Differential suppressive effects of low physiological doses of estradiol-17beta in vivo on levels of mRNAs encoding steroidogenic acute regulatory protein and three steroidogenic enzymes in previtellogenic ovarian follicles of rainbow trout

Triclosan, an antimicrobial drug, induced reproductive impairment in the freshwater fish, Anabas testudineus (Bloch, 1792)

Triclosan (TCS), an antimicrobial drug, is known to occupy different compartments in aquatic ecosystems. The present study focused to evaluate the reproductive toxicity of triclosan, at environmentally relevant (0.009 and 9 μg L-1) and sublethal (176.7 μg L-1) concentrations for 90 days in the pre-spawning phase of the fish, Anabas testudineus. The reproductive biomarkers, namely, gonadal steroidogenic enzymes, expression of aromatic genes, levels of serum gonadotropins, sex hormones, and histology of gonads were analyzed. The weight of the animal, brain weights along with gonadosomatic index decreased while mucus deposition increased significantly at all concentrations of triclosan as the primary defensive mechanism to prevent the entry of toxicants. Triclosan disrupted gonadal steroidogenesis as evidenced by a reduction in the activities of gonadal steroidogenic enzymes. The expressions of cyp19a1a and cyp19a1b genes were up-regulated in the brain of both sexes and testis, while down-regulated in the ovary indicating estrogenic effects of the compound. The endocrine-disrupting effects of triclosan were confirmed. The current results suggest that chronic exposure to triclosan altered reproductive endpoints thereby impairing normal reproductive functions in fish.

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

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

Effects of gonadotropins, 11-ketotestosterone, and insulin-like growth factor-1 on target gene expression and growth of previtellogenic oocytes from shortfinned eels, Anguilla australis, in vitro

Pituitary gonadotropins, metabolic hormones, and sex steroids are known factors affecting the advanced stages of ovarian development in teleost fish. However, the effects of these hormones and of the interactions between them on the growth of previtellogenic ovarian follicles are not known. In order to address this void in understanding, previtellogenic ovarian fragments from eel, Anguilla australis, were incubated in vitro with recombinant Japanese eel follicle-stimulating hormone (rec-Fsh), human chorionic gonadotropin (hCG), or 11-ketotestosterone (11-KT) in the presence or absence of recombinant human insulin-like growth factor-1 (IGF1). The results of long-term in vitro culture (21 days) demonstrated that rec-Fsh and 11-KT, rather than hCG, caused significant increases in the diameter of previtellogenic oocytes. Meanwhile, only 11-KT induced a significant increase in lipid accumulation. Moreover, a greater effect on oocyte growth was observed when IGF1 supplementation was combined with 11-KT rather than with rec-Fsh or hCG. For short-term culture (24 h), treatment with 11-KT in the presence or absence of IGF1 had no significant effects on mRNA levels of target genes (lhr, cyp19, cyp11b, lpl, and ldr) except for upregulation of fshr. There were no significant effects of rec-Fsh on expression of any target gene, whereas hCG downregulated the expression of these genes. There was no evidence for any interaction between the gonadotropins and IGF1 that resulted in growth of previtellogenic oocytes. Taken together, these results suggest that hormones from both the reproductive and the metabolic axes regulate the growth of previtellogenic oocytes in Anguilla australis.

Steroidogenic acute regulatory protein transcription is regulated by estrogen receptor signaling in largemouth bass ovary

Estrogenic contaminants in the environment are linked to the occurrence of reproductive abnormalities in many aquatic species, including largemouth bass (Micropterus salmoides; LMB). Previous work has shown that many different types of xenoestrogens regulate expression of the Steroidogenic Acute Regulatory protein (StAR), a cholesterol-transporting protein vital to steroid hormone biosynthesis; however, the regulatory mechanisms of StAR are incompletely characterized in fish. To learn more about endogenous expression patterns of StAR in the ovary, LMB were collected from the St. John's River (Florida, USA) over an entire breeding season to investigate StAR expression. Plasma 17β-estradiol (E2) and StAR mRNA levels were positively correlated in females, and StAR mRNA levels displayed ~ 100-fold increase between primary oocyte growth stages and final maturation. To further study the regulation of StAR, female LMB in the laboratory were fed at ≃2% of their weight on a diet laden with 17α-ethinylestradiol (EE2, 70 or 200 ng EE2 per gram feed). Diets were designed to achieve a physiologically-relevant exposure to EE2, and StAR expression was assessed in vivo. We observed a dose-dependent suppression of StAR mRNA levels, however both diets led to high, pharmacological levels in the blood and do not represent normal physiological ranges of estrogens. In the 200 ng EE2/gm feed group, ovarian StAR mRNA levels were suppressed to approximately 5% of that of the LMB control group. These investigations suggest that LMB StAR increases in expression during oocyte maturation and that it is suppressed by E2 feedback when estrogen levels are high, through the HPG axis. A 2.9 kb segment of the LMB StAR promoter was examined for putative E2 response elements using in silico software, and a putative estrogen receptor binding element (ERE/-1745) was predicted in the promoter. The functionality of the ERE was examined using MA-10 mouse Leydig cells transfected with the LMB StAR promoter. Estrogen receptor (ER) interaction with ERE/-1745 was evaluated under basal and human chorionic gonadotropin (hCG)-treated conditions in the presence and absence of E2. Chromatin immunoprecipitation (ChIP) experiments revealed that ESR1 binding to the promoter was enriched under basal conditions and E2 exposure elicited an increase in enrichment (4-fold) above that observed under basal conditions. ESR2 was not strongly enriched at the ERE/-1745 site, suggesting that StAR may be preferentially regulated by LMB estrogen receptor 1 (esr1). Taken together, these different experiments provide evidence that LMB StAR is under the control of estrogens and that ESR1 binds directly to the LMB StAR promoter in an E2-responsive manner.

In vitro exposure of vitellogenic rainbow trout ovarian follicles to endocrine disrupting chemicals can alter basal estradiol-17β production and responsiveness to a gonadotropin challenge

Endogenous estrogens play major roles in many aspects of female reproductive development in fish. In order to develop a relatively high-throughput assay to determine the potential impact on reproductive development, vitellogenic rainbow trout ovarian follicles were exposed to a suite of contaminants in vitro and then assessed for the ability to produce estradiol-17β (E2) after a 500 ng/ml salmon gonadotropin (sGTH) challenge. There was a positive correlation between ovarian follicle size and E2 production, but an inverse correlation between size and responsiveness to sGTH. Significant impacts on E2 levels were observed following treatment with different endocrine disrupting chemicals, such as 17α-ethinylestradiol (EE2), prochloraz, or trenbolone. EE2 was remarkably potent and significantly reduced ovarian follicle responsiveness to sGTH at concentrations as low as 0.1 nM. Of the other contaminants tested, only tamoxifen impacted E2 levels, and only at concentrations near the limits of solubility. Flutamide, fluoxetine, 4-hydroxy tamoxifen, hydroxyflutamide, and norfluoxetine had little or no impact. Quantitative PCR analyses of steroidogenesis-related genes were carried out on EE2 treated ovarian follicles, but significant transcriptional responses to EE2 were not observed. Overall, this study suggests that xenoestrogens and anti-estrogens are more likely to interfere with ovarian E2 synthesis than other classes of EDCs. This also provides a template for further testing of the effects of EDCs on ovarian function.

Steroidal and phenolic endocrine disrupting chemicals (EDCs) in surface water of Bahe River, China: Distribution, bioaccumulation, risk assessment and estrogenic effect on Hemiculter leucisculus

This study investigated selected steroidal and phenolic endocrine disrupting compounds (EDCs) in the surface water of the Bahe River (China) using gas chromatography mass spectrometry (GC-MS). Their effect on the wild sharpbelly Hemiculter leucisculus was investigated. The concentrations of 4-t-octylphenol, nonylphenol, bisphenol-A, estrone, 17 β-estradiol, 17 α-Ethinylestradiol, and estriol were up to 126.0, 634.8, 1573.1, 55.9, 23.9, 31.5, and 5.2 ng L^-1 in the surface water, and up to 26.4, 103.5, 146.9, 14.2, 9.3, 13.8, and 1.3 ng g^-1 in the fish muscle tissue, respectively. High estrogen equivalent levels and hazard quotients were found in the middle and lower reaches of the river, and the pollution in these regions caused enhanced growth conditions, inhibition of gonad growth, and suppression of spermatogenesis in H. leucisculus. The up-regulation of Vitellogenin mRNA expression in male fish, collected from relatively heavily EDCs contaminated areas, indicates a potential estrogenic effect. The differential expression profiles of genes related to steroidogenesis at all sampling sites suggests that these endpoints may play an important role for the pollution monitoring of estrogenic EDCs in the Bahe River.

Estrogen therapy offsets thermal impairment of vitellogenesis, but not zonagenesis, in maiden spawning female Atlantic salmon (Salmo salar)

In female Atlantic salmon (Salmo salar), exposure to warm summer temperatures causes a reduction in plasma 17β-estradiol (E2), which impairs downstream vitellogenesis and zonagenesis, and reduces egg fertility and embryo survival. The aim of the present study was to determine whether E2-treatment could offset thermal impairment of endocrine function and maintain egg quality in maiden (first-time-spawning) S. salar reared at 22 °C. Treatment with E2 at 22 °C stimulated vitellogenin (vtg) gene expression and subsequent protein synthesis which promoted oocyte growth and increased egg size relative to untreated fish at 14 and 22 °C. However, E2-treatment at 22 °C was not associated with an increase in egg fertility and embryo survival relative to untreated fish at 22 °C, despite the positive effects of E2-treatment on vitellogenesis and oocyte growth. As there was no evidence to suggest that the estrogen receptor alpha expression was suppressed by high temperature, this could be due to the lack of stimulation on zonagenesis by E2-treatment observed at high temperature during oocyte development. Our results demonstrate that treatment with E2 is not able to maintain zonagenesis or egg quality in maiden S. salar at high temperature, even when vtg gene expression, protein synthesis and subsequent oocyte growth is promoted. This implies that the mechanisms regulating zonagenesis, but not vitellogenesis are impaired at elevated temperature in female S. salar broodstock, and highlights the remarkable complexity of thermally induced endocrine disruption in fish.

Alteration in molecular markers of oocyte development and intersex condition in mullets impacted by wastewater treatment plant effluents

Wastewater Treatment Plant (WWTP) discharges are an important source of endocrine disrupting chemicals (EDCs) into the aquatic environment. Fish populations inhabiting downstream of WWTP effluents show alterations in gonad and gamete development such as intersex condition, together with xenoestrogenic effects such as vitellogenin up-regulation. However, the molecular mechanisms participating in the development of intersex condition in fish are not elucidated. The aim of this study was to assess the impact of two WWTPs effluents (Gernika and Bilbao-Galindo situated in the South East Bay of Biscay) with different contaminant loads, in thicklip grey mullet (Chelon labrosus) populations inhabiting downstream, examining the presence and severity of intersex condition, during two seasons. Molecular markers of xenoestrogenicity and oocyte differentiation and development (vtgAa, cyp19a1a, cyp19a1b, cyp11b, foxl2, dmrt1 and gtf3a) were also studied. Intersex mullets were identified downstream of both WWTPs and vtgAa was upregulated in intersex and non intersex males. Sex dependent differential transcription levels of target genes were detected in mullets from Galindo. However, no such pattern was observed in mullets from Gernika, suggesting an attenuating effect over studied genes caused by a higher presence of EDCs in this site, as indicated by the elevated prevalence of intersex mullets in this population. In conclusion, no direct association between xenoestrogenic responses and intersex condition was established. Mullets from Gernika showed signs of severe EDC exposure compared to those from Galindo, as demonstrated by the higher prevalence of intersex males and the reduction in transcription profile differences between sexes of gametogenic gene markers.

Effects of octylphenol on the expression of StAR, CYP17 and CYP19 in testis of Rana chensinensis

It has been proposed that a decline in sperm quality is associated with exposure to environmental chemicals with estrogenic activity. Seeking possible explanations for this effect, this study investigated the effects of octylphenol (OP) on the synthesis of steroid hormones in amphibian. Rana chensinensis were exposed to 10^-8, 10^-7 and 10^-6mol/L OP after 10, 20, 30 and 40 days. The cDNA fragments of StAR (274bp), CYP17 (303bp) and CYP19 (322bp) were cloned. In situ hybridization and immunohistochemistry revealed that positive signals of StAR, CYP17, CYP19 mRNA and proteins mainly in the Leydig cells of testes. Real-time PCR showed that up-regulation of StAR and CYP19, and down-regulation of CYP17 after exposure to 10^-8, 10^-7 and 10^-6mol/L OP. The results suggest that OP can alter transcriptions of StAR, CYP17 and CYP19, thus disturb the expressions of StAR, P450c17 and P450arom, thereby adversely affect steroid synthesis.

Regulation of sex steroid production and mRNAs encoding gonadotropin receptors and steroidogenic proteins by gonadotropins, cyclic AMP and insulin-like growth factor-I in ovarian follicles of rainbow trout (Oncorhynchus mykiss) at two stages of vitellogenesis

At the completion of vitellogenesis, the steroid biosynthetic pathway in teleost ovarian follicles switches from estradiol-17β (E2) to maturational progestin production, associated with decreased follicle stimulating hormone (Fsh) and increased luteinizing hormone (Lh) signaling. This study compared effects of gonadotropins, human insulin-like growth factor-I (IGF1), and cAMP/protein kinase A signaling (forskolin) on E2 production and levels of mRNAs encoding steroidogenic proteins and gonadotropin receptors using midvitellogenic (MV) and late/postvitellogenic (L/PV) ovarian follicles of rainbow trout. Fsh, Lh and forskolin, but not IGF1, increased testosterone and E2 production in MV and L/PV follicles. Fsh increased steroidogenic acute regulatory protein (star; MV), 3β-hydroxysteroid dehydrogenase/Δ(5-4) isomerase (hsd3b; MV) and P450 aromatase (cyp19a1a; MV) transcript levels. Lh increased star mRNA levels (MV, L/PV) but reduced cyp19a1a transcripts in L/PV follicles. At both follicle stages, IGF1 reduced levels of hsd3b transcripts. In MV follicles, IGF1 decreased P450 side-chain cleavage enzyme (cyp11a1) transcripts but increased cyp19a1a transcripts. In MV follicles only, forskolin increased star and hsd3b transcripts. Forskolin reduced MV follicle cyp11a1 transcripts and reduced cyp19a1a transcripts in follicles at both stages. Fsh and Lh reduced fshr transcripts in L/PV follicles. Lh also reduced lhcgr transcripts (L/PV). IGF1 had no effect on gonadotropin receptor transcripts. Forskolin reduced MV follicle fshr transcript levels and reduced lhcgr transcripts in L/PV follicles. These results reveal hormone- and stage-specific transcriptional regulation of steroidogenic protein and gonadotropin receptor genes and suggest that the steroidogenic shift at the completion of vitellogenesis involves loss of stimulatory effects of Fsh and Igfs on cyp19a1a expression and inhibition of cyp19a1a transcription by Lh.

Diethylstilbestrol at environmental levels affects the development of early life stage and target gene expression in Japanese Medaka (Oryzias latipes)

In this study, the biologic effects of DES on the early life and adult life stages of Japanese medaka (Oryzias latipes) were evaluated. At the early life stage, the fertilized eggs were exposed to 1-1000 ng/L diethylstilbestrol (DES) for 15 days and the hatched larvae were continually exposed to the same concentrations for an additional 25 days. Significant adverse effects on hatchability, time to hatching and mortality rate occurred at DES concentrations of 100 and 1000 ng/L, while the abnormality (scoliosis and abdominal swelling) rate was significantly increased at 10 ng/L and above. After exposure, the fish were maintained in charcoal-dechlorinated tap water for a further 30 days. Only the male gonadosomatic index (GSI) at 1000 ng/L was significantly increased. At concentrations greater than 1 ng/L, estrogen receptor α (ERα) mRNA in both sexes and vitellogenin-I (Vtg-I) mRNA in males were significantly down-regulated; while Vtg-I mRNA in females was significantly up-regulated. When sexually mature medaka were exposed to 10 and 1000 ng/L DES for 21 days, only the GSI in females was significantly decreased at 1000 ng/L. At 10 and 1000 ng/L, ERα mRNA in both sexes was significantly down-regulated, while Vtg-I mRNA in males was significantly up-regulated. These findings showed that DES at the environmental concentration of 10 ng/L can affect the early life stage development of medaka and alter liver ERα and Vtg-I gene expression. Therefore, if we only focused on these sensitive toxicity endpoints such as ERα and Vtg-I mRNA expression, DES has a strong estrogenic effect on Japanese medaka.

Silver nanoparticles disrupt regulation of steroidogenesis in fish ovarian cells

Despite the influx of silver nanoparticles (nAg) into the marine environment, their effects on fish reproduction remain completely unexplored. Using ovarian primary cells from marine medaka (Oryzias melastigma), in vitro studies were carried out to evaluate the effects of two differently coated nAg particles (Oleic Acid, (OA) nAg and Polyvinylpyrrolidone, (PVP) nAg) on fish ovarian tissues, using AgNO3 as a positive control. Cytotoxicity was evaluated by MTT assay and expression of key genes regulating steroidogenesis (StAR, CYP 19a, CYP 11a, 3βHSD and 20βHSD) were determined by Q-RT-PCR. EC50 values for PVP nAg, OA nAg and AgNO3 were 7.25μgL(-1), 924.4μgL(-1), and 42.0μgL(-1) respectively, showing that toxicity of silver was greatly enhanced in the PVP coated nano-form. Down regulation of CYP 19a was observed in both nAg and AgNO3 treatments, while down regulation of 3βHSD was only found in the OA nAg and AgNO3 treatments. For the first time, our results demonstrated that nAg can affect specific genes regulating steroidogenesis, implicating nAg as a potential endocrine disruptor.

Modulation of aromatase activity as a mode of action for endocrine disrupting chemicals in a marine fish

The steroidogenic enzyme aromatase catalyzes the conversion of androgens to estrogens and therefore plays a central role in reproduction. In contrast to most vertebrates, teleost fish have two distinct forms of aromatase. Because brain aromatase activity in fish is up to 1000 times that in mammals, fish may be especially susceptible to negative effects from environmental endocrine-disrupting chemicals (EDCs) that impact aromatase activity. In this study, the effects of estradiol (E2), ethynylestradiol (EE2), octylphenol (OP), and androstatrienedione (ATD) on reproduction and aromatase activity in brains and gonads from the marine fish cunner (Tautogolabrus adspersus) was investigated. The purpose of the study was to explore the relationship between changes in aromatase activity and reproductive output in a marine fish, as well as compare aromatase activity to two commonly used indicators of EDC exposure, plasma vitellogenin (VTG) and gonadosomatic index (GSI). Results with E2, EE2, and ATD indicate that aromatase activity in cunner brain and ovary are affected differently by exposure to these EDCs. In the case of E2 and EE2, male brain aromatase activity was signficantly increased by these treatments, female brain aromatase activity was unaffected, and ovarian aromatase activity was significantly decreased. Treatment with the aromatase inhibitor ATD resulted in significantly decreased aromatase activity in male and female brain, but had no significant impact on ovarian aromatase activity. Regardless of test chemical, a decrease or an increase in male brain aromatase activity relative to controls was associated with decreased egg production in cunner and was also correlated with significant changes in GSI in both sexes. E2 and EE2 significantly elevated plasma VTG in males and females, while ATD had no significant effect. Treatment of cunner with OP had no significant effect on any measured endpoint. Overall, results with these exposures indicate EDCs that impact aromatase activity also affect reproductive output in spawning cunner.

A rapid screening test for endocrine disrupting chemicals using primary cell culture of the marine medaka

While endocrine disrupting chemicals (EDCs) pose a significant threat to wildlife worldwide, their diverse chemical structures present a major challenge to their detection, particularly since they are present at very low concentrations in the environment. We here report the development of an in vitro system for rapid screening of EDCs, using primary cell cultures (pituitary, ovarian follicular and testicular cells) of the marine medaka (Oryzias melastigma). Pituitary, testis and ovary cell cultures were developed and challenged by environmentally relevant concentrations of three well known EDCs (viz. estradiol, 2,2',4,4'-tetrabromodiphenyl ether, and 4-n-nonylphenol) as well as hypoxia (which has been shown to be a potent endocrine disruptor). In general, the mRNA expression levels of gonadotropins, their receptors and steroidogenic enzymes exhibited dose response relationships to the four endocrine disruptors in different tissues. The sensitivity and responses were also comparable to in vivo responses of whole fish and in vitro responses of the H295R human adrenocortical cell line. Our results suggest that the use of marine medaka primary cultured cells can serve as a cost effective tool for rapid screening of EDCs in the marine environment, and at the same time, sheds light on the underlying mechanisms of EDCs by deciphering their specific target sites along the hypothalamus-pituitary-gonad axis of vertebrates.

Regulation of 3β-hydroxysteroid dehydrogenase/Δ⁵-Δ⁴ isomerase: a review

This review focuses on the expression and regulation of 3β-hydroxysteroid dehydrogenase/Δ⁵-Δ⁴ isomerase (3β-HSD), with emphasis on the porcine version. 3β-HSD is often associated with steroidogenesis, but its function in the metabolism of both steroids and xenobiotics is more obscure. Based on currently available literature covering humans, rodents and pigs, this review provides an overview of the present knowledge concerning the regulatory mechanisms for 3β-HSD at all omic levels. The HSD isoenzymes are essential in steroid hormone metabolism, both in the synthesis and degradation of steroids. They display tissue-specific expression and factors influencing their activity, which therefore indicates their tissue-specific responses. 3β-HSD is involved in the synthesis of a number of natural steroid hormones, including progesterone and testosterone, and the hepatic degradation of the pheromone androstenone. In general, a number of signaling and regulatory pathways have been demonstrated to influence 3β-HSD transcription and activity, e.g., JAK-STAT, LH/hCG, ERα, AR, SF-1 and PPARα. The expression and enzymic activity of 3β-HSD are also influenced by external factors, such as dietary composition. Much of the research conducted on porcine 3β-HSD is motivated by its importance for the occurrence of the boar taint phenomenon that results from high concentrations of steroids such as androstenone. This topic is also examined in this review.

Identification and transcriptional modulation of the largemouth bass, Micropterus salmoides, vitellogenin receptor during oocyte development by insulin and sex steroids

Fish vitellogenin synthesized and released from the liver of oviparous animals is taken up into oocytes by the vitellogenin receptor. This is an essential process in providing nutrient yolk to developing embryos to ensure successful reproduction. Here we disclose the full length vtgr cDNA sequence for largemouth bass (LMB) that reveals greater than 90% sequence homology with other fish vtgr sequences. We classify LMB Vtgr as a member of the low density lipoprotein receptor superfamily based on conserved domains and categorize as the short variant that is devoid of the O-glycan segment. Phylogenetic analysis places LMB Vtgr sequence into a well-supported monophyletic group of fish Vtgr. Real-time PCR showed that the greatest levels of LMB vtgr mRNA expression occurred in previtellogenic ovarian tissues. In addition, we reveal the effects of insulin, 17beta-estradiol (E(2)), and 11-ketotestosterone (11-KT) in modulation of vtgr, esr, and ar mRNAs in previtellogenic oocytes. Insulin increased vtgr expression levels in follicles ex vivo while exposure to E(2) or 11-KT did not result in modulation of expression. However, both steroids were able to repress insulin-induced vtgr transcript levels. Coexposure with insulin and E(2) or of insulin and 11-KT increased ovarian esr2b and ar mRNA levels, respectively, which suggest a role for these nuclear receptors in insulin-mediated signaling pathways. These data provide the first evidence for the ordered stage-specific expression of LMB vtgr during the normal reproductive process and the hormonal influence of insulin and sex steroids on controlling vtgr transcript levels in ovarian tissues.

Effects of ethinylestradiol and of an environmentally relevant mixture of xenoestrogens on steroidogenic gene expression and specific transcription factors in zebrafish

In natural environments fish are exposed to endocrine disrupting compounds (EDCs) present at low concentrations and with different modes of actions. Here, adult zebrafish of both sexes were exposed for 21 days to an estrogenic mixture (Mix) of eleven EDCs previously quantified in Douro River estuary (Portugal) and to 100 ng/L 17α-ethinylestradiol (EE2) as positive control. Vitellogenin mRNA and HSI in males confirmed both exposure regimes as physiologically active. Potential candidates for estrogenic disturbance of steroidogenesis were identified (StAR, 17β-HSD1, cyp19a1), but Mix only affected cyp19a1 in females. Significant differences in the response of FSHβ, cypa19a2, 20β-HSD were observed between EE2 and Mix. Mtf-1 and tfap2c transcription factor binding sites were discovered in the putative promoter regions and corresponding transcription factors were found to be differentially expressed in response to Mix and EE2. The results suggest that "non-classical effects" of estrogenic EDC in fish are mediated via transcription factors.

Characteristics of ovarian follicle steroidogenesis during vitellogenesis in an asynchronously ovulating stock of rainbow trout Oncorhynchus mykiss

This study explored several physiological criteria that could be used to assess the steroidogenic condition of the ovarian follicles of individual fish of an asynchronously ovulating captive rainbow trout Oncorhynchus mykiss stock. In these fish, the date of sampling, morphological variables such as gonado-somatic index or ovarian follicle mass and visual assessment of the ovary provided accurate indications of the maturational condition of an individual. The physiological variables measured included the in vitro basal and cyclic adenosine monophosphate (cAMP)-stimulated synthesis by ovarian follicles of 17β-oestradiol (E(2)) and testosterone (T); in addition, quantitative reverse-transcription (RT)-PCR was used to measure the relative expression of star and p450scc genes by ovarian follicles. The ratios of cAMP-stimulated E(2) and T synthesis to basal E(2) and T synthesis provided a reliable indication of differences in the steroidogenic status of the follicles of individual animals. On the basis of these criteria, together with the use of gene expression profiles, it was possible to classify individual fish as being at an early, mid or late-vitellogenic stage.

Follicle-stimulating hormone regulation of ovarian transcripts for steroidogenesis-related proteins and cell survival, growth and differentiation factors in vitro during early secondary oocyte growth in coho salmon

Little is known about follicle-stimulating hormone (FSH) function during oocyte growth in fishes. The goal of this study was to gain a fundamental understanding of FSH action on ovarian follicles during early secondary oocyte growth by examining changes in ovarian gene expression and steroidogenesis in response to FSH. Coho salmon (Oncorhynchus kisutch) mid to late cortical alveolus stage follicles were incubated with or without salmon FSH in time-course and concentration-response experiments. Steroid levels were determined in the culture medium by immunoassay and levels of target ovarian mRNAs were determined by quantitative RT-PCR. Medium estradiol-17β (E2) levels increased in response to FSH and plateaued by 36h, while testosterone levels increased similarly but were lower and more variable than E2. Gonadotropin receptor transcripts were differentially regulated, with fshr and lhcgr being down- and up- regulated, respectively. Transcripts encoding proteins involved in steroidogenesis, such as star and hsd3b were significantly upregulated by FSH, whereas aromatase (cyp19a1a) mRNA was unaffected by FSH and declined over time in culture. A recently identified teleost gene, bmp16, was suppressed by FSH and an anti-apoptotic factor, clusterin 1 (clu1), was upregulated by FSH. Lesser FSH effects were observed on igf2, cyp11a1 and cyp17a1, which were stimulated, and igf1ra, inhbb, amh and apoe, which were suppressed. As evident by the significant increases in steroid production and transcripts for specific steroidogenesis-related proteins, FSH influences steroidogenesis during early secondary growth and may be a critical signal for puberty onset. Effects of FSH on ovarian anti-apoptotic and growth factor genes suggest roles for FSH in cell survival, growth and differentiation in teleosts.