Molecular characterization of estrogen receptor genes in Gobiocypris rarus and their expression upon endocrine disrupting chemicals exposure in juveniles

Endocrine disruptors affect the expression of estrogen receptor genes and proteins in the white cloud mountain minnow Tanichthys albonubes (Teleostei: Cyprinidae)

The endocrine disruptor chemicals (EDCs) are ubiquitous in the environment, and it has raised wide public concern because of the dangers of EDCs for living organisms and the environment. In order to comparatively study the effects of EDCs [17-α-ethinylestradiol (EE2), Bisphenol A (BPA) and Nonylphenol (NP)] on the expression of estrogen receptors (ERs: erα, erβ1, and erβ2) at mRNA and protein level, total 520 adult Tanichthys albonubes were exposed to E2, EE2, BPA and NP with three concentrations respectively: EE2 (1, 5, 25 ng/l), NP (10, 50, 250 μg/l), BPA (100, 500, 2,500 μg/l) for 28 days, E2 (2, 20, 200 ng/l) being as the positive control. After treatment, the brain, eye, gill, heart, liver, gut, kidney, muscle, testis, and ovary were collected, following by the real-time quantitative PCR (RT-qPCR) and western blot methods to detect the expression levels of erα, erβ1, and erβ2 in T.albonubes at mRNA and protein level. Our results showed that high expression of terα (t means T.albonubes), terβ1, and terβ2 were detected in liver, while terβ1 and terβ2 mainly expressed in the liver, intestine, kidney, muscle and testis. EE2, BPA, and NP treatment all up-regulated the expression of terα, terβ1, and terβ2 in the brain, liver, and testis, but with some variations. Similar to mRNA level, both TERα and TERβ were up-regulated by all the EE2, BPA, and NP treatment with dose-dependent effect. In conclusion, the responses of ERs of T.albonubes to the EDCs present measurability and susceptibility, which make it possible for T. albonubes to be an efficient biomarker to monitor and evaluate the pollution of endocrine disrupting chemicals in water environment.

BPA disrupts the SC barrier integrity by activating the cytokines/JNK signaling pathway in rare minnow Gobiocypris rarus

Bisphenol-A (BPA) has been reported to disrupt blood-testis barrier (BTB) integrity in mammals. However, its effects on fish testis sertoli cell (SC) barrier and the underlying mechanisms have been largely unknown to date. To study the SC barrier toxicity induced by BPA, male rare minnows (Gobiocypris rarus) were exposed to 15 μg L ^- 1 BPA for 7, 14 and 21 d. Meanwhile, a 25 ng L^-1 17α-ethynyl estradiol (EE2) group was set up as the positive control. Results showed that BPA induced immune response in the testes and decreased offspring hatching rate. The biotin tracer assay showed that BPA exposure destroyed the integrity of the testis SC barrier. In addition, BPA exposure decreased the expressions of occludin, ZO-1, CX43 and N-cadherin proteins. The transcripts of CX43 and occludin were significantly decreased and SP1 recruitment in each gene promoter was repressed after BPA exposure. Moreover, the cytokines (TNFα and IL-1β) were significantly increased while the JNK signal pathway was activated after BPA exposure. BPA also increased the matrix metalloproteinases 1 (MMP1) and MMP2 levels in the testes. In addition, estrogenic effect did not entirely explain the mechanism by which BPA disrupted the SC barrier in G. rarus testes. These results suggested that BPA disrupted the SC barrier integrity by inhibiting SP1 enrichments within CX43 and occludin 5' flanking regions through activated cytokines/JNK signaling pathway. MMPs were also involved in the disruption of SC barrier caused by BPA exposure.

Multiple Xenosteroid Pollutants Biomarker Changes in Xultured Nile Tilapia Using Wastewater Effluents as Their Primary Water Source

Simple Summary

Estrogenic endocrine disruptive chemicals (E-EDCs) are important types of pollutants in fish farms worldwide and a globally concerned problem. In this study, Nile tilapia fish farms receiving wastewater effluents in Egypt were selected as highly, moderately polluted fish farms; besides, a putative control site was deemed low in contamination. Levels of E-EDCs (natural and synthetic steroids, and industrial phenolic compound/bisphenol A (BPA)) was recorded in farm water, and fish tissues at all sites under consideration, mainly, lower levels of testosterone, progesterone, zeranol, and 17β-estradiol were detected compared to the higher level of BPA. Moreover, the effects of these pollutants on fish biometric, reproductive genes, and hormonal biomarkers was evaluated along with the observed associated histopathological alterations. Our findings revealed the detection of some steroidal compounds with a higher level of the BPA. All analyzed biomarkers were reduced to a great extent in the highly polluted sites compared to others, and the histopathological alterations observed were supportive of other measurements. These observations warrant strict monitoring of aquatic pollution sources and the development of strategic plans to control aquaculture pollution.

Abstract

This study was undertaken to screen levels of xenosteroids (estrogenic endocrine disrupting chemicals/E-EDCs) in Nile tilapia (Oreochromis niloticus) fish farms subjected to water fill from the drain at three sites S1 (highly polluted), S2 (moderately polluted), and a putative reference site (RS). Biometric, hormonal, gene expression, and histopathological analysis were investigated. Testosterone, progesterone, and zeranol residues were detected at (0.12–3.44 µg/L) in water samples of different sites. Bisphenol-A (BPA) exhibited a very high concentration (6.5 µg/mL) in water samples from S1. Testosterone, 17β-estradiol residues were detected in fish tissues from all sites at (0.16–3.8 µg/Kg) and (1.05–5.01 µg/Kg), respectively. BPA residues were detected at a very high concentration in the liver and muscle of fish collected from S1 at higher levels of 25.9 and 48.07 µg/Kg, respectively. The detected E-EDCs, at different sites, particularly BPA, reduced the somatic and testicular growth among sites and oversampling time points. Meanwhile, hepatosomatic index (HSI) was significantly increased in S1 compared to S2. All analyzed genes estrogen receptor-type I (er-I, er-ɑ) and II (er-II, er-ß1), polypeptide 1a (cyp19a1), SRY-box containing gene 9 (sox9), and vitellogenin (vtg) and gonadotropin hormones (luteinizing hormone (LH), follicle-stimulating hormone (FSH)), testosterone, 17β-estradiol, and anti-Mullerian hormone (AMH) were significantly expressed at S1 compared to other sites. Histopathology was more evident in S1 than other sites. These findings warrant immediate strategies development to control aquatic pollution and maintain fish welfare and aquaculture sustainability.

Effects of Estrogen on the Gastrointestinal Tract

Estrogen is a kind of steroid compound that has extensive biologic activities. The effect of estrogen is pleiotropic, affecting multiple systems in the body. There is accumulating evidence that estrogen has important effects on the gastrointestinal tract. Longer exposure to estrogen may decrease the risk of gastric cancer. Use of the anti-estrogen drug tamoxifen might increase the risk of gastric adenocarcinoma. Estrogen receptor β may serve as a target for colorectal cancer prevention. In addition, estrogen has been reported to be closely related to the mucosal barrier, gastrointestinal function and intestinal inflammation. However, the role of estrogen in the gastrointestinal tract has not been systematically summarized. In this review, we aim to provide an overview of the role of estrogen in the gastrointestinal tract and evaluate it from various aspects, including estrogen receptors, the mucosal barrier, intestinal inflammation and gastrointestinal tract tumors, which may provide the basis for the development of therapeutic strategies to manage gastrointestinal diseases.

Hepatic gene expression profiles of a non-model cyprinid (Barbus plebejus) chronically exposed to river sediments

In this study, we characterized the gene expression responses of the Padanian barbel (Barbus plebejus), a native benthivorous cyprinid with a very compromised presence within the fish community of the River Po. Barbel juveniles were exposed in the laboratory to two river sediments reflecting an upstream/downstream gradient of increasing contamination and collected from one of the most anthropized tributaries of the River Po. After 7months of exposure, hepatic transcriptional changes that were diagnostic of sediment exposure were assessed. We investigated a set of 24 genes involved in xenobiotic biotransformation (cyp1a, gstα, ugt), antioxidant defense (gpx, sod, cat, hsp70), trace metal exposure (mt-I, mt-II), DNA repair (xpa, xpc), apoptosis (bax, casp3), growth (igf2), and steroid (erα, erβ1, erβ2, ar, vtg) and thyroid (dio1, dio2, trα, trβ, nis) hormone signaling pathways. In a consistent overall picture, the results showed that long-term sediment exposure mainly increased the levels of mRNAs encoding proteins involved in xenobiotic metabolism, oxidative stress defense, repair of DNA damage and activation of the apoptotic process. Transcript up-regulation of three receptor genes (erβ2, ar, trβ), likely representing compensatory responses to antagonistic/toxic effects, was also observed, confirming the exposure to disruptors of the reproductive and thyroidal axes. In contrast to expectations, a few genes showed no response (e.g., casp3) or even downregulation (vtg), further suggesting that the timing of exposure/assessment, potential compensatory effects or post-transcriptional modifications interact to modify the gene expression profiles, particularly during exposure to mixtures of contaminants.

Assessing the potential for trace organic contaminants commonly found in Australian rivers to induce vitellogenin in the native rainbowfish (Melanotaenia fluviatilis) and the introduced mosquitofish (Gambusia holbrooki)

In Australia, trace organic contaminants (TrOCs) and endocrine active compounds (EACs) have been detected in rivers impacted by sewage effluent, urban stormwater, agricultural and industrial inputs. It is unclear whether these chemicals are at concentrations that can elicit endocrine disruption in Australian fish species. In this study, native rainbowfish (Melanotaenia fluviatilis) and introduced invasive (but prevalent) mosquitofish (Gambusia holbrooki) were exposed to the individual compounds atrazine, estrone, bisphenol A, propylparaben and pyrimethanil, and mixtures of compounds including hormones and personal care products, industrial compounds, and pesticides at environmentally relevant concentrations. Vitellogenin (Vtg) protein and liver Vtg mRNA induction were used to assess the estrogenic potential of these compounds. Vtg expression was significantly affected in both species exposed to estrone at concentrations that leave little margin for safety (p<0.001). Propylparaben caused a small but statistically significant 3× increase in Vtg protein levels (p=0.035) in rainbowfish but at a concentration 40× higher than that measured in the environment, therefore propylparaben poses a low risk of inducing endocrine disruption in fish. Mixtures of pesticides and a mixture of hormones, pharmaceuticals, industrial compounds and pesticides induced a small but statistically significant increase in plasma Vtg in rainbowfish, but did not affect mosquitofish Vtg protein or mRNA expression. These results suggest that estrogenic activity represents a low risk to fish in most Australian rivers monitored to-date except for some species of fish at the most polluted sites.

Foxl2 and Its Relatives Are Evolutionary Conserved Players in Gonadal Sex Differentiation

Foxl2 is a member of the large family of Forkhead Box (Fox) domain transcription factors. It emerged during the last 15 years as a key player in ovarian differentiation and oogenesis in vertebrates and especially mammals. This review focuses on Foxl2 genes in light of recent findings on their evolution, expression, and implication in sex differentiation in animals in general. Homologs of Foxl2 and its paralog Foxl3 are found in all metazoans, but their gene evolution is complex, with multiple gains and losses following successive whole genome duplication events in vertebrates. This review aims to decipher the evolutionary forces that drove Foxl2/3 gene specialization through sub- and neo-functionalization during evolution. Expression data in metazoans suggests that Foxl2/3 progressively acquired a role in both somatic and germ cell gonad differentiation and that a certain degree of sub-functionalization occurred after its duplication in vertebrates. This generated a scenario where Foxl2 is predominantly expressed in ovarian somatic cells and Foxl3 in male germ cells. To support this hypothesis, we provide original results showing that in the pea aphid (insects) foxl2/3 is predominantly expressed in sexual females and showing that in bovine ovaries FOXL2 is specifically expressed in granulosa cells. Overall, current results suggest that Foxl2 and Foxl3 are evolutionarily conserved players involved in somatic and germinal differentiation of gonadal sex.

Oxidative stress and immunotoxic effects of bisphenol A on the larvae of rare minnow Gobiocypris rarus

Bisphenol A (BPA), a known endocrine disrupting chemical, is ubiquitous in the aquatic environment and can pose risk to the health of aquatic organisms. Studies on immunotoxicity of BPA in aquatic organisms are limited. In this study, rare minnow (Gobiocypris rarus) larvae were exposed to 1, 225 and 1000μg/L BPA for 7 days. Inflammatory effects of BPA exposure were assessed from the increased production of nitric oxide (NO) and reactive oxygen species (ROS), the change of iNOS mRNA and other TLRs-associated immune gene expression. Our findings provide evidences that different concentrations of BPA can induce a toxic response in fish to produce reactive free radicals which can affect the function of T lymphocytes and decrease the transcription levels of cytokine genes. The excess production of H2O2, induced oxidative stress and suppressed TLR4/NF-κB signaling, leading to immunosuppressive effects in fish larvae. The present results suggest that BPA has the potential to induce oxidative stress accompanied by immunosuppression in rare minnow larvae.

Actions of Bisphenol A and Bisphenol S on the Reproductive Neuroendocrine System During Early Development in Zebrafish

Bisphenol A (BPA) is a well-known environmental, endocrine-disrupting chemical, and bisphenol S (BPS) has been considered a safer alternative for BPA-free products. The present study aims to evaluate the impact of BPA and BPS on the reproductive neuroendocrine system during zebrafish embryonic and larval development and to explore potential mechanisms of action associated with estrogen receptor (ER), thyroid hormone receptor (THR), and enzyme aromatase (AROM) pathways. Environmentally relevant, low levels of BPA exposure during development led to advanced hatching time, increased numbers of GnRH3 neurons in both terminal nerve and hypothalamus, increased expression of reproduction-related genes (kiss1, kiss1r, gnrh3, lhβ, fshβ, and erα), and a marker for synaptic transmission (sv2). Low levels of BPS exposure led to similar effects: increased numbers of hypothalamic GnRH3 neurons and increased expression of kiss1, gnrh3, and erα. Antagonists of ER, THRs, and AROM blocked many of the effects of BPA and BPS on reproduction-related gene expression, providing evidence that those three pathways mediate the actions of BPA and BPS on the reproductive neuroendocrine system. This study demonstrates that alternatives to BPA used in the manufacture of BPA-free products are not necessarily safer. Furthermore, this is the first study to describe the impact of low-level BPA and BPS exposure on the Kiss/Kiss receptor system during development. It is also the first report of multiple cellular pathways (ERα, THRs, and AROM) mediating the effects of BPA and BPS during embryonic development in any species.

Steroids in teleost fishes: A functional point of view

Steroid hormones are involved in the regulation of a variety of processes like embryonic development, sex differentiation, metabolism, immune responses, circadian rhythms, stress response, and reproduction in vertebrates. Teleost fishes and humans show a remarkable conservation in many developmental and physiological aspects, including the endocrine system in general and the steroid hormone related processes in particular. This review provides an overview of the current knowledge about steroid hormone biosynthesis and the steroid hormone receptors in teleost fishes and compares the findings to the human system. The impact of the duplicated genome in teleost fishes on steroid hormone biosynthesis and perception is addressed. Additionally, important processes in fish physiology regulated by steroid hormones, which are most dissimilar to humans, are described. We also give a short overview on the influence of anthropogenic endocrine disrupting compounds on steroid hormone signaling and the resulting adverse physiological effects for teleost fishes. By this approach, we show that the steroidogenesis, hormone receptors, and function of the steroid hormones are reasonably well understood when summarizing the available data of all teleost species analyzed to date. However, on the level of a single species or a certain fish-specific aspect of physiology, further research is needed.

Activity and Transcriptional Responses of Hepatopancreatic Biotransformation and Antioxidant Enzymes in the Oriental River Prawn Macrobrachium nipponense Exposed to Microcystin-LR

Microcystins (MCs) are a major group of cyanotoxins with side effects in many organisms; thus, compounds in this group are recognized as potent stressors and health hazards in aquatic ecosystems. In order to assess the toxicity of MCs and detoxification mechanism of freshwater shrimp Macrobrachium nipponense, the full-length cDNAs of the glutathione S-transferase (gst) and catalase (cat) genes were isolated from the hepatopancreas. The transcription level and activity changes in the biotransformation enzyme (glutathione S-transferase (GST)) and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx)) in the hepatopancreas of M. nipponense exposed to MC-LR (0.2, 1, 5, and 25 μg/L) for 12, 24, 72 and 96 h were analyzed. The results showed that the isolated full-length cDNAs of cat and gst genes from M. nipponense displayed a high similarity to other crustaceans, and their mRNAs were mainly expressed in the hepatopancreas. MC-LR caused significant increase of GST activity following 48-96 h (p < 0.05) and an increase in SOD activity especially in 24- and 48-h exposures. CAT activity was activated when exposed to MC-LR in 12-, 24- and 48-h exposures and then it was inhibited at 96-h exposure. There was no significant effect on GPx activity after the 12- and 24-h exposures, whereas it was significantly stimulated after the 72- and 96-h exposures (p < 0.05). The transcription was altered similarly to enzyme activity, but the transcriptional response was generally more immediate and had greater amplitude than enzymatic response, particularly for GST. All of the results suggested that MC-LR can induce antioxidative modulation variations in M. nipponense hepatopancreas in order to eliminate oxidative damage.

Molecular characterization of heat-shock protein 90 gene and its expression in Gobiocypris rarus juveniles exposed to pentachlorophenol

Heat-shock protein 90 (HSP90) is an abundant and highly conserved molecular chaperone, and it fulfills a housekeeping function in contributing to the folding, maintenance of structural integrity, and proper regulation of a subset of cytosolic proteins. In this study, the full-length 2693-bp cDNA of HSP90 was cloned by rapid amplification of cDNA ends (RACE) technique from the liver of rare minnow (Gobiocypris rarus) for the first time, designated as GrHSP90. The complete coding sequence of GrHSP90 is 2181 bp in length, which encodes a polypeptide of 726 amino acids with a predicted molecular mass of 83.4 kDa and a theoretical isoelectric point of 4.90. Phylogenetic tree analysis indicated that deduced protein GrHSP90 had extensive sequence similarities to other fish HSP90s. Tissue distribution showed that GrHSP90 was constitutively expressed in a wide range of tissues including gill, blood, brain, fin, gonad, heart, intestine, kidney, liver, muscle, spleen, skin, and swim bladder. The highest expression was found in the gonad. Furthermore, significant increase in GrHSP90 mRNA in the liver was observed after exposure to pentachlorophenol ≥8 µg/L (p < 0.05). Our results suggest that GrHSP90 is indeed an ortholog of the HSP90 family and may be act as a biomarker to assess the effect of environmental contaminant.

Gene expression profiling of key genes in hypothalamus-pituitary-gonad axis of rare minnow Gobiocypris rarus in response to EE2

The 17α-ethinylestradiol (EE2), which could induce estrogenic effects, is found in different aquatic systems. The current study aimed to assess in vivo effects of short-term EE2 exposure on the transcriptional activity of genes in the brain and gonad tissues in order to characterize the mode of action of EE2 on the hypothalamus-pituitary-gonad axis in rare minnow (Gobiocypris rarus). The full length cDNAs of fshβ, lhβ, fshr and lhr were first characterized in G. rarus. The homology and phylogenetic analyses of the amino acid sequences revealed that these four genes share high identity in cyprinid fish. The tissue distribution analysis by qRT-PCR showed that fshβ and lhβ were mainly expressed in the brain and fshr and lhr were mainly expressed in gonads. Adult G. rarus was exposed to EE2 at 1, 5, 25 and 125 ng/L for 3 and 6 days and the expression of brain cyp19a1b, fshβ and lhβ, estrogen receptors (esr1, esr2a, and esr2b) and gonadal fshr, lhr and cyp19a1a were assessed. Cyp19a1b was significantly up-regulated in the brains of female exposed to EE2 at 1-125 ng/L for 6 days. The brain lhβ, but not fshβ was strongly suppressed in most EE2 exposure groups of both sexes. The brain esr2b was inhibited in both sexes exposed to EE2 at all of the four concentrations for 6 days. Esr2a was up-regulated in the females by 6-day EE2 treatment at 1 and 25 ng/L. The high responsiveness of brain lhβ and esr2s to EE2 and their significant correlation in both sexes suggested that the transcriptional activity of Esr2s could play key roles in modulation of lhβ expression via direct action on gonadotropic cells in response to EE2. In gonads, fshr was strongly inhibited by EE2 in males, while lhr was significantly stimulated by EE2 in females. Cyp19a1a was inhibited by EE2 in both sexes. The positive correlations of gene expressions of both fshr and lhr with cyp19a1a in testes suggest that the suppression of 17α-estradiol (E2) synthesis in testis by exogenous estrogen could mediate via both Fsh/Fshr and Lh/Lhr signaling in male G. rarus.

Gonadal development and transcript profiling of steroidogenic enzymes in response to 17α-methyltestosterone in the rare minnow Gobiocypris rarus

It is well known that natural and anthropogenic chemicals interfere with the hormonal system of vertebrate and invertebrate organisms. How these chemicals regulate gonadal steroidogenesis remains to be determined. The main objective of this study was to evaluate the effects of 17α-methyltestosterone (MT), a synthetic model androgen, on gene expression profiles of six key steroidogenic genes in adult rare minnow. The full-length cDNA encoding 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2) was firstly isolated and characterized by RT-PCR and RACE methods. The gonadal transcript changes of StAR, cyp11a1, 3β-HSD, cyp17a1, 11β-HSD2 and cyp19a1a in 6-month adult Gobiocypris rarus exposed to MT and 17α-ethinylestradiol (EE2) for 7, 14 and 21 days were detected by qRT-PCR. To make an effort to connect the transcriptional changes of steroidogenic enzymes with effects on higher levels of biological organization and on VTG, one remarkable sensitive target of steroids, body and gonad weights, histology of gonads, and hepatic vtg mRNA level were measured. MT caused varying degree of abnormalities in ovaries and testes. The hepatic vtg mRNA level was highly inhibited in females and slightly altered in males by MT. Transcripts of several steroidogenic genes including StAR, cyp17a1, and cyp11a1 showed high responsiveness to MT exposure in G. rarus. The gene expression profiles of these steroidogenic genes in MT-treated groups were much distinct with the EE2-treated group.

Toxic effects of triazophos on rare minnow (Gobiocypris rarus) embryos and larvae

Triazophos (TAP) has been widely used in agriculture for controlling insect pests and is a known organophosphorus pesticide. Due to TAP characteristics, such as high chemical and photochemical stability, its potential toxicity to aquatic organisms has gained great interest. To explore the potential developmental toxicity of TAP, Gobiocypris rarus embryos and larvae were exposed to various concentrations of TAP (0.1-15 mg L(-1)) until 72 h. Results showed that values of 72 h LC50 and EC50 were 7.44 and 5.60 mg L(-1) for embryos, 2.52 and 1.37 mg L(-1) for larvae. Increased malformation, decreased heart rate and body length provide a gradual concentration-dependent pattern. Enzyme activities and mRNA levels were significantly changed even at low concentration (0.05 mg L(-1) for embryos and 0.01 mg L(-(1) for larvae). Overall, the present study points out that TAP is likely a risk to the early development of G. rarus. The information presented in this study will be helpful in better understanding the toxicity induced by TAP in fish embryos and larvae.

Histopathological and estrogen effect of pentachlorophenol on the rare minnow (Gobiocypris rarus)

Pentachlorophenol (PCP), a typical organic pollutant and environmental endocrine disruptor, has been extensively used as a pesticide and biocide worldwide. In this study, the effects of PCP on the histological and hepatic system of the rare minnow (Gobiocypris rarus) were evaluated. Vitellogenin (VTG) was used as a biomarker to evaluate the estrogen effect of PCP. The results revealed that VTG was highly expressed and PCP exposure had histopathological effects on the rare minnow. Plasma and hepatic VTG concentrations increased when female rare minnows were exposed to ≥80 μg/L PCP and male rare minnows were exposed to 40 μg/L PCP (p < 0.05), which suggested that the VTG expression was evoked by PCP exposure. The results indicated that both plasma and liver tissue were suitable for VTG quantification. A significant decrease in the mRNA level of hepatic estrogen receptor-α (ERα) in male or juvenile was observed after exposure to ≥80 or ≥8 μg/L PCP, respectively; in contrast, increased mRNA levels of ERβ1, ERβ2, VTGI, and VTGII in male or juvenile were detected after exposure to ≥80 or ≥8 μg/L PCP, respectively. These results suggested that PCP has an estrogen effect and exists within different endocrine-disrupting pathways from other environmental contaminants. As such, VTG mRNA expression in the rare minnow may require transcription of the ERβ1 and ERβ2 genes.

Responsiveness of four gender-specific genes, figla, foxl2, scp3 and sox9a to 17α-ethinylestradiol in adult rare minnow Gobiocypris rarus

Proteins encoded by figla, foxl2, scp3 and sox9a play important roles in gonad differentiation and reproduction. In the present study, we aimed to determine the responsiveness of figla, foxl2, scp3 and sox9a to 17α-ethinylestradiol (EE2) in the gonads of adult Gobiocypris rarus. Full-length cDNAs of figla, scp3 and sox9a were cloned and characterized by RT-PCR and RACE methods. Expression patterns in adult tissues were investigated. Results indicated that figla was predominantly expressed in adult ovaries and scp3 was restrictively expressed in the male testes and sox9a was principally expressed in the brains of both genders and the testes of males. Gene expression profiles of figla, foxl2, scp3 and sox9a were analyzed in the gonads of adult G. rarus exposed to EE2 at 1, 5, 25, and 125ng/L for 3 and 6days. Three-day EE2 treatment at 1-125ng/L all caused a significant increase of figla transcript in testes and foxl2 transcript in ovaries. However, six-day EE2 exposure at 1-125ng/L repressed figla and scp3 transcript in testes and foxl2 transcript in ovaries. The present study indicates that the testicular transcripts of figla and scp3 in males and the ovarian foxl2 transcript in females have high responsiveness to EE2 and they can be used as sensitive molecular biomarkers for early warning to monitor the environmental estrogenic chemicals in fresh water environment. The present study also suggests that the effective EE2 dosage for feminization in male G. rarus might be at least 25ng/L.

Multiple structurally distinct ERα mRNA variants in zebrafish are differentially expressed by tissue type, stage of development and estrogen exposure

It is well established that estrogen-like environmental chemicals interact with the ligand-binding site of estrogen receptors (ERs) to disrupt transcriptional control of estrogen responsive targets. Here we investigate the possibility that estrogens also impact splicing decisions on estrogen responsive genes, such as that encoding ERα itself. Targeted PCR cloning was applied to identify six ERα mRNA variants in zebrafish. Sequencing revealed alternate use of transcription and translation start sites, multiple exon deletions, intron retention and alternate polyadenylation. As determined by quantitative (q)PCR, N-terminal mRNA variants predicting long (ERαA(L)) and short (ERα(S)) isoforms were differentially expressed by tissue-type, sex, stage of development and estrogen exposure. Whereas ERα(L) mRNA was diffusely distributed in liver, brain, heart, eye, and gonads, ERα(S) mRNA was preferentially expressed in liver (female>male) and ovary. Neither ERα(L) nor ERα(S) transcripts varied significantly during development, but 17β-estradiol selectively increased accumulation of ERα(S) mRNA (∼170-fold by 120 hpf), an effect mimicked by bisphenol-A and diethylstilbestrol. Significantly, a C-truncated variant (ERα(S)-Cx) lacking most of the ligand binding and AF-2 domains was transcribed exclusively from the short isoform promoter and was similar to ERα(S) in its tissue-, stage- and estrogen inducible expression. These results support the idea that promoter choice and alternative splicing of the esr1 gene of zebrafish are part of the autoregulatory mechanism by which estrogen modulates subsequent ERα expression, and further suggest that environmental estrogens could exert some of their toxic effects by altering the relative abundance of structurally and functionally distinct ERα isoforms.

Characterization of four nr5a genes and gene expression profiling for testicular steroidogenesis-related genes and their regulatory factors in response to bisphenol A in rare minnow Gobiocypris rarus

Bisphenol A (BPA) widely used in the manufacture of numerous products is ubiquitous in aquatic environment. To explore the mechanisms of BPA-mediated actions, male rare minnow Gobiocypris rarus were exposed to BPA at concentrations of 5, 15, and 50 μg/L for 14 and 35 days in the present study. Four subtypes of nr5a gene encoding important transcription factors for steroidogenesis were characterized, and tissue distribution analysis demonstrated distinct expression profiling of the four genes in G. rarus. BPA at environmentally relevant concentration (5 μg/L) caused increase of gonadosomatic index (GSI) of male fish. In response to BPA, no obvious changes on the testis development were observed. Modulation of vtg mRNA expression by BPA suggests estrogenic and/or anti-estrogenic effects of BPA were dependent on exposed duration (14 or 35 days). Gene expression profiling for testicular steroidogenesis-related genes, sexual steroid receptors, gonadotropin receptors, and transcription factors indicates differential regulation was dependent on exposure duration and dose of BPA. The correlation analysis at mRNA level demonstrates that the BPA-mediated actions on testicular steroidogenesis might involve sex steroid hormone receptor signaling, gonadotropin/gonadotropin receptor pathway, and transcription factors such as nuclear receptor subfamily 5, group A (Nr5a), fork head box protein L2 (Foxl2).

Molecular characterization of five steroid receptors from pengze crucian carp and their expression profiles of juveniles in response to 17α-ethinylestradiol and 17α-methyltestosterone

Pengze crucian carp (Carassius auratus var. pengze, Pcc), a triploid gynogenetic fish, was used in this study to investigate the cross-talk between EDCs and steroid receptors. The full-length cDNAs of five steroid receptors (esr1, er alpha2, esr2a, esr2b, ar) and partial cDNA of vtg B were isolated. The tissue distributions of these genes were analyzed in adult fish by qRT-PCR. Then the expression profiles of five steroid receptors (esrs and ar) and vtg B were detected in the juveniles exposed to 17α-ethinylestradiol (EE2, 0.1, 1 and 10ng/L) and 17α-methyltestosterone (MT, 50μg/L) for 4weeks. The results demonstrated that esrs, ar, and vtg B were predominantly expressed in liver of adult fish. However, among these detected genes, esr1 and er alpha2 mRNAs are sensitive biomarkers in response to EE2 at 0.1, 1, and 10ng/L for 1 and 2weeks compared to esr2a, esr2b, ar, and vtg B in the juveniles of mono-female gynogenetic fish. Totally, the subtypes of esrs show biphasic responses to EE2 exposures for 4weeks, and most of the EE2 exposures at 0.1, 1, and 10ng/L for 1, 2, 3 and 4weeks did not induce the mRNA expressions of vtg B. However, 1-, 2-, and 4-week 50μg/L MT all significantly stimulated vtg B transcripts. Further investigations are needed to elucidate the mechanism underlying the insensitivity or down-regulation of vtg B mRNA in response to EE2 in juvenile Pcc.

Impact of environmental estrogens on Yfish considering the diversity of estrogen signaling

Research on endocrine disruption in fish has been dominated by studies on estrogen-active compounds which act as mimics of the natural estrogen, 17β-estradiol (E2), and generally exert their biological actions by binding to and activation of estrogen receptors (ERs). Estrogens play central roles in reproductive physiology and regulate (female) sexual differentiation. In line with this, most adverse effects reported for fish exposed to environmental estrogens relate to sexual differentiation and reproduction. E2, however, utilizes a variety of signaling mechanisms, has multifaceted functions and targets, and therefore the toxicological and ecological effects of environmental estrogens in fish will extend beyond those associated with the reproduction. This review first describes the diversity of estrogen receptor signaling in fish, including both genomic and non-genomic mechanisms, and receptor crosstalk. It then considers the range of non-reproductive physiological processes in fish that are known to be responsive to estrogens, including sensory systems, the brain, the immune system, growth, specifically through the growth hormone/insulin-like growth factor system, and osmoregulation. The diversity in estrogen responses between fish species is then addressed, framed within evolutionary and ecological contexts, and we make assessments on their relevance for toxicological sensitivity as well as ecological vulnerability. The diversity of estrogen actions raises questions whether current risk assessment strategies, which focus on reproductive endpoints, and a few model fish species only, are protective of the wider potential health effects of estrogens. Available - although limited - evidence nevertheless suggests that quantitative environmental threshold concentrations for environmental protection derived from reproductive tests with model fish species are protective for non-reproductive effects as well. The diversity of actions of estrogens across divergent physiological systems, however, may lead to and underestimation of impacts on fish populations as their effects are generally considered on one functional process only and this may underrepresent the impact on the different physiological processes collectively.

Endocrine disruption by di-(2-ethylhexyl)-phthalate in Chinese rare minnow (Gobiocypris rarus)

Great concern has been raised over the potential impact of environmental contaminants on fish populations that inhabit the Three Gorge Reservoir. The present study investigated the endocrine-disrupting effects of di-(2-ethylhexyl)-phthalate (DEHP) on the Chinese rare minnow (Gobiocypris rarus), an endemic fish distributed in upstream waters in the Yangtze River. Adult rare minnow were exposed to environmentally relevant concentrations of DEHP (0 µg/L, 3.6 µg/L, 12.8 µg/L, 39.4 µg/L, and 117.6 µg/L) for a 21-d period. Then, concentrations of sex hormones in the plasma and relative transcription of various associated genes were measured in the hypothalamic-pituitary-gonadal (HPG) axis and liver of the fish. Exposure to DEHP resulted in greater circulating concentrations of testosterone (T) and lower concentrations of estradiol (E2), which were accompanied by upregulation of Cyp17 mRNA and downregulation of Cyp19a mRNA in the gonads of females. In males, increases of T and E2 levels were consistent with upregulation of Cyp17 and Cyp19a in the gonads. Furthermore, the T/E2 ratio was increased in females but reduced in males. A significant increase in the levels of hepatic vitellogenin (VTG) gene transcription was observed in both females and males. The present study showed that waterborne exposure to DEHP altered plasma sex hormone levels and modulated gene transcription profiles of associated genes in the HPG axis and liver, occurring mostly at higher concentrations (>39.4 µg/L), which suggests that environmental concentration of DEHP (5.4 µg/L) alone might not disturb the endocrine system of the rare minnow in the TGR.

Developmental toxicity of 3,4-dichloroaniline on rare minnow (Gobiocypris rarus) embryos and larvae

Gobiocypris rarus is a freshwater cyprinid, which possesses lots of attractive features (short life cycle, high fecundity, and especially the transparent trait during early life stage) that make it a suitable model in aquatic toxicity tests. In this study, the effects of 3,4-dichloroaniline (3,4-DCA) on the early life stages of G. rarus were measured. As endpoints, normal developmental parameters (survival rate, malformation rate, total body length and average heart rate) as well as biomarker genes (stress response (hsp70), organizer function and axis formation (wnt8a), vascular system development (vezf1), detoxification (cyp1a) and endocrine disruption (erα)) in the developing embryos and larvae were recorded during a 72 h exposure. The results revealed that reduced survival rate, increased malformation, changes in heart rate and total body length provide a gradual dose-response relationship, values of 72 h LC(50) were 4.146 (3.665-4.713) mg L(-1) for embryos and 1.088 (0.832-1.432) mg L(-1) for larvae. The developmental biochemical biomarkers are very promising tools to determine the severity of toxicants in the growing G. rarus embryos and larvae, even at a concentration of 1% for LC(50). Gene expressions of wnt8a and cyp1a in embryos were highly up-regulated (more than 100-fold) after exposure to 3,4-DCA. Overall, the present study points out that 3,4-DCA is high toxic to the early development of G. rarus, and offers a practicable and highly sensitive bioassay for the general assessment of chemical toxicity.

Effects of 17α-ethinylestradiol and bisphenol A on steroidogenic messenger ribonucleic acid levels in the rare minnow gonads

Previous studies showed that the endocrine disrupting chemicals (EDCs) affect reproductive physiology in teleosts. How the EDCs regulate gonadal steroidogenesis remains to be determined. The gonadal transcript changes of steroidogenic enzyme genes in adult rare minnow Gobiocypris rarus exposed to 17α-ethinylestradiol (EE2) and bisphenol A (BPA) were detected in the present study. The full-length cDNAs encoding steroidogenic enzymes, including steroidogenic acute regulatory protein (StAR), cytochrome P450-mediated side-chain cleavage enzyme (CYP11A1), 3β-hydroxysteroid dehydrogenase (3β-HSD), and cytochrome P450 17 A1 (CYP17A1) were isolated and characterized by RT-PCR and RACE methods. The homology and phylogenetic analyses of the amino acid sequences confirmed that the nucleotide sequences of these steroidogenic genes were correct. The mRNA tissue distribution results indicated that StAR, cyp11a1, and cyp17a1 mRNAs were mainly expressed in the gonads and 3β-HSD was mainly expressed in both the gonads and the brains. The 233 dpf adult G. rarus were exposed to EE2 (25ng/L) and BPA (5, 15, and 50 μg/L) dissolved in dimethyl sulfoxide (DMSO) or control for 7 days. The gonadal mRNA levels of StAR, cyp11a1, 3β-HSD, cyp17a1 and ovarian cytochrome P450 aromatase (cyp19a1a) were quantified by qRT-PCR. Our data indicated that 25 ng/L EE2 had different degrees of inhibitory effects on the expression of steroidogenic genes in the gonads. BPA at different levels caused concentration-specific effects on the mRNA expression of the steroidogenic genes. The transcripts of several ovarian steroidogenic genes were more sensitive to 15 μg/L BPA than that at other two levels. These findings suggest that EE2 could impair gonadal steroidogenesis by suppressing mRNA expression of steroidogenic genes and BPA could cause variations in gonadal steroidogenesis modulation with a potential consequence of compensation for the disturbance.

Molecular characterization of estrogen receptor genes in loach Paramisgurnus dabryanus and their expression upon 17α-ethinylestradiol exposure in juveniles

The full-length cDNAs for estrogen receptor 1 (esr1), esr2a and esr2b were isolated and characterized from the loach (Paramisgurnus dabryanus, Cobitidae, cypriniformes). P. dabryanus Esr1, Esr2a and Esr2b share high amino acids identities with their counterparts of cyprinid species. Quantitative real-time PCR (qRT-PCR) was used to analyze the tissue distribution of esr mRNAs in one-year-old P. dabryanus. The mRNA expression of esr1 in female liver was extremely higher than that in other tissues. esr2a mRNA expression in female intestine and in male muscle was higher than that in other tissues. esr2b mRNA expression was the highest in both male and female intestine. Two-month-old P. dabryanus were exposed to 17α-ethinylestradiol (EE2) for 3weeks and the changes of esr mRNA expression in brain, gonad and liver were analyzed by qRT-PCR. Results showed that EE2 at 1, 5 and 25 ng/L significantly suppressed testicular esr1 mRNA expression in male. The ovarian esr2a mRNA expression was significantly up-regulated at 1 ng/L EE2. In female brain, esr1 mRNA expression was significantly down-regulated at 5 ng/L EE2. Both in males and females, EE2 exposure increased the hepatic esr1 mRNA expression in a concentration-dependent manner. The present study suggests that different esrs in different tissues have differential responsiveness to EE2 and the hepatic esr1 is a sensitive biomarker to EE2 at environmental concentrations in P. dabryanus juveniles. So, the loach P. dabryanus, a typical demersal fish, is a promising ecological model organism to detect estrogenic chemicals in the sediment of aquatic environment by using molecular biomarkers.

Modulations in androgen and estrogen mediating genes and testicular response in male goldfish exposed to bisphenol A

Adverse effects of bisphenol A (BPA) on reproductive physiology were studied in male goldfish (Carassius auratus) exposed to nominal environmentally relevant concentrations (0.2 and 20 µg/L) for up to 90 d. Transcriptions of various reproductive genes were measured in brain, liver, and testis to investigate the BPA modes of action. Volume, density, total number, motility, and velocity of sperm were measured to assess testicular function. At 0.2 µg/L, BPA reduced steroidogenetic acute regulatory protein and increased estrogen receptors (ERs) messenger RNA (mRNA) transcript (ERβ1 in liver and ERβ2 in testis) after 90 d. At 20 µg/L, BPA increased mRNA transcript of androgen receptor in testis, brain- and testis-specific aromatase, and vitellogenin in liver after 90, 30, 60, and 60 d, respectively. Transcripts of ERs mRNA were increased after 30 to 60 d at 20 µg/L BPA; increase in ERβ1 mRNA was observed in testis after 7 d. Total number, volume, and motility of sperm were decreased in males exposed to 0.2 and 20 µg/L BPA, whereas sperm density and velocity were only reduced at 20 µg/L BPA. The results support the hypothesis that BPA may exert both anti-androgenic and estrogenic effects, depending on concentration, leading to diminished sperm quality. The findings provide a framework for better understanding of the mechanisms mediating adverse reproductive actions of BPA observed in different parts of the world.

Molecular cloning of Foxl2 gene and the effects of endocrine-disrupting chemicals on its mRNA level in rare minnow, Gobiocypris rarus

Endocrine-disrupting chemicals (EDCs) can affect normal sexual differentiation in fish. Foxl2, one forkhead transcription factor, plays an important role in ovarian differentiation in the early development of the female gonad in mammals and fish. How EDCs affect Foxl2 expression is little known. In this study, we isolated a Foxl2 cDNA from the ovary of rare minnow Gobiocypris rarus and examined its expression during early development stages and in different adult tissues. Then, we analyzed Foxl2 expression in G. rarus juvenile following 3-day exposure to 17α- ethinylestradiol (EE2), 4-n-nonylphenol (NP), and bisphenol A (BPA). Alignment of known Foxl2 sequences among vertebrates showed high identity in forkhead domain and C-terminal region with other vertebrate proteins. Quantitative RT-PCR analysis showed that Foxl2 expression was linear decrease and cyp19a1a, the downstream target gene of Foxl2, had no correlation with Foxl2 from 18 to 50 days post fertilization (dpf). Among different adult tissues, Foxl2 is mainly expressed in ovary, brain, gill, eye, and male spleen. In the 3-day exposure, the juvenile fish to EDCs, 0.1 nM EE2, and 1 nM BPA significantly up-regulated the expression of Foxl2 gene, while NP had no effect on Foxl2 expression. Altogether, these results provide basic data for further study on how Foxl2 mediates EDCs impact on the sexual differentiation in G. rarus.

Estrogenic potential of benzotriazole on marine medaka (Oryzias melastigma)

This study, for the first time, assessed the reproductive effects of benzotriazoles, widely used industrial chemicals, on marine fish. Marine medakas (Oryzias melastigma) were exposed to 0.01, 0.1, and 1mg/L benzotriazole for periods of four and 35 days. The results that are obtained showed that the expression levels of CYP1A1 were down-regulated in the liver, gills and intestines of both males and females. Vitellogenin (VTG) was highly induced in the liver, gills and intestine of both male and female marine medaka, and CYP19a was up-regulated in the ovaries especially after being exposed for 35 days. Most importantly, the results of the present study suggest that even at environmentally relevant concentrations detected in the aquatic environment, 0.01 mg/L, benzotriazole also caused notable changes in expression levels of VTG, CYP1A1 and CYP19a. More concerns about the toxicity of benzotriazoles on marine animals should be raised.

Sexually dimorphic and ontogenetic expression of dmrt1, cyp19a1a and cyp19a1b in Gobiocypris rarus

Fish have diverse sex determination and differentiation. DMRT1 and aromatase are conserved in the phyla and play pivotal roles in sex development. Gobiocypris rarus is a small fish used as a model in aquatic toxicology in China and has been used to study the effects of environmental endocrine disruptors on gene expression, but its sexual development remains elusive. Here, we report the full-length cDNA of G. rarus dmrt1 and its expression along with the expression of cyp19a1a and cyp19a1b, two genes encoding gonad and brain type aromatases, in adults and during ontogenesis. Both cyp19a1a and dmrt1 are expressed in the ovary and testis but show sexual dimorphism. Expression of cyp19a1a in the ovary is higher than in testes and dmrt1 follows the opposite pattern. Juvenile gonad histology changes at 15 days after hatching. The dimorphic expression of dmrt1 and cyp19a1a appears from 5 days after hatching, which is earlier than histological change. cyp19a1b is expressed coordinately with cyp19a1a until 15 days after hatching. These results show that dmrt1 and cyp19a1a play important roles in sex determination and sex differentiation in G. rarus.

PCR-ELISA detection of estrogen receptor β mRNA expression and plasma vitellogenin induction in juvenile sole (Solea solea) exposed to waterborne 4-nonylphenol

In this study, the effect of 4-nonylphenol (4NP) on reproductive axis of sole (Solea solea) has been investigated by using selected biomarkers of estrogenic effects: vitellogenin (VTG) and estrogen receptor β (ERβ) mRNA. Furthermore, an enzyme linked immunosorbent assay (ELISA) detection system of reverse transcriptase-polymerase chain reaction (RT-PCR) products for the analysis of sole ERβ mRNA expression was developed and validated. The proposed method allows large-scale analyses of different mRNAs in fast and not expensive way. Our results have demonstrated that the PCR-ELISA method developed shows high sensitivity, good reproducibility and also the potential for semi-quantitative analysis of hepatic ERβ mRNAs. Both plasma VTG level and ERβ mRNA expression were increased in tested animals following a short exposure to environmental relevant concentrations (10(-6)M) of 4NP, confirming the functional role of ERβ in the regulation of xenoestrogens-induced production of VTG. The methodology provided in the present study together with the preliminary results on the hepatic expression of ERβ may be useful in environmental xenoestrogens monitoring studies, using flatfish as "sentinel" species.

Expression of zona pellucida B proteins in juvenile rare minnow (Gobiocypris rarus) exposed to 17α-ethinylestradiol, 4-nonylphenol and bisphenol A

Zona pellucida (ZP) containing proteins are glycoproteins in teleost chorion and are encoded by several gene subfamilies, mainly including ZPA, ZPB, ZPC and ZPX genes. In teleost species, ZP genes are expressed either in liver under regulation of estrogen or in ovary. In the present study, five ZP gene isoforms were isolated and characterized in Gobiocypris rarus. The putative amino acid sequences of these ZP gene isoforms contain the typical trefoil motif and a ZP domain. These five G. rarus ZP gene isoforms were named as grZPB.1, grZPB.2, grZPB.3, grZPB.4 and grZPB.5. Real-time quantitative reverse transcription PCR (RT-qPCR) analysis indicated that all these ZP mRNA isoforms were exclusively expressed in ovary. G. rarus juveniles at the age of 21 days postfertilization were exposed to 17α-ethinylestradiol (EE2; 0.01, 0.1 and 1 nM), 4-nonylphenol (4-NP; 10, 100 and 1000 nM) or bisphenol A (BPA; 0.1, 1 and 10nM) for 3 days. mRNA expressions of ZPB isoforms following the exposure to xenoestrogen were detected by RT-qPCR. Data were analyzed by the 2(-△△Cq) method. The results indicate that induction by 0.1-1nM EE2 on mRNA expression of the grZPB isoforms is weaker than for vitellogenin. 4-NP exposures at three concentrations had differential effects on the grZPBs. BPA at three concentrations weakly induced mRNA expression of the grZPB isoforms.

Germ cell specific expression of Vasa in rare minnow, Gobiocypris rarus

Germ cells are set aside early with somatic cells and take roles for reproduction of species from one generation to the next generation. Vasa, a member of DEAD family is well documented as germ cell marker in the animal kingdom. Rare minnow, Gobiocypris rarus, is an emerging model fish in China to study development and toxicology, etc. A suitable germ cell marker will benefit the studies of the factors that may influence germ cell development. Here, we report the cloning and characterization of G. rarus vasa named Grvas whose protein product has the typical characteristics of Vasa proteins. RT-PCR results showed that Grvas is expressed specifically in the gonads of male and female, it is maternally deposited into the eggs for embryos and is continuously expressed in the embryos from the zygote to larvae and adult. Grvas mRNA and/or protein is restricted to the germ cells of ovary and testis. Temporal expression of Grvas mRNA is similar to that of zebrafish vasa during embryogenesis. Grvas signals are coincident with primordial germ cells. These results mean that a germ cell marker, Grvas is isolated from rare minnow and its expression is exclusively in germ cells.

Effects of sexual steroids on the expression of foxl2 in Gobiocypris rarus

Gobiocypris rarus is an emerging fish model for aquatic toxicology in China as it is sensitive to environmental hormone disruptors. Exogenous sex steroids can affect sex differentiation and the expression of sex-related genes. Foxl2, a member of forkhead-box transcription factor family, is the key gene for ovary development and its mutation causes the blepharophimosis ptosis epicanthus inversus syndrome in human. We find that two foxl2 genes exist in fish genome, one is foxl2, and the other is foxl2b. Here, we reported the isolation and expression of foxl2 in G. rarus. G. rarus foxl2 cDNA is 1700bp in length with a 921bp of open reading frame encoding 306 amino acids containing the typical FH-domain. Semi-quantitative RT-PCR revealed its predominant expression in the eye, brain, gill and gonads. Moreover, the expression level in the ovary was significantly higher than that in the testis. Quantitative RT-PCR showed that foxl2 was up regulated after treatment with estradiol and was down regulated with 2-methyl-testosterone. These results suggested that Foxl2 plays an important role in female development of G. rarus, foxl2 mRNA expression is regulated by downstream sex hormones, and foxl2 can be used as a molecular indicator monitoring the environmental endocrine disruptors.