Evidence of gender-and tissue-specific promoter methylation and the potential for ethinylestradiol-induced changes in Japanese medaka (Oryzias latipes) estrogen receptor and aromatase genes

Multigenerational impacts of EE2 on reproductive fitness and immune competence of marine medaka

Estrogenic endocrine disrupting chemicals (EEDC) have been suspected to impact offspring in a transgenerational manner via modifications of the germline epigenome in the directly exposed generations. A holistic assessment of the concentration/ exposure duration-response, threshold level, and critical exposure windows (parental gametogenesis and embryogenesis) for the transgenerational evaluation of reproduction and immune compromise concomitantly will inform the overall EEDC exposure risk. We conducted a multigenerational study using the environmental estrogen, 17α-ethinylestradiol (EE2), and the marine laboratory model fish Oryzias melastigma (adult, F0) and their offspring (F1-F4) to identify transgenerationally altered offspring generations and phenotype persistence. Three exposure scenarios were used: short parental exposure, long parental exposure, and a combined parental and embryonic exposure using two concentrations of EE2 (33ng/L, 113ng/L). The reproductive fitness of fish was evaluated by assessing fecundity, fertilization rate, hatching success, and sex ratio. Immune competence was assessed in adults via a host-resistance assay. EE2 exposure during both parental gametogenesis and embryogenesis was found to induce concentration/ exposure duration-dependent transgenerational reproductive effects in the unexposed F4 offspring. Furthermore, embryonic exposure to 113 ng/L EE2 induced feminization of the directly exposed F1 generation, followed by subsequent masculinization of the F2 and F3 generations. A sex difference was found in the transgenerationally impaired reproductive output with F4 females being sensitive to the lowest concentration of EE2 (33 ng/L) upon long-term ancestral parent exposure (21 days). Conversely, F4 males were affected by ancestral embryonic EE2 exposure. No definitive transgenerational impacts on immune competence were identified in male or female offspring. In combination, these results indicate that EEDCs can be transgenerational toxicants that may negatively impact the reproductive success and population sustainability of fish populations.

Study of DNA methylation of hsd17β, er and reproductive endocrine disrupting effects in female Chlamys farreri under benzo[a]pyrene stress

Benzo[a]pyrene (B[a]P) is one kind of persistent organic pollutants (POPs) in the marine environment which has multiple toxic effects. However, epigenetic studies correlated with reproductive endocrine disruption in invertebrates have not been explored. In our study, Chlamys farreri in the mature stage were exposed to B[a]P (0, 0.4, 2 and 10 μg/L) for 5 and 10 d to explore the effects on reproductive endocrine and DNA methylation. The results proved that B[a]P stress significantly restrained the growth of mature oocytes, reduced the content of sex hormones, and affected the expression of genes related to ovarian development. Histological observation showed that the ovarian microstructure was damaged. The detection of SAM/SAH, dnmts, GNMT in the ovary showed that the level of global DNA methylation fluctuated. Significant hypermethylation of the hsd17β promoter region in the ovary was associated with a significant downregulation of its gene expression. In summary, our results suggested that exposure to B[a]P might affect DNA methylation to regulate key reproductive genes, interfere with the synthesis of sex hormones, and inhibit ovarian development. These findings provide a basis for a better understanding of how epigenetic mechanisms are involved in the response of marine invertebrates to POPs stress, opening up new avenues for incorporating environmental epigenetic approaches into marine invertebrate management and conservation plans.

Soy Isoflavones Induce Feminization of Japanese Eel (Anguilla japonica)

Under aquaculture conditions, Japanese eels (Anguilla japonica) produce a high percentage of males. However, females gain higher body weight and have better commercial value than males, and, therefore, a high female ratio is required in eel aquaculture. In this study, we examined the effects of isoflavones, genistein, and daidzein on sex differentiation and sex-specific genes of eels. To investigate the effects of these phytoestrogens on the gonadal sex, we explored the feminizing effects of soy isoflavones, genistein, and daidzein in a dose-dependent manner. The results showed that genistein induced feminization more efficiently than daidzein. To identify the molecular mechanisms of sex-specific genes, we performed a comprehensive expression analysis by quantitative real-time PCR and RNA sequencing. Phenotypic males and females were produced by feeding elvers a normal diet or an estradiol-17β- or genistein-treated diet for 45 days. The results showed that female-specific genes were up-regulated and male-specific genes were down-regulated in the gonads, suggesting that genistein induces feminization by altering the molecular pathways responsible for eel sex differentiation.

The role of plastic and evolved DNA methylation in parallel adaptation of threespine stickleback (Gasterosteus aculeatus)

Repeated phenotypic patterns among populations undergoing parallel evolution in similar environments provide support for the deterministic role of natural selection. Epigenetic modifications can mediate plastic and evolved phenotypic responses to environmental change and might make important contributions to parallel adaptation. While many studies have explored the genetic basis of repeated phenotypic divergence, the role of epigenetic processes during parallel adaptation remains unclear. The parallel evolution of freshwater ecotypes of threespine stickleback fish (Gasterosteus aculeatus) following colonization of thousands of lakes and streams from the ocean is a classic example of parallel phenotypic and genotypic adaptation. To investigate epigenetic modifications during parallel adaptation of threespine stickleback, we reanalysed three independent data sets that investigated DNA methylation variation between marine and freshwater ecotypes. Although we found widespread methylation differentiation between ecotypes, there was no significant tendency for CpG sites associated with repeated methylation differentiation across studies to be parallel versus nonparallel. To next investigate the role of plastic versus evolved changes in methylation during freshwater adaptation, we explored if CpG sites exhibiting methylation plasticity during salinity change were more likely to also show evolutionary divergence in methylation between ecotypes. The directions of divergence between ecotypes were generally in the opposite direction to those observed for plasticity when ecotypes were challenged with non-native salinity conditions, suggesting that most plastic responses are likely to be maladaptive during colonization of new environments. Finally, we found a greater number of CpG sites showing evolved changes when ancestral marine ecotypes are acclimated to freshwater environments, whereas plastic changes predominate when derived freshwater ecotypes transition back to their ancestral marine environments. These findings provide evidence for an epigenetic contribution to parallel adaptation and demonstrate the contrasting roles of plastic and evolved methylation differences during adaptation to new environments.

Assessing integrated biomarkers of triplefin fish Forsterygion capito inhabiting contaminated marine water - A multivariate approach

The presence of multiple chemicals in aquatic ecosystems makes evaluation of their real impact on the biota difficult. Integrated biomarkers are therefore needed to evaluate how these chemicals contribute to environmental degradation. The aims of the present study were to evaluate responses to and effects of marine pollution using a series of biomarkers through multivariate analyses. Transcriptional responses of cyp1a (cytochrome P450), mt (metallothionein), vtg (vitellogenin) and cyp19b (cytochrome P450 aromatase); branchial and hepatic histological alterations; and Fulton condition factors (CF) were evaluated, as well as the metals and polycyclic aromatic hydrocarbons present in Forsterygion capito in Auckland, New Zealand. Sites were selected along a contamination gradient: four highly contaminated sites and four less contaminated. Molecular responses with a higher relative expression of the mt and cyp1a genes were detected at a highly contaminated site (Panmure). Several histological lesion types were found in the livers of fish inhabiting both types of sites, but gill lesions were present primarily at highly contaminated sites. In terms of general health status, the lowest CF values were overwhelmingly found in fish from the same site (Panmure). The multivariate approach revealed that telangiectasia and hyperplasia were associated with the presence of chemicals, and these showed negative associations with the CF values, with fish from three highly contaminated sites being most affected. In conclusion, the multivariate approach helped to integrate these biological markers in this blennioid fish, thus providing a more holistic view of the complex chemical mixtures involved. Future studies should implement these analyses.

Potential role of DNA methylation of cyp19a1a promoter during sex change in protogynous orange-spotted grouper, Epinephelus coioides

Estrogen has a pivotal role in early female differentiation and further ovarian development. Aromatase (Cyp19a) is responsible for the conversion of androgens to estrogens in vertebrates. In teleosts, cyp19a1a and it paralog cyp19a1b are mainly expressed in the ovary and hypothalamus, respectively. Decreased plasma estrogen levels and lower cyp19a1a expression are associated with the initiation of female-to-male sex change in protogynous grouper. However, an 17α-methyltestosterone (MT)-induced the sex change from a female to a precocious male is a transient phase, and a reversible sex change (induced male-to-female) occurs after chemical withdrawal. Thus, we used this characteristic to study the epigenetic modification of cyp19a1a promoter in orange-spotted grouper. CpG-rich region with a CpG island is located on the putative regulatory region of distal cyp19a1a promoter. Our results showed that cyp19a1a promoter exhibited tissue-specific methylation status. Low methylation levels of distal cyp19a1a promoter and hypomethylated (0-40%) clones of cyp19a1a promoter region were widely observed in the ovary but not shown in testis and other tissues. In femaleness, higher numbers of hypomethylated clones of cyp19a1a promoter region were observed in the vitellogenic oocyte stage compared to the primary oocyte stage. Furthermore, decreased numbers of hypomethylated clones of cyp19a1a promoter region were associated with the maleness during the female-to-male sex change. DNA methylation inhibitor (5-aza-2'-deoxycytidine) delayed the spermatogenesis process (according to germ cell stage and numbers: by decrease of sperm and increase of spermatocytes) but did not influence the reversed sex change in MT-induced bi-directional sex change. These results suggest that epigenetic modification of cyp19a1a promoter may play an important role during the sex change in orange-spotted grouper.

Early-life phenanthrene exposure inhibits reproductive ability in adult zebrafish and the mechanism of action

Phenanthrene (Phe) is a representative polycyclic aromatic hydrocarbon, and its ubiquity makes the risk assessment of Phe in aquatic ecosystems important. To assess the long-term effects of early-life Phe exposure on fish, the embryos of the model organism, zrbrafish (Danio rerio) were exposed to Phe at 0.05, 0.5, 5 and 50 nmol/L for 96 h and then raised to adulthood in clean water. Gonad development and reproductive functions were investigated in 120 day-old fish. The results showed that the percentage of spermatozoa in males and mature oocytes in females were decreased. The spawned egg numbers and the fertilization rate were reduced when the treated fish were mated with untreated fish. The transcription of genes involved in the brain-pituitary-gonadal axis was downregulated. The levels of both 17β-estradiol and testosterone were significantly decreased in the 5 and 50 nmol/L groups compared with the control group. The methylation levels in the promotor of gnrh3 (encoding gonadotropin releasing hormone) were significantly elevated in the adult fish in the 5 and 50 nmol/L treatments, which might be associated with the downregulation of gnrh3 transcription. These results suggested that embryonic exposure to Phe can inhibit the reproductive ability of adult fish, which should be adequately emphasized in its risk assessment.

Assessment of 17α-ethinylestradiol effects in Daphnia magna: life-history traits, biochemical and genotoxic parameters

The occurrence of pharmaceuticals in aquatic ecosystems and the need to study them have increased over the years since they enter continuously the environment. Besides, these compounds are not intended for applications with environmental purposes, and therefore, little is known about their ecological effects, particularly in non-target organisms, as invertebrate species. Inside these substances, endocrine disrupting compounds (EDCs) have recently come into the limelight, due to environmental concentrations and consequently their detrimental effects on different organisms. 17α-ethinylestradiol (EE2) has been detected in the aquatic environment in various locations around the globe since it is the main synthetic hormone used as a female oral contraceptive and is also applied in veterinary medicine and animal production. The present study was intended to assess the chronic effects of EE2, in the non-target organism as Daphnia magna. Thus, to analyze the individual and subindividual impact, this aquatic organism was chronically exposed (21 days) to 0.00 (control group), 0.10, 1.00, 10.0, and 100 μg/L of EE2. Results here obtained demonstrated that D. magna exposed to the EE2 concentrations had significant effects in individual (life-history) and sub-individual (biochemical levels) parameters. Alterations as anticipation in the age at first reproduction, a decrease of the growth rate, oxidative stress, and lipid peroxidation were detected, as well as genotoxic damage. Therefore, it was possible to infer that EE2 can disrupt several metabolic pathways and physiological functions of D. magna, since EE2 demonstrated ecotoxicity, at environmentally relevant concentrations. This work reinforces the importance of examining the effects of more relevant exposures (more prolonged and with ecologically pertinent concentrations) of potential endocrine disruptors like EE2, to the freshwater organisms and ecosystem.

Dicamba elevates concentrations of S-adenosyl methionine but does not induce oxidative stress or alter DNA methylation in rainbow trout (Oncorhynchus mykiss) hepatocytes

Dicamba is a benzoic acid herbicide used to target woody and broadleaf weeds in industrial, domestic, and municipal spheres. Because of its widespread use, dicamba is frequently detected in surface waters near sites of application. However, little is known regarding the effects of dicamba on freshwater fishes. In the present study, primary cultures of hepatocytes from rainbow trout (Oncorhynchus mykiss) were exposed to either an environmentally relevant (0.22 or 2.2 μg L^-1) or supra-environmental (22 μg L^-1) concentration of dicamba for 48 h to investigate if oxidative stress is a mechanism of toxicity. mRNA abundances of genes involved in the response to oxidative stress, levels of lipid peroxidation, and concentrations of glutathione and s-adenosyl methionine (SAM) were quantified. Results indicate that dicamba does not induce oxidative stress. However, exposure to 2.2 μg L^-1 of dicamba did cause a 5.24-fold increase in concentrations of SAM. To investigate the mechanisms of increased SAM, effects of dicamba on global and genome-wide DNA methylation were quantified. Dicamba did not cause changes to DNA methylation. Overall, dicamba was not acutely toxic to hepatocytes and did not cause oxidative stress or changes in DNA methylation at environmentally relevant concentrations.

Adverse effects of perfluoroalkyl acids on fish and other aquatic organisms: A review

Perfluoroalkyl acids (PFAAs) have been widely used in many industrial and consumer products. They have been detected ubiquitously in ambient water along with other environmental matrices, and their adverse effects on aquatic organisms have been a subject of active investigation. Here, we intended to summarize and synthesize the existing body of knowledge on PFAA toxicity through an extensive literature review, and shed light on areas where further research is warranted. PFAA toxicity appears to be influenced by the sex and developmental stages of aquatic organisms, but not significantly by exposure route. PFAA-induced aquatic toxicity could be classified as metabolism disturbance, reproduction disruption, oxidative stress, developmental toxicity, thyroid disruption, etc. At the molecular level, these responses can be initiated by key events, such as nuclear receptor activation, reactive oxygen species induction, or interaction with a membrane, followed by a cascade of downstream responses. PFAA-induced toxicity involves diverse metabolic processes, and therefore elucidating crosstalk or interactions among diverse metabolic pathways is a challenging task. In the presence of other chemicals, PFAAs can function as agonists or antagonists, resulting in different directions of combined toxicity. Therefore, mixture toxicity with other groups of chemicals is another research opportunity. Experimental evidence supports the trans-generational toxicity of PFAAs, suggesting that their long-term consequences for aquatic ecosystems should become of concern. A recent global ban of several PFAAs resulted in an increasing dependence on PFAA alternatives. The lack of sufficient toxicological information on this emerging group of chemicals warrant caution and rigorous toxicological assessments.

Using ovarian and brain cell culture from the Mullet, Liza klunzingeri, to assess the inhibitory effects of benzo[a]pyrene on aromatase activity

We assessed the toxic effects of benzo[a]pyrene (BaP) on cell viability, aromatase (Aro) activity and steroid production using ovarian and brain cell cultures obtained from Mullet, Liza klunzingeri. The brain and ovary were minced and digested, and the cells were suspended in Leibovitz's L-15 medium supplemented with 15% and 20% fetal bovine serum. The cell suspensions were seeded on 25-cm² cell-culture flasks at 1 × 10⁶ cells/mL and incubated at 25 °C for 2 weeks. A BaP concentration of 10^-5 mol/L was accepted as the half-maximal inhibitory concentration. Ovarian and brain cells were exposed to different concentrations of BaP [0 (control), 10^-6 , 2 × 10^-6 , 3 × 10^-6 mol/L] and incubated at 30 °C. At different sampling times (0, 12, 24 and 48 h) 40 ng/10⁵ cells of 1,4,6-androstatriene-3,17-dione (ATD) was added to each well. Aro activity, 17β-estradiol (E2) and ATD production were determined. The sensitivity of the cultivated ovarian and brain cells to BaP increased dose dependently. BaP was a potent inhibitor of Aro activity at 2 × 10^-6 and 3 × 10^-6 mol/L, both in the cultivated brain and ovarian cells at different sampling times, with 10^-6 mol/L BaP found to be the least potent Aro inhibitor. E2 production decreased from cultivated ovarian and brain cells treated by different concentrations of BaP. In conclusion, BaP is able to change the activity of Aro and disrupt the biosynthesis of estrogens, and thus affects reproduction in fish.

Transcriptome Profiling Insights the Feature of Sex Reversal Induced by High Temperature in Tongue Sole Cynoglossus semilaevis

Sex reversal induced by temperature change is a common feature in fish. Usually, the sex ratio shift occurs when temperature deviates too much from normal during embryogenesis or sex differentiation stages. Despite decades of work, the mechanism of how temperature functions during early development and sex reversal remains mysterious. In this study, we used Chinese tongue sole as a model to identify features from gonad transcriptomic and epigenetic mechanisms involved in temperature induced masculinization. Some of genetic females reversed to pseudomales after high temperature treatment which caused the sex ratio imbalance. RNA-seq data showed that the expression profiles of females and males were significantly different, and set of genes showed sexually dimorphic expression. The general transcriptomic feature of pesudomales was similar with males, but the genes involved in spermatogenesis and energy metabolism were differentially expressed. In gonads, the methylation level of cyp19a1a promoter was higher in females than in males and pseudomales. Furthermore, high-temperature treatment increased the cyp19a1a promoter methylation levels of females. We observed a significant negative correlation between methylation levels and expression of cyp19ala. In vitro study showed that CpG within the cAMP response element (CRE) of the cyp19a1a promoter was hypermethylated, and DNA methylation decreased the basal and forskolin-induced activities of cyp19a1a promoter. These results suggested that epigenetic change, i.e., DNA methylation, which regulate the expression of cyp19a1a might be the mechanism for the temperature induced masculinization in tongue sole. It may be a common mechanism in teleost that can be induced sex reversal by temperature.

Metformin-induced endocrine disruption and oxidative stress of Oryzias latipes on two-generational condition

Metformin has been treated for diabetes (type 2). Nowadays, this compound is frequently found in ambient water, influent/effluent of a wastewater treatment plant. To evaluate the metformin aquatic toxicity under a multi-generational exposure regimen, we exposed Oryzias latipes to metformin for two generations (133 d) and investigated its adverse effects. In the F0 generation, metformin significantly elevated gene expression for cytochrome P450 19a (CYP19a) and estrogen receptor α (ERα) in male fish; in female fish, the treatment decreased gene expression of vitellogenin (VTG2) and ERβ1, suggesting endocrine disruption (one-way ANOVA, p <  0.05). Intersex occurrence of F0 female fish were found in a concentration-dependent manner, whereas no significant changes in fecundity and hatching rate were observed (p <  0.05). Metformin increased the reactive oxygen species (ROS) content, and decreased the glutathione (GSH) content in F0 male fish compared with those of the control (one-way ANOVA, p >  0.05). In F0 female fish, metformin increased catalase activity compared with that of the control (p >  0.05). The results demonstrated that metformin leads to oxidative stress and two-generation endocrine disruption in O. latipes. These results may be useful for better understanding metformin toxicity mechanism.

Thyroid hormones and androgens differentially regulate gene expression in testes and ovaries of sexually mature Silurana tropicalis

A series of ex vivo exposures using testicular and ovarian tissues of sexually mature Western clawed frogs (Silurana tropicalis) were designed to examine molecular mechanisms of thyroid hormone (TH) and androgen crosstalk sans hypophyseal feedback as well as investigate potential sex-specific differences. Tissues were exposed ex vivo to either triiodothyronine (T3), iopanoic acid (IOP), one co-treatment of IOP + 5α-dihydrotestosterone (5α-DHT), 5α-DHT, 5β-dihydrotestosterone (5β-DHT), or testosterone (T). Direct exposure to different androgens led to androgen specific increases in thyroid receptor and deiodinase transcripts in testes (trβ and dio1) but a decrease in expression in ovaries (trβ and dio3), suggesting that male and female frogs can be differently affected by androgenic compounds. Moreover, exposure to select androgens differentially increased estrogen-related transcription (estrogen receptor alpha (erα) and aromatase (cyp19)) and production (estradiol) in ovaries and testes indicating the activation of alternate metabolic pathways yielding estrogenic metabolites. Sex-steroid-related transcription (i.e., steroid 5α-reductase type 2 (srd5α2) and erα) and production (i.e., 5α-DHT) were also differentially regulated by THs. The presence and frequency of transcription factor binding sites in the putative promoter regions of TH- and sex steroid-related genes were also examined in S. tropicalis, rodent, and fish models using in silico analysis. In summary, this study provides an improved mechanistic understanding of TH- and androgen-mediated actions and reveals differential transcriptional effects as a function of sex in frogs.

Embryonic exposure to benzo(a)pyrene inhibits reproductive capability in adult female zebrafish and correlation with DNA methylation

This study was conducted to investigate the effects of embryonic short-term exposure to benzo(a)pyrene (BaP), a model polycyclic aromatic hydrocarbon, on ovarian development and reproductive capability in adult female zebrafish. In 1-year-old fish after embryonic exposure to BaP for 96 h, the gonadosomatic indices and the percentage of mature oocytes were significantly decreased in the 0.5, 5 and 50 nmol/L treatments. The spawned egg number, the fertilization rate and the hatching success were significantly reduced, while the malformation rate of the F1 unexposed larvae were increased. The mRNA levels of follicle-stimulating hormone, luteinizing hormone, ovarian cytochrome P450 aromatase cyp19a1a and cyp19b, estrogen receptor esr1 and esr2, and hepatic vitellogenin vtg1 and vtg2 genes, were down-regulated in adult female zebrafish that were exposed to BaP during embryonic stage. Both 17β-estradiol and testosterone levels were reduced in the ovary of adult females. The methylation levels of the gonadotropin releasing hormone (GnRH) gene gnrh3 were significantly increased in the adult zebrafish brain, and those of the GnRH receptor gene gnrhr3 were elevated both in the larvae exposed to BaP and in the adult brain, which might cause the down-regulation of the mRNA levels of gnrh3 and gnrhr3. This epigenetic change caused by embryonic exposure to BaP might be a reason for physiological changes along the brain-pituitary-gonad axis. These results suggest that short-term exposure in early life should be included and evaluated in any risk assessment of pollutant exposure to the reproductive health of fish.

Expression and DNA methylation analysis of cyp19a1a in Chinese sea perch Lateolabrax maculatus

Cytochrome P450 aromatase (P450arom), which is encoded by cyp19a1a, can convert androgen to estrogen. Therefore, P450arom is important in gonadal differentiation and maintenance. In this study, we analyzed the expression and DNA methylation of cyp19a from Chinese sea perch Lateolabrax maculatus (sp. cyp19a1a). The sp. cyp19a1a gene consists of 9 exons, but only 3.5 kb, being smaller than the human cyp19a1a, as a result of small introns. The sp. cyp19a1a protein contains 518 amino acid residues and evolutionarily conserved domains and is clustered in the teleost subfamily on the phylogenetic tree. Amino acid alignment indicates that sp. cyp19a1a shares the highest identity (91.6%) to Epinephelus akaara and Lates calcarifer. Endogenous sp. cyp19a1a is detected mainly in stromal cells around the oocytes of stage I ovary, and the gene expression level has no difference after 40 days fresh water culture in both ovary and testis. The sp. Cyp19a1a can catalyze the production of estrogen from androgen in vitro. Seven CpG dinucleotides are found in the proximal promoter. Binding sites of the conserved predicted transcription factors include cAMP response element, steroidogenic factor-1, and SRY-Box. The deletion of this region reduces promoter activity significantly. The methylation level of the seven CpG dinucleotides in cyp19a1a promoter is higher in the testis (44.25 ± 4.04) than in the ovary (24.71 ± 3.05). The induced hypermethylation of the sp. cyp19a1a promoter suppressed promoter transcription function in vitro. These results suggest that DNA methylation may be a mechanism used for natural sex maintenance.

Exposure to E2 and EE2 environmental concentrations affect different components of the Brain-Pituitary-Gonadal axis in pejerrey fish (Odontesthes bonariensis)

The present study focuses on the effects of E₂ and EE₂ environmental concentrations on different components of the reproductive axis of pejerrey (Odontesthes bonariensis), a native fish species from Pampas lakes of Argentina. The results obtained demonstrated that E₂ and EE₂ separate or mixed, could disrupt key pathways of the pejerrey Brain-Pituitary-Gonadal axis. First, it was observed that at the brain level, gnrh-III and cyp19a1b mRNA expression increased significantly in the exposed fish. Secondly, in the pituitary fshb and lhb mRNA expression levels, the study did not show any differences between treated and control groups. Thirdly, fshr and lhcgr transcript levels showed a significant decrease at testicular level. Nevertheless, testosterone plasmatic levels remained unchanged in exposed fish. In addition, in a histological analysis, it was possible to find pyknotic nuclei in estrogen only on treated fish testis linked to a reduction in the GSI index and a decrease in the length of spermatogenic lobules. All these findings highlighted the fact that environmental concentrations of E₂, EE₂ and their mixture disrupted the endocrine-reproductive axis of pejerrey, being the testis the main direct target.

Stress and sex: does cortisol mediate sex change in fish?

Cortisol is the main glucocorticoid (GC) in fish and the hormone most directly associated with stress. Recent research suggests that this hormone may act as a key factor linking social environmental stimuli and the onset of sex change by initiating a shift in steroidogenesis from estrogens to androgens. For many teleost fish, sex change occurs as a usual part of the life cycle. Changing sex is known to enhance the lifetime reproductive success of these fish and the modifications involved (behavioral, gonadal and morphological) are well studied. However, the exact mechanism behind the transduction of the environmental signals into the molecular cascade that underlies this singular process remains largely unknown. We here synthesize current knowledge regarding the role of cortisol in teleost sex change with a focus on two well-described transformations: temperature-induced masculinization and socially regulated sex change. Three non-mutually exclusive pathways are considered when describing the potential role of cortisol in mediating teleost sex change: cross-talk between GC and androgen pathways, inhibition of aromatase expression and upregulation of amh (the gene encoding anti-Müllerian hormone). We anticipate that understanding the role of cortisol in the initial stages of sex change will further improve our understanding of sex determination and differentiation across vertebrates, and may lead to new tools to control fish sex ratios in aquaculture.

Of Oestrogens and Sperm: A Review of the Roles of Oestrogens and Oestrogen Receptors in Male Reproduction

The crucial role that oestrogens play in male reproduction has been generally accepted; however, the exact mechanism of their action is not entirely clear and there is still much more to be clarified. The oestrogen response is mediated through oestrogen receptors, as well as classical oestrogen receptors’ variants, and their specific co-expression plays a critical role. The importance of oestrogen signalling in male fertility is indicated by the adverse effects of selected oestrogen-like compounds, and their interaction with oestrogen receptors was proven to cause pathologies. The aims of this review are to summarise the current knowledge on oestrogen signalling during spermatogenesis and sperm maturation and discuss the available information on oestrogen receptors and their splice variants. An overview is given of species-specific differences including in humans, along with a detailed summary of the methodology outcome, including all the genetically manipulated models available to date. This review provides coherent information on the recently discovered mechanisms of oestrogens’ and oestrogen receptors’ effects and action in both testicular somatic and germ cells, as well as in mature sperm, available for mammals, including humans.

Environmental influences on the epigenomes of herpetofauna and fish

Herpetofauna (amphibians and reptiles) and fish represent important sentinel and indicator species for environmental and ecosystem health. It is widely accepted that the epigenome plays an important role in gene expression regulation. Environmental stimuli, including temperature and pollutants, influence gene activity, and there is growing evidence demonstrating that an important mechanism is through modulation of the epigenome. This has been primarily studied in human and mammalian models; relatively little is known about the impact of environmental conditions or pollutants on herpetofauna or fish epigenomes and the regulatory consequences of these changes on gene expression. Herein we review recent studies that have begun to address this deficiency, which have mainly focused on limited specific epigenetic marks and individual genes or large-scale global changes in DNA methylation, owing to the comparative ease of measurement. Greater understanding of the epigenetic influences of these environmental factors will depend on increased availability of relevant species-specific genomic sequence information to facilitate chromatin immunoprecipitation and DNA methylation experiments.

Parental effects of endocrine disrupting compounds in aquatic wildlife: Is there evidence of transgenerational inheritance?

The effects of endocrine disrupting compounds (EDCs) on aquatic wildlife are increasingly being recognized for their complexity. Investigators have detected alterations at multiple levels of biological organization in offspring exposed to EDCs through the blood or germ line of the parents, suggesting that generational consequences of EDCs are evident. Exposure to EDCs through the parents is concerning because if the resulting phenotype of the offspring is heritable and affects fitness, then evolutionary consequences may be evident. This review summarizes the evidence for transgenerational effects of EDCs in aquatic wildlife and illustrates cases where alterations appear to be transmitted maternally, paternally, or parentally. The literature indicates that EDC exposure to the parents induces developmental, physiological, endocrinological, and behavioral changes as well as increased mortality of offspring raised in clean environments. What is lacking, however, is a clear demonstration of heritable transgenerational effects in aquatic wildlife. Therefore, it is not known if the parental effects are the result of developmental or phenotypic plasticity or if the altered phenotypes are durably passed to subsequent generations. Epigenetic changes to gene regulation are discussed as a possible mechanism responsible for EDC induced parental effects. Additional research is needed to evaluate if heritable effects of EDCs are evident in aquatic wildlife, as has been demonstrated for terrestrial mammals.

Effects of the environmental estrogenic contaminants bisphenol A and 17α-ethinyl estradiol on sexual development and adult behaviors in aquatic wildlife species

Endocrine disrupting chemicals (EDCs), including the mass-produced component of plastics, bisphenol A (BPA) are widely prevalent in aquatic and terrestrial habitats. Many aquatic species, such as fish, amphibians, aquatic reptiles and mammals, are exposed daily to high concentrations of BPA and ethinyl estradiol (EE2), estrogen in birth control pills. In this review, we will predominantly focus on BPA and EE2, well-described estrogenic EDCs. First, the evidence that BPA and EE2 are detectable in almost all bodies of water will be discussed. We will consider how BPA affects sexual and neural development in these species, as these effects have been the best characterized across taxa. For instance, such chemicals have been in many cases reported to cause sex-reversal of males to females. Even if these chemicals do not overtly alter the gonadal sex, there are indications that several EDCs might demasculinize male-specific behaviors that are essential for attracting a mate. In so doing, these chemicals may reduce the likelihood that these males reproduce. If exposed males do reproduce, the concern is that they will then be passing on compromised genetic fitness to their offspring and transmitting potential transgenerational effects through their sperm epigenome. We will thus consider how diverse epigenetic changes might be a unifying mechanism of how BPA and EE2 disrupt several processes across species. Such changes might also serve as universal species diagnostic biomarkers of BPA and other EDCs exposure. Lastly, the evidence that estrogenic EDCs-induced effects in aquatic species might translate to humans will be considered.

Oxidative stress and hypermethylation induced by exposure of Oreochromis niloticus to complex environmental mixtures of river water from Cubatão do Sul, Brazil

In this study, we investigated the effects of oxidative stress and hypermethylation through lipid peroxidation and DNA methylation, respectively, in erythrocytes of Oreochromis niloticus exposed to environmental complex mixture of water from Cubatão do Sul River throughout the year. This river is the source of drinking water for the region of Florianópolis, the capital of Santa Catarina State, Brazil. Lipid peroxidation was quantified by the rate of malondialdehyde (MDA) formation, and DNA methylation was quantified by the rate of 5-methyldeoxycytosine (m(5)dC) formation. In all studied sites, the river water samples caused metabolic changes in O. niloticus. MDA formation rates were significantly different when compared to the negative control (except for samples from Site 1 during spring 2010, summer 2011 and fall 2011). All samples (except Site 1, spring 2010) induced increases in the m(5)dC formation rates, and at the end of the study, the values were near the values found in the positive control (potassium dichromate 2.5mg/L). The results showed that samples of environmental complex mixtures of water from Cubatão do Sul River are capable of inducing high levels of oxidative damage and hypermethylation in O. niloticus.

Early exposure of 17α-ethynylestradiol and diethylstilbestrol induces morphological changes and alters ovarian steroidogenic pathway enzyme gene expression in catfish, Clarias gariepinus

Environmental estrogens are major cause of endocrine disruption in vertebrates, including aquatic organisms. Teleosts are valuable and popular models for studying the effects of endocrine disrupting chemicals (EDCs) in the environment. In the present study, we investigated the changes caused by exposure to the synthetic estrogens 17α-ethynylestradiol (EE2 ) and diethylstilbesterol (DES) during early stages of growth and sex differentiation of air-breathing catfish, Clarias gariepinus, at the morphological, histological, and molecular levels. Catfish hatchlings, 0 day post hatch (dph) were exposed continuously to sublethal doses of EE2 (50 ng/L) and DES (10 ng/L) until 50 dph and subsequently monitored for ovarian structural changes and alteration in the gene expression of steroidogenic enzymes till adulthood. Treated fish exhibited morphological deformities such as spinal curvature, stunted growth, and yolk-sac fluid retention. In addition to ovarian atrophy, DES-treated fish showed either rudimentary or malformed ovaries. Detailed histological studies revealed precocious oocyte development as well as follicular atresia. Further, transcript levels of various steroidogenic enzyme and transcription factor genes were altered in response to EE2 and DES. Activity of the rate-limiting enzyme of estrogen biosynthesis, aromatase, in the ovary as well as the brain of treated fish was in accordance with transcript level changes. These developmental and molecular effects imparted by EE2 and DES during early life stages of catfish could demonstrate the deleterious effects of estrogen exposure and provide reliable markers for estrogenic EDCs exposure in the environment.

Abnormal ovarian DNA methylation programming during gonad maturation in wild contaminated fish

There is increasing evidence that pollutants may cause diseases via epigenetic modifications. Epigenetic mechanisms such as DNA methylation participate in the regulation of gene transcription. Surprisingly, epigenetics research is still limited in ecotoxicology. In this study, we investigated whether chronic exposure to contaminants experienced by wild female fish (Anguilla anguilla) throughout their juvenile phase can affect the DNA methylation status of their oocytes during gonad maturation. Thus, fish were sampled in two locations presenting a low or a high contamination level. Then, fish were transferred to the laboratory and artificially matured. Before hormonal treatment, the DNA methylation levels of the genes encoding for the aromatase and the receptor of the follicle stimulating hormone were higher in contaminated fish than in fish from the clean site. For the hormone receptor, this hypermethylation was positively correlated with the contamination level of fish and was associated with a decrease in its transcription level. In addition, whereas gonad growth was associated with an increase in DNA methylation in fish from the clean site, no changes were observed in contaminated fish in response to hormonal treatment. Finally, a higher gonad growth was observed in fish from the reference site in comparison to contaminated fish.

Effects of nonylphenol and ethinylestradiol on copper redhorse (Moxostoma hubbsi), an endangered species

The copper redhorse, Moxostoma hubbsi, is an endangered species endemic to Quebec. The presence of contaminants, in particular endocrine disrupting chemicals (EDCs), in its habitat has been advanced as partly responsible for the reproductive difficulties encountered by the species. In the present study, immature copper redhorse were exposed to the estrogenic surfactant nonylphenol (NP; 1, 10 and 50µg/l) and the synthetic estrogen 17α-ethinylestradiol (EE2; 10ng/l) for 21 days in a flow-through system. The endpoints investigated included general health indicators (hepatosomatic index and hematocrit), thyroid hormones, sex steroids, brain aromatase activity, plasma and mucus vitellogenin (VTG), cytochrome P4501A protein expression and ethoxyresorufin-O-deethylase activity, heat shock protein 70 (HSP70) and muscle acetylcholinesterase. Exposure to 10ng EE2/l significantly increased brain aromatase activity. Exposure to 50µg NP/l resulted in a significant reduction of plasma testosterone concentrations and a significant induction of hepatic HSP70 protein expression. NP at 50µg/l also induced plasma and mucus VTG. The presence of elevated VTG levels in the surface mucus of immature copper redhorse exposed to NP, and its correlation to plasma VTG, supports the use of mucus VTG as a non-invasive biomarker to evaluate copper redhorse exposure to EDCs in the environment and contribute to restoration efforts of the species. The results of the present study indicate that exposure to high environmentally relevant concentrations of NP and EE2 can affect molecular endpoints related to reproduction in the copper redhorse.

Environmental stressors and the epigenome

Epigenetic modification and transgenerational transfer of phenotype at the individual or population level, particularly in response to environmental change, is at the forefront of biological investigation. The plasticity of this process allows an organism to respond to changes in environmental conditions, potentially conferring a survival advantage. In this review, we discuss epigenetic transgenerational phenomena in the specific context of environmental stressors including hypoxia and environmental toxicants.:

DNA methylation in the 5' flanking region of cytochrome P450 17 in adult rare minnow Gobiocypris rarus - tissue difference and effects of 17α-ethinylestradiol and 17α-methyltestoterone exposures

Cytochrome P450 17 (CYP17) plays a vital role in hormone production in the body. In our previous study, mRNA expression of cyp17a1 was regulated by endocrine disrupting chemicals in rare minnow Gobiocypris rarus. However, the mechanism underlying the regulation is unclear. In the present study, we aim to explore whether the differential expression of cyp17a1 in distinct tissues and the modulation of its expression upon 17α-ethinylestradiol (EE2) and 17α-methyltestoterone (MT) are related to the DNA methylation status in G. rarus. The 732-bp fragment of 5' flanking region of cyp17a1 gene was isolated in G. rarus. The bisulfite sequencing PCR result showed that DNA methylation levels in 5' flanking of cyp17a1 in the gonads were significantly lower than those in the brains, which is negatively related to its mRNA expression in the 2 tissues in the previous study. The 7-day EE2 exposure of 25 ng/L caused a significant increase of methylation levels of cyp17a1 gene and a significant decrease of its transcript in testis. While 100 ng/L MT exposure for 7 days caused a significant decrease of methylation levels of cyp17a1 gene and a significant increase of its transcript in the ovary. The present findings indicate that the methylation status of cyp17a1 gene is negatively correlated with its mRNA expression in response to EE2 and MT in G. rarus. We hypothesize that the regulation of cyp17a1 expression by EE2 and MT might attribute to the change of its DNA methylation status in G. rarus.

Patterns of DNA methylation in animals: an ecotoxicological perspective

DNA methylation refers to the addition of a methyl group to nucleotides within DNA. As with other epigenetic endpoints, patterns of DNA methylation are susceptible to alterations due to exposure to environmental stressors, including contaminants. These alterations can persist in the absence of the initial stressor as cells divide, and can even be inherited between generations if they occur in the germ line. Although our knowledge concerning patterns of DNA methylation in animals is increasing, there remains a gap in the literature when it comes to species outside of those typically used for biomedical research. Here, I review the literature relating to DNA methylation in an array of taxa (mammals, fish, birds, amphibians, reptiles, and invertebrates) and discuss these data from an ecotoxicological perspective. The pattern and extent of DNA methylation is well conserved across species of vertebrates; methylation appears mainly on cytosine residues within a CpG context, and much of the genome is methylated, with the notable exception of cytosines within CpG islands in the promoters of genes. Highly methylated genes in vertebrates tend to be transcriptionally repressed. However, large differences occur between classes of vertebrates in terms of the timing and nature of reprogramming and genomic imprinting: epigenetic processes that establish patterns of DNA methylation in the early embryo and which are sensitive to environmental stress. In invertebrates, patterns of DNA methylation are extremely variable and differ significantly from the condition observed in vertebrates. Some invertebrate genomes exhibit no DNA methylation while others are methylated to a level that is comparable to vertebrates. Additionally, DNA methylation may have different functions in invertebrates, e.g., alternative splicing. This variability in basic patterns of DNA methylation among species during sensitive periods of development suggests that responses to epigenetically active environmental contaminants may be similarly variable. For example, the timing of exposure to a contaminant may be a critical factor when considered in the light of variable reprogramming schedules among species. With this in mind, I review data relating to the effects of contaminants on DNA methylation in animals, focusing on non-model organisms and on exposures in natural environments, when possible. An ecotoxicological perspective on patterns of DNA methylation in animals may improve our understanding of the range and diversity of epigenetic phenomena in the natural world.

Sexually selected traits: a fundamental framework for studies on behavioral epigenetics

Emerging evidence suggests that epigenetic-based mechanisms contribute to various aspects of sex differences in brain and behavior. The major obstacle in establishing and fully understanding this linkage is identifying the traits that are most susceptible to epigenetic modification. We have proposed that sexual selection provides a conceptual framework for identifying such traits. These are traits involved in intrasexual competition for mates and intersexual choice of mating partners and generally entail a combination of male-male competition and female choice. These behaviors are programmed during early embryonic and postnatal development, particularly during the transition from the juvenile to adult periods, by exposure of the brain to steroid hormones, including estradiol and testosterone. We evaluate the evidence that endocrine-disrupting compounds, including bisphenol A, can interfere with the vital epigenetic and gene expression pathways and with the elaboration of sexually selected traits with epigenetic mechanisms presumably governing the expression of these traits. Finally, we review the evidence to suggest that these steroid hormones can induce a variety of epigenetic changes in the brain, including the extent of DNA methylation, histone protein alterations, and even alterations of noncoding RNA, and that many of the changes differ between males and females. Although much previous attention has focused on primary sex differences in reproductive behaviors, such as male mounting and female lordosis, we outline why secondary sex differences related to competition and mate choice might also trace their origins back to steroid-induced epigenetic programming in disparate regions of the brain.

Differential incubation temperatures result in dimorphic DNA methylation patterning of the SOX9 and aromatase promoters in gonads of alligator (Alligator mississippiensis) embryos

Environmental factors are known to influence sex determination in many nonmammalian vertebrates. In all crocodilians studied thus far, temperature is the only known determinant of sex. However, the molecular mechanisms mediating the effect of temperature on sex determination are not known. Aromatase (CYP19A1) and SOX9 play critical roles in vertebrate sex determination and gonadogenesis. Here, we used a variety of techniques to investigate the potential roles of DNA methylation patterning on CYP19A1 and SOX9 expression in the American alligator, an organism that relies on temperature-dependent sex determination. Our findings reveal that developing gonads derived from embryos incubated at a male-producing temperature (MPT) show elevated CYP19A1 promoter methylation and decreased levels of gene expression relative to incubation at a female-producing temperature (FPT). The converse was observed at the SOX9 locus, with increased promoter methylation and decreased expression occurring in embryonic gonads resulting from incubation at FPT relative to that of MPT. We also examined the gonadal expression of the three primary, catalytically active DNA methyltransferase enzymes and show that they are present during critical stages of gonadal development. Together, these data strongly suggest that DNA methylation patterning is a central component in coordinating the genetic cascade responsible for sexual differentiation. In addition, these data raise the possibility that DNA methylation could act as a key mediator integrating temperature into a molecular trigger that determines sex in the alligator.

Epigenetic modifications during sex change repress gonadotropin stimulation of cyp19a1a in a teleost ricefield eel (Monopterus albus)

In vertebrates, cytochrome P450 aromatase, encoded by cyp19a1, converts androgens to estrogens and plays important roles in gonadal differentiation and development. The present study examines whether epigenetic mechanisms are involved in cyp19a1a expression and subsequent gonadal development in the hermaphroditic ricefield eel. The expression of the ricefield eel cyp19a1a was stimulated by gonadotropin via the cAMP pathway in the ovary but not the ovotestis or testis. The CpG within the cAMP response element (CRE) of the cyp19a1a promoter was hypermethylated in the ovotestis and testis compared with the ovary. The methylation levels of CpG sites around CRE in the distal region (region II) and around steroidogenic factor 1/adrenal 4 binding protein sites and TATA box in the proximal region (region I) were inversely correlated with cyp19a1a expression during the natural sex change from female to male. In vitro DNA methylation decreased the basal and forskolin-induced activities of cyp19a1a promoter. Chromatin immunoprecipitation assays indicated that histone 3 (Lys9) in both regions I and II of the cyp19a1a promoter were deacetylated and trimethylated in the testis, and in contrast to the ovary, phosphorylated CRE-binding protein failed to bind to these regions. Lastly, the DNA methylation inhibitor 5-aza-2'-deoxycytidine reversed the natural sex change of ricefield eels. These results suggested that epigenetic mechanisms involving DNA methylation and histone deacetylation and methylation may abrogate the stimulation of cyp19a1a by gonadotropins in a male-specific fashion. This may be a mechanism widely used to drive natural sex change in teleosts as well as gonadal differentiation in other vertebrates.

Effects of exposure to oestrogenic compounds on aromatase gene expression are gender dependent in the rainbowfish, Melanotaenia fluviatilis

This study investigated the influence of two endocrine disrupting chemicals (EDCs)-an exogenous oestrogen 17β-estradiol (E2) and the oestrogen mimic 4-n-nonylphenol (NP) on the expression of aromatase transcripts in both sexes of adult Murray river rainbowfish. Reproductively active mature fish were exposed to 1, 3, and 5 μg/L E2 or 100 and 500μg/L NP for 24, 48, 72 and 96 h. The results show a significant reduction in the expression of cyp19a1a isoform in ovarian tissues with complete inhibition at the higher concentrations (3 and 5 μg/L E2; 500μg/L NP between 24 and 72 h) and at all concentrations after 96 h. There was no expression of the cyp19a1a isoform in female brain, male brain or testes in any treatment. E2 significantly increased expression of cyp19a1b in female brain except at 5 μg/L after 24h exposure. In male brain tissue E2 exposure decreased cyp19a1b expression except at 1 and 5 μg/L at 24h. NP significantly upregulated cyp19a1b in the female brain (except with 500 μg/L at 72 h) and in testes tissues. NP downregulated expression of cyp19a1b in the male brain tissue. Collectively, these observations support the hypothesis that the expression of cyp19a1b is regulated via both positive and negative feedback mechanisms, with differential modulation based on the type and concentration of the exposed oestrogens, duration of exposure, fish tissue and gender of the fish. The results also imply that exogenous oestrogens can have a disruptive effect on the steroidogenic pathway and may lead to effects on sex differentiation, sexual behaviour and reproductive cycles in this fish.

Gene-environment interactions: the potential role of contaminants in somatic growth and the development of the reproductive system of the American alligator

Developing organisms interpret and integrate environmental signals to produce adaptive phenotypes that are prospectively suited for probable demands in later life. This plasticity can be disrupted when embryos are impacted by exogenous contaminants, such as environmental pollutants, producing potentially deleterious and long-lasting mismatches between phenotype and the future environment. We investigated the ability for in ovo environmental contaminant exposure to alter the growth trajectory and ovarian function of alligators at five months after hatching. Alligators collected as eggs from polluted Lake Apopka, FL, hatched with smaller body masses but grew faster during the first five months after hatching, as compared to reference-site alligators. Further, ovaries from Lake Apopka alligators displayed lower basal expression levels of inhibin beta A mRNA as well as decreased responsiveness of aromatase and follistatin mRNA expression levels to treatment with follicle stimulating hormone. We posit that these differences predispose these animals to increased risks of disease and reproductive dysfunction at adulthood.

DNA methylation of the gonadal aromatase (cyp19a) promoter is involved in temperature-dependent sex ratio shifts in the European sea bass

Sex ratio shifts in response to temperature are common in fish and reptiles. However, the mechanism linking temperature during early development and sex ratios has remained elusive. We show in the European sea bass (sb), a fish in which temperature effects on sex ratios are maximal before the gonads form, that juvenile males have double the DNA methylation levels of females in the promoter of gonadal aromatase (cyp19a), the enzyme that converts androgens into estrogens. Exposure to high temperature increased the cyp19a promoter methylation levels of females, indicating that induced-masculinization involves DNA methylation-mediated control of aromatase gene expression, with an observed inverse relationship between methylation levels and expression. Although different CpGs within the sb cyp19a promoter exhibited different sensitivity to temperature, we show that the increased methylation of the sb cyp19a promoter, which occurs in the gonads but not in the brain, is not a generalized effect of temperature. Importantly, these effects were also observed in sexually undifferentiated fish and were not altered by estrogen treatment. Thus, methylation of the sb cyp19a promoter is the cause of the lower expression of cyp19a in temperature-masculinized fish. In vitro, induced methylation of the sb cyp19a promoter suppressed the ability of SF-1 and Foxl2 to stimulate transcription. Finally, a CpG differentially methylated by temperature and adjacent to a Sox transcription factor binding site is conserved across species. Thus, DNA methylation of the aromatase promoter may be an essential component of the long-sought-after mechanism connecting environmental temperature and sex ratios in vertebrate species with temperature-dependent sex determination.

Effects of lifetime chemical inhibition of aromatase on the sexual differentiation, sperm characteristics and fertility of medaka (Oryzias latipes) and zebrafish (Danio rerio)

The deleterious effects of tributyltin (TBT) on spermiation in fish have been attributed to its role in inhibiting aromatisation of androgens to estrogens, and the critical role of the latter in sperm development. We test this hypothesis by examining sperm parameters, fertilisation and hatching success in males of two fish species exposed throughout life to doses of Fadrozole, a non-steroidal aromatase inhibitor (AI), provided in their diets. AI-treatment caused 100% male development in zebrafish, but only partial masculinisation in medaka, in both cases supporting previous studies and suggesting different roles of estrogen in sexual differentiation in the two species. Milt volume, initial sperm motility, maximum sperm swimming duration and sperm morphology did not differ significantly between Control and AI-dosed fish in either species, after excluding low milt volumes in sex-changed females in medaka. Fertilisation rates were also unaffected by the aromatase inhibition, but hatching success in medaka was 31% lower than in Control males, suggesting a previously unreported effect of aromatase on sperm quality. The slight effect of aromatase inhibition on sperm parameters in general contrasts with the marked effect of TBT on fish sperm, and suggests that a mechanism other than depressed estrogen levels is involved.

DNA methylation levels in the 5' flanking region of the vitellogenin I gene in liver and brain of adult zebrafish (Danio rerio)--sex and tissue differences and effects of 17alpha-ethinylestradiol exposure

Vitellogenin is produced in the liver of sexually mature female fish in response to endogenous estrogens. Exogenous estrogens also induce synthesis of vitellogenin in the liver of male and juvenile fish and vitellogenin is a frequently used biomarker for estrogen exposure. The epigenetic state, e.g. histone acetylation and DNA methylation, in the region of a gene or in its 5' flanking region influences the gene expression. DNA methylation positions in multicellular eukaryotes are mostly found on cytosine bases located 5' to guanine, i.e. in CpG sites. Here, we have for the first time analyzed the DNA methylation levels of three CpG sites located in the 5' flanking region of the vitellogenin I gene in liver and brain from adult zebrafish (Danio rerio) utilizing Pyrosequencing technology. This sequencing technique allows determination of methylation levels of multiple individual CpG sites. Our purpose was to assess any differences in methylation levels related to sex, tissue and exposure to estrogen. Out of the seven vitellogenin genes identified in the zebrafish, vitellogenin I is the most highly expressed during vitellogenesis. We found that the methylation levels of all three CpG sites were higher in male liver than in female liver. In brain, which does not express vitellogenin, females and males showed similar, high methylation levels in the analyzed CpG positions. Exposure of adult zebrafish to 17alpha-ethinylestradiol (100 ng/L) for 14 days decreased the methylation levels in the 5' flanking region of vitellogenin I in the liver in both females and males. These results suggest that induced expression of vitellogenin in fish following exposure to estrogens might involve alterations in DNA methylation.

Fish with thermolabile sex determination (TSD) as models to study brain sex differentiation

As fish are ectothermic animals, water temperature can affect their basic biological processes such as larval development, growth and reproduction. Similar to reptiles, the incubation temperature during early phases of development is capable to modify sex ratios in a large number of fish species. This phenomenon, known as thermolabile sex determination (TSD) was first reported in Menidia menidia, a species belonging to the family Atherinopsidae. Since then, an increasing number of fish have also been found to exhibit TSD. Traditionally, likewise in reptiles, several TSD patterns have been described in fish, however it has been recently postulated that only one, females at low temperatures and males at high temperatures, may represent the "real" or "true" TSD. Many studies regarding the influence of temperature on the final sex ratios have been focused on the expression and activity of gonadal aromatase, the enzyme involved in the conversion of androgens into estrogens and encoded by the cyp19a1a gene. In this regard, teleost fish, may be due to a whole genome duplication event, produce another aromatase enzyme, commonly named brain aromatase, encoded by the cyp19a1b gene. Contrary to what has been described in other vertebrates, fish exhibit very high levels of aromatase activity in the brain and therefore they synthesize high amounts of neuroestrogens. However, its biological significance is still not understood. In addition, the mechanism whereby temperature can induce the development of a testis or an ovary still remains elusive. In this context the present review is aimed to discuss several theories about the possible role of brain aromatase using fish as models. The relevance of brain aromatase and therefore of neuroestrogens as the possible cue for gonadal differentiation is raised. In addition, the possible role of brain aromatase as the way to keep the high levels of neurogenesis in fish is also considered. Several key examples of how teleosts and aromatase regulation can offer more insight into basic mechanisms of TSD are also reviewed.

Ethanol disrupts chondrification of the neurocranial cartilages in medaka embryos without affecting aldehyde dehydrogenase 1A2 (Aldh1A2) promoter methylation

Medaka (Oryzias latipes) embryos at different developmental stages were exposed to ethanol for 48 h, then allowed to hatch. Teratogenic effects were evaluated in hatchlings after examining chondrocranial cartilage deformities. Ethanol disrupted cartilage development in medaka in a dose and developmental stage-specific manner. Compared to controls, the linear length of the neurocranium and other cartilages were reduced in ethanol-treated groups. Moreover, the chondrification in cartilages, specifically trabeculae and polar cartilages, were inhibited by ethanol. To understand the mechanism of ethanol teratogenesis, NAD(+): NADH status during embryogenesis and the methylation pattern of Aldh1A2 promoter in whole embryos and adult tissues (brain, eye, heart and liver) were analyzed. Embryos 6 dpf had higher NAD(+) than embryos 0 or 2 dpf. Ethanol (200 or 400 mM) was able to reduce NAD(+) content in 2 and 6 dpf embryos. However, in both cases reductions were not significantly different from the controls. Moreover, no significant difference in either NADH content or in NAD(+): NADH status of the ethanol-treated embryos, with regard to controls, was observed. The promoter of Aldh1A2 contains 31 CpG dinucleotides (-705 to +154, ATG=+1); none of which were methylated. Compared to controls, embryonic ethanol exposure (100 and 400 mM) was unable to alter Aldh1A2 promoter methylation in embryos or in the tissues of adults (breeding) developmentally exposed to ethanol (300 mM, 48 hpf). From these data we conclude that ethanol teratogenesis in medaka does not induce alteration in the methylation pattern of Aldh1A2 promoter, but does change cartilage development.

Prognostic implications of and relationship between CpG island hypermethylation and repetitive DNA hypomethylation in hepatocellular carcinoma

PURPOSE

This study aims to determine the relationship between CpG island DNA hypermethylation and global genomic DNA hypomethylation and their prognostic implications in hepatocellular carcinoma. The association of DNA methylation changes with clinicopathologic factors and the chronological ordering of DNA methylation changes along multistep hepatocarcinogenesis were also assessed.

EXPERIMENTAL DESIGN

Hepatocellular carcinoma (n = 20) and nonneoplastic liver samples (n = 72) were analyzed for their methylation status at 41 CpG island loci and 3 repetitive DNA elements (LINE-1, ALU, and SAT2) using MethyLight or combined bisulfite restriction analysis. After selection of 19 CpG island loci showing cancer-specific DNA methylation, another set of 99 hepatocellular carcinoma samples was analyzed for these loci.

RESULTS

The number of methylated genes in hepatocellular carcinoma was significantly higher in hepatocellular carcinoma patients with a cirrhotic liver than in hepatocellular carcinoma patients with a noncirrhotic liver (9.9 versus 7.0, P = 0.001). Hepatocellular carcinoma from female patients showed a higher number of methylated genes than hepatocellular carcinoma from male patients (11.2 versus 8.4, P = 0.006). The genes CRABP1 and SYK showed significant association between CpG island hypermethylation and patients' poor survival. SAT2 hypomethylation occurred earlier than LINE-1 or ALU hypomethylation along the multistep hepatocarcinogenesis. Depending on the type of CpG island locus, a direct, inverse, or no relationship between CpG island hypermethylation and repetitive DNA hypomethylation was observed in hepatocellular carcinomas.

CONCLUSION

The varying relationships between the hypermethylation of individual CpG island loci and the hypomethylation of repetitive elements suggests that they are not mechanically linked. SYK and CRABP1 hypermethylation may serve as useful tumor markers for prognostication of hepatocellular carcinoma patients.

Sexual reprogramming and estrogenic sensitization in wild fish exposed to ethinylestradiol

Globally, feminization responses in wild male freshwater fish are caused by exposure to estrogenic chemicals, including natural and synthetic estrogens, contained in effluentsfromwastewater treatment works. In U.K. rivers, feminization responses, including intersex, are widespread in wild roach (Rutilus rutilus) populations, and severely affected fish have a reduced reproductive success. We exposed roach to environmentally relevant concentrations of the contraceptive estrogen 17alpha-ethinylestradiol (EE2) for up to 2 years, including intermittent and repeated exposures,to determine effects on sexual development and subsequent responsiveness to estrogen. Exposure of roach to EE2 (at 4 ng/L) for 2 years resulted in sex reversal in males, leading to an all-female population with two cohorts in terms of their stages of ovarian development one paralleling the control females and one at a significantly less advanced stage, which we propose were sex-reversed males. Differing developmental and maturing rates of the putative sex-reversed males compared with control females would question their functional capability as females in the wild. Early-life exposure to environmentally relevant concentrations of EE2 sensitized females to estrogen, as determined by the measurement of the responses of estrogen-sensitive genes in a further EE2 challenge 398 days after the original exposure. In the wild, exposure to environmentally relevant concentrations of EE2 during early life has significantly wider implications for the sexual physiology in fish than has thus far been determined.

Clotrimazole exposure modulates aromatase activity in gonads and brain during gonadal differentiation in Xenopus tropicalis frogs

Clotrimazole is a pharmaceutical used for treatment of fungal infections. It has been found in surface waters outside municipal wastewater treatment plants but data are scarce regarding its effects on aquatic organisms. It is known that clotrimazole and other imidazole fungicides are inhibitors of the enzyme aromatase (CYP 19). Aromatase converts androgens into estrogens and is suggested to be involved in the sex differentiation in amphibians. The aim of the present study was to evaluate effects of larval exposure to clotrimazole on aromatase activity in brain and gonads, and on gonadal differentiation in Xenopus tropicalis frogs. Another purpose was to determine if larval exposure to ethynylestradiol (EE(2)), at a concentration known to cause male-to-female sex reversal, affects aromatase activity in brain and gonads during gonadal differentiation. Tadpoles were exposed from shortly after hatching (Nieuwkoop and Faber developmental stages 47-48) until complete metamorphosis (NF stage 66) to 6, 41, and 375 nM clotrimazole or 100 nM (nominal) EE(2). Aromatase activity was measured in the brain and gonad/kidney complex of tadpoles during gonadal differentiation (NF stage 56) and, in the clotrimazole experiment, also at metamorphosis. In clotrimazole-exposed tadpoles gonadal aromatase activity increased over exposure time in the 41 and 375 nM groups but did not differ significantly from the control group. Gonadal aromatase activity was increased in both sexes exposed to 41 and 375 nM clotrimazole at metamorphosis. Brain aromatase activity was decreased in tadpoles (NF stage 56) exposed to 375 nM clotrimazole, but at metamorphosis no differences were seen between groups or between sexes. No effects of clotrimazole on sex ratio or gonadal histology were noted at completed metamorphosis. EE(2)-exposed tadpoles had a slightly decreased gonadal aromatase activity, though not significantly different from control group, and there was no effect of EE(2) on brain aromatase activity. All EE(2)-exposed tadpoles developed ovaries. These findings indicate that estrogen-induced ovarian differentiation is not paralleled by increased gonadal aromatase activity in X. tropicalis. Further studies are needed, especially on developmental reproductive toxicity, to assess the risk for endocrine disruption in wild amphibians posed by clotrimazole and other imidazole fungicides.