Granulosa cell tumor mutant FOXL2C134W suppresses GDF-9 and activin A-induced follistatin transcription in primary granulosa cells

Uncovering Tumor-Promoting Roles of Activin A in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers with high incidence rates of metastasis and cachexia. High circulating activin A, a homodimer of inhibin βA subunits that are encoded by INHBA gene, predicts poor survival among PDAC patients. However, it still raises the question of whether activin A suppression renders favorable PDAC outcomes. Here, the authors demonstrate that activin A is abundantly detected in tumor and stromal cells on PDAC tissue microarray and mouse PDAC sections. In orthotopic male mice, activin A suppression, which is acquired by tumor-targeted Inhba siRNA using cholesterol-modified polymeric nanoparticles, retards tumor growth/metastasis and cachexia and improves survival when compared to scramble siRNA-treated group. Histologically, activin A suppression coincides with decreased expression of proliferation marker Ki67 but increased accumulation of α-SMAhigh fibroblasts and cytotoxic T cells in the tumors. In vitro data demonstrate that activin A promotes KPC cell proliferation and induces the downregulation of α-SMA and upregulation of IL-6 in pancreatic stellate cells (PSC) in the SMAD3-dependent mechanism. Moreover, conditioned media from activin A-stimulated PSC promoted KPC cell growth. Collectively, our data provide a mechanistic basis for tumor-promoting roles of activin A and support therapeutic potentials of tumor activin A suppression for PDAC.

Immunohistochemical markers of prognosis in adult granulosa cell tumors of the ovary - a review

BACKGROUND

Granulosa cell tumors (GCT) are rare malignant ovarian tumors. The two subtypes, adult and juvenile granulosa cell tumors, differ in clinical and molecular characteristics. GCT are low-malignant tumors and are generally associated with favorable prognosis. However, relapses are common even years and decades after diagnosis. Prognostic and predictive factors are difficult to assess in this rare tumor entity. The purpose of this review is to provide a comprehensive overview of the current state of knowledge on prognostic markers of GCT to identify patients with a high risk of recurrence.

METHODS

Systematic research for adult ovarian granulosa cell tumors and prognosis revealed n = 409 English full text results from 1965 to 2021. Of these articles, n = 35 were considered for this review after title and abstract screening and topic-specific matching. A specific search for pathologic markers with prognostic relevance for GCT identified n = 19 articles that were added to this review.

RESULTS

FOXL2 mutation and FOXL2 mRNA were inverse and immunohistochemical (IHC) expression of CD56, GATA-4 and SMAD3 was associated with reduced prognosis. IHC analysis of estrogen receptor, Anti-Mullerian hormone (AMH) and inhibin was not associated with prognosis for GCT. Analyses of mitotic rate, Ki-67, p53, β-catenin and HER2 revealed inconsistent results.

Efficacy and Clinical Significance of the Zuogui Pill on Premature Ovarian Failure via the GDF-9/Smad2 Pathway

Our study aims to investigate the efficacy and clinical significance of the Zuogui pill (ZGP) on premature ovarian failure (POF) via the GDF-9/Smad2 pathway. Changes in clinical symptoms in the control group (treated with Femoston alone) and the treatment group (treated with ZGP combined with Femoston) were assessed before and after treatment. Sex hormone levels, serum inflammatory cytokine levels, and ultrasound parameters were measured before and after treatment. POF rat models were established using cyclophosphamide and the POF rats were treated with Femoston, or ZGP combined with Femoston. GDF-9 and Smad2 expression levels were determined by RT-qPCR. The follicle-stimulating hormone (FSH), luteinizing hormone (LH), interleukin (IL)-6, and IL-21 levels, and the pulsatility index (PI) and resistance index (RI) values were decreased, while the estradiol (E2) and anti-Mullerian hormone (AMH) levels, antral follicle count (AFC), ovarian volume (OV), mean ovarian diameter (MOD), and peak systolic velocity (PSV) values were increased in the treatment group compared to the control group. After treatment with ZGP combined with Femoston, GDF-9 and Smad2 expression in the ovarian tissues of POF rats increased. ZGP has a therapeutic effect on POF via modulation of the GDF-9/Smad2 pathway.

FOXO1 mitigates the SMAD3/FOXL2C134W transcriptomic effect in a model of human adult granulosa cell tumor

BACKGROUND

Adult granulosa cell tumor (aGCT) is a rare type of stromal cell malignant cancer of the ovary characterized by elevated estrogen levels. aGCTs ubiquitously harbor a somatic mutation in FOXL2 gene, Cys134Trp (c.402C < G); however, the general molecular effect of this mutation and its putative pathogenic role in aGCT tumorigenesis is not completely understood. We previously studied the role of FOXL2C134W, its partner SMAD3 and its antagonist FOXO1 in cellular models of aGCT.

METHODS

In this work, seeking more comprehensive profiling of FOXL2C134W transcriptomic effects, we performed an RNA-seq analysis comparing the effect of FOXL2WT/SMAD3 and FOXL2C134W/SMAD3 overexpression in an established human GC line (HGrC1), which is not luteinized, and bears normal alleles of FOXL2.

RESULTS

Our data shows that FOXL2C134W/SMAD3 overexpression alters the expression of 717 genes. These genes include known and novel FOXL2 targets (TGFB2, SMARCA4, HSPG2, MKI67, NFKBIA) and are enriched for neoplastic pathways (Proteoglycans in Cancer, Chromatin remodeling, Apoptosis, Tissue Morphogenesis, Tyrosine Kinase Receptors). We additionally expressed the FOXL2 antagonistic Forkhead protein, FOXO1. Surprisingly, overexpression of FOXO1 mitigated 40% of the altered genome-wide effects specifically related to FOXL2C134W, suggesting it can be a new target for aGCT treatment.

CONCLUSIONS

Our transcriptomic data provide novel insights into potential genes (FOXO1 regulated) that could be used as biomarkers of efficacy in aGCT patients.

Determination of the roles of GREM1 gene in granulosa cell proliferation and steroidogenesis of hen ovarian prehierarchical follicles

Gremlin genes are known members of the DAN family of bone morphogenetic protein (BMP) antagonists, but their functions and regulatory mechanisms in ovarian follicular development of chicken remain unknown. The current study was designed to investigate the mRNA expression patterns of gremlin1 gene (GREM1) and its protein location in the follicles sampled, and to explore the biological effect of GREM1 on the prehierarchical follicular development. This work revealed that chicken GREM1 mRNA exhibits a constant expression level across all the prehierarchical follicles (PFs) from 1-4 mm to 7-8 mm in diameter, and the preovulatory follicles (from F6 to F1) by using RT-qPCR (P > 0.05). The GREM1 protein is predominantly expressed in the oocytes and granulosa cells (GCs) of the PFs by immunohistochemistry. Furthermore, our data demonstrated that siRNA-mediated knockdown of GREM1 in the GCs resulted in a significant reduction in cell proliferation (P < 0.001); conversely, overexpression of GREM1 in the GCs led to a remarkable increase in cell proliferation (P < 0.001). Interestingly, the expression levels of proliferating cell nuclear antigen (PCNA) and cyclin D2 (CCND2) mRNA and proteins were notably increased when GREM1 expression was upregulated in the GCs (P < 0.01), however, the expression levels of CYP11A1 and StAR were markedly downregulated (P < 0.01). The current results showed that GREM1 gene plays a stimulatory role in GC proliferation during growth and development of the prehierarchical follicles in vitro but an inhibitory role in GC differentiation and steroidogenesis of the hen ovary follicles.

The Pathognomonic FOXL2 C134W Mutation Alters DNA-Binding Specificity

The somatic missense point mutation c.402C>G (p.C134W) in the FOXL2 transcription factor is pathognomonic for adult-type granulosa cell tumors (AGCT) and a diagnostic marker for this tumor type. However, the molecular consequences of this mutation and its contribution to the mechanisms of AGCT pathogenesis remain unclear. To explore these mechanisms, we engineered V5-FOXL2^WT- and V5-FOXL2^C134W-inducible isogenic cell lines and performed chromatin immunoprecipitation sequencing and transcriptome profiling. FOXL2^C134W associated with the majority of the FOXL2 wild-type DNA elements as well as a large collection of unique elements genome wide. This model enabled confirmation of altered DNA-binding specificity for FOXL2^C134W and identification of unique targets of FOXL2^C134W including SLC35F2, whose expression increased sensitivity to YM155. Our results suggest FOXL2^C134W drives AGCT by altering the binding affinity of FOXL2-containing complexes to engage an oncogenic transcriptional program. SIGNIFICANCE: A mechanistic understanding of FOXL2^C134W-induced regulatory state alterations drives discovery of a rationally designed therapeutic strategy.

FOXO1 Negates the Cooperative Action of FOXL2C134W and SMAD3 in CYP19 Expression in HGrC1 Cells by Sequestering SMAD3

Adult granulosa cell tumor (aGCT) is a rare type of ovarian cancer characterized by estrogen excess. Interestingly, only the single somatic mutation FOXL2 ^C134W was found across virtually all aGCTs. We previously reported that FOXL2^C134W stimulates CYP19 transcription synergistically with SMAD3, leading to elevated estradiol synthesis in a human granulosa cell line (HGrC1). This finding suggested a key role for FOXL2^C134W in causing the typical estrogen overload in patients with aGCTs. We have now investigated the effect of FOXO1, a tumor suppressor, on CYP19 activation by FOXL2^C134W in the presence of SMAD3. Intriguingly, FOXO1 antagonized the positive, synergistic effect of FOXL2^C134W and SMAD3 on CYP19 transcription. Similar to FOXL2^C134W, FOXO1 binds SMAD3 but not the proximal FOXL2^C134W binding site (-199 bp) of the CYP19 promoter identified in our earlier studies. The results of a competitive binding assay suggested a possible underlying mechanism in which FOXO1 sequesters SMAD3 away from FOXL2^C134W, thereby negating the cooperative action of FOXL2^C134W and SMAD3 in inducing CYP19 expression. To our knowledge, this study is the first to demonstrate the ability of FOXO1 to restore an altered CYP19 expression by FOXL2^C134W and SMAD3 and provides insight as to why FOXO1 deficiency promotes GCT development in mice.

First-in-Human Phase I Study of the Activin A Inhibitor, STM 434, in Patients with Granulosa Cell Ovarian Cancer and Other Advanced Solid Tumors

PURPOSE

STM 434 is a soluble receptor ligand trap targeting activin A, a protein in the TGFβ family that plays important roles in growth, differentiation, and cancer cachexia. This study evaluated the safety, antitumor activity, and metabolic effects of STM 434 in a first-in-human, multicenter, phase I clinical trial (NCT02262455).

PATIENTS AND METHODS

Patients with advanced solid tumors were enrolled in 8 dose cohorts ranging from 0.25 mg/kg every 4 weeks to 8 mg/kg every 2 weeks via a 3 + 3 dose-escalation design. The primary endpoint was maximum tolerated dose (MTD). Secondary endpoints included safety, pharmacokinetics, and response. As activin A is implicated in metabolism and muscle function, changes in key metabolic parameters, including lean body mass and 6-minute walk test, were serially measured.

RESULTS

Thirty-two patients were treated on study. The most common treatment-related adverse events were fatigue (41%) and mucocutaneous bleeding complications including epistaxis (34%) and gingival bleeding (22%), likely related to off-target inhibition of bone morphogenetic protein 9 (BMP9). STM 434 treatment resulted in the expected follicle-stimulating hormone level decreases in most patients and in metabolic parameter changes, including an increase in total lean body mass and 6-minute walk test distance. No responses were observed in the 30 evaluable patients, but the stable disease rate in patients with granulosa cell ovarian cancer was 10 of 12 (80%).

CONCLUSIONS

Although no direct antitumor efficacy was documented, potentially clinically meaningful dose-related metabolic effects, including treatment of cancer cachexia, were observed that support further exploration of activin A inhibitors that limit BMP9 blockade.See related commentary by Bonilla and Oza, p. 5432.

FOXL2C134W-Induced CYP19 Expression via Cooperation With SMAD3 in HGrC1 Cells

Germline knockout studies in female mice demonstrated an essential role for forkhead box L2 (FOXL2) in early follicle development, whereas an inducible granulosa cell (GC)-specific deletion of Foxl2 in adults has shown ovary-to-testis somatic sex reprogramming. In women, over 120 different germline mutations in the FOXL2 gene have been shown to cause blepharophimosis/ptosis/epicantus inversus syndrome associated with or without primary ovarian insufficiency. By contrast, a single somatic mutation (FOXL2C134W) accounts for almost all adult-type GC tumors (aGCTs). To test the hypothesis that FOXL2C134W differentially regulates the expression of aGCT markers, we investigated the effect of FOXL2C134W on inhibin B and P450 aromatase expression using a recently established human GC line (HGrC1), which we now show to bear two normal alleles of FOXL2. Neither FOXL2wt nor FOXL2C134W regulate INHBB messenger RNA (mRNA) expression. However, FOXL2C134W selectively displays a 50-fold induction of CYP19 mRNA expression dependent upon activin A. Mechanistically, the CYP19 promoter is activated in a similar way by FOXL2C134W interaction with SMAD3, but not by FOXL2wt. SMAD2 had no effect. Moreover, FOXL2C134W interactions with SMAD3 and with the FOX binding element located at -199 bp upstream of the ATG initiation codon of CYP19 are more sustainable than FOXL2wt. Thus, FOXL2C134W potentiates CYP19 expression in HGrC1 cells via enhanced recruitment of SMAD3 to a proximal FOX binding element. These findings may explain the pathophysiology of estrogen excess in patients with aGCT.

Uterine Foxl2 regulates the adherence of the Trophectoderm cells to the endometrial epithelium

BACKGROUND

Forkhead Transcription Factor L2 (FOXL2) is a member of the forkhead family with important roles in reproduction. Recent studies showed that FOXL2 is expressed in human and bovine endometrium and that its levels fluctuate during pregnancy. In this study, we aimed at evaluating the expression and function of FOXL2 in embryo implantation.

METHODS

Mouse uteri at different days of pregnancy were isolated and analyzed for the expression and localization of FOXL2. A lentiviral strategy was further employed to either knockdown or overexpress FOXL2 in non-receptive human endometrial AN3-CA cells and in receptive Ishikawa cells, respectively. These genetically modified cells were compared to cells infected with a control lentivirus to determine the function of FOXL2 in trophectoderm cells adherence to Endometrial Epithelium was associated with the expression of genes known to be involved in acquisition of uterine receptivity.

RESULTS

We report that FOXL2 is expressed in both, the luminal epithelium and the myometrium of the mouse uterus and that its expression declines prior to implantation. We found that endometrial cells expressing low FOXL2 levels, either endogenous or genetically manipulated, were associated with a higher attachment rate of mouse blastocysts or human Jeg3 spheroids and mouse blastocysts. In accordance, low-FOXL2 levels were associated with changes in the expression level of components of the Wnt/Fzd and apoptotic pathways, both of which are involved in uterine receptivity. Furthermore, FOXL2 expression was inversely correlated with G-protein signaling protein 2 (Rgs2) and cytokine expression.

CONCLUSIONS

These results suggest that FOXL2 interferes with embryo attachment. Better understanding of the function of FOXL2 in the uterus would possibly suggest novel strategies for treatment of infertility attributed to repeated implantation failure.

The molecular mechanism of ovarian granulosa cell tumors

Over these years, more and more sex cord-stromal tumors have been reported. Granulosa cell tumor (GCT) is a rare tumor in ovaries, accounts for 2% to 5% of ovarian cancers. The main different feature of GCTs from other ovarian cancers is that GCTs can lead to abnormally secreted hormones (estrogen, inhibin and Müllerian inhibiting substance). The GCT is divided into two categories according to the age of patients, namely AGCT (adult granulosa cell tumor) and JGCT (Juvenile granulosa cell tumor). AGCT patients accounts for 95%. Although the pathogenesis is not clear, FOXL2 (Forkhead box L2) mutation was considered as the most critical factor in AGCT development. The current treatment is dominated by surgery. Target therapy remains in the adjuvant therapy stage, such as hormone therapy. During these years, other pathogenic factors were also explored, such as PI3K/AKT (phosphatidylinositol-3-kinase; serine/threonine kinase), TGF-β (Transforming growth factor beta) signaling pathway, Notch signaling pathway, GATA4 and VEGF (vascular endothelial growth factor). These factors and signaling pathway play important roles in GCT cell proliferation, apoptosis, or angiogenesis. The purpose of this review is to summarize the possible pathogenic factors and signaling pathways, which may shed lights on developing potential therapeutic targets for GCT.

Pathogenesis and treatment of adult-type granulosa cell tumor of the ovary

Adult-type granulosa cell tumor is a clinically and molecularly unique subtype of ovarian cancer. These tumors originate from the sex cord stromal cells of the ovary and represent 3-5% of all ovarian cancers. The majority of adult-type granulosa cell tumors are diagnosed at an early stage with an indolent prognosis. Surgery is the cornerstone for the treatment of both primary and relapsed tumor, while chemotherapy is applied only for advanced or non-resectable cases. Tumor stage is the only factor consistently associated with prognosis. However, every third of the patients relapse, typically in 4-7 years from diagnosis, leading to death in 50% of these patients. Anti-Müllerian Hormone and inhibin B are currently the most accurate circulating biomarkers. Adult-type granulosa cell tumors are molecularly characterized by a pathognomonic somatic missense point mutation 402C->G (C134W) in the transcription factor FOXL2. The FOXL2 402C->G mutation leads to increased proliferation and survival of granulosa cells, and promotes hormonal changes. Histological diagnosis of adult-type granulosa cell tumor is challenging, therefore testing for the FOXL2 mutation is crucial for differential diagnosis. Large international collaborations utilizing molecularly defined cohorts are essential to improve and validate new treatment strategies for patients with high-risk or relapsed adult-type granulosa cell tumor. Key Messages: Adult-type granulosa cell tumor is a unique ovarian cancer with an indolent, albeit unpredictable disease course. Adult-type granulosa cell tumors harbor a pathognomonic somatic missense mutation in transcription factor FOXL2. The key challenges in the treatment of patients with adult-type granulosa cell tumor lie in the identification and management of patients with high-risk or relapsed disease.

HMGA2-FOXL2 Axis Regulates Metastases and Epithelial-to-Mesenchymal Transition of Chemoresistant Gastric Cancer

Purpose: Chemoresistance is the main cause of treatment failure in cancer and is associated with distant metastases and epithelial-to-mesenchymal transition (EMT). This study was aimed to explore the mechanism of metastases and EMT in chemoresistant gastric cancer.Experimental Design: A key molecular pathway was identified via gene profiling and a bioinformatic analysis in a chemoresistant gastric cancer model. The roles of FOXL2, HMGA2, and ITGA2 were validated via loss-of-function and gain-of-function experiments in vitro and in an orthotopic gastric cancer animal model. The regulation of FOXL2 by HMGA2 was explored via immunoprecipitation and luciferase reporter assays. The expression of these proteins in gastric cancer tissues was examined by IHC.Results: HMGA2 and FOXL2 directly regulated the metastasis and EMT of chemoresistant gastric cancer. The interaction between HMGA2 and pRb facilitated the transactivation of FOXL2 by E2F1, and ITGA2 was the downstream effector of the HMGA2-FOXL2 pathway. HMGA2, FOXL2, and ITGA2 were associated with the TNM classification and staging of gastric cancer and were increased in metastatic lymph nodes and distant metastases. Increased HMGA2, FOXL2, and ITGA2 levels were associated with reduced overall survival periods of patients with gastric cancer.Conclusions: This study demonstrated that the transactivation of FOXL2 driven by interactions between HMGA2 and pRb might exert critical effects on the metastases and EMT of chemoresistant gastric cancer. Blocking the HMGA2-FOXL2-ITGA2 pathway could serve as a new strategy for gastric cancer treatment. Clin Cancer Res; 23(13); 3461-73. ©2017 AACR.

Cooperative Effects of FOXL2 with the Members of TGF-β Superfamily on FSH Receptor mRNA Expression and Granulosa Cell Proliferation from Hen Prehierarchical Follicles

Forkhead box L2 (FOXL2) is a member of the forkhead nuclear factor 3 gene family and plays an essential role in ovarian growth and maturation in mammals. However, its potential effects and regulative mechanism in development of chicken ovarian prehierarchical follicles remain unexplored. In this study, the cooperative effects of FOXL2 with activin A, growth differentiation factor-9 (GDF9) and follistatin, three members of the transforming growth factor beta (TGF-β) superfamily that were previously suggested to exert a critical role in follicle development was investigated. We demonstrated herein, using in-situ hybridization, Northern blot and immunohistochemical analyses of oocytes and granulosa cells in various sizes of prehierarchical follicles that both FOXL2 transcripts and FOXL2 proteins are predominantly expressed in a highly similar expression pattern to that of GDF9 gene. In addition, the FOXL2 transcript was found at lower levels in theca cells in the absence of GDF9. Furthermore, culture of granulosa cells (GCs) from the prehierarchical follicles (6–8 mm) in conditioned medium revealed that in the pcDNA3.0-FOXL2 transfected GCs, there was a more dramatic increase in FSHR mRNA expression after treatment with activin A (10 ng/ml) or GDF9 (100 ng/ml) for 24 h which caused a stimulatory effect on the GC proliferation. In contrast, a significant decrease of FSHR mRNA was detected after treatment with follistatin (50 ng/ml) and resulted in an inhibitory effect on the cell proliferation. The results of this suggested that FOXL2 plays a bidirectional modulating role involved in the intracellular FSHR transcription and GC proliferation via an autocrine regulatory mechanism in a positive or negative manner through cooperation with activin A and/or GDF9, and follistatin in the hen follicle development. This cooperative action may be mediated by the examined Smad signals and simultaneously implicated in modulation of the StAR, CCND2, and CYP11A1 expression.

New insights into implication of the SLIT/ROBO pathway in the prehierarchical follicle development of hen ovary

The SLIT/Roundabout (ROBO) pathway is involved in follicle development of mammalian ovary, and 2 secreted hormones activin A and inhibin A have potential roles in modulation of the SLIT/ROBO system, but the related actions remain poorly understood in bird. The aims of the present study were to examine the spatial and temporal expression of the SLIT ligand genes (SLIT1, SLIT2, and SLIT3) and their receptor ROBO1, ROBO2, ROBO3, and ROBO4 genes in various-sized prehierarchical follicles during hen ovary development and the effects of activin A and inhibin A on the expression of these genes in the cultured hen follicles. Our result demonstrated that the transcripts of the 3 SLIT genes were highly expressed in the developing follicles and expression patterns of the SLIT transcripts were different from those of ROBO genes detected by real-time quantitative reverse transcriptase PCR. Both SLIT and ROBO transcripts were predominantly expressed in oocytes and granulosa cells from the prehierarchichal follicles examined by in situ hybridization. The localization for SLIT and ROBO proteins was revealed by immunohistochemistry similar to the spatial distribution of their transcript. In cultured follicles (4 to 8 mm in diameter), the expression levels of SLIT and ROBO members are hormonally regulated by activin A (10 ng/mL) and/or inhibin A (20 ng/mL) after treatment for 24 h. However, the expression of only SLIT2, SLIT3, and ROBO3 mRNA presented a directly opposite response to activin A and inhibin A hormones. These results indicate that SLIT/ROBO pathway is implicated in the prehierarchical follicular development of the hen ovary by an intrafollicular autocrine and/or paracrine action, and is influenced by activin A and inhibin A hormones.

Roles of binding elements, FOXL2 domains, and interactions with cJUN and SMADs in regulation of FSHβ

We previously identified FOXL2 as a critical component in FSHβ gene transcription. Here, we show that mice deficient in FOXL2 have lower levels of gonadotropin gene expression and fewer LH- and FSH-containing cells, but the same level of other pituitary hormones compared to wild-type littermates, highlighting a role of FOXL2 in the pituitary gonadotrope. Further, we investigate the function of FOXL2 in the gonadotrope cell and determine which domains of the FOXL2 protein are necessary for induction of FSHβ transcription. There is a stronger induction of FSHβ reporter transcription by truncated FOXL2 proteins, but no induction with the mutant lacking the forkhead domain. Specifically, FOXL2 plays a role in activin induction of FSHβ, functioning in concert with activin-induced SMAD proteins. Activin acts through multiple promoter elements to induce FSHβ expression, some of which bind FOXL2. Each of these FOXL2-binding sites is either juxtaposed or overlapping with a SMAD-binding element. We determined that FOXL2 and SMAD4 proteins form a higher order complex on the most proximal FOXL2 site. Surprisingly, two other sites important for activin induction bind neither SMADs nor FOXL2, suggesting additional factors at work. Furthermore, we show that FOXL2 plays a role in synergistic induction of FSHβ by GnRH and activin through interactions with the cJUN component of the AP1 complex that is necessary for GnRH responsiveness. Collectively, our results demonstrate the necessity of FOXL2 for proper FSH production in mice and implicate FOXL2 in integration of transcription factors at the level of the FSHβ promoter.

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.