T-box DNA-binding Domain Research Articles

An inherited TBX3 alteration in a prenatal case of ulnar-mammary syndrome: Clinical assessment and functional characterization in Drosophila melanogaster.

Ulnar mammary syndrome (UMS) results from heterozygous variants in the TBX3 gene and impacts limb, tooth, hair, apocrine gland, and genitalia development. The expressivity of UMS is highly variable with no established genotype-phenotype correlations. TBX3 belongs to the Tbx gene family, which encodes transcription factors characterized by the presence of a T-box DNA-binding domain. We describe a fetus exhibiting severe upper limb defects and harboring the novel TBX3:c.400 C > T (p.P134S) variant inherited from the mother who remained clinically misdiagnosed until prenatal diagnosis. Literature revision was conducted to uncover the TBX3 clinical and mutational spectrum. Moreover, we generated a Drosophila humanized model for TBX3 to study the developmental consequences of the p.P134S as well as of other variants targeting different regions of the protein. Phenotypic analysis in flies, coupled with in silico modeling on the TBX3 variants, suggested that the c.400 C > T is UMS-causing and impacts TBX3 localization. Comparative analyses of the fly phenotypes caused by the expression of all variants, demonstrated that missense changes in the T-box domain affect more significantly TBX3 activity than variants outside this domain. To improve the clinicians' recognition of UMS, we estimated the frequency of the main clinical features of the disease. Core features often present pre-pubertally include defects of the ulna and/or of ulnar ray, hypoplastic nipples and/or areolas and, less frequently, genitalia anomalies in young males. These results enhance our understanding of the molecular basis and the clinical spectrum of UMS, shedding light on the functional consequences of TBX3 variants in a developmental context.

Identification and Characterization of a Master Transcription Factor of Th1 Cells, T-bet, Within Flounder (Paralichthys olivaceus).

T-bet, a T-box family member, is a transcription factor essential for the differentiation of naive CD4+ T cells into Th1 cells that are involved in both innate and adaptive immune responses. In this study, the transcription factor T-bet of flounder (Paralichthys olivaceus) was cloned and characterized, and its expression profile after infection was analyzed. T-bet+ cells were identified in flounder, and the expression and localization of T-bet in T lymphocyte subsets and B lymphocytes were investigated. Finally, the proliferation of T-bet+ cells, T lymphocyte subsets, and B lymphocytes were studied after stimulation with IFN-γ, IL-2, and IL-6, respectively, and the variations of some transcription factors and cytokines in CD4+ T lymphocyte subsets were detected. The results showed that T-bet in flounder consists of 619 aa with a conserved T-box DNA binding domain. T-bet was abundantly expressed in the spleen, head kidney, and heart, and it was significantly upregulated after infection with Vibrio anguillarum, Edwardsiella tarda, and Hirame rhabdovirus, especially in the group of Edwardsiella tarda. A polyclonal antibody against recombinant protein of T-bet was prepared, which specifically recognized the natural T-bet molecule in flounder. T-bet+ cells were found to be distributed in the lymphocytes of peripheral blood, spleen, and head kidney, with the highest proportion in spleen, and the positive signals of T-bet occurred in the cell nucleus. T-bet was also detected in the sorted CD4-1+, CD4-2+, CD8+ T lymphocytes, and IgM+ B lymphocytes. In addition, T-bet+ cells, coordinated with CD4-1+ and CD4-2+ T lymphocytes, were proliferated after stimulation with IFN-γ, IL-2, and IL-6. Especially in sorted CD4-1+ and CD4-2+ T lymphocytes, IFN-γ and IL-2 were able to upregulate the expression of T-bet, forming a positive feedback loop in Th1-type cytokine secretion. These results suggest that T-bet may act as a master transcription factor regulating flounder CD4+ T lymphocytes involved in a Th1-type immune response.

DNA‐binding specificity of TBX5 and its coding variants associated with Holt‐Oram Syndrome

Transcription factors (TFs) are important sequence‐specific DNA binding proteins that regulate gene expression and control cellular state. Evaluation of the DNA‐binding properties of transcription factors is fundamental for understanding their possible roles in controlling gene regulatory networks. TBX5 is a transcription factor that has been identified as an important regulator in organ development. TBX5 mutations have been associated to Holt‐Oram Syndrome, a genetic disorder that affects upper limb formation and often the heart. We aim to determine the specificity of DNA‐binding of TBX5 and its T‐Box DNA‐binding domain and how it changes when the protein mutates. We have cloned TBX5 and its T‐Box domain that contains a His‐ and Strep‐Tag affinity tags that we plan to use for purifying after we overexpress it in E. coli cells. We will then analyze the DNA‐binding specificity of TBX5 and the changes it conveys when it mutates using Cognate Site Identification by High‐Throughput Systematic Evolution of Ligands by Exponential enrichment (HT‐SELEX), as this will allow us to better understand the impact of TBX5 mutations on its function.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Functional characterization of TBR1 variants in neurodevelopmental disorder

Recurrent de novo variants in the TBR1 transcription factor are implicated in the etiology of sporadic autism spectrum disorders (ASD). Disruptions include missense variants located in the T-box DNA-binding domain and previous work has demonstrated that they disrupt TBR1 protein function. Recent screens of thousands of simplex families with sporadic ASD cases uncovered additional T-box variants in TBR1 but their etiological relevance is unclear. We performed detailed functional analyses of de novo missense TBR1 variants found in the T-box of ASD cases, assessing many aspects of protein function, including subcellular localization, transcriptional activity and protein-interactions. Only two of the three tested variants severely disrupted TBR1 protein function, despite in silico predictions that all would be deleterious. Furthermore, we characterized a putative interaction with BCL11A, a transcription factor that was recently implicated in a neurodevelopmental syndrome involving developmental delay and language deficits. Our findings enhance understanding of molecular functions of TBR1, as well as highlighting the importance of functional testing of variants that emerge from next-generation sequencing, to decipher their contributions to neurodevelopmental disorders like ASD.

Crystal structure of the DNA binding domain of the transcription factor T-bet suggests simultaneous recognition of distant genome sites

The transcription factor T-bet (Tbox protein expressed in T cells) is one of the master regulators of both the innate and adaptive immune responses. It plays a central role in T-cell lineage commitment, where it controls the TH1 response, and in gene regulation in plasma B-cells and dendritic cells. T-bet is a member of the Tbox family of transcription factors; however, T-bet coordinately regulates the expression of many more genes than other Tbox proteins. A central unresolved question is how T-bet is able to simultaneously recognize distant Tbox binding sites, which may be located thousands of base pairs away. We have determined the crystal structure of the Tbox DNA binding domain (DBD) of T-bet in complex with a palindromic DNA. The structure shows a quaternary structure in which the T-bet dimer has its DNA binding regions splayed far apart, making it impossible for a single dimer to bind both sites of the DNA palindrome. In contrast to most other Tbox proteins, a single T-bet DBD dimer binds simultaneously to identical half-sites on two independent DNA. A fluorescence-based assay confirms that T-bet dimers are able to bring two independent DNA molecules into close juxtaposition. Furthermore, chromosome conformation capture assays confirm that T-bet functions in the direct formation of chromatin loops in vitro and in vivo. The data are consistent with a looping/synapsing model for transcriptional regulation by T-bet in which a single dimer of the transcription factor can recognize and coalesce distinct genetic elements, either a promoter plus a distant regulatory element, or promoters on two different genes.

Transcription Factor T-Bet in Atlantic Salmon: Characterization and Gene Expression in Mucosal Tissues during Aeromonas Salmonicida Infection.

The T-box transcription factor T-bet is expressed in a number of hematopoietic cell types in mammals and plays an essential role in the lineage determination of Th1 T-helper cells and is considered as an essential feature for both innate and adaptive immune responses in higher vertebrates. In the present study, we have identified and characterized the full-length Atlantic salmon T-bet cDNA (3502 bp). The putative primary structure of the polypeptide deduced from the cDNA sequence contained 612 aa, which possessed a T-box DNA binding domain. Phylogenetic study and gene synteny revealed it is as a homolog to mammalian T-bet. Quantitative PCR analysis of different tissues in healthy fish showed that salmon T-bet gene was highly expressed in spleen, followed by head kidney, and was expressed in intestine, skin, and liver at lower levels. Moreover, the time-dependent expression profile of T-bet, interferon gamma (IFNγ), interleukin-22 (IL-22), and natural killer enhancement factor in mucosal tissues during water-borne infection with live Aeromonas salmonicida, indicated the involvement of T-bet in mucosal immune response in Atlantic salmon.

Association of TBX20 gene polymorphism with congenital heart disease in Han Chinese neonates.

As a transcription factor mainly expressed in cardiovascular system, T-box 20 (TBX20) plays an important role in embryonic cardiovascular system development and adult heart function. Previous studies have identified associations of two SNPs in the T-box DNA-binding domain of TBX20 with congenital heart disease (CHD) in two Caucasian families, but the associations of TBX20 mutations underlying the more common populations with CHD remain to be uncovered. In this study, 25 unrelated Chinese Han neonates with CHD and 25 healthy children as controls were investigated for TBX20 mutations. SNP genotyping was performed by PCR-DNA sequencing. The selected SNPs were well genotyped and SNP rs3999941 was found to be strongly associated with CHD (p=0.007). The minor allele of rs3999941 showed a high-risk factor for CHD (OR 4.24; 95% CI 1.41-12.71). Besides, we found a new SNP site located at the 657th nucleotide of the exon 5 of TBX20 gene which may also be associated with CHD, c.657A>C. The frequency was significantly different between two groups (p=0.011), the minor allele of SNP c.657A>C also showed a risk factor for CHD (OR 2.56; 95% CI 1.02-6.46). These findings suggested that the TC genotype of SNP rs3999941 and AC genotype of the new SNP c.657A>C in the TBX20 gene may be risk factors for CHD and thus screening of these SNPs may have some implications in the prevention and treatment of CHD in Han Chinese children.

Transcription analysis of two Eomesodermin genes in lymphocyte subsets of two teleost species

Eomesodermin (Eomes), a T-box transcription factor, is a key molecule associated with function and differentiation of CD8+ T cells and NK cells. Previously, two teleost Eomes genes (Eomes-a and -b), which are located on different chromosomes, were identified and shown to be expressed in zebrafish lymphocytes. For the present study, we identified these genes in rainbow trout and ginbuna crucian carp. Deduced Eomes-a and -b amino acid sequences in both fish species contain a highly conserved T-box DNA binding domain. In RT-PCR, both Eomes transcripts were readily detectable in a variety of tissues in rainbow trout and ginbuna. The high expression of Eomes-a and -b in brain and ovary suggests involvement in neurogenesis and oogenesis, respectively, while their expression in lymphoid tissues presumably is associated with immune functions. Investigation of separated lymphocyte populations from pronephros indicated that both Eomes-a and -b transcripts were few or absent in IgM+ lymphocytes, while relatively abundant in IgM−/CD8α+ and IgM−/CD8α− populations. Moreover, we sorted trout CD8α+ lymphocytes from mucosal and non-mucosal lymphoid tissues and compared the expression profiles of Eomes-a and -b with those of other T cell-related transcription factor genes (GATA-3, T-bet and Runx3), a Th1 cytokine gene (IFN-γ) and a Th2 cytokine gene (IL-4/13A). Interestingly, the tissue distribution of Eomes-a/b, T-bet, and Runx3 versus IFN-γ transcripts did not reveal simple correlations, suggesting tissue-specific properties of CD8α+ lymphocytes and/or multiple modes that drive IFN-γ expressions.

Function of the C. elegans T-box factor TBX-2 depends on SUMOylation

T-box transcription factors are critical developmental regulators in all multi-cellular organisms, and altered T-box factor activity is associated with a variety of human congenital diseases and cancers. Despite the biological significance of T-box factors, their mechanism of action is not well understood. Here we examine whether SUMOylation affects the function of the C. elegans Tbx2 sub-family T-box factor TBX-2. We have previously shown that TBX-2 interacts with the E2 SUMO-conjugating enzyme UBC-9, and that loss of TBX-2 or UBC-9 produces identical defects in ABa-derived pharyngeal muscle development. We now show that TBX-2 is SUMOylated in mammalian cell assays, and that both UBC-9 interaction and SUMOylation depends on two SUMO consensus sites located in the T-box DNA binding domain and near the TBX-2 C-terminus, respectively. In co-transfection assays, a TBX-2:GAL4 fusion protein represses expression of a 5xGal4:tk:luciferase construct. However, this activity does not require SUMOylation, indicating SUMO is not generally required for TBX-2 repressor activity. In C. elegans, reducing SUMOylation enhances the phenotype of a temperature-sensitive tbx-2 mutant and results in ectopic expression of a gene normally repressed by TBX-2, demonstrating that SUMOylation is important for TBX-2 function in vivo. Finally, we show mammalian orthologs of TBX-2, Tbx2, and Tbx3, can also be SUMOylated, suggesting SUMOylation may be a conserved mechanism controlling T-box factor activity.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-013-1336-y) contains supplementary material, which is available to authorized users.

Molecular cloning of grass carp (Ctenopharyngodon idellus) T-bet and GATA-3, and their expression profiles with IFN-γ in response to grass carp reovirus (GCRV) infection

Both T-bet and GATA-3, Th1/Th2 lineage-specific transcription factors, play important roles in the development of T cells and Th1/Th2 differentiation. In this study, T-bet and GATA-3 genes were cloned from grass carp (Ctenopharyngodon idellus). The putative primary structure of the polypeptide deduced from the cDNA sequence of grass carp T-bet contained 608 aa, which possessed a T-box DNA binding domain. The putative primary structure of the polypeptide deduced from the cDNA sequence of grass carp GATA-3 contained 396 aa, which possessed two consensus zinc finger domains (C-X(2)-C-X(17)-C-X(2)-C). The YxKxHxxxRP motif, KRRLSA and LMEKs/n sequences were also conserved in this GATA-3. Phylogenetic analysis indicated that grass carp T-bet and GATA-3 group with their known counterparts with zebrafish T-bet and GATA-3 as the closest neighbor, respectively. RT-qPCR results showed that grass carp T-bet gene was highly expressed in head kidney, followed by spleen, and low expressed in gill, liver, kidney, and intestine, while GATA-3 gene was highly expressed in intestine, followed by spleen, and low expressed in gill, liver, kidney, and head kidney. Grass carp is one of the "four important domestic fish" in China and often infected by grass carp reovirus (GCRV). As yet, there is no evidence that T-bet and GATA-3 (Th1/Th2 subsets) are involved in anti-virus immune of teleost fish. In this study, by RT-qPCR, we analyzed the expression dynamics of grass carp T-bet and GATA-3 genes with IFN-γ gene in response to GCRV infection for the first time. The expression dynamics showed that three genes might be crucially modulated by in vivo GCRV infection: (1) GCRV mainly induced a T-bet expression profile comparing to the GATA-3 expression, while the higher expression profiles of IFN-γ correlated with the up-regulation of T-bet; (2) T-bet/IFN-γ and GATA-3 expression changes suggest that in GCRV-infected grass carp, the common immune state of head kidney further heightens, whereas the common physiological state of intestine transforms to an anti-virus immune state. From this finding, we realize that GCRV mainly induces a Th1 response, and Th1 cell-mediated recognition mechanisms play very important roles in anti-virus cellular immune of grass carp.

In Vitro Site Selection of a Consensus Binding Site for the Drosophila melanogaster Tbx20 Homolog Midline

We employed in vitro site selection to identify a consensus binding sequence for the Drosophila melanogaster Tbx20 T-box transcription factor homolog Midline. We purified a bacterially expressed T-box DNA binding domain of Midline, and used it in four rounds of precipitation and polymerase-chain-reaction based amplification. We cloned and sequenced 54 random oligonucleotides selected by Midline. Electromobility shift-assays confirmed that 27 of these could bind the Midline T-box. Sequence alignment of these 27 clones suggests that Midline binds as a monomer to a consensus sequence that contains an AGGTGT core. Thus, the Midline consensus binding site we define in this study is similar to that defined for vertebrate Tbx20, but differs from a previously reported Midline binding sequence derived through site selection.

Tbx20 Transcription Factor Is a Downstream Mediator for Bone Morphogenetic Protein-10 in Regulating Cardiac Ventricular Wall Development and Function

Bone morphogenetic protein 10 (BMP10) belongs to the TGFβ-superfamily. Previously, we had demonstrated that BMP10 is a key regulator for ventricular chamber formation, growth, and maturation. Ablation of BMP10 leads to hypoplastic ventricular wall formation, and elevated levels of BMP10 are associated with abnormal ventricular trabeculation/compaction and wall maturation. However, the molecular mechanism(s) by which BMP10 regulates ventricle wall growth and maturation is still largely unknown. In this study, we sought to identify the specific transcriptional network that is potentially mediated by BMP10. We analyzed and compared the gene expression profiles between α-myosin heavy chain (αMHC)-BMP10 transgenic hearts and nontransgenic littermate controls using Affymetrix mouse exon arrays. T-box 20 (Tbx20), a cardiac transcription factor, was significantly up-regulated in αMHC-BMP10 transgenic hearts, which was validated by quantitative RT-PCR and in situ hybridization. Ablation of BMP10 reduced Tbx20 expression specifically in the BMP10-expressing region of the developing ventricle. In vitro promoter analysis demonstrated that BMP10 was able to induce Tbx20 promoter activity through a conserved Smad binding site in the Tbx20 promoter proximal region. Furthermore, overexpression of Tbx20 in myocardium led to dilated cardiomyopathy that exhibited ventricular hypertrabeculation and an abnormal muscular septum, which phenocopied genetically modified mice with elevated BMP10 levels. Taken together, our findings demonstrate that the BMP10-Tbx20 signaling cascade is important for ventricular wall development and maturation.

Characterization of the novel interaction between muskelin and TBX20, a critical cardiogenic transcription factor

The genetic regulation necessary for the formation of a four-chambered heart is tightly regulated by transcription factors such as TBX20, a member of the T-box (TBX) transcription factor family. TBX20 is critical for proper cardiogenesis and is expressed in the heart throughout development. Missense mutations in TBX20 have been found in patients with congenital heart defects (CHD). Characterization of modifiers of TBX20 activity will help elucidate the genetic mechanisms of heart development and CHD. A yeast two-hybrid assay screening an embryonic mouse heart cDNA library with TBX20b as bait was used to identify potential modifiers of TBX20 activity and identified an interaction with muskelin (MKLN1), a primarily cytoplasmic protein with potential roles in signal transduction machinery scaffolding and nucleocytoplasmic protein shuttling. In cellular studies, MKLN1 directly binds to the T-box DNA-binding domain of only the TBX20b isoform by its kelch repeats domain. Immunostaining of mammalian cells transfected with tagged TBX20b and MKLN1 revealed colocalization primarily in the cytoplasm. Immunohistochemistry analysis of embryonic mouse hearts reveals coexpression in the developing endocardial valvular and myocardial interventricular cells. This novel interaction between TBX20b and MKLN1 may help elucidate new regulatory mechanisms within heart development.

Sequence and expression analysis of two T helper master transcription factors, T-bet and GATA3, in rainbow trout Oncorhynchus mykiss and analysis of their expression during bacterial and parasitic infection

The polarization of naïve CD4+ T cells to T helper (Th)1 or Th2 cells is specified by two master transcription factors, T-bet and GATA3, and is an essential feature of mammalian adaptive immune responses to pathogens and the development of long-lasting immunity. We report here the cloning of rainbow trout Oncorhynchus mykiss T-bet and GATA3, to allow the future evaluation of the existence of Th1 and Th2 cells in salmonid fish. The trout T-bet translation shares high amino acid identities to other fish T-bet molecules (71–72%) but low identities to mammalian T-bet genes (41–42%), although the middle T-box DNA binding domain is highly conserved among all the T-bet proteins from fish and mammals. The trout GATA3 has high amino acid sequence identities (73–88%) to all known vertebrate molecules, with two highly conserved zinc finger motifs. The identity of the trout T-bet and GATA3 molecules was confirmed by phylogenetic tree analysis. A comparable expression level of T-bet and GATA3 was seen in the spleen, head kidney and muscle in healthy trout, but a higher expression level of GATA3 was seen in the gills, brain, skin and intestine relative to that of T-bet. T-bet and GATA3 expression was modulated by different stimulants. The T cell stimulant PHA up-regulated the expression of both T-bet and GATA3 in splenocytes, suggesting that they may be mainly expressed by activated T cells. The expression of T-bet and GATA3 in the spleen was increased by acute stress, but their expression was inhibited by bacterial ( Yersinia ruckeri) infection. In a parasitic infection model, Tetracapsuloides bryosalmonae infection induced a biased gene expression profile where a large increase in the expression of T-bet, IFN-γ and IL-2 was seen, suggesting that a Th1-like response is likely induced by this disease. A better understanding of pathogen modulated expression of T-bet and GATA3, and the potential underlying host immune responses elicited as a consequence of their expression, may allow novel future control measures against disease in fish to be developed.

The retinoblastoma protein modulates Tbx2 functional specificity.

Tbx2 is a member of a large family of transcription factors defined by homology to the T-box DNA-binding domain. Tbx2 plays a key role in embryonic development, and in cancer through its capacity to suppress senescence and promote invasiveness. Despite its importance, little is known of how Tbx2 is regulated or how it achieves target gene specificity. Here we show that Tbx2 specifically associates with active hypophosphorylated retinoblastoma protein (Rb1), a known regulator of many transcription factors involved in cell cycle progression and cellular differentiation, but not with the Rb1-related proteins p107 or p130. The interaction with Rb1 maps to a domain immediately carboxy-terminal to the T-box and enhances Tbx2 DNA binding and transcriptional repression. Microarray analysis of melanoma cells expressing inducible dominant-negative Tbx2, comprising the T-box and either an intact or mutated Rb1 interaction domain, shows that Tbx2 regulates the expression of many genes involved in cell cycle control and that a mutation which disrupts the Rb1-Tbx2 interaction also affects Tbx2 target gene selectivity. Taken together, the data show that Rb1 is an important determinant of Tbx2 functional specificity.

A gain-of-function TBX20 mutation causes congenital atrial septal defects, patent foramen ovale and cardiac valve defects

BackgroundOstium secundum atrial septal defects (ASDII) account for approximately 10% of all congenital heart defects (CHD), and mutations in cardiac transcription factors, including TBX20, were identified as an underlying cause...

S06-01 Cardiac transcription factors in development and disease

The homeodomain factor Nkx2-5 is expressed in cardiac progenitor cells of the first and second heart fields, and in differentiating cardiomyocytes and conduction cells. NKX2-5 mutations cause congenital heart disease (CHD) and conduction disease (CD) in humans. Nkx2-5 acts as both a repressor and an activator, and one of its early roles is to repress, through a negative feedback loop, the expression of the Bmp2 gene, which encodes one of the upstream inducers of cardiogenesis and is itself a repressor of cardiac progenitor cell proliferation. In this way Nkx2-5 orchestrates a transition between a period of cardiac induction and one of heart progenitor cell expansion and deployment. We have also studied the Nkx2-5 transcriptional cofactor, Tbx20, a member of the T-box transcription factor family, and shown that Tbx20 mutations also cause CHD as well as adult-onset dilated cardiomyopathy (DCM). The T-box DNA binding domain of Tbx20 has unique biophysical properties, with its tertiary hydrophobic interactions existing in a state of dynamic equilibrium akin to a molten globule, a state that may facilitate formation and/or stability of transcriptional complexes. Gain-of-function mutations can exacerbate this state. These studies address CHD at the molecular, cellular and organ level and contribute to an understanding of CHD origins and patient management.

Coordinated but physically separable interaction with H3K27-demethylase and H3K4-methyltransferase activities are required for T-box protein-mediated activation of developmental gene expression

During cellular differentiation, both permissive and repressive epigenetic modifications must be negotiated to create cell-type-specific gene expression patterns. The T-box transcription factor family is important in numerous developmental systems ranging from embryogenesis to the differentiation of adult tissues. By analyzing point mutations in conserved sequences in the T-box DNA-binding domain, we found that two overlapping, but physically separable regions are required for the physical and functional interaction with H3K27-demethylase and H3K4-methyltransferase activities. Importantly, the ability to associate with these histone-modifying complexes is a conserved function for the T-box family. These novel mechanisms for T-box-mediated epigenetic regulation are essential, because point mutations that disrupt these interactions are found in a diverse array of human developmental genetic diseases.

T-box transcription factor TBX20 mutations in Chinese patients with congenital heart disease

Despite animal studies having demonstrated that Tbx20 is essential for heart development, few studies have been conducted about TBX20 and congenital heart disease (CHD) in humans. Recently two TBX20 mutations have been associated with human heart defects in two Caucasian families, but TBX20 mutations underlying the more common isolated forms of CHD are still unknown. To explore this question and to analyze the association between TBX20 and susceptibility to CHD 203 Chinese patients with a variety of predominantly sporadic CHD and 300 control subjects were investigated for TBX20 mutations. The exon 2–6 contributing to the T-box DNA-binding domain and their flanking intron sequences were amplified by polymerase chain reaction (PCR) and then were sequenced after purification. Three non-synonymous mutations (A63T, I121F, and T262M) were identified in 3 patients, which were not seen in 300 controls. I121F and T262M mutations occurred within the highly conserved T-box DNA-binding domain. Two synonymous sequence variants (N222N, T262T) and one intervening variant (IVS2-5insCT) were observed in 3 patients but not in the controls. In addition, eight SNPs were observed both in patients and controls and four (S167S, P177P, A181A, and I219I) of them are novel. These data indicate that the frequency of TBX20 missense mutations occurred in Chinese CHD children is low, but they probably contribute to the risk of atrial septal defect (ASD), total anomalous pulmonary venous connection (TAPVC) and tetralogy of Fallot (TOF) in a small subset of Chinese. The findings provide the first insight into TBX20 mutations for TOF and TAPVC. Functional study involved in the new sequence variants should be subject of further investigation.

TBX3 and its splice variant TBX3 + exon 2a are functionally similar

Tbx3, a member of the conserved family of T-box developmental transcription factors, is a transcriptional repressor required during cardiogenesis for the formation and specification of the sinoatrial node, the pacemaker of the heart. Both the TBX3 and the highly related TBX2 genes are also associated with several cancers, most likely as a consequence of their powerful anti-senescence properties mediated via suppression p14(Arf) and p21(CIP) expression. In melanoma, the TBX2 gene is frequently amplified and inhibition of Tbx2 function leads to senescence and up-regulation of p21(CIP), a Tbx2 target gene. Tbx3 + 2a is a splice variant containing an extra 20 amino acids encoded by exon 2a inserted into the highly conserved T-box DNA-binding domain. We find here that Tbx3 + 2a is evolutionary conserved and that similar insertions are largely absent from the T-box domains of other T-box factors. Tbx3 + 2a has been reported to lack DNA-binding ability and act as a functional antagonist of Tbx3. By contrast, we now demonstrate that both Tbx3 and Tbx3 + 2a bind the consensus T-element, the p21(CIP1) promoter, and the Nppa cardiac target gene. Both isoforms also function as repressors of p21(CIP1) and Nppa promoter activity and interact with homeobox factor Nkx2-5. When ectopically expressed in the embryonic heart of mice, Tbx3 and Tbx3 + 2a both suppressed chamber formation and repressed expression of cardiac chamber markers Nppa and Cx40. The results suggest that in the assays used, Tbx3 and Tbx3 + 2a are functionally equivalent and that like Tbx2, Tbx3 may also function as an anti-senescence factor in melanoma.