ERalpha Function Research Articles

Influence of oestrogen receptor alpha and beta on the immune system in aged female mice.

Oestrogen has a dichotomous effect on the immune system. T and B lymphopoiesis in thymus and bone marrow is suppressed, whereas antibody production is stimulated by oestrogen. In this study the importance of the oestrogen receptors (ER) ER-alpha and ER-beta in the aged immune system was investigated in 18 months old-wild type (WT), ER-alpha (ERKO), ER-beta (BERKO) and double ER-alpha and ER-beta (DERKO) knock-out mice, and compared with 4 months old WT mice. Cell phenotypes in bone marrow, spleen and thymus, and the frequency of immunoglobulin (Ig) spot forming cells (SFC) were determined. We show here that the 17-beta-oestradiol (E2)-induced downregulation of B lymphopoietic cells in bone marrow of young ovariectomized mice can be mediated through both ER-alpha and ER-beta. However, only ER-alpha is required for the age-related increased frequency of immunoglobulin M (IgM) SFC in the bone marrow, as well as for the increased production of interleukin-10 (IL-10) from cultured splenocytes in aged mice. Furthermore, increased age in WT mice resulted in lower levels of both pro- and pre-B cells but increased frequency of IgM SFC in the bone marrow, as well as increased frequency of both IgM and IgA SFC in the spleen. Results from this study provide valuable information regarding the specific functions of ER-alpha and ER-beta in the aged immune system.

Neurite-localized estrogen receptor-alpha mediates rapid signaling by estrogen.

Classically, estrogen acts on cells by directly activating gene transcription driven by ligand-bound nuclear estrogen receptors (ER). Accumulating evidence demonstrates that estrogen acts on neurons by utilizing diverse molecular mechanisms, including rapid signaling by proteins localized to the plasma membrane. Recent studies showing that ERalpha localizes to axons and dendrites of hippocampal neurons suggest that nonnuclear stores of the receptor may transduce estrogen signaling. Here, we have studied the subcellular localization, dynamic regulation, and function of ERalpha in mouse cortical neurons. Estrogen-stimulated mouse cortical neurons activate both estrogen response element (ERE) stimulated transcription and rapid activation of p44/42 mitogen-activated protein kinases (MAPK). We demonstrate that green fluorescent protein (GFP)-tagged ERalpha localizes to neurites in cultured cortical neurons and that the expression within neurites can be down-regulated by estrogen or up-regulated by antiestrogen administered during synthesis. Neurite ERalpha appears to be directed to neurites directly from its site of translation and not from nuclear stores. By using confocal microscopy, we show that ERalpha within neurites stimulates local activation of p44/42 MAP kinases in response to estrogen. We conclude that hormonal status alters subcellular ERalpha targeting in cortical neurons and that neurite-expressed ERalpha is important in the activation of local MAPK signaling.

Estrogen receptor (ER) beta1 and ERbetacx/beta2 inhibit ERalpha function differently in breast cancer cell line MCF7.

Estrogen receptor (ER) alpha plays an important role in the proliferation and progression of breast cancer. In order to explore the function of wild-type ERbeta (ERbeta1) and its variant form, ERbetacx/beta2, stable transformants of ERalpha-positive breast cancer MCF7 cells with ERbeta1 or ERbetacx/beta2 expression vector were established. Constitutive expression of ERbeta1 or ERbetacx/beta2 reduced the S phase population of the cell cycle in dish culture and the number of colonies in an anchorage-independent assay. DNA-protein complexes of ERE with nuclear extracts from ERbeta1 transformants were observed in the electrophoretic mobility shift assay, while no complex was observed for ERbetacx/beta2 transformants. Reporter gene assay using estrogen-responsive element (ERE)-luciferase showed less responsiveness to estrogen in these transformants compared with parental cells. Endogenous mRNA expression of two known estrogen-responsive genes, cathepsin D and IGFBP4, was weakly induced by estrogen in ERbeta1 and ERbetacx/beta2 transformants compared with parental cells. A comprehensive gene expression analysis using our custom-made cDNA microarray showed that MCF7 and ERbeta1 transformants had a similar gene expression profile, whereas ERbetacx/beta2 showed a distinct profile from others. These results indicate that ERbeta1 and ERbetacx/beta2 inhibit ERalpha function differently in MCF7 cells.

Sexually dimorphic roles of steroid hormone receptor signaling in gonadal tumorigenesis.

Sex steroids control cellular phenotypes by binding to receptor proteins that in turn regulate downstream gene expression. They are important tropic factors in hormonally responsive tissues and have been implicated in the pathogenesis of both benign proliferations and malignancies at some of these sites. Knockout mice lacking inhibins, alpha:beta heterodimeric peptide hormones of the TGFbeta superfamily, develop gonadal tumors that produce sex steroids and depend on pituitary gonadotropin hormones. To better appreciate how sex steroid receptor signaling pathways contribute to the loss of granulosa/Sertoli cell proliferation in the ovary and testis of inhibin alpha (Inhalpha) knockout mice, we are using both pharmacologic and genetic approaches. Roles of androgens in testicular tumor development have been investigated in our previous studies using double-mutant mice lacking inhibins and carrying the null testicular feminization (tfm) mutation of the androgen receptor. Herein, we report that androgens also participate in the development of ovarian tumors, as tumor development is forestalled in mice treated with flutamide, a nonsteroidal inhibitor of androgen actions. Additionally, we generated double-mutant mice lacking estrogen receptor alpha (ERalpha) and Inhalpha or ERbeta and Inhalpha, as well as triple-mutant mice lacking ERalpha, ERbeta, and Inhalpha to determine the effects of individual and combined ER signaling pathways on tumor development. Although estrogens may have proliferative effects during follicle development and are important in specifying the granulosa cell phenotype, ERalpha and ERbeta signaling are not essential for timely granulosa cell tumor development or granulosa cell-like morphological features in ovarian tumors. However, redundant ER signaling through ERalpha and ERbeta in males is critical for testicular tumor formation, as triple-knockout, but not double-knockout, males are protected from early Sertoli cell tumorigenesis and death. Together, these studies indicate important and sexually dimorphic functions of estrogens and androgens in tumor development in this mouse model and indicate, for the first time, overlapping functions of ERalpha and ERbeta in Sertoli cell pathophysiology.

Full Activation of Estrogen Receptor α Activation Function-1 Induces Proliferation of Breast Cancer Cells

The effects of estrogen and anti-estrogen are mediated through the estrogen receptors (ER) alpha and beta, which function as ligand-induced transcriptional factors. Recently, one of the phthalate esters, n-butylbenzyl phthalate (BBP), has been shown to induce estrogen receptor-mediated responses. By using the truncated types of ER mutants, we revealed that activation function-1 (AF-1) activity was necessary for the BBP-dependent transactivation function of ERalpha. AF-1 is also known to be responsible for the partial agonistic activity of tamoxifen. Whereas tamoxifen exhibits an anti-estrogenic effect on proliferation of the MCF-7 breast cancer cell line, BBP showed an estrogenic effect on MCF-7 to stimulate proliferation. In vivo and in vitro binding assays revealed that whereas 4-hydroxytamoxifen (OHT) induced binding of ERalpha to both an AF-1 coactivator complex (p68/p72 and p300) and corepressor complexes (N-CoR/SMRT), BBP selectively enhanced the binding to the AF-1 coactivators. We also showed that the transcriptional activity of OHT-bound ERalpha was modulated by the ratio between the AF-1 coactivator and corepressor complexes. Expression of a dominant-negative type of N-CoR inhibited the interaction between OHT-bound ERalpha and N-CoR/SMRT and enhanced the transcriptional activity of OHT-bound ERalpha. Furthermore, the cell growth of MCF-7 stably expressing the dominant-negative type of N-CoR was enhanced by the addition of OHT. These results indicated that fully activated AF-1 induces the stimulation of breast cancer growth and that the ratio between AF-1 coactivators and corepressors plays a key role to prevent proliferation of tumor by tamoxifen.

Identification of a structural determinant necessary for the localization and function of estrogen receptor alpha at the plasma membrane.

Estrogen receptors (ER) have been localized to the cell plasma membrane (PM), where signal transduction mediates some estradiol (E2) actions. However, the precise structural features of ER that result in membrane localization have not been determined. We obtained a partial tryptic peptide/mass spectrometry analysis of membrane mouse ERalpha protein. Based on this, we substituted alanine for the determined serine at amino acid 522 within the E domain of wild-type (wt) ERalpha. Upon transfection in CHO cells, the S522A mutant ERalpha resulted in a 62% decrease in membrane receptor number and reduced colocalization with caveolin 1 relative to those with expression of wt ERalpha. E2 was significantly less effective in stimulating multiple rapid signals from the membranes of CHO cells expressing ERalpha S522A than from those of CHO cells expressing wt ERalpha. In contrast, nuclear receptor expression and transcriptional function were very similar. The S522A mutant was also 60% less effective than wt ERalpha in binding caveolin 1, which facilitates ER transport to the PM. All functions of ERalpha mutants with other S-to-A substitutions were comparable to those of wt ER, and deletion of the A/B or C domain had little consequence for membrane localization or function. Transfection of ERalpha S522A into breast cancer cells that express native ER downregulated E2 binding at the membrane, signaling to ERK, and G1/S cell cycle events and progression. However, there was no effect on the E2 transactivation of an ERE-luciferase reporter. In summary, serine 522 is necessary for the efficient translocation and function of ERalpha at the PM. The S522A mutant also serves as a dominant-negative construct, identifying important functions of E2 that originate from activating PM ER.

Idoxifene and estradiol enhance antiapoptotic activity through estrogen receptor-beta in cultured rat hepatocytes.

Oxidative stress plays a causative role in the development of hepatic fibrosis and apoptosis. Estradiol (E2) is an antioxidant, and idoxifene is a tissue-specific selective estrogen-receptor modulator. We have previously demonstrated that E2 inhibits hepatic fibrosis in rat models of hepatic fibrosis and that the actions of E2 are mediated through estrogen receptors (ERs). This study reports on the antiapoptotic role of idoxifene and E2, and the functions of ER subtypes ER-alpha and ER-beta in hepatocytes undergoing oxidative stress. Lipid peroxidation was induced in cultured rat hepatocytes with ferric nitrilotriacetate solution with idoxifene or E2. Oxidative stress-induced early apoptosis was linked to its ability to inhibit not only the expression of Bcl-2 and Bcl-XL but the production of antioxidant enzymes as well and to stimulate Bad expression. Hepatocytes possessed functional ER-beta, but not ER-alpha, to respond directly to idoxifene and E2. Idoxifene and E2 suppressed oxidative stress-induced reactive oxygen species generation and lipid peroxidation, and their antiapoptotic effects on the activation of activator protein-1 and nuclear factor-kappaB, the loss of antioxidant enzyme activity, and Bcl-2 family protein expression in early apoptotic hepatocytes were blocked by the pure ER antagonist ICI 182,780. Our results indicate that idoxifene and E2 could enhance antiapoptotic activity through ER-beta during oxidative damage in hepatocytes.

The antiestrogen ICI 182,780 induces early effects on the adult male mouse reproductive tract and long-term decreased fertility without testicular atrophy

BackgroundEstrogen receptors (ER) have important physiological roles in both the female and male reproductive systems. Previous studies using the estrogen receptor-α knockout mouse (αERKO) or antiestrogen treatment in adult rodents have shown that ERα is essential for normal function of the male reproductive tract. In the present study, time-response effects of the antiestrogen ICI 182,780 were determined to better understand ERα function in the adult male.MethodsAdult male mice, 30 days old, were injected subcutaneously with ICI 182,780 (5 mg) once per week for 17 weeks. Tissues were fixed by vascular perfusion to study the time responses from day 2 to 125 post treatment.ResultsNo difference was seen in body weight due to treatment. Testis weight was decreased 18% on day 59 and 21.4% on day 125. Other significant treatment-related effects included the following: 1) dilation of rete testis and efferent ductule lumen; 2) decreased height of the rete testis and efferent ductule epithelium; 3) decreased height of the supranuclear epithelial cytoplasm in efferent ductules; 4) decreased height of the efferent ductule epithelial microvilli, particularly in the proximal ductules; 5) decrease in the PAS-positive granules and endocytotic vesicles in nonciliated epithelial cells of efferent ductules; 6) capping and vesiculation of narrow cells in the initial segment of the epididymis; 7) accumulation of PAS-positive granules in apical cells of the caput epididymis; 8) increase in lysosomal granules in clear cells of the corpus and cauda epididymis; 9) limited induction of atrophic seminiferous tubules and abnormal spermatogenesis; and 10) decreases in the concentration of cauda sperm, progressive sperm motility and decreased fertility.ConclusionsAntiestrogen treatment of the pubertal male mouse resulted in reproductive effects similar to those observed in the αERKO mouse as early as day 4; however, testis weight did not increase substantially and total atrophy was not observed with extended treatment.

Down but not out? A novel protein isoform of the estrogen receptor alpha is expressed in the estrogen receptor alpha knockout mouse.

The mouse knockout of the estrogen receptor alpha (ERalpha) gene, known as alphaERKO, has been extensively used for several years to study the role and function of ERalpha. Residual estradiol binding capacity in uterine tissue of 5-10% raised doubts if this knockout is a genuine null mutation of ERalpha. Although alternatively spliced ERalpha mRNA variants in the alphaERKO mouse were reported previously, the corresponding protein isoforms have not been detected to date. Here we show that a variant ERalpha protein, 61 kDa in size, is expressed in the uterine tissue of alphaERKO mice as a result of an alternative splicing. The transactivation capability of this protein is cell dependent and can be as high as 75% of the wild type ERalpha.

Roles of estrogen receptor alpha and androgen receptor in the regulation of neuronal nitric oxide synthase.

In brain and peripheral tissues, steroid hormones regulate nitric oxide synthase (nNOS). We asked whether estrogen receptor-alpha (ERalpha) and/or androgen receptor (AR) regulated nNOS immunoreactivity in mouse brain. First, we quantified cells singly labeled for nNOS immunoreactivity or labeled dually with ERalpha-immunoreactive (-ir) or AR-ir cells in the nucleus accumbens (Acb), preoptic area (POA), bed nucleus of the stria terminalis (BNST), posterior dorsal and posterior ventral regions of the medial amygdala (MePD and MePV, respectively), and paraventricular nucleus (PVN). The POA and MePD contained the greatest number of double-labeled cells. More nNOS-ir cells were colabeled with ERalpha immunoreactivity compared with AR immunoreactivity. Next, by using a double mutant mouse in which males lacked functional ERalpha, AR, or both, we investigated the roles of these steroid receptors in nNOS-ir cell numbers and immunoreactive area staining under testosterone (T) and estradiol (E2) conditions. Our data show that functional ERalpha is correlated with more nNOS-ir cells under T conditions and more immunoreactive area staining in the POA under both T and E2 conditions. However, ERalpha decreases nNOS-ir cell number in the BNST under E2 treatment. In summary, the data suggest that AR has organizational actions on nNOS-ir cell numbers in the MePV, that interactions between ERalpha and AR genes occur in PVN, and that sex differences in nNOS-ir area staining are limited to the POA. Thus, we show that ERalpha and AR interact to regulate nNOS in male and female brain in a site-specific manner.

Clinical impact of assay of estrogen receptor beta cx in breast cancer.

Since 1996 when estrogen receptor beta(ER beta) was discovered, much effort has been devoted to the question of the value of ER beta as a prognostic and/or predictive factor in breast cancer and its potential as a novel target for pharmacological intervention. When estrogen receptors are applied on sucrose gradients and quantified by ligand binding, we found that in contrast to ER alpha, which has a narrow tissue distribution, ER beta is expressed in many tissues including both normal and malignant breast tissue. Receptor protein levels in tissues can also be measured from the intensities of bands after Western blotting and can be quantified when purified and quantified receptor is used as a standard. With this technique, we found that there were some tumors which had over 600 fmol/mg of ER beta protein but no detectable estradiol binding. In such tumors, RT-PCR analysis revealed that ER beta cx is the only ER beta isoform present. ER beta cx is a splice variant which utilizes an alternative exon 8. This change in the C-terminus results in very poor binding to estradiol (E2) and has a dominant negative effect on ER alpha function. Immunohistochemical analysis with an ER beta cx specific antibody in 115 ER alpha-positive breast cancers revealed that about half of the samples expressed ER beta cx protein. Initial analysis of samples from patients with preoperative tamoxifen treatment revealed that ER alpha-positive tumors expressing ER beta cx and lacking PR seemed to be resistant to the anti-estrogen. We conclude that, in order to better characterize breast cancers and design appropriate therapy for individual patients, assays for ER beta cx must be made available to clinicians.

Cell-specific distribution of oestrogen receptor-alpha in the bovine ovary.

In this study, the expression of estrogen receptor alpha (ERalpha) in the bovine ovary is described. ERalpha was visualized by immunohistochemistry on paraffin sections of ovaries obtained from 11 non-pregnant and 2 pregnant animals. In general, ERalpha was not observed in cells of primordial, primary and secondary follicles, whereas weak expression was noticed in cells of healthy and arteric tertiary follicles. In corpora lutea cells the expression of ERalpha was obvious. Intermediate to high ERalpha expression was present in thecal cells and in cells of the superficial and deep stroma, tunica albuginea and surface epithelium. Furthermore, the expression of ERalpha in stroma and tunica albuginea cells was in general, highest in cows with the lowest plasma progesterone levels, and lowest in cows with the highest plasma progesterone levels. Remarkably, the ERalpha expression in pregnant cows was in general, lower than in non-pregnant cows with similar plasma progesterone levels. The relatively high expression of ERalpha in thecal and stromal cells in comparison with that in follicle cells suggests an indirect effect of estrogen on the follicular development. However, the exact function of ERalpha in the bovine ovary together with the cycle-dependent variations in ERalpha expression remain to be elucidated.

Human estrogen receptor-alpha: regulation by synthesis, modification and degradation.

This review aims to evaluate the impact that human estrogen receptor-alpha (ER-alpha) synthesis, modification and degradation has on estrogen-dependant physiological and pathological processes within the body. Estrogen signaling is transduced through estrogen receptors, which act as ligand-inducible transcription factors. The significance of different isoforms of ER-alpha that lack structural features of full-length ER-alpha are discussed. The influence of differential promoter usage on the amount and isoform of ER-alpha within individual cell types is also reviewed. Moreover, the potential role of phosphorylation, ubiquitination and acetylation in the function and dynamic turnover of ER-alpha is presented.

How does the estrogen receptor work?

In breast cancer, interruption of estrogen receptor (ER)-α function is an effective therapeutic strategy. Despite the clinical benefit of interruption of ER-α function, the precise biological action of ER-α in breast tumors is not completely understood. Results of a recent study show that ER-α promotes growth of breast cancer cells by targeting expression of signaling components of the insulin-like growth factor system. Intriguingly, the authors of this study raise the possibility that unliganded ER-α itself may affect gene expression and breast cancer biology, and they suggest a potential mechanism for ER-α to stimulate proliferation in breast cancer.

Antagonists selective for estrogen receptor alpha.

To develop compounds that are antagonists on ER(alpha), but not ER(beta), we have added basic side-chains typically found in nonsteroidal antiestrogens to pyrazole compounds that bind with much higher affinity to ER(alpha) than to ER(beta). In this way we have developed basic side-chain pyrazoles (BSC-pyrazoles) that are high affinity, potent, selective antagonists on ER(alpha). These BSC-pyrazoles are themselves inactive on ER(alpha) and ER(beta), and they antagonize E2 stimulation by ER(alpha) only. We investigated seven basic side-chain substituents on various alkyl-triaryl-substituted pyrazoles, and the most ER(alpha)-selective compound was methyl-piperidino-pyrazole (MPP). ER(alpha)-selective antagonism was observed on diverse reporter-promoter gene constructs containing estrogen response elements that are consensus, nonconsensus (pS2), or comprised of multiple half-estrogen response elements (NHERF/EBP50) and on genes in which ER works indirectly by tethering to other DNA-bound proteins (TGF(beta)3). In contrast to these BSC-pyrazoles, the antiestrogens trans-hydroxytamoxifen, raloxifene, and ICI 182,780 suppress E2 activity via both ER(alpha) and ER(beta). The most effective BSC-pyrazole, MPP, fully antagonized E2 stimulation of pS2 mRNA in MCF-7 breast cancer cells, consistent with the fact that these cells contain almost exclusively ER(alpha). These compounds should be useful in studying the biological functions of ER(alpha) and ER(beta) and in selectively blocking responses that are mediated through ER(alpha).

Hypoxia reduces hormone responsiveness of human breast cancer cells.

Resistance to hormonal therapy frequently occurs following successful treatment in breast cancer. The mechanism responsible for this acquired resistance is still unknown. It has been suggested that a hypoxic tumor microenvironment promotes malignant progression of cancer, i.e., hypoxia may promote estrogen‐independent growth (a more malignant phenotype) of breast cancer. To clarify this hypothesis, the effects of hypoxia on the growth responses to hormonal agents and the expression levels of estrogen receptor (ER)‐α and progesterone receptor (PgR) were investigated in two human breast cancer cell lines, ML‐20 and KPL‐1. The expression level of ER‐α was significantly decreased by hypoxia (1% O2) in a tune‐dependent manner in both cell lines. Hypoxia also significantly reduced the growth‐promoting effect of estradiol (E2) and the growth‐inhibitory effects of an antiestrogen, ICI 182 780, and a progestin, medroxyprogesterone acetate, in both cell lines. In addition, hypoxia markedly suppressed the induction of PgR mRNA and protein by E2 in both cell lines. To clarify further the effect of hypoxia on ER‐α expression, the expression levels of hypoxia‐inducible factor‐la (HIF‐lα), a marker of hypoxia and ER‐α were immunohistochemically examined in 36 breast cancer specimens. ER‐α expression (both its proportion and intensity) was significantly lower in nuclear HIF‐lα‐positive tumors than in negative tumors. These findings indicate that hypoxia down‐regulates ER‐α expression as well as ER‐α function in breast cancer cells. These processes may lead to an acquired resistance to hormonal therapy in breast cancer

Immortalized testis cell lines from estrogen receptor (ER) alpha knock-out and wild-type mice expressing functional ERalpha or ERbeta.

The surprising findings that male mice lacking the estrogen receptor (ER) alpha (alphaERKO) have atrophic testis and are infertile proved that ERalpha is involved in normal testicular function. To obtain compatible in vitro model systems for alphaERKO male mice, we immortalized different cell lines from the testis of alphaERKO and wild-type (C57BL/6) mice with the human papilloma virus E6/E7 genes. The established cell lines were characterized for Sertoli, Leydig, and peritubular cell markers by means of messenger RNA expression and functional assays. One wild-type-derived cell line showed Leydig cell-specific marker gene expression and produced testosterone after stimulation with cyclic adenosine monophosphate. Most wild-type cell lines expressed androgen receptor and a functional ERalpha as shown by high estrogenic activity in a luciferase-based transactivation assay. Most notably, the wild-type-derived WL3, and the ES4 cell line derived from alphaERKO mice expressed ERbeta and showed ER-mediated transcriptional activity, but no ERalpha protein expression. These cell lines with and without functional ERalpha or ERbeta enable the analyses of ER subtype-specific responses and their function in testicular cell signaling, morphogenesis, and neoplasia.

Quantitative analysis of estrogen receptor proteins in rat mammary gland.

Estrogen receptor alpha and beta proteins (ERalpha and ERbeta) at various stages of development of the rat mammary gland were quantified by Western blotting. ERalpha and ERbeta recombinant proteins were used as standards, and their molar concentrations were measured by ligand binding assays. In 3-week-old pregnant, lactating, and postlactating rats the ERalpha content ranged from 0.30-1.55 fmol/microg total protein (mean values). The ERbeta content of the same samples ranged between 1.06-7.50 fmol/microg total protein. At every developmental stage, the ERbeta content of the mammary gland was higher than that of ERalpha. When receptor levels were normalized against beta-actin, it was evident that ER expression changed during development, with maximum expression of both receptors during the lactation period. With an antibody raised against the 18-amino acid insert of the ERbeta variant, originally called ERbeta2 but named ERbetains in this paper, Western blots revealed that ERbetains protein was up-regulated during the lactation period. RT-PCR showed that the levels of messenger RNA of ERbetains paralleled those of the protein. Double immunohistochemical staining with anti-ERalpha and anti-ERbetains antibodies revealed that ERbetains protein colocalized with ERalpha in 70-80% of the ERalpha-expressing epithelial cells during lactation and with 30% of these cells during pregnancy. These observations indicate that expression of ERbetains is regulated not only quantitatively, but also with regard to its cellular distribution. As ERbetains acts as the dominant repressor of ERalpha, we suggest that its coexpression with ERalpha quenches ERalpha function and may be one of the factors that contribute to the previously described insensitivity of the mammary gland to estrogens during lactation.

Immunohistochemical localization of estrogen receptor-alpha in sex ducts and gonads of newborn piglets.

Estrogen receptor-alpha (ER-alpha) expression in piglet uteri has previously been reported from day 15 after birth. Nevertheless, uterine tissue has been reported to be estrogen sensitive from the day of birth. Since estrogen action in the uterine tissue is suggested to be mediated principally by ER-alpha, the present study aimed to evaluate the presence of ER-alpha in uteri of 1- to 2-day-old piglets by means of immunohistochemistry. In addition, sex ducts and gonads of both sexes were examined. The results clearly demonstrate the presence of ER-alpha immunopositive cells in uterine tissue, which explains its estrogen responsiveness. Immunostaining was most intense in the glandular epithelial cells and is suggested to indicate participation of ER-alpha in adenogenesis. In oviducts, almost all epithelial cells were immunostained moderately positive, while the stroma cells were stained comparably more positive. The functional significance of this intensity difference is uncertain but could indicate that part of the estrogen action on the epithelium is mediated through the stroma cells, as is known for the uterus. In ovaries, the surface epithelium and stroma cells were immunostained, whereas germ and granulosa cells were immunonegative. It is speculated that ER-alpha might be involved in yet unknown intraovarian mechanisms. In male sex ducts, immunostaining was virtually confined to the epithelium of efferent ducts. All cells in the epididymis as well as in vas deferens were immunonegative. The unique presence of ER-alpha in efferent ducts corresponds with localization in other species, where it has been shown to be involved in fluid reabsorption. The obtained data on localization of ER-alpha correspond with the present knowledge, obtained in ER-alpha knockout mice, of the biological function of ER-alpha within male and female gonads and sex ducts.

Sex differences in progesterone receptor immunoreactivity in neonatal mouse brain depend on estrogen receptor alpha expression.

Around the time of birth, male rats express higher levels of progesterone receptors in the medial preoptic nucleus (MPN) than female rats, suggesting that the MPN may be differentially sensitive to maternal hormones in developing males and females. Preliminary evidence suggests that this sex difference depends on the activation of estrogen receptors around birth. To test whether estrogen receptor alpha (ER alpha) is involved, we compared progesterone receptor immunoreactivity (PRir) in the brains of male and female neonatal mice that lacked a functional ER alpha gene or were wild type for the disrupted gene. We demonstrate that males express much higher levels of PRir in the MPN and the ventromedial nucleus of the neonatal mouse brain than females, and that PRir expression is dependent on the expression of ER alpha in these regions. In contrast, PRir levels in neocortex are not altered by ER alpha gene disruption. The results of this study suggest that the induction of PR via ER alpha may render specific regions of the developing male brain more sensitive to progesterone than the developing female brain, and may thereby underlie sexual differentiation of these regions.