An enzyme-linked immunosorbent assay (ELISA) for measuring vitellogenin in English sole (Pleuronectes vetulus): development, validation and cross-reactivity with other pleuronectids

Polyclonal antibody-based immunoassay of vitellogenin in Van fish (Alburnus tarichi)

Van Lake is the third largest closed lake in the world and the biggest lake in Turkey. An ELISA method has developed with the aim of determining the pollution caused by estrogens and estrogen-like chemicals that have come to the lake Van in recent years. First, the vitellogenin in estrogen-treated male fish plasma was purified by ion exchange chromatography, injected into rats, and the obtained polyclonal antibodies were tested for specificity by Western blot and immunohistochemical methods. Immunohistochemical labeling of the vitellogenin-synthesized liver resulted in the intense marking of the liver of the animals injected with estrogen, while no markings were observed in the control group. The limit of detection of the developed enzyme-linked immunosorbent assay was 4.6 µg L^-1, and the working range was 7.8 to 2000 µg L^-1. Intra- and inter-assay variations were 13.0 % and 13.3%. The highest level of vitellogenin in male fishes measured was 23.56 µg mL^-1.

Vitellogenin expression, DNA damage, health status of cells and catalase activity in Acheta domesticus selected according to their longevity after graphene oxide treatment

The increased use of graphene oxide (GO) raises worrisome questions regarding its possible threat to various ecosystems. Invertebrates represent valuable organisms for environmental studies. The lifespan can influence the ability to cope with toxins, especially those that act via oxidative stress. Two strains of Acheta domesticus, which are selected for longevity, were tested. The main aim was to investigate how GO, when administrated in food, affects: the condition of cells, DNA stability, ROS generation and the reproduction potential (the Vitellogenin (Vg) protein expression). The "recovery effect" - after removing GO from the diet for 15 days - was also measured. The results revealed different responses to GO in the wild (H) and long-living (D) strains. The D strain had a higher catalase activity compared to the H strain on the 25th day of the imago stage. Removing GO from the food resulted in a decrease in the catalase activity to the level of the control. On the 5th day of the imago stage, the H strain had a higher cell mortality than the D strain in the GO-intoxicated groups. There was more DNA damage in the H strain compared to the long-living strain. A remedial effect was seen after the GO was removed from the diet. The total Vg protein expression was higher in the H strain and lower in the D strain. The results indicated a GO concentration-dependent outcome. In both strains, removing the GO from the food led to a high Vg expression. The Vg expression after GO treatment, particularly translation and post-translational processing, should be studied in detail in the future. The D strain of crickets had more specialized mechanisms for maintaining homeostasis than the H strain. Organisms can fight off negative effects of GO, especially when they have systems that are well developed against oxidative stress.

A monoclonal antibody against Lates calcarifer vitellogenin and a competitive ELISA to evaluate vitellogenin induction after exposure to xenoestrogen

A monoclonal antibody specific to sea bass (Lates calcarifer) vitellogenin (VTG) was developed, for use as a tool for monitoring endocrine disrupting chemicals (EDCs). VTG was induced in sea bass by intramuscular injection of 17β-estradiol (E₂: 2 mg/kg) every three days. Blood was collected three days after the last injection. Plasma VTG was then purified by chromatography in hydroxyapatite and a sephacryl-S300 column. Characterizations of purified VTG were done by phospholipoglycoprotein staining on a native-PAGE with confirmation by mass spectrometry (LC-MS/MS). Antibody was raised in mice by injection of purified VTG. After monoclonal antibody production, the hybridoma clone No. 41 (MAb-sea bass VTG 41) was selected and developed for quantification of VTG by competitive enzyme-linked immunosorbent assay (ELISA). The ELISA method was sensitive with a detection limit of VTG 40 ng/mL. MAb-sea bass VTG 41 was specific to VTG from E₂-treated sea bass and others EDCs (Nonylphenol, Benzo[a]pyrene and CdCl₂). Moreover, cross-reactivity was also found in E₂-treated coral grouper (Epinephelus corallicola). The ELISA method obtained from this work can be further applied for the assessment of EDCs in Thailand and Southeast Asia's aquatic environment.

Effects of bisphenol A (BPA) on brain-specific expression of cyp19a1b gene in swim-up fry of Labeo rohita

Estrogen regulates numerous developmental and physiological processes and effects are mediated mainly by estrogenic receptors (ERs), which function as ligand-regulated transcription factor. ERs can be activated by many different types endocrine disrupting chemicals (EDCs) and interfere with behaviour and reproductive potential of living organism. Estrogenic regulation of membrane associated G protein-coupled estrogen receptor, GPER activity has also been reported. Bisphenol A (BPA), a ubiquitous endocrine disruptor is present in many household products, has been linked to many adverse effect on sexual development and reproductive potential of wild life species. The present work is aimed to elucidate how an environmentally pervasive chemical BPA affects in vivo expression of a known estrogen target gene, cyp19a1b in the brain, and a known estrogenic biomarker, vitellogenin (Vg) in the whole body homogenate of 30 days post fertilization (dpf) swim-up fry of Labeo rohita. We confirm that, like estrogen, the xenoestrogen BPA exposure for 5-15 days induces strong overexpression of cyp19a1b, but not cyp19a1a mRNA in the brain and increase concentration of vitellogenin in swim-up fry. BPA also induces strong overexpression of aromatase B protein and aromatase activity in brain. Experiments using selective modulators of classical ERs and GPER argue that this induction is largely through nuclear ERs, not through GPER. Thus, BPA has the potential to elevate the levels of aromatase and thereby, levels of endogenous estrogen in developing brain. These results indicate that L. rohita swim-up fry can be used to detect environmental endocrine disruptors either using cyp19a1b gene expression or vitellogenin induction.

Development of a lipovitellin-based sandwich ELISA for determination of vitellogenin in the marine medaka Oryzias melastigma

A lipovitellin (Lv) based sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantify vitellogenin (Vtg) in marine medaka (Oryzias melastigma). Lv and Vtg were purified from the unfertilized eggs and the whole body homogenates (WBH) of estradiol (E₂)-exposed fish. The purified Lv sample appeared as three clear bands (118, 112 and 100 kDa) in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and was identified as an Lvs mixture from VtgAa and VtgAb by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis. Polyclonal antibody against marine medaka VtgAa was also raised. Compared with Vtg, Lv was more stable to heat stress (37 °C for 8 h or 4 °C for a week) and repeated freeze/thaw stress. In addition, western blot analysis revealed that marine medaka Vtg and Lv had similar immunogenicity. Therefore, in this study, Lv was applied instead of Vtg as the standard to establish an ELISA. The Lv standard curve was parallel to serial WBH dilutions of E₂-exposed fish, and the absorbance values were very low in control male samples, suggesting the specificity and feasibility of the method for Vtg quantification. The developed assay was sensitive with the detection limit of 3.1 ng/mL and had a working range between 15.6 and 500 ng/mL. The intra- and inter-assay coefficients of variation were both below 5%. Moreover, the standard curves of Lv antigen treated under different stresses were almost identical, indicating high robustness of the assay. Overall, our study provides an important methodology reference for quantification of marine medaka Vtg.

Vitellogenin levels and others biomarkers show evidences of endocrine disruption in fish species from Iguaçu River - Southern Brazil

The adverse effects of endocrine disrupting chemicals (EDCs) on aquatic wildlife and human health represent a current issue of high public concern. Even so, they are still poorly studied in aquatic environments of South America. The aim of the present study was to investigate the impact of EDCs in five cascading reservoirs from the Iguaçu River, evaluating reproductive endpoints in three native fish species (Astyanax bifasciatus, Chrenicicla iguassuensis and Geophagus brasiliensis). Additionally, a polyclonal antiserum anti-vitellogenin from G. brasiliensis and a capture ELISA assay were developed for detection of estrogenic or anti-estrogenic activities in male and female fish, respectively. Vitellogenin (VTG) levels in male fish from the Iguacu River was observed, as well as decreased levels of vitellogenin and estradiol in the plasma of female fish. These findings were associated with immature gonads and lower gonadosomatic index in G. brasiliensis adult females from the Foz do Areia (FA) Reservoir. Additionally, both endemic species (Astyanax bifasciatus and Chrenicicla iguassuensis) displayed immature gonads and histological changes, such as degeneration of germ cells, in other studied reservoirs. The current results suggest that these reproductive responses may be associated with the bioavailability of EDCs in the Iguaçu River. These impacts are likely related to chemicals released by human activities, especially from sewage and industrial sources and agricultural production, detected in previous studies. Overall, the FA reservoir was potentially the most affected by chemicals with endocrine properties, and further studies are necessary to identify and quantify these chemicals.

Estrogen-regulated expression of cyp19a1a and cyp19a1b genes in swim-up fry of Labeo rohita

P450 aromatase is the terminal enzyme in the steroidogenic pathway and catalyzes the conversion of androgens to estrogens. The expression of cyp19a1 genes in brain and gonad of Indian major carp, Labeo rohita swim-up fry was measured by quantitative real-time polymerase chain-reaction. Results demonstrated that cyp19a1b and cyp19a1a predominate in brain and gonad respectively. Treatment of fry with an aromatase inhibitor fadrozole for 6days attenuated brain cyp19a1b expression, but not cyp19a1a of gonad. Fadrozole also attenuated brain aromatase activity. Treatment with 17β-estradiol (E2) for 6days resulted in up-regulation of brain cyp19a1b transcripts in a dose- and time-dependent manner, but not cyp19a1a. Whole-body concentration of vitellogenin also increased in response to E2. Altogether, these results indicate L. rohita swim-up fry can be used to detect environmental estrogens either using vitellogenin induction or cyp19a1b gene expression.

Purification and development of ELISAs for two forms of vitellogenin in Indian walking catfish, Clarias batrachus (L.)

Two forms of vitellogenin (Vg: Vg1 and Vg2) were purified from the plasma of estradiol-17β (E₂)-treated Indian walking catfish, Clarias batrachus, by gel filtration and adsorption chromatography. Native Vg1 and Vg2 had apparent molecular masses of 375 and 450 kDa, respectively, and both Vgs resolved into two similar major bands (95 and 67 kDa) in SDS-PAGE under reducing condition. Polyclonal antisera raised against each form of Vg were absorbed with a combination of hypophysectomized male catfish serum proteins and alternate Vg to ensure specificity. Immunological analyses verified the presence of Vg1 and Vg2 in the plasma of female catfish. Homologous ELISAs were developed for Vg1 and Vg2 using their respective harvested antisera, which exhibited the detection limit of 100 ng ml^-1 for Vg1 and 40 ng ml^-1 for Vg2, and low level of cross-reactivity (not parallel to the standard) was found with alternate Vg in each assay. Treatment of male catfish with E₂ induced both Vgs showing a proportionate ratio of Vg1 to Vg2 at 5.6:1. Plasma concentrations of both Vgs measured by ELISAs at different reproductive phases of field collected female catfish increased in accordance with the ovarian development, keeping the proportionate ratio of Vg1 to Vg2 at about 2:1 in fish undergoing vitellogenesis during prespawning period and 1:20 during spawning period, suggesting that Vg1 may be the major Vg to contribute in yolk formation, whereas Vg2, besides its role in yolk formation, may facilitate other physiological functions. The present study, thus, demonstrates the occurrence of two unequally synthesized Vgs in the catfish.

Lipovitellin as an antigen to improve the precision of sandwich ELISA for quantifying zebrafish (Danio rerio) vitellogenin

Vitellogenin (Vtg) in zebrafish (Danio rerio) is a core biomarker for screening environmental estrogens in test guidelines of the Organization for Economic Cooperation and Development. To accurately quantify zebrafish Vtg, lipovitellin (Lv), the main Vtg-derived yolk protein, was used as the antigen to establish a sandwich enzyme-linked immunosorbent assay (ELISA). The purified Lv was a phospholipoglycoprotein with apparent molecular weight of ~445kDa, and separated into three polypeptides corresponding to ~117, ~102, and ~23.8kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Immunological analysis confirmed the specificity of the anti-Lv antibody for Vtg and the immunological similarity between Vtg and Lv. Using the purified Lv and anti-Lv antibody, a sandwich ELISA with a detection limit of 4.3ng/mL and a detection range from 7.8 to 250ng/mL was developed. The intra- and inter-assay coefficients of variation were both below 10%. Moreover, the Lv standard curve was nearly identical to the Vtg standard curve, and paralleled serial whole-body homogenate dilutions of male zebrafish exposed to 17β-estradiol, demonstrating that the Lv-based ELISA could be used for quantification of zebrafish Vtg. Zebrafish Lv showed high stability during purification process, heat treatment, -80°C storage, and repeated freeze/thaw cycles. Additionally, the standard curve of Lv stored at -80°C for 3months exhibited higher robustness than that of Vtg stored under the same conditions. Finally, the usefulness of the ELISA for detecting estrogenic activity was verified by quantifying Vtg inductions in zebrafish exposed to monocrotophos.

Development of a lipovitellin-based sandwich ELISA for quantification of vitellogenin in surface mucus and plasma of goldfish (Carassius auratus)

Goldfish (Carassius auratus) vitellogenin (Vtg) is an efficient biomarker for estrogen contamination in aquatic environments. In this study, Vtg and lipovitellin (Lv) were purified from the plasma of 17β-estradiol (E2)-induced male goldfish and unfertilized eggs of females, and were used to generate polyclonal antibodies against Vtg (anti-Vtg) and Lv (anti-Lv), respectively. SDS-PAGE and Western blot were performed to confirm the specificity of the two antibodies and the immunological similarity between Vtg and Lv. As anti-Lv recognized more antigen epitopes than anti-Vtg, it was used to develop a sandwich enzyme-linked immunosorbent assay (ELISA) for goldfish Vtg with purified Lv as the standard. The detection limit of the assay was 1.82ng/mL, and the working range was 3.9-250ng/mL. The use of Lv instead of Vtg as the standard provided greater precision and strengthened the robustness of the sandwich ELISA. Western blot and the Lv-based ELISA were used to detect Vtg inductions in surface mucus and plasma of E2-induced goldfish. The surface mucus Vtg level in E2-induced males was significantly higher than that in the control males and E2-induced females, and was much closer to the plasma Vtg level in E2-induced males than that in E2-induced females. Therefore, the surface mucus Vtg level of male goldfish may be a reliable indicator of estrogenic activity in the aquatic environment.

Development of a lipovitellin-based goldfish (Carassius auratus) vitellogenin ELISA for detection of environmental estrogens

The susceptibility of vitellogenin (Vtg) to degradation is a major problem affecting the robustness of enzyme-linked immunosorbent assay (ELISA) for goldfish (Carassius auratus) Vtg. In this study, a phospholipoglycoprotein with molecular mass of ∼420kDa was purified from goldfish egg extracts and it produced a single band corresponding to ∼112kDa in SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Additionally, the amino acid composition of the purified protein was comparable to that of lipovitellin (Lv) from other fish species. Thus, the purified protein was identified as goldfish Lv. Purified Lv and anti-Lv polyclonal antiserum were used to develop an ELISA with a detection range between 31.25 and 1000ngmL(-)(1). The intra- and inter-assay coefficients of variation were 6.45% and 7.08%, respectively. The immunological similarity between goldfish Vtg and Lv was confirmed by immunoelectrophoresis and Western blot. Goldfish Lv showed higher stability than Vtg after -80°C storage, multiple freeze/thaw cycles, and heat treatment. Moreover, the use of treated Lv in the ELISA did not change the slopes of standard curves. Parallelism between the Lv standard curve and plasma dilution curves of vitellogenic females confirmed the validity of the assay for quantifying plasma Vtg. The Lv-based Vtg ELISA was further applied to evaluate the estrogenic activity of monocrotophos pesticide.

Preparation of a polyclonal antibody against goldfish (Carassius auratus) vitellogenin and its application to detect the estrogenic effects of monocrotophos pesticide

Goldfish (Carassius auratus) represents a good model to detect the estrogenic effects of chemicals, and vitellogenin (Vtg) is a vital indicator of estrogenic activity. The heterologous anti-carp Vtg antibody has previously been used for goldfish Vtg detection. Here, we report the preparation of an anti-goldfish Vtg antibody to improve the sensitivity and specificity of goldfish Vtg immunoassays. Vtg was purified from the plasma of 17β-estradiol (E2)-induced goldfish by gel filtration followed by anion-exchange chromatography. It was characterized as a phospholipoglycoprotein with an apparent molecular weight of ~460 kDa and separated into three major polypeptides corresponding to ~130, ~106, and ~81 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A polyclonal antibody against goldfish Vtg was raised in rabbits and found to be specific for goldfish Vtg through immunoelectrophoresis and Western blot. A sensitive sandwich enzyme-linked immunosorbent assay (ELISA) was developed for the quantification of plasma Vtg, with a detection limit of 3.6 ng/mL and a detection range from 7.8 to 250 ng/mL. The intra- and inter-assay coefficients of variations were 2.4-6.8% and 6.7-10.8%, respectively. Additionally, we qualitatively and quantitatively detected the induction of Vtg in male fish exposed to 0.01, 0.01, and 1.00 mg/L monocrotophos pesticide by Western blot and ELISA. The homologous sandwich ELISA based on the anti-goldfish Vtg antibody could provide a valuable tool for the study of estrogenic effects of exogenous chemicals on goldfish.

Purification and partial characterization of vitellogenin from spotted wolffish (Anarhichas minor) and development of an enzyme-linked immunosorbent assay for the determination of gender and sexual maturity

Vitellogenin (VTG) from spotted wolffish, Anarhichas minor, a candidate species for cold-water marine aquaculture, was purified by MgCl₂/EDTA precipitation followed by a two-step chromatographic procedure. VTG had an apparent molecular mass of 470 kDa, as determined by gel filtration, and an amino acid composition similar to those of other teleosts. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of the purified VTG revealed a major band with a relative molecular weight of 166 kDa and some minor bands. Spotted wolffish VTG (sw-VTG) is relatively robust to in vitro degradation, as shown when samples of purified VTG and plasma from mature females subjected to various storage conditions or multiple freeze/thaw cycles were analyzed by Western blot. We developed an indirect competitive enzyme-linked immunosorbent assay (ELISA) using an antibody against Atlantic wolffish (Anarhichas lupus) VTG and purified sw-VTG. The ELISA had a detection limit of 6.7 ng/ml and a working range of 16.2-787.5 ng/ml, with intra- and inter-assay coefficients of variation ranging from 1.5 to 7.3 % and 7.1 to 14.3 %, respectively. The assay could distinguish males from immature females and discriminate maturing females at different stage of oocyte development. These results suggest that the sw-VTG ELISA would be useful in spotted wolffish aquaculture to determine sex and monitor female maturation.

Development of an Enzyme-linked Immunosorbent Assay Using Vitellin for Vitellogenin Measurement in the Pale Chub, Zacco platypus

OBJECTIVES

Fish vitellogenin (VTG) is produced in the female liver during oogenesis through the estradiol cycle and produced in the male liver by endocrine disrupting chemicals (EDCs) such as alkylphenols. In this study, we propose that the VTG concentration in the pale chub could be detected using monoclonal antibodies and polyclonal antibodies against vitellin (Vn) in a VTG enzyme-linked immunosorbent assay (ELISA) system.

METHODS

Monoclonal antibodies and polyclonal antibodies were produced using the Vn extracted from the matured ovum of the ovary. The VTG was extracted from the plasma of the male pale chub. The Vn and VTG were confirmed by measuring the molecular weight of their proteins using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the specificity of the antibodies was checked through western blotting methods. The assay system was validated with respect to optimal assay concentrations, specificity, recovery, and intra- and inter-assay variations.

RESULTS

The Vn consisted of two protein bands with apparent molecular weights of 64 and 37 kDa. The SDS-PAGE indicated protein weights of 146 and 77 kDa in the VTG. The assay range was 15.6 ng/mL to 2,000 ng/mL, and the value of the intra- and inter-assay variations were within 10.0% and 14.7%, respectively. The recovery rate was 99.5±5.5%.

CONCLUSIONS

A sandwich ELISA was developed that could be used to qualify the VTG of pale chub in screening for EDCs. Pale chub is an ideal species for observing estrogen activity in the environment because of its extensive habitat and extensive food chain. The ELISA developed here would be more favorable than those for other species for determining the effect of long-term food chain accumulation of EDCs in aquatic environments.

Isolation and partial characterization of Asian sea bass (Lates calcarifer) Vitellogenin

A study was conducted to isolate, partial characterize Asian sea bass (Lates calcarifer) vitellogenin (vtg). Two-year-old juvenile L. calcarifer (n = 10) were given three intraperitoneal injections of 17-β estradiol (E2) at a dose of 2 mg/kg body weight to induce vitellogenesis. Blood was collected 3 days after the last injection, and plasma was purified through gel filtration chromatography. A broad single symmetrical peak consisting of vtg molecule was produced. Protein concentration was 0.059 mg/ml as determined by Bradfrod assay using bovine serum albumin as a standard. The protein appeared as one circulating form in Native PAGE considering the dimeric form of putative vtg with molecular weight of 545 kDa. In SDS-PAGE under reducing conditions, two major bands appeared at 232.86 and 118.80 kDa and minor bands at 100.60, 85.80 and 39.92 kDa, respectively. The purified vtg was used to generate a polyclonal antibody, and the specificity of antibody was assessed by Western blot analysis. Two major bands were immunoreacted, but no cross-reactivity was observed with plasma from non-induced males. The protein was characterized as phosphoglycolipoprotein as it positively stained for the presence of lipid, phosphorus and carbohydrate using Sudan Black B, methyl green and periodic acid/Schiff reagent solution, respectively. The amino acid composition was analyzed by high sensitivity amino acid analysis that showed high percentage of non-polar amino acids (~48 %). The results suggest the potential utilization of vtg as a basis tool to further study about reproductive physiology of this important economical species.

Responses of laboratory exposed catfish (Clarias gariepinus) to environmentally relevant concentrations of p,p'-DDT

Technical grade DDT is annually sprayed for malaria control in many under developed countries world wide. Despite the controversy surrounding the use of DDT, minimal research concerning the effects on indigenous fish species in these areas has been conducted. In this study, the objectives were to identify some of the effects of sprayed p,p'-DDT on the common African sharptooth catfish species (Clarias gariepinus) under laboratory conditions. The effects were assessed by exposing specimens to three environmentally relevant concentrations of p,p'-DDT (0.66, 1.36 and 2.72 μg/l) for 21 days and analysing a suite of biomarkers in the plasma, gonads and body morphometrics. The biomarkers were specifically selected based on their practicality in developing countries, which could potentially be utilised for continued monitoring, and included alkali-labile phosphate (ALP), calcium, magnesium and zinc as the indirect measures of vitellogenin, gonadosomatic index, gonad mass manipulated using analysis of covariance, and condition factor. The results showed no significant (p<0.05) dose-dependent changes in the plasma, gonads and body condition of C. gariepinus, indicating that these species were not responsive to the p,p'-DDT concentrations when exposed sub-chronically. This lack of a response suggested that mature C. gariepinus are tolerant to 21 days exposure of low levels of p,p'-DDT.

Development of an enzyme-linked immunosorbent assay for quantifying vitellogenin in Pacific salmon and assessment of field exposure to environmental estrogens

A competitive enzyme-linked immunosorbent assay was developed to quantitate vitellogenin (VTG) in plasma and serum of coho (Oncorhynchus kisutch) and chinook (O. tshawytscha) salmon. The working range of the assay was 9 to 313 ng/ml (80-20% binding), with 50% binding at 54 ng/ml. The intra-assay and interassay variations at approximately 50% binding were 8.1% (n = 9) and 9.0% (n = 9), respectively. Dilution curves of plasma or serum from coho and chinook females and estrogen-treated males were parallel to the purified coho VTG standard curve. Male plasma samples could be assayed at a minimum dilution of 1:40 (chinook) or 1:75 (coho) without assay interference because of high sample concentration, whereas minimum acceptable dilutions of male serum samples were 1:200 (chinook) or 1:600 (coho). Identification of proper techniques for preserving VTG integrity in plasma and serum samples showed that VTG from both species was robust; both sample types required no protease inhibitor despite subjection to two freeze-thaw cycles. To test its applicability, this assay was used to measure VTG in out-migrating juvenile chinook that were collected from urban and nonurban areas in Puget Sound, Washington, USA. Results showed a small but significant plasma VTG elevation at two urban sites, suggesting that these juveniles may be exposed to environmental estrogens at an early life stage. Also, wild fish tended to have higher plasma VTG levels than hatchery fish collected in the field. Elevation of mean VTG levels was similar to that previously reported in male English sole from the same area, where both males and females exhibited alterations in timing of spawning.

Characterization of vitellogenin gene expression in round goby (Neogobius melanostomus) using a quantitative polymerase chain reaction assay

A growing concern over endocrine disruption in aquatic species has prompted the development of molecular assays to monitor environmental impacts. This study describes the development of quantitative polymerase chain reaction (qPCR) assays to characterize the expression of two vitellogenin (Vtg) genes in the invasive round goby (Neogobius melanostomus). Fragments from the 18SrRNA (housekeeping gene), Vtg II, and Vtg III genes were cloned and sequenced. The qPCR assays were developed to detect hepatic Vtg expression in goby. The assays detected induction of both Vtg genes in nonreproductive males following a two-week laboratory exposure to 17β-estradiol (≥1 mg/kg i.p. injection). The assays were applied to goby from Hamilton Harbour, Lake Ontario (Canada), including those from sites where feminization and intersex of goby has been documented. Both Vtg genes had significantly higher expression in females compared to males. Male reproductive goby adopt either parental or sneaker tactics; Vtg II expression was higher in sneaker than in parental males but parental and nonreproductive males did not differ from each other. The Vtg III expression was significantly higher in sneaker males followed by parental males and nonreproductive males, respectively. The Vtg II and III expression in nonreproductive males was elevated in the contaminated site with documented intersex. This assay provides an important tool for the use of an invasive species in monitoring endocrine disruption in the Great Lakes region.

Optimization and validation of a California halibut environmental estrogen bioassay using a heterologous ELISA

Vitellogenin, the estrogen-inducible yolk protein precursor, serves as an indicator of exposure to estrogen mimicking environmental contaminants. An ELISA for the measurement of California halibut plasma vitellogenin was optimized and validated using a commercially-available antibody developed for another flatfish species, turbot. Attempts to enhance assay performance by addition of a biotinylated antibody, polyethylene glycol, and Tween-20, and altering the preincubation step are described. Inclusion of overnight preincubation was critical for low detection limits. Increasing the amount of Tween-20 to 0.05% in buffers was most effective in achieving accurate quantification of spiked plasma samples. At the IC50, the average recovery of spiked plasma samples was 104% and the interplate CV was 12%. The working range of the assay was 33-1000 ng/mL, while the detection limit in a plasma sample is 2.2 microg/mL. The performance of this assay compared very well to a homologous assay demonstrating that commercially-available antibodies can facilitate the development of bioassays for local environmentally-relevant species. The dose response relationship of halibut Vg to the model compounds 17beta-estradiol and pnonylphenol show that it is a suitable model for further studies of estrogen mimicking contaminants.

Vitellogenin in African sharptooth catfish (Clarias gariepinus): purification, characterization, and ELISA development

Vitellogenin (Vtg) induction in African sharptooth catfish (Clarias gariepinus) was assessed in order to develop a method for monitoring estrogenic pollution in African freshwater systems. Clarias gariepinus Vtg (Cg-Vtg) was purified from serum obtained from 17alpha-ethynylestradiol (EE2)-exposed fish and polyclonal antibodies against Cg-Vtg were raised. An enzyme-linked immunosorbent assay (ELISA) was developed and the induction and kinetics of Vtg were assessed in male fish in three different exposure trials using both natural estrogen (17alpha-estradiol [E2]) and synthetic EE2. Concentrations of EE2 in water and levels of EE2 conjugates in bile were quantified by liquid chromatography-mass spectrometry (LC-MS). In addition, co-administration of E2 and benzo[a]pyrene (BaP) were studied. Vtg was induced in all exposure trials and the maximum induction was observed 1 wk after exposure. Exposure of male C. gariepinus to 1.4, 2.7, and 13.9 microg/ml EE2 induced Vtg synthesis at all concentrations. BaP did not influence the Vtg kinetics. However, an increased rate of biliary excretion of EE2 was observed when BaP was additionally administered. In conclusion, Vtg is induced in male C. gariepinus after exposure to both E2 and EE2, rendering it a suitable biomarker for endocrine-disrupting chemicals in African freshwater systems.

Xenoestrogen exposure and effects in English sole (Parophrys vetulus) from Puget Sound, WA

Vitellogenin, a yolk protein produced in the liver of oviparous animals in response to estrogens, normally occurs only in sexually mature females with developing eggs. However, males can synthesize vitellogenin when exposed to environmental estrogens, making the abnormal production of vitellogenin in male animals a useful biomarker for xenoestrogen exposure. In 1997-2001, as part of the Washington State's Puget Sound Assessment and Monitoring Program, we surveyed English sole from a number of sites for evidence of xenoestrogen exposure, using vitellogenin production in males as an indicator. Significant levels of vitellogenin were found in male fish from several urban sites, with especially high numbers of fish affected in Elliott Bay, along the Seattle Waterfront. Intersex fish were rare, comprising only two fish out of more than 2900 examined. Other ovarian and testicular lesions, including oocyte atresia, were also observed, but their prevalence did not appear to be related to xenoestrogen exposure. However, at the Elliott Bay sites where abnormal vitellogenin production was observed in male sole, the timing of spawning in both male and female English sole appeared altered. Sources of xenoestrogens and types of xenoestrogens present in Elliott Bay are poorly documented, but the compounds are likely associated with industrial discharges, surface runoff, and combined sewer outfalls.

Vitellogenin, steroid plasma levels and spawning performance of cultured female Senegalese sole (Solea senegalensis)

The Senegalese sole (Solea senegalensis) is a high value market flatfish, which aquaculture is compromised by severe reproductive problems; these are mostly found in soles hatched and raised in captivity (F1 generation). To gain knowledge on the reproductive dysfunctions observed in cultured (F1) Senegalese sole, this work aimed at developing a specific vitellogenin (VTG) ELISA, for the measurement of plasma VTG levels in this species. Profiles of VTG were correlated with those of sexual steroids and spawning performance of an F1 broodstock, during three consecutive years. The Senegalese sole VTG (ssVTG) was purified by precipitation with MgCl(2)-EDTA and anion-exchange chromatography and showed a molecular mass of 172 kDa, by SDS-PAGE. Specific antibodies were obtained and used to develop a competitive ELISA, which had a sensitivity of 3.6 ng ml(-1), and inter- and intra-assay coefficients of variation of 9.5% (n=29) and 6.7% (n=12), respectively. Annual profiles of plasma VTG showed a major peak at pre-spawning, and a second minor rise around autumn, which mirrored plasma profiles of both estradiol (E(2)) and testosterone (T) levels. Spontaneous spawning occurred every year in the spring season, but no fertilized eggs were obtained. In conclusion, this study described, for the first time, the purification and development of a sensitive and specific ELISA for Senegalese sole VTG. The endocrine and spawning data suggested that F1 female broodstock showed normal VTG and steroid releasing profiles in captivity with occurrence of spontaneous spawning, but no fertilization of the eggs was recorded.

Molecular characterization and mRNA transcript profile of vitellogenin in Chinese shrimp, Fenneropenaeus chinensis

A full-length cDNA encoding vitellogenin (Vg) was cloned from Chinese shrimp, Fenneropenaeus chinensis using RACE method. The full-length cDNA consist of 7,942 nucleotides including a 7,761 bp open reading frame, which encodes 2,587 amino acid residues. The deduced amino acid sequence showed high (from 94% to 37%) identity with other known crustacean Vgs. In addition, a consensus cleavage site (R-X-K/R-R) recognized by an endopeptidase and a member of subtilisin family of serine protease were identified in the deduced Vg precursor. RT-PCR analysis shown that Vg mRNA can be detected in both ovary and hepatopancreas of vitellogenic females but not in other experimental tissues including muscle, heart, lymph organ, gill, haemocytes and intestine. These results suggest that the Vg gene may be expressed exclusively in mature females, and both ovary and hepatopancreas are the possible tissues for Vg synthesis in F. chinensis. In addition, Vg gene is detected in genomic DNA of both females and males.

Crucian carp (Carassius carassius) VTG monoclonal antibody: development and application

The vitellogenin (VTG) in fish has been used as an important biomarker for monitoring endocrine disrupting compounds (EDCs). This paper reports the development of a new monoclonal antibody (McAb) against the VTG of crucian carp (Carassius carassius). The McAb has a molecular weight of 149.4 kDa (heavy chain: 53.1 kDa; light chain: 21.6 kDa), and double diffusion indicated that it belongs to the IgG1 subclass. The titer is 10(5)-10(6) and the affinity constant (K(aff)) is 7.0 x 10(8)L/mol, showing the high specificity and sensitivity of the antibody. The established sandwich ELISA was sensitive with a detection limit of VTG 0.98 ng/mL. The cross-reactivity of antibody was detected in cyprinids such as rare minnow, zebrafish, and carp. This ELISA was used to detect the variation of VTG in crucian carp exposed to secondary effluent and reclaimed water from the Gaobeidian sewage treatment plant (SRP). The VTG induction in secondary effluent was higher than that in reclaimed effluent and the VTG levels in juvenile crucian carp increased with increasing exposure time. The VTG concentration in male fish from downstream of the Gaobeidian STP was 88.62+/-827.73 microg/mL, while that from a control site was undetectable.

Determination of alkali-labile phosphoprotein phosphorus from fish plasma using the Tb(3+)-tiron complex as a fluorescence probe

A sensitive method based on the fluorescence quenching effect of the Tb(3+)-Tiron complex is proposed for the determination of alkali-labile phosphoprotein phosphorus (ALP) released from fish plasma. The detection limit was 5.4 ng/ml (S/N = 2), and the relative standard deviation of the quenching effect (6 replicates) was 4.6%. The results obtained by the proposed method were in good agreement with those obtained by the colorimetric assay. The advantages of the present method are its relatively simple detection procedure, the lack of toxic organic solvents, and high sensitivity.

Quantitative real-time RT-PCR for determination of vitellogenin mRNA in so-iuy mullet (Mugil soiuy)

A quantitative real-time reverse transcription polymerase chain reaction (Q- RT-PCR) assay was developed for quantification of vitellogenin (Vtg) mRNA normalized to beta-actin in so-iuy mullet. Vtg mRNA in liver samples of so-iuy mullet was induced after a single injection of E2 (0.01, 0.1, 1.0 microg/g body) and a dose-response relationship was obtained. This method was applied to determine Vtg mRNA in so-iuy mullet collected from Liaodong Bay, Bohai Bay, NanDaiHe, and a control site in north China. Compared to the control, a high level of Vtg mRNA expression was detected in so-iuy mullets collected from NanDaiHe, whereas no obvious difference between Vtg mRNA expression from Liaodong Bay and Bohai Bay was found. Thus, this method is expected to be useful for further studying the potential of Vtg mRNA as a biomarker for assessing estrogenic activity in marine environments using the so-iuy mullet as a bioindicator species.

An enzyme-linked immunosorbent assay for rare minnow (Gobiocypris rarus) vitellogenin and comparison of vitellogenin responses in rare minnow and zebrafish (Danio rerio)

A competitive enzyme-linked immunosorbent assay (ELISA) was developed to determine vitellogenin (Vtg) in rare minnow (Gobiocypris rarus) based on the separation and purification of rare minnow Vtg (r-Vtg) as well as the production of polyclonal antibody against r-Vtg in rabbits. Three different ELISAs for measuring r-Vtg were then compared: (1) indirect ELISA with the antibody against carp (Cyprinus carpio) Vtg (c-Vtg) (IC-ELISA); (2) competitive ELISA with the antibody against c-Vtg, and using r-Vtg for coating the plates and preparing standard curve (CC-ELISA); (3) competitive ELISA with the antibody against r-Vtg, and using r-Vtg for coating the plates and preparing standard curve (CR-ELISA). The result showed that the homologous CR-ELISA was the most sensitive among the three assays for quantifying r-Vtg. The sensitivities to 17alpha-ethinylestradiol (EE(2)) of rare minnow and zebrafish (Danio rerio) were compared upon the establishment of homologous competitive ELISA. The lowest observed effect concentrations (LOECs) to induce Vtg were found to be 0.8 ng EE(2) l(-1) for rare minnow and 4 ng EE(2) l(-1) for zebrafish respectively. Afterwards, CR-ELISA was applied to measure Vtg concentration in whole body homogenate (WBH) of juvenile rare minnow fed by three diets (tubifex from wastewater treatment plant, Artemia nauplii and commercial pellet food), and the agreements between bioassay and GC-MS analysis demonstrated that rare minnow was a sensitive fish model for assessing estrogenic effects of endocrine disrupting compounds in aquatic environment.

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.

Vitellogenic effects of 17beta-estradiol in male Chinese loach (Misgurnus anguillicaudatus)

Male Chinese loaches (Misgurnus anguillicaudatus) were exposed to 17beta-estradiol (E2) in the ambient water at nominal concentrations of 0.5, 1, 5 and 10 mug/L continuously for 8 weeks using a semi-static system. The gonadosomatic index (GSI), total plasma protein, total plasma calcium, magnesium and zinc, and plasma vitellogenin (Vtg) were determined as test endpoints. Our results indicate no significant changes in the GSI between exposed and control groups (P<0.05). All exposure concentrations of E2 dramatically induced the production of Vtg within 7 days. The vitellogenic response of male loach was time- and dose-dependent. At higher concentrations of E2 (5 and 10 microg/L), total plasma protein, total plasma calcium, and total plasma magnesium presented a significant time- and dose-dependent increase, and the three parameters were significantly correlated with plasma Vtg. We conclude that Chinese loaches are sensitive to estrogenic compounds and may be chosen as potential sentinel species in field and laboratory studies. In addition, total plasma protein, total plasma calcium, and total plasma magnesium can be used as indirect indicators to predict Vtg levels in estrogenized Chinese loach.

Estrogenic effects in crucian carp (Carassius carassius) exposed to treated sewage effluent

To assess the estrogenicity of a municipal sewage treatment plant, sexually mature crucian carp of both sexes were exposed for 28 days to domestic treated sewage effluent running with a constant flow of water, with tap water and with different concentrations of the sewage effluent (25%, 50% and 100%). Vitellogenin (VTG), gonadosomatic index (GSI), hepatosomatic index (HSI), and histological abnormalities were used to assess the estrogenic potency of the effluent. Results show a significant (P<0.05) increase in VTG levels in all exposed male fish. A significant (P<0.05) reduction in the GSI was only observed in fish exposed to 100% effluent. Morphological changes were detected by histological evaluation, revealing severe effects on the testes. Spermatogenesis was progressively reduced to total inhibition in fish exposed to 100% effluent. One of the most pronounced effects detected was the presence of oocytes in male gonads, observed in 20% of males exposed to 100% sewage effluent.

Transcript and protein environmental biomarkers in fish--a review

The levels of contaminant-affected gene products (transcripts and proteins) are increasingly utilized as environmental biomarkers, and their appropriate implementation as diagnostic tools is discussed. The required characteristics of a gene product biomarker are accurate evaluation using properly normalized absolute units, aiming at long-term comparability of biomarker levels over a wide geographical range and among many laboratories. Quantitative RT-PCR and competitive ELISA are suggested as preferred evaluation methods for transcript and protein, respectively. Constitutively expressed RNAs or proteins which are part of the examined homogenate are suggested as normalizing agents, compensating for variable processing efficiency. Essential characterization of expression patterns is suggested, providing reference values to be compared to the monitored levels. This comparison would enable estimation of the intensity of biological effects of contaminants. Contaminant-independent reference expression patterns should include natural fluctuations of the biomarker level. Contaminant-dependent patterns should include dose response to model contaminants chronically administered in two environmentally-realistic routes, reaching extreme sub-lethal affected levels. Recent studies using fish as environmental sentinel species, applying gene products as environmental biomarkers, and implementing at least part of the depicted methodologies are reviewed.

Sandwich immunoassay for determination of vitellogenin in golden grey mullet (Liza aurata) serum as a field exposure biomarker

Vitellogenin (VTG) is a protein produced in the liver of oviparous animals in response to oestrogens. Abnormal production of VTG by males, therefore, is used as a biological indicator of exposure to xeno-oestrogens. In this study, a sandwich-ELISA for measuring VTG in Liza aurata (golden grey mullet) was developed and validated. Plasma VTG was purified from 17beta-oestradiol-injected immature individuals of mullet, by size-exclusion and ion-exchange chromatography. Polyclonal antibodies against VTG were raised in rabbits. A sensitive immunoassay was developed for measurement of vitellogenin in L. aurata serum, reaching a quantification limit of 0.01 microg mL(-1) and a dynamic range from 0.02 to 2 microg mL(-1). The assay is specific, because high levels (>100 microg mL(-1)) of carp (Cyprinus carpio), goldfish (Carassius auratus), tilapia (Oreochromis niloticus), tench (Tinca tinca), rainbow trout (Oncorhynchus mykiss), European eel (Anguilla anguilla) and frog (Rana perezi) purified VTG, give negligible responses. The assay was used to analyse plasma samples from wild mullet.

Molecular cloning of vitellogenin cDNA in rockfish (Sebastes schlegeli) and effects of 2,2'4,4'5,5'-hexachlorobiphenyl (PCB 153) on its gene expression

Many environmental chemicals are known to affect sex steroid production and vitellogenesis through agonistic or antagonistic pathways. To investigate the estrogenic effect of 2,2'4,4'5,5'-hexachlorobiphenyl (PCB 153) on reproductive function, we have constructed a cDNA library and cloned a 320 base sequence encoding a partial VTG mRNA of rockfish (rVTG), Sebastes schlegeli. We have examined the expression level of rVTG mRNA level by northern blot analysis and measured levels of plasma estradiol-17beta (E2) and testosterone (T) by radioimmunoassay (RIA). Plasma concentrations of T in female and male injected with PCB 153 were not significantly different between two dosages of 0.16 mg/kg b.w. and 0.57 mg/kg b.w. However, plasma concentrations of E2 in female fish injected with PCB 153 at 0.16 mg/kg b.w. and 0.57 mg/kg b.w. increased after 12 h and 24 h. An rVTG mRNA transcript of approximately 4.0 kilo bases was extracted from hepatic tissue for northern blot analysis, and the effects of PCB 153 on rVTG mRNA expression in vivo with both male and female juvenile rockfish were examined. The level of rVTG mRNA expression increased only in female rockfish injected with both dose levels of PCB 153 after 48 h of exposure. The results of this study suggest that PCB 153 may produce VTG in female through a synergic effect with E2 resulting in indirect disruption.

Purification of vitellogenin from smooth flounder (Pleuronectes putnami) and measurement in plasma by homologous ELISA

Male smooth flounder (Pleuronectes putnami) were induced to produce vitellogenin (VTG) by injection of 17beta-estradiol (E2). Anion exchange chromatography of precipitated plasma from E2-injected resulted in a single peak consisting of VTG. Smooth flounder VTG has an approximate molecular mass of approximately 520 kDa, determined by gel filtration with molecular weight standards. Purified VTG was used to develop a homologous enzyme-linked immunosorbent assay (ELISA). The flounder VTG ELISA is an indirect antigen competition assay with a detection limit of 15 ng.ml(-1) and a useful range of 30-950 ng.ml(-1) of diluted sample. Intra- and inter-assay precision (as %CV, n=7) ranged from 1.3% to 6.0% and 5.1%, respectively. The ELISA was evaluated using plasma samples collected from a smooth flounder population captured in the Saint Lawrence Estuary. The ELISA is sensitive enough to differentiate males and non-vitellogenic females from vitellogenic individuals during early vitellogenesis.

Abnormally elevated VTG concentrations in flounder (Platichthys flesus) from the Mersey estuary (UK)--a continuing problem

Vitellogenin (VTG) plasma concentrations were measured in flounder (Platicthys flesus L.) caught in two neighbouring UK estuaries between autumn 1997 and summer 2000. As found in previous studies, male and immature female flounder that were caught in the Mersey, but not in the Dee, had abnormally elevated concentrations of VTG in their plasma-evidence of the presence of natural and synthetic estrogens and/or xenoestrogens in the Mersey. The present study reveals a marked seasonal cycle in VTG concentrations in males. In late spring and summer, male flounder in the Mersey have relatively low concentrations of VTG (microg mL(-1) range). However, in mid-winter, mean concentrations were as high as 5 mg mL(-1). There is also evidence that there was a lessening in the degree of estrogenic endocrine disruption between 1996-1997 (the period of the initial studies on the Mersey) and 1998-2000 (the period covered by the present study). Only 0.5% of the fish contained ovotestes (intersex condition).

Development of enzyme-linked immunosorbent assays for two forms of vitellogenin in Japanese common goby (Acanthogobius flavimanus)

Two vitellogenins (Vgs) were detected in serum from estradiol-17beta (E(2))-injected Japanese common goby (Acanthogobius flavimanus). Vitellogenins with molecular masses of 530 kDa (Vg-530) and 320 kDa (Vg-320) were purified, and used to raise specific antisera in rabbits. Sandwich enzyme-linked immunosorbent assays (ELISAs) for Vg-530 and Vg-320 were developed using the antisera and the isolated Vgs. The sensitivity ranges of these ELISAs were 1.25-160 ng/ml for Vg-530 and 0.26-66 ng/ml for Vg-320, and very low cross-reactivity was found with the alternate Vg in each assay. Treatment of male gobys with E(2) by injection and immersion induced both Vgs in sera in a dose-dependent manner. The mean concentrations of the Vgs increased from 10 ng/L E(2) exposure for three weeks. Serum concentrations of the two Vgs in field-collected maturing females increased in accordance with increment of E(2) level and ovarian development, and the mean concentrations of Vg-530 were higher than those of Vg-320 in maturing female. These results indicate that the sandwich ELISAs for Vg-530 and Vg-320 developed in the present study is useful as an assay system for surveys of estrogenic activity in coastal areas of Japan.

Inhibition of oocyte development in Japanese medaka (Oryzias latipes) exposed to di-2-ethylhexyl phthalate

Di-2-ethylhexyl phthalate (DEHP) is a widely used plasticizer known to be a suspected endocrine disrupter, but its precise effects on aquatic organisms are not yet known. When Japanese medaka (Oryzias latipes) were exposed from the time of hatching to 3 months of age to an aqueous DEHP solution at nominal concentrations of 1, 10, and 50 microg/l, DEHP-treated female fish showed distinct reproductive effects as follows. First, blood vitellogenin levels in all treated test subjects markedly decreased. Second, Gonado Somatic Index (GSI) decreased to 33% and 38% of the control GSI in 10 microg/l and 50 microg/l treated female fish, respectively. Third, 54% of female fish in the control treatment had completely matured oocytes in their ovaries, but only 37%, 0% and 22% of female fish matured to the last stage in the 1, 10 and 50 microg/l treated test subjects, respectively. Unlike female fish, no change or adverse effects were observed in the male fish. In summary, DEHP hinders the development of reproductive organs in the female Japanese medaka. In this work, the possibility o f anti-estrogenic activity of DEHP is proposed as the cause.

An in vitro vitellogenin bioassay for oestrogenic substances in the medaka (Oryzias latipes)

We developed an in vitro bioassay for oestrogenic compounds based on vitellogenin as a biomarker. To quantify the induction of vitellogenin in medaka (Oryzias latipes) we established a sandwich enzyme-linked immunosorbent assay (ELISA). This ELISA was carried out with two different monoclonal antibodies specific for the yolk precursor protein vitellogenin and the high molecular weight yolk proteins (lipovitellin) of medaka. Purified lipovitellin of medaka was used as a standard for the ELISA and could be quantified down to a concentration of 9 ng/ml. The calibration curve was linear up to at least 600 ng/ml and the intra-assay coefficient of variance was 3.2%. The application of the sandwich ELISA was tested using blood samples of males and females as well as primary hepatocyte cultures of medaka. Vitellogenin synthesis in cultured liver cells of males was induced by 1 and 100 nM of the xenoestrogen 17alpha-ethynylestradiol (EE(2)). The first production of vitellogenin was detected 6 days after hormone application. In contrast, isolated liver cells of sexually mature females, which were treated in the same manner, showed vitellogenin expression from the beginning of cultivation and its synthesis increased and remained high at 100 nM EE(2). However, the induction of vitellogenin synthesis in male hepatocytes in vitro could be maintained for at least one month and this indicated viable and differentiated liver cells. The hepatocyte cultures of male medaka in combination with the sandwich ELISA were shown to be a suitable tool to detect and quantify oestrogenic activity of chemicals.

Seasonal variation and estradiol-dependent elevation of Thames estuary eel Anguilla anguilla plasma vitellogenin levels and comparisons with other United Kingdom estuaries

Eel Anguilla anguilla plasma vitellogenin was investigated as a biomarker of exposure to environmental compounds with estrogenic activity, along the tidal course of the Thames Estuary, UK. A. anguilla was chosen as a sentinel species because of their wide distribution, robustness in field and laboratory studies and also because they have a characterised normal intersex' condition where the gonad contains both developing male and female gonadal cells termed a Syrski organ. Following laboratory exposure to 17beta-estradiol (intraperitoneal injection), a plasma protein (approx. 211 kDa apparent molecular weight) was detected by monoclonal antibodies to vitellogenin of striped bass (Morone saxatilis). Western and dot blot analyses were developed and vitellogenin was isolated from 17beta-estradiol-treated fish to calibrate the quantification of the blots by image analysis. The limits of sensitivity for the Western and dot blots were 100 and 10 ng vitellogenin/ml, respectively. Levels of vitellogenin in Thames estuary samples were below the detection limits of the Western but not the dot blot, and showed no statistically significant site-specific (10 sites) and seasonal-specific (May, August, November) differences. Values were observed to be low, between 11 and 165 ng/ml, compared with 17-50 mg/ml for 17beta-estradiol-treated eels. Similar low levels of plasma vitellogenin were determined in fish sampled along the Tyne, Wear, Tees or Humber estuaries, or the Weston canal Liverpool, with mean plasma vitellogenin levels varying between 44 and 82 ng/ml. These levels of vitellogenin in A. anguilla plasma were observed to be consistent with the known biology of the eel. Immature females, or fish with syrski organs, reported both lower levels and smaller variation of plasma vitellogenin concentrations whereas the highest plasma vitellogenin concentrations were determined in fish above 45 cm consistent with female fish. These results indicate inter-species variation between the plasma vitellogenin concentrations of A. anguilla and other published fish studies undertaken along the same estuaries.

Role of two plasma vitellogenins from Indian major carp (Cirrhinus mrigala) in catfish (Clarias batrachus) vitellogenesis

Complete vitellogenesis (synthesis and incorporation of vitellogenin, Vg) in the female catfish, Clarias batrachus, during different reproductive phases (preparatory, prespawning, and postspawning) of its annual ovarian cycle is induced by administering heterologous Vg (semipurified; ULT-I and purified; HA-I and HA-II) isolated from the Indian major carp, mrigal (Cirrhinus mrigala). During the prespawning period, ULT-I, which contains both HA-I and HA-II, showed a dose-dependent response in relation to the induction of complete vitellogenesis in female catfish. In the preparatory period, daily treatment with 1 mg of ULT-I for 12 days resulted in an increase in plasma Vg level, ovarian weight, and number of stage-II (vitellogenic) oocytes along with the appearance of stage III (fully formed) yolky oocytes. In the prespawning period, 12-day administration of HA-I at the dose level of 0.5 mg/fish/day enhanced complete vitellogenesis in intact female catfish and induced Vg synthesis in hypophysectomized female catfish, whereas HA-II, at the same dose level, could only stimulate Vg synthesis, indicating their different roles during vitellogenesis. The results so far obtained may be due to the estradiol-17beta contamination in the Vg fractions. Estimation of E(2) in ULT-I, HA-I, and HA-II by E(2) ELISA indicates that HA-II contains only a small amount (106 pg/mg protein). Therefore, daily treatment with 1 mg each of delipidated ULT-I and HA-I for 12 days could synthesize very little Vg, whereas intact ULT-I at the same dose level induced not only a high plasma Vg level but also increased GSI, indicating the importance of lipid in the native molecule for the induction of vitellogenesis. During postspawning period, administration of HA-I (0.5 mg/fish/day for 21 days) to reproductively regressed female catfish pretreated with HA-II (10 microg/fish/day for 7 days) and maintained at a long photoperiod (LD 14:10) and high temperature (30 degrees ), induced complete vitellogenesis.

Development of an ELISA for vitellogenin in whole body homogenate of zebrafish (Danio rerio)

The yolk protein, lipovitellin (Lv) was purified from ovaries of mature female zebrafish (Danio rerio) by gel filtration and anion exchange chromatography. Polyclonal antibodies against Lv were raised in rabbits. Anti-Lv IgG was purified by affinity chromatography. SDS-PAGE followed by Western blotting was performed to analyse the specificity of the antibody and the immunological similarities between Lv and vitellogenin (Vtg). Anti-Lv IgG was used to develop a direct non-competitive sandwich ELISA to measure Vtg concentrations of whole body homogenate (WBH) in zebrafish. The intra- and interassay variabilities were 5.8% and 10.4%, respectively. The sensitivity was 0.2 ng Vtg x ml(-1) and the practical detection limit was 40 ng Vtg x g(-1) fish (wet weight). Adult male zebrafish were exposed to a nominal water concentration of 10 ng x l(-1) of ethinylestradiol (EE2) in a semi-static exposure system for 7 days. Compared with the control group, exposure to 10 ng EE2 x l(-1) induced a 200-fold increase in Vtg levels.

Mosquitofish (Gambusia affinis) vitellogenin: identification, purification, and immunoassay

Vitellogenin is a phospholipoglycoprotein precursor of egg yolk. In mature female fish, vitellogenin is synthesized and secreted by the liver in response to circulating estrogens. Vitellogenin is normally undetectable in the blood of male fish, but can be induced by exposure to compounds possessing estrogenic activity. Thus, the presence of vitellogenin in blood of male fish can serve as a useful biomarker for assessing previous exposure to estrogenic compounds. In the present study, we report identification and purification of vitellogenin in the mosquitofish (Gambusia affinis). Anti-vitellogenin immune serum was generated and used to develop an immunoblot assay for detection of vitellogenin. A combination of immunoblotting and densitometric scanning was used to assess the time- and dose-dependent effects of 17alpha-ethynylestradiol on vitellogenesis in male G. affinis. The results indicate that changes in the level of vitellogenin in mosquitofish blood can be reliably detected by the immunoblot assay, and that the mosquitofish may be a useful bioindicator organism for detecting estrogenic contamination of the aquatic environment.

Arctic charr (Salvelinus alpinus) vitellogenin: development and validation of an enzyme-linked immunosorbent assay

Vitellogenin (Vtg) was isolated from plasma of estradiol-17 beta-treated Arctic charr males by double precipitation with MgCl2-EDTA and distilled water, followed by ion-exchange chromatography. The monomeric form of Vtg, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was 158 kDa. The purified Vtg was used to raise a polyclonal antibody for Vtg (AbVtg), and the specificity of the AbVtg was assessed by Western blot analysis. No cross-reactivity was observed with plasma from control males. Using this AbVtg, a competitive enzyme-linked immunosorbent assay was developed. The detection limit of the assay was 2 ng ml-1, and the intra- and inter-assay variations determined from plasma samples were 8.6 and 13.3%, respectively. The assay was validated by quantification of Vtg in plasma samples obtained during a reproductive cycle of Arctic charr. Vtg of females increased gradually from 3 mg ml-1 in early March to a peak value of 22 mg ml-1 in late August, followed by a rapid drop to 2 mg ml-1 at the time of spawning in mid-October. The temporal changes in plasma Vtg of females correlate well with the reproductive cycle. Vtg was undetectable in males, except on some sampling dates during July-September when minute amounts (3-13 micrograms ml-1) were detected in some individuals.