Molecular conservation of estrogen-response associated with cell cycle regulation, hormonal carcinogenesis and cancer in zebrafish and human cancer cell lines

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.

Microparticle formulations alter the toxicity of fenofibrate to the zebrafish Danio rerio embryo

A wide variety of active pharmaceutical ingredients are released into the environment and pose a threat to aquatic organisms. Drug products using micro- and nanoparticle technology can lower these emissions into the environment by their increased bioavailability to the human patients. However, due to this enhanced efficacy, micro- and nanoscale drug delivery systems can potentially display an even higher toxicity, and thus also pose a risk to non-target organisms. Fenofibrate is a lipid-regulating agent and exhibits species-related hazards in fish. The ecotoxic effects of a fenofibrate formulation embedded into a hydroxypropyl methylcellulose microparticle matrix, as well as those of the excipients used in the formulation process, were evaluated. To compare the effects of fenofibrate without a formulation, fenofibrate was dispersed in diluted ISO water alone or dissolved in the solvent DMF and then added to diluted ISO water. The effects of these various treatments were assessed using the fish embryo toxicity test, acridine orange staining and gene expression analysis assessed by quantitative RT polymerase chain reaction. Exposure concentrations were assessed by chemical analysis. The effect threshold concentrations of fenofibrate microparticle precipitates were higher compared to the formulation. Fenofibrate dispersed in 20%-ISO-water displayed the lowest toxicity. For the fenofibrate formulation as well as for fenofibrate added as a DMF solution, greater ecotoxic effects were observed in the zebrafish embryos. The chemical analysis of the solutions revealed that more fenofibrate was present in the samples with the fenofibrate formulation as well as fenofibrate added as a DMF solution compared to fenofibrate dispersed in diluted ISO water. This could explain the higher ecotoxicity. The toxic effects on the zebrafish embryo thus suggested that the formulation as well as the solvent increased the bioavailability of fenofibrate.

Impacts of bisphenol A analogues on zebrafish post-embryonic brain

Bisphenol A (BPA) is a widely studied and well-recognised endocrine-disrupting chemical, and one of the current issues is its safe replacement by various analogues. Using larva zebrafish as a model, the present study reveals that moderate and chronic exposure to BPA analogues such as bisphenol S, bisphenol F and bisphenol AF may also affect vertebrate neurodevelopment and locomotor activity. Several parameters of embryo-larval development were investigated, such as mortality, hatching, number of mitotically active cell, as defined by 5-bromo-2'-deoxyuridine incorporation and proliferative cell nuclear antigen labelling, aromatase B protein expression in radial glial cell and locomotor activity. Our results show that exposure to several bisphenol analogues induced an acceleration of embryo hatching rate. At the level of the developing brain, a strong up-regulation of the oestrogen-sensitive Aromatase B was also detected in the hypothalamic region. This up-regulation was not associated with effects on the numbers of mitotically active progenitors nor differentiated neurones in the preoptic area and in the nuclear recessus posterior of the hypothalamus zebrafish larvae. Furthermore, using a high-throughput video tracking system to monitor locomotor activity in zebrafish larvae, we show that some bisphenol analogues, such as bisphenol AF, significantly reduced locomotor activity following 6 days of exposure. Taken together, our study provides evidence that BPA analogues can also affect the neurobehavioural development of zebrafish.

Zebrafish Models of Cancer-New Insights on Modeling Human Cancer in a Non-Mammalian Vertebrate

Zebrafish (Danio rerio) is a valuable non-mammalian vertebrate model widely used to study development and disease, including more recently cancer. The evolutionary conservation of cancer-related programs between human and zebrafish is striking and allows extrapolation of research outcomes obtained in fish back to humans. Zebrafish has gained attention as a robust model for cancer research mainly because of its high fecundity, cost-effective maintenance, dynamic visualization of tumor growth in vivo, and the possibility of chemical screening in large numbers of animals at reasonable costs. Novel approaches in modeling tumor growth, such as using transgene electroporation in adult zebrafish, could improve our knowledge about the spatial and temporal control of cancer formation and progression in vivo. Looking at genetic as well as epigenetic alterations could be important to explain the pathogenesis of a disease as complex as cancer. In this review, we highlight classic genetic and transplantation models of cancer in zebrafish as well as provide new insights on advances in cancer modeling. Recent progress in zebrafish xenotransplantation studies and drug screening has shown that zebrafish is a reliable model to study human cancer and could be suitable for evaluating patient-derived xenograft cell invasiveness. Rapid, large-scale evaluation of in vivo drug responses and kinetics in zebrafish could undoubtedly lead to new applications in personalized medicine and combination therapy. For all of the above-mentioned reasons, zebrafish is approaching a future of being a pre-clinical cancer model, alongside the mouse. However, the mouse will continue to be valuable in the last steps of pre-clinical drug screening, mostly because of the highly conserved mammalian genome and biological processes.

Testicular transcriptome alterations in zebrafish (Danio rerio) exposure to 17β-estradiol

The hormone 17β-estradiol (E₂) can be found in rivers, effluents, and even drinking water. Researches have demonstrated that E₂ affects various metabolic pathways through gene activation and may cause reproductive toxicity in fish. Therefore, the aim of this study was to evaluate E₂-induced toxicity via testicular transcriptome of zebrafish (Danio rerio) exposed to different concentrations (10 ng L^-1, and 100 ng L^-1) of E₂. A total of >600 significant differentially expressed genes (DEGs) were enriched among the three treatments. Short time-series expression miner analysis revealed five KEGG pathways including drug metabolism, other enzymes, calcium signaling pathway, ECM-receptor interaction, gap junction, and cell adhesion molecules. Twenty genes were selected to verify the accuracy of RNA-Seq. Other reported genes related to sex differentiation, development, energy metabolism, and other processes were found. One set of genes significantly increased/decreased/fluctuated over time, especially 12 h after E₂ exposure. Genes associated with ovaries (zp3c), and development (bmp15, gdf9, and sycp2l) were significantly upregulated with increasing E₂ concentration. E₂ and testosterone was significantly decreased by 10 (except for T) and 100 ng L^-1 E₂ exposure at 12 h. The current study demonstrated that sex differentiation, development, energy metabolism, immunity, and ribosome biogenesis in male zebrafish were all significantly affected by 17β-estradiol exposure through transcriptional alterations.

Transcriptomic analysis of short-term 17α-ethynylestradiol exposure in two Californian sentinel fish species sardine (Sardinops sagax) and mackerel (Scomber japonicus)

Endocrine disrupting chemicals (EDCs) are substances which disrupt normal functioning of the endocrine system by interfering with hormone regulated physiological pathways. Aquatic environments provide the ultimate reservoir for many EDCs as they enter rivers and the ocean via effluent discharges and accumulate in sediments. One EDC widely dispersed in municipal wastewater effluent discharges is 17α-ethynylestradiol (EE2), which is one of the most widely prescribed medicines. EE2 is a bio-active estrogen employed in the majority of oral contraceptive pill formulations. As evidence of the health risks posed by EDCs mount, there is an urgent need to improve diagnostic tools for monitoring the effects of pollutants. As the cost of high throughput sequencing (HTS) diminishes, transcriptional profiling of an organism in response to EDC perturbation presents a cost-effective way of screening a wide range of endocrine responses. Coastal pelagic filter feeding fish species analyzed using HTS provide an excellent tool for EDC risk assessment in the marine environment. Unfortunately, there are limited genome sequence data and annotation for many of these species including Pacific sardine (Sardinops sagax) and chub mackerel (Scomber japonicus), which limits the utility of molecular tools such as HTS to interrogate the effects of endocrine disruption. In this study, we carried out RNA sequencing (RNAseq) of liver RNA harvested from wild sardine and mackerel exposed for 5 h under laboratory conditions to a concentration of 12.5 pM EE2 in the tank water. We developed an analytical framework for transcriptomic analyses of species with limited genomic information. EE2 exposure altered expression patterns of key genes involved in important metabolic and physiological processes. The systems approach presented here provides a powerful tool for obtaining a comprehensive picture of endocrine disruption in aquatic organisms.

Effects of Estrogen and Estrogen Receptors on Transcriptomes of HepG2 Cells: A Preliminary Study Using RNA Sequencing

Men have a much higher incidence of hepatocellular carcinoma (HCC), the predominant form of liver cancer, than women, suggesting that estrogens play a protective role in liver cancer development and progression. To begin to understand the potential mechanisms of estrogens' inhibitory effects on HCC development, RNA sequencing was used to generate comprehensive global transcriptome profiles of the human HCC-derived HepG2 cell line following treatment of vehicle (control), estradiol (E2), estrogen receptor alpha- (ERα-) specific agonist 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole (PPT), or ERβ-specific agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) using a small set of cells. Gene ontology (GO) analysis identified increased expression of genes involved in the biological process (BP) of response to different stimuli and metabolic processes by E2 and ER agonists, which enhanced molecular function (MF) in various enzyme activities and chemical bindings. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional pathway analysis indicated enhanced pathways associated with carbohydrate metabolism, complement and coagulation cascades, and HIF-1 signaling pathway by E2 and ER agonists. GO analysis also identified decreased expression of genes by E2, PPT, and DPN involved in BP related to the cell cycle and cell division, which reduced MF in activity of multiple enzymes and microtubule activity. KEGG analysis indicated that E2, PPT, and DPN suppressed pathways associated with the cell cycle; E2 and PPT suppressed pathways associated with chemical carcinogenesis and drug metabolism, and DPN suppressed DNA replication, recombination, and repair. Collectively, these differentially expressed genes across HepG2 cell transcriptome involving cellular and metabolic processes by E2 and ER agonists provided mechanistic insight into protective effects of estrogens in HCC development.

The cyclin-like protein, SPY1, regulates the ERα and ERK1/2 pathways promoting tamoxifen resistance

The Ras/Raf/MEK/ERK pathway conveys growth factor and mitogen signalling to control the phosphorylation of a plethora of substrates regulating proliferation, survival, and migration. The Ras signalling pathway is frequently associated with poor prognosis and drug resistance in various cancers including those of the blood, breast and prostate. Activation of the downstream effector ERK does not always occur via a linear cascade of events; complicating the targeting of this pathway therapeutically. This work describes a novel positive feedback loop where the cell cycle regulatory factor Spy1 (RINGO; gene SPDYA) activates ERK1/2 in a MEK-independent fashion. Spy1 was originally isolated for the ability to stimulate Xenopus oocyte maturation via a MAPK-signalling pathway and is known to override apoptosis triggered by the DNA damage response. We demonstrate that mammalian Spy1-mediated ERK activation increases ligand-independent phosphorylation and activation of estrogen receptor α, correlating with a decrease in tamoxifen sensitivity. This could define a novel druggable mechanism driving proliferation and resistance in select cancers.

Stress differentially affects the systemic and leukocyte estrogen network in common carp

Both systemic and locally released steroid hormones, such as cortisol and estrogens, show immunomodulatory actions. This research gives evidence that circulating and leukocyte-derived estrogens can be involved in the regulation of the immune response in common carp, during homeostasis and upon restraining stress. It was found that stress reduced level of blood 17β-estradiol (E2) and down-regulated the gene expression of components of the "classical" estrogen system: the nuclear estrogen receptors and the aromatase CYP19, in the hypothalamus, the pituitary and in the ovaries. In contrast, higher gene expression of the nuclear estrogen receptors and cyp19a was found in the head kidney of stressed animals. Moreover, stress induced changes in the E2 level and in the estrogen sensitivity at local/leukocyte level. For the first time in fish, we showed the presence of physiologically relevant amounts of E2 and the substrates for its conversion (estrone - E1 and testosterone - T) in head kidney monocytes/macrophages and found that its production is modulated upon stress. Moreover, stress reduced the sensitivity of leukocytes towards estrogens, by down-regulation the expression of the erb and cyp19 genes in carp phagocytes. In contrast, era expression was up-regulated in the head kidney monocytes/macrophages and in PBLs derived from stressed animals. We hypothesize that, the increased expression of ERα, that was observed during stress, can be important for the regulation of leukocyte differentiation, maturation and migration. In conclusion, these results indicate that, in fish, the estrogen network can be actively involved in the regulation of the systemic and local stress response and the immune response.

Estrogen Repression of MicroRNAs Is Associated with High Guanine Content in the Terminal Loop Sequences of Their Precursors

Widespread microRNA (miRNA) repression is a phenomenon observed in mammals after exposure to cigarette smoke and in many types of cancer. A comprehensive reduction in miRNA expression after treatment with the hormone estrogen has also previously been described. Here, we reveal a conserved association of miRNA downregulation after estrogen exposure in zebrafish, mouse, and human breast cancer cell line, with a high guanine content in the terminal loop sequences of their precursors, and offer a possible link between estrogen-related miRNA-adducts formation and carcinogenesis. We also show common gene expression patterns shared by breast cancer tumors and estrogen-treated zebrafish, suggesting that this organism can be used as a powerful model system for the study of human breast cancer.

Nuclear receptor research in zebrafish

Nuclear receptors (NRs) form a superfamily of transcription factors that can be activated by ligands and are involved in a wide range of physiological processes. NRs are well conserved between vertebrate species. The zebrafish, an increasingly popular animal model system, contains a total of 73 NR genes, and orthologues of almost all human NRs are present. In this review article, an overview is presented of NR research in which the zebrafish has been used as a model. Research is described on the three most studied zebrafish NRs: the estrogen receptors (ERs), retinoic acid receptors (RARs) and peroxisome proliferator-activated receptors (PPARs). The studies on these receptors illustrate the versatility of the zebrafish as a model for ecotoxicological, developmental and biomedical research. Although the use of the zebrafish in NR research is still relatively limited, it is expected that in the next decade the full potential of this animal model will be exploited.

Contribution of G protein-coupled estrogen receptor 1 (GPER) to 17β-estradiol-induced developmental toxicity in zebrafish

Exposure to 17β-estradiol (E2) influences the regulation of multiple signaling pathways, and E2-mediated disruption of signaling events during early development can lead to malformations such as cardiac defects. In this study, we investigated the potential role of the G-protein estrogen receptor 1 (GPER) in E2-induced developmental toxicity. Zebrafish embryos were exposed to E2 from 2h post fertilization (hpf) to 76 hpf with subsequent transcriptional measurements of heart and neural crest derivatives expressed 2 (hand2), leucine rich repeat containing 10 (lrrc10), and gper at 12, 28 and 76 hpf. Alteration in the expression of lrrc10, hand2 and gper was observed at 12 hpf and 76 hpf, but not at 28 hpf. Expression of these genes was also altered after exposure to G1 (a GPER agonist) at 76 hpf. Expression of lrrc10, hand2 and gper all coincided with the formation of cardiac edema at 76 hpf as well as other developmental abnormalities. While co-exposure of G1 with G36 (a GPER antagonist) rescued G1-induced abnormalities and altered gene expression, co-exposure of E2 with G36, or ICI 182,780 (an estrogen receptor antagonist) did not rescue E2-induced cardiac deformities or gene expression. In addition, no effects on the concentrations of downstream ER and GPER signaling molecules (cAMP or calcium) were observed in embryo homogenates after E2 treatment. These data suggest that the impacts of E2 on embryonic development at this stage are complex and may involve multiple receptor and/or signaling pathways.

Effect of low doses of estradiol and tamoxifen on breast cancer cell karyotypes

Evidence supports a role of 17&-estradiol (E2) in carcinogenesis and the large majority of breast carcinomas are dependent on estrogen. The anti-estrogen tamoxifen (TAM) is widely used for both treatment and prevention of breast cancer; however, it is also carcinogenic in human uterus and rat liver, highlighting the profound complexity of its actions. The nature of E2- or TAM-induced chromosomal damage has been explored using relatively high concentrations of these agents, and only some numerical aberrations and chromosomal breaks have been analyzed. This study aimed to determine the effects of low doses of E2 and TAM (10(&8 )mol L(&1) and 10(&6 )mol L(&1) respectively) on karyotypes of MCF7, T47D, BT474, and SKBR3 breast cancer cells by comparing the results of conventional karyotyping and multi-FISH painting with cell proliferation. Estrogen receptor (ER)-positive (+) cells showed an increase in cell proliferation after E2 treatment (MCF7, T47D, and BT474) and a decrease after TAM treatment (MCF7 and T47D), whereas in ER& cells (SKBR3), no alterations in cell proliferation were observed, except for a small increase at 96 h. Karyotypes of both ER+ and ER& breast cancer cells increased in complexity after treatments with E2 and TAM leading to specific chromosomal abnormalities, some of which were consistent throughout the treatment duration. This genotoxic effect was higher in HER2+ cells. The ER&/HER2+ SKBR3 cells were found to be sensitive to TAM, exhibiting an increase in chromosomal aberrations. These in vitro results provide insights into the potential role of low doses of E2 and TAM in inducing chromosomal rearrangements in breast cancer cells.

Differential recruitment of co-regulatory proteins to the human estrogen receptor 1 in response to xenoestrogens

The diverse biological effects of xenoestrogens may be explained by their ability to differentially recruit co-regulatory proteins to the estrogen receptor (ER). We employed high-throughput receptor affinity binding and co-regulatory protein recruitment screening assays based on fluorescence polarization and time resolved florescence resonance energy transfer (TR-FRET), respectively, to assess xenoestrogen-specific binding and co-regulatory protein recruitment to the ER. Then we used a functional proteomic assay based on co-immunoprecipitation of ER-bound proteins to isolate and identify intact co-regulatory proteins recruited to a ligand-activated ER. Through these approaches, we revealed differential binding affinity of bisphenol-A (BPA) and genistein (GEN) to the human ERα (ESR1) and ligand-dependent recruitment of SRC-1 and SRC-3 peptides. Recruitment profiles were variable for each ligand and in some cases were distinct compared to 17β-estradiol (E2). For example, E2 and GEN recruited both SRC-1 and -3 peptides whereas BPA recruited only SRC-1 peptides. Results of the functional proteomic assay showed differential recruitment between ligands where E2 recruited the greatest number of proteins followed by BPA then GEN. A number of proteins share previously identified relationships with ESR1 as determined by STRING analysis. Although there was limited overlap in proteins identified between treatments, all ligands recruited proteins involved in cell growth as determined by subnetwork enrichment analysis (p<0.05). A comparative, in silico analysis revealed that fewer interactions exist between zebrafish (Danio rerio) esr1 and zebrafish orthologs of proteins identified in our functional proteomic analysis. Taken together these results identify recruitment of known and previously unknown co-regulatory proteins to ESR1 and highlight new methods to assay recruitment of low abundant and intact, endogenous co-regulatory proteins to ESR1 or other nuclear receptors, in both human and aquatic species.

Estrogenic Effects of Several BPA Analogs in the Developing Zebrafish Brain

Important set of studies have demonstrated the endocrine disrupting activity of Bisphenol A (BPA). The present work aimed at defining estrogenic-like activity of several BPA structural analogs, including BPS, BPF, BPAF, and BPAP, on 4- or 7-day post-fertilization (dpf) zebrafish larva as an in vivo model. We measured the induction level of the estrogen-sensitive marker cyp19a1b gene (Aromatase B), expressed in the brain, using three different in situ/in vivo strategies: (1) Quantification of cyp19a1b transcripts using RT-qPCR in wild type 7-dpf larva brains exposed to bisphenols; (2) Detection and distribution of cyp19a1b transcripts using in situ hybridization on 7-dpf brain sections (hypothalamus); and (3) Quantification of the cyp19a1b promoter activity in live cyp19a1b-GFP transgenic zebrafish (EASZY assay) at 4-dpf larval stage. These three different experimental approaches demonstrated that BPS, BPF, or BPAF exposure, similarly to BPA, significantly activates the expression of the estrogenic marker in the brain of developing zebrafish. In vitro experiments using both reporter gene assay in a glial cell context and competitive ligand binding assays strongly suggested that up-regulation of cyp19a1b is largely mediated by the zebrafish estrogen nuclear receptor alpha (zfERα). Importantly, and in contrast to other tested bisphenol A analogs, the bisphenol AP (BPAP) did not show estrogenic activity in our model.

17α-Ethinylestradiol (EE2) effect on global gene expression in primary rainbow trout (Oncorhynchus mykiss) hepatocytes

The potential impact of endocrine disrupting chemicals (EDCs) in the aquatic environment has driven the development of screening assays to evaluate the estrogenic properties of chemicals and their effects on aquatic organisms such as fish. However, obtaining full concentration-response relationships in animal (in vivo) exposure studies are laborious, costly and unethical, hence a need for developing feasible alternative (non-animal) methods. Use of in vitro bioassays such as primary fish hepatocytes, which retain many of the native properties of the liver, has been proposed for in vitro screening of estrogen receptor (ER) agonists and antagonists. The aim of present study was to characterize the molecular mode of action (MoA) of the ER agonist 17α-ethinylestradiol (EE2) in primary rainbow trout (Oncorhynchus mykiss) hepatocytes. A custom designed salmonid 60,000-feature (60k) oligonucleotide microarray was used to characterize the potential MoAs after 48h exposure to EE2. The microarray analysis revealed several concentration-dependent gene expression alterations including classical estrogen sensitive biomarker gene expression (e.g. estrogen receptor α, vitellogenin, zona radiata). Gene Ontology (GO) analysis displayed transcriptional changes suggesting interference of cellular growth, fatty acid and lipid metabolism potentially mediated through the estrogen receptor (ER), which were proposed to be associated with modulation of genes involved in endocrine function and reproduction. Pathway analysis supported the identified GOs and revealed modulation of additional genes associated with apoptosis and cholesterol biosynthesis. Differentially expressed genes (DEGs) related to impaired lipid metabolism (e.g. peroxisome proliferator-activated receptor α and γ), growth (e.g. insulin growth factor protein 1), phase I and II biotransformation (e.g. cytochrome P450 1A, sulfotransferase, UDP-glucuronosyltransferase and glutathione S-transferase) provided additional insight into the MoA of EE2 in primary fish hepatocytes. Results from the present study suggest that biotransformation, estrogen receptor-mediated responses, lipid homeostasis, growth and cancer/apoptosis in primary fish hepatocytes may be altered after short-term exposure to ER-agonists such as EE2. In many cases the observed changes were similar to those reported for estrogen-exposed fish in vivo. In conclusion, global transcriptional analysis demonstrated that EE2 affected a number of toxicologically relevant pathways associated with an estrogenic MoA in the rainbow trout hepatocytes.

Identification of estrogen target genes during zebrafish embryonic development through transcriptomic analysis

Estrogen signaling is important for vertebrate embryonic development. Here we have used zebrafish (Danio rerio) as a vertebrate model to analyze estrogen signaling during development. Zebrafish embryos were exposed to 1 µM 17β-estradiol (E2) or vehicle from 3 hours to 4 days post fertilization (dpf), harvested at 1, 2, 3 and 4 dpf, and subjected to RNA extraction for transcriptome analysis using microarrays. Differentially expressed genes by E2-treatment were analyzed with hierarchical clustering followed by biological process and tissue enrichment analysis. Markedly distinct sets of genes were up and down-regulated by E2 at the four different time points. Among these genes, only the well-known estrogenic marker vtg1 was co-regulated at all time points. Despite this, the biological functional categories targeted by E2 were relatively similar throughout zebrafish development. According to knowledge-based tissue enrichment, estrogen responsive genes were clustered mainly in the liver, pancreas and brain. This was in line with the developmental dynamics of estrogen-target tissues that were visualized using transgenic zebrafish containing estrogen responsive elements driving the expression of GFP (Tg(5xERE:GFP)). Finally, the identified embryonic estrogen-responsive genes were compared to already published estrogen-responsive genes identified in male adult zebrafish (Gene Expression Omnibus database). The expressions of a few genes were co-regulated by E2 in both embryonic and adult zebrafish. These could potentially be used as estrogenic biomarkers for exposure to estrogens or estrogenic endocrine disruptors in zebrafish. In conclusion, our data suggests that estrogen effects on early embryonic zebrafish development are stage- and tissue- specific.

Morpholino-mediated knockdown of ERα, ERβa, and ERβb mRNAs in zebrafish (Danio rerio) embryos reveals differential regulation of estrogen-inducible genes

Genetically distinct estrogen receptor (ER) subtypes (ERα and ERβ) play a major role in mediating estrogen actions in vertebrates, but their unique and overlapping functions are not entirely clear. Although mammals have 1 gene of each subtype (ESR1 and ESR2), teleost fish have a single esr1 (ERα) and 2 esr2 (ERβa and ERβb) genes. To determine the in vivo role of different ER isoforms in regulating estrogen-inducible transcription targets, zebrafish (Danio rerio) embryos were microinjected with esr-specific morpholino (MO) oligonucleotides to disrupt splicing of the exon III/intron III junction in the DNA-binding domain. Each MO knocked down its respective normal transcript and increased production of variants with a retained intron III (esr1 MO) or a deleted or mis-spliced exon III (esr2a and esr2b MOs). Both esr1 and esr2b MOs blocked estradiol induction of vitellogenin and ERα mRNAs, predominant hepatic genes, but esr2b was the only MO that blocked induction of cytochrome P450 aromatase B mRNA, a predominant brain gene. Knockdown of ERβa with the esr2a MO had no effect on estrogen induction of the 3 mRNAs but, when coinjected with esr1 MO, attenuated the effect of ERα knockdown. Results indicate that ERα and ERβb, acting separately or cooperatively on specific gene targets, are positive transcriptional regulators of estrogen action, but the role of ERβa, if any, is unclear. We conclude that MO technology in zebrafish embryos is an advantageous approach for investigating the interplay of ER subtypes in a true physiological context.

Perfluorooctane sulfonate (PFOS) affects hormone receptor activity, steroidogenesis, and expression of endocrine-related genes in vitro and in vivo

Perfluorooctane sulfonate (PFOS) is a widespread and persistent chemical in the environment. We investigated the endocrine-disrupting effects of PFOS using a combination of in vitro and in vivo assays. Reporter gene assays were used to detect receptor-mediated (anti-)estrogenic, (anti-)androgenic, and (anti-)thyroid hormone activities. The effect of PFOS on steroidogenesis was assessed both at hormone levels in the supernatant and at expression levels of hormone-induced genes in the H295R cell. A zebrafish-based short-term screening method was developed to detect the effect of PFOS on endocrine function in vivo. The results indicate that PFOS can act as an estrogen receptor agonist and thyroid hormone receptor antagonist. Exposure to PFOS decreased supernatant testosterone (T), increased estradiol (E2) concentrations in H295R cell medium and altered the expression of several genes involved in steroidogenesis. In addition, PFOS increased early thyroid development gene (hhex and pax8) expression in a concentration-dependent manner, decreased steroidogenic enzyme gene (CYP17, CYP19a, CYP19b) expression, and changed the expression pattern of estrogen receptor production genes (esr1, esr2b) after 500 µg/L PFOS treatment in zebrafish embryos. These results indicate that PFOS has the ability to act as an endocrine disruptor both in vitro and in vivo by disrupting the function of nuclear hormone receptors, interfering with steroidogenesis, and altering the expression of endocrine-related genes in zebrafish embryo.

Transcriptomic analyses of sexual dimorphism of the zebrafish liver and the effect of sex hormones

The liver is one of the most sex-dimorphic organs in both oviparous and viviparous animals. In order to understand the molecular basis of the difference between male and female livers, high-throughput RNA-SAGE (serial analysis of gene expression) sequencing was performed for zebrafish livers of both sexes and their transcriptomes were compared. Both sexes had abundantly expressed genes involved in translation, coagulation and lipid metabolism, consistent with the general function of the liver. For sex-biased transcripts, from in addition to the high enrichment of vitellogenin transcripts in spawning female livers, which constituted nearly 80% of total mRNA, it is apparent that the female-biased genes were mostly involved in ribosome/translation, estrogen pathway, lipid transport, etc, while the male-biased genes were enriched for oxidation reduction, carbohydrate metabolism, coagulation, protein transport and localization, etc. Sexual dimorphism on xenobiotic metabolism and anti-oxidation was also noted and it is likely that retinol x receptor (RXR) and liver x receptor (LXR) play central roles in regulating the sexual differences of lipid and cholesterol metabolisms. Consistent with high ribosomal/translational activities in the female liver, female-biased genes were significantly regulated by two important transcription factors, Myc and Mycn. In contrast, Male livers showed activation of transcription factors Ppargc1b, Hnf4a, and Stat4, which regulate lipid and glucose metabolisms and various cellular activities. The transcriptomic responses to sex hormones, 17β-estradiol (E2) or 11-keto testosterone (KT11), were also investigated in both male and female livers and we found that female livers were relatively insensitive to sex hormone disturbance, while the male livers were readily affected. E2 feminized male liver by up-regulating female-biased transcripts and down-regulating male-biased transcripts. The information obtained in this study provides comprehensive insights into the sexual dimorphism of zebrafish liver transcriptome and will facilitate further development of the zebrafish as a human liver disease model.

Identification of estrogen responsive genes using esophageal squamous cell carcinoma (ESCC) as a model

Background

Estrogen therapy has positively impact the treatment of several cancers, such as prostate, lung and breast cancers. Moreover, several groups have reported the importance of estrogen induced gene regulation in esophageal cancer (EC). This suggests that there could be a potential for estrogen therapy for EC. The efficient design of estrogen therapies requires as complete as possible list of genes responsive to estrogen. Our study develops a systems biology methodology using esophageal squamous cell carcinoma (ESCC) as a model to identify estrogen responsive genes. These genes, on the other hand, could be affected by estrogen therapy in ESCC.

Results

Based on different sources of information we identified 418 genes implicated in ESCC. Putative estrogen responsive elements (EREs) mapped to the promoter region of the ESCC genes were used to initially identify candidate estrogen responsive genes. EREs mapped to the promoter sequence of 30.62% (128/418) of ESCC genes of which 43.75% (56/128) are known to be estrogen responsive, while 56.25% (72/128) are new candidate estrogen responsive genes. EREs did not map to 290 ESCC genes. Of these 290 genes, 50.34% (146/290) are known to be estrogen responsive. By analyzing transcription factor binding sites (TFBSs) in the promoters of the 202 (56+146) known estrogen responsive ESCC genes under study, we found that their regulatory potential may be characterized by 44 significantly over-represented co-localized TFBSs (cTFBSs). We were able to map these cTFBSs to promoters of 32 of the 72 new candidate estrogen responsive ESCC genes, thereby increasing confidence that these 32 ESCC genes are responsive to estrogen since their promoters contain both: a/mapped EREs, and b/at least four cTFBSs characteristic of ESCC genes that are responsive to estrogen. Recent publications confirm that 47% (15/32) of these 32 predicted genes are indeed responsive to estrogen.

Conclusion

To the best of our knowledge our study is the first to use a cancer disease model as the framework to identify hormone responsive genes. Although we used ESCC as the disease model and estrogen as the hormone, the methodology can be extended analogously to other diseases as the model and other hormones. We believe that our results provide useful information for those interested in genes responsive to hormones and in the design of hormone-based therapies.

Functional test of Brassica self-incompatibility modifiers in Arabidopsis thaliana

The self-incompatibility (SI) system of the Brassicaceae is based on allele-specific interactions among haplotypes of the S locus. In all tested self-incompatible Brassicaceae, the S haplotype encompasses two linked genes, one encoding the S-locus receptor kinase (SRK), a transmembrane kinase displayed at the surface of stigma epidermal cells, and the other encoding its ligand, the S-locus cysteine-rich (SCR) protein, which is localized in the pollen coat. Transfer of the two genes to self-fertile Arabidopsis thaliana allowed the establishment of robust SI in several accessions, indicating that the signaling cascade triggered by this receptor-ligand interaction and the resulting inhibition of "self" pollen by the stigma have been maintained in extant A. thaliana. Based on studies in Brassica species, the membrane-tethered kinase MLPK, the ARM repeat-containing U-box protein ARC1, and the exocyst subunit Exo70A1 have been proposed to function as components of an SI signaling cascade. Here we tested the role of these molecules in the SI response of A. thaliana SRK-SCR plants. We show that the A. thaliana ARC1 ortholog is a highly decayed pseudogene. We also show that, unlike reports in Brassica, inactivation of the MLPK ortholog AtAPK1b and overexpression of Exo70A1 neither abolish nor weaken SI in A. thaliana SRK-SCR plants. These results do not support a role for these molecules in the SI response of A. thaliana.