Ablation of Indian hedgehog in the murine uterus results in decreased cell cycle progression, aberrant epidermal growth factor signaling, and increased estrogen signaling

Progesterone receptor in uterine glands is required for pregnancy establishment in mice

Embryo implantation is a critical event in the establishment of pregnancy, and implantation failure is a major cause of pregnancy loss in women. Coordinated, cell-type specific responses to the ovarian steroid hormones, estrogen, and progesterone, within the endometrium underlie successful embryo implantation and pregnancy establishment. In this study, we utilized a glandular epithelium (GE) specific Cre recombinase mouse line that is only active in the adult (Prss29-Cre) to determine the biological role of progesterone receptor (PGR) in uterine glands during pregnancy. Conditional ablation of PGR specifically in the GE compromised fertility due to defects in uterine receptivity and embryo implantation. Histological and transcriptomic analyses uncovered disruption of multiple PGR-regulated genes in the GE during the window of receptivity, including leukemia inhibitory factor (LIF), a cytokine produced specifically by the GE that is essential for embryo implantation. Interestingly, intraperitoneal injections of recombinant LIF in Pgr conditional knockout mice rescued embryo implantation and supported successful pregnancy to term. These findings underscore the vital role of PGR in regulating Lif expression in the GE, while suggesting that PGR in the glands of the uterus is unessential once pregnancy is established. Overall, these findings reveal a previously unrecognized role of PGR in uterine glands and support the hypothesis that glandular secretions, governed by PGR, are indispensable for pregnancy establishment.

Transcriptomic alterations in the ovine caruncular endometrium due to imbalanced nutrition and FSH-induced ovarian hyperstimulation

BACKGROUND

Imbalanced diet and exogenous gonadotrophins affect uterine function and morphology. In sheep, FSH-induced superovulation alters implantation-related gene expression, influenced by both treatment and diet. In this study, we used deep RNA sequencing (NGS, RNA-Seq) to expand our understanding of these effects on the caruncular endometrium.

METHODS

Ewes (n = 3-5/group) were separated into control fed (CF), overfed (OF), and underfed (UF) groups, with each group subdivided between FSH (superovulated; SOV) or saline (negative controls; CONT) treatment. Caruncular samples were collected on day 10 of diestrus of the subsequent estrous cycle, with samples from CF_CONT also collected on day 5 to assess time-dependent changes.

RESULTS

The 1484 differentially expressed genes (DEGs, P < 0.01, FDR < 0.05) identified between CF_CONT animals at days 5 and 10 were predominantly associated with increased immune activity and cellular metabolic processes and cellular proliferation. In CONT animals, imbalanced nutrition (i.e., both OF and UF) was associated with enrichment of terms associated with cell adhesion and differentiation, immune response and angiogenesis. The FSH carry-over effects resulted in a higher number of DEGs in CF animals (1374), than in OF (168) or UF (18), mostly associated with dysregulation of cell cycle and hormonal sensitivity.

CONCLUSION

The absence of genes concurrently affected by superovulation (SOV) in all feeding regimes indicates that the effects of FSH on the caruncular transcriptome are multidirectional and dependent upon body condition. Therefore, the homeostasis of ovine caruncles is influenced by both body condition and superovulation (SOV), potentially affecting uterine receptivity.

Unexpected nuclear hormone receptor and chromatin dynamics regulate estrous cycle dependent gene expression

Chromatin changes in response to estrogen and progesterone are well established in cultured cells, but how they control gene expression under physiological conditions is largely unknown. To address this question, we examined in vivo estrous cycle dynamics of mouse uterus hormone receptor occupancy, chromatin accessibility and chromatin structure by combining RNA-seq, ATAC-seq, HiC-seq and ChIP-seq. Two estrous cycle stages were chosen for these analyses, diestrus (highest estrogen) and estrus (highest progesterone). Unexpectedly, rather than alternating with each other, estrogen receptor alpha (ERα) and progesterone receptor (PGR) were co-bound during diestrus and lost during estrus. Motif analysis of open chromatin followed by hypoxia inducible factor 2A (HIF2A) ChIP-seq and conditional uterine deletion of this transcription factor revealed a novel role for HIF2A in regulating diestrus gene expression patterns that were independent of either ERα or PGR binding. Proteins in complex with ERα included PGR and cohesin, only during diestrus. Combined with HiC-seq analyses, we demonstrate that complex chromatin architecture changes including enhancer switching are coordinated with ERα and PGR co-binding during diestrus and non-hormone receptor transcription factors such as HIF2A during estrus to regulate most differential gene expression across the estrous cycle.

Implantation and Decidualization in PCOS: Unraveling the Complexities of Pregnancy

Polycystic Ovary Syndrome (PCOS) is a prevalent endocrine disorder in women of reproductive age, affecting 5-15% globally with a large proportion undiagnosed. This review explores the multifaceted nature of PCOS and its impact on pregnancy, including challenges in fertility due to hormonal imbalances and insulin resistance. Despite restoring ovulation pharmacologically, women with PCOS face lower pregnancy rates and higher risks of implantation failure and miscarriage. Our review focuses on the complexities of hormonal and metabolic imbalances that impair endometrial receptivity and decidualization in PCOS. Disrupted estrogen signaling, reduced integrity of endometrial epithelial tight junctions, and insulin resistance impair the window of endometrial receptivity. Furthermore, progesterone resistance adversely affects decidualization. Our review also examines the roles of various immune cells and inflammatory processes in the endometrium, contributing to the condition's reproductive challenges. Lastly, we discuss the use of rodent models in understanding PCOS, particularly those induced by hormonal interventions, offering insights into the syndrome's impact on pregnancy and potential treatments. This comprehensive review underscores the need for advanced understanding and treatment strategies to address the reproductive complications associated with PCOS, emphasizing its intricate interplay of hormonal, metabolic, and immune factors.

Steroid receptor coactivator-2 drives epithelial reprogramming that enables murine embryo implantation

Although we have shown that steroid receptor coactivator-2 (SRC-2), a member of the p160/SRC family of transcriptional coregulators, is essential for decidualization of both human and murine endometrial stromal cells, SRC-2's role in the earlier stages of the implantation process have not been adequately addressed. Using a conditional SRC-2 knockout mouse (SRC-2d/d ) in timed natural pregnancy studies, we show that endometrial SRC-2 is required for embryo attachment and adherence to the luminal epithelium. Implantation failure is associated with the persistent expression of Mucin 1 and E-cadherin on the apical surface and basolateral adherens junctions of the SRC-2d/d luminal epithelium, respectively. These findings indicate that the SRC-2d/d luminal epithelium fails to exhibit a plasma membrane transformation (PMT) state known to be required for the development of uterine receptivity. Transcriptomics demonstrated that the expression of genes involved in steroid hormone control of uterine receptivity were significantly disrupted in the SRC-2d/d endometrium as well as genes that control epithelial tight junctional biology and the emergence of the epithelial mesenchymal transition state, with the latter sharing similar biological properties with PMT. Collectively, these findings uncover a new role for endometrial SRC-2 in the induction of the luminal epithelial PMT state, which is a prerequisite for the development of uterine receptivity and early pregnancy establishment.

Hedgehog signaling is required for endometrial remodeling and myometrial homeostasis in the cycling mouse uterus

Decades of work demonstrate that the mammalian estrous cycle is controlled by cycling steroid hormones. However, the signaling mechanisms that act downstream, linking hormonal action to the physical remodeling of the cycling uterus, remain unclear. To address this issue, we analyzed gene expression at all stages of the mouse estrous cycle. Strikingly, we found that several genetic programs well-known to control tissue morphogenesis in developing embryos displayed cyclical patterns of expression. We find that most of the genetic architectures of Hedgehog signaling (ligands, receptors, effectors, and transcription factors) are transcribed cyclically in the uterus, and that conditional disruption of the Hedgehog receptor smoothened not only elicits a failure of normal cyclical thickening of the endometrial lining but also induces aberrant deformation of the uterine smooth muscle. Together, our data shed light on the mechanisms underlying normal uterine remodeling specifically and cyclical gene expression generally.

The endometrial transcriptome transition preceding receptivity to embryo implantation in mice

BACKGROUND

Receptivity of the uterus is essential for embryo implantation and progression of mammalian pregnancy. Acquisition of receptivity involves major molecular and cellular changes in the endometrial lining of the uterus from a non-receptive state at ovulation, to a receptive state several days later. The precise molecular mechanisms underlying this transition and their upstream regulators remain to be fully characterized. Here, we aimed to generate a comprehensive profile of the endometrial transcriptome in the peri-ovulatory and peri-implantation states, to define the genes and gene pathways that are different between these states, and to identify new candidate upstream regulators of this transition, in the mouse.

RESULTS

High throughput RNA-sequencing was utilized to identify genes and pathways expressed in the endometrium of female C57Bl/6 mice at estrus and on day 3.5 post-coitum (pc) after mating with BALB/c males (n = 3-4 biological replicates). Compared to the endometrium at estrus, 388 genes were considered differentially expressed in the endometrium on day 3.5 post-coitum. The transcriptional changes indicated substantial modulation of uterine immune and vascular systems during the pre-implantation phase, with the functional terms Angiogenesis, Chemotaxis, and Lymphangiogenesis predominating. Ingenuity Pathway Analysis software predicted the activation of several upstream regulators previously shown to be involved in the transition to receptivity including various cytokines, ovarian steroid hormones, prostaglandin E2, and vascular endothelial growth factor A. Our analysis also revealed four candidate upstream regulators that have not previously been implicated in the acquisition of uterine receptivity, with growth differentiation factor 2, lysine acetyltransferase 6 A, and N-6 adenine-specific DNA methyltransferase 1 predicted to be activated, and peptidylprolyl isomerase F predicted to be inhibited.

CONCLUSIONS

This study confirms that the transcriptome of a receptive uterus is vastly different to the non-receptive uterus and identifies several genes, regulatory pathways, and upstream drivers not previously associated with implantation. The findings will inform further research to investigate the molecular mechanisms of uterine receptivity.

Transcriptome profiling of gonad-stimulating factors in thoracic ganglia and a potential role of Indian hedgehog gene in vitellogenesis of banana shrimp Fenneropenaeus merguiensis

Shrimp reproduction is controlled by several factors. Central nervous tissues, especially thoracic ganglia and brain, are known sources of gonad stimulating factors (GSFs) in crustaceans, but the GSFs in shrimp have not yet been clarified. Hence, we aimed to characterize and study putative GSFs from thoracic ganglia of adult female Fenneropenaeus merguiensis. An analysis of thoracic ganglia transcriptome revealed 3224 putative GSFs of a total 77,681 unigenes. Only 376 putative GSFs were differentially expressed during ovarian developmental stages. Eight candidate GSFs were validated for their expression patterns in thoracic ganglia, including the Indian hedgehog gene. F. merguiensis Indian hedgehog (FmIHH) was then investigated for its role in vitellogenesis. The obtained full-length cDNA of FmIHH was similar to other crustacean IHHs rather than Sonic and Desert HHs. The FmIHH was dominantly expressed in thoracic ganglia, and its expression was significantly increased in the vitellogenic stages before being downregulated at the mature stage of ovarian development. Injection of the recombinant FmIHH (His-TF-IHH) protein stimulated vitellogenin expression in ovaries on day 3 and 7, and also increased the gonadosomatic index. In addition, crustacean hyperglycemic hormone expression and total sugar were significantly decreased in eyestalks and hemolymph, respectively, after injection of His-TF-IHH, while lactic acid was increased. Both total sugar and lactic acid were unchanged in ovaries of His-TF-IHH injected shrimp. These results suggested that FmIHH plays a crucial role in vitellogenesis and regulate sugar uptake during ovarian development.

The NR2F2-HAND2 signaling axis regulates progesterone actions in the uterus at early pregnancy

Endometrial function is dependent on a tight crosstalk between the epithelial and stromal cells of the endometrium. This communication is critical to ensure a fertile uterus and relies on progesterone and estrogen signaling to prepare a receptive uterus for embryo implantation in early pregnancy. One of the key mediators of this crosstalk is the orphan nuclear receptor NR2F2, which regulates uterine epithelial receptivity and stromal cell differentiation. In order to determine the molecular mechanism regulated by NR2F2, RNAseq analysis was conducted on the uterus of PgrCre;Nr2f2f/f mice at Day 3.5 of pregnancy. This transcriptomic analysis demonstrated Nr2f2 ablation in Pgr-expressing cells leads to a reduction of Hand2 expression, increased levels of Hand2 downstream effectors Fgf1 and Fgf18, and a transcriptome manifesting suppressed progesterone signaling with an altered immune baseline. ChIPseq analysis conducted on the Day 3.5 pregnant mouse uterus for NR2F2 demonstrated the majority of NR2F2 occupies genomic regions that have H3K27ac and H3K4me1 histone modifications, including the loci of major uterine transcription regulators Hand2, Egr1, and Zbtb16. Furthermore, functional analysis of an NR2F2 occupying site that is conserved between human and mouse was capable to enhance endogenous HAND2 mRNA expression with the CRISPR activator in human endometrial stroma cells. These data establish the NR2F2 dependent regulation of Hand2 in the stroma and identify a cis-acting element for this action. In summary, our findings reveal a role of the NR2F2-HAND2 regulatory axis that determines the uterine transcriptomic pattern in preparation for the endometrial receptivity.

TRIM28 modulates nuclear receptor signaling to regulate uterine function

Estrogen and progesterone, acting through their cognate receptors the estrogen receptor α (ERα) and the progesterone receptor (PR) respectively, regulate uterine biology. Using rapid immunoprecipitation and mass spectrometry (RIME) and co-immunoprecipitation, we identified TRIM28 (Tripartite motif containing 28) as a protein which complexes with ERα and PR in the regulation of uterine function. Impairment of TRIM28 expression results in the inability of the uterus to support early pregnancy through altered PR and ERα action in the uterine epithelium and stroma by suppressing PR and ERα chromatin binding. Furthermore, TRIM28 ablation in PR-expressing uterine cells results in the enrichment of a subset of TRIM28 positive and PR negative pericytes and epithelial cells with progenitor potential. In summary, our study reveals the important roles of TRIM28 in regulating endometrial cell composition and function in women, and also implies its critical functions in other hormone regulated systems.

Progress on the Role of Estrogen and Progesterone Signaling in Mouse Embryo Implantation and Decidualization

Embryo implantation and decidualization are key steps in establishing a successful pregnancy. Defects in embryo implantation and decidualization can cause a series of adverse chain reactions which can contribute to harmful pregnancy outcomes, such as embryo growth retardation, preeclampsia, miscarriage, premature birth, and so on. Approximately 75% of failed pregnancies are considered to be due to embryo implantation failure or defects. Decidualization, characterized by proliferation and differentiation of uterine stromal cells, is one of the essential conditions for blastocyst implantation, placental formation, and maintenance of pregnancy and is indispensable for the establishment of pregnancy in many species. Embryo implantation and decidualization are closely regulated by estrogen and progesterone secreted by the ovaries. Many cellular events and molecular signaling network pathways are involved in this process. This article reviews the recent advances in the molecular mechanisms of estrogen- and progesterone-regulating uterine receptivity establishment, blastocyst implantation, and decidualization, in order to better understand the underlying molecular mechanisms of hormonal regulation of embryo implantation and to develop new strategies for preventing or treating embryo implantation defects and improving the pregnancy rate of women.

CRC Therapy Identifies Indian Hedgehog Signaling in Mouse Endometrial Epithelial Cells and Inhibition of Ihh-KLF9 as a Novel Strategy for Treating IUA

Intrauterine adhesion (IUA) causes menstrual disturbance and infertility. There is no effective treatment available for moderate to severe IUA cases. Stem cell-based therapy has been investigated for treating IUA but is limited in clinical applications due to issues including the precise induction of differentiation, tumorigenesis, and unclear molecular mechanisms. In our recent study, we isolated and expanded the long-term cultures of conditional reprogrammed (CR) mouse endometrial epithelial cells. Treating IUA mice with these CR cells (CRCs) restored the morphology and structure of the endometrium and significantly improved the pregnancy rate. In this study, our data with high-throughput sequencing, CRISPR knockout Ihh^-/-CRCs, and transplantation identified for the first time that the Indian hedgehog (Ihh) gene plays a critical role in the regulation of endometrial epithelial cell proliferation. We also found that aberrant activated Ihh-krüppel-like factor 9 (KLF9) signaling contributes to the inhibition of normal progesterone receptor (PR) function in IUA mice. Thus, we hypothesized that inhibition of the Ihh-KLF9 pathway may be a novel strategy to treat IUA. Our data demonstrated that treatment with the hedgehog signaling inhibitor Vismodegib restored the morphology, structure, and microenvironment of the endometrium, and greatly improved the pregnancy rate in IUA mice. This study suggests a promising application of hedgehog inhibitors as a targeted drug in the IUA clinic.

Cyanidin-3-O-glucoside ameliorates cadmium induced uterine epithelium proliferation in mice

Cadmium (Cd) is an environmental pollutant and endocrine disrupter, abundantly present in water, food, and soil. Accumulation of Cd in the body can negatively affect female reproduction; especially the uterus is exceptionally sensitive to the toxic actions of Cd. The anthocyanin cyanidin-3-O-glucoside (C3G) is a naturally occurring phenolic compound in fruits and plants that can antagonize the toxic effects of Cd. This capacity makes C3G a possible candidate to prevent Cd-induced female infertility. The present study aimed to investigate: 1) whether C3G intake could prevent Cd-induced female reproductive toxicity, and 2) the underlying mechanisms responsible for this protective effect. The results of our study indicated that Cd exposure did not affect ovarian function, but induced hypertrophy of the uterine endometrium. Oral intake of C3G markedly reduced the effects of Cd exposure on the thickness of the uterine epithelium cells. Transcriptomic analysis of the endometrium revealed that C3G intake had anti-estrogenic effects, attenuating Cd-induced endometrial epithelial cell proliferation by inhibiting estrogen-responsive genes, enhancing epithelial progesterone receptor expression, and regulating Klf4 expression. The current findings implicate that C3G has the potential to be used as a dietary supplement based on its capacity to intervene in Cd-induced female reproductive toxicity.

A gene network of uterine luminal epithelium organizes mouse blastocyst implantation

Purpose

The receptive endometrium is critical for blastocyst implantation. In mice, after blastocysts enter the uterine cavities on day 4 of pregnancy (day 1 = vaginal plug), blastocyst attachment is completed within 24 h, accompanied by dynamic interactions between the uterine luminal epithelium and the blastocysts. Any failures in this process compromise subsequent pregnancy outcomes. Here, we performed comprehensive analyses of gene expression at the luminal epithelium in the peri-implantation period.

Methods

RNA-seq combined with laser microdissection (LMD) was used to reveal unique gene expression kinetics in the epithelium.

Results

We found that the prereceptive epithelium on day 3 specifically expresses cell cycle-related genes. In addition, days 3 and 4 epithelia express glutathione pathway-related genes, which are protective against oxidative stresses. In contrast, day 5 epithelium expresses genes involved in glycolysis and the regulation of cell proliferation. The genes highly expressed on days 3 and 4 compared to day 5 are related to progesterone receptor signaling, and the genes highly expressed on day 5 compared to days 3 and 4 are associated with the ones regulated by H3K27me3.

Conclusions

These results suggest that specific gene expression patterns govern uterine functions during early pregnancy, contributing to implantation success.

Uterine kisspeptin receptor critically regulates epithelial estrogen receptor α transcriptional activity at the time of embryo implantation in a mouse model

Embryo implantation failure is a major cause of infertility in women of reproductive age and a better understanding of uterine factors that regulate implantation is required for developing effective treatments for female infertility. This study investigated the role of the uterine kisspeptin receptor (KISS1R) in the molecular regulation of implantation in a mouse model. To conduct this study, a conditional uterine knockout (KO) of Kiss1r was created using the Pgr-Cre (progesterone receptor-CRE recombinase) driver. Reproductive profiling revealed that while KO females exhibited normal ovarian function and mated successfully to stud males, they exhibited significantly fewer implantation sites, reduced litter size and increased neonatal mortality demonstrating that uterine KISS1R is required for embryo implantation and a healthy pregnancy. Strikingly, in the uterus of Kiss1r KO mice on day 4 (D4) of pregnancy, the day of embryo implantation, KO females exhibited aberrantly elevated epithelial ERα (estrogen receptor α) transcriptional activity. This led to the temporal misexpression of several epithelial genes [Cftr (Cystic fibrosis transmembrane conductance regulator), Aqp5 (aquaporin 5), Aqp8 (aquaporin 8) and Cldn7 (claudin 7)] that mediate luminal fluid secretion and luminal opening. As a result, on D4 of pregnancy, the lumen remained open disrupting the final acquisition of endometrial receptivity and likely accounting for the reduction in implantation events. Our data clearly show that uterine KISS1R negatively regulates ERα signaling at the time of implantation, in part by inhibiting ERα overexpression and preventing detrimentally high ERα activity. To date, there are no reports on the regulation of ERα by KISS1R; therefore, this study has uncovered an important and powerful regulator of uterine ERα during early pregnancy.

Illuminating the "Black Box" of Progesterone-Dependent Embryo Implantation Using Engineered Mice

Synchrony between progesterone-driven endometrial receptivity and the arrival of a euploid blastocyst is essential for embryo implantation, a prerequisite event in the establishment of a successful pregnancy. Advancement of embryo implantation within the uterus also requires stromal fibroblasts of the endometrium to transform into epithelioid decidual cells, a progesterone-dependent cellular transformation process termed decidualization. Although progesterone is indispensable for these cellular processes, the molecular underpinnings are not fully understood. Because human studies are restricted, much of our fundamental understanding of progesterone signaling in endometrial periimplantation biology comes from in vitro and in vivo experimental systems. In this review, we focus on the tremendous progress attained with the use of engineered mouse models together with high throughput genome-scale analysis in disclosing key signals, pathways and networks that are required for normal endometrial responses to progesterone during the periimplantation period. Many molecular mediators and modifiers of the progesterone response are implicated in cross talk signaling between epithelial and stromal cells of the endometrium, an intercellular communication system that is critical for the ordered spatiotemporal control of embryo invasion within the maternal compartment. Accordingly, derailment of these signaling systems is causally linked with infertility, early embryo miscarriage and gestational complications that symptomatically manifest later in pregnancy. Such aberrant progesterone molecular responses also contribute to endometrial pathologies such as endometriosis, endometrial hyperplasia and cancer. Therefore, our review makes the case that further identification and functional analysis of key molecular mediators and modifiers of the endometrial response to progesterone will not only provide much-needed molecular insight into the early endometrial cellular changes that promote pregnancy establishment but lend credible hope for the development of more effective mechanism-based molecular diagnostics and precision therapies in the clinical management of female infertility, subfertility and a subset of gynecological morbidities.

The selective progesterone receptor modulator, telapristone acetate, is a mixed antagonist/agonist in the human and mouse endometrium and inhibits pregnancy in mice

OBJECTIVE

To investigate the effect of the selective progesterone receptor modulator, telapristone acetate (CDB-4124), on endometrial biology and reproductive outcomes. Ovariectomized and hormone-treated CD1 female mice, CD1 female mice with xenotransplants of reconstructed human endometrial tissue, mated wildtype female mice, and cultured human endometrial stromal cells (hESCs) were treated with CDB-4124, followed by the assessment of endometrial cell deoxyribonucleic acid (DNA) proliferation, stromal decidual response, and embryo implantation.

DESIGN

Experimental study.

SETTING

Academic research laboratory.

PATIENTS

Healthy volunteer women from the community were recruited for endometrial biopsies.

ANIMALS

CD1 out-bred mice (Charles River Laboratories) and nude mice, NU/J (Jackson Laboratories, Bar Harbor, ME).

INTERVENTION

Treatment of mice and hESCs with CDB-4124.

MAIN OUTCOME MEASURE

The effect of CDB-4124 on endometrial cell morphology and DNA synthesis, decidual response, and mouse embryo implantation.

RESULTS

CDB-4124 inhibited estradiol-induced epithelial DNA synthesis in the mouse uterus and xenotransplanted human endometrium. This antiproliferative effect was less than that of progesterone (P4) and was observed when CDB-4124 was administered alone or concomitantly with P4. In the uterine epithelium, CDB-4124 acted as a P4 agonist and partial antagonist. In contrast, CDB-4124 acted as a complete P4 antagonist in the uterine stroma, where it blocked P4's action to induce a decidual response in the pseudopregnant mouse uterus and wildtype mouse uterus after copulation. In mated female mice, CDB-4124 impaired embryo implantation. Similarly, CDB-4124 inhibited the morphological and biochemical transformations of hESCs to decidual cells in vitro.

CONCLUSION

CDB-4124 exerts mixed P4 antagonistic/agonistic effects in the human and mouse endometrium, which result in failed embryo implantation because of the absence of stromal decidualization.

Peri- and Postpubertal Estrogen Exposures of Female Mice Optimize Uterine Responses Later in Life

At birth, all female mice, including those that either lack estrogen receptor α (ERα-knockout) or that express mutated forms of ERα (AF2ERKI), have a hypoplastic uterus. However, uterine growth and development that normally accompany pubertal maturation does not occur in ERα-knockout or AF2ERKI mice, indicating ERα-mediated estrogen (E2) signaling is essential for this process. Mice that lack Cyp19 (aromatase knockout, ArKO mice), an enzyme critical for E2 synthesis, are unable to make E2 and lack pubertal uterine development. A single injection of E2 into ovariectomized adult (10 weeks old) females normally results in uterine epithelial cell proliferation; however, we observe that although ERα is present in the ArKO uterine cells, no proliferative response is seen. We assessed the impact of exposing ArKO mice to E2 during pubertal and postpubertal windows and observed that E2-exposed ArKO mice acquired growth responsiveness. Analysis of differential gene expression between unexposed ArKO samples and samples from animals exhibiting the ability to mount an E2-induced uterine growth response (wild-type [WT] or E2-exposed ArKO) revealed activation of enhancer of zeste homolog 2 (EZH2) and heart- and neural crest derivatives-expressed protein 2 (HAND2) signaling and inhibition of GLI Family Zinc Finger 1 (GLI1) responses. EZH2 and HAND2 are known to inhibit uterine growth, and GLI1 is involved in Indian hedgehog signaling, which is a positive mediator of uterine response. Finally, we show that exposure of ArKO females to dietary phytoestrogens results in their acquisition of uterine growth competence. Altogether, our findings suggest that pubertal levels of endogenous and exogenous estrogens impact biological function of uterine cells later in life via ERα-dependent mechanisms.

90 YEARS OF PROGESTERONE: New insights into progesterone receptor signaling in the endometrium required for embryo implantation

Progesterone's ability to maintain pregnancy in eutherian mammals highlighted this steroid as the 'hormone of pregnancy'. It was the unique 'pro-gestational' bioactivity of progesterone that enabled eventual purification of this ovarian steroid to crystalline form by Willard Myron Allen in the early 1930s. While a functional connection between normal progesterone responses ('progestational proliferation') of the uterus with the maintenance of pregnancy was quickly appreciated, an understanding of progesterone's involvement in the early stages of pregnancy establishment was comparatively less well understood. With the aforementioned as historical backdrop, this review focuses on a selection of key advances in our understanding of the molecular mechanisms by which progesterone, through its nuclear receptor (the progesterone receptor), drives the development of endometrial receptivity, a transient uterine state that allows for embryo implantation and the establishment of pregnancy. Highlighted in this review are the significant contributions of advanced mouse engineering and genome-wide transcriptomic and cistromic analytics which reveal the pivotal molecular mediators and modifiers that are essential to progesterone-dependent endometrial receptivity and decidualization. With a clearer understanding of the molecular landscape that underpins uterine responsiveness to progesterone during the periimplantation period, we predict that common gynecologic morbidities due to abnormal progesterone responsiveness will be more effectively diagnosed and/or treated in the future.

Molecular Studies on Pregnancy with Mouse Models

Pregnancy is a complex process that involves crosstalk among multiple cell types in both the endometrial and myometrial compartments at the maternal side to support the fetus. Genetic engineered mouse models have served as a major platform to dissect the convolute genetic interactions in a physiological context. Combining with various applications of next generation sequencing and genome editing, functional assays by mouse models have expanded the spectrum to include both coding and noncoding genome. The present review will highlight recent findings that are primarily based on studies of mouse models with emphasis on pathways for endometrial receptivity and myometrial contraction. Emerging novel technologies that may advance the research in these two aspects will also be discussed.

SIX1 Regulates Aberrant Endometrial Epithelial Cell Differentiation and Cancer Latency Following Developmental Estrogenic Chemical Exposure

Early-life exposure to estrogenic chemicals can increase cancer risk, likely by disrupting normal patterns of cellular differentiation. Female mice exposed neonatally to the synthetic estrogen diethylstilbestrol (DES) develop metaplastic and neoplastic uterine changes as adults. Abnormal endometrial glands express the oncofetal protein sine oculis homeobox 1 (SIX1) and contain cells with basal [cytokeratin (CK)14⁺/18^-] and poorly differentiated features (CK14⁺/18⁺), strongly associating SIX1 with aberrant differentiation and cancer. Here, we tested whether SIX1 expression is necessary for abnormal endometrial differentiation and DES-induced carcinogenesis by using Pgr-cre to generate conditional knockout mice lacking uterine Six1 (Six1 ^d/d). Interestingly, corn oil (CO) vehicle-treated Six1 ^d/d mice develop focal endometrial glandular dysplasia and features of carcinoma in situ as compared with CO wild-type Six1 (Six1 ^+/+) mice. Furthermore, Six1 ^d/d mice neonatally exposed to DES had a 42% higher incidence of endometrial cancer relative to DES Six1 ^+/+ mice. Although DES Six1 ^d/d mice had >10-fold fewer CK14⁺/18^- basal cells within the uterine horns as compared with DES Six1 ^+/+ mice, the appearance of CK14⁺/18⁺ cells remained a feature of neoplastic lesions. These findings suggest that SIX1 is required for normal endometrial epithelial differentiation, CK14⁺/18⁺ cells act as a cancer progenitor population, and SIX1 delays DES-induced endometrial carcinogenesis by promoting basal differentiation of CK14⁺/18⁺ cells. In human endometrial biopsies, 35% of malignancies showed CK14⁺/18⁺ expression, which positively correlated with tumor stage and grade and was not present in normal endometrium. IMPLICATIONS: Aberrant epithelial differentiation is a key feature in both the DES mouse model of endometrial cancer and human endometrial cancer. The association of CK14⁺/18⁺ cells with human endometrial cancer provides a novel cancer biomarker and could lead to new therapeutic strategies.

Uterine Glands: Developmental Biology and Functional Roles in Pregnancy

All mammalian uteri contain glands in the endometrium that develop only or primarily after birth. Gland development or adenogenesis in the postnatal uterus is intrinsically regulated by proliferation, cell-cell interactions, growth factors and their inhibitors, as well as transcription factors, including forkhead box A2 (FOXA2) and estrogen receptor α (ESR1). Extrinsic factors regulating adenogenesis originate from other organs, including the ovary, pituitary, and mammary gland. The infertility and recurrent pregnancy loss observed in uterine gland knockout sheep and mouse models support a primary role for secretions and products of the glands in pregnancy success. Recent studies in mice revealed that uterine glandular epithelia govern postimplantation pregnancy establishment through effects on stromal cell decidualization and placental development. In humans, uterine glands and, by inference, their secretions and products are hypothesized to be critical for blastocyst survival and implantation as well as embryo and placental development during the first trimester before the onset of fetal-maternal circulation. A variety of hormones and other factors from the ovary, placenta, and stromal cells impact secretory function of the uterine glands during pregnancy. This review summarizes new information related to the developmental biology of uterine glands and discusses novel perspectives on their functional roles in pregnancy establishment and success.

Di-n-butyl phthalate induced autophagy of uroepithelial cells via inhibition of hedgehog signaling in newborn male hypospadias rats

Maternal exposure to di-n-butyl phthalate (DBP) induces hypospadias via regulation of autophagy in uroepithelial cells. Here, we use gene express analysis to explore the underlying molecular mechanisms. Pregnant rats received DBP orally at a dose of 750 mg/kg/day during gestational days 14-18. Gene expression analysis showed an increased expression of the hedgehog interacting protein (HhIP) gene. In DBP-induced hypospadiac male offspring, immunohistochemistry (IHC) staining and Western blot analysis confirmed increased expression of the HhIP protein and inhibited hedgehog signaling. in vitro experiments suggest the involvement of the reactive oxygen species (ROS)-HhIP-Gli1-autophagy axis in DBP-treated primary rat urethral epithelial cells. Taken together, our findings show that prenatal exposure to DBP induces abnormal hedgehog signaling and autophagy in uroepithelial cells that may play important roles in the development of hypospadias.

Evaluation of uterine receptivity after gonadotropin releasing hormone agonist administration as an oocyte maturation trigger: a rodent model

In natural cycle or minimal stimulation cycle IVF, buserelin acetate (buserelin), a gonadotropin-releasing hormone agonist, is often used as a maturation trigger; however, its effect on pregnancy outcomes remains unclear. Therefore, in the present study, we compared uterine receptivity in buserelin-administered mice with that in human chorionic gonadotropin (hCG)-administered mice during the peri-implantation period. Implantation, decidualisation, and term-pregnancy were impaired following hCG, but not buserelin administration. hCG stimulated the synthesis and secretion of progesterone and oestradiol, whereas ovarian steroidogenesis in the buserelin-treated group was comparable with that in the control group. Furthermore, similar to the observation in controls, the buserelin-treated group exhibited activation of progesterone receptor signalling and inhibition of oestrogen receptor signalling in the endometrial epithelium on the day of implantation. However, epithelial progesterone signalling was not detected, and a high expression of genes downstream to oestrogen was observed on day 4 following hCG administration. These results suggest that buserelin administration does not impact uterine receptivity as it did not affect ovarian steroidogenesis and endometrial steroid signalling. Therefore, buserelin is preferred as an oocyte maturation trigger to optimise uterine receptivity during treatments involving timed intercourse, intrauterine insemination, or fresh embryo transfer following in vitro fertilisation.

Oestrogen, progesterone and stem cells: the discordant trio in endometriosis?

Oestrogen–progesterone signalling is highly versatile and critical for the maintenance of healthy endometrium in humans. The genomic and nongenomic signalling cascades initiated by these hormones in differentiated cells of endometrium have been the primary focus of research since 1920s. However, last decade of research has shown a significant role of stem cells in the maintenance of a healthy endometrium and the modulatory effects of hormones on these cells. Endometriosis, the growth of endometrium outside the uterus, is very common in infertile patients and the elusiveness in understanding of disease pathology causes hindrance in selection of treatment approaches to enhance fertility. In endometriosis, the stem cells are dysfunctional as it can confer progesterone resistance to their progenies resulting in disharmony of hormonal orchestration of endometrial homeostasis. The bidirectional communication between stem cell signalling pathways and oestrogen–progesterone signalling is found to be disrupted in endometriosis though it is not clear which precedes the other. In this paper, we review the intricate connection between hormones, stem cells and the cross-talks in their signalling cascades in normal endometrium and discuss how this is deregulated in endometriosis. Re-examination of the oestrogen–progesterone dependency of endometrium with a focus on stem cells is imperative to delineate infertility associated with endometriosis and thereby aid in designing better treatment modalities.

Hormone dependent uterine epithelial-stromal communication for pregnancy support

Human fertility is a relatively inefficient process. Despite the presence of visibly healthy embryos, 30% of pregnancies generated by assisted reproductive technology (ART) fail before the second trimester. The uterine microenvironment plays a critical role in establishing and maintaining a successful pregnancy that requires coordinated communication between the epithelial and stromal cells of the endometrium. The epithelial cells must cease proliferation and become permissive for the conceptus (embryo and associated extraembryonic membranes), while the stromal cells undergoes mesenchymal-to-epithelioid transformation to form the decidua in support of subsequent embryo development. The ovarian steroids Estrogen (E2) and Progesterone (P4) are the major hormones governing these processes. These hormones act via their nuclear receptors, the estrogen receptor, ESR1, and progesterone receptor, PGR, to direct the transcription of genes that orchestrate epithelial and stromal cell communication. This review will discuss the molecular mechanisms utilized by steroid hormones that regulate uterine receptivity, as well, establish and maintain pregnancy.

Mechanisms of uterine estrogen signaling during early pregnancy in mice: an update

Adherence of an embryo to the uterus represents the most critical step of the reproductive process. Implantation is a synchronized event between the blastocyst and the uterine luminal epithelium, leading to structural and functional changes for further embryonic growth and development. The milieu comprising the complex process of implantation is mediated by estrogen through diverse but interdependent signaling pathways. Mouse models have demonstrated the relevance of the expression of estrogen-modulated paracrine factors to uterine receptivity and implantation window. More importantly, some factors seem to serve as molecular links between different estrogen pathways, promoting cell growth, acting as molecular chaperones, or amplifying estrogenic effects. Abnormal expression of these factors can lead to implantation failure and infertility. This review provides an overview of several well-characterized signaling pathways that elucidates the molecular cross talk involved in the uterus during early pregnancy.

Aberrant activation of canonical Notch1 signaling in the mouse uterus decreases progesterone receptor by hypermethylation and leads to infertility

In mammalian reproduction, implantation is one of the most critical events. Failure of implantation and the subsequent decidualization contribute to more than 75% of pregnancy losses in women. Our laboratory has previously reported that inhibition of Notch signaling results in impaired decidualization in both women and a transgenic mouse model. In this study, we generated a Notch gain-of-function transgenic mouse by conditionally overexpressing the Notch1 intracellular domain (N1ICD) in the reproductive tract driven by a progesterone receptor (Pgr) -Cre. We show that the overexpression of N1ICD in the uterus results in complete infertility as a consequence of multiple developmental and physiological defects, including the absence of uterine glands and dysregulation of progesterone and estrogen signaling by a Recombination Signal Binding Protein Jκ-dependent signaling mechanism. We further show that the inhibition of progesterone signaling is caused by hypermethylation of its receptor Pgr by Notch1 overexpression through the transcription factor PU.1 and DNA methyltransferase 3b (Dnmt3b). We have generated a mouse model to study the consequence of increased Notch signaling in female reproduction and provide the first evidence, to our knowledge, that Notch signaling can regulate epigenetic modification of the Pgr.

Progesterone-Regulated Endometrial Factors Controlling Implantation

The steroid hormone progesterone (P), acting via the progesterone receptor (PR) isoforms, PR-A and PR-B, exerts a profound influence on uterine functions during early gestation. In recent years, chromatin immunoprecipitation-sequencing in combination with microarray-based gene expression profiling analyses have revealed that the PR isoforms control a substantially large cistrome and transcriptome during endometrial differentiation in the human and the mouse. Genetically engineered mouse models have established that several PR-regulated genes, such as Ihh, Bmp2, Hoxa10, and Hand2, are essential for implantation and decidualization. PR-A and PR-B also collaborate with other transcription factors, such as FOS, JUN, C/EBPβ and STAT3, to regulate the expression of many target genes that functions in concert to properly control uterine epithelial proliferation, stromal differentiation, angiogenesis, and local immune response to render the uterus 'receptive' and allow embryo implantation. This review article highlights recent work describing the key PR-regulated pathways that govern critical uterine functions during establishment of pregnancy.

Genes targeted by the Hedgehog-signaling pathway can be regulated by Estrogen related receptor β

BACKGROUND

Nuclear receptor family member, Estrogen related receptor β, and the Hedgehog signal transduction pathway are both reported to relate to tumorigenesis and induced pluripotent stem cell reprogramming. We hypothesize that Estrogen related receptor β can modulate the Hedgehog signaling pathway and affect Hedgehog driven downstream gene expression.

RESULTS

We established an estrogen related receptor β-expressing Hedgehog-responsive NIH3T3 cell line by Esrrb transfection, and performed mRNA profiling using RNA-Seq after Hedgehog ligand conditioned medium treatment. Esrrb expression altered 171 genes, while Hedgehog signaling activation alone altered 339 genes. Additionally, estrogen related receptor β expression in combination with Hedgehog signaling activation affects a group of 109 Hedgehog responsive mRNAs, including Hsd11b1, Ogn, Smoc2, Igf1, Pdcd4, Igfbp4, Stmn1, Hp, Hoxd8, Top2a, Tubb4b, Sfrp2, Saa3, Prl2c3 and Dpt.

CONCLUSIONS

We conclude that Estrogen related receptor β is capable of interacting with Hh-signaling downstream targets. Our results suggest a new level of regulation of Hedgehog signaling by Estrogen related receptor β, and indicate modulation of Estrogen related receptor β can be a new strategy to regulate various functions driven by the Hedgehog signaling pathway.

The absence of the embryo in the pseudopregnant uterus alters the deposition of some ECM molecules during decidualization in mice

The embryo-implantation promotes deep changes in the uterus resulting in the formation of a new structure at the maternal-fetal interface, the decidua. Decidualization can also be induced in pseudopregnant rodents resulting in a structure called deciduoma that is morphologically and functionally similar to the decidua. Previous studies from our and other laboratories demonstrate that in rodents, decidualization of the endometrium requires remarkable remodeling of the endometrial extracellular matrix (ECM) that is mainly coordinated by estradiol and progesterone. The influence of the embryo in this process, however, has not yet been investigated. To enlarge the knowledge on this subject, the present study investigates the behavior of a set of ECM molecules, in the absence of paracrine cues originated from the embryo. For that deciduoma was induced in pseudopregnant Swiss mice, and the distribution of collagen types I, III, IV, V and the proteoglycans decorin and biglycan was investigated by immunolabeling from the fifth to the eighth day of pseudopregnancy. It was observed the deposition of collagen types III and IV as well as decorin and biglycan was similar to that previously described by our group in the decidua. However, in the absence of the embryo, some differences occur in the distribution of collagen types I and V, suggesting that beside the major role of ovarian hormones on the endometrial ECM remodeling, molecular signals originated from the conceptus may influence this process.

Mig-6 regulates endometrial genes involved in cell cycle and progesterone signaling

Mitogen inducible gene 6 (Mig-6) is an important mediator of progesterone (P4) signaling to inhibit estrogen (E2) signaling in the uterus. Ablation of Mig-6 in the murine uterus leads to the development of endometrial hyperplasia and E2-induced endometrial cancer. To identify the molecular pathways regulated by Mig-6, we performed microarray analysis on the uterus of ovariectomized Mig-6(f/f) and PGR(cre/+)Mig-6(f/f) (Mig-6(d/d)) mice treated with vehicle or P4 for 6 h. The results revealed that 772 transcripts were significantly regulated in the Mig-6(d/d) uterus treated with vehicle as compared with Mig-6(f/f) mice. The pathway analysis showed that Mig-6 suppressed the expression of gene-related cell cycle regulation in the absence of ovarian steroid hormone. The epithelium of Mig-6(d/d) mice showed a significant increase in the number of proliferative cells compared to Mig-6(f/f) mice. This microarray analysis also revealed that 324 genes are regulated by P4 as well as Mig-6. Cited2, the developmentally important transcription factor, was identified as being regulated by the P4-Mig-6 axis. To determine the role of Cited2 in the uterus, we used the mice with Cited2 that were conditionally ablated in progesterone receptor-positive cells (PGR(cre/+)Cited2(f/f); Cited2(d/d)). Ablation of Cited2 in the uterus resulted in a significant reduction in the ability of the uterus to undergo a hormonally induced decidual reaction. Identification and analysis of these responsive genes will help define the role of P4 as well as Mig-6 in regulating uterine biology.

Role of uterine stromal-epithelial crosstalk in embryo implantation

Embryo implantation is a crucial step for successful pregnancy. Prior to implantation, the luminal epithelium undergoes steroid hormone-induced structural and functional changes that render it competent for embryo attachment. Subsequent invasion of the embryo into the maternal tissue triggers differentiation of the underlying stromal cells to form the decidua, a transient tissue which supports the developing embryo. Many molecular cues of both stromal and epithelial origin have been identified that are critical mediators of this process. An important aspect of uterine biology is the elaborate crosstalk that occurs between these tissue compartments during early pregnancy through expression of paracrine factors regulated by the steroid hormones estrogen and progesterone. Aberrant expression of these factors often leads to implantation failure and infertility. Genetically-engineered mouse models have been instrumental in elucidating what these paracrine factors are, what drives their expression, and what their effects are on neighboring cells. This review provides an overview of several well-characterized signaling pathways that span both epithelial and stromal compartments and their function during implantation in the mouse.

Crybb2 deficiency impairs fertility in female mice

Beta-B2-crystallin (CRYBB2), encoded by Crybb2 gene, is a major protein in the mammalian eye lens that plays an important role in maintaining the transparency of the ocular lens. However, CRYBB2 also plays important roles in many extra-lenticular tissues and organs such as the retina, brain and testis. Our previous studies demonstrated that male Crybb2 deficient (Crybb2(-/-)) mice have reduced fertility compared with wild-type (WT) mice, while female Crybb2(-/-) mice exhibited reduced ovary weights and shorter estrous cycle percentages. Here we specifically investigated the role of CRYBB2 in the female reproductive system. Our studies revealed that ovaries from female Crybb2(-/-) mice exhibited significantly reduced numbers of primordial, secondary and pre-ovulatory follicles when compared with WT mice, while the rate of atretic follicles was also increased. Additionally, fewer eggs were collected from the oviduct of Crybb2(-/-) female mice after superovulation. Estrogen levels were higher in the metestrus and diestrus cycles of female Crybb2(-/-) mice, while progesterone levels were lower in diestrus cycles. Furthermore, the expression of survival and cell cycle genes, Bcl-2, Cdk4 and Ccnd2, were significantly decreased in granulosa cells isolated from female Crybb2(-/-) mice, consistent with the predominant expression of CRYBB2 in ovarian granulosa cells. Our results reveal a critical role for CRYBB2 in female fertility and specific effects on the proliferation and survival status of ovarian granulosa cells.

Ovarian stimulation using human chorionic gonadotrophin impairs blastocyst implantation and decidualization by altering ovarian hormone levels and downstream signaling in mice

Ovarian stimulation induced by follicle-stimulating hormone and human chorionic gonadotrophin (hCG) is commonly used in assisted reproductive technology to increase embryo production. However, recent clinical and animal studies have shown that ovarian stimulation disrupts endometrial function and embryo development and adversely affects pregnancy outcomes. How ovarian stimulation impairs pregnancy establishment and the precise mechanisms by which this stimulation reduces the chances of conception remain unclear. In this study, we first demonstrated that ovarian stimulation using hCG alone impairs implantation, decidualization and fetal development of mice by generating abnormal ovarian hormone levels. We also showed that ovarian hormone levels were altered because of changes in the levels of the enzymes involved in their synthesis in the follicles and corpora lutea. Furthermore, we determined that anomalous ovarian hormone secretion induced by ovarian stimulation alters the spatiotemporal expression of progesterone receptors and their downstream genes, especially in the uterine epithelium. Epithelial estrogenic signaling and cell proliferation were promoted on the day of implantation in stimulated mice and these changes led to the failure of uterine transition from the prereceptive to the receptive state. Collectively, our findings indicate that ovarian stimulation using hCG induces an imbalance in steroid hormone secretion, which causes a failure of the development of uterine receptivity and subsequent implantation and decidualization by altering the expression of steroid receptors and their downstream signaling associated with embryo implantation.

Minireview: Steroid-regulated paracrine mechanisms controlling implantation

Implantation is an essential process during establishment of pregnancy in mammals. It is initiated with the attachment of the blastocyst to a receptive uterine epithelium followed by its invasion into the stromal tissue. These events are profoundly regulated by the steroid hormones 17β-estradiol and progesterone. During the past several years, mouse models harboring conditional gene knockout mutations have become powerful tools for determining the functional roles of cellular factors involved in various aspects of implantation biology. Studies using these genetic models as well as primary cultures of human endometrial cells have established that the estrogen receptor α, the progesterone receptor, and their downstream target genes critically regulate uterine growth and differentiation, which in turn control embryo-endometrial interactions during early pregnancy. These studies have uncovered a diverse array of molecular cues, which are produced under the influence of estrogen receptor α and progesterone receptor and exchanged between the epithelial and stromal compartments of the uterus during the progressive phases of implantation. These paracrine signals are critical for acquisition of uterine receptivity and functional interactions with the embryo. This review highlights recent work describing paracrine mechanisms that govern steroid-regulated uterine epithelial-stromal dialogue during implantation and their roles in fertility and disease.

The LIF-mediated molecular signature regulating murine embryo implantation

The establishment of a receptive uterus is the prime requirement for embryo implantation. In mice, the E2-induced cytokine leukemia inhibitory factor (LIF) is essential in switching the uterine luminal epithelium (LE) from a nonreceptive to a receptive state. Here we define the LIF-mediated switch using array analysis and informatics to identify LIF-induced changes in gene expression and annotated signaling pathways specific to the LE. We compare gene expression profiles at 0, 1, 3, and 6 h, following LIF treatment. During the first hour, the JAK-STAT signaling pathway is activated and the expression of 54 genes declines, primarily affecting LE cytoskeletal and chromatin organization as well as a transient reduction in the progesterone, TGFbetaR1, and ACVR1 receptors. Simultaneously 256 genes increase expression, of which 42 are transcription factors, including Sox, Kfl, Hes, Hey, and Hox families. Within 3 h, the expression of 3987 genes belonging to more than 25 biological process pathways was altered. We confirmed the mRNA and protein distribution of key genes from 10 pathways, including the Igf-1, Vegf, Toll-like receptors, actin cytoskeleton, ephrin, integrins, TGFbeta, Wnt, and Notch pathways. These data identify novel LIF-activated pathways in the LE and define the molecular basis between the refractory and receptive uterine phases. More broadly, these findings highlight the staggering capacity of a single cytokine to induce a dynamic and complex network of changes in a simple epithelium essential to mammalian reproduction and provide a basis for identifying new routes to regulating female reproduction.

The epidermal growth factor receptor critically regulates endometrial function during early pregnancy

Infertility and adverse gynecological outcomes such as preeclampsia and miscarriage represent significant female reproductive health concerns. The spatiotemporal expression of growth factors indicates that they play an important role in pregnancy. The goal of this study is to define the role of the ERBB family of growth factor receptors in endometrial function. Using conditional ablation in mice and siRNA in primary human endometrial stromal cells, we identified the epidermal growth factor receptor (Egfr) to be critical for endometrial function during early pregnancy. While ablation of Her2 or Erbb3 led to only a modest reduction in litter size, mice lacking Egfr expression are severely subfertile. Pregnancy demise occurred shortly after blastocyst implantation due to defects in decidualization including decreased proliferation, cell survival, differentiation and target gene expression. To place Egfr in a genetic regulatory hierarchy, transcriptome analyses was used to compare the gene signatures from mice with conditional ablation of Egfr, wingless-related MMTV integration site 4 (Wnt4) or boneless morphogenic protein 2 (Bmp2); revealing that not only are Bmp2 and Wnt4 key downstream effectors of Egfr, but they also regulate distinct physiological functions. In primary human endometrial stromal cells, marker gene expression, a novel high content image-based approach and phosphokinase array analysis were used to demonstrate that EGFR is a critical regulator of human decidualization. Furthermore, inhibition of EGFR signaling intermediaries WNK1 and AKT1S1, members identified in the kinase array and previously unreported to play a role in the endometrium, also attenuate decidualization. These results demonstrate that EGFR plays an integral role in establishing the cellular context necessary for successful pregnancy via the activation of intricate signaling and transcriptional networks, thereby providing valuable insight into potential therapeutic targets.

Approximately 10% of reproductive aged women are considered infertile. While great strides have been made in assisted reproductive technologies, overall success rates, especially considering the cost, remain low. Studies indicate that due to its sequential nature, nearly 75% of pregnancy failures are due to defects that occur very early in gestation. Therefore, understanding the physiological changes that occur in the endometrium during this period and how those changes are regulated is of paramount importance if we are to improve our ability to address female reproductive health concerns. We investigated a family of growth factor receptors and identified one that critically regulates the growth and survival of the endometrium in response to the implanting embryo. Furthermore, we used unbiased approaches to identify which signaling pathways and genetic networks are activated downstream of this receptor to execute each of the processes necessary for a successful pregnancy. Understanding the mechanisms and genetic networks with which pregnancy is regulated is a prerequisite to the development of effective pharmaceutical therapeutics.

Novel DNA motif binding activity observed in vivo with an estrogen receptor α mutant mouse

Estrogen receptor α (ERα) interacts with DNA directly or indirectly via other transcription factors, referred to as "tethering." Evidence for tethering is based on in vitro studies and a widely used "KIKO" mouse model containing mutations that prevent direct estrogen response element DNA- binding. KIKO mice are infertile, due in part to the inability of estradiol (E2) to induce uterine epithelial proliferation. To elucidate the molecular events that prevent KIKO uterine growth, regulation of the pro-proliferative E2 target gene Klf4 and of Klf15, a progesterone (P4) target gene that opposes the pro-proliferative activity of KLF4, was evaluated. Klf4 induction was impaired in KIKO uteri; however, Klf15 was induced by E2 rather than by P4. Whole uterine chromatin immunoprecipitation-sequencing revealed enrichment of KIKO ERα binding to hormone response elements (HREs) motifs. KIKO binding to HRE motifs was verified using reporter gene and DNA-binding assays. Because the KIKO ERα has HRE DNA-binding activity, we evaluated the "EAAE" ERα, which has more severe DNA-binding domain mutations, and demonstrated a lack of estrogen response element or HRE reporter gene induction or DNA-binding. The EAAE mouse has an ERα null-like phenotype, with impaired uterine growth and transcriptional activity. Our findings demonstrate that the KIKO mouse model, which has been used by numerous investigators, cannot be used to establish biological functions for ERα tethering, because KIKO ERα effectively stimulates transcription using HRE motifs. The EAAE-ERα DNA-binding domain mutant mouse demonstrates that ERα DNA-binding is crucial for biological and transcriptional processes in reproductive tissues and that ERα tethering may not contribute to estrogen responsiveness in vivo.

Cell-specific transcriptional profiling reveals candidate mechanisms regulating development and function of uterine epithelia in mice

All mammalian uteri have luminal (LE) and glandular epithelia (GE) in their endometrium. The LE mediates uterine receptivity and blastocyst attachment for implantation, and the GE synthesize and secrete or transport bioactive substances involved in blastocyst implantation, uterine receptivity, and stromal cell decidualization. However, the mechanisms governing uterine epithelial development after birth and their function in the adult are not fully understood. Here, comprehensive microarray analysis was conducted on LE and GE isolated by laser capture microdissection from uteri on Postnatal Day 10 (PD 10) and day of pseudopregnancy (DOPP) 2.5 and 3.5. This data was integrated with analysis of uteri from gland-containing control and aglandular progesterone-induced uterine gland knockout mice from PD 10 and DOPP 3.5. Many genes were expressed in both epithelia, but there was greater expression of genes in the LE than in the GE. In the neonate, GE-expressed genes were enriched for morphogenesis, development, migration, and retinoic acid signaling. In the adult, LE-expressed genes were enriched for metabolic processes and steroid biosynthesis, whereas retinoid signaling, tight junction, extracellular matrix, and regulation of kinase activity were enriched in the GE. The transcriptome differences in the epithelia support the idea that each cell type has a distinct and complementary function in the uterus. The candidate genes and regulatory networks identified here provide a framework to discover new mechanisms regulating development of epithelia in the postnatal uterus and their functions in early pregnancy.

STAT3 regulates uterine epithelial remodeling and epithelial-stromal crosstalk during implantation

Embryo implantation is regulated by a variety of endometrial factors, including cytokines, growth factors, and transcription factors. Earlier studies identified the leukemia inhibitory factor (LIF), a cytokine produced by uterine glands, as an essential regulator of implantation. LIF, acting via its cell surface receptor, activates the signal transducer and activator of transcription 3 (STAT3) in the uterine epithelial cells. However, the precise mechanism via which activated STAT3 promotes uterine function during implantation remains unknown. To identify the molecular pathways regulated by STAT3, we created SW(d/d) mice in which Stat3 gene is conditionally inactivated in uterine epithelium. The SW(d/d) mice are infertile due to a lack of embryo attachment to the uterine luminal epithelium and consequent implantation failure. Gene expression profiling of uterine epithelial cells of SW(d/d) mice revealed dysregulated expression of specific components of junctional complexes, including E-cadherin, α- and β-catenin, and several claudins, which critically regulate epithelial junctional integrity and embryo attachment. In addition, uteri of SW(d/d) mice exhibited markedly reduced stromal proliferation and differentiation, indicating that epithelial STAT3 controls stromal function via a paracrine mechanism. The stromal defect arose from a drastic reduction in the production of several members of the epidermal growth factor family in luminal epithelium of SW(d/d) uteri and the resulting lack of activation of epidermal growth factor receptor signaling and mitotic activity in the stromal cells. Collectively, our results uncovered an intricate molecular network operating downstream of STAT3 that regulates uterine epithelial junctional reorganization, and stromal proliferation, and differentiation, which are critical determinants of successful implantation.

Gene expression analysis of early stage endometrial cancers reveals unique transcripts associated with grade and histology but not depth of invasion

Endometrial cancer is the most common gynecologic malignancy in the United States but it remains poorly understood at the molecular level. This investigation was conducted to specifically assess whether gene expression changes underlie the clinical and pathologic factors traditionally used for determining treatment regimens in women with stage I endometrial cancer. These include the effect of tumor grade, depth of myometrial invasion and histotype. We utilized oligonucleotide microarrays to assess the transcript expression profile in epithelial glandular cells laser microdissected from 79 endometrioid and 12 serous stage I endometrial cancers with a heterogeneous distribution of grade and depth of myometrial invasion, along with 12 normal post-menopausal endometrial samples. Unsupervised multidimensional scaling analyses revealed that serous and endometrioid stage I cancers have similar transcript expression patterns when compared to normal controls where 900 transcripts were identified to be differentially expressed by at least fourfold (univariate t-test, p < 0.001) between the cancers and normal endometrium. This analysis also identified transcript expression differences between serous and endometrioid cancers and tumor grade, but no apparent differences were identified as a function of depth of myometrial invasion. Four genes were validated by quantitative PCR on an independent set of cancer and normal endometrium samples. These findings indicate that unique gene expression profiles are associated with histologic type and grade, but not myometrial invasion among early stage endometrial cancers. These data provide a comprehensive perspective on the molecular alterations associated with stage I endometrial cancer, particularly those subtypes that have the worst prognosis.

Physiological and molecular determinants of embryo implantation

Embryo implantation involves the intimate interaction between an implantation-competent blastocyst and a receptive uterus, which occurs in a limited time period known as the window of implantation. Emerging evidence shows that defects originating during embryo implantation induce ripple effects with adverse consequences on later gestation events, highlighting the significance of this event for pregnancy success. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk during implantation have been identified through gene expression studies and genetically engineered mouse models, a comprehensive understanding of the nature of embryo implantation is still missing. This review focuses on recent progress with particular attention to physiological and molecular determinants of blastocyst activation, uterine receptivity, blastocyst attachment and uterine decidualization. A better understanding of underlying mechanisms governing embryo implantation should generate new strategies to rectify implantation failure and improve pregnancy rates in women.

The regulation of embryo implantation and endometrial decidualization by progesterone receptor signaling

During the early stages of pregnancy, fertilized embryos must attach to the uterine epithelium, invade into the underlying uterine stroma, and the stroma must then differentiate in a process termed decidualization in order for a successful pregnancy to be initiated. The steroid hormone progesterone (P4) is an integral mediator of these early pregnancy events, exerting its effects via the progesterone receptor (PR). Insights gained from the use of mouse models and genomic profiling has identified many of the key molecules enlisted by PR to execute the paradigm of early pregnancy. This review describes several of the molecules through which the PR exerts its pleiotropic effects including ligands, receptors, chaperones, signaling proteins and transcription factors. Understanding these molecules and their concatenation is of vital importance to our ability to clinically treat reproductive health problems like infertility and endometriosis.

Dysregulation of uterine signaling pathways in progesterone receptor-Cre knockout of dicer

Epithelial-stromal interactions in the uterus are required for normal uterine functions such as pregnancy, and multiple signaling pathways are essential for this process. Although Dicer and microRNA (miRNA) have been implicated in several reproductive processes, the specific roles of Dicer and miRNA in uterine development are not known. To address the roles of miRNA in the regulation of key uterine pathways, we generated a conditional knockout of Dicer in the postnatal uterine epithelium and stroma using progesterone receptor-Cre. These Dicer conditional knockout females are sterile with small uteri, which demonstrate significant defects, including absence of glandular epithelium and enhanced stromal apoptosis, beginning at approximately postnatal d 15, with coincident expression of Cre and deletion of Dicer. Specific miRNA (miR-181c, -200b, -101, let-7d) were down-regulated and corresponding predicted proapoptotic target genes (Bcl2l11, Aldh1a3) were up-regulated, reflecting the apoptotic phenomenon. Although these mice had normal serum hormone levels, critical uterine signaling pathways, including progesterone-responsive genes, Indian hedgehog signaling, and the Wnt/β-catenin canonical pathway, were dysregulated at the mRNA level. Importantly, uterine stromal cell proliferation in response to progesterone was absent, whereas uterine epithelial cell proliferation in response to estradiol was maintained in adult uteri. These data implicate Dicer and appropriate miRNA expression as essential players in the regulation of multiple uterine signaling pathways required for uterine development and appropriate function.

The progesterone receptor regulates implantation, decidualization, and glandular development via a complex paracrine signaling network

Many women are affected by infertility and reproductive-associated disease such as endometriosis or endometrial cancer. Successful pregnancy is dependent on a healthy uterus that is fit to receive and support a fertilized embryo. The uterus is an endocrine organ, responsive to the presence of the ovarian steroid hormones, estrogen and progesterone, which activate transcription of target genes through the binding of their cognate receptors, the estrogen receptor and the progesterone receptor. Progesterone signaling has been demonstrated to be critical for the initiation and continuance of pregnancy. Through the induction of Ihh, Wnt, and Bmp pathways within the epithelial and stromal compartments of the uterus, embryo attachment and implantation occur followed by decidualization of the surrounding stroma. Furthermore, these pathways have been shown to be involved in uterine glandular development. This review highlights the integral role of uterine progesterone-mediated paracrine signaling in gland development and pregnancy.

Overactivation of hedgehog signaling alters development of the ovarian vasculature in mice

The hedgehog (HH) signaling pathway is critical for ovarian function in Drosophila, but its role in the mammalian ovary has not been defined. Previously, expression of a dominant active allele of the HH signal transducer protein smoothened (SMO) in Amhr2(cre/+)SmoM2 mice caused anovulation in association with a lack of smooth muscle in the theca of developing follicles. The current study examined events during the first 2 wk of life in Amhr2(cre/+)SmoM2 mice to gain insight into the cause of anovulation. Expression of transcriptional targets of HH signaling, Gli1, Ptch1, and Hhip, which are used as measures of pathway activity, were elevated during the first several days of life in Amhr2(cre/+)SmoM2 mice compared to controls but were similar to controls in older mice. Microarray analysis showed that genes with increased expression in 2-day-old mutants compared to controls were enriched for the processes of vascular and tube development and steroidogenesis. The density of platelet endothelial cell adhesion molecule (PECAM)-labeled endothelial tubes was increased in the cortex of newborn ovaries of mutant mice. Costaining of preovulatory follicles for PECAM and smooth muscle actin showed that muscle-type vascular support cells are deficient in theca of mutant mice. Expression of genes for steroidogenic enzymes that are normally expressed in the fetal adrenal gland were elevated in newborn ovaries of mutant mice. In summary, overactivation of HH signaling during early life alters gene expression and vascular development and this is associated with the lifelong development of anovulatory follicles in which the thecal vasculature fails to mature appropriately.

Sex and hedgehog: roles of genes in the hedgehog signaling pathway in mammalian sexual differentiation

The chromosome status of the mammalian embryo initiates a multistage process of sexual development in which the bipotential reproductive system establishes itself as either male or female. These events are governed by intricate cell-cell and interorgan communication that is regulated by multiple signaling pathways. The hedgehog signaling pathway was originally identified for its key role in the development of Drosophila, but is now recognized as a critical developmental regulator in many species, including humans. In addition to its developmental roles, the hedgehog signaling pathway also modulates adult organ function, and misregulation of this pathway often leads to diseases, such as cancer. The hedgehog signaling pathway acts through its morphogenetic ligands that signal from ligand-producing cells to target cells over a specified distance. The target cells then respond in a graded manner based on the concentration of the ligands that they are exposed to. Through this unique mechanism of action, the hedgehog signaling pathway elicits cell fate determination, epithelial-mesenchymal interactions, and cellular homeostasis. Here, we review current findings on the roles of hedgehog signaling in the sexually dimorphic development of the reproductive organs with an emphasis on mammals and comparative evidence in other species.