Vitellogenin gene expression in male rainbow trout (Salmo gairdneri)

Multi-approach assessment for the evaluation of spatio-temporal estrogenicity in fish from effluent-dominated surface waters under low instream flow

Current practices employed by most wastewater treatment plants (WWTP) are unable to completely remove endocrine disrupting compounds (EDCs) from reclaimed waters, and consistently discharge these substances to receiving systems. Effluent-dominated and dependent surface waters, especially during low instream flows, can increase exposure and risks to aquatic organisms due to adverse biological effects associated with EDCs. Given the ecological implications that may arise from exposure to such compounds, the present a multi-approach study examined spatio-temporal estrogenic potential of wastewater effluent to fish in East Canyon Creek (ECC), Utah, USA, a unique urban river with instream flows seasonally influenced by snowmelt. Juvenile rainbow trout (Oncorhynchus mykiss) were caged at different upstream and downstream sites from an effluent discharge during the summer and fall seasons. In the summer, where approximately 50% of the streamflow was dominated by effluent, fish from the upstream and a downstream site, located 13 miles away from the effluent discharge, presented significantly elevated concentrations of plasma vitellogenin (VTG). Similarly, significantly high 17β-estradiol to 11-ketotestosterone ratios were measured in the summer across all sites and time points, compared to the fall. In the laboratory, juvenile fish and primary hepatocytes were exposed to concentrated effluent and surface water samples. Quantification of VTG, although in significantly lower levels, resembled response patterns observed in fish from the field study. Furthermore, analytical quantification of common EDCs in wastewater revealed the presence of estriol and estrone, though these did not appear to be related to the observed biological responses, as these were more significant in sites were no EDCs were detected. These combined observations suggest potential estrogenicity for fish in ECC under continuous exposures and highlight the advantages of following weight-of-evidence (WoE) approaches for environmental monitoring, as targeted analytically-based assessments may or may not support the identification of causative contaminants for adverse biological effects.

Sex and seasonal differences in mRNA expression of estrogen receptor α (ESR1) in red-sided garter snakes (Thamnophis sirtalis parietalis)

Estrogens are important regulators of reproductive physiology including sexual signal expression and vitellogenesis. For the regulation to occur, the hormone must bind and activate receptors in target tissues, and expression of the receptors can vary by sex and/or season. By simultaneously comparing circulating hormone levels with receptor expression, a more complete understanding of hormone action can be gained. Our study species, the red-sided garter snake (Thamnophis sirtalis parietalis), provides an excellent opportunity to study the interaction between sex steroid hormones and receptor expression in addition to sexual dimorphism and seasonality. During the spring mating season, male garter snakes rely exclusively on the female's skin-based, estrogen-dependent sex pheromone to direct courtship. Males can be stimulated to produce this sexual attractiveness pheromone by treatment with estradiol (E₂), which also induces male vitellogenesis. Estrogen receptors (ESRs) are required to transduce the effects of estrogens, thus we used quantitative RT-PCR to analyze expression of ESR alpha (ERα; gene ESR1) mRNA in the skin and liver of wild caught male and female garter snakes across simulated spring and fall conditions in the laboratory. While ESR1 was present in the skin of both sexes, there were no sex or seasonal differences in expression levels. Liver expression of ESR1, however, was sexually dimorphic, with females showing greatest expression in fall when circulating E₂ concentrations were lowest. There were no statistically significant correlations between E₂ and ESR1 expression. Our data suggest that the skin of both sexes is sensitive to estrogen signaling and thus the production of sex pheromone is dependent on bioavailable levels of E₂. Female expression of ESR1 in the liver may increase in the fall to prime energy storage mechanisms required for vitellogenesis the following year.

Chronic nitrate exposure alters reproductive physiology in fathead minnows

Nitrate is a ubiquitous aquatic pollutant that is commonly associated with eutrophication and dead zones in estuaries around the world. At high concentrations nitrate is toxic to aquatic life but at environmental concentrations it has also been purported as an endocrine disruptor in fish. To investigate the potential for nitrate to cause endocrine disruption in fish, we conducted a lifecycle study with fathead minnows (Pimephales promelas) exposed to nitrate (0, 11.3, and 56.5 mg/L (total nitrate-nitrogen (NO₃-N)) from <24 h post hatch to sexual maturity (209 days). Body mass, condition factor, gonadal somatic index (GSI), incidence of intersex, and vitellogenin induction were determined in mature male and female fish and plasma 11-keto testosterone (11-KT) was measured in males only. In nitrate-exposed males both 11-KT and vitellogenin were significantly induced when compared with controls. No significant differences occurred for body mass, condition factor, or GSI among males and intersex was not observed in any of the nitrate treatments. Nitrate-exposed females also had significant increases in vitellogenin compared to controls but no significant differences for mass, condition factor, or GSI were observed in nitrate exposed groups. Estradiol was used as a positive control for vitellogenin induction. Our findings suggest that environmentally relevant nitrate levels may disrupt steroid hormone synthesis and/or metabolism in male and female fish and may have implications for fish reproduction, watershed management, and regulation of nutrient pollution.

Cloning of multiple ERα mRNA variants in killifish (Fundulus heteroclitus), and differential expression by tissue type, stage of reproduction, and estrogen exposure in fish from polluted and unpolluted environments

To test the hypothesis that alternative splicing could be an adaptive mechanism for populations subject to multi-generational estrogenic exposures, we compared estrogen receptor alpha (ERα) splicing variants in two populations of killifish (Fundulus heteroclitus): one resident in an estrogenic polluted environment (New Bedford Harbor, NBH, MA, USA) and one from a relatively uncontaminated reference site (Scorton Creek, SC, MA, USA). In total we identified 19 ERα variants, each with deletions of one or more coding exons. Four of the variants with potential functional relevance were analyzed by qPCR to test for population differences in expression by tissue type, site, sex, seasonal reproductive status and estrogen treatment. Significantly, a 5'-truncated short form variant (ERαS) was highly expressed in liver and ovary, and was associated with seasonal reproductive activity in SC but not NBH fish. Both ERαS and the full-length long variant (ERαL) were estrogen-inducible (ERαS>ERαL) but the induction response was lower in NBH than in SC fish. In contrast, NBH killifish were hyper-responsive to estrogen as measured by expression of two other estrogen responsive genes: vitellogenin (Vtg) and aromatase B (AroB). Most strikingly, two ERα deletion variants (Δ6 and Δ6-8), lacking ligand binding and activation function domains, were identified in a subset of NBH fish, where they were associated with reduced responsiveness to estrogen treatment. Together, these results support the hypothesis that alternative splicing of the esr1 gene of killifish could be an autoregulatory mechanism by which estrogen modulates the differential expression of ERα, and suggests a novel and adaptive mechanistic response to xenoestrogenic exposure.

Exposure to estrogenic chemicals induces ectopic expression of vtg in the testis of rainbowfish, Melanotaenia fluviatilis

Vitellogenin (Vtg) is the major egg-yolk precursor protein in oviparous organisms normally synthesised only in mature females. In males and juveniles, the vtg gene, although present, is silent, but its hepatic expression may be activated by xenoestrogens. Surprisingly, its induction and potential consequences in non-hepatic tissues remain unexplored. Here we test the hepatic and testicular response of vtg expression in adult male rainbowfish Melanotaenia fluviatilis exposed to either 1, 3, 5 μg/L 17β-estradiol or 100, 500 μg/L 4-n-nonylphenol for 24-96 h. Significant increase in the expression level of vtg mRNA in the liver and testes of exposed males was observed. The early (24 h), sensitive and reliable detection of the vtg induction using qPCR demonstrates the assay's robustness to monitor xenobiotic exposure particularly in smaller fish like rainbowfish, an emerging indicator species. Whilst, the ectopic induction of vtg mRNA in testes suggests a more complex Vtg pathway.

Induction and recovery of estrogenic effects after short-term 17β-estradiol exposure in juvenile rainbow trout (Oncorhynchus mykiss)

Estrogenic compounds found in the aquatic environment include natural and synthetic estrogen hormones as well as other less potent estrogenic xenobiotics. In this study, a comprehensive approach was used to examine effects on fish endocrine system endpoints during a short-term xenoestrogen exposure as well as after post-exposure recovery. Rainbow trout (Oncorhynchus mykiss) were exposed to an aqueous 17β-estradiol (E2) concentration of 0.473 μg l(-1) for 2 and 7 days (d) followed by a 14-d recovery period. At d2 and d7, plasma E2 concentrations in treated fish were 458- and 205-fold higher than in control fish and 23- and 16-fold higher than the exposure water concentration. E2 treatment resulted in significant increases in hepatosomatic index (HSI), plasma vitellogenin (VTG) protein concentrations, and liver VTG and estrogen receptor alpha mRNA levels. All of these parameters, with the exception of plasma VTG protein, returned to baseline values during the recovery period. Plasma cortisol concentrations were unaffected by treatment. This research shows varied time frames of the estrogen-responsive molecular-, biochemical-, and tissue-level alterations, as well as their persistence, in juvenile rainbow trout treated with aqueous E2. These results have implications for feral rainbow trout exposed to xenoestrogens and indicate the importance of evaluating a comprehensive suite of endpoints in assessing the impact of this type of environmental contaminant.

A dynamic model of transcriptional imprinting derived from the vitellogenesis memory effect

Transcriptional memory of transient signals can be imprinted on living systems and influence their reactivity to repeated stimulations. Although they are classically ascribed to structural chromatin rearrangements in eukaryotes, such behaviors can also rely on dynamic memory circuits with sustained self-amplification loops. However, these phenomena are either of finite duration, or conversely associated to sustained phenotypic changes. A mechanism is proposed, in which only the responsiveness of the target gene is durably reset at a higher level after primary stimulation, using the celebrated but still puzzling vitellogenesis memory effect. The basic ingredients of this system are: 1), a positive autoregulation of the estrogen receptor α gene; 2), a strongly cooperative action of the estradiol receptor on vitellogenin expression; and 3), a variant isoform of the estradiol receptor with two autonomous transcription-activating modules, one of which is signal-independent and the other, signal-dependent. Realistic quantification supports the possibility of a multistationary situation in which ligand-independent activity is unable by itself to prime the amplification loop, but can click the system over a memory threshold after a primary stimulation. This ratchet transcriptional mechanism can have developmental and ecotoxicological importance and explain lifelong imprinting of past exposures without apparent phenotypic changes before restimulation and without need for persistent chromatin modifications.

Uptake of 17β-estradiol and biomarker responses in brown trout (Salmo trutta) exposed to pulses

In streams, chemicals such as 17β-estradiol (E2) are likely to occur in pulses. We investigated uptake and biomarker responses in juvenile brown trout (Salmo trutta) of 3- or 6-h pulses of concentrations up to 370 ng E2 L(-1). Uptake by the fish was estimated from disappearance of E2 from tank water. A single 6-h pulse of 370 ng E2 L(-1) increased the plasma vitellogenin concentration, liver Erα- and vitellogenin-mRNA. Exposure to 150-160 ng E2 L(-1) for 6 h increased vitellogenin in one experiment but not in another. Two 6-h pulses had a larger effect one pulse. Brown trout in the size range 24-74 g took up E2 linearly with time and exposure concentration with a concentration ratio rate of 20.2 h(-1). In conclusion, the threshold for induction of estrogenic effects in juvenile brown trout at short term pulse exposure appears to be in the range 150-200 ng E2 L(-1).

Detection of vitellogenin incorporation into zebrafish oocytes by FITC fluorescence

BACKGROUND

Large volumes of lymph can be collected from the eye-sacs of bubble-eye goldfish. We attempted to induce vitellogenin (Vtg) in the eye-sac lymph of bubble-eye goldfish and develop a method for visualizing Vtg incorporation by zebrafish oocytes using FITC-labeling.

METHODS

Estrogen efficiently induced Vtg in the eye-sac lymph of goldfish. After FITC-labeled Vtg was prepared, it was injected into mature female zebrafish.

RESULTS

Incorporation of FITC-labeled Vtg by zebrafish oocytes was detected in in vivo and in vitro experiments. The embryos obtained from zebrafish females injected with FITC-labeled Vtg emitted FITC fluorescence from the yolk sac and developed normally.

CONCLUSION

This method for achieving Vtg incorporation by zebrafish oocytes could be useful in experiments related to the development and endocrinology of zebrafish oocytes.

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).

Molecular characterization of Japanese sillago vitellogenin and changes in its expression levels on exposure to 17beta-estradiol and 4-tert-octylphenol

We cloned a full-length cDNA encoding vitellogenin (VTG) from a marine teleost, the Japanese sillago Sillago japonica. The cloned sillago VTG contained signal peptide, lipovitellin heavy chain, phosvitin, lipovitellin light chain, and beta'-component in the order from the N-terminus. An exposure to 17beta-estradiol significantly increased the levels of plasma VTG, but not hepatic VTG mRNA in males. Neither plasma VTG nor hepatic VTG mRNA levels were affected by the exposure to 4-tert-octylphenol. Hepatic VTG mRNA levels in males increased at 1 day after intraperitoneal administration of 17beta-estradiol but decreased in the subsequent 5 days. However, plasma VTG levels remained high for 5 days after administration, suggesting that the accumulation period of plasma VTG is longer than that of hepatic VTG mRNA in males. Therefore, VTG mRNA may be a suitable indicator of temporal exposure to estrogenic chemicals in the environment, whereas plasma VTG is useful to detect consecutive exposure.

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.

Protein and gene expression of VTG in response to 4-nonylphenol in rockfish (Sebastes schlegeli)

To investigate the in vivo estrogenic activity of 4-nonylphenol (4-NP) on reproductive function, we have measured the expression level of rockfish vitellogenin (rVTG) mRNA, concentration of plasma VTG and levels of plasma estradiol-17beta(E(2)) and testosterone (T) by radioimmunoassay (RIA). An rVTG mRNA transcript of approximately 4.0 kb was extracted from hepatic tissue for Northern blot analysis, and the effects of 4-NP on rVTG mRNA expression in vivo with both male and female juvenile rockfish were examined. The level of rVTG mRNA expression was increased 48 h after injection with 4-NP of 10 mg/kg body mass and after injection in both male and female rockfish. The level of rVTG mRNA expression was increased 24 h after injection in male rockfish injected with 4-NP of 25 mg/kg body mass, while the level of rVTG mRNA expression was increased 12h after injection in female injected with same dosage. Concentrations of plasma rVTG in female injected with 4-NP of 10 and 25 mg/kg b.w. were increased 72 h after injection and reached 35 and 66 mg/mL, respectively. In male, rVTG concentrations with the dosage of 25 mg/kg body mass were increased 72 h after injection and reached to 14 and 65 mg/mL at 168 h, respectively. Plasma concentrations of T and E(2) in female and male injected with 4-NP were not significantly different between two 4-NP dosages. These results suggest that 4-NP may disrupt the reproductive system of immature rockfish by acting directly on vitellogenesis. Immature females injected with 4-NP were more sensitive than immature males, but VTG in immature males is likely to return to normal conditions slowly. There are obviously large interspecies differences in response of fish to 4-NP.

Effects of 4-n-Nonylphenol and Tamoxifen on Salmon Gonadotropin-Releasing Hormone, Estrogen Receptor, and Vitellogenin Gene Expression in Juvenile Rainbow Trout

Alkylphenols such as nonylphenol (NP) are one of a wide variety of environmental chemicals reported to have estrogenic effects in both in vitro and in vivo studies. Induction of hepatic vitellogenin (Vg) gene expression is widely used as a biomarker for xenoestrogen exposure in fish. However, little work has been done to characterize the molecular effects of xenoestrogens on other potential target organs such as the brain. To evaluate brain and liver effects of 4-n-nonylphenol (4-NP), juvenile rainbow trout (Oncorhynchus mykiss) were exposed to waterborne 4-NP or 17beta-estradiol (E(2)). Changes in mRNA levels of salmon gonadotropin-releasing hormone (sGnRH) and estrogen receptor alpha (ERalpha) isoforms in the brain and ERalpha isoforms and Vg in the liver were measured after 3 and 6 days of exposure, with the help of a relative RT-PCR-based quantification method. Fish were treated with increasing doses of 4-NP ranging from 0.01 to 10 microM (2.2 microg/l to 2.2 mg/l), and results were compared to the effect of E(2) or tamoxifen, a specific ER modulator. In liver, E(2) and the highest doses of 4-NP increased Vg and ERalpha long-isoform mRNA levels within 3 or 6 days of exposure, but 4-NP did not have any effect on ERalpha short-isoform transcription level. In the brain, 4-NP reduced sGnRH2 gene expression in a dose-dependent manner, but did not modify sGnRH1 or ERalpha mRNA levels.

Vitellogenin induction in the endangered goodeid fish Girardinichthys viviparus: vitellogenin characterization and estrogenic effects of polychlorinated biphenyls

Vitellogenin (VTG) is a widely used biomarker in studies of endocrine disruption induced by xenobiotics such as polychlorinated biphenyls (PCBs). This study evaluates the estrogenic effects of these compounds on the black-fin goodeid Girardinichthys viviparus, an endangered fish species in Mexico with a reduced range of distribution due to pollution of its natural environment. Adult fish born in the laboratory were exposed to half the LC(0) of Inerteen commercial PCB mixture. VTG was determined through an inhibition enzyme-linked immunosorbent assay (ELISA) using a homologous-heterologous system. Male and female fish were killed after 1, 2, 4, 8 and 16 days of exposure. The distal third of each specimen was used for analysis. VTG was obtained from cultured hepatocytes and blood serum of males previously exposed to 17beta-estradiol. VTG molecular mass was 348 kDa. PCBs were found to elicit greater estrogenic effects on VTG induction in males than in females (p<0.05) and sex differences were noted. Time-dependent VTG induction kinetics in males and a stationary phase in females were also observed.

Purification of two lipovitellins and development of immunoassays for two forms of their precursors (vitellogenins) in medaka (Oryzias latipes)

Two distinct yolk proteins (YP1 and YP2) were purified from the ovary of medaka, and specific antisera against YPs were generated to characterize YPs and reveal their relation to two vitellogenins (Vg1 and Vg2). The molecular masses of purified YP1 and YP2 on gel filtration were 270 and 380 kDa, respectively. YPs were confirmed to be lipoproteins by staining with Sudan black. Amino acid compositions of YP1 and YP2 were similar to those of Vg1 and Vg2, respectively. In double immunodiffusion using anti-Vg1, a precipitin line of YP1 formed a spur against the Vg1 line. YP2 and Vg2 were reacted with anti-Vg2, and a precipitin line of YP2 formed a fuse against the Vg2 line. These biochemical and immunological analyses of purified YPs revealed that YP1 is lipovitellin 1 (Lv1) derived from Vg1 and YP2 is lipovitellin 2 (Lv2) derived from Vg2. Using specific antibodies against Lvs and Vgs, specific, high sensitivity chemiluminescent immunoassays (CLIAs) for two Vgs were developed to reveal basal Vg levels and response to exogenous estradiol-17beta (E2). The measurable range of both CLIAs was from 0.975 to 1000 ng/ml. The cross-reactivity to the alternative Vg in each CLIA was extremely low (<or=0.57%). When immature fish were immersed in water containing E2 for 1 h, both Vgs were induced by 0.5 microg/L of E2 at 24 h after treatment. Vg1 increased in a concentration-dependant manner up to 100 microg/L E2, while Vg2 reached a plateau at 10 microg/L of E2. The ratio of Vg1:Vg2 in E2-treated fish changed in a concentration-dependent manner from 1.5:1 to 8.5:1. The results from E2-treatment suggest that differential regulation may control the expression of medaka Vgs.

Identification of the herbicide Surflan and its active ingredient oryzalin, a dinitrosulfonamide, as xenoestrogens

Numerous environmental contaminants have been identified as endocrine disruptors (EDs)--substances that alter endocrine homeostasis by interfering with the biological action, production, or pharmacokinetics of endogenous hormones. Xenoestrogens are those EDs whose biological activity is similar to endogenous estrogen. This report presents data that identified Surflan, a proprietary herbicide emulsion, and its active ingredient oryzalin as xenoestrogens. In vitro, Surflan and oryzalin activated an estrogen-inducible reporter gene, and oryzalin competitively displaced 17beta-estradiol from the estrogen receptor. In vivo, Surflan and oryzalin induced expression of estrogen-regulated high-molecular-weight choriogenin genes in medaka (Oryzias latipes). These results are consistent with the characteristics of previously identified xenoestrogens and indicate that Surflan and oryzalin have the potential to adversely affect numerous estrogen-regulated biological processes.

17beta-estradiol induced vitellogenesis is inhibited by cortisol at the post-transcriptional level in Arctic char (Salvelinus alpinus)

This study was performed to investigate stress effects on the synthesis of egg yolk precursor, vitellogenin (Vtg) in Arctic char (Salvelinus alpinus). In particular the effect of cortisol (F) was determined since this stress hormone has been suggested to interfere with vitellogenesis and is upregulated during sexual maturation in teleosts. Arctic char Vtg was purified and polyclonal antibodies were produced in order to develop tools to study regulation of vitellogenesis. The Vtg antibodies were used to develop an enzyme-linked immunosorbent assay. The corresponding Vtg cDNA was cloned from a hepatic cDNA library in order to obtain DNA probes to measure Vtg mRNA expression. Analysis of plasma from juvenile Arctic char, of both sexes, exposed to different steroids showed that production of Vtg was induced in a dose dependent fashion by 17beta-estradiol (E2), estrone and estriol. Apart from estrogens a high dose of F also upregulated Vtg. In addition, F, progesterone (P) and tamoxifen were tested to determine these compounds ability to modulate E2 induced Vtg synthesis at both the mRNA and protein level. Tamoxifen was found to inhibit E2 induced Vtg mRNA and protein upregulation. P did not alter the Vtg induction while F reduced the Vtg protein levels without affecting the Vtg mRNA levels. Furthermore the inhibition of Vtg protein was found to be dose dependent. Thus, the inhibitory effect of F on Vtg appears to be mediated at the post-transcriptional level.

Cadmium: an endocrine disrupter that affects gene expression in the liver and brain of juvenile rainbow trout

An inhibition of vitellogenesis is observed in fish exposed to cadmium (Cd), either in natural or in experimental conditions. To investigate whether this correlates or not with modifications in the expression of several genes involved in reproduction, we have performed a study on juvenile rainbow trout (Oncorhynchus mykiss) exposed to waterborne Cd in combination with estradiol (E2). A relative reverse transcription-PCR protocol was used to evaluate the effect of Cd exposure on the expression of several genes. We quantified vitellogenin, rainbow trout estradiol receptor alpha (rtERalpha), short and long isoforms (rtERalphaS and rtERalphaL), mRNA levels in liver, and salmon GnRH1, salmon GnRH2, rtERalphaS, and rtERalphaL mRNA levels in the brain. In liver, Cd reduced the E2-stimulated mRNA levels of vitellogenin as well as these of both rtERalpha isoforms in a dose-dependent manner. In brain tissue, our results indicate that rtERalpha mRNA levels are not enhanced by E2. Cd treatments did not modify rtERalphaS isoform expression but reduced rtERalphaL expression in the brain. Focusing on the expression of salmon GnRH (sGnRH) genes, E2 did not affect mRNA levels, but experiments with Cd alone greatly enhanced sGnRH 1 as well as sGnRH 2 gene expression in a dose-dependant manner. This study supports the idea that Cd is an important endocrine disrupter that could act through an inhibition of E2-stimulated genes in the liver and also through a central effect on sGnRH gene expression. Cd may affect a number of E2 signaling pathways but could also affect the reproductive axis by nonestrogenic mechanisms.

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.

Characterization and de novo sequencing of Atlantic salmon vitellogenin protein by electrospray tandem and matrix-assisted laser desorption/ionization mass spectrometry

Vitellogenin (VTG) is a protein produced by the liver of oviparous animals in response to circulating estrogens. In the plasma of males and immature females, VTG is undetectable. VTG has been used as a biomarker for exposure to endocrine disruptors in many species. In the present study, characterization of intact Atlantic salmon VTG was effected using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI ToF MS). Tryptic digest peptides were analyzed by MALDI ToF MS to obtain a peptide mass fingerprint. De novo sequencing of the tryptic peptides used low-energy collisionally-induced dissociation (CID) in an electrospray ionization quadrupole-ToF orthogonal hybrid mass spectrometer (ESI Q-ToF MS/MS). The interpretation of the product-ion spectra obtained from the ESI Q-ToF MS/MS was done by Lutefisk, a computer-based software algorithm. The molecular mass of the intact protein was found to be 187335 Da. A total of 14 tryptic peptides were sequenced and compared with the complete rainbow trout VTG and the partial Atlantic salmon VTG sequences found in the Swiss-Prot database. De novo sequencing by CID MS/MS of 11 Atlantic salmon tryptic digest peptides with selected precursor ions at m/z 788.24, 700.20, 794.75, 834.31, 889.28, 819.79, 865.27, 843.81, 572.20, 573.66 and 561.68 showed high homology with the known sequence of rainbow trout VTG. The last two precursor peptide ions, found at m/z 573.66 and m/z 561.68, also specifically matched the known portion of the Atlantic salmon VTG sequence. Finally, three tryptic precursor peptide ions found at m/z 795.18, 893.28 and 791.05, provided product-ion spectra, which were exclusive to the unsequenced portion of the Atlantic salmon VTG.

Molecular markers of endocrine disruption in aquatic organisms

A wide range of organic contaminant compounds prevalent in the aquatic environment has been shown to exhibit hormone-disrupting activity. The actual potency of such compounds are low compared with endogenous hormones, such as 17beta-estradiol, but may still produce detrimental biological effects. Induced hormone levels are routinely measured using commercial testing kits, though these fail to relate to actual effects. Field and laboratory studies on the biological effects of environmental estrogens have, in the past, largely relied on assays of vitellogenin (vtg) induction in male fish, reduced growth in testes formation, and intersex incidence. Here, we critically review the current and potential application of molecular techniques in assessing the adverse biological reproductive effects of endocrine-disrupting chemicals in aquatic organisms. The role of fish (estrogen, androgen, and progestogen) hormone receptors and invertebrate (ecdysone) hormone receptor, egg production (vtg and chorion) proteins, steroid biosynthesis enzymes (aromatase, sulfotransferase, and hydroxysteroid dehydrogenase), DNA damage, apoptosis, and their potential development as biomarkers are discussed in turn. In each case, the sequences characterized are presented and homologies across species are highlighted. Molecular methods of gauging vtg and zona radiata (ZR) expression and protein concentrations have included immunoassay and reverse transcription polymerase chain reaction (RT-PCR). Suggestions for the isolation for key gene expression products (aromatase, ZR, and vtg, for instance), from a wider range of fish species using degenerate primers, are given. Endocrine disruption in invertebrates has received less attention compared with fish, partly because the knowledge regarding invertebrate endocrinology is limited. Here we review and suggest alternate isolation strategies for key players in the imposex induction process: vitellin (Vn), aromatase, and Ala-Pro-Gly-Trp (APGW) amide neurohormone. Current molecular-level techniques rely on ligand-binding assays, enzyme-linked immunosorbent assay (ELISA), and, more recently, gene expression. In the future, more reliance will be placed on the development of gene expression assays using reporter systems combined with cross-species PCR-based or polyclonal antibody-based assays. We discuss the use of recombinant receptors as a means of primary screening of environmental samples for estrogenicity and antiestrogenicity, which avoids species and seasonal variation in receptor response to ligand binding, a recognized problem of earlier bioassays. Most exciting is the potential that microarray and proteomics approaches have to offer. Such techniques are now used routinely in medical research to identify specific genes and proteins affected by treatment with endocrine disruptors, including estradiol. The technique has yet to be used to screen aquatic organisms, but it has the potential to implicate previously unsuspected estradiol-sensitive genes that may later become molecular markers of endocrine disruption.

Effects of progesterone and estradiol on the reproductive axis in immature diploid and triploid rainbow trout

In fish species, many studies demonstrated the crucial role of estradiol (E2) in the development of the reproductive axis, but progesterone (P) has been described mainly as a precursor steroid and no clear role by itself has been reported. Moreover, a cooperative effect of P (or another progestin) and E2 in fish has never been reported to our knowledge. In the present work, we investigated the effects of P, alone or in combination with E2, on the reproductive-axis of immature rainbow trout (Oncorhynchus mykiss). Liver vitellogenin and estradiol receptor (rtER) mRNA levels increased after E2 treatment, but were unchanged by P treatments as a reflection of peripheral action of steroids. In contrast, at the pituitary level, LH contents increased after E2 and/or P treatments. Focusing on the brain level, we confirmed a clear up regulation of rtER expression by E2 in sterile triploid females, and we also demonstrated a similar stimulating effect of P alone but no cooperative effect together with E2. In conclusion, our data demonstrate that in immature trout, prior to the beginning of the first reproductive cycle, unlike E2, P is able to stimulate the reproductive brain-pituitary axis without affecting vitellogenin synthesis in the liver.

Waterborne ethynylestradiol induces vitellogenin and alters metallothionein expression in lake trout (Salvelinus namaycush)

Estrogenic contaminants isolated from waters receiving sewage treatment plant effluents are known to induce the egg yolk precursor vitellogenin (VTG) in male fish. Levels of the metal binding protein metallothionein (MT) have also been shown to be affected by estrogens in fish. It has been postulated that MT declines in estrogen exposed fish to facilitate transfer of the essential metal Zn to cellular components required for VTG synthesis. To examine the changes in MT and VTG concentrations in fish exposed to an estrogen contaminant, lake trout (Salvelinus namaycush) were exposed to waterborne ethynylestradiol at 0, 4, 40 or 400 ng/l(-1) for 21 days. Blood and tissues were collected after 21 days of exposure to measure circulating levels of VTG as well as MT concentrations in liver and kidney. VTG increased in male and female fish from all three exposure groups compared to control fish. MT in liver significantly decreased in males and females compared to the controls, in the two highest exposures. MT in kidney was significantly higher in both sexes of fish exposed to the two highest concentrations of ethynylestradiol. These data are supportive of a relationship between estrogen exposure and the regulation of MT. Further studies to examine the specific links between estrogen exposure, VTG induction and regulation of essential metals like Zn are required.

Characterisation of the intact rainbow trout vitellogenin protein and analysis of its derived tryptic and cyanogen bromide peptides by matrix-assisted laser desorption/ionisation time-of-flight-mass spectrometry and electrospray ionisation quadrupole/time-of-flight mass spectrometry

Vitellogenin (VTG) is a protein produced by the liver of oviparous animals. It is being used as a biomarker for exposure to endocrine disruptors in many species. Rainbow trout Vtg has recently been sequenced by the conventional cDNA nucleotide approach. We focused on protein characterization of the intact protein and its derived tryptic and cyanogen bromide peptides by matrix-assisted laser desorption/ionisation and electrospray ionisation mass spectrometry. The molecular mass of the intact protein was found to be 183127 Da. A large number of unidentified peptide ions encourage further structural analysis to propose possible sequence variants and post-translational modifications.

Gene expression analysis of largemouth bass exposed to estradiol, nonylphenol, and p,p'-DDE

The purpose of this study was to determine the specific expression profile of 132 genes, some of which are estrogen responsive, in largemouth bass (LMB) following exposure to estradiol (E(2)), or to two hormonally active agents, 4-nonylphenol (4-NP) and 1,1-dichloro-2, 2-bis (p-chlorophenyl) ethylene (p,p'-DDE), using gene array technology. The results of these experiments show that LMB exposed to E(2) and 4-NP had similar, but not identical genetic signatures for the genes examined, some of which are known to be estrogen-responsive genes. The differences suggest that 4-NP may have additional modes of action that are independent of the estrogen receptor (ER). We have also shown that exposure of male LMB to p,p'-DDE results in an increase in some estrogen-responsive genes. But in female LMB, the observed changes were a down-regulation of the normally up-regulated estrogen responsive genes. Other genes were also down-regulated. These results suggest that p,p'-DDE may affect regulation of genes differently in male and female LMB. This study further suggests that gene arrays have the potential to map out the gene activation pathways of hormonally active compounds.

Lipovitellins and phosvitins of the fertilized eggs during embryo growth in the oviparous lizard Podarcis sicula

In the lizard Podarcis sicula, the major vitellogenin (VTG)-derived yolk proteins, lipovitellins and phosvitins, were extracted from the yolk globules of laid and fertilized eggs at different periods of incubation up to 44 days close to hatching. Embryonic development was almost over at this time. Yolk proteins were isolated by precipitation in saturated (NH(4))(2)SO(4), separated on SDS-PAGE and detected by Western blotting with homologous polyclonal anti/VTG antibody. Two lipovitellins of 110 and 116 kDa were always present in the yolk of laid eggs after 1, 10, 18, and 44 days from oviposition. Both these proteins were glycosylated and were recognized by the anti/VTG antibody; their N-terminal sequences were analyzed. Four phosvitins were detected in freshly laid eggs, but their number decreased during incubation, and after 44 days only a single protein of approximately 6.5 kDa was present. The results indicated that, in this lizard, during embryonic development, lipovitellins remain unchanged, whereas the phosphorylated components of yolk undergo continuous degradation.

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

Vitellogenin (Vtg) and estrogen receptor (ER) gene expression levels were measured in largemouth bass to evaluate the activation of the ER-mediated pathway by estradiol (E(2)). Single injections of E(2) ranging from 0.0005 to 5 mg/kg up-regulated plasma Vtg in a dose-dependent manner. Vtg and ER mRNAs were measured using partial cDNA sequences corresponding to the C-terminal domain for Vtg and the ligand-binding domain of ER alpha sequences. After acute E(2)-exposures (2 mg/kg), Vtg and ER mRNAs and plasma Vtg levels peaked after 2 days. The rate of ER mRNA accumulation peaked 36-42 h earlier than Vtg mRNA. The expression window for ER defines the primary response to E(2) in largemouth bass and that for Vtg a delayed primary response. The specific effect of E(2) on other estrogen-regulated genes was tested during these same time windows using differential display RT-PCR. Specific up-regulated genes that are expressed in the same time window as Vtg were ERp72 (a membrane-bound disulfide isomerase) and a gene with homology to an expressed gene identified in zebrafish. Genes that were expressed in a pattern that mimics the ER include the gene for zona radiata protein ZP2, and a gene with homology to an expressed gene found in winter flounder. One gene for fibrinogen gamma was down-regulated and an unidentified gene was transiently up-regulated after 12 h of exposure and returned to basal levels by 48 h. Taken together these studies indicate that the acute molecular response to E(2) involves a complex network of responses over time.

Effects of long-term nonylphenol exposure on gonadal development and biomarkers of estrogenicity in juvenile rainbow trout Oncorhynchus mykiss

Environmental pollutants with estrogenic activity including nonylphenol (NP) have the potential to alter gonadal development and reproduction of wild fish. To investigate the estrogenic action of environmentally relevant concentrations of NP, rainbow trout (Oncorhynchus mykiss) were continuously exposed during the embryonic, larval and juvenile life stage to 1.05 and 10.17 microg/l NP for 1 year, and sexual differentiation, vitellogenin (VG), VG mRNA, and zona radiata protein (ZRP) expression were examined after that period. The applied NP concentrations did not affect mortality and hatching rates, and did not have an influence on the body weight of 1-year-old fish. No occurrence of testis-ova was observed and sex-ratios of NP exposed groups of fish were unchanged when compared with control groups. The induction of VG and ZRP expression was a more sensitive reaction to the presence of NP than the formation of testis-ova and the reversal of sex. Increased VG expression in trout liver occurred already at 1.05 microg/l NP, whereas VG mRNA levels, quantified by competitive RT-PCR, were not significantly elevated in NP exposed fish. ZRP contents were significantly higher at 10.17 microg/l NP. Since induction of VG did not occur in all fish exposed to 1 or 10 microg/l NP and ZRP induction did not occur in all fish exposed to 10 microg/l, some individuals may be more affected by exposure to NP than others. This study demonstrates that NP concentrations typically found in sewage treatment effluents and some rivers do not affect sexual differentiation in rainbow trout, but induce VG and ZRP expression in the liver of exposed fish.

Vitellogenin mRNA regulation and plasma clearance in male sheepshead minnows, (Cyprinodon variegatus) after cessation of exposure to 17 beta-estradiol and p-nonylphenol

Research was conducted to determine the kinetics of hepatic vitellogenin (VTG) mRNA regulation and plasma VTG accumulation and clearance in male sheepshead minnows (Cyprinodon variegatus) during and after cessation of exposure to either 17 beta-estradiol (E2) or para-nonylphenol (NP). Adult fish were continuously exposed to aqueous measured concentrations of 0.089 and 0.71 microg E2 per l, and 5.6 and 59.6 microg NP per l for 16 days using an intermittent flow-through dosing apparatus. Fish were sampled on days 8 and 16 of exposure followed by sampling at discrete intervals for up to 96 days post-exposure. At each interval five fish were randomly sampled from each concentration and hepatic VTG mRNA and serum VTG levels for individual fish determined by slot blot and direct enzyme-linked immunosorbent assay (ELISA), respectively. Exposure to E2 and NP resulted in a dose dependent increase in hepatic VTG mRNA and plasma VTG over the course of the 16-day exposure period. Mean plasma VTG levels at day 16 were >100 mg/ml for both high doses of E2 and NP, and >20 mg/ml for the low exposure treatments. Within 8 days post-exposure, hepatic VTG mRNA levels returned to baseline in both high and low E2 treatments but remained elevated 2-4 fold in the NP treatments. Due to a shortened sampling period, a clearance rate for plasma VTG in the 5.6 microg NP per l treatment could not determined. In the 0.089, 0.71 microg E2 per l, and 59.6 microg NP per l treatments, VTG levels began decreasing within 4 days after exposure cessation and exhibited an exponential rate of elimination from plasma. Clearance rates for 0.71 microg E2 per l and 59.6 microg NP per l were not significantly different (P=0.47), however, both demonstrated significantly higher rates of clearance (P<0.02) than observed in the 0.089 microg E2 per l treatment. Our results indicate that hepatic VTG mRNA rapidly diminishes after cessation of estrogenic exposure in sheepshead minnows, but plasma VTG clearance is concentration and time dependent and may be detected at measurable levels for months after initial exposure to an estrogenic compound.

Changes in hepatic vitellogenin mRNA levels during oocyte development in the Japanese eel, Anguilla japonica

The induction of vitellogenesis is a complex process requiring coordinated control and expression of many hepatic gene products, such as vitellogenin (VTG). To investigate the regulation of VTG synthesis, knowledge of the molecular genetics of VTG is required. Here, the authors have isolated a partial cDNA encoding Japanese eel VTG using an immunoscreening technique. This cDNA contained an open reading frame of 1629 bp, predicted to encode 543 amino acid residues, the sequence of which showed high homology with the VTG of other fishes. Northern blot analysis yielded a VTG transcript of approximately 5.8 kb from eel hepatic tissue. Experimentally, VTG synthesis could be induced by treatment with salmon pituitary homogenate. The levels of VTG mRNA in the liver during the artificial maturation of female Japanese eels correspond well to levels of E2 and VTG in the serum.

Uptake, metabolism and excretion of bisphenol A in the rainbow trout (Oncorhynchus mykiss)

The uptake, metabolism and excretion of the oestrogenic chemical bisphenol A (BPA) were studied in juvenile rainbow trout (Oncorhynchus mykiss). BPA was detectable in plasma, liver and muscle after 2 h of water exposure at 0.44 microM (100 microg BPA/l), and a steady state was reached within 12-24 h. The concentration of the glucuronidated degradation product in the plasma was about twice that of the parent compound. A plasma half life of BPA was calculated as 3.75 h following injection of the compound. The vitellogenin synthesis was measured in response to the BPA treatment, and a lag period of 5 and 7 days between injection of the compound and a significant vitellogenin response was observed for females and males, respectively. At the time of the vitellogenin response no BPA could be detected in the liver tissue from either male or female fish. These results indicate that fish briefly exposed to elevated levels of oestrogenic chemicals might develop a response several days later.

Development and validation of a homologous zebrafish (Danio rerio Hamilton-Buchanan) vitellogenin enzyme-linked immunosorbent assay (ELISA) and its application for studies on estrogenic chemicals

Vitellogenin (VTG) was isolated by anion exchange chromatography from plasma of female zebrafish (Danio rerio) induced with 17alpha-ethinylestradiol (EE2). The purity of the VTG isolate was confirmed by polyacrylamide gel electrophoresis (SDS-PAGE). Purified VTG was used to raise polyclonal antibodies in rabbits and the specificity of the antisera for VTG confirmed by Western blot analysis of plasma proteins separated by SDS-PAGE. The antibodies cross-reacted with two proteins in the plasma of female zebrafish, with molecular masses of approximately 142 and 171 kDa. No cross-reactivity was observed with any other plasma proteins. A competitive enzyme-linked immunosorbent assay (ELISA) was developed using the polyclonal zebrafish VTG (z-VTG) antibodies and purified z-VTG as ligand and standard, respectively. The z-VTG ELISA was sensitive with a detection limit of between 2.0 and 3.0 ng purified VTG/ml, and a working range between 3 and 500 ng/ml (30-85% binding). The ELISA demonstrated precision, with inter- and intra-assay variations of 7.5+/-2.7 and 4.9+/-1.4%, respectively. Plasma from adult zebrafish and whole body homogenates from juvenile zebrafish diluted parallel with the z-VTG standard in the ELISA, validating the assay for quantifying z-VTG in both of these tissues. Exposure of adult male zebrafish to EE2 via water induced a concentration-dependent induction of VTG with a lowest observed effect concentration (LOEC) < or =1.67 ng EE2/l (for a 21-day exposure). The homologous z-VTG ELISA provides a valuable tool for the study of environmental estrogens in zebrafish.

Hepatopancreas is the extraovarian site of vitellogenin synthesis in black tiger shrimp, Penaeus monodon

The site of yolk protein synthesis in crustaceans has long been a subject of controversy. The vitellogenin gene structure was partially reported only very recently in Macrobrachium rosenbergii, after which the hepatopancreas was confirmed as the extraovarian site of vitellogenin synthesis in that species. Ovaries are the most frequently reported as the site of yolk protein synthesis in penaeid shrimp. Using cDNA reversed-transcribed from mRNA isolated from the hepatopancreas of vitellogenic female shrimp, Penaeus monodon, we found that its deduced amino acid sequence had high identity of 48% with that from M. rosenbergii vitellogenin. A similar location of the intron in the sequenced region of genomic DNA was also found between these two species. We therefore concluded that the hepatopancreas the extraovarian site of vitellogenin synthesis in P. monodon in vivo. The partial structure of vitellogenin gene is presented in this study.

Expression of three vitelline envelope protein genes in arctic char

Several studies have shown effects of estrogenic substances on endocrine and reproductive systems in wildlife. Measurement of plasma vitellogenin (VTG) is a commonly used method to determine exposure to estrogenic substances in fish. There is, however, a growing need for additional sensitive and accurate methods to detect estrogenic substances in vivo. The vitelline envelope proteins (VEPs) have been suggested, in other studies, as suitable biomarkers for estrogenic substances. The present study investigates the induction of VEPs in juvenile Arctic char (Salvelinus alpinus). The results demonstrate that VEP mRNA exhibits earlier induction than estrogen receptor mRNA or VTG mRNA following injection of juvenile Arctic char with a single dose of 17beta-estradiol (E2; 10 mg/kg bw). These results indicate that the VEPs have a higher sensitivity for E2 than VTG. However, an early and sex-independent expression of VEPbeta in estrogen-unchallenged juvenile Arctic char was observed. These findings suggests that the regulatory mechanisms of VEPs might be more complex than previously thought, which in turn may have implications for the usage of VEPs as biomarkers for xenoestrogen exposure.

Induction of gene expression in sheepshead minnows (Cyprinodon variegatus) treated with 17beta-estradiol, diethylstilbestrol, or ethinylestradiol: the use of mRNA fingerprints as an indicator of gene regulation

The recent interest in hormonally active environmental contaminants has sparked a drive to find sensitive methods to measure their effects on wildlife. A molecular-based assay has been developed to measure the induction of gene expression in sheepshead minnows (Cyprinodon variegatus) exposed in vivo to the natural and pharmaceutical estrogens 17beta-estradiol, ethinylestradiol, and diethylstilbestrol. This method used differential display reverse transcriptase polymerase chain reaction assays to compare the expression of individual mRNAs from control and estrogen-exposed fish. Forty-eight differentially expressed cDNAs were isolated by this method, including cDNAs for vitelline envelope proteins and vitellogenin. The mRNA expression patterns for fish injected with a pharmacological dose of estradiol (5 mg/kg) were identical to those obtained in fish receiving constant aqueous exposure to 212 ng estradiol/liter. Further, the cDNA "fingerprint" pattern observed in the estradiol-treated fish also matched that obtained in fish receiving continuous-flow aqueous exposures to 192 ng ethinyl estradiol/liter and a nominal concentration of 200 ng diethylstilbestrol/liter. The results demonstrate a characteristic expression pattern for genes upregulated by exposure to a variety of natural and anthropogenic estrogens and suggest this approach may be valuable to examine the potential effects of environmental contaminants on other endocrine-mediated pathways of reproduction, growth, and development.

Vitellogenin-induced pathology in male summer flounder (Paralichthys dentatus)

Male summer flounder (Paralichthys dentatus) were given two injections (initially and 2 weeks later) of 17beta-estradiol (E2) totaling 0.2 (2 x 0.1), 2.0 (2 x 1.0) or 20.0 (2 x 10.0) mg E2/kg body weight. Blood and tissue samples were collected 4, 6 and 8 weeks after the initial injection in the (2 x 0.1) mg/kg treatment, 4, 6, 8, and 15 weeks after the first injection in the (2 x 1.0) mg/kg treatment and at 4 weeks only in the (2 x 10.0) mg/kg treatment. Five of the 12 fish injected twice with 10.0 mg/kg were moribund before the first sampling period. Circulating levels of vitellogenin (VTG) in the blood of all E2-injected fish from all treatments were comparable with those concentrations found in the blood of wild male carp (Cyprinus carpio) and walleye (Stezostedion vitreum) previously collected near a sewage treatment plant (0.1-10.0 mg VTG/ml plasma). Excessive hyalin material accumulated in the livers, kidneys and testes of the treated fish. A portion of that material was identified as VTG by immunohistochemistry. The accumulation of VTG, and possibly other estrogen-inducible proteins, resulted in hepatocyte hypertrophy, disruption of spermatogenesis, and obstruction or rupture of renal glomeruli.

Quantification of rainbow trout (Oncorhynchus mykiss) zona radiata and vitellogenin mRNA levels using real-time PCR after in vivo treatment with estradiol-17 beta or alpha-zearalenol

Estrogen receptor-mediated induction of zona radiata (ZR) and vitellogenin (VTG) mRNA and protein in rainbow trout (Oncorhynchus mykiss) was compared to assess their utility as biomarkers for exposure to estrogenic compounds. Partial sequences of rainbow trout ZR and beta-actin were cloned by reverse transcriptase polymerase chain reaction (RT-PCR) using degenerate primers based on conserved regions across a number of species. A 549 bp fragment of the rainbow trout ZR-gene showed a high degree of amino acid sequence identity to that of salmon (77%), winter flounder (64%), carp ZP2 (63%) and medaka (61%) ZR-proteins. The 1020 bp beta-actin fragment was approximately 100% identical to sequences from several species. Real-time PCR was used to quantify the induction of ZR-gene and VTG in rainbow trout liver after in vivo exposure to estradiol-17 beta (E(2)) (0.01, 0.1, 1.0 or 10 mg/kg body weight (bw) fish) or alpha-zearalenol (alpha-ZEA) (0.1, 1.0 or 10 mg/kg bw). Real-time PCR and indirect enzyme-linked immunosorbent assay (ELISA) showed that ZR and VTG were induced in both the liver and the plasma after a single injection of E(2) or alpha-ZEA. ZR was more responsive to low levels of E(2) and alpha-ZEA than VTG, and real-time PCR was shown to be more sensitive than the ELISA. Rainbow trout ZR-gene and proteins provide a sensitive biomarker for assessing estrogenic activity.

Estrogen-induced vitellogenin mRNA and protein in sheepshead minnow (Cyprinodon variegatus)

Many environmentally persistent xenobiotic chemicals appear to disrupt normal endocrine function by acting as ligands for endogenous steroid receptors, including the estrogen receptor. Xenobiotics that bind to the estrogen receptor may elicit several effects, one of which is activating estrogen-responsive genes, such as vitellogenin (Vtg). Primers to vitellogenin mRNA have been used to amplify a portion of the coding sequence in sheepshead minnow (SHM) (Cyprinodon variegatus). Two Vtg cDNA fragments from SHM were isolated exhibiting 72% sequence homology and corresponding to the two Vtg genes identified in the mummichog, Fundulus heteroclitus. Using these Vtg cDNA fragments as sensitive genetic probes, we evaluated the initial estrogenic response of fish exposed to natural or anthropogenic chemicals. These probes were used to study in vivo gene induction in SHM exposed to 17beta-estradiol (E(2)) and ethinylestradiol (EE(2)) under controlled laboratory conditions. Hepatic Vtg mRNA was upregulated and plasma Vtg synthesis in estrogen-induced SHM was assessed. Two in vivo time-course experiments were conducted; a single injection of E(2) followed over 72 h and a double E(2) injection examined for 12 days. These two protocols provided evidence for differential hepatic Vtg mRNA regulation resulting from a single or a double injection. In a separate experiment using an aqueous flowthrough system, constant exposures to low doses of E(2) (200 ng/L) and EE(2) (100 ng/L) induced hepatic Vtg mRNA and plasma Vtg to levels comparable with the E(2) injections. Larger aqueous exposure doses (2000 ng/L E(2) or 1000 ng/L EE(2)) in the flowthrough experiment resulted in greater responses of hepatic Vtg mRNA and plasma Vtg at 7 days. Constant aqueous exposure to E(2) (2000 ng/L) or EE(2) (1000 ng/L) may thus be more effective than a single large-dose injection (5 mg/kg) to stimulate Vtg gene activation and synthesis.

Contrasting effects of estrogen on transthyretin and vitellogenin expression in males of the marine fish, Sparus aurata

A partial cDNA encoding for the C-terminus of vitellogenin (VTG) was cloned from liver of Sparus aurata male treated with 17beta-estradiol (E(2)). E(2) treatment of S. aurata males resulted in increased synthesis and secretion of VTG protein into the plasma, determined by a specific enzyme-linked immunosorbent assay (ELISA) in a time-dependent manner. While VTG mRNA was induced by E(2) treatment, transthyretin (TTR) mRNA levels were reduced. These data provide the first demonstration that estrogen exhibits contrasting effect on VTG and on TTR gene expression in teleosts.

Aluminium and cadmium inhibit vitellogenin and its mRNA induction by estradiol-17 beta in the primary culture of hepatocytes in the rainbow trout Oncorhynchus mykiss

Effects of Al and Cd on vitellogenin (VTG) and VTG mRNA induction by estradiol-17 beta (E(2)) were examined in primary hepatocyte cultures of rainbow trout. Hepatocytes were precultured for 2 days and then E(2) (2 x 10(-6) M) and Al (10(-6)-10(-4) M) or Cd (10(-9)-10(-6) M) were simultaneously added to the incubation medium. Hepatocytes were cultured for 5 more days. Media and hepatocytes were then analyzed by SDS-PAGE and Northern blotting for VTG and VTG mRNA, respectively. These metals had no appreciable effect on the viability of hepatocytes in culture. However, Al and Cd interfered with VTG production and VTG mRNA expression. Al reduced VTG production in a concentration-dependent way and a significant reduction occurred at Al concentrations greater than 5 x 10(-5) M. VTG mRNA expression also decreased with a negative correlation with Al concentrations (r = -0.98). The inhibition of VTG production by Cd was not concentration-dependent. This metal markedly inhibited VTG production and VTG mRNA expression at 10(-6) M. The Al-induced inhibition of VTG production was restored 7 days after Al removal, but the Cd-induced inhibition was not restored. These results suggest that Al and Cd inhibit VTG production at the transcriptional level to reduce VTG mRNA expression by different mechanisms.

Comparative estrogenicity of estradiol, ethynyl estradiol and diethylstilbestrol in an in vivo, male sheepshead minnow (Cyprinodon variegatus), vitellogenin bioassay

An in vivo bioasssay for vitellogenin (VTG) synthesis was developed to screen individual chemicals or mixtures of chemicals for potentially estrogenic effects in a marine teleost model. An enzyme-linked immunosorbent assay (ELISA) was used to quantitate VTG synthesis in male sheepshead minnows (Cyprinodon variegatus) exposed to five concentrations of the natural estrogen (17beta-estradiol), a synthetic, steroidal pharmaceutical estrogen (17alpha-ethynyl estradiol), or a synthetic, non-steroidal, pharmaceutical estrogen (diethystilbestrol) for 16 days. At an exposure concentration of 20 ng/l, only diethystilbestrol elicited a vitellogenic response. At all test concentrations greater than 100 ng/l, VTG appeared in the plasma in a dose-dependent manner for the three estrogen treatments. Liver VTG mRNA measurements were also made, exhibiting no clear correlations between quantities, nor temporal appearance of the message and mature protein were apparent. This assay is short-term, relatively inexpensive, shows a direct response, and easily quantitated.