Estrogen receptor subtypes localization shifts in cultured mouse ovarian follicles

Genomics of sexual cell fate transdifferentiation in the mouse gonad

Sex determination in mammals hinges on a cell fate decision in the fetal bipotential gonad between formation of male Sertoli cells or female granulosa cells. While this decision normally is permanent, loss of key cell fate regulators such as the transcription factors Dmrt1 and Foxl2 can cause postnatal transdifferentiation from Sertoli to granulosa-like (Dmrt1) or vice versa (Foxl2). Here, we examine the mechanism of male-to-female transdifferentiation in mice carrying either a null mutation of Dmrt1 or a point mutation, R111G, that alters the DNA-binding motif and causes human XY gonadal dysgenesis and sex reversal. We first define genes misexpressed during transdifferentiation and then show that female transcriptional regulators driving transdifferentiation in the mutant XY gonad (ESR2, LRH1, FOXL2) bind chromatin sites related to those normally bound in the XX ovary. We next define gene expression changes and abnormal chromatin compartments at the onset of transdifferentiation that may help destabilize cell fate and initiate the transdifferentiation process. We model the R111G mutation in mice and show that it causes dominant gonadal dysgenesis, analogous to its human phenotype but less severe. We show that R111G partially feminizes the testicular transcriptome and causes dominant disruption of DMRT1 binding specificity in vivo. These data help illuminate how transdifferentiation occurs when sexual cell fate maintenance is disrupted and identify chromatin sites and transcripts that may play key roles in the transdifferentiation process.

The effects of polycyclic aromatic compounds (PACs) on mammalian ovarian function

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Toxicity of polycyclic aromatic compounds (PACs) is limited to a subset of PACs.

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Exposure to these compounds impact major processes necessary for ovarian function.

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PAC exposure causes follicle loss and aberrant steroid production and angiogenesis.

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PAC exposure may increase the risk for impaired fertility and ovarian pathologies.

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The study of PACs as ovarian toxicants should include additional compounds.

Polycyclic aromatic compounds (PACs) are a broad class of contaminants ubiquitously present in the environment due to natural and anthropogenic activities. With increasing industrialization and reliance on petroleum worldwide, PACs are increasingly being detected in different environmental compartments. Previous studies have shown that PACs possess endocrine disruptive properties as these compounds often interfere with hormone signaling and function. In females, the ovary is largely responsible for regulating reproductive and endocrine function and thus, serves as a primary target for PAC-mediated toxicity. Perturbations in the signaling pathways that mediate ovarian folliculogenesis, steroidogenesis and angiogenesis can lead to adverse reproductive outcomes including polycystic ovary syndrome, premature ovarian insufficiency, and infertility. To date, the impact of PACs on ovarian function has focused predominantly on polycyclic aromatic hydrocarbons like benzo(a)pyrene, 3-methylcholanthrene and 7,12-dimethylbenz[a]anthracene. However, investigation into the impact of substituted PACs including halogenated, heterocyclic, and alkylated PACs on mammalian reproduction has been largely overlooked despite the fact that these compounds are found in higher abundance in free-ranging wildlife. This review aims to discuss current literature on the effects of PACs on the ovary in mammals, with a particular focus on folliculogenesis, steroidogenesis and angiogenesis, which are key processes necessary for proper ovarian functions.

Expression of MTNR1A, steroid (ERα, ERβ, and PR) receptor gene transcripts, and the concentration of melatonin and steroid hormones in the ovarian follicles of buffalo

High ambient temperature exhibits a retrograde effect on buffalo reproduction because of heat stress. Moreover, melatonin is known to regulate reproductive changes in seasonally reproductive animals by binding to high affinity, G protein-coupled receptors. The MTNR1A gene is a prime receptor, mediating the effect of melatonin at the neuroendocrine level to control seasonal reproduction. In sheep, the role of melatonin is well known; however, studies have not been conducted in buffalo to determine its effect during favorable and unfavorable breeding seasons. Therefore, the present study aimed to (1) determine the expression of MTNR1A, ERα, ERβ, and PR gene transcripts in the ovarian follicles of buffalo during the summer and winter seasons and (2) analyze melatonin, 17β-estradiol, and progesterone concentrations in the follicular fluid of buffalo during both seasons. Murrah buffalo ovaries were collected during both the summer (May-June) and winter (December-January) seasons. All visible ovarian follicles were allocated into one of three groups: (1) small (8-9.9 mm); (2) medium (10-11.9 mm); and (3) large (12-14 mm). Follicular fluid was aspirated from each group of follicles for hormone analyses. The granulosa cells were processed for RNA extraction. Furthermore, they were subjected to real-time quantitative PCR to analyze the expression (relative quantification) of MTNR1A, ERα, ERβ, and PR in each follicular group. The expression of MTNR1A gene transcript decreased with the increasing size of the follicle and intrafollicular melatonin concentration. Expression of ERα and PR remained unaffected by the season and was similar (P > 0.05) in all groups. Expression of ERβ was higher (P < 0.05) in summer than winter; nevertheless, small-sized follicles from the summer exhibited higher (P < 0.05) expressions than medium- and large-sized follicles. The overall intrafollicular melatonin concentration was positively correlated (P < 0.05) with 17β-estradiol and progesterone concentrations. In conclusion, the decreased expression of MTNR1A and increased concentration of intrafollicular melatonin with the increasing size of the follicle indicates a probable role in folliculogenesis and ovulation in buffalo.

Equol: A Microbiota Metabolite Able to Alleviate the Negative Effects of Zearalenone during In Vitro Culture of Ovine Preantral Follicles

The impact of zearalenone (ZEN) on female reproduction remains an issue, since its effects may differ among exposed cell types. Besides the use of decontaminants in animal diet, other approaches should be considered to minimise ZEN effects after exposure. Since the first organ in contact with ZEN is the gastrointestinal tract, we hypothesise that products of microbiota metabolism may play a role in ZEN detoxification. We aimed to evaluate the effect of 1 µmol/L ZEN and 1 µmol/L equol (a microbial metabolite), alone or in combination, on the survival and morphology of in vitro cultured ovarian preantral follicles. Ovaries from 12 sheep were collected at a local abattoir and fragmented, and the ovarian pieces were submitted to in vitro culture for three days in the presence or absence of the test compounds. The follicular morphology was impaired by ZEN, but equol could alleviate the observed degeneration rates. While ZEN decreased cell proliferation in primary and secondary follicles, as well as induced DNA double-strand breaks in primordial follicles, all these observations disappeared when equol was added to a culture medium containing ZEN. In the present culture conditions, equol was able to counteract the negative effects of ZEN on ovarian preantral follicles.

The transcription factor FOXL2 mobilizes estrogen signaling to maintain the identity of ovarian granulosa cells

FOXL2 is a lineage determining transcription factor in the ovary, but its direct targets and modes of action are not fully characterized. In this study, we explore the targets of FOXL2 and five nuclear receptors in murine primary follicular cells. We found that FOXL2 is required for normal gene regulation by steroid receptors, and we show that estrogen receptor beta (ESR2) is the main vector of estradiol signaling in these cells. Moreover, we found that FOXL2 directly modulates Esr2 expression through a newly identified intronic element. Interestingly, we found that FOXL2 repressed the testis-determining gene Sox9 both independently of estrogen signaling and through the activation of ESR2 expression. Altogether, we show that FOXL2 mobilizes estrogen signaling to establish a coherent feed-forward loop repressing Sox9. This sheds a new light on the role of FOXL2 in ovarian maintenance and function.

DOI:http://dx.doi.org/10.7554/eLife.04207.001

In female mammals, granulosa cells in the ovaries help egg cells to grow and develop by secreting nutrients and estrogens—the female sex hormones. A protein called FOXL2 helps granulosa cells to develop and functions by binding to the DNA of the cells to switch certain genes either on or off.

In humans, mutations in the gene that codes for the FOXL2 protein are associated with granulosa cell tumors and with a loss of female fertility in early adulthood. In addition, if the amount of FOXL2 is artificially reduced in granulosa cells in female mice, the cells take on many of the characteristics of supporting cells found in the testes of males.

To investigate in more detail how FOXL2 works, Georges et al. grew mouse granulosa cells in the laboratory to identify the DNA sequences where FOXL2 will bind, and to uncover how this binding affects gene expression. Georges et al. conclude that FOXL2 orchestrates a network involving many different proteins that allows estrogen to be produced and used by granulosa cells; and in doing so these cells maintain their identity as ovarian cells. FOXL2 was also shown to work closely with the receptor proteins that detect the sex hormones, and which help to control whether particular sex-specific genes are switched on or off.

One particularly important role of FOXL2 in granulosa cells is that it represses a gene called Sox9. By repressing Sox9, the granulosa cells do not transform into their counterparts normally found in testes. Although FOXL2 was previously reported to directly regulate the Sox9 gene, Georges et al. find that it also acts through other molecules, and that there are alternative ways in which it can do so.

Although Georges et al. have established some of the ways that FOXL2 functions, this protein can work via other pathways; these will require further investigation to be fully understood.

DOI:http://dx.doi.org/10.7554/eLife.04207.002

Daidzein affects steroidogenesis and oestrogen receptor expression in medium ovarian follicles of pigs

Daidzein, a phytoestrogen present in soybean products used in swine feed, has been demonstrated to affect both reproductive and endocrine functions. The aims of this study were to examine the in vitro effects of daidzein on (1) progesterone (P4) and oestradiol (E2) secretion by porcine luteinised granulosa cells harvested from medium follicles, and (2) the mRNA and protein expression of oestrogen receptors α and β (ERα and ERβ) in these cells. The influence of E2 on P4 secretion and ERα and ERβ expression in the granulosa cells of pigs was also investigated. It was found that daidzein inhibited progesterone secretion by luteinised granulosa cells isolated from medium follicles. In contrast, E2 did not affect progesterone production by these cells. Moreover, daidzein did not alter the granulosal secretion of E2. Both daidzein and E2 decreased mRNA expression of ERα in the cells examined. The expression of ERβ mRNA was not affected by daidzein but was inhibited by E2. ERα protein was not detected while ERβ protein was found in the nuclei of the cells. Daidzein and E2 upregulated the expression of ERβ protein in the cells. In summary, the phytoestrogen daidzein directly affected the porcine ovary by inhibiting progesterone production and increasing ERβ protein expression. Daidzein-induced changes in follicular steroidogenesis and granulosal sensitivity to oestrogens may disturb reproductive processes in pigs.

Differential regulation of ovarian anti-müllerian hormone (AMH) by estradiol through α- and β-estrogen receptors

BACKGROUND

Anti-müllerian hormone (AMH) is a member of the TGF-β family, which limits follicle maturation. Recently serum AMH has been recognized as a useful diagnostic and prognostic tool in human reproductive endocrinology.

OBJECTIVE

The aim of this study was to investigate the regulation of human ovarian AMH by estradiol and FSH.

METHODS

AMH mRNA were quantified by real time RT-PCR in human granulosa cells (GC). AMH transcription was studied in KK1 GC cotransfected with estrogen receptors (ER)-β or ERα, and normal human AMH promoter-luciferase construct (hAMH-luc) or mutated AMH promoter reporter constructs. Binding sites for estradiol (estrogen response element half-site) and steroidogenic factor 1 were disrupted by targeted mutagenesis. The level of ER in GC was determined by quantitative RT-PCR and Western blotting.

RESULTS

In KK1 cells, estradiol up-regulated and inhibited hAMH-luc in the presence of ERα and ERβ respectively. Disruption of estrogen response element half-site and/or steroidogenic factor 1 binding sites did not modify ERβ-mediated effect of estradiol on hAMH-luc, whereas it affected that conveyed by ERα. The FSH enhancement of hAMH-luc was abolished by estradiol in cells overexpressing ERβ. When both ER were transfected, estradiol inhibited hAMH-luc or had no effect. Estradiol repressed AMH mRNAs in human GC, which express a little more ERα than ERβ mRNA.

CONCLUSIONS

Our results show that AMH expression can be differentially regulated by estradiol depending on the ER and suggest that its decrease in GC of growing follicles, which mainly express ERβ, and during controlled ovarian hyperstimulation is due to the effect of estradiol.

In vitro follicle growth under non-attachment conditions and decreased FSH levels reduces Lhcgr expression in cumulus cells and promotes oocyte developmental competence

PURPOSE

The in-vitro environment influences oocyte competence and gene expression in cumulus cells and oocytes. Effects of culturing under non-attachment conditions and varying follicle exposure to FSH were investigated at the mRNA level and on oocyte developmental capacity.

METHODS

Quantitative PCR analysis of Gdf9, Mater, Nmp2 (in oocytes), Lhcgr and Amh (in cumulus cells), and oocyte developmental competence after in vitro follicle culture were evaluated.

RESULTS

Follicle survival (98.7%) and polar body rate (94%) were similar for all conditions. Estradiol and progesterone production were significantly lower in non-attachment follicles (10-fold and 3-fold, respectively). Under non-attachment conditions, a higher two-cell rate (69.9%) and total blastocyst yield (48.5%) were obtained and, by decreasing FSH levels during culture, Lhcgr transcripts were significantly reduced to levels similar to in-vivo. Levels of oocyte-specific transcripts were not significantly influenced by in-vitro conditions.

CONCLUSION

Non-attachment conditions influence follicle steroid secretory capacity and, together with dynamic FSH doses, positively influence cumulus cell gene expression and oocyte developmental competence.

FOXL2 versus SOX9: a lifelong "battle of the sexes"

Testis determination in most mammals is regulated by a genetic hierarchy initiated by the SRY gene. Early ovarian development has long been thought of as a default pathway switched on passively by the absence of SRY. Recent studies challenge this view and show that the ovary constantly represses male-specific genes, from embryonic stages to adulthood. Notably, the absence of the crucial ovarian transcription factor FOXL2 (alone or in combination with other factors) induces a derepression of male-specific genes during development, postnatally and, even more interestingly, during adulthood. Strikingly, in the adult, targeted ablation of Foxl2 leads to a molecular transdifferentiation of the supporting cells of the ovary, which acquire cytological and transcriptomic characteristics of the supporting cells of the testes. These studies bring many answers to the field of gonadal determination, differentiation and maintenance, but also open many questions.

Extending the knowledge in histochemistry and cell biology

Central to modern Histochemistry and Cell Biology stands the need for visualization of cellular and molecular processes. In the past several years, a variety of techniques has been achieved bridging traditional light microscopy, fluorescence microscopy and electron microscopy with powerful software-based post-processing and computer modeling. Researchers now have various tools available to investigate problems of interest from bird's- up to worm's-eye of view, focusing on tissues, cells, proteins or finally single molecules. Applications of new approaches in combination with well-established traditional techniques of mRNA, DNA or protein analysis have led to enlightening and prudent studies which have paved the way toward a better understanding of not only physiological but also pathological processes in the field of cell biology. This review is intended to summarize articles standing for the progress made in "histo-biochemical" techniques and their manifold applications.

Differences in collagen expression in cumulus cells after exposure to highly purified menotropin or recombinant follicle-stimulating hormone in a mouse follicle culture model

Extracellular matrix (ECM) formation by cumulus cells is an important process that determines fertilization and embryo quality. Several collagen types are present in the ovarian follicular ECM and are related to proliferation, steroidogenesis, and luteinization. In vitro mouse follicles can optimally grow and provide developmentally competent oocytes with 10 IU/L recombinant follicle-stimulating hormone (rFSH). As a model for superovulation, experiments with 100 IU/L rFSH or 100 IU/L highly purified menotropin (HP-hMG) exposure during antral growth were undertaken. Col4a1, Col4a2, and Col6a2 expression levels were analyzed at three time points during antral growth and at a 4-h interval up to 16 h after ovulation induction using quantitative PCR. The presence and induction of the collagen mRNA and protein were confirmed in cumulus from in vivo- and in vitro-grown follicles, and TGFBs 1 and 2 were assayed as potential regulators. The study revealed that exposure to 100 IU/L FSH, as in both superovulation conditions, significantly influenced the follicle morphology and slowed down nuclear maturation and mucification (P < 0.05). This coincided with an increased expression of the three collagens in the cumulus-oocyte complex at the end of antral growth and in the first hours following the ovulatory dose of human chorionic gonadotropin (P < 0.05). The increased expression might reflect a differentiation but is most likely due to a precocious luteinization of the cumulus. Growth in HP-hMG resulted in higher Tgfb1 mRNA and protein levels, fewer COCs with an increased collagen expression and with a more synchronous nuclear maturation. This suggests that the presence of luteinizing hormone activity tempered the effect of the elevated FSH dose.

Functional AR signaling is evident in an in vitro mouse follicle culture bioassay that encompasses most stages of folliculogenesis

Androgens have distinct physiological functions within the ovary. The biological action of androgens is primarily exerted through transcriptional regulation by the nuclear androgen receptor (AR), but the molecular cascades governed by AR remain largely unknown. At present, there is imminent concern that environmental man-made chemicals with antiandrogenic properties, among others, are capable of modulating hormonal responses, thereby interfering with normal physiological processes that are critical to fertility. In the present study, we aimed to further characterize a standardized and reproducible follicle culture system in terms of AR expression during in vitro folliculogenesis to be able to use it as a bioassay to study effects of antiandrogens on follicular and oocyte growth, steroid secretion profile, and oocyte meiotic maturation capacity. Immunohistochemical analysis revealed that cytoplasmic AR protein was translocated to the nucleus of granulosa and theca cells in response to endogenous androgen production in theca cells during preantral follicular development. During the antral phase in vitro, AR was differentially expressed in mural and cumulus cells, implying an oocyte-mediated regulation. Treatment of follicles with hydroxyflutamide or bicalutamide, two model antiandrogenic compounds, resulted in reduced follicular growth during the preantral phase, altered steroidogenic environment, and arrest in oocyte meiotic maturation in response to human chorionic gonadotropin. Androgen receptor expression in the culture model corresponded well to what is described in vivo, and this system revealed several ovarian functions targeted by AR antagonists that can be further investigated using more in-depth molecular techniques.

State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology

Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.