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Development of heart valves requires Gata4 expression in endothelial-derived cells

ABSTRACT: Cardiac malformations due to aberrant development of the atrioventricular (AV) valves are among the most common forms of congenital heart disease. At localized swellings of extracellular matrix known as the endocardial cushions, the endothelial lining of the heart undergoes an epithelial to mesenchymal transition (EMT) to form mesenchymal progenitors of the AV valves. Further growth and differentiation of these mesenchymal precursors results in formation of portions of the atrial and ventricular septae, and generation of thin, pliable valves. The transcription factor Gata4 is expressed in the endothelium and mesenchyme of the AV valves. Using a Tie2-Cre transgene, we selectively inactivated Gata4 within endothelial-derived cells. Mutant endothelium failed to undergo EMT, resulting in hypocellular cushions. Mutant cushions had decreased levels of Erbb3, an EGF-family receptor essential for EMT in the atrioventricular cushions. In Gata4 mutant embryos, Erbb3 downregulation was associated with impaired activation of Erk, which is also required for EMT. Expression of a Gata4 mutant protein defective in interaction with Friend of Gata (FOG) cofactors rescued the EMT defect, but resulted in decreased proliferation of mesenchyme and hypoplastic cushions that failed to septate the ventricular inlet. We demonstrate two novel functions of Gata4 in development of the AV valves. First, Gata4 functions as an upstream regulator of an Erbb3-Erk pathway necessary for EMT, and second, Gata4 acts to promote cushion mesenchyme growth and remodeling. Keywords: genetic modification

ORGANISM(S): Mus musculus

PROVIDER: GSE5298 | GEO | 2006/07/14

SECONDARY ACCESSION(S): PRJNA95397

REPOSITORIES: GEO

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Project description:E12.5 AV cushion and E17.5 AV valve from wild-type FVB/N mice and in vitro cultured MC3T3 cells; In the study we demonstrated shared gene expression in embryonic heart valve development and Osteoblast progenitor cells. The atrioventricular (AV) valves of the heart develop from undifferentiated mesenchymal endocardial cushions, that later remodel into stratified valves with diversified extracellular matrix (ECM). Because the mature valves express genes associated with osteogenesis and exhibit disease-associated calcification, we hypothesized the existence of shared regulatory pathways active in the remodeling AV valves and in bone progenitor cells. In order to define gene regulatory programs of valvulogenesis relative to osteoblast progenitors, we undertook Affymetrix gene expression profiling analysis of murine embryonic day (E)12.5 AV cushions compared to E17.5 remodeled AV valves (mitral and tri-cuspid) and to pre-osteoblast MC3T3-E1 (subclone4) cells. Overall MC3T3 cells were significantly more similar to E17.5 valves than to E12.5 cushions, supporting the hypothesis that valve remodeling involves the expression of many genes also expressed in osteoblasts. Several transcription factors characteristic of mesenchymal and osteoblast precursor cells, including Twist1 are predominant in E12.5 cushion. Valve remodeling also includes differential regulation of matrix metalloproteinases and their inhibitors as well as characteristic collagen isoform switching. Among the most highly enriched genes during valvulogenesis were members of the small leucine-rich proteoglycan (SLRP) family including Asporin, a known negative regulator of osteoblast differentiation and mineralization. Together, these data support shared gene expression profiles of the remodeling valves and osteoblast bone precursor cells in normal valve development and homeostasis with potential functions in calcific valve disease. Experiment Overall Design: In the study, we hybridized RNA from E12.5 AV cushion and E17.5 AV valve from wild-type FVB/N mice and in vitro cultured MC3T3 cells to Affymetrix MOE430 2 GeneChipÂ® arrays.

Project description:Rationale: A critical step in heart development is the coordinated formation of nodal myocardium and cushion tissue from the atrioventricular canal (AVC). After its specification, the myocardium of the AVC aligns the chambers, forms the AV node, and induces the formation of the mesenchymal AV cushions, primordia of valves and septa, while it resists working myocardial differentiation. Objective: To assess what roles Tbx2 and Tbx3, two closely related T-box transcription factors expressed in the AVC, play in these processes. Methods and Results: We analyzed mice ectopically expressing Tbx3 in the atrial myocardium by genome-wide microarray and expression analysis. We found a prominent role for Tbx3 in defining the nodal phenotype by repressing working myocardial genes (sarcomeric, mitochondrial, fast conduction) and cell proliferation regulators, and in inducing node-associated genes. Moreover, there was a striking induction of genes associated with endocardial cushions and mesenchyme. Using gain-of-function models, we found that in the developing heart both Tbx2 and Tbx3 induce ectopic Bmp2 and Tgfb2 expression and endocardial cushion formation. Analysis of compound Tbx2/Tbx3 mutant embryos revealed that upon loss of more than two functional alleles, expansion of the AV myocardium does not occur and AV cushions fail to form. Conclusions: Tbx2 and Tbx3 locally stimulate development of the AVC myocardium, induce the AV nodal phenotype therein and trigger AV cushion formation from the overlying AV endocardium, providing a mechanism for the colocalization and coordination of these two important processes in heart development. Nppa-Cre4 (Cre4) mice were crossed with CT mice to obtain efficient activation of Tbx3 in atria of double transgenic Cre4-CT mice, as previously described (Hoogaars et al., 2007). To investigate the gene expression profile of atria of Cre4-CT mice, we performed whole genome microarray analysis using Sentrix Mouse-6 oligonucleotide beadchips. We compared the atrial gene expression profiles of six male double transgenic Cre4-CT mice and six male Cre4 control mice.

Project description:Malformations of the cardiovascular system are the most common type of birth defect in humans, affecting predominantly the formation of valves and septa. During heart valve and septa formation, cells from the atrio-ventricular canal (AVC) and outflow tract (OFT) regions of the heart undergo an epithelial-to-mesenchymal transformation (EMT) and invade the underlying extracellular matrix to give rise to endocardial cushions. Subsequent maturation of newly formed mesenchyme cells leads to thin stress-resistant leaflets. TWIST1 is a basic helix-loop-helix transcription factor expressed in newly formed mesenchyme cells of the AVC and OFT that has been shown to play roles in cell survival, cell proliferation and differentiation. However, the role and downstream targets of TWIST1 during heart valve formation remain unclear. To identify genes important for heart valve development downstream of Twist1 we performed global gene expression profiling of AVC, OFT, atria and ventricles of the embryonic day 10.5 mouse heart by tag-sequencing (Tag-seq). Using this resource we identified a novel set of 1246 genes, including 201 regulators of transcription, enriched in the valve forming regions of the heart. We compared these genes to a Tag-seq library from the Twist1 null developing valves revealing significant gene expression changes. These changes were consistent with a role of TWIST1 in controlling differentiation of mesenchymal cells following their transformation from endothelium in the mouse. To study the role of TWIST1 at the DNA level we performed chromatin immunoprecipitation and identified novel direct targets of TWIST1 in the developing heart valves. Our findings are consistent with a role for TWIST1 in the differentiation of AVC mesenchyme post-EMT in the mouse, and suggest that TWIST1 exerts its function by direct DNA binding to activate valve specific gene expression. Profiled the AVC, OFT, atria and ventricles of the embryonic day 10.5 mouse heart by tag-sequencing (Tag-seq) (no replicates). We also produced a Tag-seq library from Twist1 null developing valves to reveal the gene expression changes associated with loss of this gene.

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Development of heart valves requires Gata4 expression in endothelial-derived cells

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