Estradiol-induced gene expression in largemouth bass (Micropterus salmoides)

The New Roles of traf6 Gene Involved in the Development of Zebrafish Liver and Gonads

Traf6, an adaptor protein, exhibits non-conventional E3 ubiquitin ligase activity and was well studied as an important factor in immune systems and cancerogenesis. In mice, the traf6-null caused a perinatal death, so that the underlying pathophysiology of traf6-defeciency is still largely unclear in animals. Here, in the present study, a traf6 knockout zebrafish line (traf6-/-) was generated and could survive until adulthood, providing a unique opportunity to demonstrate the functions of traf6 gene in animals' organogenesis beyond the mouse model. The body of traf6-/- fish was found to be significantly shorter than that of the wildtype (WT). Likewise, a comparative transcriptome analysis showed that 866 transcripts were significantly altered in the traf6-/- liver, mainly involved in the immune system, metabolic pathways, and progesterone-mediated oocyte maturation. Especially, the mRNA expression of the pancreas duodenum homeobox protein 1 (pdx1), glucose-6-phosphatase (g6pcb), and the vitellogenesis genes (vtgs) were significantly decreased in the traf6-/- liver. Subsequently, the glucose was found to be accumulated in the traf6-/- liver tissues, and the meiotic germ cell was barely detected in traf6-/- testis or ovary. The findings of this study firstly implied the pivotal functions of traf6 gene in the liver and gonads' development in fish species.

Reproductive condition of the black-lip pearl oyster Pinctada margaritifera during the lunar phase

This study analyzed the relationship between the lunar phase and the reproductive cycle of Pinctada margaritifera inhabiting Weno Island, Chuuk Lagoon, Micronesia. We measured indicators of maturity (gonadosomatic index [GSI] and sexual maturation-related genes) and investigated changes in the gonadal maturity stages (GMS) of P. margaritifera over lunar cycle. GSI was higher around the full moon. GMS of P. margaritifera were classified as the early gametogenesis stage, ripe and spawning stage, and spent and degenerating stage. A large percentage of oysters was observed in the ripe and spawning stage at the first quarter moon in female and the full moon in male as well as in the spent and degenerating stages at the third quarter moon in both sexes. In addition, the expression of doublesex- and mab-3-related transcription factor 2 (DMRT2) in the male P. margaritifera black-lip pearl oyster was the highest during the full and third quarter moon phases, whereas no difference in expression was observed with the lunar phase in females. In contrast, the expression of vitellogenin (VTG) was the highest in female P. margaritifera during the first and third quarters. No difference in expression was observed according to the lunar phase in males. The results suggest that the lunar phase directly affects the expression of sexually mature gonads in P. margaritifera black-lip pearl oyster.

Metamifop as an estrogen-like chemical affects the pituitary-hypothalamic-gonadal (HPG) axis of female rice field eels (Monopterus albus)

Metamifop (MET) is a widely used herbicide. It is likely for it to enter water environment when utilized, thus potential impacts may be produced on aquatic animals. Little information is available about its effects on the endocrine system of fish to date. In the current study, female rice field eels (Monopterus albus) were exposed to different MET concentrations (0, 0.2, 0.4, 0.6, 0.8 mg L -1) for 96 h to examine the effect of MET on the hypothalamic-pituitary-gonadal (HPG) axis and sexual reversal. The results showed that high concentrations of MET exposure increased vitellogenin (VTG) levels in liver and plasma, but plasma sex hormone levels were not affected by MET exposure. MET exposure increased the expression of CYP19A1b and CYP17 that regulate sex hormone production in the brain, but the expression of genes (CYP19A1a, CYP17, FSHR, LHCGR, hsd11b2, 3β-HSD) associated with sex hormone secretion in the ovary and the estrogen receptor genes (esr1, esr2a, esr2b) in the liver were all suppressed. In addition, the expression of sex-related gene (Dmrt1) was suppressed. This study revealed for the first time that MET has estrogen-like effects and has a strong interference with the expression of HPG axis genes. MET did not show the ability to promote the sexual reversal in M. albus, on the contrary, the genes expression showed that the occurrence of male pathway was inhibited.

Reproductive and thyroid endocrine axis cross-talk in rainbow trout (Oncorhynchus mykiss) alevins

The goal of this study was to characterize morphological and molecular effects in rainbow trout alevins after waterborne exposures to 17β-estradiol (E2; 0.0008 to 0.5 μg/L), triiodothyronine (T3; 0.52 to 65 μg/L), and various co-treatments for 21 to 23 days. Interestingly, there was no consistent evidence that E2 alone influenced growth, development or deformity rates, however, 65 μg/L T3 alone expedited development, and both 13 μg/L and 65 μg/L alone caused a unique opercular deformity not previously reported. In addition, some potentiation between E2 and T3 at lower concentrations suggests some cross-talk between these two hormonal pathways may also contribute to the development of this opercular deformity. Gene expression changes were observed, including induction of vtg in rainbow trout alevins at 0.02 μg/L concentration of E2, which is the lowest concentration reported to induce vtg in rainbow trout alevins. These data suggest low-level E2 does not negate abnormal growth and development caused by hyperthyroidism, and examining more time points is likely required to demonstrate a stronger response profile for individual hormones and endocrine axes cross-talk.

Effects of polycyclic aromatic hydrocarbons on biomarker responses in Gambusia yucatana, an endemic fish from Yucatán Peninsula, Mexico

Polycyclic aromatic hydrocarbons (PAHs) are petroleum components that, when dissolved in the aquatic environment, can disrupt normal animal physiological functions and negatively affect species populations. Gambusia yucatana is an endemic fish of the Yucatán Peninsula that seems to be particularly sensitive to the presence of PAHs dissolved in the water. Here, we examined PAH effects on gene expressions linked to endocrine disruption and biotransformation in this species. Specifically, we examined the expression of vitellogenin I (vtg1), vitellogenin II (vtg2), oestrogen receptor α (esr1), oestrogen receptor β (esr2), aryl hydrocarbon receptor (AhR) and the cytochrome P4503A (CYP3A) genes. We exposed G. yucatana to different concentrations of PAHs (3.89, 9.27, 19.51 μg/L) over a period of 72 h and found changes associated with reproduction, such as increases in hepatic expression of vtg, esr, AhR and CYP3A, mainly at concentrations of 9.27 and 19.51 μg/L. Our results also indicate that benzo[a]pyrene was probably the main PAH responsible for the observed effects. The genes examined here can be used as molecular markers of endocrine-disrupting compounds, as the PAHs, present in the environment, as gene expression increases could be observed as early as after 24 h. These biomarkers can help researchers and conservationists rapidly identify the impacts of oil spills and improve mitigation before the detrimental effects of environmental stressors become irreversible.

Genistein Induces Adipogenic and Autophagic Effects in Rainbow Trout (Oncorhynchus mykiss) Adipose Tissue: In Vitro and In Vivo Models

Soybeans are one of the most used alternative dietary ingredients in aquafeeds. However, they contain phytoestrogens like genistein (GE), which can have an impact on fish metabolism and health. This study aimed to investigate the in vitro and in vivo effects of GE on lipid metabolism, apoptosis, and autophagy in rainbow trout (Oncorhynchus mykiss). Primary cultured preadipocytes were incubated with GE at different concentrations, 10 or 100 μM, and 1 μM 17β-estradiol (E2). Furthermore, juveniles received an intraperitoneal injection of GE at 5 or 50 µg/g body weight, or E2 at 5 µg/g. In vitro, GE 100 μM increased lipid accumulation and reduced cell viability, apparently involving an autophagic process, indicated by the higher LC3-II protein levels, and higher lc3b and cathepsin d transcript levels achieved after GE 10 μM. In vivo, GE 50 µg/g upregulated the gene expression of fatty acid synthase (fas) and glyceraldehyde-3-phosphate dehydrogenase in adipose tissue, suggesting enhanced lipogenesis, whereas it increased hormone-sensitive lipase in liver, indicating a lipolytic response. Besides, autophagy-related genes increased in the tissues analyzed mainly after GE 50 µg/g treatment. Overall, these findings suggest that an elevated GE administration could lead to impaired adipocyte viability and lipid metabolism dysregulation in rainbow trout.

Gonadotropin-releasing hormone-independent effects of recombinant vertebrate ancient long opsin in the goldfish Carassius auratus reveal alternative reproduction pathways

Vertebrate ancient long (VAL)-opsin is a green-sensitive photoreceptor that shows high sequence similarity to vertebrate ancient opsin, which is considered to play a role in sexual maturation via gonadotropin-releasing hormone (GnRH); however, the role of VAL-opsin in vertebrate sexual maturity remains unclear. Therefore, we investigated the possible role of VAL-opsin in reproduction in the goldfish Carassius auratus under a state of GnRH inhibition. Goldfish were injected with recombinant VAL-opsin protein (0.5 μg/g body mass) and/or the GnRH antagonist cetrorelix (0.5 μg/fish), and changes in the mRNA expression levels of genes associated with goldfish reproduction were measured by quantitative polymerase chain reaction, including those involved in the hypothalamus-pituitary-gonad (HPG) axis, VAL-opsin, GnRH, the gonadotropins (GTHs) luteinizing hormone and follicle-stimulating hormone, and estrogen receptor (ER). Moreover, the fish were irradiated with a green light-emitting diode (520 nm) to observe the synergistic effect on the HPG axis with VAL-opsin. Green LED exposure significantly and slightly increased the VAL-opsin and GnRH levels, respectively; however, these effects were blocked in groups injected with cetrorelix at all time points. Cetrorelix significantly decreased the mRNA levels of GTHs and ER, whereas these hormones recovered by co-treatment with VAL-opsin. These results indicate that green LED is an effective light source to promote the expression of sex hormones in fish. Moreover, VAL-opsin not only affects activity of the HPG axis but also appears to act on the pituitary gland directly to stimulate a new sexual maturation pathway that promotes the secretion of GTHs independent of GnRH.

Neurodevelopmental effects of natural and synthetic ligands of estrogen and progesterone receptors in zebrafish eleutheroembryos

Natural and synthetic estrogens and progestins are widely used in human and veterinary medicine and are detected in waste and surface waters. Our previous studies have clearly shown that a number of these substances targets the brain to induce the estrogen-regulated brain aromatase expression but the consequences on brain development remain virtually unexplored. The aim of the present study was therefore to investigate the effect of estradiol (E2), progesterone (P4) and norethindrone (NOR), a 19-nortestosterone progestin, on zebrafish larval neurogenesis. We first demonstrated using real-time quantitative PCR that nuclear estrogen and progesterone receptor brain expression is impacted by E2, P4 and NOR. We brought evidence that brain proliferative and apoptotic activities were differentially affected depending on the steroidal hormone studied, the concentration of steroids and the region investigated. Our findings demonstrate for the first time that steroid compounds released in aquatic environment have the capacity to disrupt key cellular events involved in brain development in zebrafish embryos further questioning the short- and long-term consequences of this disruption on the physiology and behavior of organisms.

Experimental Approaches for Characterizing the Endocrine-Disrupting Effects of Environmental Chemicals in Fish

Increasing industrial and agricultural activities have led to a disturbing increase of pollutant discharges into the environment. Most of these pollutants can induce short-term, sustained or delayed impacts on developmental, physiological, and behavioral processes that are often regulated by the endocrine system in vertebrates, including fish, thus they are termed endocrine-disrupting chemicals (EDCs). Physiological impacts resulting from the exposure of these vertebrates to EDCs include abnormalities in growth and reproductive development, as many of the prevalent chemicals are capable of binding the receptors to sex steroid hormones. The approaches employed to investigate the action and impact of EDCs is largely dependent on the specific life history and habitat of each species, and the type of chemical that organisms are exposed to. Aquatic vertebrates, such as fish, are among the first organisms to be affected by waterborne EDCs, an attribute that has justified their wide-spread use as sentinel species. Many fish species are exposed to these chemicals in the wild, for either short or prolonged periods as larvae, adults, or both, thus, studies are typically designed to focus on either acute or chronic exposure at distinct developmental stages. The aim of this review is to provide an overview of the approaches and experimental methods commonly used to characterize the effects of some of the environmentally prevalent and emerging EDCs, including 17 α-ethinylestradiol, nonylphenol, BPA, phthalates, and arsenic; and the pervasive and potential carriers of EDCs, microplastics, on reproduction and growth. In vivo and in vitro studies are designed and employed to elucidate the direct effects of EDCs at the organismal and cellular levels, respectively. In silico approaches, on the other hand, comprise computational methods that have been more recently applied with the potential to replace extensive in vitro screening of EDCs. These approaches are discussed in light of model species, age and duration of EDC exposure.

Early-life exposure to 17β-estradiol and 4-nonylphenol impacts the growth hormone/insulin-like growth-factor system and estrogen receptors in Mozambique tilapia, Oreochromis mossambicus

It is widely recognized that endocrine disrupting chemicals (EDCs) released into the environment through anthropogenic activities can have short-term impacts on physiological and behavioral processes and/or sustained or delayed long-term developmental effects on aquatic organisms. While numerous studies have characterized the effects of EDCs on temperate fishes, less is known on the effects of EDCs on the growth and reproductive physiology of tropical species. To determine the long-term effects of early-life exposure to common estrogenic chemicals, we exposed Mozambique tilapia (Oreochromis mossambicus) yolk-sac fry to 17β-estradiol (E2) and nonylphenol (NP) and subsequently characterized the expression of genes involved in growth and reproduction in adults. Fry were exposed to waterborne E2 (0.1 and 1 μg/L) and NP (10 and 100 μg/L) for 21 days. After the exposure period, juveniles were reared for an additional 112 days until males were sampled. Gonadosomatic index was elevated in fish exposed to E2 (0.1 μg/L) while hepatosomatic index was decreased by exposure to NP (100 μg/L). Exposure to E2 (0.1 μg/L) induced hepatic growth hormone receptor (ghr) mRNA expression. The high concentration of E2 (1 μg/L), and both concentrations of NP, increased hepatic insulin-like growth-factor 1 (igf1) expression; E2 and NP did not affect hepatic igf2 and pituitary growth hormone (gh) levels. Both E2 (1 μg/L) and NP (10 μg/L) induced hepatic igf binding protein 1b (igfbp1b) levels while only NP (100 μg/L) induced hepatic igfbp2b levels. By contrast, hepatic igfbp6b was reduced in fish exposed to E2 (1 μg/L). There were no effects of E2 or NP on hepatic igfbp4 and igfbp5a expression. Although the expression of three vitellogenin transcripts was not affected, E2 and NP stimulated hepatic estrogen receptor (erα and erβ) mRNA expression. We conclude that tilapia exposed to E2 and NP as yolk-sac fry exhibit subsequent changes in the endocrine systems that control growth and reproduction during later life stages.

Interaction of nuclear ERs and GPER in vitellogenesis in zebrafish

Estrogens exert their biological functions through the estrogen receptors (ERs). In zebrafish, three nuclear estrogen receptors (nERs) named ERα, ERβ1 and ERβ2 and one membrane-bound G protein-coupled estrogen receptor (GPER) are identified. Vitellogenin (Vtg) is predominantly expressed in liver and strongly response to the stimulation of estrogen. It has been proposed that all three nERs are functionally involved in vitellogenesis and ERα may act as the major mediator in teleost. However, the role of GPER and its interaction with nERs in this process are not yet defined in teleost species. In the present study, we provide genetic evidence for the functional significance of ERα that the expression of Vtg genes (vtg1, vtg2, vtg3) and their response to estradiol stimulation were significantly decreased in esr1 mutant zebrafish. Activation of ERβ1 and ERβ2 induced Vtg expression through ERα. Moreover, the involvement of GPER in vitellogenesis and its interaction with nERs in zebrafish were firstly proposed in this work. Activation of GPER induced Vtg genes expression while inhibition of GPER significantly attenuated the estrogenic effect on Vtg. Both treatments altered the expression levels of nERs, suggesting GPER acts interactively with nERs. Collectively, the involvement of both nERs and GPER in regulation of vitellogenesis is demonstrated. ERα is the central factor, acting interactively with ERβ1, ERβ2 and GPER, and GPER regulates vitellogenesis directly and interactively with nERs.

In vivo effects of 17α-ethinylestradiol, 17β-estradiol and 4-nonylphenol on insulin-like growth-factor binding proteins (igfbps) in Atlantic salmon

Feminizing endocrine disrupting compounds (EDCs) affect the growth and development of teleost fishes. The major regulator of growth performance, the growth hormone (Gh)/insulin-like growth-factor (Igf) system, is sensitive to estrogenic compounds and mediates certain physiological and potentially behavioral consequences of EDC exposure. Igf binding proteins (Igfbps) are key modulators of Igf activity, but their alteration by EDCs has not been examined. We investigated two life-stages (fry and smolts) of Atlantic salmon (Salmo salar), and characterized how the Gh/Igf/Igfbp system responded to waterborne 17α-ethinylestradiol (EE₂), 17β-estradiol (E₂) and 4-nonylphenol (NP). Fry exposed to EE₂ and NP for 21 days had increased hepatic vitellogenin (vtg) mRNA levels while hepatic estrogen receptor α (erα), gh receptor (ghr), igf1 and igf2 mRNA levels were decreased. NP-exposed fry had reduced body mass and total length compared to controls. EE₂ and NP reduced hepatic igfbp1b1, -2a, -2b1, -4, -5b2 and -6b1, and stimulated igfbp5a. In smolts, hepatic vtg mRNA levels were induced following 4-day exposures to all three EDCs, while erα only responded to EE₂ and E₂. EDC exposures did not affect body mass or fork length; however, EE₂ diminished plasma Gh and Igf1 levels in parallel with reductions in hepatic ghr and igf1. In smolts, EE₂ and E₂ diminished hepatic igfbp1b1, -4 and -6b1, and stimulated igfbp5a. There were no signs of compromised ionoregulation in smolts, as indicated by unchanged branchial ion pump/transporter mRNA levels. We conclude that hepatic igfbps respond (directly and/or indirectly) to environmental estrogens during two key life-stages of Atlantic salmon, and thus may modulate the growth and development of exposed individuals.

17β-Estradiol induces cyto-genotoxicity on blood cells of common carp (Cyprinus carpio)

17β-Estradiol, a natural hormone present at high concentrations in aquatic ecosystems, affects and modifies endocrine function in animals. In recent years research workers have expressed concern over its potential effects on aquatic organisms; however, little is known about its capacity to induce genetic damage or the pro-apoptotic effects of such damage on fish. Therefore, this study aimed to evaluate 17β-estradiol-induced cyto-genotoxicity in blood cells of the common carp Cyprinus carpio exposed to different concentrations (1 ng, 1 μg and 1 mg L^-1). Peripheral blood samples were collected and evaluated by comet assay, micronucleus test, determination of caspase-3 activity and TUNEL assay at 12, 24, 48, 72 and 96 h of exposure. Increases in frequency of micronuclei, TUNEL-positive cells and caspase-3 activity were observed, particularly at the highest concentration. In contrast, the comet assay detected significant increases at 24 and 96 h with the 1 μg and 1 ng L^-1 concentrations respectively. The set of assays used in the present study constitutes a reliable early warning biomarker for evaluating the toxicity induced by this type of emerging contaminants on aquatic species.

Gene Expression Profiling in Fish Toxicology: A Review

In this review, we present an overview of transcriptomic responses to chemical exposures in a variety of fish species. We have discussed the use of several molecular approaches such as northern blotting, differential display reverse transcription-polymerase chain reaction (DDRT-PCR), suppression subtractive hybridization (SSH), real time quantitative PCR (RT-qPCR), microarrays, and next-generation sequencing (NGS) for measuring gene expression. These techniques have been mainly used to measure the toxic effects of single compounds or simple mixtures in laboratory conditions. In addition, only few studies have been conducted to examine the biological significance of differentially expressed gene sets following chemical exposure. Therefore, future studies should focus more under field conditions using a multidisciplinary approach (genomics, proteomics and metabolomics) to understand the synergetic effects of multiple environmental stressors and to determine the functional significance of differentially expressed genes. Nevertheless, recent developments in NGS technologies and decreasing costs of sequencing holds the promise to uncover the complexity of anthropogenic impacts and biological effects in wild fish populations.

Direct Regulation of Aromatase B Expression by 17β-Estradiol and Dopamine D1 Receptor Agonist in Adult Radial Glial Cells

Aromatase cytochrome P450arom (cyp19) is the only enzyme that has the ability to convert androgens into estrogens. Estrogens, which are produced locally in the vertebrate brain play many fundamental roles in neuroendocrine functions, reproductive functions, socio-sexual behaviors, and neurogenesis. Radial glial cells (RGCs) are neuronal progenitor cells that are abundant in fish brains and are the exclusive site of aromatase B expression and neuroestrogen synthesis. Using a novel in vitro RGC culture preparation we studied the regulation of aromatase B by 17β-estradiol (E2) and dopamine (DA). We have established that activation of the dopamine D1 receptor (D1R) by SKF 38393 up-regulates aromatase B gene expression most likely through the phosphorylation of cyclic AMP response element binding protein (CREB). This up-regulation can be enhanced by low concentration of E2 (100 nM) through increasing the expression of D1R and the level of p-CREB protein. However, a high concentration of E2 (1 μM) and D1R agonist together failed to up-regulate aromatase B, potentially due to attenuation of esr2b expression and p-CREB levels. Furthermore, we found the up-regulation of aromatase B by E2 and DA both requires the involvement of esr1 and esr2a. The combined effect of E2 and DA agonist indicates that aromatase B in the adult teleost brain is under tight control by both steroids and neurotransmitters to precisely regulate neuroestrogen levels.

Potential estrogenic effects of wastewaters on gene expression in Pimephales promelas and fish assemblages in streams of southeastern New York

Direct linkages between endocrine-disrupting compounds (EDCs) from municipal and industrial wastewaters and impacts on wild fish assemblages are rare. The levels of plasma vitellogenin (Vtg) and Vtg messenger ribonucleic acid (mRNA) in male fathead minnows (Pimephales promelas) exposed to wastewater effluents and dilutions of 17α-ethinylestradiol (EE2), estrogen activity, and fish assemblages in 10 receiving streams were assessed to improve understanding of important interrelations. Results from 4-d laboratory assays indicate that EE2, plasma Vtg concentration, and Vtg gene expression in fathead minnows, and 17β-estradiol equivalents (E2Eq values) were highly related to each other (R(2)  = 0.98-1.00). Concentrations of E2Eq in most effluents did not exceed 2.0 ng/L, which was possibly a short-term exposure threshold for Vtg gene expression in male fathead minnows. Plasma Vtg in fathead minnows only increased significantly (up to 1136 μg/mL) in 2 wastewater effluents. Fish assemblages were generally unaffected at 8 of 10 study sites, yet the density and biomass of 79% to 89% of species populations were reduced (63-68% were reduced significantly) in the downstream reach of 1 receiving stream. These results, and moderate to high E2Eq concentrations (up to 16.1 ng/L) observed in effluents during a companion study, suggest that estrogenic wastewaters can potentially affect individual fish, their populations, and entire fish communities in comparable systems across New York, USA.

Omics for aquatic ecotoxicology: control of extraneous variability to enhance the analysis of environmental effects

There are multiple sources of biological and technical variation in a typical ecotoxicology study that may not be revealed by traditional endpoints but that become apparent in an omics dataset. As researchers increasingly apply omics technologies to environmental studies, it will be necessary to understand and control the main source(s) of variability to facilitate meaningful interpretation of such data. For instance, can variability in omics studies be addressed by changing the approach to study design and data analysis? Are there statistical methods that can be employed to correctly interpret omics data and make use of unattributed, inherent variability? The present study presents a review of experimental design and statistical considerations applicable to the use of omics methods in systems toxicology studies. In addition to highlighting potential sources that contribute to experimental variability, this review suggests strategies with which to reduce and/or control such variability so as to improve reliability, reproducibility, and ultimately the application of omics data for systems toxicology.

Nonmonotonic response of vitellogenin and estrogen receptor α gene expression after octylphenol exposure of Cichlasoma dimerus (Perciformes, Cichlidae)

In oviparous vertebrates, vitellogenin (VTG) is mainly produced by the liver in response to estrogen (E2) and its synthesis is traditionally coupled to estrogen receptor alpha induction. Even though VTG is a female-specific protein, chemicals that mimic natural estrogens, known as xenoestrogens, can activate its expression in males causing endocrine disruption to wildlife and humans. Alkylphenols such as nonylphenol (NP) and octylphenol (OP) are industrial additives used in the manufacture of a wide variety of plastics and detergents, and can disrupt endocrine functions in exposed animals. For more than a decade, the freshwater cichlid fish Cichlasoma dimerus has been used for ecotoxicological studies in our laboratory. We recently found an up-regulation of VTG gene expression in livers of male fish exposed to OP, from a silent state to values similar to those of E2-induced fish. To better understand the underlying mechanisms behind the action of xenoestrogens, the aim of this study was to analyze the dose-response relationship of C. dimerus VTG and estrogen receptors (ERs) gene expression after waterborne exposure to 0.15, 1.5, 15, and 150μg/L OP for up to 1 month (0, 1, 3, 7, 14, 21, and 28 days). At the end of the experiment, histological features of exposed fish included active hepatocytes with basophilic cytoplasm and high eosinophilic content in their vascular system due to augmented expression of VTG. In testis, high preponderance of sperm was found in fish exposed to 150μg/L OP. A classic dose-response down-regulation of the expression of Na(+)/K(+)-ATPase, a "non-gender specific gene" used for comparison, was found with increasing OP concentrations. No VTG and very low levels of ERα were detected in control male livers, but an up-regulation of both genes was found in males exposed to 0.15 or 150μg/L OP. Moreover, VTG transcripts were significant as early as day 3 or day 1 of exposure to these OP concentrations, respectively. Nearly no response was detected in 1.5 and 15μg/L OP exposed-fish. Data was curve-fitted evidencing a nonmonotonic dose-response curve. Interestingly, ERβ2 mRNA expression was augmented above baseline levels only when males were exposed to the lowest OP concentration. We speculate that genomic control of vitellogenesis is under control of multiple steroid receptors with different affinities for ligands. ERβ isoform, only up-regulated with very low concentrations of ligand, would act as a sensors of OP (or E2) to induce ERα and VTG. With high OP concentrations, the expression of ERα isoform is promptly augmented, with the concomitant VTG transactivation.

The Expression of Leptin, Estrogen Receptors, and Vitellogenin mRNAs in Migrating Female Chum Salmon, Oncorhynchus keta: The Effects of Hypo-osmotic Environmental Changes

Leptin plays an important role in energy homeostasis and reproductive function in fish, especially in reproduction. Migrating fish, such as salmonoids, are affected by external environmental factors, and salinity changes are a particularly important influence on spawning migrations. The aim of this study was to test whether changes in salinity affect the expression of leptin, estrogen receptors (ERs), and vitellogenin (VTG) in chum salmon (Oncorhynchus keta). The expression and activity of leptin, the expression of ERs and VTG, and the levels of estradiol-17β and cortisol increased after the fish were transferred to FW, demonstrating that changes in salinity stimulate the HPG axis in migrating female chum salmon. These findings reveal details about the role of elevated leptin levels and sex steroid hormones in stimulating sexual maturation and reproduction in response to salinity changes in chum salmon.

Kisspeptin regulates the hypothalamus-pituitary-gonad axis gene expression during sexual maturation in the cinnamon clownfish, Amphiprion melanopus

Kisspeptins (Kiss) have been recognized as potent regulators of reproduction in teleosts, and Kiss is suggested to be a key regulator of the hypothalamus-pituitary-gonad axis (HPG). However, its regulatory role on reproduction in fish remains unclear. Therefore, to investigate the role of Kiss on fish reproduction, this study aimed to test differences in the hormones of the HPG axis, Kiss as neuropeptides, and sex steroids on the sexual maturation of paired cinnamon clownfish, Amphiprion melanopus, following treatment with Kiss. We investigated the actions of sex maturation hormones, including HPG axis hormones and sex steroid hormones, such as gonadotropin-releasing hormones, gonadotropin hormones (GTHs), GTH receptors, estrogen receptors, and vitellogenin in the pituitary, gonads, and liver following treatment with Kiss. The expression levels of HPG axis genes increased after the Kiss injection. In addition, the levels of plasma 17α-hydroxypregnenolone, estradiol-17β, and 11-ketotestosterone increased. These results support the hypothesis that Kiss play important roles in the regulation of the HPG axis and are most likely involved in gonadal development and sexual maturation in cinnamon clownfish.

Estrogen receptor function and regulation in fish and other vertebrates

Estrogens, steroid hormones critically involved in reproductive processes of vertebrates, signal primarily through their intracellular estrogen receptors (ERs). The ERs belong to a superfamily of nuclear receptors that act as ligand inducible transcription factors. Herein, we review what is known about ER structure, subtypes, mechanism(s) of action and auto-regulation by estrogens. Focus is placed on the ER in fish but comparisons are made to mammals and other vertebrates. Finally, we provide context and a proposed model integrating our knowledge on autoregulation of the receptor and its functions in the liver. Future areas of study are suggested, along with cautions when designing experiments, especially for the detection of endocrine disruptors.

The physiology functions of estrogen receptor α (ERα) in reproduction cycle of ovoviviparous black rockfish, Sebastes schlegeli Hilgendorf

This paper revealed the expression pattern of ERα in the ovoviviparous teleost, Sebastes schlegeli. In this paper, we isolated the cDNA encoding for estrogen receptor alpha of black rockfish (S. schlegeli) from its ovary, named as black rockfish ERα (brfERα). The cDNA sequence of brfERα consists of 2972bp with an open reading frame encoding a 624 amino acid putative protein which exhibits high identities with other teleosts'. The tissue distribution of brfERα mRNA was examined using RT-PCR. BrfERα showed generally expressions in most tissues of female black rockfish, besides, the higher degree of expressions were seen in ovary, liver, duodenum and fat, whereas it had a more restricted distribution in male fish. In ovary, the expression level of brfERα was as similar as the serum levels of E2 and P in female. However, it was a different situation in male, where the serum concentration of E2 showed higher levels after spermiation and Serum concentration of P did not show any significant changes during a year. Based on the present study, it is supposed that brfERα plays an important role in ovary and other target organs during the reproductive cycle, Further studies will focus on the transcriptional regulation and localization of brfERα in gonad in order to get a better understand of the physiological function of brfERα in ovoviviparous teleost. This study indicates that the black rockfish may be a good candidate for understanding the mechanism of estrogen in ovoviviparous fish.

Developmental expression and estrogen responses of endocrine genes in juvenile yellow perch (Perca flavescens)

The present study examines the expression of growth-regulating genes (gh, prl, smtl and igf1b), the estrogen receptors (esr1 and esr2a) and aromatase (cyp19a1a) in developing yellow perch. To gain an initial understanding into the endocrine control of growth preceding and involved with sexual size dimorphism (SSD), where females have been reported to grow faster and larger than males, young of the year fish were sampled for length, weight and tissues at several time points (102-421 days post-hatch (dph)). Positive growth was seen in both sexes over the sampling interval, but SSD was not manifested. Using real-time quantitative PCR, we found that pituitary growth hormone (gh) and liver insulin-like growth factor-1b (igf1b) mRNA levels were significantly affected by dph and levels were found to be correlated with growth in both sexes. Liver cyp19a1a, esr1 and esr2a mRNA levels were significantly influenced by dph, whereas there was a significant dph*sex interaction on liver esr2a mRNA levels with males having higher levels than females at 379 and 421 dph. Ovarian cyp19a1a decreased with dph, but there were no changes in esr1 or esr2a mRNA levels. Dietary treatment of juvenile (∼300 dph) females with 20 mg/kg diet 17β-estradiol resulted in significantly higher liver esr1 mRNA levels and a sustained hepatosomatic index (I(H)). Across all data sets liver esr2a mRNA levels showed the most significant positive correlation with liver igf1b mRNA levels. These findings show that growth is accompanied by increases in pituitary gh, liver igf1b and liver esr1 and esr2a mRNAs in juvenile yellow perch.

Early expression of zona pellucida proteins under octylphenol exposure in Cichlasoma dimerus (Perciformes, Cichlidae)

An increasing number of widely used industrial and agricultural chemicals are being found to cause endocrine disruption. In fishes, xenoestrogens can induce female proteins, and in some cases, the development of testis-ova, demonstrating feminization of males. In this study we analyzed the effect of an acute exposure of adult male Cichlasoma dimerus fish to estradiol (E(2)) and octylphenol (OP). E(2) and OP were injected at 10 and 50 μg/g body weight doses, respectively. After a single OP dose, liver was processed for RNA extraction at 1, 3, 12, 24, and 72 h. PCR was performed using cDNA and primers for egg coat or zona pellucida proteins (ZP). Genes encoding ZPB and ZPC isoforms were sequenced. E(2)-induced fish were sacrificed at 72 h. Using multiple OP or E(2) injections, blood and surface mucus were sampled on days 0, 3, 6, 9, and 13. On day 13 fish were sacrificed for liver and testis dissection. Histological examination of E(2) and OP-treated fish livers showed cellular disarray and intense cytoplasmatic basophilia within hepatocytes, probably due to increased mRNA synthesis, as well as hypertrophied euchromatic nuclei, and conspicuous nucleoli, indicative of augmented cell activity. An abnormal amount of sperm and immature germ cells within the testis lumen were seen in treated fish, suggesting reproductive impairment. Both plasma and mucus revealed the presence of ZP (and vitellogenin) at day 3 and thereafter with E(2) treatment, using Western and Dot blot techniques; OP effects were delayed in time. These results validate the analysis of mucus by Dot blot as an easy and rapid technique to address endocrine disruption caused by OP. Quantitative gene expression showed induction of liver ZPB and ZPC upon OP injection; muscle, brain, and intestine did not express any ZP. Both ZPs were induced at 1h post injection, but only ZPB expression was statistically significant. At 12h, both ZPs increased significantly, reaching the same levels of E(2)-challenged males after 72 h. Therefore, OP mimicked the action of E(2) with a prompt and strong xenoestrogenic effect, evidenced by the early response through mRNA and protein expression of ZP and the concomitant histological liver and testis alterations.

Mechanisms and significance of nuclear receptor auto- and cross-regulation

The number of functional hormone receptors expressed by a cell in large part determines its responsiveness to the hormonal signal. The regulation of hormone receptor gene expression is therefore a central component of hormone action. Vertebrate steroid and thyroid hormones act by binding to nuclear receptors (NR) that function as ligand-activated transcription factors. Nuclear receptor genes are regulated by diverse and interacting intracellular signaling pathways. Nuclear receptor ligands can regulate the expression of the gene for the NR that mediates the hormone's action (autoregulation), thus influencing how a cell responds to the hormone. Autoregulation can be either positive or negative, the hormone increasing or decreasing, respectively, the expression of its own NR. Positive autoregulation (autoinduction) is often observed during postembryonic development, and during the ovarian cycle, where it enhances cellular sensitivity to the hormonal signal to drive the developmental process. By contrast, negative autoregulation (autorepression) may become important in the juvenile and adult for homeostatic negative feedback responses. In addition to autoregulation, a NR can influence the expression other types of NRs (cross-regulation), thus modifying how a cell responds to a different hormone. Cross-regulation by NRs is an important means to temporally coordinate cell responses to a subsequent (different) hormonal signal, or to allow for crosstalk between hormone signaling pathways.

Environmentally relevant exposure to 17alpha-ethinylestradiol affects the telencephalic proteome of male fathead minnows

Estrogens are key mediators of neuronal processes in vertebrates. As such, xenoestrogens present in the environment have the potential to alter normal central nervous system (CNS) function. The objectives of the present study were (1) to identify proteins with altered abundance in the male fathead minnow telencephalon as a result of low-level exposure to 17alpha-ethinylestradiol (EE(2)), and (2) to better understand the underlying mechanisms of 17beta-estradiol (E(2)) feedback in this important neuroendocrine tissue. Male fathead minnows exposed to a measured concentration of 5.4 ng EE(2)/L for 48 h showed decreased plasma E(2) levels of approximately 2-fold. Of 77 proteins that were quantified statistically, 14 proteins were down-regulated after EE(2) exposure, including four histone proteins, ATP synthase, H+ transporting subunits, and metabolic proteins (lactate dehydrogenase B4, malate dehydrogenase 1b). Twelve proteins were significantly induced by EE(2) including microtubule-associated protein tau (Mapt), astrocytic phosphoprotein, ependymin precursor, and calmodulin. Mapt showed an increase in protein abundance but a decrease in mRNA expression after EE(2) exposure(,) suggesting there may be a negative feedback response in the telencephalon to decreased mRNA transcription with increasing Mapt protein abundance. These results demonstrate that a low, environmentally relevant exposure to EE(2) can rapidly alter the abundance of proteins involved in cell differentiation and proliferation, neuron network morphology, and long-term synaptic potentiation. Together, these findings provide a better understanding of the molecular responses underlying E(2) feedback in the brain and demonstrate that quantitative proteomics can be successfully used in ecotoxicology to characterize affected cellular pathways and endocrine physiology.

Linear dynamic range for signal detection in fluorescent differential display

We have determined the linear dynamic range in signal detection by Fluorescent Differential Display (FDD) using conditionally induced mRNA expression of the p53 tumor-suppressor gene as a control. By serial spiking of p53-induced RNA into that of non-induced RNA, we were able to quantitatively measure up to 100-fold change in p53 mRNA expression level. The linear dynamic range of signal detection per mRNA message was determined to be from 1000 up to 20,000 in fluorescence signal, in which the signals for the majority of mRNAs reside. Thus, FDD can be used to accurately quantify differences in mRNA expression among eukaryotic cells.

Upregulation of estrogen receptor subtypes and vitellogenin mRNA in cinnamon clownfish Amphiprion melanopus during the sex change process: profiles on effects of 17beta-estradiol

In the present study, we investigated the expression pattern of estrogen receptors (esr) and vitellogenin (vtg) mRNA in the gonads and liver during sex change in cinnamon clownfish by using quantitative polymerase chain reaction. We divided gonadal development during the sex change from male to female into 3 stages (mature male, male at 90days after removing female, and mature female) and investigated esr and vtg mRNA expressions during the sex change. With female, the esr and vtg mRNA expressions increased. In western blot analysis, Esr1 protein was detected only in the ovaries of female cinnamon clownfish. Also, to understand the effect of 17beta-estradiol (E(2)), we investigated the esr and vtg mRNA expression patterns in the gonads and liver, and the changes in plasma E(2) level after E(2) injection. E(2) treatment increased both mRNA expression levels of esr and vtg and plasma E(2) levels. The present study describes the molecular characterization of esr subtypes and the interactions between esr and vtg after E(2) treatment in cinnamon clownfish.

Induction of vitellogenin production in male tilapia (Oreochromis mossambicus) by commercial fish diets

Mozambique tilapia, (Oreochromis mossambicus), are a euryhaline teleost and an important biological model species. Captive male tilapia frequently have high levels of the estrogen-induced yolk precursor protein vitellogenin (Vg), a common indicator of exposure to estrogenic compounds. Sex steroids are found in commercial fish diets, but relatively few studies have examined the relationship between commercial diets and Vg production. In a fasting experiment to ascertain a dietary role in male Vg production, plasma Vg was reduced to negligible levels after 2 weeks of fasting, while no change in estrogen receptor (ER) expression was seen. When male tilapia were fed a squid-based diet that replaced the commercial trout diet, plasma Vg was reduced to undetectable levels over 40 days, concomitant with significant reductions in hepatic expression of Vgs A, B, and C, and ERbeta, compared with control fish fed commercial trout diet. Female tilapia fed the squid-based for 20 days had no change in these parameters. When male tilapia were fed a defined, soy-based diet, plasma Vg reduced to 20% of levels in fish given either commercial trout diet or a defined, fishmeal-based diet. Overall, results from these studies suggest that estrogens in a commercial trout diet induce vitellogenin production by increasing expression of Vg, but not ER genes in male tilapia.

Effects of environmental relevant doses of pollutants from offshore oil production on Atlantic cod (Gadus morhua)

The release of produced water (PW), a by-product of offshore oil production, has increased in Norwegian waters in recent years. Alkylphenols (AP), a major component of PW, have been shown to have endocrine disrupting effects on several fish species. In the present study, four groups of female Atlantic cod (Gadus morhua) were orally exposed for 20 weeks to two different concentrations of a mixture of C4-C7 APs, PW or 17beta-estradiol. The transcriptional responses in the liver of Atlantic female cod were studied using a custom-made cDNA microarray. The largest transcriptional effects were seen in cod exposed to the lowest dose of APs. Several biological processes such as glycolysis, apoptosis and the general stress response were affected by exposure to APs. In addition, genes coding for the detoxification enzymes CYP1A and sulfotransferase 2 were up-regulated in the low exposure group. Significant reduction in gonadosomatic index (GSI) and the concentration of plasma vitellogenin were seen in both AP and 17beta-estradiol exposed cod. Exposure to PW had little effect on GSI and the regulation of stress responsive genes. The findings indicate that chronic exposure to low levels of APs may cause a stress response and delayed maturation in female cod.

Localisation of estrogen responsive genes in the liver and testis of Murray rainbowfish Melanotaenia fluviatilis exposed to 17beta-estradiol

The localisation of estrogen receptors (ERalpha and ERbeta) and vitellogenin (VTG) transcripts were examined in the liver and testis in male rainbowfish exposed to 17beta-estradiol (E2; 0, 50 and 500 ng/L) via the water for up to 7 days. The ER transcripts were localised within the perinuclear region of the hepatocytes and were up-regulated with E2 exposure. A parallel induction of liver VTG transcripts and protein was observed within 24h, followed by a time-dependent increase in VTG protein. In the testis, both ERs were up-regulated in the germ and epithelial cells, while VTG protein was detected in the cellular space surrounding the spermatids and in association with the connective tissue of the sperm tubules. These results indicate that the ERs are positively auto-regulated in the liver and testis of male rainbowfish. The cellular localisation of VTG within the testis may suggest implication in the mediation of adverse effects of endocrine disrupting chemicals such as testicular growth inhibition, testis-ova and sex reversal.

Effects of o,p'-DDE, heptachlor, and 17beta-estradiol on vitellogenin gene expression and the growth hormone/insulin-like growth factor-I axis in the tilapia, Oreochromis mossambicus

Effects of two endocrine disruptors, o,p'-DDE and heptachlor, and 17beta-estradiol (E(2)) on vitellogenin (Vg) and the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis were examined in male tilapia. In the first experiment, fish were given 5 weekly injections of either E(2), o,p'-DDE or heptachlor (5 microg/g). E(2) treatment increased plasma Vg and hepatic expression of three Vg genes (Vgs A, B, and C) and estrogen receptor alpha (ERalpha), while reducing plasma levels of IGF-I and suppressing the expression of IGF-I, the GH receptor (GHR2) and the putative somatolactin receptor (GHR1). Neither pesticide greatly affected the other parameters examined, except for a significant reduction in expression of GHR2 and increased plasma IGF-I. In the second experiment, fish were given a single injection of o,p'-DDE or heptachlor (100 microg/g), or E(2) (5 microg/g) and sacrificed 5 days post-injection. Treatment with E(2) stimulated expression of all three Vg genes. Both o,p'-DDE and heptachlor increased expression of VgB, whereas only o,p'-DDE increased VgA expression. There was no effect of o,p'-DDE or heptachlor on VgC expression or plasma Vg levels. Treatment with o,p'-DDE and heptachlor as well as E(2) increased ERalpha and ERbeta transcript levels. Similarly, both pesticides increased GHR1 and IGF-I expression, whereas no significant effect of E(2) was observed on GHR1, GHR2 or IGF-I expression. These results indicate that o,p'-DDE and heptachlor have varying temporal and dose effects on modulation of Vg and the GH/IGF-I axis that are distinct from E(2).

Seasonal and sex-specific mRNA levels of key endocrine genes in adult yellow perch (Perca flavescens) from Lake Erie

To better understand the endocrine mechanisms that underlie sexually dimorphic growth (females grow faster) in yellow perch (Perca flavescens), real-time quantitative polymerase chain reaction (qPCR) was used to measure pituitary, liver, and ovary mRNA levels of genes related to growth and reproduction-sex in this species. Adult perch were collected from Lake Erie and body mass, age, gonadosomatic index (I (G)), hepatosomatic index (I (H)), and gene expression for growth hormone (GH), prolactin, somatolactin, insulin-like growth factor Ib (IGF-Ib), estrogen receptor alpha (esr1), estrogen receptor betaa (esr2a), and aromatase (cyp19a1a) were measured. Females had higher body mass, I (H), and liver esr1 mRNA level than males, while males had higher liver IGF-Ib, liver esr2a, and liver cyp19a1a mRNA levels. In both sexes, season had a significant effect on GH and liver IGF-Ib mRNAs with higher levels occurring in spring, which also corresponded with higher liver cyp19a1a mRNA levels. For females, I (G), liver esr1, and ovary cyp19a1a mRNA levels were higher in autumn than the spring, and ovary cyp19a1a mRNA levels showed a significant negative correlation with pituitary GH and liver IGF-Ib mRNA levels. The most significant (p </= 0.001) relationships across the parameters measured were positive correlations between liver IGF-Ib and esr2a mRNA levels and liver IGF-Ib and cyp19a1a mRNA levels. This study shows significant effects of season and sex on adult yellow perch endocrine physiology.

Differential mass spectrometry of rat plasma reveals proteins that are responsive to 17beta-estradiol and a selective estrogen receptor modulator PPT

Estrogens are a class of steroid hormones that interact with two related but distinct nuclear receptors, estrogen receptor (ER) alpha and beta. To identify potential ER biomarkers, we profiled the rat plasma glycoproteome after treatment with vehicle or 17beta-estradiol (E2) or an ERalpha-selective agonist PPT by differential mass spectrometry. Our comparative proteomic experiment identifies novel E2- and PPT-responsive proteins, such as serine protease inhibitor family members.

Gender-specific expression of multiple estrogen receptors, growth hormone receptors, insulin-like growth factors and vitellogenins, and effects of 17 beta-estradiol in the male tilapia (Oreochromis mossambicus)

Gender-specific expression of estrogen receptors (ER alpha and ER beta), growth hormone receptors (GHR1 and GHR2), insulin-like growth factors (IGF-I and IGF-II) and three vitellogenins (Vgs A-C) was examined in the liver, gonad, pituitary, and brain of sexually mature male, female, and 17 beta-estradiol (E2)-treated male tilapia (Oreochromis mossambicus). Reflecting greater growth rate in male tilapia, hepatic expression of GHR1, GHR2, IGF-I and IGF-II as well as plasma IGF-I levels were higher in males than in females, whereas the expression of Vgs A-C and ER alpha was higher in females. On the other hand, expression of all genes measured was higher in the ovary than in testis. Forty eight hours after E2 injection (5 microg/g) into male fish, hepatic expression of most transcripts measured were altered to levels that were similar to those seen in females. The changes included decreased expression of GHR1, GHR2, IGF-I, and IGF-II, and increased expression of ER alpha and Vgs A-C. E2 treatment also increased Vg and decreased IGF-I in the plasma. Brain expression of ER alpha, ER beta, GHR1, and IGF-I was higher in females than in males, whereas pituitary expression of GHR2 and IGF-I was lower in females; only brain expression of GHR1 was increased by E2 treatment. These findings suggest that E2 stimulates Vg production primarily through activation of ER alpha and down-regulation of the GH/IGF-I axis, thus shifting energy from somatic growth towards vitellogenesis at the level of the liver.

Effects of 17alpha-ethynylestradiol on hormonal responses and xenobiotic biotransformation system of Atlantic salmon (Salmo salar)

Pharmaceuticals are ubiquitous pollutants in the aquatic environment where their potential effects on non-target species like fish has only recently become subject of systematic investigations. In the present study, experiments were undertaken to examine the effects of a synthetic pharmaceutical endocrine disruptor, ethynylestradiol (EE2), given in water at 5 or 50 ng/L and sampled at days 0 (control), 3 and 7 after exposure, on hepatic phase I and II biotransformation and hormonal pathways of juvenile salmon using quantitative (real-time) polymerase chain reaction (qPCR), Vtg ELISA and 7-ethoxyresorufin O-deethylase (EROD) catalytic activity. Our data show that EE2 produced time- and concentration-specific modulation of estrogen receptor isoforms (ERalpha, ERbeta) and androgen receptor-beta (ARbeta). EE2 produced a concentration-specific induction of vitellogenin (Vtg) and zona radiata protein (Zr-protein) at day 3 after exposure. At day 7, Vtg and Zr-protein mRNA (and plasma Vtg protein) expression were significantly decreased in the group given 5 ng EE2/L, compared to dimethyl sulfoxide (DMSO) control group. In the xenobiotic biotransformation pathway, EE2 produced a significant increase of aryl hydrocarbon receptor-alpha (AhRalpha) at day 3 in the group given 5 ng EE2/L and AhRbeta was decreased at the same concentration at day 7. While CYP3A was not significantly affected by EE2 exposure, the CYP1A1, AhR nuclear translocator (Arnt) and AhR repressor (AhRR) mRNA showed an apparent EE2 concentration and time-dependent decrease. The expression of uridine diphosphoglucuronosyl transferase (UGT) and glutathione S-transferase class pi-like (GSTpi-like) mRNA were decreased after exposure to 50ng EE2/L at both day 3 and 7 after exposure. The effect of EE2 on the CYP1A1 gene expressions paralleled effect on EROD and AhRR mRNA, suggesting a direct role of EE2 in controlling cellular detoxification machinery. Interestingly, the carrier vehicle, DMSO produced significant time-dependent induction of estrogenic (ERalpha, Vtg and Zr-protein) responses, compared with blank (i.e. without DMSO) controls at day 7 post-exposure. The effect of DMSO totally underscored the observed EE2 effect at day 7 after exposure. In general, these findings support previous reports on the endocrine effects of EE2, in addition to effects on hepatic biotransformation system. In view of the data presented here and our recent studies, the use of DMSO as carrier vehicle in endocrine toxicological experimental studies should be re-evaluated.

Induction of three vitellogenins by 17beta-estradiol with concurrent inhibition of the growth hormone-insulin-like growth factor 1 axis in a euryhaline teleost, the tilapia (Oreochromis mossambicus)

The objective of the present study was to utilize the male Mozambique tilapia (Oreochromis mossambicus) as a model for examining the molecular mechanisms that mediate the physiological transition between somatic and gonadal growth in female teleost fish, and in vertebrates in general. Partial cDNAs that encode multiple forms of vitellogenin (Vtg), which is the major precursor of yolk proteins, were cloned from estrogen-treated males and utilized to develop real-time quantitative RT-PCR assays, which were supplemented by an assay for Vtg immunoreactivity in the plasma. Alignment analyses of the amino acid sequences deduced from the vtg cDNAs revealed three distinct tilapia Vtgs, which were categorized as Aa-, Ab-, and C-type Vtgs. A single injection of male tilapias with 17beta-estradiol (E(2)) at 5 microg/g body weight significantly increased the plasma E(2) and hepatic levels of all three vtg transcripts within 1 day. Plasma E(2) levels declined after 3 days, whereas the plasma Vtg immunoreactivity and hepatic levels of the three vtg transcripts continued to increase. Hepatic expression of the estrogen receptor (esr) 1 gene, but not the esr2 gene, also increased markedly 1 day after E(2) injection and remained elevated for 5 days. While plasma growth hormone (Gh) levels were unaffected, hepatic expression of transcripts that encoded the Gh receptor and insulin-like growth factor 1 (Igf1) was suppressed by E(2), as were the plasma Igf1 levels. These results clearly suggest a distinct negative interplay between the growth and reproductive axes at the molecular level of key hepatic regulatory pathways involved in the control of energy utilization by gonadal and somatic growth processes.

Expression Profiling of Endocrine-Disrupting Compounds Using a Customized Cyprinus carpio cDNA Microarray

Exposure to a variety of anthropogenic compounds has been shown to interfere with normal development, physiology, and reproduction in a wide range of organisms, both in laboratory studies and wildlife. We have developed a Cyprinus carpio cDNA microarray consisting of endocrine-related genes. In the current study, we investigated the applicability of this microarray (1) to study the molecular effects induced by exposure to a variety of endocrine-disrupting compounds (EDCs) in fish and (2) to discriminate the specific transcriptional profiles associated with these compounds. To that purpose, gene expression profiles were generated in livers of juvenile carp exposed to 14 Organization of Economical Cooperation Development (OECD)-recommended reference EDCs (17beta-estradiol, 17alpha-ethinylestradiol, 4-nonylphenol, bisphenol A, tamoxifen, 17alpha-methyltestosterone, 11-ketotestosterone, dibutyl phthalate, flutamide, vinclozolin, hydrocortisone, CuCl(2), propylthiouracil, and a mixture of L-triiodothyronine and L-thyroxine). Our results show that, in addition to some expression similarities between analogous acting substances, each individual compound produced its own unique expression pattern on the array, distinct from the profiles generated by the other compounds. In addition, we were able to identify a minimal subset of genes, which also allowed to discriminate between the different compounds. Overall, our findings suggest that the developed cDNA array has great promise to screen new and existing chemicals on their endocrine-disruptive potential and to identify distinct classes of EDCs.

Biotransformation, stress and genotoxic effects of 17beta-estradiol in juvenile sea bass (Dicentrarchus labrax L.)

The effects of 17beta-estradiol (E(2)) on fish became a matter of concern, since significant levels of this hormone were detected in the aquatic environment released mainly by domestic sewage treatment plants. In this perspective, the current study was focused on E(2) effects upon biotransformation, stress and genotoxic responses of juvenile Dicentrarchus labrax L. (sea bass). Fish were exposed to E(2) during 10 days in two different ways: water diluted (200 ng/L or 2,000 ng/L) and i.p. injected (0.5 mg/kg or 5 mg/kg). A battery of biological responses was evaluated: liver ethoxyresorufin-O-deethylase (EROD) and alanine transaminase (ALT) activities, liver somatic index (LSI), plasma cortisol, glucose and lactate concentrations, as well as erythrocytic nuclear abnormalities (ENA). All the exposure conditions induced endocrine disruption, measured as plasma cortisol decrease, and genotoxicity, measured as ENA increase. Thus, no differences were detected either between different exposure routes or tested concentrations. Concerning liver EROD and ALT activities, as well as plasma glucose and lactate concentrations no differences were found between treated and control groups. LSI was the only parameter to respond differently in the two exposure routes, as only E(2) water diluted induced a significant increase in this hepatic indicator.

Identification of estrogen-responsive genes in the testis of sea bream (Sparus auratus) using suppression subtractive hybridization

There is growing evidence that estrogens play important roles in both normal and xenoestrogen disrupted testis physiology. However, the mechanisms and signaling pathways involved, in particular in fish, are largely unknown. We have used suppression subtractive hybridization to isolate 152 candidate estrogen-responsive genes in the testis of male estradiol (E2)-treated sea bream (Sparus aurata). The E2 up-regulation of some of the genes (e.g., choriogenin L and H, vitellogenin I and II, apolipoprotein A-I, fibrinogen beta and gamma, and thyroid receptor interacting protein 4) was confirmed by reverse transcriptase polymerase chain reaction in fish treated with 0.1-10 mg/kg E2. Many of these genes are typical E2-induced genes in liver, and this is the first report of its up regulation with E2 in testis. Moreover, low levels of expression were also found for nontreated fish. Hepatic differential expression for these genes was also confirmed, although, contrary to testis, fibrinogen beta, and gamma were downregulated. The possible significance of these findings in normal testis physiology and in endocrine disruption is discussed.

Gene expression patterns in estrogen (nonylphenol) and aryl hydrocarbon receptor agonists (PCB-77) interaction using rainbow trout (Oncorhynchus Mykiss) primary hepatocyte culture

It was previously reported that in vivo exposure of fish to combined aryl hydrocarbon receptor agonist (AhR; 3,3',4,4'-tetrachlorobiphenyl, PCB-77) and estrogen receptor agonist (ER; nonylphenol, NP) resulted in potentiation and inhibition (depending on dose ratio, sequential order of exposure, and seasonal changes) of NP-induced responses by PCB-77. The experiments described in this report extend this study by testing whether the effects of PCB-77 on NP-induced ER signaling are mediated through AhR-induced transcriptional suppression of target genes. Trout hepatocytes were isolated by a two-step collagenase perfusion method. After 48-h culture, hepatocytes were exposed to 5 or 10 microM nonylphenol (NP) singly and in combination with PCB-77 at 0.1, 1, and 10 microM. Cells were harvested after 96-h exposure and processed for RNA isolation. Gene expression patterns were quantified using real-time polymerase chain reaction (PCR) with specific primer sets and by Northern blot. Exposure of cells to NP caused significant elevation of ERalpha, ERbeta, Vtg, and Zrp mRNA expressions, while combined exposure with PCB-77 concentration inhibited NP-induced ERs and their target gene expressions. Exposure of trout hepatocytes to PCB-77 alone caused a rapid induction of cytochrome P-450 (CYP) 1A1 mRNA, and combined exposure with NP caused significant reduction in PCB-77 induced CYP1A1 gene expression. Exposure of cells to PCB-77 concentrations induced significant reduction in AhRalpha mRNA (except 1 microM PCB-77, which caused the induction of AhRalpha mRNA levels). AhRbeta mRNA levels in the cells were inhibited after 96-h exposure to PCB-77, while combined exposure with 5 microM NP restored the PCB-77-inhibited AhRbeta mRNA levels to baseline. Taken together, the overall results in this study show that PCB-77 suppresses the gene expression of the ERs and their target genes by transcription mechanism(s). The roles of AhRs in mediating these responses seem to involve the ligand-activated AhR transcriptional induction of CYP1A1. In addition to their frequently described functions as activators of metabolic potentiation and detoxification of various foreign chemicals, data presented in the present study point to other endogenous functions of AhRs that need to be studied further.

Temporal gene induction patterns in sheepshead minnows exposed to 17β-estradiol

Gene arrays provide a powerful method to examine changes in gene expression in fish due to chemical exposures in the environment. In this study, we expanded an existing gene array for sheepshead minnows (Cyprinodon variegatus) (SHM) and used it to examine temporal changes in gene expression for male SHM exposed to 100 ng 17beta-estradiol (E(2))/L for five time points between 0 and 48 hr. We found that in addition to the induction of genes involved in oocyte development (vitellogenin [VTG], zona radiata [ZRP]), other genes involved in metabolism and the inflammatory response are also affected. We identified five patterns of temporal induction in genes whose expression was modified due to E(2) exposure. We validated the gene array data for the expression of VTG 1, VTG 2, ZRP 2 and ZRP 3 and found that with low levels of exogenous E(2) (100 ng E(2)/L) exposure, ZRP expression precedes VTG expression. However, at higher concentrations of E(2) (500 ng E(2)/L), the difference in temporal expression appears to be lost. Exposure to high levels of environmental contaminants may affect the normal ordered expression of genes required for reproduction. Gene expression profiling using arrays promises to be a valuable tool in the field of environmental toxicology. As more genes are identified for species used in toxicological testing, researchers will be better able to predict adverse effects to chemical exposures and to understand the relationships between changes in gene expression and changes in phenotype.

Toxicogenomic profiling of the hepatic tumor promoters indole-3-carbinol, 17beta-estradiol and beta-naphthoflavone in rainbow trout

Indole-3-carbinol (I3C), from cruciferous vegetables, has been found to suppress or enhance tumors in several animal models. We previously reported that dietary I3C promotes hepatocarcinogenesis in rainbow trout (Oncorhynchus mykiss) at concentrations that differentially activated estrogen receptor (ER) or aryl hydrocarbon receptor (AhR)-mediated responses based on individual protein biomarkers. In this study, we evaluated the relative importance of these pathways as potential mechanisms for I3C on a global scale. Hepatic gene expression profiles were examined in trout after dietary exposure to 500 and 1500 ppm I3C and 3,3'-diindolylmethane (DIM), a major in vivo component of I3C, and were compared to the transcriptional signatures of two model hepatic tumor promoters: 17beta-estradiol (E2), an ER agonist, and beta-naphthoflavone, an AhR agonist. We demonstrate that I3C and DIM acted similar to E2 at the transcriptional level based on correlation analysis of expression profiles and clustering of gene responses. Of the genes regulated by E2 (fold change >or =2.0 or < or =0.50), most genes were regulated similarly by DIM (87-92%) and I3C (71%), suggesting a common mechanism of action. Of interest were upregulated genes associated with signaling pathways for cell growth and proliferation, vitellogenesis, and protein folding, stability, and transport. Other genes downregulated by E2, including those involved in acute-phase immune response, were also downregulated by DIM and I3C. Gene regulation was confirmed by qRT-PCR and Western blot. These data indicate I3C promotes hepatocarcinogenesis through estrogenic mechanisms in trout liver and suggest DIM may be an even more potent hepatic tumor promoter in this model.

Distribution of estrogen receptor alpha mRNA in the brain and inner ear of a vocal fish with comparisons to sites of aromatase expression

Among vertebrates, teleost fish have the greatest capacity for estrogen production in the brain. Previously, we characterized the distribution of the estrogen-synthesizing enzyme aromatase in the brain of the midshipman fish. Here, we investigated the distribution of estrogen receptor alpha (ERalpha). A partial cDNA of ERalpha was cloned and used to generate midshipman-specific primers for RT and real-time PCR which identified transcripts in liver and ovary, the CNS, and the sensory epithelium of the main auditory endorgan (sacculus). In situ hybridization revealed abundant expression throughout the preoptic area, a vocal-acoustic site in the hypothalamus, amygdala homologs of the dorsal pallium, the pineal organ, the inner ear, the pituitary, and the ovary. Weaker expression was found in the midbrain's nucleus of the medial longitudinal fasciculus and in the dimorphic vocal motor nucleus. ERalpha expression in the pineal, gonad, and pituitary axis may function to time seasonal abiotic cues to reproductive state, while expression in the vocal motor and auditory systems support neurophysiological evidence for estrogen as a modulator of vocal motor and auditory encoding mechanisms in midshipman fish. While ERalpha is restricted to specific nuclei, aromatase expression is abundant in glial cells throughout the entire forebrain, and high in midbrain and hindbrain - spinal vocal regions. The only site of aromatase-containing neurons is in the peripheral auditory system, where it is localized to ganglion cells in the auditory nerve. Estrogen production proximal to ERalpha-positive neurons may provide for focal sites of estrogen effects on reproductive-, vocal-, and auditory-related neurons.

Gene expression fingerprints of largemouth bass (Micropterus salmoides) exposed to pulp and paper mill effluents

Effluents from pulp and paper mills that historically have used elemental chlorine in the bleaching process have been implicated in inhibiting reproduction in fish. Compounds with estrogenic and androgenic binding affinities have been found in these effluents, suggesting that the impairment of reproduction is through an endocrine-related mode of action. To date, a great deal of attention has been paid to phytoestrogens and resin acids that are present in mill process streams as a result of pulping trees. Estrogen and estrogen mimics interact directly with the estrogen receptor and have near immediate effects on gene transcription by turning on the expression of a unique set of genes. Using differential display (DD) RT-PCR, we examined changes in gene expression induced by exposure to paper mill effluents. Largemouth bass were exposed to 0, 10, 20, 40, and 80% paper mill effluent concentrations in large flow-through tanks for varied periods of time including 7, 28 or 56 days. Plasma hormone levels in males and females and plasma vitellogenin (Vtg) in females decreased with dose and time. Measurements of changes in gene expression using DD RT-PCR suggest that the gene expression patterns of male fish do not change much with exposure, except for the induction of a few genes including CYP 1A, a protein that is induced through the action of the Ah receptor in response to dioxin and similar polyaromatic hydrocarbons. However, in the case of females, exposure to these effluents resulted in an up-regulation of CYP 1A that was accompanied by a generalized down-regulation of genes normally expressed during the reproductive season. These antiestrogenic changes are in agreement with previous studies in bass exposed to these effluents, and could result in decreased reproductive success in affected populations.

Differential gene expression analysis in fish exposed to endocrine disrupting compounds

This review discusses various methodologies that can be used to understand, at the gene level, the consequences to fish upon exposure to endocrine disrupting compounds (EDCs). Several approaches for measuring expression of gene transcripts are discussed, including directed approaches, such as Northern blotting and quantitative reverse transcriptase polymerase chain reaction (RT-PCR) as well as open-ended approaches, such as differential display RT-PCR, subtractive hybridizations, and gene arrays. Each of these systems has advantages and disadvantages, strengths and weaknesses. Conducting experiments with each of these methods provides important information about the molecular mechanisms that result from exposure to EDCs, information which can be used in risk assessment of polluted sites found in the environment.

Differential expression of largemouth bass (Micropterus salmoides) estrogen receptor isotypes alpha, beta, and gamma by estradiol

The expression levels of three estrogen receptor (ER) isotypes alpha, beta, and gamma were quantified in female largemouth bass (Micropterus salmoides) (LMB) liver, ovary, brain, and pituitary tissues. ER alpha and beta expression predominated in the liver, while ERs beta and gamma predominated in the other tissues. Temporally in females, ER alpha was highly up-regulated, ER gamma was slightly up-regulated, and ER beta levels remained unchanged in the liver when plasma 17-beta estradiol (E2) and vitellogenin (Vtg) levels were elevated in the spring. In ovarian tissue from these same fish, all three ERs were maximally expressed in the fall, during early oocyte development and prior to peak plasma E2 levels. When males were injected with E2, ER alpha was highly inducible, ER gamma was moderately up-regulated, and ER beta levels were not affected. None of the ER isotypes were induced by E2 in gonadal tissues. These results combined suggest that the ERs themselves are not regulated in the same manner by E2, and furthermore, do not contribute equally to the transcriptional regulation of genes involved in fish reproduction such as Vtg.