking simulation analysis revealed that BPC interaction potential for medaka ERα LBD was the most potent, followed by BPAF and BPA. Comparing this with carp ERα LBD revealed that the interaction potentials of these BPs to medaka ERα LBD were more stable than to carp ERα LBD. Furthermore, we identified key amino acid residues in medaka ERα LBD that interacted with BPC (Glu356, Arg397, and Cys533), BPAF (Thr350 and Glu356), and BPA (Glu356 and Met424), and found some differences in these key amino acid residues between medaka and carp ERα LBDs. These results of in vivo and in silico analyses showed potential estrogenic effects of BPs in teleost fish, and they also indicated that the differences in interaction potentials and key amino acid residues between medaka and carp ERα LBDs may be due to the differences between the species and estrogenic potencies of the selected BPs.

Hexestrol- and nonylphenol-induced differential vitellogenin synthesis in female and male barfin plaice Liopsetta pinnifasciata

The effects of hexestrol (HXS) and nonylphenol (NP) on plasma vitellogenin (Vtg) concentration in barfin plaice Liopsetta pinnifasciata was studied during spring and autumn experiment. In L. pinnifasciata two "complete" forms of Vtgs, namely VtgAa and VtgAb, were previously described which may be separated due to molecular mass of their largest polypeptide in SDS-PAGE. In spring, the injection of HXS led to an increase in Vtg concentrations in both females and males. SDS-PAGE analysis of plasma from HXS-exposed fish produced only one prominent band at a molecular mass of 180 kDa that corresponds to an increase in VtgAb levels. NP injected in fish in spring induced statistically significant increasing of Vtg concentration in males, and only one type of Vtg, as in case of HXS, accumulated in plasma. In autumn, the injection of HXS results to the increase of Vtg concentration in the plasma of females and males, electrophoretic analysis of plasma proteins showed that only a 98 kDa polypeptide, corresponding to the VtgAa-type showed a significant increase. The blood plasma ratios of VtgAa and VtgAb in experimental fish are discussed in relation to the season and stage of reproductive cycle.

A real-time PCR assay for differential expression of vitellogenin I and II genes in the liver of the sentinel fish species Lipophrys pholis

Abstract The recent advances in molecular biology techniques have prompted the use of vitellogenin (VTG) gene expression as a sensitive and reliable indicator of estrogenic chemicals (EC) exposure. However, data on the dynamic response of the different VTGs genes upon EC exposure is still poorly understood, particularly in sentinel fish species used in field monitoring studies. Hence, the present study aimed at developing a sensitive real-time PCR assay for determining the response of VTG I and II in the recently proposed marine sentinel species Lipophrys pholis upon exposure to the model EC 17α-ethinylestradiol (EE2). The findings of the laboratory study indicate that L. pholis VTG I proved to be not only more inducible but also more sensitive to EE2 exposure than VTG II, for the same range of concentrations. In fact, VTG I gene induction was 475-fold higher than VTG II at 15 ng/L EE2, and 13-fold at 5 ng/L EE2. Overall, the findings of the present study indicate that in the field, expression of VTG I in L. pholis should be preferentially used in the screening of EC exposure because of its higher sensitivity. Furthermore, the present study favors L. pholis integration in monitoring programs associated with EC's pollution within the European water policy legislation.

Biomarker gene response in male Medaka (Oryzias latipes) chronically exposed to silver nanoparticle

The chronic toxicity test has been conducted for twenty-eight days to characterize the hepatic expression levels of eight stress-related genes after exposing Medaka to two doses of silver nitrate or a silver nanoparticle (Ag-NP) using real time RT-PCR analysis. This extends our previously published work to include three additional biomarkers and three later time points. In comparing with the control, the significant induction of MT and GST genes in livers of the fish exposed to 1 μg/l Ag-NPs was observed at various time points during the test period. The Orla C3-1 (Medaka) gene was slightly induced only with 1 μg/l Ag-NPs at 7-day exposure while the suppression of p53 and HSP70 was recorded in all exposures at the end of the test. The gene encoding transferrin was repressed at day 21 by both silver types and at every exposure dosage. These results revealed that the Ag-NPs increase metal detoxification, oxidative and inflammatory stress, and finally stimulate immune responses in Medaka. The conspicuous induction of choriogenin L and vitellogenin 1 in male fish exposed to Ag-NPs, especially at 7- and 21-day, compared with the exposures of AgNO(3) or control was the first attempt to examine estrogenic effects of Ag-NPs.