Misregulated Wnt/beta-catenin signaling leads to ovarian granulosa cell tumor development

Transgenic mouse models in the study of reproduction: insights into GATA protein function

For the past 2 decades, transgenic technology in mice has allowed for an unprecedented insight into the transcriptional control of reproductive development and function. The key factor among the mouse genetic tools that made this rapid advance possible is a conditional transgenic approach, a particularly versatile method of creating gene deletions and substitutions in the mouse genome. A centerpiece of this strategy is an enzyme, Cre recombinase, which is expressed from defined DNA regulatory elements that are active in the tissue of choice. The regulatory DNA element (either genetically engineered or natural) assures Cre expression only in predetermined cell types, leading to the guided deletion of genetically modified (flanked by loxP or ‘floxed’ byloxP) gene loci. This review summarizes and compares the studies in which genes encoding GATA family transcription factors were targeted either globally or by Cre recombinases active in the somatic cells of ovaries and testes. The conditional gene loss experiments require detailed knowledge of the spatial and temporal expression of Cre activity, and the challenges in interpreting the outcomes are highlighted. These studies also expose the complexity of GATA-dependent regulation of gonadal gene expression and suggest that gene function is highly context dependent.

YAP regulates cell proliferation, migration, and steroidogenesis in adult granulosa cell tumors

The Hippo signaling pathway has been implicated as a conserved regulator of organ size in both Drosophila and mammals. Yes-associated protein (YAP), the central component of the Hippo signaling cascade, functions as an oncogene in several malignancies. Ovarian granulosa cell tumors (GCT) are characterized by enlargement of the ovary, excess production of estrogen, a high frequency of recurrence, and the potential for malignancy and metastasis. Whether the Hippo pathway plays a role in the pathogenesis of GCT is unknown. This study was conducted to examine the expression of YAP in human adult GCTs and to determine the role of YAP in the proliferation and steroidogenesis of GCT cells. Compared with age-matched normal human ovaries, GCT tissues exhibited higher levels of YAP expression. YAP protein was predominantly expressed in the nucleus of tumor cells, whereas the non-tumor ovarian stromal cells expressed very low levels of YAP. YAP was also expressed in cultured primary human granulosa cells and in KGN and COV434 GCT cell lines. siRNA-mediated knockdown of YAP in KGN cells resulted in a significant reduction in cell proliferation (P<0.001). Conversely, overexpression of wild type YAP or a constitutively active YAP (YAP1) mutant resulted in a significant increase in KGN cell proliferation and migration. Moreover, YAP knockdown reduced FSH-induced aromatase (CYP19A1) protein expression and estrogen production in KGN cells. These results demonstrate that YAP plays an important role in the regulation of GCT cell proliferation, migration, and steroidogenesis. Targeting the Hippo/YAP pathway may provide a novel therapeutic approach for GCT.

Genetically engineered mouse models for epithelial ovarian cancer: are we there yet?

The development of preclinical spontaneous genetically engineered mouse models (GEMMs) requires an understanding of the genetic basis of the human disease. Such robust models have proven invaluable for increasing understanding of human malignancies as well as identifying new biomarkers and testing new therapies for these diseases. While GEMMs have been reported for ovarian cancer, the majority have proven disappointing overall in their recapitulation of paired genetic and histological features especially for serous ovarian epithelial cancer. This review describes GEMMs for ovarian cancer, in particular, high grade serous ovarian cancer and assesses these in light of recent changes in our understanding of the human malignancy.

Wnt/β-catenin signaling regulates follicular development by modulating the expression of Foxo3a signaling components

Wnt signaling is an evolutionarily conserved pathway that regulates cell proliferation, differentiation and apoptosis. To investigate the possible role of Wnt signaling in the regulation of ovarian follicular development, secondary follicles were isolated and cultured in vitro in the presence or absence of its activator (LiCl or Wnt3a) or inhibitor (IWR-1). We have demonstrated that activation of β-catenin signals by activators dramatically suppressed follicular development by increasing granulosa cell apoptosis and inhibiting follicle steroidogenesis. In contrast, inhibition of Wnt signaling by IWR-1 was observed with better developed follicles and increased steroidogenesis. Further studies have shown that the transcription factor Forkhead box O3a (Foxo3a) and its downstream target molecules were modulated by the activators or the inhibitor. These findings provide evidence that Wnt signaling might negatively regulate follicular development potentially through Foxo3a signaling components.

FOXL2: a central transcription factor of the ovary

Forkhead box L2 (FOXL2) is a gene encoding a forkhead transcription factor preferentially expressed in the ovary, the eyelids and the pituitary gland. Its germline mutations are responsible for the blepharophimosis ptosis epicanthus inversus syndrome, which includes eyelid and mild craniofacial defects associated with primary ovarian insufficiency. Recent studies have shown the involvement of FOXL2 in virtually all stages of ovarian development and function, as well as in granulosa cell (GC)-related pathologies. A central role of FOXL2 is the lifetime maintenance of GC identity through the repression of testis-specific genes. Recently, a highly recurrent somatic FOXL2 mutation leading to the p.C134W subtitution has been linked to the development of GC tumours in the adult, which account for up to 5% of ovarian malignancies. In this review, we summarise data on FOXL2 modulators, targets, partners and post-translational modifications. Despite the progresses made thus far, a better understanding of the impact of FOXL2 mutations and of the molecular aspects of its function is required to rationalise its implication in various pathophysiological processes.

Canonical WNT signaling inhibits follicle stimulating hormone mediated steroidogenesis in primary cultures of rat granulosa cells

Beta-catenin (CTNNB1), a key component of wingless-type mouse mammary tumor virus integration site family (WNT) signaling, participates in follicle stimulated hormone-mediated regulation of estrogen (E2) production. The purpose of these studies was to determine if CTNNB1's contribution to FSH-mediated steroidogenesis in primary rat granulosa cells was due in part to extracellular stimulation of the canonical WNT signaling pathway. To achieve this purpose, primary cultures of rat granulosa cells were exposed to vehicle or a canonical member of the WNT signaling pathway, WNT3A, before co-culture and in the presence or absence of FSH for 24 h. Activation of the canonical WNT signaling pathway was determined by dose-dependent induction of Axin2 mRNA expression and stimulation of the CTNNB1/T cell factor promoter-reporter TOPflash. WNT pathway induction was demonstrated at doses of 50 and 500 ng/mL of WNT3A. Granulosa cells treated with WNT3A in combination with FSH had enhanced CTNNB1/T cell factor transcriptional activity above cells treated with WNT3A alone. Steroidogenic enzymes and ovarian differentiation factor mRNAs were quantified via quantitative PCR. Expression of steroidogenic enzyme mRNAs aromatase (Cyp19a1), P450 side chain cleavage (Cyp11a1), and steroidogenic acute regulatory protein (Star) were increased following FSH treatment. Co-incubation of WNT3A and FSH reduced the ability of FSH to stimulate steroidogenic enzymes and subsequent E2 and progesterone (P4) production. Concomitant activation of FSH and WNT pathways results in marked reduction of ovarian differentiation factors, LH receptor (Lhcgr) and inhibin-alpha (Inha). Therefore, WNT inhibits FSH target genes and steroid production associated with maturation and differentiation of the ovarian follicle.

Translocator protein/peripheral benzodiazepine receptor is not required for steroid hormone biosynthesis

Molecular events that regulate cellular biosynthesis of steroid hormones have been a topic of intense research for more than half a century. It has been established that transport of cholesterol into the mitochondria forms the rate-limiting step in steroid hormone production. In current models, both the steroidogenic acute regulatory protein (StAR) and the translocator protein (TSPO) have been implicated to have a concerted and indispensable effort in this cholesterol transport. Deletion of StAR in mice resulted in a critical failure of steroid hormone production, but deletion of TSPO in mice was found to be embryonic lethal. As a result, the role of TSPO in cholesterol transport has been established only using pharmacologic and genetic tools in vitro. To allow us to explore in more detail the function of TSPO in cell type-specific experimental manipulations in vivo, we generated mice carrying TSPO floxed alleles (TSPOfl/fl). In this study we made conditional knockout mice (TSPOcΔ/Δ) with TSPO deletion in testicular Leydig cells by crossing with an anti-Mullerian hormone receptor type II cre/+ mouse line. Genetic ablation of TSPO in steroidogenic Leydig cells in mice did not affect testosterone production, gametogenesis, and reproduction. Expression of StAR, cytochrome P450 side chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase type I, and TSPO2 in TSPOcΔ/Δ testis was unaffected. These results challenge the prevailing dogma that claims an essential role for TSPO in steroid hormone biosynthesis and force reexamination of functional interpretations made for this protein. This is the first study examining conditional TSPO gene deletion in mice. The results show that TSPO function is not essential for steroid hormone biosynthesis.

Transgenic mice expressing inhibin α-subunit promoter (inhα)/Simian Virus 40 T-antigen (Tag) transgene as a model for the therapy of granulosa cell-derived ovarian cancer

Granulosa cell tumors are rare, 3-7.6% of primary ovarian tumors, although with poor prognosis as the tumor-related mortality rate is 37.3%, with 80% of deaths occurring on recurrence. We have created a transgenic (TG) murine model for gonadal somatic cell tumors by expressing the powerful viral oncogene, Simian Virus 40 T-antigen (Tag), under the regulation of murine inhibin α-subunit 6 kb promoter (inhα/Tag). Gonadotropin dependent ovarian granulosa cell tumors were formed in females by the age of 5-6 months, with a 100% penetrance. We have successfully used the inhα/Tag model to test different treatment strategies for ovarian tumors. With a gene therapy trial in inhα/Tag mice crossbred with inhα/HSV-TK (herpes simplex virus thymidine kinase) mice (double TG), we proved the principle that targeted expression of HSV-TK gene in gonadal somatic cell tumors enabled tumor ablation by anti-herpes treatment. When we aimed at targeted destruction of luteinizing hormone/chorionic gonadotropin receptor (LHCGR) expressing inhα/Tag tumor cells in vivo by a lytic peptide Hecate-CGβ conjugate, we could successfully kill the tumor cells, sparing the normal cells. We recently found high zona pellucida glycoprotein 3 (ZP3) expression in inhα/Tag granulosa cell tumors, as well as in human granulosa cell tumors. We tested the concept of treating the ovarian tumors of inhα/Tag mice by vaccination against the ectopically expressed ZP3. Immunotherapy with recombinant human (rh) ZP3 was highly successful with no objective side effects in inhα/Tag females, suggesting rhZP3 immunization as a novel strategy for the immunotherapy of ovarian granulosa cell tumors.

Secreted frizzled related proteins: Implications in cancers

The Wnt (wingless-type) signaling pathway plays an important role in embryonic development, tissue homeostasis, and tumor progression becaluse of its effect on cell proliferation, migration, and differentiation. Secreted frizzled-related proteins (SFRPs) are extracellular inhibitors of Wnt signaling that act by binding directly to Wnt ligands or to Frizzled receptors. In recent years, aberrant expression of SFRPs has been reported to be associated with numerous cancers. As gene expression of SFRP members is often lost through promoter hypermethylation, inhibition of methylation through the use of epigenetic modifying agents could renew the expression of SFRP members and further antagonize deleterious Wnt signaling. Several reports have described epigenetic silencing of these Wnt signaling antagonists in various human cancers, suggesting their possible role as tumor suppressors. SFRP family members thus come across as potential tools in combating Wnt-driven tumorigenesis. However, little is known about SFRP family members and their role in different cancers. This review comprehensively covers all the available information on the role of SFRP molecules in various human cancers.

Treatment with anticancer agents induces dysregulation of specific Wnt signaling pathways in human ovarian luteinized granulosa cells in vitro

Chemotherapy has been associated with premature ovarian failure and infertility in women with cancer. It is well known that anticancer drugs reduce the primordial follicle pool and harm the ovarian blood vascularization leading to ovarian atrophy. However, their mechanism of injury still remains unclear. The aim of this study was to identify the cellular mechanisms involved in the toxicity of chemotherapy drugs belonging to different classes on human ovarian luteinized granulosa cells (LGCs). Treatment with doxorubicin (DXR), paclitaxel (PC), and cisplatin (CP) affected LGCs viability by inducing apoptosis and downregulating both estrogen receptor β and follicle-stimulating hormone receptor in a dose-dependent manner. Several members of the WNT signaling pathway are expressed in granulosa cells where they regulate follicle development, ovulation, and luteinization. Here we show that treatment with DXR, PC, and CP induced upregulation of WNT4 expression, whereas WNT3 expression was downregulated by DXR and PC and upregulated by CP. Analysis of the WNT3 downstream signaling pathway showed that total β-catenin protein levels were reduced upon treatment with DXR and PC. Additionally, restoration of β-catenin signaling by lithium chloride protected LGCs from the injury induced by chemotherapy. The in vitro LGC toxicity model described might represent a tool to identify components of specific signaling pathways, such as the Wnt pathway, that can be targeted in order to limit the follicular damage caused by chemotherapy.

Lhcgr Expression in Granulosa Cells: Roles for PKA-Phosphorylated β-Catenin, TCF3, and FOXO1

Ovarian follicles lacking FSH or FSH receptors fail to progress to a preovulatory stage, resulting in infertility. One hallmark of the preovulatory follicle is the presence of luteinizing hormone/choriogonadotropin receptors (LHCGR) on granulosa cells (GCs). However, the mechanisms by which FSH induces Lhcgr gene expression are poorly understood. Our results show that protein kinase A (PKA) and phosphoinositide 3-kinase (PI3K)/AKT pathways are required for FSH to activate both the murine Lhcgr-luciferase reporter and expression of Lhcgr mRNA in rat GCs. Based on results showing that an adenovirus (Ad) expressing a steroidogenic factor 1 (SF1) mutant that cannot bind β-catenin abolished FSH-induced Lhcgr mRNA, we evaluated the role of β-catenin in the regulation of Lhcgr gene expression. FSH promoted the PKA-dependent, PI3K-independent phosphorylation of β-catenin on Ser552 and Ser665. FSH activated the β-catenin/T-cell factor (TCF) artificial promoter-reporter TOPFlash via a PKA-dependent, PI3K-independent pathway, and dominant-negative (DN) TCF abolished FSH-activated Lhcgr-luciferase reporter and induction of Lhcgr mRNA. Microarray analysis of GCs treated with Ad-DN-TCF and FSH identified the Lhcgr as the most down-regulated gene. Chromatin immunoprecipitation results placed β-catenin phosphorylated on Ser552 and Ser675 and SF1 on the Lhcgr promoter in FSH-treated GCs; TCF3 was constitutively associated with the Lhcgr promoter. Transduction with an Ad-phospho-β-catenin mutant (Ser552/665/Asp) enhanced Lhcgr mRNA expression in FSH-treated cells greater than 3-fold. Finally, we identified a recognized PI3K/AKT target, forkhead box O1, as a negative regulator of Lhcgr mRNA expression. These results provide new understanding of the complex regulation of Lhcgr gene expression in GCs.

CTNNB1 in mesenchyme regulates epithelial cell differentiation during Müllerian duct and postnatal uterine development

Müllerian duct differentiation and development into the female reproductive tract is essential for fertility, but mechanisms regulating these processes are poorly understood. WNT signaling is critical for proper development of the female reproductive tract as evident by the phenotypes of Wnt4, Wnt5a, Wnt7a, and β-catenin (Ctnnb1) mutant mice. Here we extend these findings by determining the effects of constitutive CTNNB1 activation within the mesenchyme of the developing Müllerian duct and its differentiated derivatives. This was accomplished by crossing Amhr2-Cre knock-in mice with Ctnnb1 exon (ex) 3(f/f) mice. Amhr2-Cre(Δ/+); Ctnnb1 ex3(f/+) females did not form an oviduct, had smaller uteri, endometrial gland defects, and were infertile. At the cellular level, stabilization of CTNNB1 in the mesenchyme caused alterations within the epithelium, including less proliferation, delayed uterine gland formation, and induction of an epithelial-mesenchymal transition (EMT) event. This EMT event is observed before birth and is complete within 5 days after birth. Misexpression of estrogen receptor α in the epithelia correlated with the EMT before birth, but not after. These studies indicate that regulated CTNNB1 in mesenchyme is important for epithelial cell differentiation during female reproductive tract development.

Plasticity of granulosa cells: on the crossroad of stemness and transdifferentiation potential

The ovarian follicle represents the basic functional unit of the ovary and consists of an oocyte, which is surrounded by granulosa cells (GCs). GCs play an important role in the growth and development of the follicle. They are subject to increased attention since it has recently been shown that the subpopulation of GCs within the growing follicle possesses exceptionally plasticity showing stem cell characteristics. In assisted reproduction programs, oocytes are retrieved from patients together with GCs, which are currently discarded daily, but could be an interesting subject to be researched and potentially used in regenerative medicine in the future. Isolated GCs expressed stem cell markers such as OCT-4, NANOG and SOX-2, showed high telomerase activity, and were in vitro differentiated into other cell types, otherwise not present within ovarian follicles. Recently another phenomenon demonstrated in GCs is transdifferentiation, which could explain many ovarian pathological conditions. Possible applications in regenerative medicine are also given.

Liver receptor homologue-1 expression in ovarian epithelial and granulosa cell tumours

Granulosa cell tumours of the ovary (GCT) express aromatase and produce oestrogens. The ovarian-specific aromatase promoter (pII) is regulated by members of the group 5A nuclear receptor family, SF-1 and LRH-1. Since both SF-1 and LRH-1 are implicated in proliferation and cancer, we hypothesised that alteration in the expression of either or both receptors may be associated with GCT. We therefore determined the expression of LRH-1, SF-1 and aromatase in a cohort of GCT, mucinous and serous cystadenocarcinomas, and normal ovaries. LRH-1 mRNA was present at low level in normal ovary and serous cystadenocarcinoma, but was elevated approximately 30-fold in GCT, and 8-fold in mucinous cystadenocarcinoma, compared to normal ovary. LRH-1 protein expression was confirmed in GCT by immunohistochemistry. SF-1 mRNA was significantly lower that of LRH-1 in all samples and not significantly altered in GCT, compared to normal ovary. Aromatase mRNA was present at low level in normal ovary and serous and mucinous cystadenocarcinoma, and significantly elevated (18-fold) in GCT compared to normal ovary. Despite the coordinate over-expression of both LRH-1 and aromatase in GCT versus normal ovary, their levels did not correlate in individual patients; rather, aromatase expression correlated with that of SF-1. Finally, although both LRH-1 and SF-1 activated aromatase promoter activity in transient transfection studies, gel-shift and chromatin immunoprecipitation data indicated that SF-1, but not LRH-1, bound to the aromatase promoter. We conclude that SF-1 regulates aromatase expression in GCT; over-expression of LRH-1 suggests that this receptor may be involved in the pathogenesis of GCT by mechanisms other than the regulation of aromatase. Its role in this disease therefore warrants further investigation.

MicroRNAs and Recent Insights into Pediatric Ovarian Cancers

Ovarian cancer is the most common pediatric gynecologic malignancy. When diagnosed in children, ovarian cancers present unique challenges that differ dramatically from those faced by adults. Here, we review the spectrum of ovarian cancers found in young women and girls and discuss the biology of these diseases. A number of advances have recently shed significant new understanding on the potential causes of ovarian cancer in this unique population. Particular emphasis is placed on understanding how altered expression of non-coding RNA transcripts known as microRNAs play a key role in the etiology of ovarian germ cell and sex cord-stromal tumors. Emerging transgenic models for these diseases are also reviewed. Lastly, future challenges and opportunities for understanding pediatric ovarian cancers, delineating clinically useful biomarkers, and developing targeted therapies are discussed.

Transforming growth factor alpha (TGFα) regulates granulosa cell tumor (GCT) cell proliferation and migration through activation of multiple pathways

Granulosa cell tumors (GCTs) are the most common ovarian estrogen producing tumors, leading to symptoms of excessive estrogen such as endometrial hyperplasia and endometrial adenocarcinoma. These tumors have malignant potential and often recur. The etiology of GCT is unknown. TGFα is a potent mitogen for many different cells. However, its function in GCT initiation, progression and metastasis has not been determined. The present study aims to determine whether TGFα plays a role in the growth of GCT cells. KGN cells, which are derived from an invasive GCT and have many features of normal granulosa cells, were used as the cellular model. Immunohistochemistry, Western blot and RT-PCR results showed that the ErbB family of receptors is expressed in human GCT tissues and GCT cell lines. RT-PCR results also indicated that TGFα and EGF are expressed in the human granulosa cells and the GCT cell lines, suggesting that TGFα might regulate GCT cell function in an autocrine/paracrine manner. TGFα stimulated KGN cell DNA synthesis, cell proliferation, cell viability, cell cycle progression, and cell migration. TGFα rapidly activated EGFR/PI3K/Akt and mTOR pathways, as indicated by rapid phosphorylation of Akt, TSC2, Rictor, mTOR, P70S6K and S6 proteins following TGFα treatment. TGFα also rapidly activated the EGFR/MEK/ERK pathway, and P38 MAPK pathways, as indicated by the rapid phosphorylation of EGFR, MEK, ERK1/2, P38, and CREB after TGFα treatment. Whereas TGFα triggered a transient activation of Akt, it induced a sustained activation of ERK1/2 in KGN cells. Long-term treatment of KGN cells with TGFα resulted in a significant increase in cyclin D2 and a decrease in p27/Kip1, two critical regulators of granulosa cell proliferation and granulosa cell tumorigenesis. In conclusion, TGFα, via multiple signaling pathways, regulates KGN cell proliferation and migration and may play an important role in the growth and metastasis of GCTs.

Elevated level of 17β-estradiol is associated with overexpression of FSHR, CYP19A1, and CTNNB1 genes in porcine ovarian follicles after prenatal and neonatal flutamide exposure

Recent studies suggest that disturbed androgen action during gestational and neonatal periods leads to reprogramming of the trajectory of ovarian development, manifested by altered follicular functioning in adulthood. In this study, we tested whether prenatal and neonatal exposure to antiandrogen flutamide affected ovarian 17β-estradiol (E(2)) synthesis and the associated gene expression in large antral follicles of adult pigs. Flutamide was injected into pregnant gilts between Days 80 and 88 of gestation and into female piglets between Days 2 and 10 postnatally. After animals reached sexual maturity, the ovaries were collected from treated and nontreated (control) pigs. The analysis of E(2) concentration in follicular tissues, as well as FSH and LH levels in plasma of control and flutamide-treated animals were conducted. In addition, the expression of mRNAs and proteins for FSH receptor (FSHR), cytochrome P450 aromatase (CYP19A1) and β-catenin (CTNNB1) was examined in large antral follicles of adult pigs. The E(2) concentration was greater in response to flutamide administered prenatally (P < 0.05) and neonatally (P < 0.01), whereas there was no changes in plasma gonadotropin concentration. Real-time polymerase chain reaction analysis revealed significant upregulation of FSHR, CYP19A1, and CTNNB1 at the mRNA level after maternal (P < 0.001, P < 0.01, P < 0.05, respectively) and neonatal (P < 0.001, P < 0.001, P < 0.01, respectively) flutamide exposure. The expression of FSHR protein was higher (P < 0.01) only after neonatal exposure to flutamide, whereas CYP19A1 and CTNNB1 proteins were upregulated in response to both prenatal (P < 0.01) and neonatal (P < 0.001) flutamide administration. Furthermore, membranous CTNNB1 immunolocalization indicates that it is not involved in regulation of FSH-mediated CYP19A1 activity as a transcription factor, but rather contributes to the intercellular adhesion. Concluding, it appears that the higher E(2) level in response to flutamide treatments is a result of the intensified aromatization and local E(2) action at the ovary level. The observed changes might influence the normal follicle development and pig fertility as a consequence.

Regulation of the ovarian reserve by members of the transforming growth factor beta family

Genetic or environmental factors that affect the endowment of oocytes, their assembly into primordial follicles, or their subsequent entry into the growing follicle pool can disrupt reproductive function and may underlie disorders such as primary ovarian insufficiency. Mouse models have been instrumental in identifying genes important in ovarian development, and a number of genes now associated with ovarian dysfunction in women were first identified as causing reproductive defects in knockout mice. The transforming growth factor beta (TGFB) family consists of developmentally important growth factors that include the TGFBs, anti-Müllerian hormone (AMH), activins, bone morphogenetic proteins (BMPs), and growth and differentiation factor 9 (GDF9). The ovarian primordial follicle pool is the source of oocytes in adults. Development of this pool can be grossly divided into three key processes: (1) establishment of oocytes during embryogenesis followed by (2) assembly and (3) activation of the primordial follicle. Disruptions in any of these processes may cause reproductive dysfunction. Most members of the TGFB family show pivotal roles in each of these areas. Understanding the phenotypes of various mouse models for this protein family will be directly relevant to understanding how disruptions in TGFB family signaling result in reproductive diseases in women and will present new areas for development of tailored diagnostics and interventions for infertility.

The Müllerian inhibiting substance type 2 receptor suppresses tumorigenesis in testes with sustained β-catenin signaling

Dysregulated WNT/β-catenin signaling in murine testes results in a phenotype with complete germ cell loss that resembles human Sertoli cell-only syndrome. In other systems, including the ovary, dysregulated WNT/β-catenin induces tumorigenesis but no tumors are observed in the mutant testes without deletion of a tumor suppressor, such as phosphatase and tensin homolog (PTEN). Müllerian inhibiting substance (MIS, also known as AMH), a member of the transforming growth factor-β family of growth factors responsible for Müllerian duct regression in fetal males, has been shown to inhibit tumor growth in vitro and in vivo but its role as an endogenous tumor suppressor has never been reported. We have deleted the MIS type 2 receptor (MISR2), and thus MIS signaling, in mice with dysregulated WNT/β-catenin and show that these mice develop testicular stromal tumors with 100% penetrance within a few months postnatal. The tumors are highly proliferative and have characteristics of either Sertoli cell tumors or progenitor Leydig cell tumors based on their marker profiles and histology. Phosphorylated Sma and mothers against decapentaplegic-related homolog 1/5/8 is absent in the tumors and β-catenin target genes are induced. The tumor suppressor TP53 is also highly expressed in the tumors, as is phosphorylated γH2AX, which is indicative of DNA damage. The phenotype of these tumors closely resembles those observed when PTEN is also deleted in mice with dysregulated WNT/β-catenin. Tumorigenesis in these mice provides conclusive evidence that physiological MIS signaling is a tumor suppressor mechanism and suggests that targeted treatment of MISR2-expressing cancers with therapeutic MIS should have a beneficial effect on tumor progression.

Pharmacological targeting of mammalian target of rapamycin inhibits ovarian granulosa cell tumor growth

Few targeted therapies have been developed for ovarian granulosa cell tumor (GCT), even though it represents 5% of all malignant ovarian tumors in women. As misregulation of PI3K/AKT signaling has been implicated in GCT development, we hypothesized that the AKT signaling effector mammalian target of rapamycin (mTOR) may play a role in the pathogenesis of GCT and could represent a therapeutic target. Analyses of human GCT samples showed an increase in protein levels of mTOR and its downstream effectors RPS6KB1, RPS6, eIF4B and PPARG relative to normal granulosa cells, suggestive of an increase in mTOR pathway activity and increased translational activity and/or protein stability. We next sought to evaluate mTOR as a GCT therapeutic target using the Pten (tm1Hwu/tmiHwu);Ctnnb1 (tm1Mmt/+);Amhr2 (tm3(cre)Bhr/+) (PCA) mouse model, in which mTOR, RPS6KB1, eIF4B and PPARG are upregulated in tumor cells in a manner similar to human GCT. Treatment of PCA mice with the mTOR-specific inhibitor everolimus reduced tumor growth rate (1.5-fold; P < 0.05) and also reduced total tumor burden (4.7-fold; P < 0.05) and increased survival rate (78 versus 44% in the vehicle group) in a PCA surgical model of GCT peritoneal carcinomatosis. Everolimus decreased tumor cell proliferation and tumor cell volume relative to controls (P < 0.05), whereas apoptosis was unaffected. Phosphorylation of RPS6KB1 and RPS6 were decreased (P < 0.05) by everolimus, but RPS6KB1, RPS6, eIF4B and PPARG expressions were not affected. These results suggest that mTOR is a valid and clinically useful pharmacological target for the treatment of GCT, although its inhibition does not reverse all consequences of aberrant PI3K/AKT signaling in the PCA model.

Proteomic profiling of a mouse model for ovarian granulosa cell tumor identifies VCP as a highly sensitive serum tumor marker in several human cancers

The initial aim of this study was to identify novel serum diagnostic markers for the human ovarian granulosa cell tumor (GCT), a tumor that represents up to 5% of all ovarian cancers. To circumvent the paucity of human tissues available for analyses, we used the Ctnnb1^tm1Mmt/+;Pten^{tm1Hwu/tmiHwu};Amhr2^{tm3(cre)Bhr/+} transgenic mouse model, which features the constitutive activation of CTNNB1 signaling combined with the loss of Pten in granulosa cells and develops GCTs that mimic aggressive forms of the human disease. Proteomic profiling by mass spectrometry showed that vinculin, enolase 1, several heat shock proteins, and valosin containing protein (VCP) were more abundantly secreted by cultured mouse GCT cells compared to primary cultured GC. Among these proteins, only VCP was present in significantly increased levels in the preoperative serum of GCT cancer patients compared to normal subjects. To determine the specificity of VCP, serum levels were also measured in ovarian carcinoma, non-Hodgkin's lymphoma and breast, colon, pancreatic, lung, and prostate cancer patients. Increased serum VCP levels were observed in the majority of cancer cases, with the exception of patients with lung or prostate cancer. Moreover, serum VCP levels were increased in some GCT, ovarian carcinoma, breast cancer, and colon cancer patients who did not otherwise display increased levels of widely used serum tumor markers for their cancer type (e.g. inhibin A, inhibin B, CA125, CEA, or CA15.3). These results demonstrate the potential use of VCP as highly sensitive serum marker for GCT as well as several other human cancers.

Characterization of Wnt2 overexpression in a rat granulosa cell line (DC3): effects on CTNNB1 activation

WNTs comprise a family of secreted glycoproteins that are essential for normal embryonic development of the female reproductive system. The functional role that WNTs play in the postnatal ovary is poorly defined. We have shown previously that Wnt2 and Fzd4 mRNAs are expressed in granulosa cells of the postnatal rat ovary. Here we examine the effects of Wnt2 overexpression in a rat granulosa cell line (DC3) that displays characteristics of granulosa cells at an early stage of follicular development. We show that DC3 cells express a 7.7-kb Fzd4 mRNA transcript similar in size to that detected in the rat and human ovary. Our results demonstrate that Wnt2 overexpression in DC3 promotes cytosolic and nuclear accumulation of beta-catenin (CTNNB1), but does not stimulate CTNNB1/TCF-dependent (pGL3-OT) transcriptional activity. We show that chibby (CBY1), a nuclear CTNNB1-associated antagonist of the WNT pathway, is expressed in DC3 cells and associates with CTNNB1 in the presence and absence of Wnt2 overexpression, suggesting that Cby1 contributes to suppression of CTNNB1/TCF-dependent transcription in these cells. Our results show that Wnt2 overexpression in DC3 cells increases follistatin (Fst) mRNA expression and promotes resistance to activin-induced cell deletion. Taken together, our results suggest that WNT2 opposes activin activity in granulosa cells by up-regulating expression of the activin antagonist Fst in a CTNNB1/TCF-independent manner, and that rat granulosa cells express factors, including Cby1, that suppress CTNNB1/TCF-dependent signal transduction in the presence of a WNT signal.

Consequences of RAS and MAPK activation in the ovary: the good, the bad and the ugly

This review summarizes studies providing evidence (1) that endogenous RAS activation regulates important physiological events during ovulation and luteinization (2) that expression of the mutant, active KRAS(G12D) in granulosa cells in vivo causes abnormal follicle growth arrest leading to premature ovarian failure and (3) that KRAS(G12D) expression in ovarian surface epithelial (OSE) cells renders them susceptible to the pathological outcome of transformation and tumor formation. These diverse effects of RAS highlight how critical its activation is linked to cell- and stage-specific events in the ovary that control normal processes and that can also lead to altered granulosa cell and OSE cell fates.

Bone morphogenetic protein signaling transcription factor (SMAD) function in granulosa cells

The transforming growth factor β (TGFβ) family of proteins are key regulators of growth and differentiation. Members of this family, including multiple TGFβs, activins, bone morphogenetic proteins (BMPs), and growth and differentiation factor 9 (GDF9), are expressed from oocytes or their associated follicular somatic cells (granulosa and thecal cells) with cell-type and stage-dependent specificity. Granulosa cells are the target cells for many of these ligands. Granulosa cell-specific knockout mice for all of the receptor-regulated SMADs, as well as the common regulatory SMAD4, have recently been generated and highlight the importance of this family in most stages of folliculogenesis. These models have also uncovered a novel role for the BMPs in suppression of granulosa cell tumor development and metastasis. This review summarizes the phenotypes of these mouse models and their contribution to our understanding of the complexity of BMP function during follicle development.

Luteinizing hormone regulates inhibin-α subunit expression through multiple signaling pathways involving steroidogenic factor-1 and beta-catenin in the macaque corpus luteum

We employed different experimental model systems to define the role of GATA4, beta-catenin, and steroidogenic factor (SF-1) transcriptional factors in the regulation of monkey luteal inhibin secretion. Reverse transcription polymerase chain reactions and western blotting analyses show high expression of inhibin-α, GATA4, and beta-catenin in corpus luteum (CL) of the mid-luteal phase. Gonadotropin-releasing hormone receptor antagonist-induced luteolysis model suggested the significance of luteinizing hormone (LH) in regulating these transcriptional factors. Inducible cyclic AMP early repressor mRNA expression was detected in the CL and no change was observed in different stages of CL. Following amino acid sequence analysis, interaction between SF-1 and beta-catenin in mid-stage CL was verified by reciprocal co-immunoprecipitation experiments coupled to immunoblot analysis. Electrophoretic mobility shift analysis support the role of SF-1 in regulating luteal inhibin-α expression. Our results suggest a possible multiple crosstalk of Wnt, cAMP, and SF-1 in the regulation of luteal inhibin secretion.

Minireview: animal models and mechanisms of ovarian cancer development

Ovarian cancer in women is a complex and deadly disease, where the molecular events that initiate and control tumor formation remain poorly defined. Therefore, mouse models provide one approach for determining the mechanisms by which specific oncogenic factors cause ovarian surface epithelial cell and granulosa cell transformation. This minireview summarizes the phenotypes of current mouse models that have been generated and some of the underlying mechanisms they have provided.

Either Kras activation or Pten loss similarly enhance the dominant-stable CTNNB1-induced genetic program to promote granulosa cell tumor development in the ovary and testis

WNT, RAS or phosphoinositide 3-kinase signaling pathways control specific stages of ovarian follicular development. To analyze the functional interactions of these pathways in granulosa cells during follicular development in vivo, we generated specific mutant mouse models. Stable activation of the WNT signaling effector β-catenin (CTNNB1) in granulosa cells results in the formation of premalignant lesions that develop into granulosa cell tumors (GCTs) spontaneously later in life or following targeted deletion of the tumor suppressor gene Pten. Conversely, expression of oncogenic KRAS(G12D) dramatically arrests proliferation, differentiation and apoptosis in granulosa cells, and consequently, small abnormal follicle-like structures devoid of oocytes accumulate in the ovary. Because of the potent anti-proliferative effects of KRAS(G12D) in granulosa cells, we sought to determine whether KRAS(G12D) would block precancerous lesion and tumor formation in follicles of the CTNNB1-mutant mice. Unexpectedly, transgenic Ctnnb1;Kras-mutant mice exhibited increased GC proliferation, decreased apoptosis and impaired differentiation and developed early-onset GCTs leading to premature death in a manner similar to the Ctnnb1;Pten-mutant mice. Microarray and reverse transcription-PCR analyses revealed that gene regulatory processes induced by CTNNB1 were mostly enhanced by either KRAS activation or Pten loss in remarkably similar patterns and degree. The concomitant activation of CTNNB1 and KRAS in Sertoli cells also caused testicular granulosa cell tumors that showed gene expression patterns that partially overlapped those observed in GCTs of the ovary. Although the mutations analyzed herein have not yet been linked to adult GCTs in humans, they may be related to juvenile GCTs or to tumors in other tissues where CTNNB1 is mutated. Importantly, the results provide strong evidence that CTNNB1 is the driver in these contexts and that KRAS(G12D) and Pten loss promote the program set in motion by the CTNNB1.

Ovarian steroid cell tumor with biallelic adenomatous polyposis coli inactivation in a patient with familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant cancer predisposition syndrome that accounts for approximately 0.5-1% of all colorectal cancer cases. It is caused by germline mutations in the gene encoding the adenomatous polyposis coli (APC) tumor suppressor. Somatic APC inactivation due to mutation or loss of heterozygosity (LOH) promotes the development of adenomatous polyps by stabilizing the transcriptional coactivator β-catenin. Although colorectal cancer is by far the most common malignancy seen in FAP patients, the widespread use of prophylactic colectomy in these patients has increased the clinical importance of extracolonic tumors that are part of the neoplastic spectrum in FAP. Many of these tumors exhibit LOH or somatic APC mutation, strongly supporting a causative role of APC inactivation in their pathogenesis. Here we describe a 47-year-old female FAP patient with clinical manifestations of virilization who was found to have an ovarian steroid cell tumor, a rare neoplasm not known to be associated with FAP. Immunohistochemical analysis of the ovarian tumor demonstrated strong nuclear β-catenin staining consistent with somatic APC inactivation, and molecular analysis confirmed biallelic APC inactivation in the tumor. Our findings provide the first evidence that ovarian steroid cell tumors may be an extracolonic manifestation of FAP and implicate β-catenin activation as an oncogenic mechanism in ovarian steroid cell tumorigenesis.

Connective tissue growth factor is required for normal follicle development and ovulation

Connective tissue growth factor (CTGF) is a cysteine-rich protein the synthesis and secretion of which are hypothesized to be selectively regulated by activins and other members of the TGF-β superfamily. To investigate the in vivo roles of CTGF in female reproduction, we generated Ctgf ovarian and uterine conditional knockout (cKO) mice. Ctgf cKO mice exhibit severe subfertility and multiple reproductive defects including disrupted follicle development, decreased ovulation rates, increased numbers of corpus luteum, and smaller but functionally normal uterine horns. Steroidogenesis is disrupted in the Ctgf cKO mice, leading to increased levels of serum progesterone. We show that disrupted follicle development is accompanied by a significant increase in granulosa cell apoptosis. Moreover, despite normal cumulus expansion, Ctgf cKO mice exhibit a significant decrease in oocytes ovulated, likely due to impaired ovulatory process. During analyses of mRNA expression, we discovered that Ctgf cKO granulosa cells show gene expression changes similar to our previously reported granulosa cell-specific knockouts of activin and Smad4, the common TGF-β family intracellular signaling protein. We also discovered a significant down-regulation of Adamts1, a progesterone-regulated gene that is critical for the remodeling of extracellular matrix surrounding granulosa cells of preovulatory follicles. These findings demonstrate that CTGF is a downstream mediator in TGF-β and progesterone signaling cascades and is necessary for normal follicle development and ovulation.

Loss of gremlin delays primordial follicle assembly but does not affect female fertility in mice

The transforming growth factor beta (TGFB) protein family is renowned for its diverse roles in developmental biology including reproduction. Gremlin is a member of the differential screening-selected gene aberrative in neuroblastoma (DAN)/cerberus family of bone morphogenetic protein (BMP) antagonists. Recent studies on gremlin focus on its involvement in embryonic skeletal, lung, and kidney development. To define the role of gremlin (Grem1) in female reproduction, we analyzed postnatal folliculogenesis using global and conditional knockout (cKO) mice for gremlin. Grem1(-/-) mice die within 48 h after birth, and ovaries collected from neonatal Grem1(-/-) mice demonstrated reduced oocyte numbers and delayed primordial follicle development. Transplanting Grem1(-/-) neonatal ovaries showed that folliculogenesis proceeded to large antral follicle stage, but Grem1(-/-) ovaries contained corpora lutea-like structures not found in control-transplanted ovaries. However, Grem1 cKO mice had comparable fertility to control mice. These data suggest that gremlin plays a previously uncharacterized role in the regulation of oocyte numbers and the timing of primordial follicle development, but either it is not required for later folliculogenesis or its loss is possibly compensated by other BMP antagonists.

Mammalian target of rapamycin is a therapeutic target for murine ovarian endometrioid adenocarcinomas with dysregulated Wnt/β-catenin and PTEN

Despite the fact that epithelial ovarian cancers are the leading cause of death from gynecological cancer, very little is known about the pathophysiology of the disease. Mutations in the WNT and PI3K pathways are frequently observed in the human ovarian endometrioid adenocarcinomas (OEAs). However, the role of WNT/β-catenin and PTEN/AKT signaling in the etiology and/or progression of this disease is currently unclear. In this report we show that mice with a gain-of-function mutation in β-catenin that leads to dysregulated nuclear accumulation of β-catenin expression in the ovarian surface epithelium (OSE) cells develop indolent, undifferentiated tumors with both mesenchymal and epithelial characteristics. Combining dysregulated β-catenin with homozygous deletion of PTEN in the OSE resulted in development of significantly more aggressive tumors, which was correlated with inhibition of p53 expression and cellular senescence. Induced expression of both mTOR kinase, a master regulator of proliferation, and phosphorylation of its downstream target, S6Kinase was also observed in both the indolent and aggressive mouse tumors, as well as in human OEA with nuclear β-catenin accumulation. Ectopic allotransplants of the mouse ovarian tumor cells with a gain-of-function mutation in β-catenin and PTEN deletion developed into tumors with OEA histology, the growth of which were significantly inhibited by oral rapamycin treatment. These studies demonstrate that rapamycin might be an effective therapeutic for human ovarian endometrioid patients with dysregulated Wnt/β-catenin and Pten/PI3K signaling.

Nuclear localization of E-cadherin but not beta-catenin in human ovarian granulosa cell tumours and normal ovarian follicles and ovarian stroma

AIMS

The role of misregulated Wnt/beta-catenin signalling in human ovarian granulosa cell tumour (GCT) has not been well characterized. The aim of this study was to confirm subcellular localization of key molecules of Wnt signalling (beta-catenin and E-cadherin) in human ovarian GCTs.

METHODS AND RESULTS

Tissue samples taken from 32 human ovarian GCTs and 19 human normal ovaries containing 68 follicles were stained immunohistochemically using monoclonal anti-beta-catenin and anti-E-cadherin antibodies. None of the 32 GCTs and none of the 68 ovarian follicles showed beta-catenin nuclear expression (0%). On the other hand, 28 of 32 GCTs (88%) and 53 of 68 normal ovarian follicles (78%) showed nuclear expression of E-cadherin in granulosa cells. The ovarian stroma in all 19 normal ovaries showed nuclear expression of E-cadherin but not beta-catenin. Membranous and cytoplasmic expression was observed variously in ovarian GCT, follicles and stroma.

CONCLUSIONS

We have confirmed frequent nuclear localization of E-cadherin but not beta-catenin in human ovarian GCT, ovarian follicles and stroma. There is no evidence of misregulated Wnt/beta-catenin signalling (represented by nuclear expression of beta-catenin) in human ovarian GCT. Nuclear translocation of E-cadherin might contribute to ovarian folliculogenesis or granulosa/stromal cell differentiation.

Regulatory roles of transforming growth factor beta family members in folliculogenesis

Bidirectional signaling between the oocyte and surrounding somatic cells is absolutely essential for successful germ cell development in mammals. Oocytes secrete proteins that are necessary for granulosa cells growth and differentiation, whilst granulosa cells regulate oocyte development and integrate ovarian function with the rest of the body by orchestrating gonadal steroidogenesis. The importance of communication between the oocyte and granulosa cells is highlighted by genetic deletion of members of the transforming growth factor beta (TGFβ) family and their downstream signaling components. Such knockout models have uncovered an interesting spectrum of reproductive phenotypes that have greatly advanced our knowledge of ovarian function and dysfunction. The current review focuses on some of the more recent transgenic mouse models that elucidate the intraovarian TGFβ signaling vital for oocyte and granulosa cell development.

CRH and SRIF have opposite effects on the Wnt/β-catenin signalling pathway through PKA/GSK-3β in corticotroph pituitary cells

The Wnt/ß-catenin signalling pathway is involved in tumorigenesis including endocrine tumors. We investigated the Wnt/ß-catenin pathway's modulation by corticotropin-releasing hormone (CRH) and somatostatin or somatotropin release-inhibiting factor (SRIF) in mouse pituitary AtT-20 corticotroph cells. The Wnt/β-catenin signalling pathway was activated by CRH and inhibited by SRIF. We provide evidence that cAMP/PKA signalling is involved affecting the GSK-3β phosphorylation status at phospho-GSK-3β (Ser9), thereby altering β-catenin degradation downstream. Furthermore, CRH and SRIF showed concordant effects on cell proliferation. Our data demonstrate an important role of the Wnt/β-catenin pathway in the proliferative control of pituitary corticotroph cells and describe a mechanism for its regulation by CRH and SRIF.

Defective gonadotropin-dependent ovarian folliculogenesis and granulosa cell gene expression in inhibin-deficient mice

Inhibin-α knockout (Inha-/-) female mice develop sex cord-stromal ovarian cancer with complete penetrance and previous studies demonstrate that the pituitary gonadotropins (FSH and LH) are influential modifiers of granulosa cell tumor development and progression in inhibin-deficient females. Recent studies have demonstrated that Inha-/- ovarian follicles develop precociously to the early antral stage in prepubertal mice without any increase in serum FSH. These studies suggest that in the absence of inhibins, granulosa cells differentiate abnormally and thus at sexual maturity may undergo an abnormal response to gonadotropin signaling contributing to tumor development. To test this hypothesis, we stimulated immature wild-type and Inha-/- female mice with gonadotropin analogs prior to tumor formation and subsequently examined gonadotropin-induced ovarian follicle development as well as preovulatory and human chorionic gonadotropin-induced gene expression changes in granulosa cells. We find that at 3 wk of age, inhibin-deficient ovaries do not show further antral development or undergo cumulus expansion. In addition, there are widespread alterations in the transcriptome of gonadotropin-treated Inha-/- granulosa cells, with significant changes in genes involved in extracellular matrix and cell-cell communication. These data indicate the gonadotropins initiate an improper program of cell differentiation prior to tumor formation in the absence of inhibins.

WNT4 is required for normal ovarian follicle development and female fertility

To study the role of WNT4 in the postnatal ovary, a mouse strain bearing a floxed Wnt4 allele was created and mated to the Amhr2(tm3(cre)Bhr) strain to target deletion of Wnt4 to granulosa cells. Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice had reduced ovary weights and produced smaller litters (P<0.05). Serial follicle counting demonstrated that Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice were born with a normal ovarian reserve and maintained normal numbers of small follicles until puberty but had only 25.2% of the normal number of healthy antral follicles. Some Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice had no antral follicles or corpora lutea and underwent premature follicle depletion. RT-PCR analyses of Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) granulosa cells and cultured granulosa cells that overexpress WNT4 demonstrated that WNT4 regulates the expression of Star, Cyp11a1, and Cyp19, steroidogenic genes previously identified as downstream targets of the WNT signaling effector CTNNB1. Decreased serum progesterone levels were found in immature, gonadotropin-treated Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice (P<0.05). WNT4- and CTNNB1-overexpressing cultured granulosa cells were analyzed by microarray for alterations in gene expression, which showed that WNT4 regulates additional genes involved in late follicle development via the WNT/CTNNB1 signaling pathway. Together, these data indicate that WNT4 is required for normal antral follicle development and may act by regulating granulosa cell functions including steroidogenesis.

Beta-catenin (CTNNB1) promotes preovulatory follicular development but represses LH-mediated ovulation and luteinization

Wingless-type mouse mammary tumor virus integration site family (WNT)/beta-catenin (CTNNB1) pathway components are expressed in ovarian granulosa cells, direct female gonad development, and are regulated by the pituitary gonadotropins. However, the in vivo functions of CTNNB1 during preovulatory follicular development, ovulation, and luteinization remain unclear. Using a mouse model Ctnnb1((Ex3)fl/fl);Cyp19-Cre (Ctnnb1((Ex3)gc-/-)), expressing dominant stable CTNNB1 in granulosa cells of small antral and preovulatory follicles, we show that CTNNB1 facilitates FSH-induced follicular growth and decreases the follicle atresia (granulosa cell apoptosis). At the molecular level, WNT signaling and FSH synergistically promote the expression of genes required for cell proliferation and estrogen biosynthesis, but decrease FOXO1, which negatively regulates proliferation and steroidogenesis. Conversely, dominant stable CTNNB1 represses LH-induced oocyte maturation, ovulation, luteinization, and progesterone biosynthesis. Specifically, granulosa cells in the Ctnnb1((Ex3)gc)(-/-) mice showed compromised responses to the LH surge and decreased levels of the epidermal growth factor-like factors (Areg and Ereg) that in vivo and in vitro mediate LH action. One underlying mechanism by which CTNNB1 prevents LH responses is by reducing phosphorylation of cAMP-responsive element-binding protein, which is essential for the expression of Areg and Ereg. By contrast, depletion of Ctnnb1 using the Ctnnb1(fl/fl);Cyp19-Cre mice did not alter FSH regulation of preovulatory follicular development or female fertility but dramatically enhanced LH induction of genes in granulosa cells in culture. Thus, CTNNB1 can enhance FSH and LH actions in antral follicles but overactivation of CTNNB1 negatively effects LH-induced ovulation and luteinization, highlighting the cell context-dependent and developmental stage-specific interactions of WNT/CTNNB1 pathway and G protein-coupled gonadotropin receptors in female fertility.

The ovary: basic biology and clinical implications

The classical view of ovarian follicle development is that it is regulated by the hypothalamic-pituitary-ovarian axis, in which gonadotropin-releasing hormone (GnRH) controls the release of the gonadotropic hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and that ovarian steroids exert both negative and positive regulatory effects on GnRH secretion. More recent studies in mice and humans indicate that many other intra-ovarian signaling cascades affect follicular development and gonadotropin action in a stage- and context-specific manner. As we discuss here, mutant mouse models and clinical evidence indicate that some of the most powerful intra-ovarian regulators of follicular development include the TGF-beta/SMAD, WNT/FZD/beta-catenin, and RAS/ERK1/2 signaling pathways and the FOXO/FOXL2 transcription factors.

What a fish can learn from a mouse: principles and strategies for modeling human cancer in mice

This review highlights the current techniques used to generate transgenic mouse models of cancer, with an emphasis on recent advances in the use of ubiquitous promoters, models that use Cre-loxP and Flip-FRT recombinase technology, inducible systems, RNAi to target genes, and transposon mutagenesis. A concluding section discusses new imaging systems that visualize tumor progression and the microenvironment in vivo. In this review, these techniques and strategies used in mouse models of cancer are highlighted, as they are pertinent and relevant to the development of zebrafish models of cancer.

Wide-field four-channel fluorescence imager for biological applications

A wide-field four-channel fluorescence imager has been developed. The instrument uses four expanded laser beams to image a large section (6 mm x 9 mm). An object can be sequentially illuminated with any combination of 408-, 532-, 658-, and 784-nm lasers for arbitrary (down to 1 ms) exposure times for each laser. Just two notch filters block scattered light from all four lasers. The design approach described here offers great flexibility in treatment of objects, very good sensitivity, and a wide field of view at low cost. There appears to be no commercial instrument capable of simultaneous fluorescence imaging of a wide field of view with four-laser excitation. Some possible applications are following events such as flow and mixing in microchannel systems, the transmission of biological signals across a culture, and following simulations of biological membrane diffusion. It can also be used in DNA sequencing by synthesis to follow the progress of the photolytic removal of dye and terminator. Without utilizing its time resolution, it can be used to obtain four independent images of a single tissue section stained with four targeting agents, with each coupled to a different dye matching one of the lasers.

WNT2 regulates DNA synthesis in mouse granulosa cells through beta-catenin

WNTs are secreted extracellular signaling molecules that transduce their signals by binding to G protein-coupled receptors of the frizzled (FZD) family. They control diverse developmental processes, such as cell fate specification, cell proliferation, cell differentiation, and apoptosis. Although WNT signaling has been shown to be essential for development of the ovary, its mechanistic role in folliculogenesis within the adult ovary has not been studied extensively. Therefore, the objective of this study was to investigate the regulation and function of WNT2 signaling in mouse granulosa cells. Immunostaining identified WNT2 as being expressed in granulosa cells throughout folliculogenesis, but with varying signal strength: in sequential sections, WNT2 immunoreactivity was strongest in healthy antral follicles but weak in atretic follicles. Knockdown of WNT2 expression using transfected short interfering RNA decreased DNA synthesis in granulosa cells, whereas WNT2 overexpression using a recombinant viral vector enhanced it. WNT2 knockdown led to accumulation of glycogen synthase kinase-3beta (GSK3B) in the cytoplasm but reduced the expression of beta-catenin. Conversely, WNT2 overexpression reduced the expression of GSK3B in the cytoplasm and induced beta-catenin translocation from the membrane into the nucleus. Beta-catenin knockdown also inhibited DNA synthesis in granulosa cells and neutralized the effect of WNT2 overexpression. WNT2/beta-catenin signaling had a slight effect on the apoptosis of granulosa cells. Taken together, the data indicate that WNT2 regulates beta-catenin localization in granulosa cells, and WNT2/beta-catenin signaling contributes to regulating their proliferation.

New insights into ovarian function

Infertility adversely affects many couples worldwide. Conversely, the exponential increase in world population threatens our planet and its resources. Therefore, a greater understanding of the fundamental cellular and molecular events that control the size of the primordial follicle pool and follicular development is of utmost importance to develop improved in vitro fertilization as well as to design novel approaches to regulate fertility. In this review we attempt to highlight some new advances in basic research of the mammalian ovary that have occurred in recent years focusing primarily on mouse models that have contributed to our understanding of ovarian follicle formation, development, and ovulation. We hope that these new insights into ovarian function will trigger more research and translation to clinically relevant problems.

WNT signaling in ovarian follicle biology and tumorigenesis

The WNTS are an expansive family of glycoprotein signaling molecules known mostly for the roles they play in embryonic development. WNT signaling first caught the attention of ovarian biologists when it was reported that the inactivation of Wnt4 in mice results in partial female-to-male sex reversal and oocyte depletion. More recently, studies using loss- and gain-of-function transgenic mouse models demonstrated the requirement for Wnt4, Fzd4 and Ctnnb1, components of the WNT pathway, for normal folliculogenesis, luteogenesis and steroidogenesis, and showed that dysregulated WNT signaling can cause granulosa cell tumor development. This review covers our current knowledge of WNT signaling in ovarian follicles, highlighting both the great promise and the many unresolved questions of this emerging field of research.

Smad1-Smad5 ovarian conditional knockout mice develop a disease profile similar to the juvenile form of human granulosa cell tumors

Granulosa cell tumors (GCTs) of the ovary are rare sex cord stromal tumors. Although generally indolent, GCTs recur, and if not diagnosed and treated in early stages, survival rates are significantly shortened. Very little is known regarding GCT etiology. Because of the low incidence of cases and lack of standard diagnostics, mouse models for granulosa cell tumors are a valuable tool for studying GCTs and provide models for developing diagnostic and treatment strategies. We recently developed a novel mouse model of metastatic granulosa cell tumors by genetic deletion of the bone morphogenetic protein signaling transcription factors (SMADs) in granulosa cells of the ovary. Histological and serum hormone analyses reveal that this mouse model most closely resembles the juvenile form of GCT. We further analyzed samples of human juvenile GCT (JGCT) for expression of anti-Müllerian hormone and activation of two major signaling pathways: TGFbeta/SMAD2/3 and wingless-related mouse mammary tumor virus integration site (Wnt)/beta-catenin. The TGFbeta family is active in mouse Smad1-Smad5 double knockout tumors, and here we show that this pathway, but not the beta-catenin pathway, is activated in samples of human JGCT. These data suggest that the SMAD family, possibly through disruption of SMAD1/5 or activation of SMAD2/3 may contribute to the pathogenesis of JGCT in humans.

Convergence of 3',5'-cyclic adenosine 5'-monophosphate/protein kinase A and glycogen synthase kinase-3beta/beta-catenin signaling in corpus luteum progesterone synthesis

Progesterone secretion by the steroidogenic cells of the corpus luteum (CL) is essential for reproduction. Progesterone synthesis is under the control of LH, but the exact mechanism of this regulation is unknown. It is established that LH stimulates the LH receptor/choriogonadotropin receptor, a G-protein coupled receptor, to increase cAMP and activate cAMP-dependent protein kinase A (PKA). In the present study, we tested the hypothesis that cAMP/PKA-dependent regulation of the Wnt pathway components glycogen synthase kinase (GSK)-3beta and beta-catenin contributes to LH-dependent steroidogenesis in luteal cells. We observed that LH via a cAMP/PKA-dependent mechanism stimulated the phosphorylation of GSK3beta at N-terminal Ser9 causing its inactivation and resulted in the accumulation of beta-catenin. Overexpression of N-terminal truncated beta-catenin (Delta90 beta-catenin), which lacks the phosphorylation sites responsible for its destruction, significantly augmented LH-stimulated progesterone secretion. In contrast, overexpression of a constitutively active mutant of GSK3beta (GSK-S9A) reduced beta-catenin levels and inhibited LH-stimulated steroidogenesis. Chromatin immunoprecipitation assays demonstrated the association of beta-catenin with the proximal promoter of the StAR gene, a gene that expresses the steroidogenic acute regulatory protein, which is a cholesterol transport protein that controls a rate-limiting step in steroidogenesis. Collectively these data suggest that cAMP/PKA regulation of GSK3beta/beta-catenin signaling may contribute to the acute increase in progesterone production in response to LH.

Minireview: physiological and pathological actions of RAS in the ovary

The small G proteins of the RAS superfamily act as molecular switches in the transduction of cellular signals critical for a wide range of normal developmental events as well as pathological processes. However, the functions of Ras genes in ovarian cells have only started to be unveiled. RAS, most likely KRAS that is highly expressed in granulosa cells of growing follicles, appears crucial for mediating the gonadotropin-induced events associated with the unique physiological process of ovulation. By contrast, conditional expression of a constitutively active Kras(G12D) mutant in granulosa cells results in ovulation defects due to the complete disruption of normal follicular growth, cessation of granulosa cell proliferation, and blockage of granulosa cell apoptosis and differentiation. When the tumor suppressor Pten is disrupted conditionally in the Kras(G12D)-expressing granulosa cells, granulosa cell tumors fail to develop. However, ovarian surface epithelial cells expressing the same Pten;Kras(G12D) mutations rapidly become ovarian surface epithelial serous cystadenocarcinomas. In this minireview, we summarize some of the physiological as well as pathological functions of RAS in the rodent ovary, discuss the implications of the Kras(G12D) mutant mouse models for understanding human diseases such as premature ovarian failure and ovarian cancers, and highlight new questions raised by the results of recent studies.

The mammalian ovary from genesis to revelation

Two major functions of the mammalian ovary are the production of germ cells (oocytes), which allow continuation of the species, and the generation of bioactive molecules, primarily steroids (mainly estrogens and progestins) and peptide growth factors, which are critical for ovarian function, regulation of the hypothalamic-pituitary-ovarian axis, and development of secondary sex characteristics. The female germline is created during embryogenesis when the precursors of primordial germ cells differentiate from somatic lineages of the embryo and take a unique route to reach the urogenital ridge. This undifferentiated gonad will differentiate along a female pathway, and the newly formed oocytes will proliferate and subsequently enter meiosis. At this point, the oocyte has two alternative fates: die, a common destiny of millions of oocytes, or be fertilized, a fate of at most approximately 100 oocytes, depending on the species. At every step from germline development and ovary formation to oogenesis and ovarian development and differentiation, there are coordinated interactions of hundreds of proteins and small RNAs. These studies have helped reproductive biologists to understand not only the normal functioning of the ovary but also the pathophysiology and genetics of diseases such as infertility and ovarian cancer. Over the last two decades, parallel progress has been made in the assisted reproductive technology clinic including better hormonal preparations, prenatal genetic testing, and optimal oocyte and embryo analysis and cryopreservation. Clearly, we have learned much about the mammalian ovary and manipulating its most important cargo, the oocyte, since the birth of Louise Brown over 30 yr ago.