Generation of an estrogen receptor beta-iCre knock-in mouse

Granulosa cell expression of Fos is critical for regulating ovulatory gene expressions in the mouse ovary

A previous study showed that female Fos null mice fail to ovulate even when given gonadotropins, suggesting that ovarian expression of Fos is critical for successful ovulation. However, the expression of FOS and function of FOS have not been determined in the mouse ovary. FOS, a member of the Fos family (Fos, Fosb, Fosl1, and Fosl2), functions as a transcription factor by forming a heterodimer complex with a member of Jun family (Jun, Junb, and Jund). This study demonstrated rapid increases in Fos, along with other Fos and Jun family members, after hCG administration in the ovary of immature PMSG-primed mice and after the LH surge in naturally cycling animals. ChIP-seq analysis identified 1965 FOS-binding genes in granulosa cells collected at 3 h post-hCG, including Pgr, Ptgs2, Tnfiap6, and Edn2, genes known to be involved in the ovulatory process. When super-ovulation was induced, the number of oocytes released was significantly reduced in Esr2cre/+-driven granulosa cell-specific Fos knockout (gcFosKO) mice. This reduction was accompanied by lower expressions of Pgr, Ptgs2, Ptgs1, and Edn2 in preovulatory follicles of gcFosKO mice compared to those in control littermates. In addition, gcFosKO mice showed a trend toward a decreased average litter size. Together, the present study indicates that the preovulatory induction of Fos expression is crucial for increasing the expression of key ovulatory genes, yet the role of FOS may be partially substituted by other Fos and Jun family members induced in the preovulatory follicle in the gcFosKO mouse ovary.

A Dynamic Shift in Estrogen Receptor Expression During Granulosa Cell Differentiation in the Ovary

This study uncovers a dynamic shift in estrogen receptor expression during granulosa cell (GC) differentiation in the ovary, highlighting a transition from estrogen receptor alpha (ESR1) to estrogen receptor beta (ESR2). Using a transgenic mouse model with Esr1-iCre-mediated Esr2 deletion, we demonstrate that ESR2 expression is absent in GCs derived from ESR1-expressing ovarian surface epithelium (OSE) cells. Single-cell analysis of the OSE-GC lineage reveals a developmental trajectory from Esr1-expressing OSE cells to Foxl2-expressing pre-GCs, culminating in GCs exclusively expressing Esr2. Transcriptome analyses identified vasculature-derived TGFβ1 ligands as key regulators of this transition. Supporting this, TGFβ1 treatment of cultured embryonic ovaries reduced Esr1 expression while promoting Esr2 expression. This study underscores the capability of GCs to switch from ESR1 to ESR2 expression as a fundamental aspect of normal differentiation.

Normal Ovarian Function in Subfertile Mouse with Amhr2-Cre-Driven Ablation of Insr and Igf1r

Insulin receptor signaling promotes cell differentiation, proliferation, and growth which are essential for oocyte maturation, embryo implantation, endometrial decidualization, and placentation. The dysregulation of insulin signaling in women with metabolic syndromes including diabetes exhibits poor pregnancy outcomes that are poorly understood. We utilized the Cre/LoxP system to target the tissue-specific conditional ablation of insulin receptor (Insr) and insulin-like growth factor-1 receptor (Igf1r) using an anti-Mullerian hormone receptor 2 (Amhr2) Cre-driver which is active in ovarian granulosa and uterine stromal cells. Our long-term goal is to examine insulin-dependent molecular mechanisms that underlie diabetic pregnancy complications, and our conditional knockout models allow for such investigation without confounding effects of ligand identity, source and cross-reactivity, or global metabolic status within dams. Puberty occurred with normal timing in all conditional knockout models. Estrous cycles progressed normally in Insrd/d females but were briefly stalled in diestrus in Igf1rd/d and double receptor (DKO) mice. The expression of vital ovulatory genes (Lhcgr, Pgr, Ptgs2) was not significantly different in 12 h post-hCG superovulated ovaries in knockout mice. Antral follicles exhibited an elevated apoptosis of granulosa cells in Igf1rd/d and DKO mice. However, the distribution of ovarian follicle subtypes and subsequent ovulations was normal in all insulin receptor mutants compared to littermate controls. While ovulation was normal, all knockout lines were subfertile suggesting that the loss of insulin receptor signaling in the uterine stroma elicits implantation and decidualization defects responsible for subfertility in Amhr2-Cre-derived insulin receptor mutants.

Optimized Mouse-on-mouse Immunohistochemical Detection of Mouse ESR2 Proteins with PPZ0506 Monoclonal Antibody

Despite the physiological significance of ESR2, a lack of well-validated detection systems for ESR2 proteins has hindered progress in ESR2 research. Thus, recent identification of a specific anti-human ESR2 monoclonal antibody (PPZ0506) and its specific cross-reactivity against mouse and rat ESR2 proteins heightened momenta toward development of appropriate immunohistochemical detection systems for rodent ESR2 proteins. Building upon our previous optimization of ESR2 immunohistochemical detection in rats using PPZ0506, in this study, we further aimed to optimize mouse-on-mouse immunohistochemical detection using PPZ0506. Our assessment of several staining conditions using paraffin-embedded ovary sections revealed that intense heat-induced antigen retrieval, appropriate blocking, and appropriate antibody dilutions were necessary for optimization of mouse-on-mouse immunohistochemistry. Subsequently, we applied the optimized immunostaining method to determine expression profiles of mouse ESR2 proteins in peripheral tissues and brain subregions. Our analyses revealed more localized distribution of mouse ESR2 proteins than previously assumed. Moreover, comparison of these results with those obtained in humans and rats using PPZ0506 revealed interspecies differences in ESR2 expression. We expect that our optimized methodology for immunohistochemical staining of mouse ESR2 proteins will help researchers to solve multiple lines of controversial evidence concerning ESR2 expression.

Estrogens: Two nuclear receptors, multiple possibilities

Much is known about estrogen action in experimental animal models and in human physiology. This article reviews the mechanisms of estrogen activity in animals and humans and the role of its two receptors α and β in terms of structure and mechanisms of action in various tissues in health and in relationship with human pathologies (e.g., osteoporosis). Recently, the spectrum of clinical pictures of estrogen resistance caused by estrogen receptors gene variants has been widened by our description of a woman with β-receptor defect, which could be added to the already known descriptions of α-receptor defect in women and men and β-receptor defect in men. The essential role of the β-receptor in the development of the gonad stands out. We summarize the clinical pictures due to estrogen resistance in men and women and focus on long-term follow-up of two women, one with α- and the other with β-receptor resistance. Some open questions remain on the complex interactions between the two receptors on bone metabolism and hypothalamus-pituitary-gonadal axis, which need further deepening and research.

Estrogen Receptor α Inactivation in 2 Sisters: Different Phenotypic Severities for the Same Pathogenic Variant

CONTEXT

Estrogens play an essential role in reproduction. Their action is mediated by nuclear α and β receptors (ER) and by membrane receptors. Only 3 females and 2 males, from 3 families, with a loss of ERα function have been reported to date.

OBJECTIVE

We describe here a new family, in which 2 sisters display endocrine and ovarian defects of different severities despite carrying the same homozygous rare variant of ESR1.

METHODS

A 36-year-old woman from a consanguineous Jordanian family presented with primary amenorrhea and no breast development, with high plasma levels of 17β-estradiol (E2), follicle-stimulating hormone and luteinizing hormone, and enlarged multifollicular ovaries, strongly suggesting estrogen resistance. Her 18-year-old sister did not enter puberty and had moderately high levels of E2, high plasma gonadotropin levels, and normal ovaries.

RESULTS

Genetic analysis identified a homozygous variant of ESR1 leading to the replacement of a highly conserved glutamic acid with a valine (ERα-E385V). The transient expression of ERα-E385V in HEK293A and MDA-MB231 cells revealed highly impaired ERE-dependent transcriptional activation by E2. The analysis of the KISS1 promoter activity revealed that the E385V substitution induced a ligand independent activation of ERα. Immunofluorescence analysis showed that less ERα-E385V than ERα-WT was translocated into the nucleus in the presence of E2.

CONCLUSION

These 2 new cases are remarkable given the difference in the severity of their ovarian and hormonal phenotypes. This phenotypic discrepancy may be due to a mechanism partially compensating for the ERα loss of function.

Progesterone Receptor Serves the Ovary as a Trigger of Ovulation and a Terminator of Inflammation

Ovulation is triggered by the gonadotropin surge that induces the expression of two key genes, progesterone receptor (Pgr) and prostaglandin-endoperoxide synthase 2 (Ptgs2), in the granulosa cells of preovulatory follicles. Their gene products PGR and PTGS2 activate two separate pathways that are both essential for successful ovulation. Here, we show that the PGR plays an additional essential role: it attenuates ovulatory inflammation by diminishing the gonadotropin surge-induced Ptgs2 expression. PGR indirectly terminates Ptgs2 expression and PGE2 synthesis in granulosa cells by inhibiting the nuclear factor κB (NF-κB), a transcription factor required for Ptgs2 expression. When the expression of PGR is ablated in granulosa cells, the ovary undergoes a hyperinflammatory condition manifested by excessive PGE2 synthesis, immune cell infiltration, oxidative damage, and neoplastic transformation of ovarian cells. The PGR-driven termination of PTGS2 expression may protect the ovary from ovulatory inflammation.

Core Binding Factors are essential for ovulation, luteinization, and female fertility in mice

Core Binding Factors (CBFs) are a small group of heterodimeric transcription factor complexes composed of DNA binding proteins, RUNXs, and a non-DNA binding protein, CBFB. The LH surge increases the expression of Runx1 and Runx2 in ovulatory follicles, while Cbfb is constitutively expressed. To investigate the physiological significance of CBFs, we generated a conditional mutant mouse model in which granulosa cell expression of Runx2 and Cbfb was deleted by the Esr2Cre. Female Cbfbflox/flox;Esr2cre/+;Runx2flox/flox mice were infertile; follicles developed to the preovulatory follicle stage but failed to ovulate. RNA-seq analysis of mutant mouse ovaries collected at 11 h post-hCG unveiled numerous CBFs-downstream genes that are associated with inflammation, matrix remodeling, wnt signaling, and steroid metabolism. Mutant mice also failed to develop corpora lutea, as evident by the lack of luteal marker gene expression, marked reduction of vascularization, and excessive apoptotic staining in unruptured poorly luteinized follicles, consistent with dramatic reduction of progesterone by 24 h after hCG administration. The present study provides in vivo evidence that CBFs act as essential transcriptional regulators of both ovulation and luteinization by regulating the expression of key genes that are involved in inflammation, matrix remodeling, cell differentiation, vascularization, and steroid metabolisms in mice.

Principles of Genetic Engineering

Genetic engineering is the use of molecular biology technology to modify DNA sequence(s) in genomes, using a variety of approaches. For example, homologous recombination can be used to target specific sequences in mouse embryonic stem (ES) cell genomes or other cultured cells, but it is cumbersome, poorly efficient, and relies on drug positive/negative selection in cell culture for success. Other routinely applied methods include random integration of DNA after direct transfection (microinjection), transposon-mediated DNA insertion, or DNA insertion mediated by viral vectors for the production of transgenic mice and rats. Random integration of DNA occurs more frequently than homologous recombination, but has numerous drawbacks, despite its efficiency. The most elegant and effective method is technology based on guided endonucleases, because these can target specific DNA sequences. Since the advent of clustered regularly interspaced short palindromic repeats or CRISPR/Cas9 technology, endonuclease-mediated gene targeting has become the most widely applied method to engineer genomes, supplanting the use of zinc finger nucleases, transcription activator-like effector nucleases, and meganucleases. Future improvements in CRISPR/Cas9 gene editing may be achieved by increasing the efficiency of homology-directed repair. Here, we describe principles of genetic engineering and detail: (1) how common elements of current technologies include the need for a chromosome break to occur, (2) the use of specific and sensitive genotyping assays to detect altered genomes, and (3) delivery modalities that impact characterization of gene modifications. In summary, while some principles of genetic engineering remain steadfast, others change as technologies are ever-evolving and continue to revolutionize research in many fields.

Lymphatic Function and Dysfunction in the Context of Sex Differences

Endothelial cells are the building blocks of the blood vascular system and exhibit well-characterized sexually dimorphic phenotypes with regard to chromosomal and hormonal sex, imparting innate genetic and physiological differences between male and female vascular systems and cardiovascular disease. However, even though females are predominantly affected by disorders of lymphatic vascular function, we lack a comprehensive understanding of the effects of sex and sex hormones on lymphatic growth, function, and dysfunction. Here, we attempt to comprehensively evaluate the current understanding of sex as a biological variable influencing lymphatic biology. We first focus on elucidating innate and fundamental differences between the sexes in lymphatic function and development. Next, we delve into lymphatic disease and explore the potential underpinnings toward bias prevalence in the female population. Lastly, we incorporate more broadly the role of the lymphatic system in sex-biased diseases such as cancer, cardiovascular disease, reproductive disorders, and autoimmune diseases to explore whether and how sex differences may influence lymphatic function in the context of these pathologies.

Characterization of a BAC transgenic mouse expressing Krt19-driven iCre recombinase in its digestive organs

Cytokeratin 19 (KRT19) protein is highly expressed in the epithelium of the gastrointestinal (GI) tract, hepatobiliary tissues, and pancreas of humans and mice. In the present study, we used an improved Cre (iCre) gene to enhance the efficiency of Cre expression in mammalian cells. We established a new transgenic Krt19-iCre bacterial artificial chromosome (BAC) mouse model using the BAC recombineering strategy. Site-specific iCre expression pattern was examined in embryos, adults, and elderly Krt19-iCre mice crossed with Tomato or LacZ reporter mice. Both iCre and reporter protein expressions in adult Krt19-iCre;Tomato^flox/+(Krt19-iCre Tomato reporter) mice were observed mainly in the epithelial cells of the GI tract, hepatobiliary tissues, and pancreas. However, the expression in the intrahepatic and small pancreatic duct were lower than those in the common bile and large pancreatic duct. In the Krt19-iCre; LacZ reporter embryos, β-galactosidase for the LacZ reporter was expressed in the glandular epithelial cells of the GI tract in 9.5-day embryos, 12-day embryos, and newborn mice. The reporter protein expression in Krt19-iCre-Tomato reporter mice was consistent with the KRT19 expression in human GI tissues. In conclusion, Krt19-iCre BAC transgenic mice can be used to investigate developmental and pathological conditions using the iCre-loxP system.

Early-Onset Complete Ovarian Failure and Lack of Puberty in a Woman With Mutated Estrogen Receptor β (ESR2)

CONTEXT

Estrogen resistance due to mutations in the estrogen receptor α gene (ESR1) has been described in men and women and is characterized by osteoporosis, delayed bone age and continuous growth in adulthood, and delayed puberty and multiple ovarian cysts in women. Although mutations in the estrogen receptor β gene ESR2 were found in 46, XY patients with differences of sex development, no genetic variants of ESR2 were linked to gonadal defects in women.

SETTINGS AND PATIENT

Here we describe a 16-year-old female patient who came to our tertiary care hospital with complete lack of estrogen action, as demonstrated by absent breast development, primary amenorrhea, and osteoporosis, resembling patients with ESR1 mutation. However, her gonads were clearly abnormal (streak), a finding not observed in ESR1-deficient patients.

DESIGN

To gain insights into the molecular consequences of the ESR2 defect, whole exome sequencing and extensive functional transactivation studies in ovarian, bone, and breast cells were conducted, with or without the natural activator of estrogen receptors, 17β-estradiol.

RESULTS

We identified a loss-of-function heterozygous mutation of a highly conserved residue in ESR2 that disrupts estradiol-dependent signaling and has a dominant negative effect, most likely due to failure to interact with its coactivator, nuclear coactivator 1.

CONCLUSIONS

This is a report of a loss-of-function mutation in the estrogen receptor β in a young woman with complete ovarian failure, suggesting that ESR2 is necessary for human ovarian determination and/or maintenance and that ESR1 is not sufficient to sustain ovarian function in humans.

Estrogen Receptors: New Directions in the New Millennium

Nineteen years have passed since our previous review in this journal in 1999 regarding estrogen receptors. At that time, we described the current assessments of the physiological activities of estrogen and estrogen receptors. Since that time there has been an explosion of progress in our understanding of details of estrogen receptor-mediated processes from the molecular and cellular level to the whole organism. In this review we discuss the basic understanding of estrogen signaling and then elaborate on the progress and current understanding of estrogen receptor actions that have developed using new models and continuing clinical studies.

Bisphenol A and Phthalates Modulate Peritoneal Macrophage Function in Female Mice Involving SYMD2-H3K36 Dimethylation

Ample evidence suggests that environmental and occupational exposure to bisphenol A (BPA) and phthalate, two chemicals widely used in the plastics industry, disturbs homeostasis of innate immunity and causes inflammatory diseases. However, the underlying molecular mechanisms of these toxicants in the regulation of macrophage inflammatory functions remain poorly understood. In this study, we addressed the effect of chronic exposure to BPA or phthalate at levels relevant to human exposure, either in vitro or in vivo, on the inflammatory reprograming of peritoneal macrophages. Our studies revealed that BPA and phthalates adversely affected expression levels of the proinflammatory cytokines and mediators in response to lipopolysaccharide stimulation. Exposure to these toxicants also affected gene expression of scavenger receptors and phagocytic capacity of peritoneal macrophages. Our studies revealed that the epigenetic inhibitors differentially modulated target gene expression in these cells. Further analysis revealed that certain histone modification enzymes were aberrantly expressed in response to BPA or phthalate exposure, leading to alteration in the levels of H3K36 acetylation and dimethylation, two chromatin modifications that are critical for transcriptional efficacy and accuracy. Our results further revealed that silencing of H3K36-specific methyltransferase Smyd2 expression or inhibition of SMYD2 enzymatic activity attenuated H3K36 dimethylation and enhanced interleukin-6 and tumor necrosis factor-α expression but dampened the phagocytic capacity of peritoneal macrophages. In summary, our results indicate that peritoneal macrophages are vulnerable to BPA or phthalate at levels relevant to human exposure. These environmental toxicants affect phenotypic programming of macrophages via epigenetic mechanisms involving SMYD2-mediated H3K36 modification.

Generation and characterization of an estrogen receptor alpha-iCre knock-in mouse

Two estrogen receptors, ESR1 and ESR2, are responsible for the classical actions of estrogens in mammalian species. They display different spatiotemporal expression patterns and nonoverlapping functions in various tissues and physiological conditions. In this study, a novel knock-in mouse line that expresses codon-improved Cre recombinase (iCre) under regulation of the natural Esr1 promoter (Esr1-iCre) was developed. Functional characterization of iCre expression by crossing them with reporter lines (ROSA26-lacZ or Ai9-RFP) showed that iCre is faithfully expressed in Esr1-lineage cells. This novel transgenic mouse line will be a useful animal model for lineage-tracing Esr1-expressing cells, selective gene ablation in the Esr1-lineage cells and for generating global Esr1 knockout mice.

Estrogens in Male Physiology

Estrogens have historically been associated with female reproduction, but work over the last two decades established that estrogens and their main nuclear receptors (ESR1 and ESR2) and G protein-coupled estrogen receptor (GPER) also regulate male reproductive and nonreproductive organs. 17β-Estradiol (E2) is measureable in blood of men and males of other species, but in rete testis fluids, E2 reaches concentrations normally found only in females and in some species nanomolar concentrations of estrone sulfate are found in semen. Aromatase, which converts androgens to estrogens, is expressed in Leydig cells, seminiferous epithelium, and other male organs. Early studies showed E2 binding in numerous male tissues, and ESR1 and ESR2 each show unique distributions and actions in males. Exogenous estrogen treatment produced male reproductive pathologies in laboratory animals and men, especially during development, and studies with transgenic mice with compromised estrogen signaling demonstrated an E2 role in normal male physiology. Efferent ductules and epididymal functions are dependent on estrogen signaling through ESR1, whose loss impaired ion transport and water reabsorption, resulting in abnormal sperm. Loss of ESR1 or aromatase also produces effects on nonreproductive targets such as brain, adipose, skeletal muscle, bone, cardiovascular, and immune tissues. Expression of GPER is extensive in male tracts, suggesting a possible role for E2 signaling through this receptor in male reproduction. Recent evidence also indicates that membrane ESR1 has critical roles in male reproduction. Thus estrogens are important physiological regulators in males, and future studies may reveal additional roles for estrogen signaling in various target tissues.

Granulosa cell endothelin-2 expression is fundamental for ovulatory follicle rupture

Ovulation is dependent upon numerous factors mediating follicular growth, vascularization, and ultimately oocyte release via follicle rupture. Endothelin-2 (EDN2) is a potent vasoconstrictor that is transiently produced prior to follicle rupture by granulosa cells of periovulatory follicles and induces ovarian contraction. To determine the role of Edn2 expression, surgical transplant and novel conditional knockout mice were super-ovulated and analyzed. Conditional knockout mice utilized a new iCre driven by the Esr2 promoter to selectively remove Edn2. Follicle rupture and fertility were significantly impaired in the absence of ovarian Edn2 expression. When ovaries of Edn2KO mice were transplanted in wild type recipients, significantly more corpora lutea containing un-ovulated oocytes were present after hormonal stimulation (1.0 vs. 5.4, p = 0.010). Following selective ablation of Edn2 in granulosa cells, Esr2-Edn2KO dams had reduced oocytes ovulated (3.8 vs. 16.4 oocytes/ovary) and smaller litters (4.29 ± l.02 vs. 8.50 pups/dam). However, the number of pregnancies per pairing was not different and the reproductive axis remained intact. Esr2-Edn2KO ovaries had a higher percentage of antral follicles and fewer corpora lutea; follicles progressed to the antral stage but many were unable to rupture. Conditional loss of endothelin receptor A in granulosa cells also decreased ovulation but did not affect fecundity. These data demonstrate that EDN2-induced intraovarian contraction is a critical trigger of normal ovulation and subsequent fecundity.

Mouse Models for the Study of Synthesis, Secretion, and Action of Pituitary Gonadotropins

Gonadotropins play fundamental roles in reproduction. More than 30years ago, Cga transgenic mice were generated, and more than 20years ago, the phenotypes of Cga null mice were reported. Since then, numerous mouse strains have been generated and characterized to address several questions in reproductive biology involving gonadotropin synthesis, secretion, and action. More recently, extragonadal expression, and in some cases, functions of gonadotropins in nongonadal tissues have been identified. Several genomic and proteomic approaches including novel mouse genome editing tools are available now. It is anticipated that these and other emerging technologies will be useful to build an integrated network of gonadotropin signaling pathways in various tissues. Undoubtedly, research on gonadotropins will continue to provide new knowledge and allow us transcend from benchside to the bedside.