GATA4 regulates mesenchymal stem cells via direct transcriptional regulation of the WNT signalosome

GATA4 is a transcription factor that regulates osteoblast differentiation. However, GATA4 is expressed at a higher level in mesenchymal stem cells (MSCs) than in osteoblasts. Therefore, the role of GATA4 in limb bud mesenchyme differentiation was investigated in mice by knocking out Gata4 using Cre-recombinase controlled by the Prx1 promoter (herein called Gata4 Prx-cKO mice). μCT analysis of the Gata4 Prx-cKO mice showed a decrease in trabecular bone properties compared with wildtype (Gata4^fl/fl) littermates. Gata4 Prx-cKO mice have fewer MSCs as measured by CFU-F assays, mesenchymal progenitor cells (MPC2) (flow cytometry of Sca1⁺/CD45^-/CD34^-/CD44^hi) and nestin immunofluorescence. Gata4 Prx-cKO bone marrow-derived MSCs have a significant reduction in WNT ligands, including WNT10B, and WNT signalosome components compared to control cells. Chromatin immunoprecipitation demonstrates that GATA4 is recruited to enhancers near Wnt3a, Wnt10b, Fzd6 and Dkk1. GATA4 also directly represses YAP in wildtype cells, and the absence of Gata4 leads to increased YAP expression. Together, we show that the decrease in MSCs is due to loss of Gata4 and a WNT10B-dependent positive autoregulatory loop. This leads to a concurrent increase of YAP and less activated β-catenin. These results explain the decreased trabecular bone in Gata4 Prx-cKO mice. We suggest that WNT signalosome activity in MSCs requires Gata4 and Wnt10b expression for lineage specification.

GATA4 is a negative regulator of contractility in mouse testicular peritubular myoid cells

Reduced contractility of the testicular peritubular myoid (PTM) cells may contribute to human male subfertility or infertility. Transcription factor GATA4 in Sertoli and Leydig cells is essential for murine spermatogenesis, but limited attention has been paid to the potential role of GATA4 in PTM cells. In primary cultures of mouse PTM cells, siRNA knockdown of GATA4 increased the contractile activity, while GATA4 overexpression significantly attenuated the contractility of PTM cells using a collagen gel contraction assay. Using RNA sequencing and qRT-PCR, we identified a set of genes that exhibited opposite expressional alternation between Gata4 siRNA vs nontargeting siRNA-treated PTM cells and Gata4 adenovirus vs control adenovirus-treated PTM cells. Notably, ion channels, smooth muscle function, cytokines and chemokines, cytoskeleton, adhesion and extracellular matrix were the top four enriched pathways, as revealed by cluster analysis. Natriuretic peptide type B (NPPB) content was significantly upregulated by GATA4 overexpression in both PTM cells and their culture supernatant. More importantly, the addition of 100 μM NPPB could abolish the promoting effect of Gata4 silencing on PTM cell contraction. Taken together, we suggest that the inhibitory action of GATA4 on PTM cell contraction is mediated at least partly by regulating genes belonging to smooth muscle contraction pathway (e.g. Nppb).

Ex vivo cultures combined with vivo-morpholino induced gene knockdown provide a system to assess the role of WT1 and GATA4 during gonad differentiation

Gonad morphogenesis relies on the correct spatiotemporal expression of a number of genes that together fulfill the differentiation of the bipotential gonad into testes or ovaries. As such, the transcription factors WT1 and GATA4 are pivotal for proper gonadal development. Here we address the contributions of GATA4 and WT1 to the sex differentiation phase in testes and ovaries. We applied an ex vivo technique for cultivating gonads in hanging droplets of media that were supplemented with vivo-morpholinos to knockdown WT1 and GATA4 either alone or in combination at the same developmental stage. We show that WT1 is equally important for both, the initial establishment and the maintenance of the sex-specific gene expression signature in testes and ovaries. We further identified Foxl2 as a novel putative downstream target gene of WT1. Moreover, knockdown of WT1 reduced mRNA levels of several molecular components of the hedgehog signaling pathway in XY gonads, whereas Gata4 vivo-morpholino treatment increased transcripts of Dhh and Ptch1 in embryonic testes. The data suggest that for its proper function, WT1 relies on the correct expression of the GATA4 protein. Furthermore, GATA4 down-regulates several ovarian promoting genes in testes, such as Ctnnb1, Fst, and Bmp2, suggesting that this repression is required for maintaining the male phenotype. In conclusion, this study provides novel insights into the role of WT1 and GATA4 during the sex differentiation phase and represents an approach that can be applied to assess other proteins with as yet unknown functions during gonadal development.

Combined loss of the GATA4 and GATA6 transcription factors in male mice disrupts testicular development and confers adrenal-like function in the testes

The roles of the GATA4 and GATA6 transcription factors in testis development were examined by simultaneously ablating Gata4 and Gata6 with Sf1Cre (Nr5a1Cre). The deletion of both genes resulted in a striking testicular phenotype. Embryonic Sf1Cre; Gata4(flox/flox) Gata6(flox/flox) (conditional double mutant) testes were smaller than control organs and contained irregular testis cords and fewer gonocytes. Gene expression analysis revealed significant down-regulation of Dmrt1 and Mvh. Surprisingly, Amh expression was strongly up-regulated and remained high beyond postnatal day 7, when it is normally extinguished. Neither DMRT1 nor GATA1 was detected in the Sertoli cells of the mutant postnatal testes. Furthermore, the expression of the steroidogenic genes Star, Cyp11a1, Hsd3b1, and Hsd17b3 was low throughout embryogenesis. Immunohistochemical analysis revealed a prominent reduction in cytochrome P450 side-chain cleavage enzyme (CYP11A1)- and 3β-hydroxysteroid dehydrogenase-positive (3βHSD) cells, with few 17α-hydroxylase/17,20 lyase-positive (CYP17A1) cells present. In contrast, in postnatal Sf1Cre; Gata4(flox/flox) Gata6(flox/flox) testes, the expression of the steroidogenic markers Star, Cyp11a1, and Hsd3b6 was increased, but a dramatic down-regulation of Hsd17b3, which is required for testosterone synthesis, was observed. The genes encoding adrenal enzymes Cyp21a1, Cyp11b1, Cyp11b2, and Mcr2 were strongly up-regulated, and clusters containing numerous CYP21A2-positive cells were localized in the interstitium. These data suggest a lack of testis functionality, with a loss of normal steroidogenic testis function, concomitant with an expansion of the adrenal-like cell population in postnatal conditional double mutant testes. Sf1Cre; Gata4(flox/flox) Gata6(flox/flox) animals of both sexes lack adrenal glands; however, despite this deficiency, males are viable in contrast to the females of the same genotype, which die shortly after birth.

GATA4 represses an ileal program of gene expression in the proximal small intestine by inhibiting the acetylation of histone H3, lysine 27

GATA4 is expressed in the proximal 85% of small intestine where it promotes a proximal intestinal ('jejunal') identity while repressing a distal intestinal ('ileal') identity, but its molecular mechanisms are unclear. Here, we tested the hypothesis that GATA4 promotes a jejunal versus ileal identity in mouse intestine by directly activating and repressing specific subsets of absorptive enterocyte genes by modulating the acetylation of histone H3, lysine 27 (H3K27), a mark of active chromatin, at sites of GATA4 occupancy. Global analysis of mouse jejunal epithelium showed a statistically significant association of GATA4 occupancy with GATA4-regulated genes. Occupancy was equally distributed between down- and up-regulated targets, and occupancy sites showed a dichotomy of unique motif over-representation at down- versus up-regulated genes. H3K27ac enrichment at GATA4-binding loci that mapped to down-regulated genes (activation targets) was elevated, changed little upon conditional Gata4 deletion, and was similar to control ileum, whereas H3K27ac enrichment at GATA4-binding loci that mapped to up-regulated genes (repression targets) was depleted, increased upon conditional Gata4 deletion, and approached H3K27ac enrichment in wild-type control ileum. These data support the hypothesis that GATA4 both activates and represses intestinal genes, and show that GATA4 represses an ileal program of gene expression in the proximal small intestine by inhibiting the acetylation of H3K27.

Induction of cardiomyocyte-like cells in infarct hearts by gene transfer of Gata4, Mef2c, and Tbx5

RATIONALE

After myocardial infarction (MI), massive cell death in the myocardium initiates fibrosis and scar formation, leading to heart failure. We recently found that a combination of 3 cardiac transcription factors, Gata4, Mef2c, and Tbx5 (GMT), reprograms fibroblasts directly into functional cardiomyocytes in vitro.

OBJECTIVE

To investigate whether viral gene transfer of GMT into infarcted hearts induces cardiomyocyte generation.

METHODS AND RESULTS

Coronary artery ligation was used to generate MI in the mouse. In vitro transduction of GMT retrovirus converted cardiac fibroblasts from the infarct region into cardiomyocyte-like cells with cardiac-specific gene expression and sarcomeric structures. Injection of the green fluorescent protein (GFP) retrovirus into mouse hearts, immediately after MI, infected only proliferating noncardiomyocytes, mainly fibroblasts, in the infarct region. The GFP expression diminished after 2 weeks in immunocompetent mice but remained stable for 3 months in immunosuppressed mice, in which cardiac induction did not occur. In contrast, injection of GMT retrovirus into α-myosin heavy chain (αMHC)-GFP transgenic mouse hearts induced the expression of αMHC-GFP, a marker of cardiomyocytes, in 3% of virus-infected cells after 1 week. A pooled GMT injection into the immunosuppressed mouse hearts induced cardiac marker expression in retrovirus-infected cells within 2 weeks, although few cells showed striated muscle structures. To transduce GMT efficiently in vivo, we generated a polycistronic retrovirus expressing GMT separated by 2A "self-cleaving" peptides (3F2A). The 3F2A-induced cardiomyocyte-like cells in fibrotic tissue expressed sarcomeric α-actinin and cardiac troponin T and had clear cross striations. Quantitative RT-PCR also demonstrated that FACS-sorted 3F2A-transduced cells expressed cardiac-specific genes.

CONCLUSIONS

GMT gene transfer induced cardiomyocyte-like cells in infarcted hearts.

Alterations of folliculogenesis in women with polycystic ovary syndrome

The objective of the present study was to examine some factors involved in follicular development of women with polycystic ovary syndrome (PCOS). Women with PCOS showed increased levels of serum luteinizing hormone (LH) but decreased follicular production of progesterone and estradiol by pre-ovulatory follicles. The mRNA expression corresponding to steroidogenic acute regulatory protein (StAR), and 20alpha-hydroxysteroid dehydrogenase (20α-HSD) was increased, while that corresponding to cytochrome P450 aromatase (P450arom) was decreased in PCOS follicles as compared to controls. No changes in the mRNA expression for 3beta-hydroxysteroid dehydrogenase 2 (3β-HSD2), cytochrome P450 side-chain cleavage (P450scc), cytochrome P450 17 alpha hydroxylase/lyase (P450c17), cyclooxygenase 2 (COX2), and transcription factors (GATA-4 and GATA-6) were found. We conclude that despite the hyper-luteinized environment of PCOS follicles, these follicles produce lower levels of progesterone and estradiol, and that this is characterized by increased degradation of progesterone and decreased estradiol synthesis. Our data demonstrate that the synthesis of prostaglandin F2α (PGF2α) may be affected in PCOS-follicles and that the transcription factors GATA-4 and GATA-6 are present in PCOS-follicles but they are not involved in the abnormal transcription observed in the steroidogenic enzymes.

Loss of intestinal GATA4 prevents diet-induced obesity and promotes insulin sensitivity in mice

Transcriptional regulation of small intestinal gene expression controls plasma total cholesterol (TC) and triglyceride (TG) levels, which are major determinants of metabolic diseases. GATA4, a zinc finger domain transcription factor, is critical for jejunal identity, and intestinal GATA4 deficiency leads to a jejunoileal transition. Although intestinal GATA4 ablation is known to misregulate jejunal gene expression, its pathophysiological impact on various components of metabolic syndrome remains unknown. Here, we used intestine-specific GATA4 knockout (GATA4iKO) mice to dissect the contribution of GATA4 on obesity development. We challenged adult GATA4iKO mice and control littermates with a Western-type diet (WTD) for 20 wk. Our findings show that WTD-fed GATA4iKO mice are resistant to diet-induced obesity. Accordingly, plasma TG and TC levels are markedly decreased. Intestinal lipid absorption in GATA4iKO mice was strongly reduced, whereas luminal lipolysis was unaffected. GATA4iKO mice displayed a greater glucagon-like peptide-1 (GLP-1) release on normal chow and even after long-term challenge with WTD remained glucose sensitive. In summary, our findings show that the absence of intestinal GATA4 has a beneficial effect on decreasing intestinal lipid absorption causing resistance to hyperlipidemia and obesity. In addition, we show that increased GLP-1 release in GATA4iKO mice decreases the risk for development of insulin resistance.

Control of sex development

The process of sexual differentiation is central for reproduction of almost all metazoan, and therefore, for maintenance of practically all multicellular organisms. In sex development, we can distinguish two different processes, sex determination, that is the developmental decision that directs the undifferentiated embryo into a sexually dimorphic individual. In mammals, sex determination equals gonadal development. The second process known as sex differentiation takes place once the sex determination decision has been made through factors produced by the gonads that determine the development of the phenotypic sex. Most of the knowledge on the factors involved in sexual development came from animal models and from studies of cases in whom the genetic or the gonadal sex does not match the phenotypical sex, that is, patients affected by disorders of sex development (DSDs). Generally speaking, factors influencing sex determination are transcriptional regulators, whereas factors important for sex differentiation are secreted hormones and their receptors. This review focuses on these factors and whenever possible, references regarding the 'prismatic' clinical cases are given.

Transgenic mice expressing small interfering RNA against Gata4 point to a crucial role of Gata4 in the heart and gonads

Homozygous deficiency of the transcription factor Gata4 in mice causes lethality due to defects in ventral morphogenesis and heart tube formation. There is increasing evidence demonstrating that GATA4 function is also relevant for normal developed organ systems, including the heart and endocrinum. To analyze the implication of Gata4 beyond development, we generated transgenic mice expressing inducible small interfering RNA against Gata4. In longitudinal analysis, efficient suppression of Gata4 mRNA (down to 80% of wild-type levels) and protein expression in the heart was detected 38 days after induction of Gata4 short hairpin RNA. Decreased Gata4 expression was associated with reduction in the expression of known cardiac target genes, but the function of the heart remained unperturbed at 20-30% of normal Gata4 levels. Interestingly, Gata4 expression was almost abolished in the ovary and testis. This was accompanied in the testis by a significant reduction of GATA4 downstream target genes, such as the genes encoding Mullerian inhibiting substance (MIS) and steroidogenic acute regulatory (StAR) protein. By contrast, expression levels of Mis and Star were only slightly modified in the ovary, and concentrations of circulating FSH and LH were normal in female transgenic mice after induction of Gata4 short hairpin RNA. However, inhibition of Gata4 expression led to the formation of ovarian teratoma in 10% of females. Histology of the teratomas showed predominantly ectodermal and mesodermal structures. Our data demonstrate that Gata4 is critically involved in the function and integrity of the gonads in vivo.

Regulation of P450c17 expression in the early embryo depends on GATA factors

The enzyme P450c17 is required for glucocorticoid, sex steroid, and some neurosteroid biosynthesis. Defective human P450c17 causes sexual infantilism and 46,XY sex reversal but is compatible with life, whereas ablation of the corresponding mouse gene causes embryonic lethality at around E7. Normal mouse embryos express P450c17 protein and activity in the embryonic endoderm at E7. Adult adrenal and gonadal steroidogenesis requires steroidogenic factor-1 (SF-1), but SF-1 is not expressed in the early mouse embryo. We show that P450c17 is expressed in differentiated mouse parietal and visceral endoderm lineages, in cultured mouse F9 embryonic carcinoma stem cells, in mouse embryonic stem cells, and in cultured mouse P19 stem cells. Bases -110 to -55 (which contain an SF-1 site and two potential GATA sites) of the rat cyp17 gene confer promoter activity in F9 cells. Overexpression of SF-1 has no effect, whereas overexpression of GATA4 in F9 cells increases transcription from -110/-55 fused to a reporter and increases endogenous P450c17 mRNA. Chromatin immunoprecipitation assays show that GATA4 binds to -215/+55 of mouse cyp17. Stimulating F9 cells with retinoic acid and cAMP differentiates them into visceral and parietal endoderm. Commensurate with cell differentiation, quantitative PCR showed increased GATA4 and GATA6 mRNAs, temporally followed by increased P450c17 mRNA. Small interfering RNA inhibition of GATA4 or GATA6 in undifferentiated or differentiated F9 cells diminished endogenous cyp17 expression. Thus, P450c17 is expressed in mouse embryonic stem cells, its expression increases upon differentiation to an early embryonic endoderm lineage, and GATA4/6 are responsible for activation of P450c17 gene expression at this early stage of embryonic development.

PcG proteins, DNA methylation, and gene repression by chromatin looping

Many DNA hypermethylated and epigenetically silenced genes in adult cancers are Polycomb group (PcG) marked in embryonic stem (ES) cells. We show that a large region upstream (∼30 kb) of and extending ∼60 kb around one such gene, GATA-4, is organized—in Tera-2 undifferentiated embryonic carcinoma (EC) cells—in a topologically complex multi-loop conformation that is formed by multiple internal long-range contact regions near areas enriched for EZH2, other PcG proteins, and the signature PcG histone mark, H3K27me3. Small interfering RNA (siRNA)–mediated depletion of EZH2 in undifferentiated Tera-2 cells leads to a significant reduction in the frequency of long-range associations at the GATA-4 locus, seemingly dependent on affecting the H3K27me3 enrichments around those chromatin regions, accompanied by a modest increase in GATA-4 transcription. The chromatin loops completely dissolve, accompanied by loss of PcG proteins and H3K27me3 marks, when Tera-2 cells receive differentiation signals which induce a ∼60-fold increase in GATA-4 expression. In colon cancer cells, however, the frequency of the long-range interactions are increased in a setting where GATA-4 has no basal transcription and the loops encompass multiple, abnormally DNA hypermethylated CpG islands, and the methyl-cytosine binding protein MBD2 is localized to these CpG islands, including ones near the gene promoter. Removing DNA methylation through genetic disruption of DNA methyltransferases (DKO cells) leads to loss of MBD2 occupancy and to a decrease in the frequency of long-range contacts, such that these now more resemble those in undifferentiated Tera-2 cells. Our findings reveal unexpected similarities in higher order chromatin conformation between stem/precursor cells and adult cancers. We also provide novel insight that PcG-occupied and H3K27me3-enriched regions can form chromatin loops and physically interact in cis around a single gene in mammalian cells. The loops associate with a poised, low transcription state in EC cells and, with the addition of DNA methylation, completely repressed transcription in adult cancer cells.

Polycomb group (PcG) proteins and DNA methylation are fundamental epigenetic regulators of gene expression. The mechanisms underlying such regulation, the crosstalk between these mechanisms, and the role of higher order chromatin folding in mediating transcriptional control of involved genes remains unclear. Abnormal DNA methylation at gene promoters in cancer has been linked to PcG promoter occupancy and PcG-mediated maintenance of genes in a poised, low expression state in embryonic cells. We now strengthen these links and show that PcG occupancy around an entire gene, GATA-4, represses transcription by maintaining a series of long-range chromatin interactions. In embryonic cells, where DNA methylation is largely absent, GATA-4 is in a low, poised transcription state, and the loops can be virtually eliminated by retinoid-induced cellular differentiation, with attendant robust transcriptional up-regulation. When GATA-4 is DNA hypermethylated in colon cancer cells, the intensity of the long-range interactions is increased and associates with complete lack of transcription. Removal of DNA methylation in the cancer cells only slightly loosens the loops and restores expression to a low, poised state. Together, these findings suggest that both repressive pathways operate in part by the formation of chromatin higher order structures and provide important translational ramifications for targeting re-expression of epigenetically silenced genes for cancer therapy.

Chromatin regions enriched for Polycomb group proteins physically interact in a series of loops around a single gene in mammalian cells. This higher order structure maintains a poised, low transcription state in embryonic cancer cells and, with addition of DNA methylation, a completely repressed transcription in adult cancer cells.

GATA4 reduction enhances 3',5'-cyclic adenosine 5'-monophosphate-stimulated steroidogenic acute regulatory protein messenger ribonucleic acid and progesterone production in luteinized porcine granulosa cells

Previous studies with cultured granulosa cells implicated GATA4 in gonadotropin regulation of the steroidogenic acute regulatory protein (STAR) gene. Caveats to these prior studies exist. First, GATA4 levels are reduced in granulosa-luteal cells after the LH surge when GATA6 expression is relatively high. Second, STAR mRNA expression is negligible in granulosa cells until after the LH surge. Both exogenous GATA4 and GATA6 can transactivate STAR gene promoter constructs. We used an RNA interference (RNAi) approach to determine the contributions of GATA4 and GATA6 to cAMP analog regulation of the endogenous STAR gene in luteinizing granulosa cells. STAR mRNA was stimulated by cAMP under control RNAi conditions. Surprisingly, GATA4 reduction by its respective RNAi approximately doubled the cAMP induction of STAR mRNA. At 24 h cAMP treatment, this augmentation was abolished by co-down-regulation of GATA4+GATA6. GATA6 down-regulation by itself did not alter STAR mRNA levels. GATA4+GATA6 co-down-regulation elevated basal CYP11A mRNA at 24 h treatment but did not affect its induction by cAMP. Basal levels of HSD3B mRNA were reduced by GATA4 RNAi conditions leading to a greater fold induction of its mRNA by cAMP. Fold cAMP-stimulated progesterone production was enhanced by GATA4 down-regulation but not by GATA4+GATA6 co-down-regulation. These data implicate GATA6 as the facilitator in cAMP-stimulated STAR mRNA and downstream progesterone accumulation under reduced GATA4 conditions. Data also demonstrate that basal levels of GATA4/6 are not required for cAMP induction of the STAR gene. The altered ratio of GATA4 to GATA6 after ovulation may allow GATA6 to enhance STAR mRNA accumulation.

GATA-4 regulates Bcl-2 expression in ovarian granulosa cell tumors

Excessive cell proliferation and decreased apoptosis have been implicated in the pathogenesis of ovarian granulosa cell tumors (GCTs). We hypothesized that transcription factor GATA-4 controls expression of the antiapoptotic factor Bcl-2 and the cell cycle regulator cyclin D2 in normal and neoplastic granulosa cells. To test this hypothesis, a tissue microarray based on 80 GCTs was subjected to immunohistochemistry for GATA-4, Bcl-2, and cyclin D2, and the data were correlated to clinical and histopathological parameters. In addition, quantitative RT-PCR for GATA-4, Bcl-2, and cyclin D2 was performed on 21 human GCTs. A mouse GCT model was used to complement these studies. The role of GATA-4 in the regulation of Bcl2 and ccdn2 (coding for cyclin D2) was studied by transactivation assays, and by disrupting GATA-4 function with dominant negative approaches in mouse and human GCT cell lines. We found that GATA-4 expression correlated with Bcl-2 and cyclin D2 expression in human and murine GCTs. Moreover, GATA-4 enhanced Bcl-2 and cyclin D2 promoter activity in murine GCT cells. Whereas GATA-4 overexpression up-regulated and dominant negative GATA-4 suppressed Bcl-2 expression in human GCT cells, the effects on cyclin D2 were negligible. Our results reveal a previously unknown relationship between GATA-4 and Bcl-2 in mammalian granulosa cells and GCTs, and suggest that GATA-4 influences granulosa cell fate by transactivating Bcl-2.

GATA4/FOG2 transcriptional complex regulates Lhx9 gene expression in murine heart development

BACKGROUND

GATA4 and FOG2 proteins are required for normal cardiac development in mice. It has been proposed that GATA4/FOG2 transcription complex exercises its function through gene activation as well as repression; however, targets of GATA4/FOG2 action in the heart remain elusive.

RESULTS

Here we report identification of the Lhx9 gene as a direct target of the GATA4/FOG2 complex. We demonstrate that the developing mouse heart normally expresses truncated isoforms of Lhx9 - Lhx9alpha and Lhx9beta, and not the Lhx9-HD isoform that encodes a protein with an intact homeodomain. At E9.5 Lhx9alpha/beta expression is prominent in the epicardial primordium, septum transversum while Lhx9-HD is absent from this tissue; in the E11.5 heart LHX9alpha/beta-positive cells are restricted to the epicardial mesothelium. Thereafter in the control hearts Lhx9alpha/beta epicardial expression is promptly down-regulated; in contrast, mouse mutants with Fog2 gene loss fail to repress Lhx9alpha/beta expression. Chromatin immunoprecipitation from the E11.5 hearts demonstrated that Lhx9 is a direct target for GATA4 and FOG2. In transient transfection studies the expression driven by the cis-regulatory regions of Lhx9 was repressed by FOG2 in the presence of intact GATA4, but not the GATA4ki mutant that is impaired in its ability to bind FOG2.

CONCLUSION

In summary, the Lhx9 gene represents the first direct target of the GATA4/FOG2 repressor complex in cardiac development.

Positive regulation of steroidogenic acute regulatory protein gene expression through the interaction between Dlx and GATA-4 for testicular steroidogenesis

Split hand/foot malformation (SHFM) is syndromic ectrodactyly often associated with mental retardation and/or craniofacial defects. Several clinical reports previously described urogenital dysplasia such as micropenis, hypospadias, and small testis in SHFM patients. Genetic lesions in the Dlx5 and Dlx6 (Dlx5/6) locus are associated with the human genetic disorder SHFM type 1. Although Dlx5/6 are expressed in the testis, their possible function of Dlx5/6 during testis differentiation has not been described. In this study, we show that Dlx5/6 are expressed in the fetal Leydig cells during testis development. We examined the effect of Dlx5 expression on the promoter activation of the steroidogenic acute regulatory protein (StAR) gene, which is essential for gonadal and adrenal steroidogenesis, in a Leydig cell line. Dlx5 efficiently activates the StAR promoter when GATA-4, another transcription factor essential for testicular steroidogenesis, was coexpressed. The transcriptional activation required the GATA-4-recognition element in the StAR promoter region and Dlx5 can physically interact with GATA-4. Furthermore, we herein show that the double inactivation of Dlx5 and Dlx6 in the mouse leads to decreased testosterone level and abnormal masculinization phenotype. These results suggest that Dlx5 and Dlx6 participate in the control of steroidogenesis during testis development. The findings of this study may open the way to analyze human congenital birth defects.

Specific GATA-binding elements in the GnRH promoter are required for gene expression pulse activity: role of GATA-4 and GATA-5 in this intermittent process

Recent evidence reveals that several GATA factors act as versatile transcriptional modulators in neuroendocrine gene expression. The rat GnRH promoter is expressed in an episodic fashion that requires a portion of the promoter termed the neuron-specific enhancer (NSE) for activity. In this study, we examined whether certain GATA regulatory elements in the NSE are necessary for this intermittent activity. When injected into individual living GT1-7 cells, luciferase reporter constructs containing mutations of either GATA-A- or GATA-B-binding sites resulted in a marked reduction in gene expression pulse frequency, while mutations of both sites virtually abolished pulses. In subsequent studies, RT-PCR and western blot analysis revealed for the first time that GATA-5 and GATA-6 were expressed in GT1-7 cells, but electrophoretic mobility shift assays demonstrated further that GATA-5 bound to one of these GATA sites: GATA-A. Chromatin immunoprecipitation analysis revealed that all three factors, GATA-4, GATA-5, and GATA-6, were associated with the GnRH promoter in vivo. Interestingly though, immunoneutralization of GATA-5 or GATA-4 (reported to bind GATA-B) abolished gene expression pulses, but injection of GATA-6 antibody did not, indicating that of these factors just GATA-5 and GATA-4 are critical for intermittent activity. Finally, gel shift competition experiments revealed an interaction between proteins binding at the GATA-A site and those associating with an adjacent OCT1 site, previously shown to be necessary for pulse formation. These findings indicate that episodic GnRH gene expression pulses are mediated by GATA-5 and GATA-4, likely acting through the GATA-binding sites in the GnRH NSE region. Moreover, our observations that factors associated with GATA sites may also interact with OCT1 sites and that both are critical for pulse activity raise the intriguing possibility that GnRH pulse elaboration is a highly complex process that may require the coordinated interaction of several NSE-binding elements of the GnRH promoter.

Transcription factors Csx/Nkx2.5 and GATA4 distinctly regulate expression of Ca2+ channels in neonatal rat heart

The cardiac transcription factors Csx/Nkx2.5 and GATA4 play important roles in vertebrate heart development. Although mutations of Csx/Nkx2.5 or GATA4 are associated with various congenital heart diseases, their mechanism of action on cardiomyocyte function is not completely elucidated. In this study, we therefore investigated the actions of these transcription factors on the electrophysiological features and expression of ion channels in cardiomyocytes. Genes for transcription factors Csx/Nkx2.5 and GATA4 were transfected into rat neonatal cardiomyocytes by adenoviral infection. Action potentials, L-, T-type Ca(2+) channels and hyperpolarization-activated cation current (I(h)) of rat neonatal myocytes were recorded by patch clamp technique after adenoviral infection. Expression of ion channels was confirmed by real-time PCR. In Csx/Nkx2.5 overexpression myocytes, the spontaneous beating rate was markedly increased with an up-regulation of the Ca(v)3.2 T-type Ca(2+) channel, while in GATA4 overexpression myocytes, the T-type Ca(2+) channel was unchanged. On the other hand, the L-type Ca(2+) channel was down-regulated by both Csx/Nkx2.5 and GATA4 overexpression; the level of Ca(v)1.3 mRNA was dramatically decreased by Csx/Nkx2.5 overexpression. These results indicate that Csx/Nkx2.5 and GATA4 play important roles on the generation of pacemaker potentials modulating voltage-dependent Ca(2+) channels in the neonatal cardiomyocyte.

Screening and biochemical analysis of GATA4 sequence variations identified in patients with congenital heart disease

Few known monogenic causes of non-syndromic congenital heart disease (CHD) have been identified. Mutations in NKX2.5 were initially implicated in familial cases of cardiac septal defects and subsequently, functionally significant NKX2.5 mutations were found in diverse forms of non-syndromic CHD. Similarly, mutations in GATA4, which encodes a cardiac transcription factor, were first identified in familial cases of cardiac septal defects. We hypothesize that individuals with non-syndromic CHD may harbor GATA4 mutations and that these mutations alter the biochemical properties of the protein. The coding region encompassing the six exons of GATA4 was screened in a study population of 157 patients with CHD. We identified several sequence variations in GATA4. We tested these novel sequence variations that altered evolutionarily conserved amino acids and other previously reported GATA4 mutations in various biochemical assays. The novel sequence variations had no biochemical deficits while a previously reported, but unstudied, missense mutation in GATA4 (S52F) functioned as a hypomorph in transactivation assays. We did not identify any novel GATA4 mutations in our patient population with non-syndromic CHD. Consistent with previous findings, GATA4 mutations that result in deficits in transactivation ability are consistently associated with CHD suggesting that normal transactivation properties of GATA4 are required for proper cardiac development.

Gata4 and Hnf1alpha are partially required for the expression of specific intestinal genes during development

The terminal differentiation phases of intestinal development in mice occur during cytodifferentiation and the weaning transition. Lactase-phlorizin hydrolase (LPH), liver fatty acid binding protein (Fabp1), and sucrase-isomaltase (SI) are well-characterized markers of these transitions. With the use of gene inactivation models in mature mouse jejunum, we have previously shown that a member of the zinc finger transcription factor family (Gata4) and hepatocyte nuclear factor-1alpha (Hnf1alpha) are each indispensable for LPH and Fabp1 gene expression but are both dispensable for SI gene expression. In the present study, we used these models to test the hypothesis that Gata4 and Hnf1alpha regulate LPH, Fabp1, and SI gene expression during development, specifically focusing on cytodifferentiation and the weaning transition. Inactivation of Gata4 had no effect on LPH gene expression during either cytodifferentiation or suckling, whereas inactivation of Hnf1alpha resulted in a 50% reduction in LPH gene expression during these same time intervals. Inactivation of Gata4 or Hnf1alpha had a partial effect ( approximately 50% reduction) on Fabp1 gene expression during cytodifferentiation and suckling but no effect on SI gene expression at any time during development. Throughout the suckling period, we found a surprising and dramatic reduction in Gata4 and Hnf1alpha protein in the nuclei of absorptive enterocytes of the jejunum despite high levels of their mRNAs. Finally, we show that neither Gata4 nor Hnf1alpha mediates the glucocorticoid-induced precocious maturation of the intestine but rather are downstream targets of this process. Together, these data demonstrate that specific intestinal genes have differential requirements for Gata4 and Hnf1alpha that are dependent on the developmental time frame in which they are expressed.

Adrenocortical tumorigenesis, luteinizing hormone receptor and transcription factors GATA-4 and GATA-6

Luteinizing hormone (LH/hCG) responsiveness of normal and pathological human adrenal glands as well as the possibility of constitutive expressions of luteinizing hormone receptor (LHR) in adrenal cortex has been reported. Some recent studies showed a correlation between the LHR and abundant GATA-4 expression in both metastasizing and non-metastasizing human adrenocortical tumors, but not in normal adrenals, implicating the putative relevance of LHR and GATA-4 for adrenocortical pathophysiology. However, the physio- and pathophysiological significance of LHR and GATA-4 in the mechanism of adrenocortical tumorigenesis remains unclear. The paucity of suitable models for adrenal tumorigenesis makes the establishment of proper animal models highly important. LHR expression in the murine adrenal gland is an exception and not found in wild-type (WT) animal. We have previously shown that ectopic LHR expression in the murine adrenal gland can be induced by chronically elevated LH levels. We have generated a gonadotropin-responsive adrenal tumor model in gonadectomized transgenic (TG) mice expressing the inhibin alpha promoter/Simian Virus 40 T antigen transgene (inhalpha/Tag). Given the induction of expression and regulation of GATA-4 and GATA-6 zinc finger transcription factors in the gonads by gonadotropins, this review will explore their relationship to LHR expression and their role in adrenocortical tumorigenesis. A functional link between LHR and GATA-4 actions in the adrenal pathophysiology is proposed.

Identification and functional analysis of a novel human CYP2E1 far upstream enhancer

Both transcriptional and post-transcriptional CYP2E1 regulatory mechanisms are known, resulting in 20-fold or greater variation in CYP2E1 expression. To evaluate functional regulatory elements controlling transcription, CYP2E1 promoter constructs were used to make adenovirus vectors containing CYP2E1 promoter-driven luciferase reporters for analyses in both primary human hepatocytes and HepG2 cells. A 1.2-kilobase pair portion of the CYP2E1 promoter was associated with 5- to 10-fold greater luciferase activity. This upstream region contained five direct repeats of 59 base pairs (bp) that increased thymidine kinase-driven luciferase reporter activity in HepG2 cells more than 5-fold, regardless of orientation. Electrophoretic mobility shift assays (EMSAs) identified sequence-specific nuclear protein binding to the 59-bp repeats that was dependent on a 17-bp sequence containing a canonical GATA binding site (WGATAR). Competitive and supershift EMSA identified the participation of GATA4, another GATA family member or GATA-like factor, and a third factor unrelated to the GATA family. Involvement of the tricho-rhino-phalangeal syndrome-1 factor, which also binds a GATA sequence, was eliminated. Rather, competitive EMSA using known binding sequences for the orphan nuclear receptors, steroidogenic factor-1 (or NR5A1), and fetoprotein transcription factor (or NR5A2) implicated an NR5A member in binding a sequence overlapping the canonical GATA. Chromatin immunoprecipitation assay demonstrated in vivo binding of NR5A2 to the enhancer sequence in human hepatocytes. The enhancer sequence is conserved within the human population but seems species-specific. The identification of this novel enhancer and its putative mechanism adds to the complexities of human CYP2E1 regulation.

Gata4 is necessary for normal pulmonary lobar development

Mutations of Fog2 in mice result in a phenotype that includes pulmonary lobar defects. To determine whether formation of the accessory lobe bronchus is mediated by a Gata family cofactor, we evaluated embryonic lungs from mice carrying missense mutations that cause loss of FOG-GATA protein interaction. Lungs from embryos carrying a missense mutation in Gata6 were structurally normal, while lungs from embryos carrying mutations of either Gata4 or of both Gata4 and Gata6 had a structural phenotype that matched the Fog2 mutant phenotype. Expression analysis showed that Gata4 and Fog2 are expressed in the ventral and medial pulmonary mesenchyme during secondary budding. Although Gata4 has not previously been suspected as playing a role in lung development, we have found that a Fog2-Gata4 interaction is critical for the development of normal pulmonary lobar structure, and this phenotype is not influenced by the additional loss of Gata6 interaction. Fog2 and Gata4 in the early pulmonary mesenchyme participate in patterning the secondary bronchus of the accessory lobe.

Re-employment of developmental transcription factors in adult heart disease

A finite number of transcription factors constitute a combinatorial code that orchestrates cardiac development and the specification and differentiation of myocytes. Many, if not all of these same transcription factors are re-employed in the adult heart in response to disease stimuli that promote hypertrophic enlargement and/or dilated cardiomyopathy, as part of the so-called "fetal gene program". This review will discuss the transcription factors that regulate the hypertrophic growth response of the adult heart, with a special emphasis on those regulators that participate in cardiac development.

The human Cx40 promoter polymorphism -44G-->A differentially affects transcriptional regulation by Sp1 and GATA4

Expression of the tissue-specific gap junction protein connexin(Cx)40 is regulated by the interaction of ubiquitous and tissue-specific factors such as Sp1 and GATA4. Cardiac Cx40 expression is altered under pathological conditions such as atrial fibrillation. A human promoter polymorphism, a G-->A change at position -44 that has been associated with atrial-specific arrhythmias, is located between the TBE-NKE-Sp and GATA consensus transcription factor binding sites important for the regulation of the mouse Cx40 gene. The presence of the A-allele at position -44 in promoter-reporter constructs significantly reduces promoter activity. Using electrophoretic mobility shift assays and luciferase reporter assays in various cell types, we show that Sp1 and GATA4 are important regulators of human Cx40 gene transcription and that the -44 G-->A polymorphism negatively affects the promoter regulation by the transcription factors Sp1 and GATA4.

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

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 the mesenchymal progenitors of the AV valves. Further growth and differentiation of these mesenchymal precursors results in the formation of portions of the atrial and ventricular septae, and the generation of thin, pliable valves. Gata4, which encodes a zinc finger transcription factor, 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 a 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.

A threshold of GATA4 and GATA6 expression is required for cardiovascular development

The zinc-finger transcription factors GATA4 and GATA6 play critical roles in embryonic development. Mouse embryos lacking GATA4 die at embryonic day (E) 8.5 because of failure of ventral foregut closure and cardiac bifida, whereas GATA6 is essential for development of the visceral endoderm. Although mice that are heterozygous for either a GATA4 or GATA6 null allele are normal, we show that compound heterozygosity of GATA4 and GATA6 results in embryonic lethality by E13.5 accompanied by a spectrum of cardiovascular defects, including thin-walled myocardium, ventricular and aortopulmonary septal defects, and abnormal smooth muscle development. Myocardial hypoplasia in GATA4/GATA6 double heterozygous mutant embryos is associated with reduced proliferation of cardiomyocytes, diminished expression of the myogenic transcription factor MEF2C (myocyte enhancer factor 2C), and down-regulation of beta-myosin heavy chain expression, a key determinant of cardiac contractility. These findings reveal a threshold of GATA4 and GATA6 activity that is required for gene expression in the developing cardiovascular system and underscore the potential of recessive mutations to perturb the delicate regulation of cardiovascular development.

Transcriptional activation of the steroidogenic acute regulatory protein (StAR) gene: GATA-4 and CCAAT/enhancer-binding protein beta confer synergistic responsiveness in hormone-treated rat granulosa and HEK293 cell models

Steroidogenic acute regulatory protein (StAR) mediates translocation of cholesterol to the inner membranes of steroidogenic mitochondria, where it serves as a substrate for steroid synthesis. Transcription of StAR in the gonads and adrenal cells is upregulated by trophic hormones, involves downstream signaling pathways and a cohort of trans-factors acting as activators or suppressors of StAR transcription. This study suggests that a 21 basepair long sequence positioned at -81/-61 of the murine StAR promoter is sufficient to confer a robust hormonal activation of transcription in ovarian granulosa cells treated with FSH. We show that recombinant GATA-4 and CCAAT/enhancer-binding protein beta (C/EBPbeta) bind to the promoter at -66/-61 and -81/-70 and activate transcription of a reporter gene when co-expressed in heterologous human embryonic kidney 293 (HEK293) cells. In this cell model, C/EBPbeta and GATA-4 synergize in a sequence dependent manner and p300/CBP further maximizes their joint activities. Inhibitors of the transcriptional activators, such as liver-enriched inhibiting protein (C/EBPbeta-LIP), Friend of GATA-4 (FOG-2) protein and the viral E1A protein abolished the respective factor-dependent activities in HEK293 cells. Binding assays suggest that a dual binding of C/EBPbeta and GATA-4 to the promoter depends on the molar ratio of the factors present while demonstrating GATA-4 predominant association with the promoter DNA. This pattern may reflect on StAR expression at the time of corpus luteum formation when C/EBPbeta levels peak, as does StAR expression.

Cardiac-specific deletion of Gata4 reveals its requirement for hypertrophy, compensation, and myocyte viability

The transcription factor GATA4 is a critical regulator of cardiac gene expression where it controls embryonic development, cardiomyocyte differentiation, and stress responsiveness of the adult heart. Traditional deletion of Gata4 caused embryonic lethality associated with endoderm defects and cardiac malformations, precluding an analysis of the role of GATA4 in the adult myocardium. To address the function of GATA4 in the adult heart, Gata4-loxP-targeted mice (Gata4fl/fl) were crossed with mice containing a beta-myosin heavy chain (beta-MHC) or alpha-MHC promoter-driven Cre transgene, which produced viable mice that survived into adulthood despite a 95% and 70% loss of GATA4 protein, respectively. However, cardiac-specific deletion of Gata4 resulted in a progressive and dosage-dependent deterioration in cardiac function and dilation in adulthood. Moreover, pressure overload stimulation induced rapid decompensation and heart failure in cardiac-specific Gata4-deleted mice. More provocatively, Gata4-deleted mice were compromised in their ability to hypertrophy following pressure overload or exercise stimulation. Mechanistically, cardiac-specific deletion of Gata4 increased cardiomyocyte TUNEL at baseline in embryos and adults as they aged, as well as dramatically increased TUNEL following pressure overload stimulation. Examination of gene expression profiles in the heart revealed a number of profound alterations in known GATA4-regulated structural genes as well as genes with apoptotic implications. Thus, GATA4 is a necessary regulator of cardiac gene expression, hypertrophy, stress-compensation, and myocyte viability.

GATA-4:FOG interactions regulate gastric epithelial development in the mouse

Transcription factor GATA-4 is a key participant in cytodifferentiation of the mouse hindstomach. Here we show that GATA-4 cooperates with a Friend-of-GATA (FOG) cofactor to direct gene expression in this segment of gut. Immunohistochemical staining revealed that GATA-4 and FOG-1 are co-expressed in hindstomach epithelial cells from embryonic days (E) 11.5 to 18.5. The other member of the mammalian FOG family, FOG-2, was not detected in gastric epithelium. To show that GATA-4:FOG interactions influence stomach development, we analyzed Gata4(ki/ki) mice, which express a mutant GATA-4 that cannot bind FOG cofactors. Sonic Hedgehog, an endoderm-derived signaling molecule normally down-regulated in the distal stomach, was over-expressed in hindstomach epithelium of E11.5 Gata4(ki/ki) mice, and there was a concomitant decrease in fibroblast growth factor-10 in adjacent mesenchyme. We conclude that functional interaction between GATA-4 and a member of the FOG family, presumably FOG-1, is required for proper epithelial-mesenchymal signaling in the developing stomach.

Retinoic acid signaling is essential for formation of the heart tube in Xenopus

Retinoic acid is clearly important for the development of the heart. In this paper, we provide evidence that retinoic acid is essential for multiple aspects of cardiogenesis in Xenopus by examining embryos that have been exposed to retinoic acid receptor antagonists. Early in cardiogenesis, retinoic acid alters the expression of key genes in the lateral plate mesoderm including Nkx2.5 and HAND1, indicating that early patterning of the lateral plate mesoderm is, in part, controlled by retinoic acid. We found that, in Xenopus, the transition of the heart from a sheet of cells to a tube required retinoic acid signaling. The requirement for retinoic acid signaling was determined to take place during a narrow window of time between embryonic stages 14 and 18, well before heart tube closure. At the highest doses used, the lateral fields of myocardium fail to fuse, intermediate doses lead to a fusion of the two sides but failure to form a tube, and embryos exposed to lower concentrations of antagonist form a heart tube that failed to complete all the landmark changes that characterize looping. The myocardial phenotypes observed when exposed to the retinoic acid antagonist resemble the myocardium from earlier stages of cardiogenesis, although precocious expression of cardiac differentiation markers was not seen. The morphology of individual cells within the myocardium appeared immature, closely resembling the shape and size of cells at earlier stages of development. However, the failures in morphogenesis are not merely a slowing of development because, even when allowed to develop through stage 40, the heart tubes did not close when embryos were exposed to high levels of antagonist. Indeed, some aspects of left-right asymmetry also remained even in hearts that never formed a tube. These results demonstrate that components of the retinoic acid signaling pathway are necessary for the progression of cardiac morphogenesis in Xenopus.

Convergence of protein kinase C and JAK-STAT signaling on transcription factor GATA-4

Angiotensin II (AII), a potent vasoactive hormone, acts on numerous organs via G-protein-coupled receptors and elicits cell-specific responses. At the level of the heart, AII stimulation alters gene transcription and leads to cardiomyocyte hypertrophy. Numerous intracellular signaling pathways are activated in this process; however, which of these directly link receptor activation to transcriptional regulation remains undefined. We used the atrial natriuretic factor (ANF) gene (NPPA) as a marker to elucidate the signaling cascades involved in AII transcriptional responses. We show that ANF transcription is activated directly by the AII type 1 receptor and precedes the development of myocyte hypertrophy. This response maps to STAT and GATA binding sites, and the two elements transcriptionally cooperate to mediate signaling through the JAK-STAT and protein kinase C (PKC)-GATA-4 pathways. PKC phosphorylation enhances GATA-4 DNA binding activity, and STAT-1 functionally and physically interacts with GATA-4 to synergistically activate AII and other growth factor-inducible promoters. Moreover, GATA factors are able to recruit STAT proteins to target promoters via GATA binding sites, which are sufficient to support synergy. Thus, STAT proteins can act as growth factor-inducible coactivators of tissue-specific transcription factors. Interactions between STAT and GATA proteins may provide a general paradigm for understanding cell specificity of cytokine and growth factor signaling.

Cardiac development: new concepts

Understanding normal development is a prerequisite to unraveling the mechanisms that underlie congenital heart disease, a critical step if one is to design rational new therapies. Over the past 20 years, human molecular genetics and developmental biology have provided a group of powerful tools to uncover a number of now well-defined pathways. There is now a confluence of new technologies and experimental systems that may allow for a more profound understanding in the near future.

Perception of differentiation cues by GATA factors in primitive endoderm lineage determination of mouse embryonic stem cells

The formation of the primitive endoderm covering the inner cell mass of early mouse embryos can be simulated in vitro by the differentiation of mouse embryonic stem (ES) cells in culture following either aggregation of suspended cells or stimulation of cell monolayers with retinoic acid. The developmentally regulated transcription factors GATA-4 and GATA-6 have determining role in mouse extraembryonic endoderm development. We analyzed the in vitro differentiation of mouse embryonic stem cells deficient of GATA factors and conclude that GATA-4 is required for ES cells to perceive a cell positioning (cell aggregation) signal and GATA-6 is required to sense morphogenic (retinoic acid) signal. The collaboration between GATA-6 and GATA-4, or GATA-6 and GATA-5 which can substitute for GATA-4, is involved in the perception of differentiation cues by embryonic stem cells in their determination of endoderm lineage. This study indicates that the lineage differentiation of ES cells can be manipulated by the expression of GATA factors.