T-box Transcription Factor TBX1 Research Articles

Significant improvement of cardiac outflow tract septation defects in a DiGeorge syndrome model after minoxidil treatment

The T-BOX transcription factor TBX1 is essential for the development of the pharyngeal apparatus and it is haploinsufficient in DiGeorge syndrome (DGS), a developmental anomaly associated with congenital heart disease and other abnormalities. The murine model recapitulates the heart phenotype and showed collagen accumulation.We first used a cellular model to study gene expression during cardiogenic differentiation of WT and Tbx1−/− mouse embryonic stem cells. Then we used a mouse model of DGS to test whether interfering with collagen accumulation using an inhibitor of lysyl hydroxylase would modify the cardiac phenotype of the mutant.We found that loss of Tbx1 in a precardiac differentiation model was associated with up regulation of a subset of ECM-related genes, including several collagen genes. In the in vivo model, early prenatal treatment with Minoxidil, a lysyl hydroxylase inhibitor, ameliorated the cardiac outflow tract septation phenotype in Tbx1 mutant fetuses, but it had no effect on septation in WT fetuses. We conclude that TBX1 suppresses a defined subset of ECM-related genes. This function is critical for OFT septation because the inhibition of collagen cross-linking in the mutant reduces significantly the penetrance of septation defects.

The effect of glatiramer acetate, IFNβ-1a, fingolimod, and dimethyl fumarate on the expression of T-bet, IFN-γ, and MEG3 in PBMC of RRMS patients

ObjectiveMultiple sclerosis (MS) is a progressing neurodegenerative disease marked by chronic central nervous system inflammation and degeneration.This study investigates gene expression profiles of T-box transcription factor TBX21 (T-bet), interferon-gamma (IFN-γ), and long non-coding RNA MEG3 in peripheral blood mononuclear cells (PBMCs) from treatment-naïve Relapsing-Remitting Multiple Sclerosis patients (RRMS), healthy controls, and RRMS patients on different Disease Modifying Therapies (DMTs). The aim is to understand the role of T-bet, IFN-γ, and MEG3 in MS pathogenesis and their potential as diagnostic and therapeutic targets.ResultsElevated T-bet expression is observed in treatment-naïve RRMS patients compared to healthy individuals. RRMS patients treated with Interferon beta-1alpha (IFNβ-1a) and fingolimod exhibit downregulated T-bet and MEG3 expression levels, respectively, with more pronounced effects in females. Healthy individuals show a moderate positive correlation between T-bet and MEG3 and between IFN-γ and T-bet. In RRMS patients treated with Glatiramer Acetate (GA), a strong positive correlation is observed between MEG3 and IFN-γ. Remarkably, RRMS patients treated with Dimethyl Fumarate (DMF) exhibit a significant positive correlation between T-bet and MEG3. These findings underscore the diagnostic potential of T-bet in RRMS, warranting further exploration of MEG3, T-bet, and IFN-γ interplay in RRMS patients.

Induced regulatory T cells modified by knocking down T-bet in combination with ectopic expression of inhibitory cytokines effectively protect graft-versus-host disease

Induced regulatory T (iTreg) cells play a vital role in immune tolerance and in controlling chronic inflammation. Generated in the periphery, iTreg cells are suitable for responding to alloantigens and preventing transplant rejection. Nevertheless, their clinical application has been impeded by the plasticity and instability attributed to the loss of forkhead box protein 3 expression, raising concerns that iTreg may be converted to effector T cells and even exert a pathogenic effect. Herein, second-generation short hairpin RNAs loaded with 3 pairs of small interfering RNAs were utilized to target the T-box transcription factor TBX21. In addition, 2 immunosuppressive cytokines, namely, transforming growth factor beta and interleukin 10, were constitutively expressed. This novel engineering strategy allowed the generation of stably induced regulatory T (SI Treg) cells, which maintained the expression of forkhead box protein 3 even in an unfavorable environment and exerted potent immunosuppressive functions in vitro. Furthermore, SI Treg cells demonstrated an effector transcriptional profile. Finally, SI Treg cells showed a significant protective effect against graft-versus-host disease–related deaths in a xenotransplantation model. Collectively, these results signify that SI Treg cells hold great promise for future clinical application and offer a rational therapeutic approach for transplant rejection.

Role of Diospyros peregrina fruit preparation in suppressing regulatory T (Treg) cells in the tumor microenvironment of breast and lung cancer

BackgroundThe most frequent cancers in the world are breast cancer and lung cancer. Regulatory T cells (Treg) are the subtype of T cells that promotes equilibrium between immunological surveillance and immune tolerance, and they are commonly found in high amounts within tumours. The presence of Treg cells in the tumour microenvironment results in immune suppression, due to which immune cells are not able to kill the tumour cells. Diospyros peregrina (Gaertn.) Gürke is an ethnomedicinal plant with hypoglycaemic, diuretic, and anti-cancer effects. This genus, Diospyros, is native to India but distributed throughout the tropics and is characterized by its ability to produce triterpenes of the lupine series and various other bioactive compounds. Diospyros peregrina fruit preparation (DFP) substantially increases tumour protective immunity by suppressing Treg cells. PurposeThis project aims to suppress the regulatory T cells in the tumour microenvironment by giving Diospyros peregrina fruit preparation (DFP) treatment to Treg cells, which will help in controlling and combating breast cancer and lung cancer. MethodFor this project's work, we isolated peripheral blood mononuclear cells from the blood, and the isolated peripheral blood mononuclear cells were used to isolate CD4+CD25+ Treg cells. Then, Diospyros peregrina fruit preparation (DFP) was prepared, which was used to treat CD4+CD25+ Treg cells. Lactate dehydrogenase (LDH) assays, enzyme-linked immunosorbent assays (ELISA), and RT-qPCR were used to determine the effect of DFP treatment on Treg cells. ResultDiospyros peregrina fruit preparation (DFP) treatment suppresses the expression of CD4+CD25+ Foxp3+Treg cells within tumours. DFP-treated CD4+CD25+Foxp3+ Treg cells increase the cytotoxicity within the tumours compared to non-treated Treg cells. DFP treatment help in reducing the release of (T helper type 2) TH2 cell cytokines (Interleukin-10) IL-10 as well as (Interleukin-4) IL-4 and escalating the release of (T helper type 1) TH1 cell cytokines (Interleukin-12) IL-12 and (Interferon-γ) IFN-γ, it also increases the transcriptional activity of T-box transcription factor TBX21 (TBX21) and reduces the expression of the transcription factor FOXP3 and GATA3. ConclusionDiospyros peregrina fruit preparation (DFP) treatment augments the expressions of TH1-specific cytokines and transcription factors, and DFP treatment diminishes the expressions of both TH2 and Treg-specific cytokines and transcription factors.

Neonate with Respiratory Distress, Bilateral Microtia, Hypocalcemia, and Lymphopenia.

Neonate with Respiratory Distress, Bilateral Microtia, Hypocalcemia, and Lymphopenia.

Gestational Leucylation Suppresses Embryonic T-Box Transcription Factor 5 Signal and Causes Congenital Heart Disease.

Dysregulated maternal nutrition, such as vitamin deficiencies and excessive levels of glucose and fatty acids, increases the risk for congenital heart disease (CHD) in the offspring. However, the association between maternal amino‐acid levels and CHD is unclear. Here, it is shown that increased leucine levels in maternal plasma during the first trimester are associated with elevated CHD risk in the offspring. High levels of maternal leucine increase embryonic lysine‐leucylation (K‐Leu), which is catalyzed by leucyl‐tRNA synthetase (LARS). LARS preferentially binds to and catalyzes K‐Leu modification of lysine 339 within T‐box transcription factor TBX5, whereas SIRT3 removes K‐Leu from TBX5. Reversible leucylation retains TBX5 in the cytoplasm and inhibits its transcriptional activity. Increasing embryonic K‐Leu levels in high‐leucine‐diet fed or Sirt3 knockout mice causes CHD in the offspring. Targeting K‐Leu using the leucine analogue leucinol can inhibit LARS activity, reverse TBX5 K‐Leu modification, and decrease the occurrence of CHD in high‐leucine‐diet fed mice. This study reveals that increased maternal leucine levels increases CHD risk in the offspring through inhibition of embryonic TBX5 signaling, indicating that leucylation exerts teratogenic effects during heart development and may be an intervening target of CHD.

Tbx5 drives Aldh1a2 expression to regulate a RA-Hedgehog-Wnt gene regulatory network coordinating cardiopulmonary development.

The gene regulatory networks that coordinate the development of the cardiac and pulmonary systems are essential for terrestrial life but poorly understood. The T-box transcription factor Tbx5 is critical for both pulmonary specification and heart development, but how these activities are mechanistically integrated remains unclear. Here using Xenopus and mouse embryos, we establish molecular links between Tbx5 and retinoic acid (RA) signaling in the mesoderm and between RA signaling and sonic hedgehog expression in the endoderm to unveil a conserved RA-Hedgehog-Wnt signaling cascade coordinating cardiopulmonary (CP) development. We demonstrate that Tbx5 directly maintains expression of aldh1a2, the RA-synthesizing enzyme, in the foregut lateral plate mesoderm via an evolutionarily conserved intronic enhancer. Tbx5 promotes posterior second heart field identity in a positive feedback loop with RA, antagonizing a Fgf8-Cyp regulatory module to restrict FGF activity to the anterior. We find that Tbx5/Aldh1a2-dependent RA signaling directly activates shh transcription in the adjacent foregut endoderm through a conserved MACS1 enhancer. Hedgehog signaling coordinates with Tbx5 in the mesoderm to activate expression of wnt2/2b, which induces pulmonary fate in the foregut endoderm. These results provide mechanistic insight into the interrelationship between heart and lung development informing CP evolution and birth defects.

Abstract P484: Defining Disease Specific Cardiac Regulatory Networks

The transcriptional basis of homeostasis and disease is implied by the non-coding nature of genetic variation identified by GWAS. Functional genomic approaches to unveil the gene regulatory networks (GRNs) relevant to disease are therefore a high priority. Most models for transcriptional dysregulation presume that perturbation of a wild-type gene regulatory network causes disease risk. For example, the T-box transcription factor (TF) TBX5, is essential for atrial rhythm homeostasis and directly drives a physiologically relevant GRN composed of cardiac channel genes. Alternatively, the expression of many genes pertinent to cardiac pathology are upregulated after the removal of Tbx5, implicating a disease-specific GRN absent from the wild-type atrium. We applied TF-dependent noncoding RNA (ncRNA) profiling, using differential deep ncRNA sequencing from atria of wild-type and Tbx5 mutant mice, to identify TBX5-dependent enhancers and ncRNAs that were only activated following TBX5 removal. We hypothesized that these regulatory elements would reveal disease-response enhancers, essential for coping with atrial dysfunction. To identify the cell-specific regulatory elements, we generated cell-type specific Assay from Transposase-Accessible Chromatin (ATAC) datasets for left atrial tissue, cardiac fibroblasts, and cardiomyocytes. Overlap with the Tbx5 -repressed ncRNAs defined candidate cell-type specific regulatory elements. Candidate regulatory elements were identified upstream of Sox9, a known modulator of cardiac fibrosis, along with other cardiac stress-response pathways, including mediators of TGF-β signaling. Activation of the enhancer at Sox9 was confirmed in isolated cardiac fibroblasts treated with TGF-β. We hypothesized that the disease-acquired GRN in TBX5 mutant atria may be generalizable to other cardiac insults. We therefore examined the transcriptional and genomic changes in the left atria of the heart failure Transverse Aortic Constriction (TAC) mouse model. This analysis revealed remarkable correlation between differentially expressed genes and ncRNAs between TAC and TBX5 mutant disease models. The conservation of the coding and non-coding transcriptional response between arrhythmia and heart failure models supports a paradigm of a common disease-specific GRN that mediates the physiologic consequences of distinct cardiac diseases.

Exhausted T cells in systemic lupus erythematosus patients in long-standing remission.

The mechanisms that drive systemic lupus erythematosus (SLE) patients to achieve remission are unknown; one possible explanation might be T cell exhaustion. The aim of the present study was to measure CD4+ and CD8+ T cell exhaustion in SLE patients in prolonged remission (PR-SLE) and compared them with patients with active SLE (Act-SLE) and healthy subjects. We included 15PR-SLE patients, 15Act-SLE and 29healthy subjects. T cell exhaustion was determined by flow cytometry according to the expression of programmed cell death 1 (PD)-1, T cell immunoglobulin and mucin 3 (Tim-3), natural killer cell receptor (2B4), eomesodermin (EOMES) and T-box transcription factor TBX21 (T-bet) in CD4+ and CD8+ T cells. Dimensionality reduction using the T-distributed stochastic neighbor-embedding algorithm and clustering analysis was used for the identification of relevant populations. Percentages of CD3+ , CD4+ and CD8+ T cells were similar among groups. We identified five subpopulations of CD8+ and seven of CD4+ cells. The CD4+ T-bet+ CD45RO+ cells identified in the unsupervised analysis were significantly increased in PR-SLE versus Act-SLE [median=0·20, interquartile range (IQR)=1·74-30·50 versus 1·68, IQR=0·4-2·83; P<0·01]. CD4+ EOMES+ cells were also increased in PR-SLE versus Act-SLE (5·24, IQR=3·38-14·70 versus 1·39, IQR=0·48-2·87; P<0·001). CD8+ EOMES+ cells were increased in PR-SLE versus Act-SLE (37·6, IQR=24·9-53·2 versus 8·13, IQR=2·33-20·5; P<0·001). Exhausted and activated T cells presented an increased frequency of PD-1, CD57 and EOMES in SLE patients versus healthy subjects. Some subpopulations of T cells expressing markers associated with exhaustion are increased in patients in remission, supporting T cell exhaustion as a tolerance mechanism in SLE. Exhaustion of specific populations of T cells might represent a potential therapeutic tool that will contribute to the goal of achieving sustained remission in these patients.

Immunology of IL-12: An update on functional activities and implications for disease.

As its first identified member, Interleukin-12 (IL-12) named a whole family of cytokines. In response to pathogens, the heterodimeric protein, consisting of the two subunits p35 and p40, is secreted by phagocytic cells. Binding of IL-12 to the IL-12 receptor (IL-12R) on T and natural killer (NK) cells leads to signaling via signal transducer and activator of transcription 4 (STAT4) and subsequent interferon gamma (IFN-γ) production and secretion. Signaling downstream of IFN-γ includes activation of T-box transcription factor TBX21 (Tbet) and induces pro-inflammatory functions of T helper 1 (TH1) cells, thereby linking innate and adaptive immune responses. Initial views on the role of IL-12 and clinical efforts to translate them into therapeutic approaches had to be re-interpreted following the discovery of other members of the IL-12 family, such as IL-23, sharing a subunit with IL-12. However, the importance of IL-12 with regard to immune processes in the context of infection and (auto-) inflammation is still beyond doubt. In this review, we will provide an update on functional activities of IL-12 and their implications for disease. We will begin with a summary on structure and function of the cytokine itself as well as its receptor and outline the signal transduction and the transcriptional regulation of IL-12 secretion. In the second part of the review, we will depict the involvement of IL-12 in immune-mediated diseases and relevant experimental disease models, while also providing an outlook on potential translational approaches.

Chromatin and Transcriptional Response to Loss of TBX1 in Early Differentiation of Mouse Cells.

The T-box transcription factor TBX1 has critical roles in the cardiopharyngeal lineage and the gene is haploinsufficient in DiGeorge syndrome, a typical developmental anomaly of the pharyngeal apparatus. Despite almost two decades of research, if and how TBX1 function triggers chromatin remodeling is not known. Here, we explored genome-wide gene expression and chromatin remodeling in two independent cellular models of Tbx1 loss of function, mouse embryonic carcinoma cells P19Cl6, and mouse embryonic stem cells (mESCs). The results of our study revealed that the loss or knockdown of TBX1 caused extensive transcriptional changes, some of which were cell type-specific, some were in common between the two models. However, unexpectedly we observed only limited chromatin changes in both systems. In P19Cl6 cells, differentially accessible regions (DARs) were not enriched in T-BOX binding motifs; in contrast, in mESCs, 34% (n = 47) of all DARs included a T-BOX binding motif and almost all of them gained accessibility in Tbx1–/– cells. In conclusion, despite a clear transcriptional response of our cell models to loss of TBX1 in early cell differentiation, chromatin changes were relatively modest.

Peptidoglycan-treated tumor antigen-pulsed dendritic cells impart complete resistance against tumor rechallenge.

Solid tumors elicit suppressive T cell responses which impair antigen-presenting cell (APC) functions. Such immune suppression results in uncontrolled tumor growth and mortality. Addressing APC dysfunction, dendritic cell (DC)-mediated anti-tumor vaccination was extensively investigated in both mice and humans. These studies never achieved full resistance to tumor relapse. Herein, we describe a repetitive RM-1 murine tumor rechallenge model for recurrence in humans. Using this newly developed model, we show that priming with tumor antigen-pulsed, Toll-like receptor (TLR)2 ligand-activated DCs elicits a host-protective anti-tumor immune response in C57BL/6 mice. Upon stimulation with the TLR2 ligand peptidoglycan (PGN), the tumor antigen-pulsed DCs induce complete resistance to repetitive tumor challenges. Intra-tumoral injection of PGN reduces tumor growth. The tumor resistance is accompanied by increased expression of interleukin (IL)-27, T-box transcription factor TBX21 (T-bet), IL-12, tumor necrosis factor (TNF)-α and interferon (IFN)-γ, along with heightened cytotoxic T lymphocyte (CTL) functions. Mice primed four times with PGN-stimulated tumor antigen-pulsed DCs remain entirely resistant to repeat challenges with RM-1 tumor cells, suggesting complete prevention of relapse and recurrence of tumor. Adoptive transfer of T cells from these mice, which were fully protected from RM-1 rechallenge, confers anti-tumor immunity to syngeneic naive recipient mice upon RM-1 challenge. These observations indicate that PGN-activated DCs induce robust host-protective anti-tumor T cells that completely resist tumor growth and recurrence.

TOPK promotes epithelial-mesenchymal transition and invasion of breast cancer cells through upregulation of TBX3 in TGF-β1/Smad signaling

TOPK has been suggested to contribute to invasion of lung, prostate, gastric, pancreatic or breast cancer cells. However, how TOPK mediates TGF-β1/Smad signaling leading to epithelial-mesenchymal transition (EMT) and invasion of breast cancer cells remains unknown. Here we report that TOPK upregulates T-box transcription factor TBX3 to enhance TGF-β1-induced EMT and invasion of MDA-MB-231 breast cancer cells. Expression of endogenous TOPK was promoted by TGF-β1 treatment of MDA-MB-231 cells time-dependently. In addition, knockdown of TOPK attenuated TGF-β1-induced phosphorylation or transcriptional activity of Smad3. Meanwhile, levels of both mRNA and protein of TBX3 induced by TGF-β1 were abolished by TOPK depletion. Also, knockdown of TBX3 inhibited TGF-β1 induction of EMT-related genes Snail, Slug or Fibronectin. Furthermore, ablation of TOPK or TBX3 suppressed TGF-β1-induced MDA-MB-231 cell invasion. Collectively, we conclude that TOPK positively regulates TBX3 in TGF-β1/Smad signaling pathway, thereby enhancing EMT and invasion of breast cancer cells, implying a mechanistic role of TOPK in TGF-β1/Smad signaling.

Urban Air Pollution Particulates Suppress Human T-Cell Responses to Mycobacterium Tuberculosis.

Tuberculosis (TB) and air pollution both contribute significantly to the global burden of disease. Epidemiological studies show that exposure to household and urban air pollution increase the risk of new infections with Mycobacterium tuberculosis (M.tb) and the development of TB in persons infected with M.tb and alter treatment outcomes. There is increasing evidence that particulate matter (PM) exposure weakens protective antimycobacterial host immunity. Mechanisms by which exposure to urban PM may adversely affect M.tb-specific human T cell functions have not been studied. We, therefore, explored the effects of urban air pollution PM2.5 (aerodynamic diameters ≤2.5µm) on M.tb-specific T cell functions in human peripheral blood mononuclear cells (PBMC). PM2.5 exposure decreased the capacity of PBMC to control the growth of M.tb and the M.tb-induced expression of CD69, an early surface activation marker expressed on CD3+ T cells. PM2.5 exposure also decreased the production of IFN-γ in CD3+, TNF-α in CD3+ and CD14+ M.tb-infected PBMC, and the M.tb-induced expression of T-box transcription factor TBX21 (T-bet). In contrast, PM2.5 exposure increased the expression of anti-inflammatory cytokine IL-10 in CD3+ and CD14+ PBMC. Taken together, PM2.5 exposure of PBMC prior to infection with M.tb impairs critical antimycobacterial T cell immune functions.

COL1A2 is a TBX3 target that mediates its impact on fibrosarcoma and chondrosarcoma cell migration.

The developmentally important T-box transcription factor TBX3, is overexpressed in several cancers and contributes to tumorigenesis as either a tumour promoter or tumour suppressor. For example, TBX3 promotes cell proliferation, migration and invasion of chondrosarcoma cells but inhibits these processes in fibrosarcoma cells. This suggests that the cellular context influences TBX3 oncogenic functions, but the mechanism(s) involved has not been elucidated. COL1A2 encodes type I collagen and, like TBX3, plays important roles during embryogenesis and can act as either oncogene or tumour suppressor. Here we explore the possibility that COL1A2 may be a TBX3 target gene responsible for mediating its opposing oncogenic roles in chondrosarcoma and fibrosarcoma cells. Results from qRT-PCR, western blotting, luciferase reporter and chromatin immunoprecipitation assays show that TBX3 binds and activates the COL1A2 promoter. Furthermore, we show that TBX3 levels are regulated by AKT1 and that pseudo-phosphorylation of TBX3 at an AKT consensus serine site, enhances its ability to activate COL1A2. Importantly, we demonstrate that COL1A2 mediates the pro- and anti-migratory effects of TBX3 in chondrosarcoma and fibrosarcoma cells respectively. Our data reveal that the AKT1/TBX3/COL1A2 axis plays an important role in sarcomagenesis.

Chitin Micro Particles Regulate Splenocytes Immune Response in Experimental Autoimmune Encephalomyelitis

Contrasting studies are reported on the induction of IL-10 and IFN-γ via chitin microparticles (CMPs) during immune stimulation. Our previous studies have shown marked protection among CMP treated Leishmania-infected mice via regulated IL-10/IFN-γ response, at the present study, once more, examined the inconsistent responses regarding the immunologic response of CMPS. To verify whether CMPs could indeed up-regulate IL-10/IFN-γ axis, isolated spleen cells from the myelin oligodendrocyte glycoprotein (MOG) induced experimental autoimmune encephalomyelitis (EAE) mice were cultured in the presence of MOG peptide and/or CMPs. The effects of CMPs on IL-10, IFN-γ and IL-17 production were evaluated by Enzyme-linked Immunosorbent Assay (ELISA). Moreover, GATA binding protein 3 (Gata3), T-box transcription factor TBX21 (Tbx21), and RAR-related orphan receptor gamma (RORγT) expressions (real-time PCR) were investigated. MOG alone stimulated the production of IFN-γ (p≤0.004) but not, IL-10 (p≤0.140). MOG/chitin stimulation resulted in a significant increase in IFN-γ and IL-10 levels, respectively; (p≤0.004 and p≤0.003) rather than MOG. Additionally, the expression of Tbx21 (p≤0.001), but not Gata3 (p≤0.08), was increased in the MOG/chitin-treated spleen cells. All in all, CMP supports Gata3 independent IL-10 production and promotes Tbx21 dependent IFN-γ induction. These results, alongside our previous data, indicate that CMPs has particular adjuvant effects.

A calcium transport mechanism for atrial fibrillation in Tbx5-mutant mice.

Risk for Atrial Fibrillation (AF), the most common human arrhythmia, has a major genetic component. The T-box transcription factor TBX5 influences human AF risk, and adult-specific Tbx5-mutant mice demonstrate spontaneous AF. We report that TBX5 is critical for cellular Ca2+ homeostasis, providing a molecular mechanism underlying the genetic implication of TBX5 in AF. We show that cardiomyocyte action potential (AP) abnormalities in Tbx5-deficient atrial cardiomyocytes are caused by a decreased sarcoplasmic reticulum (SR) Ca2+ ATPase (SERCA2)-mediated SR calcium uptake which was balanced by enhanced trans-sarcolemmal calcium fluxes (calcium current and sodium/calcium exchanger), providing mechanisms for triggered activity. The AP defects, cardiomyocyte ectopy, and AF caused by TBX5 deficiency were rescued by phospholamban removal, which normalized SERCA function. These results directly link transcriptional control of SERCA2 activity, depressed SR Ca2+ sequestration, enhanced trans-sarcolemmal calcium fluxes, and AF, establishing a mechanism underlying the genetic basis for a Ca2+-dependent pathway for AF risk.

Fetal Arrhythmias: Genetic Background and Clinical Implications.

Fetal arrhythmias are a common phenomenon of pregnancies. However, debates remain with regard to the etiologies and early treatment of choices for severe fetal arrhythmias. The gene regulatory networks govern cardiac conduction system development to produce distinct nodal and fast conduction phenotypes. The slow conduction properties of nodes that display automaticity are determined by the cardiac ion channel genes, whereas the fast conduction properties are regulated by the transcription factors. Mutations of genes specific for the developmental processes and/or functional status of cardiac conduction system including ion channel promoter (minK-lacZ), GATA family of zinc finger proteins (GATA4), the homeodomain transcription factor (Nkx2.5), the homeodomain-only protein (Hop) and the T-box transcription factors (Tbx2, Tbx3 and Tbx5), hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) and connexins, may cause fetal arrhythmias. It is expected that development of investigational antiarrhythmic agents based on genetic researches on cardiac conduction system, and clinical application of percutaneously implantable fetal pacemaker for thetreatment of fetal arrhythmias would come to true.

Loss of Tbx3 in murine neural crest reduces enteric glia and causes cleft palate, but does not influence heart development or bowel transit

Transcription factors that coordinate migration, differentiation or proliferation of enteric nervous system (ENS) precursors are not well defined. To identify novel transcriptional regulators of ENS development, we performed microarray analysis at embryonic day (E) 17.5 and identified many genes that were enriched in the ENS compared to other bowel cells. We decided to investigate the T-box transcription factor Tbx3, which is prominently expressed in developing and mature ENS. Haploinsufficiency for TBX3 causes ulnar-mammary syndrome (UMS) in humans, a multi-organ system disorder. TBX3 also regulates several genes known to be important for ENS development. To test the hypothesis that Tbx3 is important for ENS development or function, we inactivated Tbx3 in all neural crest derivatives, including ENS progenitors using Wnt1-Cre and a floxed Tbx3 allele. Tbx3 fl/fl; Wnt1-Cre conditional mutant mice die shortly after birth with cleft palate and difficulty feeding. The ENS of mutants was well-organized with a normal density of enteric neurons and nerve fiber bundles, but small bowel glial cell density was reduced. Despite this, bowel motility appeared normal. Furthermore, although Tbx3 is expressed in cardiac neural crest, Tbx3 fl/fl; Wnt1-Cre mice had structurally normal hearts. Thus, loss of Tbx3 within neural crest has selective effects on Tbx3-expressing neural crest derivatives.

Polycomb Repressive Complex 2 is essential for development and maintenance of a functional TEC compartment

Thymic epithelial cells (TEC) are essential for thymocyte differentiation and repertoire selection. Despite their indispensable role in generating functional T cells, the molecular mechanisms that orchestrate TEC development from endodermal progenitors in the third pharyngeal pouch (3rd PP) are not fully understood. We recently reported that the T-box transcription factor TBX1 negatively regulates TEC development. Although initially expressed throughout the 3rd PP, Tbx1 becomes downregulated in thymus-fated progenitors and when ectopically expressed impairs TEC progenitor proliferation and differentiation. Here we show that ectopic Tbx1 expression in thymus fated endoderm increases expression of Polycomb repressive complex 2 (PRC2) target genes in TEC. PRC2 is an epigenetic modifier that represses gene expression by catalyzing trimethylation of lysine 27 on histone H3. The increased expression of PRC2 target genes suggests that ectopic Tbx1 interferes with PRC2 activity and implicates PRC2 as an important regulator of TEC development. To test this hypothesis, we used Foxn1Cre to delete Eed, a PRC2 component required for complex stability and function in thymus fated 3rd PP endoderm. Proliferation and differentiation of fetal and newborn TEC were disrupted in the conditional knockout (EedCKO) mutants leading to severely dysplastic adult thymi. Consistent with PRC2-mediated transcriptional silencing, the majority of differentially expressed genes (DEG) were upregulated in EedCKO TEC. Moreover, a high frequency of EedCKO DEG overlapped with DEG in TEC that ectopically expressed Tbx1. These findings demonstrate that PRC2 plays a critical role in TEC development and suggest that Tbx1 expression must be downregulated in thymus fated 3rd PP endoderm to ensure optimal PRC2 function.