The 'Marx' of Groucho on development and disease

Notch2 Regulates the Function of Bovine Follicular Granulosa Cells via the Wnt2/β-Catenin Signaling Pathway

Ovarian follicular GCs are strongly implicated in the growth, development, and atresia of ovarian follicles. The Wnt/β-catenin and Notch signaling pathways participate in GC proliferation, differentiation, apoptosis, and steroid hormone production during follicular development. However, the crosstalk between Wnt and Notch signaling in GCs remains unclear. This study investigated this crosstalk and the roles of these pathways in apoptosis, cell cycle progression, cell proliferation, and steroid hormone secretion in bovine follicular GCs. The interaction between β-catenin and Notch2 in GCs was assessed by overexpressing CTNNB1, which encodes β-catenin. The results showed that inhibiting the Notch pathway by Notch2 silencing in GCs arrested the cell cycle, promoted apoptosis, reduced progesterone (P4) production, and inhibited the Wnt2-mediated Wnt/β-catenin pathway in GCs. IWR-1 inhibited Wnt2/β-catenin and Notch signaling, reduced GC proliferation, stimulated apoptosis, induced G1 cell cycle arrest, and reduced P4 production. CTNNB1 overexpression had the opposite effect and increased 17β-estradiol (E2) production and Notch2 protein expression. Co-immunoprecipitation assays revealed that Notch2 interacted with β-catenin. These results elucidate the crosstalk between the Wnt/β-catenin and Notch pathways and the role of these pathways in bovine follicular GC development.

The transcriptional cofactor Tle3 reciprocally controls effector and central memory CD8+ T cell fates

Antigen-experienced CD8+ T cells form effector and central memory T cells (TEM and TCM cells, respectively); however, the mechanism(s) controlling their lineage plasticity remains incompletely understood. Here we show that the transcription cofactor Tle3 critically regulates TEM and TCM cell fates and lineage stability through dynamic redistribution in antigen-responding CD8+ T cell genome. Genetic ablation of Tle3 promoted CD8+ TCM cell formation at the expense of CD8+ TEM cells. Lineage tracing showed that Tle3-deficient CD8+ TEM cells underwent accelerated conversion into CD8+ TCM cells while retaining robust recall capacity. Tle3 acted as a coactivator for Tbet to increase chromatin opening at CD8+ TEM cell-characteristic sites and to activate CD8+ TEM cell signature gene transcription, while engaging Runx3 and Tcf1 to limit CD8+ TCM cell-characteristic molecular features. Thus, Tle3 integrated functions of multiple transcription factors to guard lineage fidelity of CD8+ TEM cells, and manipulation of Tle3 activity could favor CD8+ TCM cell production.

Tle4 controls both developmental acquisition and early post-natal maturation of corticothalamic projection neuron identity

Identities of distinct neuron subtypes are specified during embryonic development, then maintained during post-natal maturation. In cerebral cortex, mechanisms controlling early acquisition of neuron-subtype identities have become increasingly understood. However, mechanisms controlling neuron-subtype identity stability during post-natal maturation are largely unexplored. We identify that Tle4 is required for both early acquisition and post-natal stability of corticothalamic neuron-subtype identity. Embryonically, Tle4 promotes acquisition of corticothalamic identity and blocks emergence of core characteristics of subcerebral/corticospinal projection neuron identity, including gene expression and connectivity. During the first post-natal week, when corticothalamic innervation is ongoing, Tle4 is required to stabilize corticothalamic neuron identity, limiting interference from differentiation programs of developmentally related neuron classes. We identify a deacetylation-based epigenetic mechanism by which TLE4 controls Fezf2 expression level by corticothalamic neurons. This contributes to distinction of cortical output subtypes and ensures identity stability for appropriate maturation of corticothalamic neurons.

Roles of transducin-like enhancer of split (TLE) family proteins in tumorigenesis and immune regulation

Mammalian transducin-like enhancer of split family proteins (TLEs) are homologous to Drosophila Groucho (Gro) and are essential transcriptional repressors. Seven TLE family members, TLE1-7, have been identified to date. These proteins do not bind DNA directly; instead, they bind a set of transcription factors and thereby inhibit target gene expression. Loss of TLEs in mice usually leads to defective early development; however, TLE functions in developmentally mature cells are unclear. Recent studies have revealed that TLEs are dysregulated in certain human cancer types and may function as oncogenes or tumor suppressors in different contexts. TLE levels also affect the efficacy of cancer treatments and the development of drug resistance. In addition, TLEs play critical roles in the development and function of immune cells, including macrophages and lymphocytes. In this review, we provide updates on the expression, function, and mechanism of TLEs; discuss the roles played by TLEs in tumorigenesis and the inflammatory response; and elaborate on several TLE-associated signaling pathways, including the Notch, Wnt, and MAPK pathways. Finally, we discuss potential strategies for targeting TLEs in cancer therapy.

Tle4z1 Facilitate the Male Sexual Differentiation of Chicken Embryos

Background

Sex differentiation is a complex and precisely regulated process by multiple genes in chicken. However, it is still unclear on the key genes of sex differentiation.

Objective

To explore the function of Tle4z1 screened by RNA-seq sequencing on sex differentiation during the development of chicken embryos.

Methods

Tle4z1 was differentially expressed from the RNA-seq of ESCs and PGCs in male and female chickens. Then, we established an effective method to overexpression or knocking down the expression of Tle4z1 in ovo and in vitro, respectively. Histomorphological observation, qRT-PCR and ELISA were applied to detect the function of Tle4z1 in the process of male sex differentiation by injecting vectors into embryos at day 0.

Results

It showed that Tle4z1 has significant male preference in embryonic day 4.5, such phenomenon persisted during the growth period of chicken embryos. Morphological observation results showed that the gonads on both sides of genetic male (ZZ) embryos with Tle4z1 knocking down developed asymmetrically, the gonadal cortex became thicker showing the typical characteristics of genetic female (ZW) gonads. Furthermore, the expression of Cyp19a1, which dominates female differentiation, was significantly increased, while the expression of male marker genes Dmrt1, Sox9, WT1 and AR was significantly downregulated. In addition, the concentration of testosterone also significantly decreased, which was positively correlated with the expression of Tle4z1 (P < 0.01). Conversely, the ZW embryo showed defeminized development when Tle4z1 was overexpressed.

Conclusion

We prove that the Tle4z1 is a novel gene through the male sexual differentiation via gene regulation process and synthesis of testosterone, which construct the basis for understanding the molecular mechanism of sex differentiation in chickens.

Maternal effect factors that contribute to oocytes developmental competence: an update

Oocyte developmental competence is defined as the capacity of the female gamete to be fertilized and sustain development to the blastocyst stage. Epigenetic reprogramming, a correct cell division pattern, and an efficient DNA damage response are all critical events that, before embryonic genome activation, are governed by maternally inherited factors such as maternal-effect gene (MEG) products. Although these molecules are stored inside the oocyte until ovulation and exert their main role during fertilization and preimplantation development, some of them are already functioning during folliculogenesis and oocyte meiosis resumption. This mini review summarizes the crucial roles played by MEGs during oocyte maturation, fertilization, and preimplantation development with a direct/indirect effect on the acquisition or maintenance of oocyte competence. Our aim is to inspire future research on a topic with potential clinical perspectives for the prediction and treatment of female infertility.

A proteomics study of the subacute toxicity of rat brain after long-term exposure of Gelsemium elegans

BACKGROUND

Gelsemium elegans (G. elegans) has been shown to have strong pharmacological and pharmacodynamic effects in relevant studies both in China and USA. G. elegans has been used as a traditional medicine to treat a variety of diseases and even has the potential to be an alternative to laboratory synthesized drugs. However, its toxicity severely limited its application and development. At present, there is little attention paid to protein changes in toxicity.

AIM

This study investigated the toxicity effects after long-term exposure of G. elegans of the rat brain through proteomic.

METHOD

11 differential abundance proteins were detected, among which 8 proteins were higher in the G. elegans- exposure group than in the control group, including Ig-like domain-containing protein (N/A), receptor-type tyrosine-protein phosphatase C (Ptprc), disheveled segment polarity protein 3 (Dvl3), trafficking protein particle complex 12 (Trappc12), seizure-related 6 homolog-like (Sez6l), transmembrane 9 superfamily member 4 (Tm9sf4), DENN domain-containing protein 5A (Dennd5a) and Tle4, whereas the other 3 proteins do the opposite including Golgi to ER traffic protein 4 (Get4), vacuolar protein sorting 4 homolog B (Vps4b) and cadherin-related 23 (CDH23). Furthermore, we performed validation of WB analysis on the key protein CDH23.

RESULT

Finally, only fewer proteins and related metabolic pathways were affected, indicating that there was no accumulative toxicity of G. elegans. G. elegans has the potential to develop and utilize of its pharmacological activity. CHD23, however, is a protein associated with hearing.

CONCLUSION

Whether the hearing impairment is a sequela after G. elegans exposure remains to be further studied.

The prognostic role of the Transducin-like Enhancer of split protein family in lung adenocarcinoma

Background

Lung cancer claims more lives than any other cancer worldwide. Lung adenocarcinoma (LUAD) accounts for approximately 40% of all lung cancers. Members of the Transducin-like Enhancer of split (TLE) protein family repress transcription through multiple mechanisms; however, their prognostic value in LUAD is still unclear.

Methods

A dataset from The Cancer Genome Atlas was used to analyze the relationship between the expression of TLE family members and outcomes of LUAD. The expression of TLE family members in 59 normal and 513 tumor samples in the TCGA dataset was selected. For paired analysis, 57 normal and 57 tumor paired tissues were selected. Gene Ontology (GO) term and Reactome pathway enrichment analyses of the TLE family members were performed. Progression-free survival (PFS) and overall survival (OS) served as endpoints in this study. All statistical analyses were performed with R 3.6.0.

Results

The expression levels of TLE family proteins differed between 59 normal and 513 tumor samples. High TLE1 and low TLE2 levels were associated with poor progression-free and OS (all P<0.050). Multivariate analysis demonstrated that high TLE1 expression and low TLE2 expression were independent risk factors for a poor outcome in LUAD. Moreover, the combined expression of these two proteins was a good tool for prognostication.

Conclusions

High TLE1 expression and low TLE2 are independent adverse prognostic factors in LUAD and can serve as prognostic biomarkers.

Groucho co-repressor proteins regulate β cell development and proliferation by repressing Foxa1 in the developing mouse pancreas

Groucho-related genes (GRGs) are transcriptional co-repressors that are crucial for many developmental processes. Several essential pancreatic transcription factors are capable of interacting with GRGs; however, the in vivo role of GRG-mediated transcriptional repression in pancreas development is still not well understood. In this study, we used complex mouse genetics and transcriptomic analyses to determine that GRG3 is essential for β cell development, and in the absence of Grg3 there is compensatory upregulation of Grg4 Grg3/4 double mutant mice have severe dysregulation of the pancreas gene program with ectopic expression of canonical liver genes and Foxa1, a master regulator of the liver program. Neurod1, an essential β cell transcription factor and predicted target of Foxa1, becomes downregulated in Grg3/4 mutants, resulting in reduced β cell proliferation, hyperglycemia, and early lethality. These findings uncover novel functions of GRG-mediated repression during pancreas development.

Temporal mechanisms of myogenic specification in human induced pluripotent stem cells

Understanding the mechanisms of myogenesis in human induced pluripotent stem cells (hiPSCs) is a prerequisite to achieving patient-specific therapy for diseases of skeletal muscle. hiPSCs of different origin show distinctive kinetics and ability to differentiate into myocytes. To address the unique cellular and temporal context of hiPSC differentiation, we perform a longitudinal comparison of the transcriptomic profiles of three hiPSC lines that display differential myogenic specification, one robust and two blunted. We detail temporal differences in mechanisms that lead to robust myogenic specification. We show gene expression signatures of putative cell subpopulations and extracellular matrix components that may support myogenesis. Furthermore, we show that targeted knockdown of ZIC3 at the outset of differentiation leads to improved myogenic specification in blunted hiPSC lines. Our study suggests that β-catenin transcriptional cofactors mediate cross-talk between multiple cellular processes and exogenous cues to facilitate specification of hiPSCs to mesoderm lineage, leading to robust myogenesis.

Differential functions of TLE1 and TLE3 depending on a specific phosphorylation site

Mammalian Transducin-like enhancer of split (TLE) confer global repression of numerous target genes in conjunction with a myriad of DNA-binding repressors. These factors have a major role in the regulation of multiple signal transduction pathways. Evidence have been obtained regarding the possible role of some of these proteins in cancer. TLE3 was suggested as a marker for increased chemosensitivity from pathological studies. Here we demonstrate, using the TCGA data base, differences in expression of this gene compared to TLE1 in several cancers. In-vitro transduction of a retrovirus encoding TLE3 to A549 lung cancer cells increased paclitaxel effectivity while TLE1 introduction to these cells decreased it. While TLE1 and TLE3 share ∼80% amino acid identity, we show that mutating or reconstituting an amino-terminal phosphorylation site, which is present only in TLE1 but absent from TLE3, and is evolutionary conserved, converts the activity of TLE1 to that of TLE3 like and vice versa. We repeated these results in an adipocytes differentiation system. Our results reveal how a single phosphorylation site can confer distinct qualitative or quantitative activities on highly homologous transcriptional regulators.

Reduction of T-Box 15 gene expression in tumor tissue is a prognostic biomarker for patients with hepatocellular carcinoma

Genome-wide analysis is widely applied to detect molecular alterations during oncogenesis and tumor progression. We analyzed DNA methylation profiles of hepatocellular carcinoma (HCC), and investigated the clinical role of most heypermethylated of tumor, encodes T-box 15 (TBX15), which was originally involved in mesodermal differentiation. We conducted a genome-wide analysis of DNA methylation of tumor and non-tumor tissue of 15 patients with HCC, and revealed TBX15 was the most hypermethylated gene of tumor (Beta-value in tumor tissue = 0.52 compared with non-tumor tissue). Another validation set, which comprised 58 HCC with radical resection, was analyzed to investigate the relationships between tumor phenotype and TBX15 mRNA expression. TBX15 mRNA levels in tumor tissues were significantly lower compared with those of nontumor tissues (p < 0.0001). When we assigned a cutoff value = 0.5-fold, the overall survival 5-year survival rates of the low-expression group (n = 17) were significantly shorter compared with those of the high-expression group (n = 41) (43.3% vs. 86.2%, p = 0.001). Multivariate analysis identified low TBX15 expression as an independent prognostic factor for overall and disease-free survival. Therefore, genome-wide DNA methylation profiling indicates that hypermethylation and reduced expression of TBX15 in tumor tissue represents a potential biomarker for predicting poor survival of patients with HCC.

Limited Availability of General Co-Repressors Uncovered in an Overexpression Context during Wing Venation in Drosophila melanogaster

Cell fate is determined by the coordinated activity of different pathways, including the conserved Notch pathway. Activation of Notch results in the transcription of Notch targets that are otherwise silenced by repressor complexes. In Drosophila, the repressor complex comprises the transcription factor Suppressor of Hairless (Su(H)) bound to the Notch antagonist Hairless (H) and the general co-repressors Groucho (Gro) and C-terminal binding protein (CtBP). The latter two are shared by different repressors from numerous pathways, raising the possibility that they are rate-limiting. We noted that the overexpression during wing development of H mutants H^dNT and H^LD compromised in Su(H)-binding induced ectopic veins. On the basis of the role of H as Notch antagonist, overexpression of Su(H)-binding defective H isoforms should be without consequence, implying different mechanisms but repression of Notch signaling activity. Perhaps excess H protein curbs general co-repressor availability. Supporting this model, nearly normal wings developed upon overexpression of H mutant isoforms that bound neither Su(H) nor co-repressor Gro and CtBP. Excessive H protein appeared to sequester general co-repressors, resulting in specific vein defects, indicating their limited availability during wing vein development. In conclusion, interpretation of overexpression phenotypes requires careful consideration of possible dominant negative effects from interception of limiting factors.

Identifying the RNA signatures of coronary artery disease from combined lncRNA and mRNA expression profiles

Coronary artery disease (CAD) is the most common cardiovascular disease. CAD research has greatly progressed during the past decade. mRNA is a traditional and popular pipeline to investigate various disease, including CAD. Compared with mRNA, lncRNA has better stability and thus may serve as a better disease indicator in blood. Investigating potential CAD-related lncRNAs and mRNAs will greatly contribute to the diagnosis and treatment of CAD. In this study, a computational analysis was conducted on patients with CAD by using a comprehensive transcription dataset with combined mRNA and lncRNA expression data. Several machine learning algorithms, including feature selection methods and classification algorithms, were applied to screen for the most CAD-related RNA molecules. Decision rules were also reported to provide a quantitative description about the effect of these RNA molecules on CAD progression. These new findings (CAD-related RNA molecules and rules) can help understand mRNA and lncRNA expression levels in CAD.

Regulated repression governs the cell fate promoter controlling yeast meiosis

Intrinsic signals and external cues from the environment drive cell fate decisions. In budding yeast, the decision to enter meiosis is controlled by nutrient and mating-type signals that regulate expression of the master transcription factor for meiotic entry, IME1. How nutrient signals control IME1 expression remains poorly understood. Here, we show that IME1 transcription is regulated by multiple sequence-specific transcription factors (TFs) that mediate association of Tup1-Cyc8 co-repressor to its promoter. We find that at least eight TFs bind the IME1 promoter when nutrients are ample. Remarkably, association of these TFs is highly regulated by different nutrient cues. Mutant cells lacking three TFs (Sok2/Phd1/Yap6) displayed reduced Tup1-Cyc8 association, increased IME1 expression, and earlier onset of meiosis. Our data demonstrate that the promoter of a master regulator is primed for rapid activation while repression by multiple TFs mediating Tup1-Cyc8 recruitment dictates the fate decision to enter meiosis.

Elucidating the pathogenic and biomarker potentials of FOXG1 in glioblastoma

Glioblastoma (GB) is an extremely pugnacious brain cancer originating from neural stem (NS) cell-like cells. Forkhead box G1 (FOXG1; previously recognized as BF-1, qin, Chicken Brain Factor 1, or XBF-1 and renamed FOXG1 for mouse and human, and FoxG1 for other chordates) is an evolutionary preserved transcription factor driven from the forkhead box group of proteins FOXG1 modulates the speed of neurogenesis by maintaining progenitor cells in a proliferative mode as well as obstructing their differentiation into neurons during the initial periods of cortical formation. FOXG1 has been implicated in the formation of central nervous system (CNS) tumors and precisely GBs. Pathophysiologically, joint actions of FOXG1 and phosphatidylinositol- 3-kinases (PI3K) intermediate in intrinsic resistance of human GB cells to transforming growth factor-beta (TGF-β) stimulation of cyclin-dependent kinase inhibitor 1(p21Cip1) as well as growth inhibition. FOXG1 and NOTCH signaling pathways may functionally interrelate at different stages to facilitate gliomagenesis. Furthermore, FoxG1 actively contributed to the formation of transcription suppression complexes with corepressors of the Groucho/transducin-like Enhancer of split (Gro/TLEs). Also, FOXG1 was stimulated by Gro/TLE1 and abridged by Grg6. FOXG1 silencing in brain tumor-initiating cells (BTICs) also resulted in diminished secretion of markers characteristic undifferentiated natural neural stem/progenitor cells (NSPC) states, such as Oligodendrocyte transcription factor (OLIG2), (sex determining region Y)-box 2. (SOX2) and B lymphoma Mo-MLV insertion region 1 homolog (BMI1). This review therefore focuses on the pathogenic and biomarker potentials of FOXG1 in GB.

dTcf/Pangolin suppresses growth and tumor formation in Drosophila

Wnt/Wingless (Wg) signaling controls many aspects of animal development and is deregulated in different human cancers. The transcription factor dTcf/Pangolin (Pan) is the final effector of the Wg pathway in Drosophila and has a dual role in regulating the expression of Wg target genes. In the presence of Wg, dTcf/Pan interacts with β-catenin/Armadillo (Arm) and induces the transcription of Wg targets. In absence of Wg, dTcf/Pan partners with the transcriptional corepressor TLE/Groucho (Gro) and inhibits gene expression. Here, we use the wing imaginal disk of Drosophila as a model to examine the functions that dTcf/Pan plays in a proliferating epithelium. We report a function of dTcf/Pan in growth control and tumorigenesis. Our results show that dTcf/Pan can limit tissue growth in normal development and suppresses tumorigenesis in the context of oncogene up-regulation. We identify the conserved transcription factors Sox box protein 15 (Sox15) and Ftz transcription factor 1 (Ftz-f1) as genes controlled by dTcf/Pan involved in tumor development. In conclusion, this study reports a role for dTcf/Pan as a repressor of normal and oncogenic growth and identifies the genes inducing tumorigenesis downstream of dTcf/Pan.

Hes1 attenuates type I IFN responses via VEGF-C and WDFY1

Transcription factor Hes1 acts as a homeostatic negative regulator of type I interferon production to restrain interferon-mediated immune responses, including antiviral immunity and autoimmune conditions. Mechanistically, Hes1 suppresses interferon expression by targeting a regulatory circuit composed of WDFY1 and VEGF-C.

Induction of type I interferons (IFNs) is critical for eliciting competent immune responses, especially antiviral immunity. However, uncontrolled IFN production contributes to pathogenesis of autoimmune and inflammatory diseases. We found that transcription factor Hes1 suppressed production of type I IFNs and expression of IFN-stimulated genes. Functionally, Hes1-deficient mice displayed a heightened IFN signature in vivo, mounted enhanced resistance against encephalomyocarditis virus infection, and showed signs of exacerbated experimental lupus nephritis. Mechanistically, Hes1 did not suppress IFNs via direct transcriptional repression of IFN-encoding genes. Instead, Hes1 attenuated activation of TLR upstream signaling by inhibition of an adaptor molecule, WDFY1. Genome-wide assessment of Hes1 occupancy revealed that suppression of WDFY1 was secondary to direct binding and thus enhancement of expression of VEGF-C by Hes1, making Vegfc a rare example of an Hes1 positively regulated gene. In summary, these results identified Hes1 as a homeostatic negative regulator of type I IFNs for the maintenance of immune balance in the context of antiviral immunity and autoimmune diseases.

Spatial distribution of the full-length members of the Grg family during embryonic neurogenesis reveals a "Grg-mediated repression map" in the mouse telencephalon

The full-length members of the Groucho/Transducin-like Enhancer of split gene family, namely Grg1-4, encode nuclear corepressors that act either directly, via interaction with transcription factors, or indirectly by modifying histone acetylation or chromatin structure. In this work we describe a detailed expression analysis of Grg1-4 family members during embryonic neurogenesis in the developing murine telencephalon. Grg1-4 presented a unique, complex yet overlapping expression pattern; Grg1 and Grg3 were mainly detected in the proliferative zones of the telencephalon, Grg2 mainly in the subpallium and finally, Grg4 mainly in the subpallial post mitotic neurons. In addition, comparative analysis of the expression of Grg1-4 revealed that, at these stages, distinct telencephalic progenitor domains or structures are characterized by the presence of different combinations of Grg repressors, thus forming a “Grg-mediated repression map”.

Groucho related gene 5 (GRG5) is involved in embryonic and neural stem cell state decisions

Groucho related gene 5 (GRG5) is a multifunctional protein that has been implicated in late embryonic and postnatal mouse development. Here, we describe a previously unknown role of GRG5 in early developmental stages by analyzing its function in stem cell fate decisions. By both loss and gain of function approaches we demonstrate that ablation of GRG5 deregulates the Embryonic Stem Cell (ESC) pluripotent state whereas its overexpression leads to enhanced self-renewal and acquisition of cancer cell-like properties. The malignant characteristics of teratomas generated by ESCs that overexpress GRG5 reveal its pro-oncogenic potential. Furthermore, transcriptomic analysis and cell differentiation approaches underline GRG5 as a multifaceted signaling regulator that represses mesendodermal-related genes. When ESCs exit pluripotency, GRG5 promotes neuroectodermal specification via Wnt and BMP signaling suppression. Moreover, GRG5 promotes the neuronal reprogramming of fibroblasts and maintains the self-renewal of Neural Stem Cells (NSCs) by sustaining the activity of Notch/Hes and Stat3 signaling pathways. In summary, our results demonstrate that GRG5 has pleiotropic roles in stem cell biology functioning as a stemness factor and a neural fate specifier.

Tle corepressors are differentially partitioned to instruct CD8+ T cell lineage choice and identity

Xing et al demonstrate the requirements for Tle transcriptional corepressors in CD8⁺ T cell development. Tle proteins are differentially partitioned to the Runx and Tcf/Lef complexes to promote CD8⁺ lineage choice and establish CD8⁺ T cell identity, respectively.

Tle/Groucho proteins are transcriptional corepressors interacting with Tcf/Lef and Runx transcription factors, but their physiological roles in T cell development remain unknown. Conditional targeting of Tle1, Tle3 and Tle4 revealed gene dose–dependent requirements for Tle proteins in CD8⁺ lineage cells. Upon ablating all three Tle proteins, generation of CD8⁺ T cells was greatly diminished, largely owing to redirection of MHC-I–selected thymocytes to CD4⁺ lineage; the remaining CD8-positive T cells showed aberrant up-regulation of CD4⁺ lineage-associated genes including Cd4, Thpok, St8sia6, and Foxp3. Mechanistically, Tle3 bound to Runx-occupied Thpok silencer, in post-selection double-positive thymocytes to prevent excessive ThPOK induction and in mature CD8⁺ T cells to silence Thpok expression. Tle3 also bound to Tcf1-occupied sites in a few CD4⁺ lineage-associated genes, including Cd4 silencer and St8sia6 introns, to repress their expression in mature CD8⁺ T cells. These findings indicate that Tle corepressors are differentially partitioned to Runx and Tcf/Lef complexes to instruct CD8⁺ lineage choice and cooperatively establish CD8⁺ T cell identity, respectively.

Characterization of a FOXG1:TLE1 transcriptional network in glioblastoma-initiating cells

Glioblastoma (GBM) is the most common and deadly malignant brain cancer of glial cell origin, with a median patient survival of less than 20 months. Transcription factors FOXG1 and TLE1 promote GBM propagation by supporting maintenance of brain tumour-initiating cells (BTICs) with stem-like properties. Here, we characterize FOXG1 and TLE1 target genes in GBM patient-derived BTICs using ChIP-Seq and RNA-Seq approaches. These studies identify 150 direct FOXG1 targets, several of which are also TLE1 targets, involved in cell proliferation, differentiation, survival, chemotaxis and angiogenesis. Negative regulators of NOTCH signalling, including CHAC1, are among the transcriptional repression targets of FOXG1:TLE1 complexes, suggesting a crosstalk between FOXG1:TLE1 and NOTCH-mediated pathways in GBM. These results provide previously unavailable insight into the transcriptional programs underlying the tumour-promoting functions of FOXG1:TLE1 in GBM.

Wor1 establishes opaque cell fate through inhibition of the general co-repressor Tup1 in Candida albicans

The pathogenic fungus Candida albicans can undergo phenotypic switching between two heritable states: white and opaque. This phenotypic plasticity facilitates its colonization in distinct host niches. The master regulator WOR1 is exclusively expressed in opaque phase cells. Positive feedback regulation by Wor1 on the WOR1 promoter is essential for opaque formation, however the underlying mechanism of how Wor1 functions is not clear. Here, we use tandem affinity purification coupled with mass spectrometry to identify Wor1-interacting proteins. Tup1 and its associated complex proteins are found as the major factors associated with Wor1. Tup1 occupies the same regions of the WOR1 promoter as Wor1 preferentially in opaque cells. Loss of Tup1 is sufficient to induce the opaque phase, even in the absence of Wor1. This is the first such report of a bypass of Wor1 in opaque formation. These genetic analyses suggest that Tup1 is a key repressor of the opaque state, and Wor1 functions via alleviating Tup1 repression at the WOR1 promoter. Opaque cells convert to white en masse at 37°C. We show that this conversion occurs only in the presence of glycolytic carbon sources. The opaque state is stabilized when cells are cultured on non-glycolytic carbon sources, even in a MTLa/α background. We further show that temperature and carbon source affect opaque stability by altering the levels of Wor1 and Tup1 at the WOR1 promoter. We propose that Wor1 and Tup1 form the core regulatory circuit controlling the opaque transcriptional program. This model provides molecular insights on how C. albicans adapts to different host signals to undergo phenotypic switching for colonization in distinct host niches.

Role of the extracellular matrix in cancer-associated epithelial to mesenchymal transition phenomenon

The epithelial to mesenchymal transition (EMT) program is a crucial component in the processes of morphogenesis and embryonic development. The transition of epithelial to mesenchymal phenotype is associated with numerous structural and functional changes, including loss of cell polarity and tight cell-cell junctions, the acquisition of invasive abilities, and the expression of mesenchymal proteins. The switch between the two phenotypes is involved in human pathology and is crucial for cancer progression. Extracellular matrices (ECMs) are multi-component networks that surround cells in tissues. These networks are obligatory for cell survival, growth, and differentiation as well as tissue organization. Indeed, the ECM suprastructure, in addition to its supportive role, can process and deliver a plethora of signals to cells, which ultimately regulate their behavior. Importantly, the ECM derived signals are critically involved in the process of EMT during tumorigenesis. This review discusses the multilayer interaction between the ECM and the EMT process, focusing on contributions of discrete mediators, a strategy that may identify novel potential target molecules. Developmental Dynamics 247:368-381, 2018. © 2017 Wiley Periodicals, Inc.

A D53 repression motif induces oligomerization of TOPLESS corepressors and promotes assembly of a corepressor-nucleosome complex

TOPLESS are tetrameric plant corepressors of the conserved Tup1/Groucho/TLE (transducin-like enhancer of split) family. We show that they interact through their TOPLESS domains (TPDs) with two functionally important ethylene response factor-associated amphiphilic repression (EAR) motifs of the rice strigolactone signaling repressor D53: the universally conserved EAR-3 and the monocot-specific EAR-2. We present the crystal structure of the monocot-specific EAR-2 peptide in complex with the TOPLESS-related protein 2 (TPR2) TPD, in which the EAR-2 motif binds the same TPD groove as jasmonate and auxin signaling repressors but makes additional contacts with a second TPD site to mediate TPD tetramer-tetramer interaction. We validated the functional relevance of the two TPD binding sites in reporter gene assays and in transgenic rice and demonstrate that EAR-2 binding induces TPD oligomerization. Moreover, we demonstrate that the TPD directly binds nucleosomes and the tails of histones H3 and H4. Higher-order assembly of TPD complexes induced by EAR-2 binding markedly stabilizes the nucleosome-TPD interaction. These results establish a new TPD-repressor binding mode that promotes TPD oligomerization and TPD-nucleosome interaction, thus illustrating the initial assembly of a repressor-corepressor-nucleosome complex.

TLE1 function and therapeutic potential in cancer

Groucho (Gro)/Transducin-like enhancer of split (TLE) family proteins act as co-repressors of many transcription factors, and are involved in key signaling pathways. TLE1 negatively regulates inflammation and has potential roles in various diseases, including cancer. Previous studies suggest TLE1 could be used as a diagnostic marker and is a possible therapeutic target in various malignancies. It is therefore important to elucidate the mechanisms underlying TLE1 function during cancer initiation and metastasis. In this review, we highlight the functions of TLE1 in cancer and explore targeted approaches for cancer diagnosis and treatment. In particular, we discuss the TLE1 function in pancreatic cancer.

Ras-Erk signaling induces phosphorylation of human TLE1 and downregulates its repressor function

Signaling mediated by the Ras-extracellular signal-regulated kinase (Erk) pathway often leads to the phosphorylation of transcriptional regulators, thereby modulating their activity and causing concerted changes in gene expression. In Drosophila, the induction of multiple Ras-Erk pathway target genes depends on prior phosphorylation of the general co-repressor Groucho, a modification that downregulates its repressive function. Here, we show that TLE1, one of the four human Groucho orthologs, is similarly phosphorylated in response to Ras-Erk pathway activation, and that this modification attenuates its capacity to repress transcription. Specifically, unphosphorylated TLE1 dominantly suppresses the induction of Ras-Erk pathway target genes in cultured human cells, and the expression of an unphosphorylatable TLE1 derivative causes severe phenotypes in a transgenic Drosophila model system, whereas a phosphomimetic variant of TLE1 exerts only negligible effects. We present data indicating that TLE1 is rapidly excluded from the nucleus following epidermal growth factor receptor pathway activation, an effect that likely accounts for its inability to mediate effective repression under such conditions. Significantly, we find that unphosphorylated TLE1 blocks oncogenic phenotypes induced by mutated H-Ras in human mammary cells, both in vitro and following their implantation in mice. Collectively, our data strongly indicate that phosphorylation of TLE family members and the consequent downregulation of their repressor function is a key conserved step in the transcriptional responses to Ras-Erk signaling, and possibly a critical event in the tumorigenic effects caused by excessive Ras-Erk pathway activity.

Epithelial Plasticity During Human Breast Morphogenesis and Cancer Progression

Understanding the complex events leading to formation of an epithelial-based organ such as the breast requires a detailed insight into the crosstalk between epithelial and stromal compartments. These interactions occur both through heterotypic cellular interactions and between cells and matrix components. While in vivo models may partially capture these complex interactions, there is a need for in- vitro models to study these events. In this review we discuss cell-cell interactions in breast development focusing on the stem cell niche and branching morphogenesis. Given the recent understanding that the basic developmental events underlying branching morphogenesis are closely related to pathways important to cancer progression, i.e. epithelial plasticity and epithelial to mesenchymal transition (EMT), we will also discuss aspects relevant to cancer progression. In cancer, the adoption of mesenchymal phenotype by the malignant cells allows stromal invasion and subsequent intravasation to blood- or lymphatic vessels, a route that is a prerequisite for metastasis. A number of publications have demonstrated that tumor initiating cells, sometimes referred to as cancer stem cells adapt an EMT phenotype that renders them more resistant to apoptosis and drug therapy. The mechanism behind this phenomenon is currently unknown but this may partially explain relapse in breast cancer patients. Increased understanding of branching morphogenesis in the breast gland and the regulation of EMT and its reverse process mesenchymal to epithelial transition (MET) may hold the keys for future development of methods/drugs that neutralize the invading properties of cancer cells.

TLE4 promotes colorectal cancer progression through activation of JNK/c-Jun signaling pathway

The Groucho transcriptional co-repressor TLE4 protein has been shown to be a tumor suppressor in a subset of acute myeloid leukemia. However, little is known about its role in development and progression of solid tumor. In this study, we found that the expression of TLE4 in colorectal cancer (CRC) tissues was significantly higher than that in their matched adjacent intestine epithelial tissues. In addition, high expression of TLE4 was significantly correlated with advanced Dukes stage, lymph node metastasis and poor prognosis of CRC. Moreover, enforced expression of TLE4 in CRC cell lines significantly enhanced proliferation, invasion and tumor growth. On the contrary, knock down of TLE4 repressed cell proliferation, invasion and tumor growth. Furthermore, our study exhibited that the TLE4 promoted cell proliferation and invasion partially via activation of JNK-c-Jun pathway and subsequently increased cyclinD1 and decreased P27Kip1 expression. In conclusion, these results suggested that TLE4, a potential prognostic biomarker for CRC, plays an important role in the development and progression of human CRC.

TLE3 represses colorectal cancer proliferation by inhibiting MAPK and AKT signaling pathways

Background

Transducin-like enhancer of Split3 (TLE3) serves as a transcriptional corepressor during cell differentiation and shows multiple roles in different kinds of cancers. Recently, TLE3 together with many other genes involved in Wnt/β-catenin pathway were detected hyper-methylated in colorectal cancer (CRC). However, the potential role and the underlying mechanism of TLE3 in CRC progression remain scarce.

Methods

Gene expression profiles were analyzed in The Cancer Genome Atlas (TCGA) microarray dataset of 41 normal colorectal intestine tissues and 465 CRC tissues. Western blot and Real-time Quantitative PCR (RT-qPCR) were respectively performed to detect protein and mRNA expression in 8 pairs of CRC tissue and matched adjacent normal mucosa. Immunohistochemistry (IHC) was conducted to evaluate TLE3 protein expression in 105 paraffin-embedded, archived human CRC tissues from patients, whose survival data were analyzed with Kaplan-Meier method. In vitro experiments including MTT assay, colony formation assay, and soft agar formation assay were used to investigate the effects of TLE3 on CRC cell growth and proliferation. Additionally, subcutaneous tumorigenesis assay was performed in nude mice to confirm the effects of TLE3 in vivo. Furthermore, gene set enrichment analysis (GSEA) was run to explore potential mechanism of TLE3 in CRC, and then we measured the distribution of CRC cell cycle phases and apoptosis by flow cytometry, as well as the impacts of TLE3 on MAPK and AKT signaling pathways by Western blot and RT-qPCR.

Results

TLE3 was significantly down-regulated in 465 CRC tissues compared with 41 normal tissues. Both protein and mRNA expressions of TLE3 were down-regulated in CRC compared with matched adjacent normal mucosa. Lower expression of TLE3 was significantly associated with poorer survival of patients with CRC. Besides, knock down of TLE3 promoted CRC cell growth and proliferation, while overexpression of TLE3 showed suppressive effects. Furthermore, overexpression of TLE3 caused G1-S phase transition arrest, inhibition of MAPK and AKT pathways, and up-regulation of p21Cip1/WAF1 and p27Kip1.

Conclusion

This study indicated that TLE3 repressed CRC proliferation partly through inhibition of MAPK and AKT signaling pathways, suggesting the possibility of TLE3 as a biomarker for CRC prognosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0426-8) contains supplementary material, which is available to authorized users.

Promoter methylation and downregulated expression of the TBX15 gene in ovarian carcinoma

TBX15 is a gene involved in the development of mesodermal derivatives. As the ovaries and the female reproductive system are of mesodermal origin, the aim of the present study was to determine the methylation status of the TBX15 gene promoter and the expression levels of TBX15 in ovarian carcinoma, which is the most lethal and aggressive type of gynecological tumor, in order to determine the role of TBX15 in the pathogenesis of ovarian carcinoma. This alteration could be used to predict tumor development, progression, recurrence and therapeutic effects. The study was conducted on 80 epithelial ovarian carcinoma and 17 control cases (normal ovarian and tubal tissues). TBX15 promoter methylation was first determined by pyrosequencing following bisulfite modification, then by cloning and sequencing, in order to obtain information about the epigenetic haplotype. Immunohistochemical analysis was performed to evaluate the correlation between the methylation and protein expression levels. Data revealed a statistically significant increase of the TBX15 promoter region methylation in 82% of the tumor samples and in various histological subtypes. Immunohistochemistry showed an inverse correlation between methylation levels and the expression of the TBX15 protein. Furthermore, numerous tumor samples displayed varying degrees of intratumor heterogeneity. Thus, the present study determined that ovarian carcinoma typically expresses low levels of TBX15 protein, predominantly due to an epigenetic mechanism. This may have a role in the pathogenesis of ovarian carcinoma independent of the histological subtype.

The T-box transcription factor Midline regulates wing development by repressing wingless and hedgehog in Drosophila

Wingless (Wg) and Hedgehog (Hh) signaling pathways are key players in animal development. However, regulation of the expression of wg and hh are not well understood. Here, we show that Midline (Mid), an evolutionarily conserved transcription factor, expresses in the wing disc of Drosophila and plays a vital role in wing development. Loss or knock down of mid in the wing disc induced hyper-expression of wingless (wg) and yielded cocked and non-flat wings. Over-expression of mid in the wing disc markedly repressed the expression of wg, DE-Cadherin (DE-Cad) and armadillo (arm), and resulted in a small and blistered wing. In addition, a reduction in the dose of mid enhanced phenotypes of a gain-of-function mutant of hedgehog (hh). We also observed repression of hh upon overexpression of mid in the wing disc. Taken together, we propose that Mid regulates wing development by repressing wg and hh in Drosophila.

Evidence for the Induction of Key Components of the NOTCH Signaling Pathway via Deltamethrin and Azamethiphos Treatment in the Sea Louse Caligus rogercresseyi

The extensive use of organophosphates and pyrethroids in the aquaculture industry has negatively impacted parasite sensitivity to the delousing effects of these antiparasitics, especially among sea lice species. The NOTCH signaling pathway is a positive regulator of ABC transporter subfamily C expression and plays a key role in the generation and modulation of pesticide resistance. However, little is known about the molecular mechanisms behind pesticide resistance, partly due to the lack of genomic and molecular information on the processes involved in the resistance mechanism of sea lice. Next-generation sequencing technologies provide an opportunity for rapid and cost-effective generation of genome-scale data. The present study, through RNA-seq analysis, determined that the sea louse Caligus rogercresseyi (C. rogercresseyi) specifically responds to the delousing drugs azamethiphos and deltamethrin at the transcriptomic level by differentially activating mRNA of the NOTCH signaling pathway and of ABC genes. These results suggest that frequent antiparasitic application may increase the activity of inhibitory mRNA components, thereby promoting inhibitory NOTCH output and conditions for increased resistance to delousing drugs. Moreover, data analysis underscored that key functions of NOTCH/ABC components were regulated during distinct phases of the drug response, thus indicating resistance modifications in C. rogercresseyi resulting from the frequent use of organophosphates and pyrethroids.

A genes eye view of ontogeny: de novo assembly and profiling of the Gryllus rubens transcriptome

Crickets (Orthoptera:Gryllidae) are widely used model organisms for developmental, evolutionary, neurobiological and behavioural research. Here, we developed a de novo transcriptome from pooled RNA-seq Illumina data spanning seven stages in the life cycle of Gryllus rubens. Approximately 705 Mbp of data was assembled and filtered to form 27 312 transcripts. We were able to annotate 52% of our transcripts using BLAST and assign at least one gene ontology term to 41%. Pooled samples from three different ontogenetic stages were used for transcriptomic profiling revealing patterns of differential gene expression that highlight processes in the different life stages. Embryonic and early instar development was enriched for ecdysteroid metabolism, cytochrome P450s and glutathione production. Late instar development was enriched for regulation of gene expression and many of the genes highly expressed during this stage were involved in conserved developmental signalling pathways suggesting that these developmental pathways are active beyond embryonic development. Adults were enriched for fat transport (mostly relating to egg production) and production of octopamine, an important neurohormone. We also identified genes involved in conserved developmental pathways (Hedgehog, Hippo, Wnt, JAK/STAT, TGF-beta, Notch, and MEK/ERK). This is the first transcriptome spanning ontogeny in Gryllus rubens and a valuable resource for future work on development and evolution in Orthoptera.

The Central Region of the Drosophila Co-repressor Groucho as a Regulatory Hub

Groucho (Gro) is a Drosophila co-repressor that regulates the expression of a large number of genes, many of which are involved in developmental control. Previous studies have shown that its central region is essential for function even though its three domains are poorly conserved and intrinsically disordered. Using these disordered domains as affinity reagents, we have now identified multiple embryonic Gro-interacting proteins. The interactors include protein complexes involved in chromosome organization, mRNA processing, and signaling. Further investigation of the interacting proteins using a reporter assay showed that many of them modulate Gro-mediated repression either positively or negatively. The positive regulators include components of the spliceosomal subcomplex U1 small nuclear ribonucleoprotein (U1 snRNP). A co-immunoprecipitation experiment confirms this finding and suggests that a sizable fraction of nuclear U1 snRNP is associated with Gro. The use of RNA-seq to analyze the gene expression profile of cells subjected to knockdown of Gro or snRNP-U1-C (a component of U1 snRNP) showed a significant overlap between genes regulated by these two factors. Furthermore, comparison of our RNA-seq data with Gro and RNA polymerase II ChIP data led to a number of insights, including the finding that Gro-repressed genes are enriched for promoter-proximal RNA polymerase II. We conclude that the Gro central domains mediate multiple interactions required for repression, thus functioning as a regulatory hub. Furthermore, interactions with the spliceosome may contribute to repression by Gro.

Morphogens and blood-brain barrier function in health and disease

The microvasculature of the brain forms a protective blood-brain barrier (BBB) that ensures a homeostatic environment for the central nervous system (CNS), which is essential for optimal brain functioning. The barrier properties of the brain endothelial cells are maintained by cells surrounding the capillaries, such as astrocytes and pericytes. Together with the endothelium and a basement membrane, these supporting cells form the neurovascular unit (NVU). Accumulating evidence indicates that the supporting cells of the NVU release a wide variety of soluble factors that induce and control barrier properties in a concentration-dependent manner. The current review provides a comprehensive overview of how such factors, called morphogens, influence BBB integrity and functioning. Since impaired BBB function is apparent in numerous CNS disorders and is often associated with disease severity, we also discuss the potential therapeutic value of these morphogens, as they may represent promising therapies for a wide variety of CNS disorders.

Gene Signature of Human Oral Mucosa Fibroblasts: Comparison with Dermal Fibroblasts and Induced Pluripotent Stem Cells

Oral mucosa is a useful material for regeneration therapy with the advantages of its accessibility and versatility regardless of age and gender. However, little is known about the molecular characteristics of oral mucosa. Here we report the first comparative profiles of the gene signatures of human oral mucosa fibroblasts (hOFs), human dermal fibroblasts (hDFs), and hOF-derived induced pluripotent stem cells (hOF-iPSCs), linking these with biological roles by functional annotation and pathway analyses. As a common feature of fibroblasts, both hOFs and hDFs expressed glycolipid metabolism-related genes at higher levels compared with hOF-iPSCs. Distinct characteristics of hOFs compared with hDFs included a high expression of glycoprotein genes, involved in signaling, extracellular matrix, membrane, and receptor proteins, besides a low expression of HOX genes, the hDFs-markers. The results of the pathway analyses indicated that tissue-reconstructive, proliferative, and signaling pathways are active, whereas senescence-related genes in p53 pathway are inactive in hOFs. Furthermore, more than half of hOF-specific genes were similarly expressed to those of hOF-iPSC genes and might be controlled by WNT signaling. Our findings demonstrated that hOFs have unique cellular characteristics in specificity and plasticity. These data may provide useful insight into application of oral fibroblasts for direct reprograming.

Structural basis for recognition of diverse transcriptional repressors by the TOPLESS family of corepressors

TOPLESS (TPL) and TOPLESS-related (TPR) proteins comprise a conserved family of plant transcriptional corepressors that are related to Tup1, Groucho, and TLE (transducin-like enhancer of split) corepressors in yeast, insects, and mammals. In plants, TPL/TPR corepressors regulate development, stress responses, and hormone signaling through interaction with small ethylene response factor-associated amphiphilic repression (EAR) motifs found in diverse transcriptional repressors. How EAR motifs can interact with TPL/TPR proteins is unknown. We confirm the amino-terminal domain of the TPL family of corepressors, which we term TOPLESS domain (TPD), as the EAR motif-binding domain. To understand the structural basis of this interaction, we determined the crystal structures of the TPD of rice (Os) TPR2 in apo (apo protein) state and in complexes with the EAR motifs from Arabidopsis NINJA (novel interactor of JAZ), IAA1 (auxin-responsive protein 1), and IAA10, key transcriptional repressors involved in jasmonate and auxin signaling. The OsTPR2 TPD adopts a new fold of nine helices, followed by a zinc finger, which are arranged into a disc-like tetramer. The EAR motifs in the three different complexes adopt a similar extended conformation with the hydrophobic residues fitting into the same surface groove of each OsTPR2 monomer. Sequence alignments and structure-based mutagenesis indicate that this mode of corepressor binding is highly conserved in a large set of transcriptional repressors, thus providing a general mechanism for gene repression mediated by the TPL family of corepressors.

Regulation of cerebral cortical neurogenesis by the Pax6 transcription factor

Understanding brain development remains a major challenge at the heart of understanding what makes us human. The neocortex, in evolutionary terms the newest part of the cerebral cortex, is the seat of higher cognitive functions. Its normal development requires the production, positioning, and appropriate interconnection of very large numbers of both excitatory and inhibitory neurons. Pax6 is one of a relatively small group of transcription factors that exert high-level control of cortical development, and whose mutation or deletion from developing embryos causes major brain defects and a wide range of neurodevelopmental disorders. Pax6 is very highly conserved between primate and non-primate species, is expressed in a gradient throughout the developing cortex and is essential for normal corticogenesis. Our understanding of Pax6’s functions and the cellular processes that it regulates during mammalian cortical development has significantly advanced in the last decade, owing to the combined application of genetic and biochemical analyses. Here, we review the functional importance of Pax6 in regulating cortical progenitor proliferation, neurogenesis, and formation of cortical layers and highlight important differences between rodents and primates. We also review the pathological effects of PAX6 mutations in human neurodevelopmental disorders. We discuss some aspects of Pax6’s molecular actions including its own complex transcriptional regulation, the distinct molecular functions of its splice variants and some of Pax6’s known direct targets which mediate its actions during cortical development.

Fezf2 promotes neuronal differentiation through localised activation of Wnt/β-catenin signalling during forebrain development

Brain regionalisation, neuronal subtype diversification and circuit connectivity are crucial events in the establishment of higher cognitive functions. Here we report the requirement for the transcriptional repressor Fezf2 for proper differentiation of neural progenitor cells during the development of the Xenopus forebrain. Depletion of Fezf2 induces apoptosis in postmitotic neural progenitors, with concomitant reduction in forebrain size and neuronal differentiation. Mechanistically, we found that Fezf2 stimulates neuronal differentiation by promoting Wnt/β-catenin signalling in the developing forebrain. In addition, we show that Fezf2 promotes activation of Wnt/β-catenin signalling by repressing the expression of two negative regulators of Wnt signalling, namely lhx2 and lhx9. Our findings suggest that Fezf2 plays an essential role in controlling when and where neuronal differentiation occurs within the developing forebrain and that it does so by promoting local Wnt/β-catenin signalling via a double-repressor model.

The subcortical maternal complex controls symmetric division of mouse zygotes by regulating F-actin dynamics

Maternal effect genes play critical roles in early embryogenesis of model organisms where they have been intensively investigated. However, their molecular function in mammals remains largely unknown. Recently, we identified a subcortical maternal complex (SCMC) that contains four proteins encoded by maternal effect genes (Mater, Filia, Floped and Tle6). Here we report that TLE6, similar to FLOPED and MATER, stabilizes the SCMC and is necessary for cleavage beyond the two-cell stage of development. We document that the SCMC is required for formation of the cytoplasmic F-actin meshwork that controls the central position of the spindle and ensures symmetric division of mouse zygotes. We further demonstrate that the SCMC controls formation of the actin cytoskeleton specifically via Cofilin, a key regulator of F-actin assembly. Our results provide molecular insight into the physiological function of TLE6, its interaction with the SCMC and their roles in the symmetric division of the zygote in early mouse development.

The Groucho co-repressor is primarily recruited to local target sites in active chromatin to attenuate transcription

Gene expression is regulated by the complex interaction between transcriptional activators and repressors, which function in part by recruiting histone-modifying enzymes to control accessibility of DNA to RNA polymerase. The evolutionarily conserved family of Groucho/Transducin-Like Enhancer of split (Gro/TLE) proteins act as co-repressors for numerous transcription factors. Gro/TLE proteins act in several key pathways during development (including Notch and Wnt signaling), and are implicated in the pathogenesis of several human cancers. Gro/TLE proteins form oligomers and it has been proposed that their ability to exert long-range repression on target genes involves oligomerization over broad regions of chromatin. However, analysis of an endogenous gro mutation in Drosophila revealed that oligomerization of Gro is not always obligatory for repression in vivo. We have used chromatin immunoprecipitation followed by DNA sequencing (ChIP-seq) to profile Gro recruitment in two Drosophila cell lines. We find that Gro predominantly binds at discrete peaks (<1 kilobase). We also demonstrate that blocking Gro oligomerization does not reduce peak width as would be expected if Gro oligomerization induced spreading along the chromatin from the site of recruitment. Gro recruitment is enriched in “active” chromatin containing developmentally regulated genes. However, Gro binding is associated with local regions containing hypoacetylated histones H3 and H4, which is indicative of chromatin that is not fully open for efficient transcription. We also find that peaks of Gro binding frequently overlap the transcription start sites of expressed genes that exhibit strong RNA polymerase pausing and that depletion of Gro leads to release of polymerase pausing and increased transcription at a bona fide target gene. Our results demonstrate that Gro is recruited to local sites by transcription factors to attenuate rather than silence gene expression by promoting histone deacetylation and polymerase pausing.

Repression by transcription factors plays a central role in gene regulation. The Groucho/Transducin-Like Enhancer of split (Gro/TLE) family of co-repressors interacts with many different transcription factors and has many essential roles during animal development. Groucho/TLE proteins form oligomers that are necessary for target gene repression in some contexts. We have profiled the genome-wide recruitment of the founding member of this family, Groucho (from Drosophila) to gain insight into how and where it binds with respect to target genes and to identify factors associated with its binding. We find that Groucho binds in discrete peaks, frequently at transcription start sites, and that blocking Groucho from forming oligomers does not significantly change the pattern of Groucho recruitment. Although Groucho acts as a repressor, Groucho binding is enriched in chromatin that is permissive for transcription, and we find that it acts to attenuate rather than completely silence target gene expression. Thus, Groucho does not act as an “on/off” switch on target gene expression, but rather as a “mute” button.

Transcription factors FOXG1 and Groucho/TLE promote glioblastoma growth

Glioblastoma (GBM) is the most common and deadly malignant brain cancer, with a median survival of less than two years. GBM displays a cellular complexity that includes brain tumour-initiating cells (BTICs), which are considered as potential key targets for GBM therapies. Here we show that the transcription factors FOXG1 and Groucho/TLE are expressed in poorly differentiated astroglial cells in human GBM specimens and in primary cultures of GBM-derived BTICs, where they form a complex. FOXG1 knockdown in BTICs causes downregulation of neural stem/progenitor and proliferation markers, increased replicative senescence, upregulation of astroglial differentiation genes, and decreased BTIC-initiated tumour growth upon intracranial transplantation into host mice. These effects are phenocopied by Groucho/TLE knockdown or dominant-inhibition of the FOXG1:Groucho/TLE complex. These results provide evidence that transcriptional programs regulated by FOXG1 and Groucho/TLE are important for BTIC-initiated brain tumour growth, implicating FOXG1 and Groucho/TLE in GBM tumorigenesis.