GATA-5 is involved in leukemia inhibitory factor-responsive transcription of the beta-myosin heavy chain gene in cardiac myocytes.
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Leukemia inhibitory factor is a member of a family of structurally related cytokines sharing the receptor component gp130. Activation of gp130 by leukemia inhibitory factor is sufficient to induce myocardial cell hypertrophy accompanied by specific changes in the pattern of gene expression. However, the molecular mechanisms that link gp130 activation to these changes have not been clarified. The present study investigated the transcriptional pathways by which leukemia inhibitory factor activates beta-myosin heavy chain expression during myocardial cell hypertrophy. Mutation of the GATA motif in the beta-myosin heavy chain promoter totally abolished leukemia inhibitory factor-responsive transcription without changing basal transcriptional activity. In contrast, endothelin-1 responsiveness was unaffected by the GATA mutation. Among members of the cardiac GATA transcription factor subfamily (GATA-4, -5, and -6), GATA-5 was the sole and potent transactivator for the beta-myosin heavy chain promoter. This transactivation was dependent on sequence-specific binding of GATA-5 to the beta-myosin heavy chain GATA element. Cardiac nuclear factors that bind to to the beta-myosin heavy chain GATA element were induced by leukemia inhibitory factor stimulation. Last, leukemia inhibitory factor stimulation markedly increased transcripts of cardiac GATA-5, the expression of which is normally restricted to the early embryo. Thus, GATA-5 may be involved in gp130 signaling in cardiac myocytes. (+info)
Induction of the mesendoderm in the zebrafish germ ring by yolk cell-derived TGF-beta family signals and discrimination of mesoderm and endoderm by FGF.
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The endoderm forms the gut and associated organs, and develops from a layer of cells which emerges during gastrula stages in the vertebrate embryo. In comparison to mesoderm and ectoderm, little is known about the signals which induce the endoderm. The origin of the endoderm is intimately linked with that of mesoderm, both by their position in the embryo, and by the molecules that can induce them. We characterised a gene, zebrafish gata5, which is expressed in the endoderm from blastula stages and show that its transcription is induced by signals originating from the yolk cell. These signals also induce the mesoderm-expressed transcription factor no tail (ntl), whose initial expression coincides with gata5 in the cells closest to the blastoderm margin, then spreads to encompass the germ ring. We have characterised the induction of these genes and show that ectopic expression of activin induces gata5 and ntl in a pattern which mimics the endogenous expression, while expression of a dominant negative activin receptor abolishes ntl and gata5 expression. Injection of RNA encoding a constitutively active activin receptor leads to ectopic expression of gata5 and ntl. gata5 is activated cell-autonomously, whereas ntl is induced in cells distant from those which have received the RNA, showing that although expression of both genes is induced by a TGF-beta signal, expression of ntl then spreads by a relay mechanism. Expression of a fibroblast growth factor (eFGF) or a dominant negatively acting FGF receptor shows that ntl but not gata5 is regulated by FGF signalling, implying that this may be the relay signal leading to the spread of ntl expression. In embryos lacking both squint and cyclops, members of the nodal group of TGF-beta related molecules, gata5 expression in the blastoderm is abolished, making these factors primary candidates for the endogenous TGF-beta signal inducing gata5. (+info)
p300 protein as a coactivator of GATA-5 in the transcription of cardiac-restricted atrial natriuretic factor gene.
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A cellular target of adenovirus E1A oncoprotein, p300 is a transcriptional coactivator and a negative regulator of cellular proliferation. A previous study suggests that the p300 family is also involved in cell type-specific transcription in cardiac myocytes. However, nothing is known about which cardiac transcription factor(s) interact with and transactivate through these proteins. The transcription factors GATA-4/5/6 have been implicated as key regulators of cardiogenesis, and they participate in the transcription of many cardiac-specific genes. Here we show that E1A represses the GATA-5-dependent transactivation of a promoter derived from the cardiac-restricted atrial natriuretic factor gene. This repression is correlated with the interaction of E1A with p300, indicating that p300 participates in GATA-5-dependent transactivation. E1A markedly down-regulates endogenous atrial natriuretic factor expression, as well as disrupts the interaction between p300 and GATA-5. A small fragment of p300 containing the carboxyl-terminal cysteine/histidine-rich domain, sufficient to interact with GATA-5, prevents transcriptional activation by GATA-5 as a dominant-negative mutant. Consistent with its role as a coactivator, p300 markedly potentiates GATA-5-activated transcription. These results implicate p300 as an important component of myocardial cell differentiation and provide an insight into the relationship between mechanisms that mediate cell type-specific transcription and cell cycle regulation during cardiogenesis. (+info)
Gata5 is required for the development of the heart and endoderm in zebrafish.
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The mechanisms regulating vertebrate heart and endoderm development have recently become the focus of intense study. Here we present evidence from both loss- and gain-of-function experiments that the zinc finger transcription factor Gata5 is an essential regulator of multiple aspects of heart and endoderm development. We demonstrate that zebrafish Gata5 is encoded by the faust locus. Analysis of faust mutants indicates that early in embryogenesis Gata5 is required for the production of normal numbers of developing myocardial precursors and the expression of normal levels of several myocardial genes including nkx2.5. Later, Gata5 is necessary for the elaboration of ventricular tissue. We further demonstrate that Gata5 is required for the migration of the cardiac primordia to the embryonic midline and for endodermal morphogenesis. Significantly, overexpression of gata5 induces the ectopic expression of several myocardial genes including nkx2.5 and can produce ectopic foci of beating myocardial tissue. Together, these results implicate zebrafish Gata5 in controlling the growth, morphogenesis, and differentiation of the heart and endoderm and indicate that Gata5 regulates the expression of the early myocardial gene nkx2.5. (+info)
A role for GATA-4/5/6 in the regulation of Nkx2.5 expression with implications for patterning of the precardiac field.
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Interactions between the key regulatory genes of the cardiogenic pathway, including those from the GATA and Nkx2 transcription factor families, are not well defined. Treating neurula-stage Xenopus embryos with retinoic acid (RA) causes a specific block in cardiomyocyte development that correlates with a progressive reduction in the region of the presumptive heart-forming region expressing Nkx2.5. In contrast, RA does not block expression of the GATA-4/5/6 genes, which are transcribed normally in an overlapping pattern with Nkx2.5 throughout cardiogenesis. Instead, GATA-4/5/6 transcription levels are increased, including an expansion of the expression domain corresponding to lateral plate mesoderm that is part of the early heart field, but that normally is progressively restricted in its ability to contribute to the myocardium. GATA-dependent regulatory sequences of the Nkx2.5 gene that implicate GATA-4/5/6 as upstream positive regulators were described recently. However, our experiments also indicate that GATA factors might normally antagonize transcription of Nkx2.5. To test this hypothesis we generated a dominant negative isoform of GATA-4 (SRG4) capable of inhibiting transcription of GATA-dependent target genes. Ectopic expression of SRG4 results in a transient expansion of the Nkx2.5 transcript pattern, indicating that a normal function of GATA factors is to limit the boundary of the Nkx2.5 expression domain to the most anterior ventral region of the heart field. Regulatory mechanisms altered by excess RA must function normally to limit GATA-4/5/6 expression levels, to define the region of Nkx2.5 expression and regulate myocardial differentiation. (+info)
Modular regulation of cGATA-5 gene expression in the developing heart and gut.
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The evolutionarily conserved GATA-5 transcription factor is an early and persistent marker of heart and gut development in diverse vertebrate species. To search for control regions that might regulate the chicken GATA-5 (cGATA-5) gene, we assayed a set of cGATA-5/lacZ constructs in transgenic mice and found evidence for two functionally conserved control regions that regulate different facets of cGATA-5 gene expression. The more distal control region is activated in embryonic endoderm at the head-fold stage, whereas the other control region contains a regulatory module that is activated in a restricted region of endoderm following closure of the gut tube. Remarkably, the latter control region also contains a complex regulatory module that is activated in the cardiac crescent at the head-fold stage and subsequently functions in several mesodermal components of the developing heart, including the outer (epicardial) layer. We discuss these results in terms of possible contributions of epicardial-derived cells to the formation of heart valves, conduction tissue, and compact myocardium. These transgenes thus reveal, and provide a means to further analyze, transcriptional programs for several facets of heart morphogenesis and gut development. (+info)
Anterior endoderm is sufficient to rescue foregut apoptosis and heart tube morphogenesis in an embryo lacking retinoic acid.
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The vitamin A deficient (VAD) quail embryo lacks active retinoids, fails to express normally GATA-4, and develops a nonlooping heart tube morphogenetic defect that is a model for congenital cardiomyopathy. VAD quail embryos, or chick embryos depleted specifically for GATA factors, show in addition abnormal foregut development, characterized by apoptosis of the endoderm cells associated with presumptive myocardium during the process of heart tube formation. Exogenous retinoic acid or transplantation of normal chick embryo anterior endoderm is sufficient to rescue apoptosis as well as GATA-4 expression and results in normal development and heart tube morphogenesis. Normal posterior endoderm also contains retinoids but is unable to rescue the VAD defect. Our results indicate that a retinoid-dependent transcriptional program, mediated at least in part by GATA factors, is critical in presumptive foregut endoderm for normal heart tube morphogenesis. (+info)
BMP2 is required for early heart development during a distinct time period.
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BMP2, like its Drosophila homologue dpp, is an important signaling molecule for specification of cardiogenic mesoderm in vertebrates. Here, we analyzed the time-course of BMP2-requirement for early heart formation in whole chick embryos and in explants of antero-lateral plate mesoderm. Addition of Noggin to explants isolated at stage 4 and cultured for 24 h resulted in loss of NKX2.5, GATA4, eHAND, Mef2A and vMHC expression. At stages 5-8 the individual genes showed differential sensitivity to Noggin addition. While expression of eHAND, NKX2.5 and Mef2A was clearly reduced by Noggin vMHC was only marginally affected. In contrast, GATA4 expression was enhanced after Noggin treatment. The developmental period during which cardiac mesoderm required the presence of BMP signaling in vivo was assessed by implantation of Noggin expressing cells into stage 4-8 embryos which were then cultured until stage 10-11. Complete loss of NKX2.5 and eHAND expression was observed in embryos implanted at stages 4-6, and expression was still suppressed in stages 7 and 8 implanted embryos. GATA4 expression was also blocked by Noggin at stage 4, however increased at stages 5, 6 and 7. Explants of central mesendoderm, that normally do not form heart tissue were employed to study the time-course of BMP2-induced cardiac gene expression. The induction of cardiac lineage markers in central mesendoderm of stage 5 embryos was distinct for different genes. While GATA4, -5, -6 and MEF2A were induced to maximal levels within 6 h after BMP2 addition, eHAND and dHAND required 12 h to reach maximum levels of expression. NKX2.5 was induced by 6 h and accumulated over 48 h. vMHC and titin were induced at significant levels only after 48 h of BMP2 addition. These results indicate that cardiac marker genes display distinct expression kinetics after BMP2 addition and differential response to Noggin treatment suggesting complex regulation of myocardial gene expression in the early tubular heart. (+info)