Microarray analysis of Tbx2-directed gene expression: a possible role in osteogenesis

A Novel Osteochondrodysplasia With Empty Sella Associates With a TBX2 Variant

Skeletal dysplasias comprise a heterogenous group of developmental disorders of skeletal and cartilaginous tissues. Several different forms have been described and the full spectrum of their clinical manifestations and underlying genetic causes are still incompletely understood. We report a three-generation Finnish family with an unusual, autosomal dominant form of osteochondrodysplasia and an empty sella. Affected individuals (age range 24-44 years) exhibit unusual codfish-shaped vertebrae, severe early-onset and debilitating osteoarthritis and an empty sella without endocrine abnormalities. Clinical characteristics also include mild dysmorphic features, reduced sitting height ratio, and obesity. Whole-exome sequencing excluded known skeletal dysplasias and identified a novel heterozygous missense mutation c.899C>T (p.Thr300Met) in TBX2, confirmed by Sanger sequencing. TBX2 is important for development of the skeleton and the brain and three prior reports have described variations in TBX2 in patients portraying a complex phenotype with vertebral anomalies, craniofacial dysmorphism and endocrine dysfunctions. Our mutation lies near a previously reported disease-causing variant and is predicted pathogenic with deleterious effects on protein function. Our findings expand the current spectrum of skeletal dysplasias, support the association of TBX2 mutations with skeletal dysplasia and suggest a role for TBX2 in development of the spinal and craniofacial structures and the pituitary gland.

Cuticle Collagen Expression Is Regulated in Response to Environmental Stimuli by the GATA Transcription Factor ELT-3 in Caenorhabditis elegans

The nematode Caenorhabditis elegans is protected from the environment by the cuticle, an extracellular collagen-based matrix that encloses the animal. Over 170 cuticular collagens are predicted in the C. elegans genome, but the role of each individual collagen is unclear. Stage-specific specialization of the cuticle explains the need for some collagens; however, the large number of collagens suggests that specialization of the cuticle may also occur in response to other environmental triggers. Missense mutations in many collagen genes can disrupt cuticle morphology, producing a helically twisted body causing the animal to move in a stereotypical pattern described as rolling. We find that environmental factors, including diet, early developmental arrest, and population density can differentially influence the penetrance of rolling in these mutants. These effects are in part due to changes in collagen gene expression that are mediated by the GATA family transcription factor ELT-3 We propose a model by which ELT-3 regulates collagen gene expression in response to environmental stimuli to promote the assembly of a cuticle specialized to a given environment.

Cardiac Differentiation of Adipose Tissue-Derived Stem Cells Is Driven by BMP4 and bFGF but Counteracted by 5-Azacytidine and Valproic Acid

Objective

Bone morphogenetic protein 4 (BMP4) and basic fibroblast growth factor (bFGF) play important roles in embryonic heart development. Also, two epigenetic modifying molecules, 5'-azacytidine (5'-Aza) and valproic acid (VPA) induce cardiomyogenesis in the infarcted heart. In this study, we first evaluated the role of BMP4 and bFGF in cardiac trans-differentiation and then the effectiveness of 5´-Aza and VPA in reprogramming and cardiac differentiation of human adipose tissue-derived stem cells (ADSCs).

Materials and Methods

In this experimental study, human ADSCs were isolated by collagenase I digestion. For cardiac differentiation, third to fifth-passaged ADSCs were treated with BMP4 alone or a combination of BMP4 and bFGF with or without 5'-Aza and VPA pre-treatment. After 21 days, the expression of cardiac-specific markers was evaluated by reverse transcription polymerase chain reaction (RT-PCR), quantitative real-time PCR, immunocytochemistry, flow cytometry and western blot analyses.

Results

BMP4 and more prominently a combination of BMP4 and bFGF induced cardiac differentiation of human ADSCs. Epigenetic modification of the ADSCs by 5'-Aza and VPA significantly upregulated the expression of OCT4A, SOX2, NANOG, Brachyury/T and GATA4 but downregulated GSC and NES mRNAs. Furthermore, pre-treatment with 5'-Aza and VPA upregulated the expression of TBX5, ANF, CX43 and CXCR4 mRNAs in three-week differentiated ADSCs but downregulated the expression of some cardiac-specific genes and decreased the population of cardiac troponin I-expressing cells.

Conclusion

Our findings demonstrated the inductive role of BMP4 and especially BMP4 and bFGF combination in cardiac trans-differentiation of human ADSCs. Treatment with 5'-Aza and VPA reprogrammed ADSCs toward a more pluripotent state and increased tendency of the ADSCs for mesodermal differentiation. Although pre-treatment with 5'-Aza and VPA counteracted the cardiogenic effects of BMP4 and bFGF, it may be in favor of migration, engraftment and survival of the ADSCs after transplantation.

Molecular determinants of mesenchymal cell activation in fibroproliferative diseases

Uncontrolled scarring, or fibrosis, can interfere with the normal function of virtually all tissues of the body, ultimately leading to organ failure and death. Fibrotic diseases represent a major cause of death in industrialized countries. Unfortunately, no curative treatments for these conditions are yet available, highlighting the critical need for a better fundamental understanding of molecular mechanisms that may be therapeutically tractable. The ultimate indispensable effector cells responsible for deposition of extracellular matrix proteins that comprise scars are mesenchymal cells, namely fibroblasts and myofibroblasts. In this review, we focus on the biology of these cells and the molecular mechanisms that regulate their pertinent functions. We discuss key pro-fibrotic mediators, signaling pathways, and transcription factors that dictate their activation and persistence. Because of their possible clinical and therapeutic relevance, we also consider potential brakes on mesenchymal cell activation and cellular processes that may facilitate myofibroblast clearance from fibrotic tissue-topics that have in general been understudied.

T-Box20 inhibits osteogenic differentiation in adipose-derived human mesenchymal stem cells: the role of T-Box20 on osteogenesis

Background

Skeletal development and its cellular function are regulated by various transcription factors. The T-box (Tbx) family of transcription factors have critical roles in cellular differentiation as well as heart and limbs organogenesis. These factors possess activator and/or repressor domains to modify the expression of target genes. Despite the obvious effects of Tbx20 on heart development, its impact on bone development is still unknown.

Methods

To investigate the consequence by forced Tbx20 expression in the osteogenic differentiation of human mesenchymal stem cells derived from adipose tissue (Ad-MSCs), these cells were transduced with a bicistronic lentiviral vector encoding Tbx20 and an enhanced green fluorescent protein.

Results

Tbx20 gene delivery system suppressed the osteogenic differentiation of Ad-MSCs, as indicated by reduction in alkaline phosphatase activity and Alizarin Red S staining. Consistently, reverse transcription-polymerase chain reaction analyses showed that Tbx20 gain-of-function reduced the expression levels of osteoblast marker genes in osteo-inductive Ad-MSCs cultures. Accordingly, Tbx20 negatively affected osteogenesis through modulating expression of key factors involved in this process.

Conclusion

The present study suggests that Tbx20 could inhibit osteogenic differentiation in adipose-derived human mesenchymal stem cells.

Apabetalone downregulates factors and pathways associated with vascular calcification

BACKGROUND AND AIMS

Apabetalone is an inhibitor of bromodomain and extraterminal (BET) proteins. In clinical trials, apabetalone reduced the incidence of major adverse cardiac events (MACE) in patients with cardiovascular disease and reduced circulating factors that promote vascular calcification (VC). Because VC contributes to MACE, effects of apabetalone on pro-calcific processes were examined.

METHODS AND RESULTS

Apabetalone inhibited extracellular calcium deposition and opposed induction of transdifferentiation markers in human coronary artery vascular smooth muscle cells (VSMCs) under osteogenic culture conditions. Tissue-nonspecific alkaline phosphatase (TNAP) is a key contributor to VC, and apabetalone suppressed osteogenic induction of the mRNA, protein and enzyme activity. The liver is a major source of circulating TNAP, and apabetalone also downregulated TNAP expression in primary human hepatocytes. BRD4, a transcriptional regulator and target of apabetalone, has been linked to calcification. Osteogenic transdifferentiation of VSMCs resulted in disassembly of 100 BRD4-rich enhancers, with concomitant enlargement of remaining enhancers. Apabetalone reduced the size of BRD4-rich enhancers, consistent with disrupting BRD4 association with chromatin. 38 genes were uniquely associated with BRD4-rich enhancers in osteogenic conditions; 11 were previously associated with calcification. Apabetalone reduced levels of BRD4 on many of these enhancers, which correlated with decreased expression of the associated gene. Bioinformatics revealed BRD4 may cooperate with 7 specific transcription factors to promote transdifferentiation and calcification.

CONCLUSIONS

Apabetalone counters transdifferentiation and calcification of VSMCs via an epigenetic mechanism involving specific transcription factors. The mechanistic findings, combined with evidence from clinical trials, support further development of apabetalone as a therapeutic for VC.

Microphthalmia-associated transcription factor/T-box factor-2 axis acts through Cyclin D1 to regulate melanocyte proliferation

OBJECTIVES

Control of cell proliferation is critical for accurate cell differentiation and tissue formation, during development and regeneration. Here, we have analysed the role of microphthalmia-associated transcription factor MITF and its direct target, T-box factor TBX2, in regulating proliferation of mammalian neural crest-derived melanocytes.

MATERIALS AND METHODS

Immunohistochemistry was used to examine spatial and temporal expression of TBX2 in melanocytes in vivo. RNAi and cell proliferation analysis were used to investigate functional roles of TBX2. Furthermore, quantitative RT-PCR, western blot analysis and flow cytometry were used to further scrutinize molecular mechanisms underlying TBX2-dependent cell proliferation.

RESULTS

TBX2 was found to be co-expressed with MITF in melanocytes of mouse hair follicles. Specific Tbx2 knockdown in primary neural crest cells led to inhibition MITF-positive melanoblast proliferation. Tbx2 knockdown in melan-a cells led to reduction in Cyclin D1 expression and G1-phase cell cycle arrest. TBX2 directly activated Ccnd1 transcription by binding to a specific sequence in the Ccnd1 promoter, and the defect in cell proliferation could be rescued partially by overexpression of Cyclin D1 in Tbx2 knockdown melanocytes.

CONCLUSIONS

Results suggest that the Mitf-Tbx2-Cyclin D1 pathway played an important role in regulation of melanocyte proliferation, and provided novel insights into the complex physiology of melanocytes.

Characteristic expression of MSX1, MSX2, TBX2 and ENTPD1 in dental pulp cells

Dental pulp cells (DPCs) are a promising source of transplantable cells in regenerative medicine. However, DPCs have not been fully characterized at the molecular level. The aim of the present study was to distinguish DPCs from various source-derived mesenchymal stem cells (MSCs), fibroblasts (FBs) and other cells by the expression of several DPC-characteristic genes. DPCs were isolated from human pulp tissues by the explant method or the enzyme digestion method, and maintained with media containing 10% serum or 7.5% platelet-rich plasma. RNA was isolated from the cells and from dental pulp tissue specimens. The mRNA levels were determined by DNA microarray and quantitative polymerase chain reaction analyses. The msh homeobox 1, msh homeobox 2, T-box 2 and ectonucleoside triphosphate diphosphohydrolase 1 mRNA levels in DPCs were higher than that of the levels identified in the following cell types: MSCs derived from bone marrow, synovium and adipose tissue; and in cells such as FBs, osteoblasts, adipocytes and chondrocytes. The enhanced expression in DPCs was consistently observed irrespective of donor age, tooth type and culture medium. In addition, these genes were expressed at high levels in dental pulp tissue in vivo. In conclusion, this gene set may be useful in the identification and characterization of DPCs in basic studies and pulp cell-based regeneration therapy.

Tbx2/3 is an essential mediator within the Brachyury gene network during Ciona notochord development

T-box genes are potent regulators of mesoderm development in many metazoans. In chordate embryos, the T-box transcription factor Brachyury (Bra) is required for specification and differentiation of the notochord. In some chordates, including the ascidian Ciona, members of the Tbx2 subfamily of T-box genes are also expressed in this tissue; however, their regulatory relationships with Bra and their contributions to the development of the notochord remain uncharacterized. We determined that the notochord expression of Ciona Tbx2/3 (Ci-Tbx2/3) requires Ci-Bra, and identified a Ci-Tbx2/3 notochord CRM that necessitates multiple Ci-Bra binding sites for its activity. Expression of mutant forms of Ci-Tbx2/3 in the developing notochord revealed a role for this transcription factor primarily in convergent extension. Through microarray screens, we uncovered numerous Ci-Tbx2/3 targets, some of which overlap with known Ci-Bra-downstream notochord genes. Among the Ci-Tbx2/3 notochord targets are evolutionarily conserved genes, including caspases, lineage-specific genes, such as Noto4, and newly identified genes, such as MLKL. This work sheds light on a large section of the notochord regulatory circuitry controlled by T-box factors, and reveals new components of the complement of genes required for the proper formation of this structure.

The T box transcription factor TBX2 promotes epithelial-mesenchymal transition and invasion of normal and malignant breast epithelial cells

The T box transcription factor TBX2, a master regulator of organogenesis, is aberrantly amplified in aggressive human epithelial cancers. While it has been shown that overexpression of TBX2 can bypass senescence, a failsafe mechanism against cancer, its potential role in tumor invasion has remained obscure. Here we demonstrate that TBX2 is a strong cell-autonomous inducer of the epithelial-mesenchymal transition (EMT), a latent morphogenetic program that is key to tumor progression from noninvasive to invasive malignant states. Ectopic expression of TBX2 in normal HC11 and MCF10A mammary epithelial cells was sufficient to induce morphological, molecular, and behavioral changes characteristic of EMT. These changes included loss of epithelial adhesion and polarity gene (E-cadherin, ß-catenin, ZO1) expression, and abnormal gain of mesenchymal markers (N-cadherin, Vimentin), as well as increased cell motility and invasion. Conversely, abrogation of endogenous TBX2 overexpression in the malignant human breast carcinoma cell lines MDA-MB-435 and MDA-MB-157 led to a restitution of epithelial characteristics with reciprocal loss of mesenchymal markers. Importantly, TBX2 inhibition abolished tumor cell invasion and the capacity to form lung metastases in a Xenograft mouse model. Meta-analysis of gene expression in over one thousand primary human breast tumors further showed that high TBX2 expression was significantly associated with reduced metastasis-free survival in patients, and with tumor subtypes enriched in EMT gene signatures, consistent with a role of TBX2 in oncogenic EMT. ChIP analysis and cell-based reporter assays further revealed that TBX2 directly represses transcription of E-cadherin, a tumor suppressor gene, whose loss is crucial for malignant tumor progression. Collectively, our results uncover an unanticipated link between TBX2 deregulation in cancer and the acquisition of EMT and invasive features of epithelial tumor cells.

The retinoblastoma protein modulates Tbx2 functional specificity

This study demonstrates that Tbx2 binds Rb1. The interaction with Rb1 increases Tbx2 DNA-binding activity and enhances the ability of Tbx2 to repress transcription. The results show that Tbx2 regulates the expression of genes involved in cell division and DNA replication and that Rb1 modulates Tbx2 target gene recognition and 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.

The T-box transcription factor Tbx2: its role in development and possible implication in cancer

Tbx2 is a member of the T-box family of transcription factors that are crucial in embryonic development. Recent studies suggest that T-box factors may also play a role in controlling cell cycle progression and in the genesis of cancer. Tbx2 has been implicated in several developmental processes such as coordinating cell fate, patterning and morphogenesis of a wide range of tissues and organs including limbs, kidneys, lungs, mammary glands, heart, and craniofacial structures. Importantly, Tbx2 is overexpressed in several cancers including melanoma, small cell lung carcinoma, breast, pancreatic, liver, and bladder cancers and can suppress senescence, a cellular process, which serves as a barrier to cancer development. This review presents a state of the art overview of the role and regulation of Tbx2 in early embryonic development and in cancer.

Tbx2 misexpression impairs deployment of second heart field derived progenitor cells to the arterial pole of the embryonic heart

Tbx2 is a member of the T-box family of transcription factors that play important roles during heart development. In the embryonic heart tube, Tbx2 is expressed in non-chamber myocardium (outflow tract and interventricular canal) and has been shown to block chamber formation. We have developed a genetic system to conditionally misexpress Tbx2 in the embryonic mouse heart at early stages of development. We show that Tbx2 expression throughout the myocardium of the heart tube both represses proliferation and impairs secondary heart field (SHF) progenitor cell deployment into the outflow tract (OFT). Repression of proliferation is accompanied by the upregulation of Ndrg2 and downregulation of Ndrg4 expression, both genes believed to be involved in cell growth and proliferation. Impaired deployment of SHF cells from the pharyngeal mesoderm is accompanied by downregulation of the cell adhesion molecules Alcam and N-cadherin in the anterior part of the embryonic heart. Tbx2 misexpression also results in downregulation of Tbx20 within the OFT, indicating complex and region-specific transcriptional cross-regulation between the two T-box genes.

T-box 3 negatively regulates osteoblast differentiation by inhibiting expression of osterix and runx2

T-box (Tbx)3, a known transcriptional repressor, is a member of a family of transcription factors, which contain a highly homologous DNA binding domain known as the Tbx domain. Based on the knowledge that mutation of the Tbx3 gene results in limb malformation, Tbx3 regulates osteoblast proliferation and its expression increases during osteoblast differentiation, we predicted that Tbx3 is an important regulator of osteoblast cell functions. In this study, we evaluated the consequence of transgenic overexpression of Tbx3 on osteoblast differentiation. Retroviral overexpression increased Tbx3 expression >100-fold at the mRNA and protein level. Overexpression of Tbx3 blocked mineralized nodule formation (28 +/- 8 vs. 7 +/- 1%) in MC3T3-E1 cells. In support of these data, alkaline phosphatase (ALP) activity was reduced 33-70% (P < 0.05) in both MC3T3-E1 cells and primary calvaria osteoblasts overexpressing Tbx3. In contrast, Tbx3 overexpression did not alter ALP activity in bone marrow stromal cells. Tbx3 overexpression blocked the increase in expression of key osteoblast marker genes, ALP, bone sialoprotein, and osteocalcin that occurs during normal osteoblast differentiation, but had little or no effect on expression of proliferation genes p53 and Myc. In addition, Tbx3 overexpression abolished increased osterix and runx2 expression observed during normal osteoblast differentiation, but the change in Msx1 and Msx2 expression over time was similar between control and Tbx3 overexpressing cells. Interestingly, osterix and runx2, but not Msx1 and Msx2, contain Tbx binding site in the regulatory region. Based on these data and our previous findings, we conclude that Tbx3 promotes proliferation and suppresses differentiation of osteoblasts and may be involved in regulating expression of key transcription factors involved in osteoblast differentiation.

A role for Tbx2 in the regulation of the alpha2(1) collagen gene in human fibroblasts

The T-box gene family encodes highly conserved transcription factors that play important roles in embryonic development and have been implicated in carcinogenesis. One member of the family, Tbx2, is generally regarded as a transcriptional repressor but appears to be capable of functioning as an activator depending on the cellular context. This study shows that Tbx2 is expressed in normal human fibroblasts but is drastically reduced in several transformed fibroblast cell lines. This pattern of Tbx2 expression correlated with that observed for the human alpha2(1) collagen gene (COL1A2). Interestingly, stable expression of transfected Tbx2 in transformed fibroblast cell lines further reduces expression of the human endogenous COL1A2 gene. This ability of Tbx2 to repress the human COL1A2 gene was confirmed in luciferase reporter assays and shown to be independent of the consensus T-box binding element.

Analysis of gene expression in the tumor-associated macrophage

INTRODUCTION

The tumor-associated macrophage (TAM) is at the front line of the host's defense against malignancy and provides an attractive target for immune-modulatory therapy. However, factors present within the tumor microenvironment can alter macrophage phenotype, preventing its cytotoxic activity and reducing its susceptibility to interferon-gamma and lipopolysaccharide-mediated stimulation.

METHODS

Macrophages were isolated from subcutaneous B16 melanoma tumors implanted in C57 BL/6 mice. Wound macrophages were harvested from subcutaneously-implanted PVA sponges, and resting peritoneal macrophages were harvested by peritoneal lavage. Gene expression was analyzed using an Atlas cDNA array (Clontech, Mountain View, CA).

RESULTS

TAM demonstrated a pattern of gene expression distinct from both wound and peritoneal macrophage. There is an increase in proliferation-associated genes and in genes encoding the ultrastructural proteins cofillin, zyxin, and vimentin more commonly associated with fibroblast-like cells. In addition, an observed decrease in expression of the CD14 gene, and increase in inhibitory pathways including osteopontin and its receptor CD44, the inositol 1,4,5-triphosphate receptor, and the receptors for interleukin-4 and granulocyte monocyte-colony stimulating factor could explain the resistance of TAM to lipopolysaccharide-mediated stimulation. There was also a significant decrease in the expression of the interferon-gamma second messenger, IRF-1.

CONCLUSIONS

This study has identified a number of pathways involved in the suppression of TAM function. Targeting of these pathways may allow for the generation of more effective immune-modulatory anti-neoplastic therapy.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Cluster analysis and gene expression profiles: a cDNA microarray system-based comparison between human dental pulp stem cells (hDPSCs) and human mesenchymal stem cells (hMSCs) for tissue engineering cell therapy

We investigated gene expression patterns and functional classifications regarding the clusters of human dental pulp stem cells (hDPSCs) and human mesenchymal stem cells (hMSCs)--which possess a multipotent ability--because little is known about the precise moleculobiological clues by which these cells activate their differentiating ability or functionality to eventually form dentin and bone, respectively. We first verified the expressions of the alkaline phosphatase (ALP) gene, dentin matrix protein 1 (DMP-1), and dentinsialophosphoprotein (DSPP) by real-time reverse-transcriptase polymerase chain reaction (RT-PCR) and consequently discovered the high expressions of these genes. Total RNA was also followed by hybridization with a human microarray system consisting of 12,814 genes. Analyses of gene expression patterns indicated several genes which encode extracellular matrix components, cell adhesion molecules, growth factors, and transcription regulators. Functional and clustering analyses of differences in gene expression levels revealed cell signaling, cell communication, or cell metabolism. In the future, information on the gene expression patterns of hDPSCs and hMSCs might be useful in determining the detailed functional roles of the relevant genes and applicable to stem cell therapies, and these cells could also be used as multipotent cell sources for gene technology and tissue engineering technology.

Key stages of mammary gland development: molecular mechanisms involved in the formation of the embryonic mammary gland

The development of the embryonic mammary gland involves communication between the epidermis and mesenchyme and is coordinated temporally and spatially by various signaling pathways. Although many more genes are likely to control mammary gland development, functional roles have been identified for Wnt, fibroblast growth factor, and parathyroid hormone-related protein signaling. This review describes what is known about the molecular mechanisms that regulate embryonic mammary gland development.

The relative role of the T-domain and flanking sequences for developmental control and transcriptional regulation in protein chimeras of Drosophila OMB and ORG-1

optomotor-blind (omb) and optomotor-blind related-1 (org-1) encode T-domain DNA binding proteins in Drosophila. Members of this family of transcription factors play widely varying roles during early development and organogenesis in both vertebrates and invertebrates. Functional specificity differs in spite of similar DNA binding preferences of all family members. Using a series of domain swap chimeras, in which different parts of OMB and ORG-1 were mutually exchanged, we investigated the relevance of individual domains in vitro and in vivo. In cell culture transfection assays, ORG-1 was a strong transcriptional activator, whereas OMB appeared neutral. The main transcriptional activation function was identified in the C-terminal part of ORG-1. Also in vivo, OMB and ORG-1 showed qualitative differences when the proteins were ectopically expressed during development. Gain-of-function expression of OMB is known to counteract eye formation and resulted in the loss of the arista, whereas ORG-1 had little effect on eye development but caused antenna-to-leg transformations and shortened legs in the corresponding gain-of-function situations. The functional properties of OMB/ORG-1 chimeras in several developmental contexts was dominated by the origin of the C-terminal region, suggesting that the transcriptional activation potential can be one major determinant of developmental specificity. In late eye development, we observed, however, a strong influence of the T-domain on ommatidial differentiation. The specificity of chimeric omb/org-1transgenes, thus, depended on the cellular context in which they were expressed. This suggests that both transcriptional activation/repression properties as well as intrinsic DNA binding specificity can contribute to the functional characteristics of T-domain factors.

Differential target gene activation by TBX2 and TBX2VP16: evidence for activation domain-dependent modulation of gene target specificity

The determinants of in vivo target site selectivity by transcription factors are poorly understood. To find targets for the developmentally regulated transcription factor TBX2, we generated stable transfectants of human embryonic kidney cells (293) that express a TBX2-ecdysone receptor (EcR) chimeric protein. While constitutive expression of TBX2 is toxic to 293 cells, clones expressing TBX2EcR are viable in the absence of an EcR ligand. Using cDNA arrays and quantitative PCR, we discovered nine genes whose expression was increased, but no genes whose expression was reduced, following 24 h of induction with Ponasterone A (PonA), a ligand for EcR. Since TBX2 was reported previously to be a transcriptional repressor, we also generated cell lines expressing a TBX2VP16EcR protein which we showed was a potent conditional transcriptional activator in transient transfection assays. Treatment of these cells with PonA induced the expression of five genes, none of which were affected in TBX2EcR-expressing cells. This discordance between TBX2- and TBX2VP16-regulated genes strongly suggests that specific transactivation domains can be a major determinant of gene target site selectivity by transcription factors that possess the same DNA-binding domain.

Sonic hedgehog signaling regulates Gli3 processing, mesenchymal proliferation, and differentiation during mouse lung organogenesis

Lack of Sonic hedgehog (Shh) signaling, mediated by the Gli proteins, leads to severe pulmonary hypoplasia. However, the precise role of Gli genes in lung development is not well established. We show Shh signaling prevents Gli3 proteolysis to generate its repressor forms (Gli3R) in the developing murine lung. In Shh(-/-) or cyclopamine-treated wild-type (WT) lung, we found that Gli3R level is elevated, and this upregulation appears to contribute to defects in proliferation and differentiation observed in the Shh(-/-) mesenchyme, where Gli3 is normally expressed. In agreement, we found Shh(-/-);Gli3(-/-) lungs exhibit enhanced growth potential. Vasculogenesis is also enhanced; in contrast, bronchial myogenesis remains absent in Shh(-/-);Gli3(-/-) compared with Shh(-/-) lungs. Genes upregulated in Shh(-/-);Gli3(-/-) relative to Shh(-/-) lung include Wnt2 and, surprisingly, Foxf1 whose expression has been reported to be Shh-dependent. Cyclins D1, D2, and D3 antibody labelings also reveal distinct expression patterns in the normal and mutant lungs. We found significant repression of Tbx2 and Tbx3, both linked to inhibition of cellular senescence, in Shh(-/-) and partial derepression in Shh(-/-); Gli3(-/-) lungs, while Tbx4 and Tbx5 expressions are less affected in the mutants. Our findings shed light on the role of Shh signaling on Gli3 processing in lung growth and differentiation by regulating several critical genes.

T-box binding protein type two (TBX2) is an immediate early gene target in retinoic-acid-treated B16 murine melanoma cells

Retinoic acid induces growth arrest and differentiation in B16 mouse melanoma cells. Using gene arrays, we identified several early response genes whose expression is altered by retinoic acid. One of the genes, tbx2, is a member of T-box nuclear binding proteins that are important morphogens in developing embryos. Increased TBX2 mRNA is seen within 2 h after addition of retinoic acid to B16 cells. The effect of retinoic acid on gene expression is direct since it does not require any new protein synthesis. We identified a degenerate retinoic acid response element (RARE) between -186 and -163 in the promoter region of the tbx2 gene. A synthetic oligonucleotide spanning this region was able to drive increased expression of a luciferase reporter gene in response to retinoic acid; however, this induction was lost when a point mutation was introduced into the RARE. This oligonucleotide also specifically bound RAR in nuclear extracts from B16 cells. TBX2 expression and its induction by retinoic acid was also observed in normal human and nonmalignant mouse melanocytes.

T-box transcription factor Tbx2 represses differentiation and formation of the cardiac chambers

Specific regions of the embryonic heart tube differentiate into atrial and ventricular chamber myocardium, whereas the inflow tract, atrioventricular canal, inner curvatures, and outflow tract do not. These regions express Tbx2, a transcriptional repressor. Here, we tested its role in chamber formation. The temporal and spatial pattern of Tbx2 mRNA and protein expression in mouse hearts was found to be complementary to that of chamber myocardium-specific genes Nppa, Cx40, Cx43, and Chisel, and was conserved in human. In vitro, Tbx2 repressed the activity of regulatory fragments of Cx40, Cx43, and Nppa. Hearts of transgenic embryos that expressed Tbx2 in the prechamber myocardium completely failed to form chambers and to express the chamber myocardium-specific genes Nppa, Cx40, and Chisel, whereas other cardiac genes were normally expressed. These findings provide the first evidence that Tbx2 is a determinant in the local repression of chamber-specific gene expression and chamber differentiation.

The role of Tbx2 and Tbx3 in mammary development and tumorigenesis

TBX2 and TBX3 are members of a family of genes encoding developmental transcription factors, characterized by a 200 amino acid DNA binding domain (T-box). Tbx2 and Tbx3 are closely related T-box proteins that have been implicated in development of a number of different tissues including the mammary gland. TBX3 is required for normal mammary development in mouse models and in patients with ulnar-mammary syndrome (UMS). In addition to a role in development, TBX2 and TBX3 have been implicated in tumor development through downregulation of the alternative reading frame (ARF) tumor suppressor and an associated bypass of senescence. Here we review the current information on the roles of Tbx2 and Tbx3 in mammary gland development and tumorigenesis.

Tension–Induced Reduction in Connexin 43 Expression in Cranial Sutures Is Linked to Transcriptional Regulation by TBX2

Cranial sutures produce bone at precisely the right rate and time to maintain homeostasis. Connexin 43 (CX43), a protein important for communication in bone, is downregulated during cell proliferation and is released from suppression or upregulated during differentiation. Our previous studies have shown that binding sites for the transcription regulatory protein TBX2 are located in the promoter sequence, upstream of the Cx43 gene. We have shown that TBX2 binding suppresses Cx43 expression. The current study uses transgenic mice in which the TBX2 promoter has been spliced upstream of the coding sequence for green fluorescent protein (GFP). This study shows upregulation of TBX2 after stretching. RNA from stretched and unstretched sutures was used for GeneChip and Western analysis. The results show an increase in Tbx2 and a decrease in Cx43 gene and protein expression with stretch. Our findings support a model of strain-regulated bone formation with feedback inhibition that maintains sutural patency during development.

A fractal analysis of human cranial sutures

OBJECTIVES

Many biological structures are products of repeated iteration functions. As such, they demonstrate characteristic, scale-invariant features. Fractal analysis of these features elucidates the mechanism of their formation. The objectives of this project were to determine whether human cranial sutures demonstrate self-similarity and measure their exponents of similarity (fractal dimensions).

DESIGN

One hundred three documented human skulls from the Terry Collection of the Smithsonian Institution were used. Their sagittal sutures were digitized and the data converted to bitmap images for analysis using box-counting method of fractal software.

RESULTS

The log-log plots of the number of boxes containing the sutural pattern, N(r), and the size of the boxes, r, were all linear, indicating that human sagittal sutures possess scale-invariant features and thus are fractals. The linear portion of these log-log plots has limits because of the finite resolution used for data acquisition. The mean box dimension, D(b), was 1.29289 +/- 0.078457 with a 95% confidence interval of 1.27634 to 1.30944.

CONCLUSIONS

Human sagittal sutures are self-similar and have a fractal dimension of 1.29 by the box-counting method. The significance of these findings includes: sutural morphogenesis can be described as a repeated iteration function, and mathematical models can be constructed to produce self-similar curves with such D(b). This elucidates the mechanism of actual pattern formation. Whatever the mechanisms at the cellular and molecular levels, human sagittal suture follows the equation log N(r) = 1.29 log 1/r, where N(r) is the number of square boxes with sides r that are needed to contain the sutural pattern and r equals the length of the sides of the boxes.

Negative transcriptional regulation of connexin 43 by Tbx2 in rat immature coronal sutures and ROS 17/2.8 cells in culture

BACKGROUND

Tbx2 is a member of the T-box family of transcriptional regulatory genes with an extensive but not yet fully understood role in embryonic development. This study explores the potential role of Tbx2 in calvarial morphogenesis.

OBJECTIVES

To explore the hypothesis that Tbx2 has a negative regulatory effect on the expression of connexin 43 (Cx43), a protein necessary for cell-to-cell communication; document the presence of Tbx2 protein in the developing cranial sutures; and determine the spatial pattern of expression of this developmentally regulated transcription factor in calvariae.

DESIGN

The osteoblast-like cell line ROS 17/2.8 was stably transfected with sense or antisense Tbx2. Immunohistochemistry and Western blotting was used to study Tbx2 and Cx43 expression in these cells and sections of embedded developing coronal sutures.

RESULTS

The ROS 17/2.8 cells transfected with antisense Tbx2 showed a decrease in expression of Tbx2 protein and an increase in expression of endogenous Cx43. The reverse is seen with sense-transfected cells. Both of these proteins are expressed in rat developing coronal sutures. The pattern of Tbx2 expression in the developing was also reciprocal to the pattern of Cx43 expression. Tbx2 protein is concentrated in the center of the sutural blastema, an area devoid of Cx43 protein localization. Conversely, Tbx2 protein expression is low in the periphery of the sutures, in which there is high Cx43 protein expression.

CONCLUSIONS

Taken together, these studies suggest that Tbx2 protein is a negative regulator of Cx43 expression at the transcriptional level in cranial sutures in vivo.

Coquillette, a sea urchin T-box gene of the Tbx2 subfamily, is expressed asymmetrically along the oral-aboral axis of the embryo and is involved in skeletogenesis

Transcription factors of the T-domain family regulate many developmental processes. We have isolated from the sea urchin a new member of the Tbx2 subfamily: coquillette. Coquillette has a late zygotic expression whose localization is dynamic: at the blastula stage it is restricted to the aboral side of most of the presumptive ectoderm and endoderm territories and from gastrulation on, to the aboral-most primary mesenchyme cells. Perturbation of coquillette function delays gastrulation and strongly disorganizes the skeleton of the larva. Coquillette is sensitive to alteration of the oral-aboral (OA) axis and we identify goosecoid, which controls oral and aboral fates in the ectoderm, as a probable upstream regulator. Coquillette appears to be an integral part of the patterning system along the OA axis.

The 17q23 amplicon and breast cancer

A novel region of amplification in breast tumors was recently identified on chromosome 17q23. Extensive mapping of the amplicon by Southern blotting and fluorescence in situ hybridization (FISH) in breast cancer cell lines determined that the amplicon can be up to 4 Mbp in size and may contain 50 genes. Copy number analysis at 50-75 kb resolution in breast cancer cell lines and breast tumors identified several independently amplified regions within the amplicon, suggesting that a number of genes are selected for amplification because they independently contribute to tumor formation and progression. Support for this hypothesis comes from studies demonstrating that many of the amplified genes are over-expressed in breast cancer cell lines and tumors, and that the RPS6KB1, TBX2, and PPM1D genes from the region, that are amplified and over-expressed in breast tumors and cell lines, contribute to tumor formation and/or tumor progression. In this review we summarize the structural studies of the amplicon that have been carried out, we outline the evidence implicating the RPS6KB1, TBX2, and PPM1D genes as oncogenes, and we describe some of the other candidate oncogenes from the region.

Apc modulates embryonic stem-cell differentiation by controlling the dosage of beta-catenin signaling

The Wnt signal-transduction pathway induces the nuclear translocation of membrane-bound beta-catenin (Catnb) and has a key role in cell-fate determination. Tight somatic regulation of this signal is essential, as uncontrolled nuclear accumulation of beta-catenin can cause developmental defects and tumorigenesis in the adult organism. The adenomatous polyposis coli gene (APC) is a major controller of the Wnt pathway and is essential to prevent tumorigenesis in a variety of tissues and organs. Here, we have investigated the effect of different mutations in Apc on the differentiation potential of mouse embryonic stem (ES) cells. We provide genetic and molecular evidence that the ability and sensitivity of ES cells to differentiate into the three germ layers is inhibited by increased doses of beta-catenin by specific Apc mutations. These range from a severe differentiation blockade in Apc alleles completely deficient in beta-catenin regulation to more specific neuroectodermal, dorsal mesodermal and endodermal defects in more hypomorphic alleles. Accordingly, a targeted oncogenic mutation in Catnb also affects the differentiation potential of ES cells. Expression profiling of wildtype and Apc-mutated teratomas supports the differentiation defects at the molecular level and pinpoints a large number of downstream structural and regulating genes. Chimeric experiments showed that this effect is cell-autonomous. Our results imply that constitutive activation of the Apc/beta-catenin signaling pathway results in differentiation defects in tissue homeostasis, and possibly underlies tumorigenesis in the colon and other self-renewing tissues.

Gene expression in Peyronie's disease

Currently, surgical intervention is the only efficacious treatment for Peyronie's disease (PD), a fibromatosis of the tunica albuginea of the penis. Therapies based on the molecular pathways for this disease could provide alternatives to surgical treatment but only recently has the pathophysiology of the Peyronie's disease plaque been investigated at the molecular level. In this review, we examine the current knowledge of gene expression in the PD plaque and the relationship of PD with other fibrotic conditions such as Dupytren's disease. TGFbeta1, along with other growth factors, pro-fibrotic genes, and collagen, are expressed in fibroblasts and myofibroblasts. Myofibroblasts are normally involved in wound contracture and largely eliminated via apoptosis during the late stages of wound remodeling. In the PD plaque, however, these cells persist and may play an important role in the PD plaque fibrosis. The expression levels of TGFbeta1 and pro- and anti-fibrotic gene products, along with the nitric oxide/reactive oxygen species (NO/ROS) ratio in the tunica albuginea, appear to be essential for the formation and progression of the PD plaque and effect the expression of multiple genes. This can be assessed with the recently developed DNA-based chip arrays and results with the PD plaque have been encouraging. OSF-1 (osteoblast recruitment), MCP-1 (macrophage recruitment), procollagenase IV (collagenase degradation), and other fibrotic genes have been identified as being possible candidate regulatory genes. Finally, possible therapeutic avenues for gene-based therapy in the treatment of PD are discussed that may eventually reduce the need for surgical intervention.

Two novel tumor suppressor gene loci on chromosome 6q and 15q in human osteosarcoma identified through comparative study of allelic imbalances in mouse and man

We have performed a comparative study of allelic imbalances in human and murine osteosarcomas to identify genetic changes critical for osteosarcomagenesis. Two adjacent but discrete loci on mouse chromosome 9 were found to show high levels of allelic imbalance in radiation-induced osteosarcomas arising in (BALB/cxCBA/CA) F1 hybrid mice. The syntenic human chromosomal regions were investigated in 42 sporadic human osteosarcomas. For the distal locus (OSS1) on mouse chromosome 9 the syntenic human locus was identified on chromosome 6q14 and showed allelic imbalance in 77% of the cases. Comparison between the human and mouse syntenic regions narrowed the locus down to a 4 Mbp fragment flanked by the marker genes ME1 and SCL35A1. For the proximal locus (OSS2) on mouse chromosome 9, a candidate human locus was mapped to chromosome 15q21 in a region showing allelic imbalance in 58% of human osteosarcomas. We have used a combination of synteny and microsatellite mapping to identify two potential osteosarcoma suppressor gene loci. This strategy represents a powerful tool for the identification of new genes important for the formation of human tumors.

The molecular genetics of bone formation: implications for therapeutic interventions in bone disorders

Skeletal biology is a complex process involving the developmental commitment and differentiation of chondrocytes and osteoblasts which produce and mineralize cartilage and bone matrix during growth and postnatal life. Several genes are involved in controlling osteogenesis by acting on target cells in a very complex manner. Manipulation of genes in mice and studies of genetic mutations affecting the skeleton in humans have enabled the assessment of the role of transcription factors, bone matrix proteins and regulatory factors involved in the control of chondrocyte and osteoblast differentiation, and have considerably improved our understanding of the bone formation process. Clinical studies and gene polymorphism analyses suggest that the variable expression of particular genes may be linked to clinical osteoporosis. A major challenge in the future will be to develop molecularly targeted approaches to stimulating bone formation and increasing bone mass. The use of mouse strain models and transgenic animals with variable bone density may be useful to identify genetic determinants of bone mass which may serve as a basis for drug discovery and development. On the other hand, the availability of gene microarrays and other emerging genomic techniques are promising tools to identify genes that are distinctly expressed in health and disease. These technologies may also serve to test the mechanisms of action of drugs aimed at increasing bone formation. Genetic studies of the molecular signaling pathways involved in normal and pathological osteogenesis may also help to identify genes that could be targeted for therapeutic intervention. Candidate approaches include selective gene transfection in target cells and the use of drugs acting on gene promoters to selectively enhance gene expression in osteoblasts. The development of these strategies is expected not only to bring new insight into the molecular mechanisms that govern bone formation in normal and pathological situations but, in the long term, may also result in the identification of novel molecular targets for therapeutic interventions for bone formation disorders.

Cooperative action of Tbx2 and Nkx2.5 inhibits ANF expression in the atrioventricular canal: implications for cardiac chamber formation

During heart development, chamber myocardium forms locally from the embryonic myocardium of the tubular heart. The atrial natriuretic factor (ANF) gene is specifically expressed in this developing chamber myocardium and is one of the first hallmarks of chamber formation. We investigated the regulatory mechanism underlying this selective expression. Transgenic analysis shows that a small fragment of the ANF gene is responsible for the developmental pattern of endogenous ANF gene expression. Furthermore, this fragment is able to repress cardiac troponin I (cTnI) promoter activity selectively in the embryonic myocardium of the atrioventricular canal (AVC). In vivo inactivation of a T-box factor (TBE)- or NK2-homeobox factor binding element (NKE) within the ANF fragment removed the repression in the AVC without affecting its chamber activity. The T-box family member Tbx2, encoding a transcriptional repressor, is expressed in the embryonic myocardium in a pattern mutually exclusive to ANF, thus suggesting a role in the suppression of ANF. Tbx2 formed a complex with Nkx2.5 on the ANF TBE-NKE, and was able to repress ANF promoter activity. Our data provide a potential mechanism for chamber-restricted gene activity in which the cooperative action of Tbx2 and Nkx2.5 inhibits expression in the AVC.

Microarray detection of gene expression changes induced by 1,25(OH)(2)D(3) and a Ca(2+) influx-activating analog in osteoblastic ROS 17/2.8 cells

1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) treatment of osteoblastic ROS 17/2.8 cells initiates membrane-initiated rapid responses through activation of Ca(2+) influx and longer-term nuclear receptor-mediated changes in gene expression. Ca(2+) influx triggers a change in the phosphorylation state of the bone matrix protein, osteopontin (OPN), detectable at 3 h and prior to nuclear receptor-mediated events. This study aimed to determine if Ca(2+) influx induced by 1,25(OH)(2)D(3) would produce nuclear receptor-independent changes in gene expression. We employed a rat cDNA microarray strategy to screen the transcriptional changes at 3 h of treatment with 1,25(OH)(2)D(3) and with an analog of 1,25(OH)(2)D(3) (25(OH)-16ene-23yne-D(3) [AT]) that we previously showed to activate Ca(2+) influx without binding to the nuclear receptor. Arrays also were screened with cDNA from ROS 17/2.8 cells treated for 24 h, when nuclear receptor-mediated transcriptional events would occur. Rat gene filters (GeneFilter, Research Genetics) were hybridized with labeled cDNA probes from treatment groups. Among 5000 different clones on the array filters, we identified a family of genes which were altered 2-fold or greater following treatment with 1,25(OH)(2)D(3) or analog AT for 3 h. Cluster analysis also revealed genes whose expression was significantly up-regulated at 24 h, including OPN. Analysis of rapid changes in gene expression revealed changes affecting a diverse range of cellular pathways and functions, including protein kinases and phosphatases, Ca(2+) signaling, cell adhesion and secretion. These findings provide clear evidence of rapid changes in gene expression associated with Ca(2+) influx mediated by 1,25(OH)(2)D(3), and shed light on the nuclear-receptor independent signaling pathway affecting OPN phosphorylation.

The T-box transcription factor Brachyury mediates cartilage development in mesenchymal stem cell line C3H10T1/2

The BMP2-dependent onset of osteo/chondrogenic differentiation in the acknowledged pluripotent murine mesenchymal stem cell line (C3H10T1/2) is accompanied by the immediate upregulation of Fibroblast Growth Factor Receptor 3 (FGFR3) and a delayed response by FGFR2. Forced expression of FGFR3 in C3H10T1/2 is sufficient for chondrogenic differentiation, indicating an important role for FGF-signaling during the manifestation of the chondrogenic lineage in this cell line. Screening for transcription factors exhibiting a chondrogenic capacity in C3H10T1/2 indentified that the T-box containing transcription factor Brachyury is upregulated by FGFR3-mediated signaling. Forced expression of Brachyury in C3H10T1/2 was sufficient for differentiation into the chondrogenic lineage in vitro and in vivo after transplantation into muscle. A dominant-negative variant of Brachyury, consisting of its DNA-binding domain (T-box), interferes with BMP2-mediated cartilage formation. These studies indicate that BMP-initiated FGF-signaling induces a novel type of transcription factor for the onset of chondrogenesis in a mesenchymal stem cell line. A potential role for this T-box factor in skeletogenesis is further delineated from its expression profile in various skeletal elements such as intervertebral disks and the limb bud at late stages (18.5 d.p.c.) of murine embryonic development.

Murine Tbx2 contains domains that activate and repress gene transcription

T-box (Tbx) genes represent a phylogenetically conserved family of transcription factors that play important roles during embryonic development. Tbx family members have been shown to either activate or inhibit gene expression. However, little is known about the domains within Tbx proteins responsible for mediating gene transcription. While Tbx2 is known to repress gene expression, the domain(s) within Tbx2 remains poorly defined. Deletion of the carboxy-terminus of Tbx2, which contains a domain that is highly conserved with Tbx3 and ET, which has been demonstrated to contain a repression domain, only minimally diminishes the ability of Tbx2 to repress gene expression. However, in combination with the carboxy-terminal truncation, deletion of the amino acids located amino-terminal to the T-box abolished the ability of Tbx2 to repress gene expression. Both of these domains were capable of repressing gene expression when linked to the GAL4 DNA binding domain. In contrast to these two repression domains, the T-box was capable of weakly activating gene expression depending on the promoter context. Deletion analysis of the T-box suggests that this activation domain is located in the amino-terminal end of the T-box. These results reveal a novel transcription repression domain, confirm the presence of a previously implicated domain, and suggest a novel role for the T-box. Taken together, these results provide the basis for understanding the molecular mechanism whereby Tbx2 regulates gene expression and subsequently controls embryonic development.