Estrogen receptor beta expression and role in cancers.

Estrogen drives the growth of some cancers, such as breast cancer, via estrogen receptor alpha (ERα). Estrogen also activates ERß, but whether ERß is expressed and has a role in different cancers is debated. The use of nonspecific antibodies has contributed to the confusion, and this review delves into ERß's controversial role in cancer and focuses on tumor expression that can be supported by non-antibody-dependent assays. We discuss its expression at the transcript level and focus on its potential role in lymphoma, granulosa cell tumors, testicular, and adrenal cancers, emphasizing recent findings and the complexities that necessitate further research.

Estrogen receptor activation remodels TEAD1 gene expression to alleviate hepatic steatosis.

Sex-based differences in obesity-related hepatic malignancies suggest the protective roles of estrogen. Using a preclinical model, we dissected estrogen receptor (ER) isoform-driven molecular responses in high-fat diet (HFD)-induced liver diseases of male and female mice treated with or without an estrogen agonist by integrating liver multi-omics data. We found that selective ER activation recovers HFD-induced molecular and physiological liver phenotypes. HFD and systemic ER activation altered core liver pathways, beyond lipid metabolism, that are consistent between mice and primates. By including patient cohort data, we uncovered that ER-regulated enhancers govern central regulatory and metabolic genes with clinical significance in metabolic dysfunction-associated steatotic liver disease (MASLD) patients, including the transcription factor TEAD1. TEAD1 expression increased in MASLD patients, and its downregulation by short interfering RNA reduced intracellular lipid content. Subsequent TEAD small molecule inhibition improved steatosis in primary human hepatocyte spheroids by suppressing lipogenic pathways. Thus, TEAD1 emerged as a new therapeutic candidate whose inhibition ameliorates hepatic steatosis.

Ovarian ERß cistrome and transcriptome reveal chromatin interaction with LRH-1.

BACKGROUND: Estrogen receptor beta (ERß, Esr2) plays a pivotal role in folliculogenesis and ovulation, yet its exact mechanism of action is mainly uncharacterized. RESULTS: We here performed ERß ChIP-sequencing of mouse ovaries followed by complementary RNA-sequencing of wild-type and ERß knockout ovaries. By integrating the ERß cistrome and transcriptome, we identified its direct target genes and enriched biological functions in the ovary. This demonstrated its strong impact on genes regulating organism development, cell migration, lipid metabolism, response to hypoxia, and response to estrogen. Cell-type deconvolution analysis of the bulk RNA-seq data revealed a decrease in luteal cells and an increased proportion of theca cells and a specific type of cumulus cells upon ERß loss. Moreover, we identified a significant overlap with the gene regulatory network of liver receptor homolog 1 (LRH-1, Nr5a2) and showed that ERß and LRH-1 extensively bound to the same chromatin locations in granulosa cells. Using ChIP-reChIP, we corroborated simultaneous ERß and LRH-1 co-binding at the ERß-repressed gene Greb1 but not at the ERß-upregulated genes Cyp11a1 and Fkbp5. Transactivation assay experimentation further showed that ERß and LRH-1 can inhibit their respective transcriptional activity at classical response elements. CONCLUSIONS: By characterizing the genome-wide endogenous ERß chromatin binding, gene regulations, and extensive crosstalk between ERß and LRH-1, along with experimental corroborations, our data offer genome-wide mechanistic underpinnings of ovarian physiology and fertility.

ERß in Granulosa Cell Tumors and Its Clinical Potential.

Granulosa cell tumors (GCTs) are rare ovarian tumors comprising an adult and a juvenile subtype. They have a generally good prognosis, but the survival rate drastically declines in patients with late-stage or recurring tumors. Due to the rarity of GCTs, the tumor type is largely understudied and lacks a specific treatment strategy. Estrogen receptor beta (ERß/ESR2) has been found to be highly expressed in GCTs, which could be of therapeutic importance since it can be targeted with small molecules. However, its role in GCTs is not known. In this review, we summarize the current knowledge about the action of ERß in the ovary and discuss its prospective role in GCTs.

High-fat diet and estrogen modulate the gut microbiota in a sex-dependent manner in mice.

A high-fat diet can lead to gut microbiota dysbiosis, chronic intestinal inflammation, and metabolic syndrome. Notably, resulting phenotypes, such as glucose and insulin levels, colonic crypt cell proliferation, and macrophage infiltration, exhibit sex differences, and females are less affected. This is, in part, attributed to sex hormones. To investigate if there are sex differences in the microbiota and if estrogenic ligands can attenuate high-fat diet-induced dysbiosis, we used whole-genome shotgun sequencing to characterize the impact of diet, sex, and estrogenic ligands on the microbial composition of the cecal content of mice. We here report clear host sex differences along with remarkably sex-dependent responses to high-fat diet. Females, specifically, exhibited increased abundance of Blautia hansenii, and its levels correlated negatively with insulin levels in both sexes. Estrogen treatment had a modest impact on the microbiota diversity but altered a few important species in males. This included Collinsella aerofaciens F, which we show correlated with colonic macrophage infiltration. In conclusion, male and female mice exhibit clear differences in their cecal microbial composition and in how diet and estrogens impact the composition. Further, specific microbial strains are significantly correlated with metabolic parameters.

Long-term SARS-CoV-2 surveillance in the wastewater of Stockholm: What lessons can be learned from the Swedish perspective?

Wastewater-based epidemiology (WBE) can be used to track the spread of SARS-CoV-2 in a population. This study presents the learning outcomes from over two-year long monitoring of SARS-CoV-2 in Stockholm, Sweden. The three main wastewater treatment plants in Stockholm, with a total of six inlets, were monitored from April 2020 until June 2022 (in total 600 samples). This spans five major SARS-CoV-2 waves, where WBE data provided early warning signals for each wave. Further, the measured SARS-CoV-2 content in the wastewater correlated significantly with the level of positive COVID-19 tests (r = 0.86; p << 0.0001) measured by widespread testing of the population. Moreover, as a proof-of-concept, six SARS-CoV-2 variants of concern were monitored using hpPCR assay, demonstrating that variants can be traced through wastewater monitoring. During this long-term surveillance, two sampling protocols, two RNA concentration/extraction methods, two calculation approaches, and normalization to the RNA virus Pepper mild mottle virus (PMMoV) were evaluated. In addition, a study of storage conditions was performed, demonstrating that the decay of viral RNA was significantly reduced upon the addition of glycerol to the wastewater before storage at -80 °C. Our results provide valuable information that can facilitate the incorporation of WBE as a prediction tool for possible future outbreaks of SARS-CoV-2 and preparations for future pandemics.

ERß and Inflammation.

Estrogen, through the regulation of cytokine production, can act both as pro-inflammatory and anti-inflammatory signals dependent on the tissue context. In breast cancer cells, ERα is known to modulate inflammatory signaling through interaction with NFκB. Whether ERß has a role in inflammation is less explored. Low levels of ERß have been corroborated in several immune-related organs and, for example, in colonic epithelial cells. Specifically, an impact of ERß on colitis and colitis-associated colorectal cancer (CRC) is experimentally supported, using ERß-selective agonists, full-body ERß knockout mice and, most recently, intestinal epithelial-specific knockout mice. An intricate crosstalk between ERß and TNFα/NFκB signaling in the colon is supported, and ERß activation appears to reduce macrophage infiltration also during high fat diet (HFD)-induced colon inflammation. Finally, the gut microbiota plays a fundamental role in the pathogenesis of colitis and ERß has been indicated to modulate the microbiota diversity during colitis and colitis-induced CRC. ERß is thus proposed to protect against colitis, by modulating NFκB signaling, immune cell infiltration, and/or microbiota composition. Selective activation of ERß may therefore constitute a suitable preventative approach for the treatment of for example colitis-associated CRC.

Colitis Induces Sex-Specific Intestinal Transcriptomic Responses in Mice.

There are significant sex differences in colorectal cancer (CRC), including in incidence, onset, and molecular characteristics. Further, while inflammatory bowel disease (IBD) is a risk factor for CRC in both sexes, men with IBD have a 60% higher risk of developing CRC compared to women. In this study, we investigated sex differences during colitis-associated CRC (CAC) using a chemically induced CAC mouse model. The mice were treated with azoxymethane (AOM) and dextran sodium sulfate (DSS) and followed for 9 and 15 weeks. We performed RNA-sequencing of colon samples from males (n = 15) and females (n = 15) to study different stages of inflammation and identify corresponding transcriptomic sex differences in non-tumor colon tissue. We found a significant transcriptome response to AOM/DSS treatment in both sexes, including in pathways related to inflammation and cell proliferation. Notably, we found a stronger response in males and that male-specific differentially expressed genes were involved in NFκB signaling and circadian rhythm. Further, an overrepresented proportion of male-specific gene regulations were predicted to be targets of Stat3, whereas for females, targets of the glucocorticoid receptor (Gr/Nr3c1) were overrepresented. At 15 weeks, the most apparent sex difference involved genes with functions in T cell proliferation, followed by the regulation of demethylases. The majority of sex differences were thus related to inflammation and the immune system. Our novel data, profiling the transcriptomic response to chemically induced colitis and CAC, indicate clear sex differences in CRC initiation and progression.

Expression Profiles of Estrogen-Regulated MicroRNAs in Cancer Cells.

MicroRNAs play critical roles through their impact on posttranscriptional gene regulation. In cancer, they can act as oncogenes or tumor suppressors and can also function as biomarkers. Here, we describe a method for robust characterization of estrogen-regulated microRNA profiles. The activity of estrogen is mediated by two nuclear receptors, estrogen receptor alpha and estrogen receptor beta, and a transmembrane G-protein coupled estrogen receptor 1. This chapter details how to prepare cells for optimal estrogen response, directions for estrogen treatment, RNA extraction, different microRNA profiling approaches, and subsequent confirmations.

Estrogen Receptor Beta Influences the Inflammatory p65 Cistrome in Colon Cancer Cells.

Inflammation is a primary component of both initiation and promotion of colorectal cancer (CRC). Cytokines secreted by macrophages, including tumor necrosis factor alpha (TNFα), activates the pro-survival transcription factor complex NFκB. The precise mechanism of NFκB in CRC is not well studied, but we recently reported the genome-wide transcriptional impact of TNFα in two CRC cell lines. Further, estrogen signaling influences inflammation in a complex manner and suppresses CRC development. CRC protective effects of estrogen have been shown to be mediated by estrogen receptor beta (ERß, ESR2), which also impacts inflammatory signaling of the colon. However, whether ERß impacts the chromatin interaction (cistrome) of the main NFκB subunit p65 (RELA) is not known. We used p65 chromatin immunoprecipitation followed by sequencing (ChIP-Seq) in two different CRC cell lines, HT29 and SW480, with and without expression of ERß. We here present the p65 colon cistrome of these two CRC cell lines. We identify that RELA and AP1 motifs are predominant in both cell lines, and additionally describe both common and cell line-specific p65 binding sites and correlate these to transcriptional changes related to inflammation, migration, apoptosis and circadian rhythm. Further, we determine that ERß opposes a major fraction of p65 chromatin binding in HT29 cells, but enhances p65 binding in SW480 cells, thereby impacting the p65 cistrome differently in the two cell lines. However, the biological functions of the regulated genes appear to have similar roles in both cell lines. To our knowledge, this is the first time the p65 CRC cistrome is compared between different cell lines and the first time an influence by ERß on the p65 cistrome is investigated. Our work provides a mechanistic foundation for a better understanding of how estrogen influences inflammatory signaling through NFκB in CRC cells.

Genome-wide estrogen receptor ß chromatin binding in human colon cancer cells reveals its tumor suppressor activity.

Colorectal cancer (CRC) is the third leading cause of cancer death in the western world. In women, menopausal hormone therapy has been shown to reduce CRC incidence by 20%. Studies demonstrate that estrogen activating estrogen receptor beta (ERß) protects against CRC. ERß is a nuclear receptor that regulates gene expression through interactions with the chromatin. This molecular mechanism is, however, not well characterized in colon. Here, we present for the first time, the cistrome of ERß in different colon cancer cell lines. We use cell lines engineered to express ERß, optimize and validate an ERß antibody for chromatin-immunoprecipitation (ChIP), and perform ChIP-Seq. We identify key binding motifs, including ERE, AP-1, and TCF sites, and we determine enrichment of binding to cis-regulatory chromatin sites of genes involved in tumor development, cell migration, cell adhesion, apoptosis, and Wnt signaling pathways. We compare the corresponding cistromes of colon and breast cancer and find that they are conserved for about a third of genes, including GREB1, but that ERß tethering to TCF and KLF family motifs is characteristic for colon. We exemplify upregulation of putative CRC tumor suppressor gene CST5 where ERß in colon cells binds to cis-regulatory regions nearby (-351 bp) the transcriptional start site. Our work provides a foundation for understanding the mechanism of action of ERß in CRC prevention.

Blocking Fra-1 sensitizes triple-negative breast cancer to PARP inhibitor.

The AP-1 member Fra-1 is overexpressed in TNBC and plays crucial roles in tumor progression and treatment resistance. In a previous large-scale screen, we identified PARP1 to be among 118 proteins that interact with endogenous chromatin-bound Fra-1 in TNBC cells. PARP1 inhibitor (olaparib) is currently in clinical use for treatment of BRCA-mutated TNBC breast cancer. Here, we demonstrate that the Fra-1-PARP1 interaction impacts the efficacy of olaparib treatment. We show that PARP1 interacts with and downregulates Fra-1, thereby reducing AP-1 transcriptional activity. Olaparib treatment, or silencing of PARP1, consequently, increases Fra-1 levels and enhances its transcriptional activity. Increased Fra-1 can have adverse effect, including treatment resistance. We also found that a large fraction of PARP1-regulated genes was dependent on Fra-1. We show that by inhibiting Fra-1/AP-1, non-BRCA-mutated TNBC cells can become sensitized to olaparib treatment. We identify that high PARP1 expression is indicative of a poor clinical outcome in breast cancer patients overall (P = 0.01), but not for HER-2 positive patients. In conclusion, by exploring the functionality of the Fra-1 and PARP1 interaction, we propose that targeting Fra-1 could serve as a combinatory therapeutic approach to improve olaparib treatment outcome for TNBC patients.

Intestinal estrogen receptor beta suppresses colon inflammation and tumorigenesis in both sexes.

Estrogen hormones protect against colorectal cancer (CRC) and a preventative role of estrogen receptor beta (ERß) on CRC has been supported using full knockout animals. However, it is unclear through which cells or organ ERß mediates this effect. To investigate the functional role of intestinal ERß during colitis-associated CRC we used intestine-specific ERß knockout mice treated with azoxymethane and dextran sodium sulfate, followed by ex vivo organoid culture to corroborate intrinsic effects. We explored genome-wide impact on TNFα signaling using human CRC cell lines and chromatin immunoprecipitation assay to mechanistically characterize the regulation of ERß. Increased tumor formation in males and tumor size in females was noted upon intestine-specific ERß knockout, accompanied by enhanced local expression of TNFα, deregulation of key NFκB targets, and increased colon ulceration. Unexpectedly, we noted especially strong effects in males. We corroborated that intestinal ERß protects against TNFα-induced damage intrinsically, and characterized an underlying genome-wide signaling mechanism in CRC cell lines whereby ERß binds to cis-regulatory chromatin areas of key NFκB regulators. Our results support a protective role of intestinal ERß against colitis-associated CRC, proposing new therapeutic strategies.

Sex-specific lipid molecular signatures in obesity-associated metabolic dysfunctions revealed by lipidomic characterization in ob/ob mouse.

The response to overfeeding is sex dependent, and metabolic syndrome is more likely associated to obesity in men or postmenopausal women than in young fertile women. We hypothesized that obesity-induced metabolic syndrome is sex dependent due to a sex-specific regulation of the fatty acid (FA) synthesis pathways in liver and white adipose depots. We aimed to identify distinctive molecular signatures between sexes using a lipidomics approach to characterize lipid species in liver, perigonadal adipose tissue, and inguinal adipose tissue and correlate them to the physiopathological responses observed. Males had less total fat but lower subcutaneous on visceral fat ratio together with higher liver weight and higher liver and serum triglyceride (TG) levels. Males were insulin resistant compared to females. Fatty acid (FA) and TG profiles differed between sexes in both fat pads, with longer chain FAs and TGs in males compared to that in females. Remarkably, hepatic phospholipid composition was sex dependent with more abundant lipotoxic FAs in males than in females. This may contribute to the sexual dimorphism in response to obesity towards more metaflammation in males. Our work presents an exhaustive novel description of a sex-specific lipid signature in the pathophysiology of metabolic disorders associated with obesity in ob/ob mice. These data could settle the basis for future pharmacological treatment in obesity.

Skeletal muscle as a target of LXR agonist after long-term treatment: focus on lipid homeostasis.

The liver X receptors (LXR)α and LXRß are transcription factors belonging to the nuclear receptor family, which play a central role in metabolic homeostasis, being master regulators of key target genes in the glucose and lipid pathways. Wild-type (WT), LXRα(-/-), and LXRß(-/-) mice were fed a chow diet with (treated) or without (control) the synthetic dual LXR agonist GW3965 for 5 wk. GW3965 raised intrahepatic triglyceride (TG) level but, surprisingly, reduced serum TG level through the activation of serum lipase activity. The serum TG reduction was associated with a repression of both catecholamine-stimulated lipolysis and relative glucose incorporation into lipid in isolated adipocytes through activation of LXRß. We also demonstrated that LXRα is required for basal (nonstimulated) adipocyte metabolism, whereas LXRß acts as a repressor of lipolysis. On the contrary, in skeletal muscle (SM), the lipogenic and cholesterol transporter LXR target genes were markedly induced in WT and LXRα(-/-) mice and to a lesser extent in LXRß(-/-) mice following treatment with GW3965. Moreover, TG content was reduced in SM of LXRß(-/-) mice, associated with increased expression of the main TG-lipase genes Hsl and Atgl. Energy expenditure was increased, and a switch from glucose to lipid oxidation was observed. In conclusion, we provide evidence that LXR might be an essential regulator of the lipid balance between tissues to ensure appropriate control of the flux of fuel. Importantly, we show that, after chronic treatment with GW3965, SM becomes the target tissue for LXR activation, as opposed to liver, in acute treatment.

LXR activation by GW3965 alters fat tissue distribution and adipose tissue inflammation in ob/ob female mice.

To investigate the role of liver X receptor (LXR) in adipose tissue metabolism during obesity, ob/ob mice were treated for 5 weeks with the synthetic LXR agonist GW3965. MRI analysis revealed that pharmacological activation of LXR modified fat distribution by decreasing visceral (VS) fat and inversely increasing subcutaneous (SC) fat storage without affecting whole body fat content. This was concordant with opposite regulation by GW3965 of the lipolytic markers hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) in the two fat depots; moreover, the expression of genes involved in lipogenesis was significantly induced in SC fat. Lipidomic analysis suggested that changes in lipid composition in response to GW3965 also varied between VS and SC fat. In both depots, the observed alteration in lipid composition indicated an overall change toward less lipotoxic lipids. Flow cytometry analysis showed decreased immune cell infiltration in adipose tissue of ob/ob mice in response to GW3965 treatment, which in VS fat mainly affected the macrophage population and in SC fat the lymphocyte population. In line with this, the expression and secretion of proinflammatory markers was decreased in both fat deposits with GW3965 treatment.

Fasting-induced FGF21 is repressed by LXR activation via recruitment of an HDAC3 corepressor complex in mice.

The liver plays a pivotal role in the physiological adaptation to fasting and a better understanding of the metabolic adaptive responses may give hints on new therapeutic strategies to control the metabolic diseases. The liver X receptors (LXRs) are well-established regulators of lipid and glucose metabolism. More recently fibroblast growth factor 21 (FGF21) has emerged as an important regulator of energy homeostasis. We hypothesized that the LXR transcription factors could influence Fgf21 expression, which is induced in response to fasting. Wild-type, LXRα(-/-), and LXRß(-/-) mice were treated for 3 d with vehicle or the LXR agonist GW3965 and fasted for 12 h prior to the killing of the animals. Interestingly, serum FGF21 levels were induced after fasting, but this increase was blunted when the mice were treated with GW3965 independently of genotypes. Compared with wild-type mice, GW3965-treated LXRα(-/-) and LXRß(-/-) mice showed improved insulin sensitivity and enhanced ketogenic response at fasting. Of note is that during fasting, GW3965 treatment tended to reduce liver triglycerides as opposed to the effect of the agonist in the fed state. The LXR-dependent repression of Fgf21 seems to be mainly mediated by the recruitment of LXRß onto the Fgf21 promoter upon GW3965 treatment. This repression by LXRß occurs through the recruitment and stabilization of the repressor complex composed of retinoid-related orphan receptor-α/Rev-Erbα/histone deacetylase 3 onto the Fgf21 promoter. Our data clearly demonstrate that there is a cross talk between the LXR and FGF21 signaling pathways in the adaptive response to fasting.

Liver X receptors regulate de novo lipogenesis in a tissue-specific manner in C57BL/6 female mice.

The liver X receptors (LXRs) play a key role in cholesterol and bile acid metabolism but are also important regulators of glucose metabolism. Recently, LXRs have been proposed as a glucose sensor affecting LXR-dependent gene expression. We challenged wild-type (WT) and LXRαß(-/-) mice with a normal diet (ND) or a high-carbohydrate diet (HCD). Magnetic resonance imaging showed different fat distribution between WT and LXRαß(-/-) mice. Surprisingly, gonadal (GL) adipocyte volume decreased on HCD compared with ND in WT mice, whereas it slightly increased in LXRαß(-/-) mice. Interestingly, insulin-stimulated lipogenesis of isolated GL fat cells was reduced on HCD compared with ND in LXRαß(-/-) mice, whereas no changes were observed in WT mice. Net de novo lipogenesis (DNL) calculated from Vo(2) and Vco(2) was significantly higher in LXRαß(-/-) than in WT mice on HCD. Histology of HCD-fed livers showed hepatic steatosis in WT mice but not in LXRαß(-/-) mice. Glucose tolerance was not different between groups, but insulin sensitivity was decreased by the HCD in WT but not in LXRαß(-/-) mice. Finally, gene expression analysis of adipose tissue showed induced expression of genes involved in DNL in LXRαß(-/-) mice compared with WT animals as opposed to the liver, where expression of DNL genes was repressed in LXRαß(-/-) mice. We thus conclude that absence of LXRs stimulates DNL in adipose tissue, but suppresses DNL in the liver, demonstrating opposite roles of LXR in DNL regulation in these two tissues. These results show tissue-specific regulation of LXR activity, a crucial finding for drug development.

Both liver-X receptor (LXR) isoforms control energy expenditure by regulating brown adipose tissue activity.

Brown adipocytes are multilocular lipid storage cells that play a crucial role in nonshivering thermogenesis. Uncoupling protein 1 (UCP1) is a unique feature of brown fat cells that allows heat generation on sympathetic nervous system stimulation. As conventional transcriptional factors that are activated in various signaling pathways, liver-X receptors (LXRs) play important roles in many physiological processes. The role of LXRs in the regulation of energy homeostasis remains unclear, however. Female WT, LXRαß(-/-), LXRα(-/-), and LXRß(-/-) mice were fed with either a normal diet (ND) or a high-carbohydrate diet (HCD) supplemented with or without GW3965-LXR agonist. LXRαß(-/-) mice exhibited higher energy expenditure (EE) as well as higher UCP1 expression in brown adipose tissue (BAT) compared with WT mice on the HCD. In addition, long-term treatment of WT mice with GW3965 showed lower EE at thermoneutrality (30 °C) and lower Ucp1 expression level in BAT. Furthermore, H&E staining of the BAT of LXRαß(-/-) mice exhibited decreased lipid droplet size compared with WT mice on the HCD associated with a more intense UCP1-positive reaction. Quantification of triglyceride (TG) content in BAT showed lower TG accumulation in LXRß(-/-) mice compared with WT mice. Surprisingly, GW3965 treatment increased TG content (twofold) in the BAT of WT and LXRα(-/-) mice but not in LXRß(-/-) mice. Furthermore, glucose transporter (GLUT4) in the BAT of LXRα(-/-) and LXRß(-/-) mice was sixfold and fourfold increased, respectively, compared with WT mice on the ND. These findings suggest that LXRα as well as LXRß could play a crucial role in the regulation of energy homeostasis in female mice and may be a potential target for the treatment of obesity and energy regulation.

Levels of 17beta-estradiol receptors expressed in embryonic and adult zebrafish following in vivo treatment of natural or synthetic ligands.

The nuclear receptors encompass a group of regulatory proteins involved in a number of physiological processes. The estrogen receptors (ERs), of which one alpha and one beta form exist in mammals function as transcription factors in response to 17beta-estradiol (E2). In zebrafish there are three gene products of estrogen receptors and they are denoted esr1 (ERalpha), esr2a (ERbeta2) and esr2b (ERbeta1). Total RNA of zebrafish early life stages (<3, 6, 12, 24, 48, 72, 96 and 120 hours post fertilization) and of adult fish (liver, intestine, eye, heart, brain, ovary, testis, gill, swim bladder and kidney) were isolated following in vivo exposures. Using specific primers for each of the three zebrafish ERs the expression levels were quantified using real time PCR methodology. It was shown that in absence of exposure all three estrogen receptors were expressed in adult fish. The levels of expression of two of these three ER genes, the esr1 and esr2a were altered in organs such as liver, intestine, brain and testis in response to ligand (E2, diethylstilbestrol or 4-nonylphenol). During embryogenesis two of the three receptor genes, esr1 and esr2b were expressed, and in presence of ligand the mRNA levels of these two genes increased. The conclusions are i) estrogen receptor genes are expressed during early development ii) altered expression of esr genes in response to ligand is dependent on the cellular context; iii) the estrogenic ligand 4-nonylphenol, a manufactured compound commonly found in sewage of water treatment plants, acts as an agonist of the estrogen receptor during development and has both agonist and antagonist properties in tissues of adult fish. This knowledge of esr gene function in development and in adult life will help to understand mechanisms of interfering mimicking endocrine chemicals in vivo.