Evidence for estrogen receptor expression in germ cell and somatic cell subpopulations in the ovary of the newly hatched chicken

Sodium Fluoride In Vitro Treatment Affects the Expression of Gonadotropin and Steroid Hormone Receptors in Chicken Embryonic Gonads

Simple Summary

Effects of in vitro sodium fluoride (NaF) treatment on the mRNA expression of luteinizing hormone receptor (LHR), follicle-stimulating hormone receptor (FSHR), estrogen receptors (ESR1 and ESR2), progesterone receptor (PGR), and the immunolocalization of PGRs were examined in gonads of 14-day-old chicken embryos. In the ovary, the NaF treatment significantly increased mRNA levels of all investigated receptors. In the testes, the lowest applied dose of NaF (1.7 mM) significantly decreased the expression of FSHR, ESR1, ESR2, and PGR. Alternatively, the higher NaF dose (7.1 mM) elevated PGR mRNA level in the male gonad. Immunohistochemical analysis revealed that the NaF exposure increased PGR expression in the ovarian cortex, while it decreased its expression in the testes. Collectively, these data indicate that: (i) NaF may disturb the chicken embryonic development, and (ii) different mechanisms of this toxicant action exist within the female and male gonads.

Abstract

Sodium fluoride (NaF), in addition to preventing dental decay may negatively affect the body. The aim of this study was to examine the effect of a 6 h in vitro treatment of gonads isolated from 14-day-old chicken embryos with NaF at doses of 1.7 (D1), 3.5 (D2), 7.1 (D3), and 14.2 mM (D4). The mRNA expression of luteinizing hormone receptor (LHR), follicle-stimulating hormone receptor (FSHR), estrogen receptors (ESR1 and ESR2), progesterone receptor (PGR), and the immunolocalization of progesterone receptors were examined in the tissue. In the ovary, the expression of FSHR and LHR increased following the NaF treatment. In the case of FSHR the highest stimulatory effect was noticed in the D2 group, while the expression of LHR increased in a dose-dependent manner. A gradual increase in ESR1 and PGR mRNA levels was also observed in the ovary following the NaF treatment, but only up to the D3 dose of NaF. The highest ESR2 level was also found in the D3 group. In the testes, the lowest dose of NaF significantly decreased the expression of FSHR, ESR1, ESR2, and PGR. On the other hand, an increase in PGR expression was observed in the D3 group. The expression of LHR in the testes was not affected by the NaF treatment. Immunohistochemical analysis showed that NaF exposure increased progesterone receptor expression in the ovarian cortex, while it decreased its expression in the testes. These results reveal that NaF may disturb the chicken embryonic development and different mechanisms of this toxicant action exist within the females and males.

Transcriptome Sequencing and Comparative Analysis of Amphoteric ESCs and PGCs in Chicken (Gallus gallus)

Chicken (Gallus gallus) pluripotent embryonic stem cells (ESCs) and primordial germ cells (PGCs) can be broadly applied in the research of developmental and embryonic biology, but the difference between amphoteric ESCs and PGCs is still elusive. This study determined the sex of collected samples by identifying specific sex markers via polymerase chain reaction (PCR) and fluorescence activated cell sorter (FACS). RNA-seq was utilized to investigate the transcriptomic profile of amphoteric ESCs and PGCs in chicken. The results showed no significant differentially expressed genes (DEGs) in amphoteric ESCs and 227 DEGs exhibited in amphoteric PGCs. Moreover, those 227 DEGs were mainly enriched in 17 gene ontology (GO) terms and 27 pathways according to Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Furthermore, qRT-PCR was performed to verify RNA-seq results, and the results demonstrated that Notch1 was highly expressed in male PGCs. In summary, our results provided a knowledge base of chicken amphoteric ESCs and PGCs, which is helpful for future research in relevant biological processes.

Changes in estrogen receptor expression in the chick thymus during late embryonic development

In chickens, although estrogen receptors (ER) are reported to be associated with the immunological processes, detailed information about the differences in ER expression in the tissues related to the development of lymphocytes is not fully known, especially during the developmental stage. To learn more about this immunological relationship, we used semi-quantitative polymerase chain reaction method to detect the ER expression levels in the thymus tissues of chicks during the developmental stage. Furthermore, ER-expressing cells were detected by immunohistochemistry. The results of this study show that the expression level of ER increased on embryonic day 16 and decreased on day 20. Furthermore, ER expression was significantly higher in male than in female chickens at day 16. The increased expression on day 16 and decreased level on day 20 were also reproduced in the incidence of immunoreactive cells, although there was a 1-day delay in the elevated incidence of the cells. This study revealed the changes in ER expression and the incidence of ER-positive cells in the thymus of chickens during the developmental stage.

Effects of estrogen on estrogen receptor expression in the bursal cells of chick embryos and steroidogenic enzymes gene expression in the bursa: relevance of estrogen receptor and estrogen synthesis in the bursa of chick embryos

Estrogen has been reported to act on B cell genesis in the bursa of Fabricius of chick embryos. In this study, we attempted to demonstrate the hypothesis that B cell genesis is controlled by estrogen receptor (ER) in the bursal cells and steroidogenic enzymes synthesized in the bursa. We previously reported the presence of estrogen receptor α (ERα) in the bursa during the late stage of embryogenesis and an increase in the expression of ERα messenger RNA (mRNA) between the 13th day and 16th day. The number of ER-positive cells was maximal on the 16th day. In the present study, ER-positive cells in the bursa during the late stage of embryogenesis increased 4 h after β-estradiol treatment on the 14th to 18th day. The concentration of β-estradiol in the embryonic bursa increased. These results suggest that this stage of embryogenesis is critical in B cell development in the bursa in connection with the effect of estrogen treatment. Our findings also showed that the mRNA expression of five steroidogenic enzymes occurred in the bursa of chick embryos. These results suggest that estrogen is synthesized in the embryonic bursa and estrogen acts on the bursal cells in a paracrine fashion.

Theca-specific estrogen receptor-alpha knockout mice lose fertility prematurely

Estrogen receptor-alpha (Esr1) mediates estrogen action in regulating at all levels of the hypothalamic-pituitary-ovarian axis. Whereas the importance of Esr1 in hypothalamus and pituitary has been demonstrated by loss of fertility in the neuron- and pituitary-specific Esr1 knockout mice, whether Esr1 plays a critical role in the ovary remains to be determined. In the ovary, Esr1 is mainly expressed in the theca/interstitial cells and germinal epithelium and thus is believed to mediate estrogen action in these cells. In this study, we assessed the importance of Esr1 in the ovarian theca cells in regulating female reproduction. The Cre-LoxP approach was used to selectively delete the Esr1 gene in the theca cells, and the reproductive consequence of the deletion was measured. Adolescent theca-specific Esr1 knockout (thEsr1KO) mice (<4 months of age) are fertile and cycling. However, they begin to display an erratic pattern of estrous cycles and become infertile before they reach the age of 6 months. The ovaries of thEsr1KOmice (>or=4 months) have fewer corpora lutea but more antral follicles than the age-matching wild-type mice. The numbers of 17-hydroxylase-expressing cells are largely increased in the interstitium of the thEsr1KO mouse ovary. Interestingly, whereas basal levels of serum testosterone and FSH were mildly elevated, LH level was either markedly lower or undetectable in the thEsr1KO mice. When superstimulated by exogenous gonadotropins, thEsr1KO mice released significantly fewer oocytes that wild-type littermates and developed multiple hemorrhagic cysts. Taken together, this study demonstrates that theca Esr1 plays a critical role in regulating female reproduction.

Cloning and expression of the estrogen receptor-alpha (Esr1) from the Harderian gland of the sea turtle (Lepidochelys olivacea)

The effects of estradiol on the Harderian gland (HG) are believed to be partially regulated by the transcriptional regulation of the estrogen-related genes via estrogen receptor (ER). In reptiles, however, it has not been well established whether the HG contains or expresses steroid nuclear receptors. As a first step toward investigating the molecular mechanisms of estrogen signalling in the HG, we isolated the cDNA for ERalpha in the sea turtle Lepidochelys olivacea. ERalpha was cloned using RT-PCR coupled with 5' and 3' RACE procedures. The cDNA contains a complete open reading frame encoding 588 amino acid residues. Comparative analysis of this amino acid sequence showed moderate to strong conservation of the ERalpha (Esr1) gene within divergent vertebrate groups. In transfection studies, the cloned ER displayed high affinity K(d)=0.25nM and high specificity for 17beta-estradiol. Binding assays using sucrose density gradients demonstrated a specific 7-7.5 S binding component in the HG cytosolic fractions. RT-qPCR analysis showed significant ERalpha mRNA expression in the liver, HG, lung and brain. Altogether, these results provide evidence for the expression of intracellular ERs in the HG of the sea turtle and suggest that ERalpha may be an important modulator of the estrogen-mediated response in the HG of reptiles.

Estrogenic and antioxidant effects of a phytoestrogen daidzein on ovarian germ cells in embryonic chickens

The estrogenic and antioxidant effects of the phytoestrogen daidzein (DAI) on germ cell proliferation were evaluated by a chicken ovarian germ-somatic cell coculture model. Ovarian cells were dispersed from 18-day-old embryos, cultured in serum-free McCoy's 5A medium and challenged with DAI alone or in combinations with estrogen receptor antagonist tamoxifen for 48 h. The number of germ cells was counted and the proliferating cells were identified by immunocytochemistry of proliferating cell nuclear antigen (PCNA). The labeling index (LI) was determined for germ cells. Results showed that DAI significantly increased the number of germ cells (P<0.05) and this stimulating effect was inhibited by tamoxifen in a dose-dependent manner. Furthermore, PCNA-LI of germ cells displayed similar changes with the number of germ cells. To estimate the antioxidant action of DAI, ovarian cells were exposed to the reactive oxygen species (ROS)-producing system hypoxanthine/xanthine oxidase (HX/XO). The changes of superoxide dismutase (SOD) activity and glutathione (GSH) level were measured for estimation of the antioxidant status. Ovarian cells were severely damaged by free radicals and this deteriorating effect could be prevented by DAI. Moreover, HX/XO-induced decrease in SOD activity and GSH level was restored by DAI (P<0.05). These results indicated that DAI promoted proliferation of cultured ovarian germ cells by estrogenic action and attenuated ROS-induced toxicity by antioxidant action in embryonic chickens.

Stimulating effects of androgen on proliferation of cultured ovarian germ cells through androgenic and estrogenic actions in embryonic chickens

The effect of androgen on germ cell proliferation was evaluated by a chicken ovarian germ-somatic cell co-culture model and the mechanisms were explored. Ovarian cells were dispersed from 18-day-old embryos, cultured in serum-free McCoy's 5A medium and challenged with testosterone (T) alone or in combinations with androgen receptor antagonist Flutamide, estrogen receptor antagonist Tamoxifen or aromatase inhibitor Letrozole for 48 h. Germ cells were identified by c-kit immunocytochemistry. The number of germ cells was counted and the proliferating cells were identified by immunocytochemistry of proliferating cell nuclear antigen (PCNA). The labeling index (LI) was determined for germ cells. Results showed that T (10(-7) to 10(-6)M) significantly increased the number of germ cells (P<0.05) and this stimulating effect was inhibited by Flutamide (10-1000 ng/ml), Tamoxifen (10-1000 ng/ml) or Letrozole (10(-9) to 10(-7)M) in a dose-dependent manner. Furthermore, PCNA-LI of germ cells displayed similar changes with the numbers of germ cells. These results indicated that T-stimulated proliferation of cultured ovarian germ cells through both, androgenic and estrogenic actions in embryonic chickens.

The cDNA cloning and tissue expression of the cytochrome P450scc from Syrian hamster (Mesocricetus auratus)

In this study we report the cloning and sequencing of a cDNA for cholesterol side chain cleavage cytochrome P450scc from Syrian hamster adrenal glands. Isolation of P450scc mRNA was carried out with degenerate primer PCR together with 5' and 3' RACE protocol. The full-length cDNA comprises an open reading frame of 1563 bp encoding a polypeptide of 520 amino acid residues. The predicted protein sequence exhibits well-preserved heme- and steroid-binding domains and shares 89% amino acid sequence identity with rat and mouse enzymes. Transient transfection of HEK-293 cells with the cloned cDNA leads to the formation of pregnenolone from 25-hydroxycholesterol. Northern blot analysis showed expression of mRNAs for P450scc in the major steroidogenic tissues, namely, the adrenal cortex, testis, and ovary. In addition, tissue distribution analysis using the coupled reaction of RT-PCR and Southern blotting revealed that the mRNA of the enzyme is also expressed in various nonendocrine tissues, including the epididymis, Harderian gland, and lungs. The relative abundance of specific transcripts at these novel sites suggests that P450scc could potentially play an important role in regulating local steroid hormone synthesis.

Follicle-stimulating hormone regulates steroidogenic enzymes in cultured cells of the chick embryo ovary

This investigation addresses the potential regulation of enzymes involved in the biosynthesis of steroid hormones during early stages of gonadal development by follicle-stimulating hormone (FSH). Gonadal cells of 10-day-old chick embryo and cells of the left ovary of 18-day-old chick embryo were cultured for 60 h in a defined medium with or without the addition of FSH (2.0 IU/ml). At the end of the culture, cells were recovered and evaluated by biotransformation of tritiated steroid precursors and mRNA levels were evaluated by RT-PCR. The production of estrone from androstenedione was increased in the FSH-treated cells, both human FSH (hFSH) and recombinant human FSH (rhFSH), indicating a stimulatory effect on aromatase (P450arom). Similarly, the intensity of the band corresponding to P450arom mRNA was higher in hFSH and rhFSH than in control and chorionic gonadotropin (hCG) groups. The P450arom stimulation was observed in the ovary of 10- and 18-day-old chick embryo. The transformation of dehydroepiandrosterone to androstenedione was taken as evidence of 3beta-hydroxysteroid dehydrogenase function. This enzyme was stimulated in the cultured ovarian cells of 18-day-old chick embryos treated with hFSH and rhFSH compared with controls. The production of pregnenolone in the mitocondrial fraction of 18-day-old chick embryo ovary was increased when cultured with hFSH and rhFSH. This observation together with the increase in the band intensity corresponding to mRNA of P450 cholesterol side-chain cleavage indicates stimulation by FSH treatment; hCG produced a similar effect. Somatic cells of the medullary cords are proposed to be FSH target cells in the ovary of the chick embryo.