Genomic exploration of the targets of FOXL2 and ESR2 unveils their implication in cell migration, invasion, and adhesion

Role of ERβ in the ovary and ovary related diseases

Estrogen and estrogen receptors (ERα and ERβ) regulate a multitude of complicated physiological and pathological processes. Jan-Ake Gustafsson's group discovered ERβ in 1996, this crucial finding gives us new insights into the understanding of estrogen signaling. ERβ is highly expressed in the ovary and particularly exists in granulosa cells (GCs). ERβ is a key transcription factor in the maintenance of ovarian granulosa cell growth, differentiation, and homeostasis, and the ovulation function of ovarian follicles and oocytes. Additionally, ERβ can modulate the steroidogenic transcriptional program through phosphorylation and regulate both gonadotropin response and FOXL2 expression within the ovary. In this review, we focus on the role of ERβ in regulating ovarian granulosa cell development and homeostasis, particularly its significance in ovarian cancer (OC), premature ovarian failure (POF), and polycystic ovary syndrome (PCOS). It also highlights the prospects of small molecule compounds targeting ERβ, providing a new strategy for the treatment of ovarian-related diseases.

FOXL2 interaction with different binding partners regulates the dynamics of ovarian development

The transcription factor FOXL2 is required in ovarian somatic cells for female fertility. Differential timing of Foxl2 deletion, in embryonic versus adult mouse ovary, leads to distinctive outcomes, suggesting different roles across development. Here, we comprehensively investigated FOXL2's role through a multi-omics approach to characterize gene expression dynamics and chromatin accessibility changes, coupled with genome-wide identification of FOXL2 targets and on-chromatin interacting partners in somatic cells across ovarian development. We found that FOXL2 regulates more targets postnatally, through interaction with factors regulating primordial follicle formation and steroidogenesis. Deletion of one interactor, ubiquitin-specific protease 7 (Usp7), results in impairment of somatic cell differentiation, germ cell nest breakdown, and ovarian development, leading to sterility. Our datasets constitute a comprehensive resource for exploration of the molecular mechanisms of ovarian development and causes of female infertility.

Deletion of cis-regulatory Element in FOXL2 Promoter in a Chinese Family of Type II Blepharophimosis-ptosis-epicanthus Inversus Syndrome with Polydactyly

Blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) is a relatively uncommon autosomal-dominant genetic disorder, primarily attributed to mutations in the forkhead box L2 (FOXL2) gene. Albeit the involvement of protein-coding regions of FOXL2 has been observed in the majority of BPES cases, whether deficiencies in regulatory elements lead to the pathogenesis remains poorly understood. Herein, an autosomal-dominant BPES type II family was included. Peripheral venous blood has been collected, and genomic DNA has been extracted from leukocytes. A whole exome sequencing analysis has been performed and analyzed (Deposited in NODE database: OER422653). The promoter region of FOXL2 was amplified using polymerase chain reaction (PCR). The luciferase reporter assay was performed to identify the activity of this region. In this study, we present a Chinese family diagnosed with type II BPES, characterized by the presence of small palpebral fissures, ptosis, telecanthus, and epicanthus inversus. Notably, all male individuals within the family display polydactyly. A 225-bp deletion in the 556-bp 5'-upstream to transcription start site of FOXL2 , decorated by multiple histone modifications, was identified in affected members of the family. This deletion significantly decreased FOXL2 promoter activity, as measured by the luciferase assay. Conclusively, a novel 255-bp-deletion of the FOXL2 promoter was identified in Chinese families with BPES. Our results expand the spectrum of known FOXL2 mutations and provide additional insight into the genotype-phenotype relationships of the BPES pathogenesis. In addition, this study indicates the important role of genetic screening of cis-regulatory elements in testing heritable diseases.

The forkhead DNA-binding domain binds specific G2-rich RNA sequences

Transcription factors contain a DNA-binding domain ensuring specific recognition of DNA target sequences. The family of forkhead (FOX) transcription factors is composed of dozens of paralogs in mammals. The forkhead domain (FHD) is a segment of about 100 amino acids that binds an A-rich DNA sequence. Using DNA and RNA PCR-SELEX, we show that recombinant FOXL2 proteins, either wild-type or carrying the oncogenic variant C134W, recognize similar DNA-binding sites. This suggests that the oncogenic variant does not alter the intrinsic sequence-specificity of FOXL2. Most importantly, we show that FOXL2 binds G2-rich RNA sequences whereas it virtually fails to bind similar sequences in DNA chemistry. Interestingly, a statistically significant subset of genes responding to the knock-down of FOXL2/Foxl2 harbor such G2-rich sequences and are involved in crucial signaling pathways and cellular processes. In addition, we show that FOXA1, FOXO3a and chimeric FOXL2 proteins containing the FHD of the former are also able to interact with some of the preferred FOXL2-binding sequences. Our results point to an unexpected and novel characteristic of the forkhead domain, the biological relevance of which remains to be explored.

Core conserved transcriptional regulatory networks define the invasive trophoblast cell lineage

The invasive trophoblast cell lineages in rat and human share crucial responsibilities in establishing the uterine-placental interface of the hemochorial placenta. These observations have led to the rat becoming an especially useful animal model for studying hemochorial placentation. However, our understanding of similarities or differences between regulatory mechanisms governing rat and human invasive trophoblast cell populations is limited. In this study, we generated single-nucleus ATAC-seq data from gestation day 15.5 and 19.5 rat uterine-placental interface tissues, and integrated the data with single-cell RNA-seq data generated at the same stages. We determined the chromatin accessibility profiles of invasive trophoblast, natural killer, macrophage, endothelial and smooth muscle cells, and compared invasive trophoblast chromatin accessibility with extravillous trophoblast cell accessibility. In comparing chromatin accessibility profiles between species, we found similarities in patterns of gene regulation and groups of motifs enriched in accessible regions. Finally, we identified a conserved gene regulatory network in invasive trophoblast cells. Our data, findings and analysis will facilitate future studies investigating regulatory mechanisms essential for the invasive trophoblast cell lineage.

CORE CONSERVED TRANSCRIPTIONAL REGULATORY NETWORKS DEFINE THE INVASIVE TROPHOBLAST CELL LINEAGE

The invasive trophoblast cell lineage in rat and human share crucial responsibilities in establishing the uterine-placental interface of the hemochorial placenta. These observations have led to the rat becoming an especially useful animal model to study hemochorial placentation. However, our understanding of similarities or differences between regulatory mechanisms governing rat and human invasive trophoblast cell populations is limited. In this study, we generated single-nucleus (sn) ATAC-seq data from gestation day (gd) 15.5 and 19.5 rat uterine-placental interface tissues and integrated the data with single-cell RNA-seq data generated at the same stages. We determined the chromatin accessibility profiles of invasive trophoblast, natural killer, macrophage, endothelial, and smooth muscle cells, and compared invasive trophoblast chromatin accessibility to extravillous trophoblast (EVT) cell accessibility. In comparing chromatin accessibility profiles between species, we found similarities in patterns of gene regulation and groups of motifs enriched in accessible regions. Finally, we identified a conserved gene regulatory network in invasive trophoblast cells. Our data, findings and analysis will facilitate future studies investigating regulatory mechanisms essential for the invasive trophoblast cell lineage.

The Oncogenic FOXL2 C134W Mutation Is a Key Driver of Granulosa Cell Tumors

Adult-type granulosa cell tumors (AGCT) are the most common type of malignant ovarian sex cord-stromal tumors. Most AGCTs carry the somatic variant c.402C>G (p.C134W) affecting the transcription factor FOXL2. Germline dominant variants in FOXL2 are responsible for blepharophimosis syndrome, which is characterized by underdevelopment of the eyelid. In this work, we generated a mouse model harboring the C134W variant of FOXL2 to evaluate in vivo the poorly understood oncogenic role of FOXL2. The mutation was dominant regarding eyelid hypoplasia, reminiscent of blepharophimosis syndrome. Interestingly, Foxl2+/C134W female mice had reduced fertility and developed AGCTs through a progression from abnormal ovaries with aberrant granulosa cells to ovaries with stromal hyperplasia and atypia and on to tumors in adut mice. The genes dysregulated in mouse AGCTs exhibited the hallmarks of cancer and were consistent with a gain-of-function of the mutated allele affecting TGFβ signaling. A comparison of these data with previous results on human AGCTs indicated similar deregulated pathways. Finally, a mutational analysis of mouse AGCT transcriptomic data suggested the absence of additional driver mutations apart from FOXL2-C134W. These results provide a clear in vivo example in which a single mutational hit triggers tumor development associated with profound transcriptomic alterations.

SIGNIFICANCE

A newly generated mouse model carrying a FOXL2 mutation characteristic of adult-type granulosa cell tumors shows that FOXL2 C134W shifts the transcriptome towards a signature of granulosa cell cancer and drives tumorigenesis.

Non-Coding Genome, Transcription Factors, and Sex Determination

In vertebrates, gonadal sex determination is the process by which transcription factors drive the choice between the testicular and ovarian identity of undifferentiated somatic progenitors through activation of 2 different transcriptional programs. Studies in animal models suggest that sex determination always involves sex-specific transcription factors that activate or repress sex-specific genes. These transcription factors control their target genes by recognizing their regulatory elements in the non-coding genome and their binding motifs within their DNA sequence. In the last 20 years, the development of genomic approaches that allow identifying all the genomic targets of a transcription factor in eukaryotic cells gave the opportunity to globally understand the function of the nuclear proteins that control complex genetic programs. Here, the major transcription factors involved in male and female vertebrate sex determination and the genomic profiling data of mouse gonads that contributed to deciphering their transcriptional regulation role will be reviewed.