Estrogen receptor function and regulation in fish and other vertebrates

Is there potential for estradiol receptor signaling in lophotrochozoans?

Estrogen receptors (ERs) are thought to be the ancestor of all steroid receptors and are present in most lophotrochozoans studied to date, including molluscs, annelids, and rotifers. A number of studies have investigated the functional role of estrogen receptors in invertebrate species, although most are in molluscs, where the receptor is constitutively active. In vitro experiments provided evidence for ligand-activated estrogen receptors in annelids, raising important questions about the role of estrogen signalling in lophotrochozoan lineages. Here, we review the concordant and discordant evidence of estradiol receptor signalling in lophotrochozoans, with a focus on annelids and rotifers. We explore the de novo synthesis of estrogens, the evolution and expression of estrogen receptors, and physiological responses to activation of estrogen receptors in the lophotrochozoan phyla Annelida and Rotifera. Key data are missing to determine if de novo biosynthesis of estradiol in non-molluscan lophotrochozoans is likely. For example, an ortholog for the CYP11 gene is present, but confirmation of substrate conversion and measured tissue products is lacking. Orthologs CYP17 and CYP19 are lacking, yet intermediates or products (e.g. estradiol) in tissues have been measured. Estrogen receptors are present in multiple species, and for a limited number, in vitro data show agonist binding of estradiol and/or transcriptional activation. The expression patterns of the lophotrochozoan ERs suggest developmental, reproductive, and digestive roles but are highly species dependent. E2 exposures suggest that lophotrochozoan ERs may play a role in reproduction, but no strong dose-response relationship has been established. Therefore, we expect most lophotrochozoan species, outside of perhaps platyhelminths, to have an ER but their physiological role remains elusive. Mining genomes for orthologs gene families responsible for steroidogenesis, coupled with in vitro and in vivo studies of the steroid pathway are needed to better assess whether lophotrochozoans are capable of estradiol biosynthesis. One major challenge is that much of the data are divided across a diversity of species. We propose that the polychaetes Capitella teleta or Platyneris dumerilii, and rotifer Brachionus manjavacas may be strong species choices for studies of estrogen receptor signalling, because of available genomic data, established laboratory culture techniques, and gene knockout potential.

Chronic exposure to gestodene impairs reproductive system in adult female zebrafish (Daniarerio)

Gestodene (GES) is widely used in human therapy and animal husbandry and is frequently detected in aquatic environments. Although GES adversely affects aquatic organisms at trace levels, its effects on the reproductive biology of fish remain inconclusive. In this study, female zebrafish (Danio rerio) were exposed to environmentally relevant levels of GES for the evaluation of the effects of GES on the reproductive system by using endpoints including gene expression, plasma steroid concentrations, histological and morphological analyses, copulatory behavior, and reproductive output. Adult female zebrafish exposed to environmentally relevant concentrations of GES (4.0, 40.2, and 372.7 ng/L) for 60 d demonstrated stagnant ovarian oocyte development, evidenced by an increase in the percentage of perinuclear and atretic oocytes and a decrease in the percentage of late vitellogenic oocytes. GES-exposed females were less attractive to males and had lower copulatory intimacy than females in control. Consequently, spawning (44.3-49.2 %) and egg fertilization rates (27.9-32.0 %) were decreased. The decreased survival of fertilized eggs and hatching rates were accompanied by increased malformations. These negative effects were associated with abnormal transcriptional levels of gonadal steroid hormones, which were regulated by genes (Hsd17β3, Hsd11β2, Hsd20β, Cyp19a1a, and Cyp11b). Overall, our findings suggest that GES impairs the reproductive system of zebrafish, which may threaten population stability.

Evolutionary history and functional characterization of duplicated G protein-coupled estrogen receptors in European sea bass

Across vertebrates, the numerous estrogenic functions are mainly mediated by nuclear and membrane receptors, including the G protein-coupled estrogen receptor (GPER) that has been mostly associated with rapid non-genomic responses. Although Gper-mediated signalling has been characterized in only few fish species, Gpers in fish appear to present more mechanistic functionalities as those of mammals due to additional gene duplicates. In this study, we ran a thorough investigation of the fish Gper evolutionary history in light of available genomes, we carried out the functional characterization of the two gper gene duplicates of European sea bass (Dicentrarchus labrax) using luciferase reporter gene transactivation assays, validated it with natural and synthetic estrogen agonists/antagonists and applied it to other chemicals of aquaculture and ecotoxicological interest. Phylogenetic and synteny analyses of fish gper1 and gper1-like genes suggest their duplication may have not resulted from the teleost-specific whole genome duplication. We confirmed that both sbsGper isoforms activate the cAMP signalling pathway and respond differentially to distinct estrogenic compounds. Therefore, as observed for nuclear estrogen receptors, both sbsGpers duplicates retain estrogenic activity although they differ in their specificity and potency (Gper1 being more potent and more specific than Gper1-like), suggesting a more conserved role for Gper1 than for Gper1-like. In addition, Gpers were able to respond to estrogenic environmental pollutants known to interfere with estrogen signalling, such as the phytoestrogen genistein and the anti-depressant fluoxetine, a point that can be taken into account in aquatic environment pollution screenings and chemical risk assessment, complementing previous assays for sea bass nuclear estrogen receptors.

Genome-wide association study for body weight and feed consumption traits in Japanese quail using Bayesian approaches

The aim of this study was to perform a genome-wide association study (GWAS) based on Bayes A and Bayes B statistical methods to identify genomic loci and candidate genes associated with body weight gain, feed intake, and feed conversion ratio in Japanese quail. For this purpose, genomic data obtained from Illumina iSelect 4K quail SNP chip were utilized. After implementing various quality control steps, genotype data from a total of 875 birds for 2,015 SNP markers were used for subsequent analyses. The Bayesian analyses were performed using hibayes package in R (version 4.3.1) and Gibbs sampling algorithm. The results of the analyses showed that Bayes A accounted for 11.43, 11.65, and 11.39% of the phenotypic variance for body weight gain, feed intake, and feed conversion ratio, respectively, while the variance explained by Bayes B was 7.02, 8.61, and 6.48%, respectively. Therefore, in the current study, results obtained from Bayes A were used for further analyses. In order to perform the gene enrichment analysis and to identify the functional pathways and classes of genes that are over-represented in a large set of genes associated with each trait, all markers that accounted for more than 0.1% of the phenotypic variance for each trait were used. The results of this analysis revealed a total of 23, 38, and 14 SNP markers associated with body weight gain, feed intake, and feed conversion ratio in Japanese quail, respectively. The results of the gene enrichment analysis led to the identification of biological pathways (and candidate genes) related to lipid phosphorylation (TTC7A gene) and cell junction (FGFR4 and FLRT2 genes) associated with body weight gain, calcium signaling pathway (ADCY2 and CAMK1D genes) associated with feed intake, and glycerolipid metabolic process (LIPC gene), lipid metabolic process (ADGRF5 and ESR1 genes), and glutathione transferase (GSTK1 gene) associated with feed conversion ratio. Overall, the findings of this study can provide valuable insights into the genetic architecture of growth and feed consumption traits in Japanese quail.

Arginine vasopressin injection rescues delayed oviposition in cyp19a1b-/- mutant female zebrafish

In zebrafish, estrogens produced in the ovaries via Cyp19a1a activity are required for both sexual differentiation of the ovary during early development as well as maintenance of the ovarian state during adulthood. The importance of Cyp19a1b that is highly expressed in the brain for female reproduction is still under study. We previously reported that female cyp19a1b -/- mutant zebrafish have significantly lower brain estradiol levels and impaired spawning behavior characterized by an increased latency to oviposition during dyadic sexual behavior encounters. In the current study, we provide evidence that the delayed oviposition in female cyp19a1b -/- mutants is linked to impaired arginine vasopressin (Avp) signaling. Droplet digital PCR experiments revealed that levels of the estrogen receptors, avp, and oxytocin (oxt) are lower in the hypothalamus of mutant females compared to wildtype fish. We then used acute intraperitoneal injections of Avp and Oxt, along with mixtures of their respective receptor antagonists, to determine that Avp can uniquely rescue the delayed oviposition in female cyp19a1b -/- mutants. Using immunohistochemistry, we demonstrated that Cyp19a1b-expressing radial glial cell (RGC) fibers surround and are in contact with Avp-immunopositive neurons in the preoptic areas of the brain. This could provide the neuroanatomical proximity for RGC-derived estrogens to diffuse to and activate estrogen receptors and regulate avp expression levels. Together these findings identify a positive link between Cyp19a1b and Avp for female zebrafish sexual behavior. They also suggest that the female cyp19a1b -/- mutant behavioral phenotype is likely a consequence of impaired processing of Avp-dependent social cues important for mate identification and assessment.

Assessment of reproductive toxicity in adult zebrafish (Danio rerio) following sublethal exposure to penthiopyrad

Penthiopyrad (PO), a succinate dehydrogenase inhibitor (SDHI) fungicide, poses a potential risk to fish. Here, we investigated the adverse effects of PO on endocrine regulation and reproductive capacity in zebrafish during a 21-d sublethal exposure to PO concentrations ranging from 0.02 to 2.00 mg/L. Following exposure to PO (0.20 and 2.00 mg/L), female-specific effects including follicle necrosis, structural disturbance of the yolk follicle, fusion of cortical follicles appeared in ovarian tissue of adult females, which led to a significant reduction in fertility. Correspondingly, 0.20 and 2.00 mg/L PO led to a marked reduction in the GSI values of females, and 2.00 mg/L PO caused a 31% decline in the proportion of perinucleolar oocytes (PCO) in oocytes. In addition, testosterone (T) level was obviously suppressed and 17β-estradiol (E2) level was increased in females after exposure to 2.00 mg/L PO. Male zebrafish treated with 0.20 and 2.00 mg/L of PO exhibited significant interstitial enlargement, edema in the testes, and reduced diameter of seminiferous tubules, along with a thinner basement membrane. The effects of PO on males were associated with significant increase in E2 level, suggesting that PO has an estrogenic effect on male fish. Greater E2 levels in serum were further supported by increased transcription levels of genes linked to the hypothalamic-pituitary-gonad-liver (HPGL) axis. Notably, transcription levels of cyp19a, er2b, era, and cyp19b was remarkably increased, exhibiting a clear link with variations in E2 levels. Overall, the present study demonstrates that PO induces reproductive impairment in zebrafish by promoting steroidogenesis.

Alterations in Gene Expression and the Fatty Acid Profile Impact but Do Not Compromise the In Vitro Maturation of Zebrafish (Danio rerio) Stage III Ovarian Follicles after Cryopreservation

The vitrification of ovarian follicles is a strategic tool that may contribute to advances in aquaculture and the conservation of many important species. Despite the difficulties inherent to the cryopreservation of oocytes, some successful protocols have been developed for different species, but little is known about the capacity of oocytes to develop after thawing. Therefore, the profiles of the reproductive pathway genes and fatty acid membrane composition during the initial stages of development were analyzed in fresh ovarian follicles and follicles after the vitrification process. There were differences in the expression of the hypothalamic-pituitary-gonad axis genes during the follicular development in the control group as well as in the vitrified group. Similarly, alterations in the composition of fatty acids were observed after vitrification. Despite this, many alterations were observed in the vitrified group; more than half of the stage III ovarian follicles were able to grow and mature in vitro. Therefore, the vitrification of ovarian follicles may impact them at molecular and membrane levels, but it does not compromise their capability for in vitro maturation, which indicates that the technique can be a strategic tool for aquaculture.

Reproductive toxicity induced by lead exposure: Effects on gametogenesis and sex steroid signaling in teleost fish

Lead (Pb) is an emerging contaminant widely distributed in aquatic environments, which has serious effects on human and animal health. In this study, we determined whether Pb exposure affects gametogenesis, sex steroids, estrogen (ERα and ERβ), and androgen (AR) receptors. Adult specimens of Astyanax bimaculatus were exposed in duplicate to 15, 50, and 100 μg/L of lead acetate, whereas the control group was not exposed. After 28 days of exposure, fish were euthanized and samples of the gonads, liver, and blood were collected for analysis. The results indicated a reduction in the gonadosomatic index as well as the diameters of the vitellogenic follicles and seminiferous tubules in the exposed groups. Morphometry of gametogenesis revealed inhibition of the secondary oocyte growth and a reduction in the number of spermatozoa in the 50 and 100 μg/L Pb-treated groups. In females, plasma 17β-estradiol (E2) increased following 15 and 50 μg/L Pb treatment, whereas males exhibited an increase in E2 and 11-ketotestosterone following treatment with 15 and 100 μg/L Pb, respectively. Vitellogenin was significantly reduced in females exposed to 100 μg/L Pb, but metallothionein levels were unchanged. ERα, ERβ, and AR were immunolocalized in the somatic and germ cells, with increased ovarian expression of ERα and Erβ in the 100 μg/L Pb-treated group, but no significant difference in AR among the groups. In males, only ERα increased in the 100 μg/L Pb-treated group. These results indicate that Pb exposure impairs gametogenesis, disrupts estrogen receptor signaling, and affects the expression of major reproductive biomarkers in A. bimaculatus.

Tissue-specific promoters regulate the transcription of cyp19a1 in the brain-pituitary-gonad axis of Japanese eel (Anguilla japonica)

Aromatase is a key enzyme that catalyzes the biosynthesis of estrogens. Previous study indicated that putative tissue-specific promoters of the one aromatase gene (cyp19a1) may drive the differential regulatory mechanisms of cyp19a1 expression in Anguilla japonica. In the present study, for elucidating the transcription characteristics and the function of putative tissue-specific promoters of cyp19a1 in the brain-pituitary-gonad (BPG) axis during vitellogenesis, we investigated the transcriptional regulation of cyp19a1 by 17β-estrogen (E2), testosterone (T), or human chorionic gonadotropin (HCG) in A. japonica. The expression of estrogen receptor (esra), androgen receptor (ara), or luteinizing hormone receptor (lhr) was up-regulated as cyp19a1 in response to E2, T, or HCG, respectively in the telencephalon, diencephalon, and pituitary. The expression of cyp19a1 was also upregulated in the ovary by HCG or T in a dose-dependent manner. Unlike in the brain and pituitary, the expression of esra and lhr, rather than ara, was upregulated by T in the ovary. Subsequently, four primary subtypes of 5'-untranslated terminal regions of cyp19a1 transcripts and the corresponding two 5' flanking regions (promoter P.I and P.II) were identified. The P.II existed in all BPG axis tissues, whereas the P.I with strong transcriptional activity was brain- and pituitary-specific. Furthermore, the transcriptional activity of promoters, the core promoter region, and the three putative hormone receptor response elements were validated. The transcriptional activity did not change when the HEK291T cells co-transfected with P.II and ar vector were exposed to T. These results suggested that the expression of cyp19a1 was upregulated indirectly through esra and lhr rather than ara by T in the ovary, whereas the expression of cyp19a1 was upregulated directly through androgen receptor and the downstream androgen response element of tissue-specific P.I in the brain and pituitary. The results of the study reveal the regulatory mechanisms of estrogen biosynthesis and provide a reference for optimizing the technology of artificially induced maturation in eels.

Using Hepatic Gene Expression Assays in English Sole (Parophrys vetulus) to Investigate the Effects of Metro Vancouver Wastewater Effluents

The present study has investigated the effects of Metro Vancouver's wastewater treatment plant (WWTP) effluents on English sole (Parophrys vetulus) hepatic gene expression using novel targeted gene expression assays to complement the 2017 Burrard Inlet Ambient Monitoring Program conducted by Metro Vancouver. Seven locations of varying distance to the WWTPs were included. Twelve genes involved in xenobiotic defense (CYP1A, HSP70), thyroid function (DIO1), lipid and glucose metabolism (FABP1, FASN, GLUT2, PPARδ, PPARγ), protein synthesis (18S rRNA, RPS4X), and reproduction (ERα, VTG) revealed several differences between these impacted sites. A key finding of the present study was that males exhibited VTG transcript levels either equivalent or exceeding female levels of this gene at all sites investigated, indicating widespread exposure of estrogenic contaminants throughout Burrard Inlet. Furthermore, the induction of hepatic CYP1A was observed due to possible downstream sites being subjected to a larger influx of certain planar halogenated and non-halogenated hydrocarbons from multiple industrial contributors. This study also revealed significant differences between the sites examined and in genes involved in transcriptional regulation and synthesis of proteins, lipids and glucose metabolism, and thyroid hormone metabolism. Collectively, this study demonstrates the potential of molecular biomarkers of urban contaminant exposure in wild caught English sole for use in diagnosing a broader range of adverse health effects when combined with conventional whole organism health indicators.

Is Hormone Replacement Therapy a Risk Factor or a Therapeutic Option for Alzheimer's Disease?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that accounts for more than half of all dementia cases in the elderly. Interestingly, the clinical manifestations of AD disproportionately affect women, comprising two thirds of all AD cases. Although the underlying mechanisms for these sex differences are not fully elucidated, evidence suggests a link between menopause and a higher risk of developing AD, highlighting the critical role of decreased estrogen levels in AD pathogenesis. The focus of this review is to evaluate clinical and observational studies in women, which have investigated the impact of estrogens on cognition or attempted to answer the prevailing question regarding the use of hormone replacement therapy (HRT) as a preventive or therapeutic option for AD. The articles were retrieved through a systematic review of the databases: OVID, SCOPUS, and PubMed (keywords "memory", "dementia," "cognition," "Alzheimer's disease", "estrogen", "estradiol", "hormone therapy" and "hormone replacement therapy" and by searching reference sections from identified studies and review articles). This review presents the relevant literature available on the topic and discusses the mechanisms, effects, and hypotheses that contribute to the conflicting findings of HRT in the prevention and treatment of age-related cognitive deficits and AD. The literature suggests that estrogens have a clear role in modulating dementia risk, with reliable evidence showing that HRT can have both a beneficial and a deleterious effect. Importantly, recommendation for the use of HRT should consider the age of initiation and baseline characteristics, such as genotype and cardiovascular health, as well as the dosage, formulation, and duration of treatment until the risk factors that modulate the effects of HRT can be more thoroughly investigated or progress in the development of alternative treatments can be made.

Exposure to acetaminophen impairs gametogenesis and fertility in zebrafish (Danio rerio)

Acetaminophen (ACE; paracetamol) is one of the most widely used nonsteroidal anti-inflammatory drugs worldwide and is often found in aquatic systems, where it can act on nontarget species and impair fish reproduction. This study aimed to investigate the effects of chronic exposure to environmentally relevant ACE concentrations (0.5, 5 and 50 µg/L) on multiple reproductive parameters in zebrafish (Danio rerio). Gametogenesis was analyzed using histology, morphometry, cell proliferation, and apoptosis. This study also evaluated sex steroids, and prostaglandin E₂ (PGE₂) levels, gene expression for sex steroids and PGE₂ receptors, fertilization rate, and semen quality. In females, exposure to 5 and 50 µg/L ACE induced larger and more abundant vitellogenic follicles and increased follicular atresia. In these treatments, males showed a lower proportion and proliferation of undifferentiated spermatogonia and a higher proportion of TUNEL-positive differentiated spermatogonia, spermatids, and spermatozoa, resulting in lower sperm production. ACE increased 17β-estradiol (E₂) and reduced 11-ketotestosterone levels in the testis, whereas only E₂ increased in the ovaries. In both sexes, gonadal PGE₂ levels were reduced. ACE at 50 µg/L induced an increase in the gene expression of androgen, estrogen, and PGE₂ receptors in the ovaries, and reduced expression in the testes. Results also showed lower egg production and fertilization rate from 28 days of exposure with reduced sperm quality. These results demonstrated that ACE impairs the reproductive performance of zebrafish, affecting multiple reproductive parameters, which may be caused by the synergistic action of the imbalance of sex steroids, with a reduction of PGE₂ and its receptors.

Reproductive toxicity of long-term exposure to environmental relevant concentrations of cyprodinil in female zebrafish (Danio rerio)

In recent years, the widespread use of the pesticide cyprodinil has attracted attention due to its harmful effects on aquatic organisms. The purpose of this study was to evaluate the adverse effects of long-term exposure to cyprodinil on the reproductive system of female zebrafish. After the embryos had been treated with 0.1, 1 and 10 μg/L cyprodinil for 180 days, we observed that female fish treated with 1 and 10 μg/L cyprodinil showed decreased sexual attractiveness, a decreased proportion of primordial follicles in the ovary, an increased proportion of mature follicles, and increased egg production. Moreover, exposed females that mated with normal males produced offspring with increased rates of mortality and deformity (the F1 generation). In addition, the levels of gonadotropin and testosterone (T) were increased in females after cyprodinil exposure, especially in the 10 μg/L treated group. After cyprodinil treatment, some key genes in the hypothalamic-pituitary-gonad axis underwent significant changes. For example, gene expression of brain gonadotropin-releasing hormone receptors (gnrhr1, gnrhr2 and gnrhr4) was significantly downregulated after cyprodinil treatment. The study found that expression of the aromatase (cytochrome P450 family 19 subfamily A polypeptide 1a, cyp19a1a) responsible for converting T into estradiol was significantly downregulated after cyprodinil treatment, consistent with elevated T levels in the ovaries and muscles. In summary, these data provide a more comprehensive understanding of the toxicity of cyprodinil and may inform evaluation of the ecotoxicity of cyprodinil to female reproduction at environmentally relevant concentrations.

Effects of Low Temperature on Antioxidant and Heat Shock Protein Expression Profiles and Transcriptomic Responses in Crayfish (Cherax destructor)

Low temperature is a critical factor restricting the growth and survival of aquatic animals, but research on the mechanism of response to low temperature in Cherax destructor is limited. C. destructor is one of the most important freshwater crustaceans with strong adaptability in Australia, and it has been commercialized gradually in recent years. Here, growth indicators, antioxidant parameters, anti-stress gene expression, and transcriptome sequencing were used on crayfish following 8 weeks of low-temperature acclimation. The results showed that weight gain, length gain, and molting rates decreased as the temperature decreased. The activity of antioxidant enzymes decreased, while the content of antioxidant substances and the expression of anti-stress genes increased. Transcriptome sequencing identified 589 differentially expressed genes, 279 of which were upregulated and 310 downregulated. The gene functions and pathways for endocrine disorders, glucose metabolism, antioxidant defense, and immune responses were identified. In conclusion, although low-temperature acclimation inhibited the basal metabolism and immune ability of crayfish, it also increased the antioxidant substance content and anti-stress-gene expression to protect the organism from low-temperature damage. This study provided molecular insights into the study of low-temperature responses of low-temperature-tolerant crustacean species.

Distinct Roles of Estrogen Receptors in the Regulation of Vitellogenin Expression in Orange-Spotted Grouper (Epinephelus coioides)

During their breeding season, estrogen induces vitellogenin (VTG) production in the liver of teleost fish through estrogen receptors (ERs) that support oocyte vitellogenesis. There are at least three ER subtypes in teleost fish, but their roles in mediating E₂-induced VTG expression have yet to be ascertained. In this study, we investigated the expression of vtgs and ers in the liver of orange-spotted grouper (Epinephelus coioides). Their expression levels were significantly increased in the breeding season and were upregulated by an estradiol (E₂) injection in female fish, except for the expression of erβ1. The upregulation of vtgs, erα and erβ2 by E₂ was also observed in primary hepatocytes, but these stimulatory effects could be abolished by ER antagonist ICI182780 treatment. Subsequent studies showed that ERβ antagonist Cyclofenil downregulated the E₂-induced expression of vtg, erα, and erβ2, while the ERβ agonist DPN simulated their expression. Knockdown of erβ2 by siRNA further confirmed that ERβ2 mediated the E₂-induced expression of vtgs and erα. To reveal the mechanism of ERβ2 in the regulation of erα expression, the erα promoter was cloned, and its activity was examined in cells. E₂ treatment simulated the activity of the erα promoter in the presence of ERβ2. Deletions and site-directed mutations showed that the E₂ up-regulated transcriptional activity of erα occurs through a classical half-estrogen response element- (ERE) dependent pathway. This study reveals the roles of ER subtypes in VTG expression in orange-spotted grouper and provides a possible explanation for the rapid and efficient VTG production in this species during the breeding season.

Widespread alterations upon exposure to the estrogenic endocrine disruptor ethinyl estradiol in the liver proteome of the marine male fish Cyprinodon variegatus

Quantitative proteomic changes in the liver of adult males of Sheepshead minnow (Cyprinodon variegatus) upon exposure to ethinyl estradiol (EE2) were assessed to provide an advanced understanding of the metabolic pathways affected by estrogenic endocrine disruption in marine fish, and to identify potential novel molecular biomarkers for the environmental exposure to estrogens. From a total of 3188 identified protein groups (hereafter proteins), 463 showed a statistically significant difference in their abundance between EE2 treatment and solvent control samples. The most affected biological processes upon EE2 exposure were related to ribosomal biogenesis, protein synthesis and transport of nascent proteins to endoplasmic reticulum, and nuclear mRNA catabolism. Within the group of upregulated proteins, a subset of 14 proteins, involved in egg production (Vitellogenin, Zona Pellucida), peptidase activity (Cathepsine E, peptidase S1, Serine/threonine-protein kinase PRP4 homolog, Isoaspartyl peptidase and Whey acidic protein), and nucleic acid binding (Poly [ADP-ribose] polymerase 14) were significantly upregulated with fold-change values higher than 3. In contrast, Collagen alpha-2, involved in the process of response to steroid hormones, among others, was significantly downregulated (fold change = 0.2). This pattern of alterations in the liver proteome of adult males of C. variegatus can be used to identify promising novel biomarkers for the characterization of exposure of marine fish to estrogens. The Whey acidic protein-like showed the highest upregulation in EE2-exposed individuals (21-fold over controls), suggesting the utility of abundance levels of this protein in male liver as a novel biomarker of xenoestrogen exposure.

Inhibitory effects of estrogenic endocrine disrupting chemicals on fin regeneration in zebrafish are dependent on estrogen receptors

For fish and other aquatic organisms, disrupting their capacity for repair and regeneration will reduce their quality of life and survivorship in the wild. Studies have shown that 17α-ethinylestradiol (EE2), a synthetic estrogenic endocrine disrupting chemical (EEDC), can inhibit caudal fin regeneration in larval zebrafish following fin amputation. However, whether the inhibitory effects of EE2 are dependent on estrogen receptor (ER) remains unknown. Therefore, in this study, amputated zebrafish larvae were exposed to the ER agonist EE2 alone and in combination with the ER antagonist ICI 182,780 (ICI), and the change in regenerative capacity was determined. The inhibition of fin regeneration caused by EE2 alone (100 ng/L) was ameliorated after combination with ICI (30-300 μg/L), and these changes in regeneration-related signaling and the immune system corresponded with morphological observations, implying that the effects of EE2 on regeneration were possibly initiated by the activation of ER. Furthermore, the role of ER was confirmed with a natural ligand of ER, namely, 17β-estradiol (E2), and as expected, the effects of E2 (10, 100 and 1000 ng/L) paralleled those of EE2. In conclusion, EEDCs can disrupt the regenerative capacity in zebrafish, possibly due to the binding and activation of ERs and the consequent alteration of signaling pathways that regulate fin regeneration and immune competence. Given that EEDCs appear to be ubiquitous in the aquatic environment, the risk of these chemicals might be readdressed regarding their potential effects on tissue repair and regeneration.

Preself-Feeding Medaka Fry Provides a Suitable Screening System for in Vivo Assessment of Thyroid Hormone-Disrupting Potential

Endocrine-disrupting chemicals are assessed based on their physiological potential and their potential associated adverse effects. However, suitable end points for detection of chemicals that interfere with the thyroid hormone (TH) system have not been established in nonmammals, with the exception of amphibian metamorphosis. The aims of the current study were to develop an in vivo screening system using preself-feeding medaka fry (Oryzias latipes) for the detection of TH-disrupting chemicals and elucidate the underlying molecular mechanism. 17α-Ethinylestradiol (EE2: <100 ng/L) did not induce mRNA expression of estrogen-responsive genes, vitellogenins (vtgs) mRNA. Meanwhile, coexposure with thyroxin (T4) induced an increase of vtg expression. TH-disrupting chemicals (thiourea (TU), perfluorooctanoic acid (PFOA), and tetrabromobisphenol A (TBBPA)) significantly suppressed EE2 (1,000 ng/L)-induced vtg1 expression, while T4 rescued their expression as well as that of thyroid hormone receptor α (tRα) and estrogen receptors (esrs). These results were supported by in silico analysis of the 5'-transcriptional regulatory region of these genes. Furthermore, the esr1 null mutant revealed that EE2-induced vtg1 expression requires mainly esr2a and esr2b in a TH-dependent manner in preself-feeding fry. Application of preself-feeding medaka fry as a screening system might help decipher the in vivo mechanisms of action of TH-disrupting molecules, while providing an alternative to the traditional animal model.

The bisphenol A metabolite MBP causes proteome alterations in male Cyprinodon variegatus fish characteristic of estrogenic endocrine disruption

The toxicological status of bisphenol A (BPA) is under strong debate. Whereas in vitro it is an agonist of the estrogen receptor with a potency ca. 10⁵-fold lower than the natural female hormone estradiol, in vivo exposure causes only mild effects at concentration thresholds environmentally not relevant and inconsistent among species. By using a proteomic approach, shotgun liver proteome analysis, we show that 7-d exposure to 10 μg/L of the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), and not the same exposure to the parental molecule BPA, alters the liver proteome of male Cyprinodon variegatus fish. Different physiological and environmental conditions leading to biotransformation of BPA to MBP may partly explain the conflicting results so far reported for in vivo BPA exposures. The pattern of alteration induced by MBP is similar to that caused by estradiol, and indicative of estrogenic endocrine disruption. MBP enhanced ribosomal activity, protein synthesis and transport, with upregulation of 91% of the ribosome-related proteins, and 12 proteins whose expression is regulated by estrogen-responsive elements, including vitellogenin and zona pellucida. Whey acidic protein (WAP) was the protein most affected by MBP exposure (FC = 68). This result points at WAP as novel biomarker for xenoestrogens.

sox19 regulates ovarian steroidogenesis in common carp

In teleost, ovarian steroidogenesis governed by the neuroendocrine system is also regulated by several transcription factors of gonadal origin. Investigating the synchronized interactions between the transcriptional and the hormonal factors is vital to comprehend the mechanisms that lead to gonadal differentiation. This study signifies the role of sry-related box (sox) 19 in ovarian steroidogenesis regulation of the common carp, Cyprinus carpio. Analysis of tissue distribution displayed higher sox19 expression in brain and ovary, and gonadal ontogeny showed higher expression of sox19 at 80 days post hatch (dph). Higher sox19 mRNA expression during spawning and increase of sox19 post human chorionic gonadotropin induction substantiate gonadotropin dependency. Estradiol-17β treatment but not 17α-methyl-di-hydroxy-testosterone to 50 dph common carp for inducing mono-sex, elevated sox19 expression substantially. Sox19 protein was observed in granulosa cells of the follicular layer in common carp ovary. Higher sox19 expression was detected in isolated granulosa and theca cells, in vitro. Transient gene silencing with sox19-siRNA caused downregulation of various ovary-related genes including those specific to activator protein-1 factors, fibroblast growth factors, wnt-signaling, steroidogenic genes along with certain transcription factors. Serum 17α, 20β-dihydroxy-4-pregnen-3-one and estradiol-17β reduced significantly post sox19 silencing, in vivo. Concomitantly, a decrease in aromatase activity was detected post sox19-siRNA treatment, in vivo. This study demonstrates the impact of sox19 in the regulation of common carp ovarian growth and steroidogenesis.

Metabolic Changes During Growth and Reproductive Phases in the Liver of Female Goldfish (Carassius auratus)

Hormones of the brain-pituitary-peripheral axis regulate metabolism, gonadal maturation, and growth in vertebrates. In fish, reproduction requires a significant energy investment to metabolically support the production of hundreds of eggs and billions of sperms in females and males, respectively. This study used an LC-MS-based metabolomics approach to investigate seasonally-related changes in metabolic profile and energy allocation patterns in female goldfish liver. We measured basal metabolic profile in female goldfish at three phases of the reproductive cycle, including 1) Maximum growth period in postovulatory regressed phase, 2) mid recrudescence in fish with developing follicles, and 3) late recrudescence when the ovary contains mature ovulatory follicles. We also investigated changes in the liver metabolism following acute treatments with GnRH and GnIH, known to be involved in controlling reproduction and growth in goldfish. Chemometrics combined with pathway-driven bioinformatics revealed significant changes in the basal and GnRH/GnIH-induced hepatic metabolic profile, indicating that metabolic energy allocation is regulated to support gonadal development and growth at different reproductive cycles. Overall, the findings support the hypothesis that hormonal control of reproduction involves accompanying metabolic changes to energetically support gonadotropic and somatotropic activities in goldfish and other oviparous vertebrates.

A New Perspective on Thyroid Hormones: Crosstalk with Reproductive Hormones in Females

Accumulating evidence has shown that thyroid hormones (THs) are vital for female reproductive system homeostasis. THs regulate the reproductive functions through thyroid hormone receptors (THRs)-mediated genomic- and integrin-receptor-associated nongenomic mechanisms, depending on TH ligand status and DNA level, as well as transcription and extra-nuclear signaling transduction activities. These processes involve the binding of THs to intracellular THRs and steroid hormone receptors or membrane receptors and the recruitment of hormone-response elements. In addition, THs and other reproductive hormones can activate common signaling pathways due to their structural similarity and shared DNA consensus sequences among thyroid, peptide, and protein hormones and their receptors, thus constituting a complex and reciprocal interaction network. Moreover, THs not only indirectly affect the synthesis, secretion, and action of reproductive hormones, but are also regulated by these hormones at the same time. This crosstalk may be one of the pivotal factors regulating female reproductive behavior and hormone-related diseases, including tumors. Elucidating the interaction mechanism among the aforementioned hormones will contribute to apprehending the etiology of female reproductive diseases, shedding new light on the treatment of gynecological disorders.

Estrogen Receptors Mediated Negative Effects of Estrogens and Xenoestrogens in Teleost Fishes-Review

Estrogen receptors (ERs) play a key role in many biochemical and physiological processes, that are involved in maintaining organism homeostasis. At the most basic level, they can be divided into nuclear estrogen receptors and membrane estrogen receptors that imply their effect in two ways: slower genomic, and faster non-genomic. In these ways, estrogens and xenoestrogens can negatively affect animal health and welfare. Most of the available literature focuses on human and mammalian physiology, and clearly, we can observe a need for further research focusing on complex mutual interactions between different estrogens and xenoestrogens in aquatic animals, primarily fishes. Understanding the mechanisms of action of estrogenic compounds on the ERs in fishes and their negative consequences, may improve efforts in environmental protection of these animals and their environment and benefit society in return. In this review, we have summarized the ER-mediated effects of xenoestrogens and estrogens on teleost fishes metabolism, their carcinogenic potential, immune, circulatory, and reproductive systems.

Analysis of neuroendocrine factors in response to conditional stress in zebrafish Danio rerio (Cypriniformes: Cyprinidae)

Challenges in the aquatic environment disrupt the homeostasis mechanisms of many teleost fishes. Induction of stress affects the circulating levels of catecholamine and has an impact on development and reproduction. It is not known how osmotic and hypoxic stress could affect the catecholamine and serotonin levels in zebrafish despite its well-known action in the vertebrate brain. This study thus investigates how serotonin (5-HT), epinephrine (E), norepinephrine (NE), and dopamine (DA) in the brain of female zebrafish respond to hypoxic (air) and osmotic conditions (salinity of 10 ppt). Analysis of zebrafish brain utilizing HPLC with PDA detector using reverse-phase PrimeSep column indicated that osmotic stress, air response and its combination modified 5-HT, NE and E levels. The tested stressors elevated 5-HT (>2.8 μM) while lowering NE (<3.00 μM) and E (<1.02 μM) levels in the brain as opposed to exposure to non-stressed fish. In addition, reproductive markers such as vitellogenin (Vtg1) and estrogen receptor (ERα) mRNA expression in the brain were up-regulated after osmotic stress, whereas air exposure down-regulated ERα mRNA expression but up-regulated Vtg1 compared to non-stressed fish. Overall, the data indicate that acute osmotic stress and air exposure that lowered catecholamine E and NE and elevated 5-HT levels could up-regulate mRNA expression of ERα and Vtg1 genes in the zebrafish brain, thus presenting evidence for a role of neurotransmitters on reproductive signals during acute conditional stress in the brain of wild zebrafish.

Our evolving understanding of how 27-hydroxycholesterol influences cancer

Cholesterol has been implicated in the pathophysiology and progression of several cancers now, although the mechanisms by which it influences cancer biology are just emerging. Two likely contributing mechanisms are the ability for cholesterol to directly regulate signaling molecules within the membrane, and certain metabolites acting as signaling molecules. One such metabolite is the oxysterol 27-hydroxycholesterol (27HC), which is a primary metabolite of cholesterol synthesized by the enzyme Cytochrome P450 27A1 (CYP27A1). Physiologically, 27HC is involved in the regulation of cholesterol homeostasis and contributes to cholesterol efflux through liver X receptor (LXR) and inhibition of de novo cholesterol synthesis through the insulin-induced proteins (INSIGs). 27HC is also a selective modulator of the estrogen receptors. An increasing number of studies have identified its importance in cancer progression of various origins, especially in breast cancer. In this review, we discuss the physiological roles of 27HC targeting these two nuclear receptors and the subsequent contribution to cancer progression. We describe how 27HC promotes tumor growth directly through cancer-intrinsic factors, and indirectly through its immunomodulatory roles which lead to decreased immune surveillance and increased tumor invasion. This review underscores the importance of the cholesterol metabolic pathway in cancer progression and the potential therapeutic utility of targeting this metabolic pathway.

Polymorphism analysis and expression profile of the estrogen receptor 2 gene in Leizhou black duck

Our previous study on the ovarian transcriptomic analysis in Leizhou black duck revealed that the ESR2 gene was involved in hormone regulation in reproduction and the estrogen signaling pathway related to reproductive performance was enriched. This suggested that ESR2 may have a functional role in the reproductive performance of the Leizhou black duck. Thus, this study aimed at evaluating the polymorphism of the ESR2 gene and its association with egg-laying traits and the distribution pattern of ESR2 mRNA in laying and non-laying Leizhou black ducks. In this study, genomic DNA was extracted from blood samples of 101 Leizhou black ducks to identify single nucleotide polymorphisms (SNPs) of the ESR2 gene to elucidate molecular markers highly associated with egg-laying traits. Four each of laying and non-laying Leizhou black ducks were selected to collect different tissues to analyze the ESR2 gene expression. A total of 23 SNPs were identified and association analysis of the single SNP sites showed that SNPs g.56805646 T>C and exon 3-20G>A were significantly (P < 0.05) associated with egg weight. Ducks with CT and AG genotypes had significantly higher (P < 0.05) egg weights than their respective other genotypes. Haplotype association analysis of g.56805646 T>C and exon 3-20G>A showed that the haplotypes were significantly associated with egg weight. Higher egg weight was seen in individuals with H3H4 haplotypes. In the hypothalamus-pituitary-gonadal (HPG) axis, the results of qRT/PCR showed that ESR2 mRNA was significantly (P < 0.05) expressed in the ovaries of both duck groups than in the hypothalamus and pituitary. In the oviduct, ESR2 was significantly (P < 0.05) higher in the infundibulum and magnum of laying and non-laying ducks respectively. This study provides a molecular marker for selecting Leizhou black ducks for egg production. In addition, it offers theoretical knowledge for studying the related biological functions of the ESR2 gene at the cellular level.

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

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

Endocrine disruption in the sub Antarctic fish Patagonotothen tessellata (Perciformes, Notothenidae) from Beagle Channel associated to anthropogenic impact

Situated in the sub-Antarctic region, Beagle Channel represents a unique marine ecosystem due to the connection between the Pacific and the Atlantic Oceans, and its proximity to the Antarctic Peninsula. Ushuaia city, the biggest settlement on the channel, exerts an increasing anthropogenic pressure by discharges of urban and industrial effluents. In the present work, we use Patagonotothen tessellata, one of the most abundant and widespread species in the channel, as a bioindicator species in order to evidence anthropic impact from Ushuaia Bay and surrounding areas. We first analyzed and characterized real time gene expression of androgen receptor, estrogen receptor and different forms of vitellogenin (VTG), under laboratory conditions. This was achieved by induction with estradiol of P. tessellata males. Then, the selected genes were used as biomarkers for an environmental biomonitoring study. Morphometric indices and circulating sex steroids (estradiol and testosterone) were also quantified in male fish collected from different sites. The qPCR analysis showed that vtgAb form is more inducible than vtgAa or vtgC forms after estrogen induction. The field survey revealed the up-regulation of vtgAb and the androgen receptor in fish from sites with higher anthropogenic influence. Sex steroids followed seasonal variations according to their reproductive cycle, with higher levels of estradiol and testosterone in winter and summer seasons. The use of biomarkers such as gene expression of VTG demonstrates that fish from Ushuaia Bay are likely to be exposed to endocrine disrupting compounds. To our knowledge, this research is the first attempt to assess the endocrine disruption associated to anthropic impact in a widespread fish of the Beagle Channel and contributes to a better understanding of the reproductive physiology of sub Antarctic ichthyofauna.

Effects of bisphenol A or diethyl phthalate on cartilage development and the swimming behavior of zebrafish (Danio rerio) through maternal exposure

Waterborne bisphenol A (BPA) and diethyl phthalate (DEP) are endocrine disruptive chemicals that impact the reproductive system of fish. The present study checks the effectiveness of the reproductive capacity on zebrafish after BPA and DEP exposure, and consequently investigates its effect on their development and the swimming behavior of its offspring. The exposure of BPA and DEP to zebrafish reveals that the levels of ovarian 17β-estradiol (E2) and relative mRNA expression (RRE) ratios (Treatment/Control) of hepatic vitellogenin (vtg1) could be induced and decreased. Liver RRE levels in estrogen receptors (ERs) are also affected. Among the ERs, esr2a significantly increased upon BPA exposure, and esr1 and esr2b decreased upon DEP exposure. In addition, the ceratohyal cartilage (CH) angle of larvae whose mothers were exposed to BPA (F-BPA) was significantly bigger, but the CH angle of larvae whose mothers were exposed to DEP (F-DEP) was significantly smaller than the control. The swimming performance of larvae from F-DEP was more compromised than the control, but the situation did not appear in the larvae from the F-BPA group. The success rate of larvae hatching from F-BPA and F-DEP was lower than control group. Moreover, the successful rate of female spawns was higher in the control group compared to the treatment groups exposed to BPA and DEP. We suggested that both maternal BPA and DEP disrupt E2 levels, and influence the CH development of larvae, resulting in a decrease in successful hatching. Only the swimming behavior of larvae from maternal DEP was disrupted.

Evaluation of the oestrogenic potential of oestrone and bisphenol-A on the reproduction of Astyanax bimaculatus males after subacute exposure

In the last decades, oestrogenic compounds have often been reported in environmentally relevant concentrations in aquatic environments around the world. Most laboratory studies of oestrogens try to understand the effects of a single contaminant, but in natural environments, the effects may be quite different due to interactions with other compounds. The present study aimed to compare the action of oestrone (E1) and bisphenol-A (BPA), acting singularly and in combination, on the spermatogenesis of Astyanax bimaculatus. After exposure to 100 ng/L of E1, BPA and a mixture of the two for 15 days, our results showed that E1 and the E1 + BPA mixture significantly altered the number of spermatogenic cells. BPA presented high cytotoxicity when compared to other treatments. Analysis of the two oestrogenic compounds suggests that the E1 + BPA mixture has no additive or synergistic effects. Together, the results of the present study indicate that endocrine-disrupting chemicals (EDCs) analysed alone may behave differently than when administered with other substances.

Roles of Estrogens in the Healthy and Diseased Oviparous Vertebrate Liver

The liver is a vital organ that sustains multiple functions beneficial for the whole organism. It is sexually dimorphic, presenting sex-biased gene expression with implications for the phenotypic differences between males and females. Estrogens are involved in this sex dimorphism and their actions in the liver of several reptiles, fishes, amphibians, and birds are discussed. The liver participates in reproduction by producing vitellogenins (yolk proteins) and eggshell proteins under the control of estrogens that act via two types of receptors active either mainly in the cell nucleus (ESR) or the cell membrane (GPER1). Estrogens also control hepatic lipid and lipoprotein metabolisms, with a triglyceride carrier role for VLDL from the liver to the ovaries during oogenesis. Moreover, the activation of the vitellogenin genes is used as a robust biomarker for exposure to xenoestrogens. In the context of liver diseases, high plasma estrogen levels are observed in fatty liver hemorrhagic syndrome (FLHS) in chicken implicating estrogens in the disease progression. Fishes are also used to investigate liver diseases, including models generated by mutation and transgenesis. In conclusion, studies on the roles of estrogens in the non-mammalian oviparous vertebrate liver have contributed enormously to unveil hormone-dependent physiological and physiopathological processes.

Reproductive potential of mosquitofish is reduced by the masculinizing effect of a synthetic progesterone, gestodene: Evidence from morphology, courtship behaviour, ovary histology, sex hormones and gene expressions

The ever-increasing use of synthetic hormones, especially progestins, for medical applications has drawn growing concerns due to their potential endocrine disrupting effects that may diminish the reproductive outputs of aquatic organisms. Using mosquitofish (Gambusia affinis) as a model species, we tested whether gestodene (GES), a commonly used progestin, can alter the expressions of genes associated with sex hormone synthesis and cause ensuing changes in morphological features, courtship behaviour and oocyte development. After exposing to GES at environmentally relevant concentrations (2.96, 32.9 and 354 ng L^-1) for 40 days, we found that GES, especially at 354 ng L^-1, induced masculinization of female fish, indicated by the reduced body weight to length ratio and development of gonopodia (i.e. anal fins of male fish). Thus, the males showed less intimacy and mating interest towards the GES-exposed females, indicated by the reduced time spent on attending, following and mating behaviours. While oocyte development was seemingly unaffected by GES, spermatogonia were developed in the ovary. All the aforementioned masculinizing effects of GES were associated with the increased testosterone level and decreased estradiol level, driven by upregulating androgen receptor genes (Arα and Arβ). Overall, our findings suggest that progestins could undermine the reproductive potential of aquatic organisms and hence their persistence in the progestin-contaminated environment.

DNA methylation and expression of estrogen receptor alpha in fathead minnows exposed to 17α-ethynylestradiol

The gene expression response thought to underlie the negative apical effects resulting from estrogen exposure have been thoroughly described in fish. Although epigenetics are believed to play a critical role translating environmental exposures into the development of adverse apical effects, they remain poorly characterized in fish species. This study investigated alterations of DNA methylation of estrogen receptor alpha (esr1) in brain and liver tissues from 8 to 10 month old male fathead minnows (Pimephales promelas) after a 2d exposure to either 2.5 ng/L or 10 ng/L 17α-ethynylestradiol (EE2). Changes in the patterns of methylation were evaluated using targeted deep sequencing of bisulfite treated DNA in the 5' region of esr1. Methylation and gene expression were assessed at 2d of exposure and after a 7 and 14d depuration period. After 2d EE2 exposure, males exhibited significant demethylation in the 5' upstream region of esr1 in liver tissue, which was inversely correlated to gene expression. This methylation pattern reflected what was seen in females. No gene body methylation (GBM) was observed for liver of exposed males. Differential methylation was observed for a single upstream CpG site in the liver after the 14d depuration. A less pronounced methylation response was observed in the upstream region in brain tissue, however, several CpGs were necessarily excluded from the analysis. In contrast to the liver, a significant GBM response was observed across the entire gene body, which was sustained until at least 7d post-exposure. No differential expression was observed in the brain, limiting functional interpretation of methylation changes. The identification of EE2-dependent changes in methylation levels strongly suggests the importance of epigenetic mechanisms as a mediator of the organismal response to environmental exposures and the need for further characterization of the epigenome. Further, differential methylation following depuration indicates estrogenic effects persist well after the active exposure, which has implications for the risk posed by repeated exposures..

Case Study in 21st Century Ecotoxicology: Using In Vitro Aromatase Inhibition Data to Predict Short-Term In Vivo Responses in Adult Female Fish

The present study evaluated whether in vitro measures of aromatase inhibition as inputs into a quantitative adverse outcome pathway (qAOP) construct could effectively predict in vivo effects on 17β-estradiol (E2) and vitellogenin (VTG) concentrations in female fathead minnows. Five chemicals identified as aromatase inhibitors in mammalian-based ToxCast assays were screened for their ability to inhibit fathead minnow aromatase in vitro. Female fathead minnows were then exposed to 3 of those chemicals: letrozole, epoxiconazole, and imazalil in concentration-response (5 concentrations plus control) for 24 h. Consistent with AOP-based expectations, all 3 chemicals caused significant reductions in plasma E2 and hepatic VTG transcription. Characteristic compensatory upregulation of aromatase and follicle-stimulating hormone receptor (fshr) transcripts in the ovary were observed for letrozole but not for the other 2 compounds. Considering the overall patterns of concentration-response and temporal concordance among endpoints, data from the in vivo experiments strengthen confidence in the qualitative relationships outlined by the AOP. Quantitatively, the qAOP model provided predictions that fell within the standard error of measured data for letrozole but not for imazalil and epoxiconazole. However, the inclusion of measured plasma concentrations of the test chemicals as inputs improved model predictions, with all predictions falling within the range of measured values. Results highlight both the utility and limitations of the qAOP and its potential use in 21st century ecotoxicology. Environ Toxicol Chem 2021;40:1155-1170. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Distribution and expression of GnRH 1, kiss receptor 2, and estradiol α and ß receptors in the anterior brain of females of Chirostoma humboldtianum

Reproduction in vertebrates is a complex process regulated by many hormones, and by paracrine factors and their receptors. This study aimed to examine the expression of pjGonadotropin-releasing hormone (GnRH 1), the kisspeptin receptor 2 (kissr2), and estradiol receptors α and β (ER α and ER β) during different stages of the sexual cycle and their distribution within the anterior brain of females of Chirostoma humboldtianum. Among these molecules, the kissr2 showed the maximal variation in expression, while GnRH 1 showed minimal variation of expression, and ERβ and ERα had intermediate variation of expression. The distribution of these molecules in the anterior brain was consistent with their levels of expression; kissr2 was widely distributed throughout the telencephalon and diencephalon, while ER and GnRH 1 showed more restricted distributions. No coexpression of kissr2 and ER in GnRH 1ergic neurons, suggesting that regulation of this GnRH variant is indirectly mediated by kisspeptin and estradiol.

Relationship between gut microbiota and host-metabolism: Emphasis on hormones related to reproductive function

It has been well recognized that interactions between the gut microbiota and host-metabolism have a proven effect on health. The gut lumen is known for harboring different bacterial communities. Microbial by-products and structural components, which are derived through the gut microbiota, generate a signaling response to maintain homeostasis. Gut microbiota is not only involved in metabolic disorders, but also participates in the regulation of reproductive hormonal function. Bacterial phyla, which are localized in the gut, allow for the metabolization of steroid hormones through the stimulation of different enzymes. Reproductive hormones such as progesterone, estrogen and testosterone play a pivotal role in the successful completion of reproductive events. Disruption in this mechanism may lead to reproductive disorders. Environmental bacteria can affect the metabolism, and degrade steroid hormones and their relevant compounds. This behavior of the bacteria can safely be implemented to eliminate steroidal compounds from a polluted environment. In this review, we summarize the metabolism of steroid hormones on the regulation of gut microbiota and vice-versa, and also examined the significant influence this process has on various events of reproductive function. Altogether, the evidence suggests that steroid hormones and gut microbiota exert a central role in the modification of host bacterial action and impact the reproductive efficiency of animals and humans.

Hepatic expression profiles of three subtypes of vitellogenin and estrogen receptor during vitellogenesis in cultured female yellowtail

Estradiol-17β (E₂) promotes the transcription of vitellogenin (Vtg) via nuclear estrogen receptor (ER). Three Vtg (VtgAa, VtgAb, and VtgC) and ER subtypes (ERα, ERβ1, and ERβ2) have been reported in perciform fish; however, the relationship between the transcriptional regulation of Vtg and ER subtypes remains unclear. Molecular characterization was performed and the expression profiles of vtg and er subtypes were investigated to elucidate mechanisms of synthesis of vtg subtypes in yellowtail, Seriola quinqueradiata. Primary structures and promoter regions were revealed in three subtypes of vtg and er, and all the vtg subtypes and erα were presumed to be estrogen-responsive genes. When all vtg subtypes were expressed significantly in the liver, hepatic expression levels of all the er subtypes also increased. Conversely, although plasma E₂ concentrations did not change significantly, the concentrations were high at the same time. Hepatic expression levels of all the vtg subtypes were highly correlated with hepatic erα, rather than with hepatic erβ subtypes and plasma E₂. A high positive correlation was also observed between erβ1 and β2, which seemed to be highly expressed at the pre- and late-vitellogenic stages. The results of the present study suggest that the transcription of the three vtg subtypes are regulated by three ER subtypes jointly, and ERα is the key transcription factor regulating the three vtg subtypes in yellowtail.

Effect of short-term intermittent exposure to waterborne estradiol on the reproductive physiology of the round goby (Neogobius melanostomus)

The objective of this study was to determine how the short-term exposure to a supraphysiological concentration of waterborne 17β-estradiol (E₂) influences on melatonin (Mel) and thyroxine (T₄) concentrations in plasma and E₂ and 11-ketotestosterone (11-KT) concentrations in plasma and gonads in both sexes of round goby (Neogobius melanostomus) during the pre-spawning, spawning, late spawning and non-spawning phases. The experimental protocol was based on short-term, repeated exposures of fish to a supraphysiological dose of waterborne E₂. Mel level was unchanged on exposure to E₂ during the investigated phases, and its role in determining a time frame for spawning in both sexes of round goby seems to be stable in those conditions. T₄ and sex steroids (E₂ and 11-KT) were sensitive to the exposure of E₂, and those changes influence gonads by accelerating oocyte development, ovulation and regression and inhibiting spermatogenesis in this species. The results demonstrate that the physiological responses of fish in all investigated phases were altered over a short window of exposure, indicating that short-term exposure to a supraphysiological dose of E₂ may impact fish in the wild. Furthermore, round goby can be recommended as a very suitable model for studying endocrine disruptors, which is sensitive to even short exposure to E₂.

Nonylphenol ethoxylates biodegradation increases estrogenicity of textile wastewater in biological treatment systems

The formation of estrogenic intermediates, i.e. nonylphenol diethoxylate (NP2EO), nonylphenol monoethoxylate (NP1EO), and nonylphenol (NP), following nonylphenol ethoxylates (NPEOs) biodegradation in textile wastewater raises concerns about its endocrine disruptive activity, but the estrogenicity changes of textile wastewater throughout biological treatment processes remain unknown. In the present study, the estrogenicity of textile wastewater sampled from 10 wastewater treatment plants (WWTPs) were investigated using the reporter gene-based T47D-KBluc bioassay. Results showed that the estrogenicity of the textile wastewater significantly increased after either anaerobic or aerobic treatment in all WWTPs, with an average fold change of 3.21, although traditional pollutants were effectively removed. The estradiol equivalents of the effluent (ranging from 1.50 to 4.12 ng-E2/L) were generally higher than published effect based trigger values, indicating an increased risk for the receiving waters. Removal efficiency was high (84.46%) for NPEOs, but was low for NP2EO and NP1EO in the biological treatment processes. Nevertheless, NP had increased concentrations after the treatment. Bioanalytical equivalent concentration of the textile wastewater and that of NP2EO, NP1EO, and NP showed a good linear correlation, of which NP alone contributed more than 70% to the observed estrogenicity. Extending hydraulic retention time was found effective in reducing the estrogenicity as it allows relatively complete degradation of NP, which was further confirmed by running lab-scale A/O reactors fed with NP10EO. The results may extend our knowledge regarding the estrogenicity of textile wastewater and its reduction technologies used in WWTPs.

Identification and structural characterization of the factors involved in vitellogenesis and its regulation in the African Osteoglossiforme of aquacultural interest Heterotis niloticus (Cuvier, 1829)

The African bonytongue (Heterotis niloticus) is an excellent candidate for fish farming because it has outstanding biological characteristics and zootechnical performances. However, the absence of sexual dimorphism does not favor its reproduction in captivity or the understanding of its reproductive behavior. Moreover, no molecular data related to its reproduction is yet available. This study therefore focuses on the structural identification of the different molecular actors of vitellogenesis expressed in the pituitary gland, the liver and the ovary of H. niloticus. A transcriptomic approach based on de novo RNA sequencing of the pituitary gland, ovary and liver of females in vitellogenesis led to the creation of three transcriptomes. In silico analysis of these transcriptomes identified the sequences of pituitary hormones such as prolactin (PRL), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and their ovarian receptors (PRLR, FSHR, LHR). In the liver and ovary, estrogen receptors (ER) beta and gamma, liver vitellogenins (VtgB and VtgC) and their ovarian receptors (VLDLR) were identified. Finally, the partial transcript of an ovarian Vtg weakly expressed compared to hepatic Vtg was identified based on structural criteria. Moreover, a proteomic approach carried out from mucus revealed the presence of one Vtg exclusively in females in vitellogenesis. In this teleost fish that does not exhibit sexual dimorphism, mucus Vtg could be used as a sexing biomarker based on a non-invasive technique compatible with the implementation of experimental protocols in vivo.

Reproductive viability of paradoxically masculinised Gambusia holbrooki generated following diethylstilbestrol (DES) treatment

Hormonal sex reversal can produce monosex fish stocks and provide insights into their gamity and reproductive physiology. However, paradoxical effects have been reported in several fish species that remain largely ignored as anomalies, particularly those of masculinisation. As a first step, this study examined reproductive viability of paradoxically masculinised Gambusia holbrooki produced following oral administration (20-100 mg/kg feed) of a feminizing hormone diethylstilbestrol (DES). Contrary to expectation, all treatment groups produced 100% male populations. Survival, mating behaviour, gamete production, breeding output as well as expression of anti-Mullerian hormone (amh), ovarian (cyp19a1a) and brain (cyp19a1b) aromatase of masculinised fish were also examined. Survival (≤ 54.1 ± 7.3%) at termination of DES treatment was significantly lower compared with controls (88.6 ± 4.3%) but remained unaffected post treatment. Gonopodium thrusting frequency (33 ± 9.8 per 10 min) was not significantly different to untreated males just as sperm abundance (3.9 ± 1.5 × 10⁸/male) and their motility (88.6 ± 29.1%). Importantly, paradoxically masculinised fish mated with virgin females and produced clutch sizes (22 ± 4) and progeny survival (87.0 ± %) that were comparable to that of untreated males. Masculinised testes showed high amh and low cyp19a1a expression, a pattern resembling those of untreated males. Production of paradoxically sex-reversed males with a capability to produce viable offspring has not been reported previously in this or other fish species. The outcomes support a feed-back regulation of oestrogenic pathways in this viviparous fish and could be useful for ecological applications such as controlling invasive fish populations.

Estrogen Receptors and Estrogen-Induced Uterine Vasodilation in Pregnancy

Normal pregnancy is associated with dramatic increases in uterine blood flow to facilitate the bidirectional maternal–fetal exchanges of respiratory gases and to provide sole nutrient support for fetal growth and survival. The mechanism(s) underlying pregnancy-associated uterine vasodilation remain incompletely understood, but this is associated with elevated estrogens, which stimulate specific estrogen receptor (ER)-dependent vasodilator production in the uterine artery (UA). The classical ERs (ERα and ERβ) and the plasma-bound G protein-coupled ER (GPR30/GPER) are expressed in UA endothelial cells and smooth muscle cells, mediating the vasodilatory effects of estrogens through genomic and/or nongenomic pathways that are likely epigenetically modified. The activation of these three ERs by estrogens enhances the endothelial production of nitric oxide (NO), which has been shown to play a key role in uterine vasodilation during pregnancy. However, the local blockade of NO biosynthesis only partially attenuates estrogen-induced and pregnancy-associated uterine vasodilation, suggesting that mechanisms other than NO exist to mediate uterine vasodilation. In this review, we summarize the literature on the role of NO in ER-mediated mechanisms controlling estrogen-induced and pregnancy-associated uterine vasodilation and our recent work on a “new” UA vasodilator hydrogen sulfide (H₂S) that has dramatically changed our view of how estrogens regulate uterine vasodilation in pregnancy.

Critical Review of Read-Across Potential in Testing for Endocrine-Related Effects in Vertebrate Ecological Receptors

Recent regulatory testing programs have been designed to evaluate whether a chemical has the potential to interact with the endocrine system and could cause adverse effects. Some endocrine pathways are highly conserved among vertebrates, providing a potential to extrapolate data generated for one vertebrate taxonomic group to others (i.e., biological read-across). To assess the potential for biological read-across, we reviewed tools and approaches that support species extrapolation for fish, amphibians, birds, and reptiles. For each of the estrogen, androgen, thyroid, and steroidogenesis (EATS) pathways, we considered the pathway conservation across species and the responses of endocrine-sensitive endpoints. The available data show a high degree of confidence in the conservation of the hypothalamus-pituitary-gonadal axis between fish and mammals and the hypothalamus-pituitary-thyroid axis between amphibians and mammals. Comparatively, there is less empirical evidence for the conservation of other EATS pathways between other taxonomic groups, but this may be due to limited data. Although more information on sensitive pathways and endpoints would be useful, current developments in the use of molecular target sequencing similarity tools and thoughtful application of the adverse outcome pathway concept show promise for further advancement of read-across approaches for testing EATS pathways in vertebrate ecological receptors. Environ Toxicol Chem 2020;39:739-753. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Mummichog (Fundulus heteroclitus) are less sensitive to 17α-ethinylestradiol (EE2) than other common model teleosts: A comparative review of reproductive effects

The environmental estrogen 17α-ethinylestradiol (EE₂) will depress or completely inhibit egg production in many common model teleosts at low concentrations (≤0.5 ng/L; Runnalls et al., 2015). This inhibition is not seen in the estuarine killifish, or mummichog (Fundulus heteroclitus), even when exposed to 100 ng/L EE₂. This relative insensitivity to EE₂ exposure indicates species-specific mechanisms for compensating for exogenous estrogenic exposure. This review compares various reproductive responses elicited by EE₂ in mummichog to other common model teleosts, such as zebrafish (Danio rerio) and fathead minnow (Pimephales promelas), identifying key endpoints where mummichog differ from other studied fish. For example, EE₂ accumulates primarily in the liver/gall bladder of mummichog, which is different than zebrafish and fathead minnow in which accumulation is predominantly in the carcass. Despite causing species-specific differences in fecundity, EE₂ has been shown to consistently induce hepatic vitellogenin in males and cause feminization/sex reversal during gonadal differentiation in larval mummichog, similar to other species. In addition, while gonadal steroidogenesis and plasma steroid levels respond to exogenous EE_2, it is generally at higher concentrations than observed in other species. In mummichog, production of 17β-estradiol (E₂) by full grown ovarian follicles remains high; unlike other teleost models where E₂ synthesis decreases as 17α,20β-dihydroxy-4-prenen-3-on levels increase to induce oocyte maturation. New evidence in mummichog indicates some dissimilarity in gonadal steroidogenic gene expression responses compared to gene expression responses in zebrafish and fathead minnow exposed to EE₂. The role of ovarian physiology continues to warrant investigation regarding the tolerance of mummichog to exogenous EE₂ exposure. Here we present a comprehensive review, highlighting key biological differences in response to EE₂ exposure between mummichog and other commonly used model teleosts.

Embryo/larval toxicity and transcriptional effects in zebrafish (Danio rerio) exposed to endocrine active riverbed sediments

Sediment toxicity plays a fundamental role in the health of inland fish communities; however, the assessment of the hazard potential of contaminated sediments is not a common objective in environmental diagnostics or remediation. This study examined the potential of transcriptional endpoints investigated in zebrafish (Danio rerio) exposed to riverbed sediments in ecotoxicity testing. Embryo-larval 10-day tests were conducted on sediment samples collected from five sites (one upstream and four downstream of the city of Milan) along a polluted tributary of the Po River, the Lambro River. Sediment chemistry showed a progressive downstream deterioration in river quality, so that the final sampling site showed up to eight times higher concentrations of, for example, triclosan, galaxolide, PAH, PCB, BPA, Ni, and Pb, compared with the uppermost site. The embryo/larval tests showed widespread toxicity although the middle river sections evidenced worse effects, as evidenced by delayed embryo development, hatching rate, larval survival, and growth. At the mRNA transcript level, the genes encoding biotransformation enzymes (cyp1a, gst, ugt) showed increasing upregulations after exposure to sediment from further downstream sites. The genes involved in antioxidant responses (sod, gpx) suggested that more critical conditions may be present at downstream sites, but even upstream of Milan there seemed to be some level of oxidative stress. Indirect evidences of potential apoptotic activity (bcl2/bax < 1) in turn suggested the possibility of genotoxic effects. The genes encoding for estrogen receptors (erα, erβ1, erβ2) showed exposure to (xeno)estrogens with a progressive increase after exposure to sediments from downstream sites, paralleled by a corresponding downregulation of the ar gene, likely related to antiandrogenic compounds. Multiple levels of thyroid disruption were also evident particularly in downstream zebrafish, as for thyroid growth (nkx2.1), hormone synthesis and transport (tg, ttr, d2), and signal transduction (trα, trβ). The inhibition of the igf2 gene reasonably reflected larval growth inhibitions. Although none of the sediment chemicals could singly explain fish responses, principal component analysis suggested a good correlation between gene transcripts and the overall trend of contamination. Thus, the combined impacts from known and unknown covarying chemicals were proposed as the most probable explanation of fish responses. In summary, transcriptional endpoints applied to zebrafish embryo/larval test can provide sensitive, comprehensive, and timeliness information which may greatly enable the assessment of the hazard potential of sediments to fish, complementing morphological endpoints and being potentially predictive of longer studies.

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

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

Changes in vitellogenin and estrogen receptor expression and 17β-estradiol concentration in male juvenile tilapia can be used to evaluate endocrine-disrupting chemicals

The effects of endocrine disruption with respect to potential human toxicities have been extensively evaluated to date. However, the standard testing methods used have not always taken the most pertinent approach. In this study, we used juvenile male tilapia (Oreochromis niloticus) as an animal model to test for endocrine disruption by chemicals. We measured 17β-estradiol (E2) concentrations, and the mRNA relative expression ratio (RER; treatment/control) of vitellogenin (vtg2) and estrogen receptors (ERs) to assess whether the effluent concentration of selected plasticizers disrupt E2 function in fish. We found that the vtg2 RER was significantly increased after exposure to 2.52 nM E2 for 5 days, 0.438 μM of bisphenol A (BPA) for 7 days, or 2.865 μM Cd²⁺ for 7 days. These data support vtg2 transcript level as a sensitive biomarker to evaluate contamination of water by endocrine disrupting chemicals (EDCs). However, vtg2 expression did not respond to fluctuations of E2 concentrations in the tilapia juveniles exposed to selected plasticizers. However, the RER of three types of ERs appeared to change dramatically upon exposure to plasticizers. ERα significantly increased, but ERβ2 decreased with 3.6 μM DEP exposure. Both ERα and ERβ2 decreased significantly after 1.44 μM DIBP exposure. We suggest that changes of vtg2 mRNA RER, E2 levels and ERs mRNA expression should be taken into consideration at the same time to determine if chemical contaminants in the water are endocrine disrupters.