Estrogen receptor alpha and beta expression in the porcine ovary

In order to investigate the expression of estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) in the porcine ovary, in situ hybridization was applied. Specific ovine ERalpha and bovine ERbeta cDNA probes were labeled with [-32S]dCTP. In the porcine ovary, positive signals for ERbeta were found in both granulosa and theca cells of all types of antral follicles as well as in the corpora lutea at all stages of regression. ERalpha mRNA was limited exclusively to the granulosa cells of preovulatory follicles and was present in a few cells of early corpora lutea. Thus, we showed differential expression of ERalpha and ERbeta at the mRNA level. Large antral follicles and early corpora lutea are the site, where both forms of estrogen receptor are expressed.     

A comparative study of estrogen receptors alpha and beta in the rat uterus.

The uterus is an important target organ for steroid hormones. The effects of these hormones are mediated via specific receptors. The aim of this study was to compare the expression, distribution, and regulation of estrogen receptor (ER) alpha and beta in the rat uterus in order to establish possible different biological roles for the two receptor forms. Ovariectomized rats were treated with either estradiol (E(2)), progesterone (P(4)), or combinations of these for 24 or 48 h. The mRNA levels were measured by solution hybridization. Distribution of the mRNAs and receptor proteins was detected by in situ hybridization and immunohistochemistry. The results showed that ERalpha is the dominating subtype in the rat uterus. E(2) seemed to increase the ERalpha mRNA level in the glandular and luminal epithelium, but it caused a decrease of the immunostaining intensity in the glandular epithelium. P(4) reduced ERalpha expression in luminal epithelium whereas no effect was seen in the glandular epithelium. E(2) or P(4) did not alter the expression of ERbeta, on either the mRNA or protein level. In conclusion, the distribution and regulation of ERalpha and ERbeta differ in the different compartments of the rat uterus. The complex uterine responses to E(2) and P(4) are directly or indirectly mediated by differential cell-specific expression of their receptors. The low expression in the uterus and the limited regulation by gonadal steroids in this study suggest that ERbeta probably plays a minor role in the regulation of uterine physiology.     

Expression of estrogen receptor alpha and beta in myometrium of premenopausal and postmenopausal women

Although a clear role for estrogen receptor (ER) alpha has been established, the contribution of ERbeta in estrogen-dependent development, growth and functions of the myometrium is not understood. As a first step towards understanding the role of ERbeta, we have examined the expression of ERalpha and ERbeta in the human myometrium. With competitive RT-PCR assays, the level of ERbeta mRNA was 10-200 times lower than that of ERalpha mRNA in both premenopausal and postmenopausal myometrium. In premenopausal myometrium, the expression pattern of ERbeta mRNA during the menstrual cycle was similar to that of ERalpha mRNA, with highest levels in peri-ovulatory phase. In postmenopausal myometrium, ERbeta mRNA was significantly higher than it was in premenopausal myometrium, while the level of ERalpha mRNA was lower. The net result was a change in the ratio of ERbeta to ERalpha mRNA expression. The ratio changed from 0.6-1.5 in premenopausal to 2.5-7.6 in postmenopausal myometrium. In premenopausal women, the gonadotropin releasing hormone analogue, leuprorelin acetate, elicited a decrease in ERalpha and an increase in ERbeta mRNA expression to cause a postmenopausal receptor phenotype. Estradiol, on the other hand, reversed ERalpha and ERbeta mRNA expression and their ratio in postmenopausal myometrium to those of premenopausal myometrium. Immunohistochemical staining and Western blot analysis of ERalpha and ERbeta with semiquantitative analysis showed good agreement between mRNA and protein levels. The data indicate that coordinated expression of ERalpha and ERbeta might be necessary for normal estrogen action in myometrium. Furthermore, estrogen appears a dominant regulator of both receptors in the myometrium.     

Messenger RNA levels of estrogen receptors alpha and beta and progesterone receptors in the cyclic and inseminated/early pregnant sow uterus

The aim of the present study was to investigate differences in the expression of mRNAs for ERalpha, ERbeta and PR in the sow uterus at different stages of the estrous cycle as well as in inseminated sows at estrus and during early pregnancy by use of solution hybridization and in relation to plasma levels of estradiol and progesterone. Uterine samples were collected at different stages of the estrous cycle and after insemination/early pregnancy. In the endometrium, the expression of ERalpha mRNA and PR mRNA was similar for cyclic and early pregnant groups. Both were highest at early diestrus/70 h after ovulation and ERalpha mRNA was lowest at late diestrus/d 19 while PR mRNA was lowest at diestrus and late diestrus/d 11 and d 19. The expression of endometrial ERbeta was constantly low during the estrous cycle but higher expression was found in inseminated/early pregnant sows at estrus and 70 h after ovulation. In the myometrium, high expression of ERalpha mRNA and PR mRNA was observed at proestrus and estrus in cyclic sows and at estrus in newly inseminated sows. Higher expression of myometrial ERbeta mRNA was found in inseminated/early pregnant sows compared with cyclic sows, although significant only at estrus. In conclusion, the expression of mRNAs for ERalpha, ERbeta and PR in the sow uterus differed between endometrium and myometrium as well as with stages of the estrous cycle and early pregnancy. In addition to plasma steroid levels, the differences between cyclic and inseminated/early pregnant sows suggest that other factors, e.g. insemination and/or the presence of embryos, influence the expression of these steroid receptor mRNAs in the sow uterus.     

Expression of estrogen receptor beta is developmentally regulated in reproductive tissues of male and female mice

By the use of ribonuclease protection assay (RPA) combined with immunohistochemical techniques, the expression of estrogen receptor (ER) alpha and ERbeta was mapped in the developing gonads and reproductive tracts of male and female mice from fetal day 14 to postnatal day 26 (PND 26). This study was designed to determine the pattern of expression of both ER subtypes in specific tissue compartments during development. In ovaries, ERalpha mRNA was detected at all ages examined; ERbeta mRNA was seen as early as PND 1, and its expression increased with age. Immunolocalization showed ERbeta in differentiating granulosa cells of the ovary, whereas ERalpha was predominantly seen in interstitial cells. The remainder of the female reproductive tract showed ERalpha mRNA at all ages examined with little or no significant levels of ERbeta, except on PND 1 when a low level of message appeared. In males, ERalpha and ERbeta mRNA were detected in the fetal testis; however, ERbeta gradually increased until PND 5 and subsequently diminished to undetectable levels by PND 26. Immunolocalization showed ERalpha in the interstitial compartment of the testis, whereas ERbeta was seen predominantly in developing spermatogonia. The remainder of the male reproductive tract showed varying amounts of both receptors by RPA and immunostaining throughout development. These studies provide information useful in studying the role of both ER subtypes in normal differentiation, and they provide indications of differential tissue expression during development.     

Silymarin is a selective estrogen receptor beta (ERbeta) agonist and has estrogenic effects in the metaphysis of the femur but no or antiestrogenic effects in the uterus of ovariectomized (ovx) rats

Silymarin is a widely used standardized mixture of flavonolignans and its major component Silybinin binds to cytosolic estrogen receptors. Here, we demonstrate that this binding is exclusive to the estrogen receptor beta (ERbeta). Treatment of ovariectomized (ovx) rats with silymarin or estradiol (E2) may allow differentiation of biological effects mediated by the ERalpha or ERbeta. E2 inhibited serum LH, cholesterol, LDL and HDL concentrations in the blood and increased gene expression of IGF1, HbEGF and C3 in the uterus, while silymarin was totally ineffective or antagonistic in altering these parameters. Both, E2 and silymarin inhibited expression of uterine ERbeta gene. Hence, in the pituitary, liver (where the lipoproteins are synthesized) and uterus E2 acts primarily via the ERalpha. Exclusive estrogenic effects of silymarin were observed in the metaphysis of the femur (MF), on osteoblast parameters (gene expression of IGF1, TGFbeta1, osteoprotegerin, collagen-1alpha1, osteocalcin (OC)) and on the osteoclast activity marker tartrate resistant acid phosphatase (TRAP) gene expression of adult ovx rats. Our RT-PCR method detects ERbeta gene expression in all organs including developing bones but not in the MF of adult ovx rats. We conclude therefore, that the effects of silymarin in this part of the bone cannot be exerted via the ERalpha because it does not bind to this receptor subtype. Despite the failure to detect ERbeta mRNA in the MF of our animals the possibility exists that ERbeta protein is present and may mediate the effects of silymarin. Another possibility may be that the effect of silymarin and therefore possibly also of E2 in the MF may be mediated via other possibly not yet identified receptors or via an ERbeta splice variant which is not detected by our PCR-method.