Mouse GATA-4: a retinoic acid-inducible GATA-binding transcription factor expressed in endodermally derived tissues and heart

Combinatorial regulation of tissue specification by GATA and FOG factors

The development of complex organisms requires the formation of diverse cell types from common stem and progenitor cells. GATA family transcriptional regulators and their dedicated co-factors, termed Friend of GATA (FOG) proteins, control cell fate and differentiation in multiple tissue types from Drosophila to man. FOGs can both facilitate and antagonize GATA factor transcriptional regulation depending on the factor, cell, and even the specific gene target. In this review, we highlight recent studies that have elucidated mechanisms by which FOGs regulate GATA factor function and discuss how these factors use these diverse modes of gene regulation to control cell lineage specification throughout metazoans.

Pancreas-specific deletion of mouse Gata4 and Gata6 causes pancreatic agenesis

Pancreatic agenesis is a human disorder caused by defects in pancreas development. To date, only a few genes have been linked to pancreatic agenesis in humans, with mutations in pancreatic and duodenal homeobox 1 (PDX1) and pancreas-specific transcription factor 1a (PTF1A) reported in only 5 families with described cases. Recently, mutations in GATA6 have been identified in a large percentage of human cases, and a GATA4 mutant allele has been implicated in a single case. In the mouse, Gata4 and Gata6 are expressed in several endoderm-derived tissues, including the pancreas. To analyze the functions of GATA4 and/or GATA6 during mouse pancreatic development, we generated pancreas-specific deletions of Gata4 and Gata6. Surprisingly, loss of either Gata4 or Gata6 in the pancreas resulted in only mild pancreatic defects, which resolved postnatally. However, simultaneous deletion of both Gata4 and Gata6 in the pancreas caused severe pancreatic agenesis due to disruption of pancreatic progenitor cell proliferation, defects in branching morphogenesis, and a subsequent failure to induce the differentiation of progenitor cells expressing carboxypeptidase A1 (CPA1) and neurogenin 3 (NEUROG3). These studies address the conserved and nonconserved mechanisms underlying GATA4 and GATA6 function during pancreas development and provide a new mouse model to characterize the underlying developmental defects associated with pancreatic agenesis.

Dual function of the UNC-45b chaperone with myosin and GATA4 in cardiac development

Cardiac development requires interplay between the regulation of gene expression and the assembly of functional sarcomeric proteins. We report that UNC-45b recessive loss-of-function mutations in C3H and C57BL/6 inbred mouse strains cause arrest of cardiac morphogenesis at the formation of right heart structures and failure of contractile function. Wild-type C3H and C57BL/6 embryos at the same stage, E9.5, form actively contracting right and left atria and ventricles. The known interactions of UNC-45b as a molecular chaperone are consistent with diminished accumulation of the sarcomeric myosins, but not their mRNAs, and the resulting decreased contraction of homozygous mutant embryonic hearts. The novel finding that GATA4 accumulation is similarly decreased at the protein but not mRNA levels is also consistent with the function of UNC-45b as a chaperone. The mRNAs of known downstream targets of GATA4 during secondary cardiac field development, the cardiogenic factors Hand1, Hand2 and Nkx-2.5, are also decreased, consistent with the reduced GATA4 protein accumulation. Direct binding studies show that the UNC-45b chaperone forms physical complexes with both the alpha and beta cardiac myosins and the cardiogenic transcription factor GATA4. Co-expression of UNC-45b with GATA4 led to enhanced transcription from GATA promoters in naïve cells. These novel results suggest that the heart-specific UNC-45b isoform functions as a molecular chaperone mediating contractile function of the sarcomere and gene expression in cardiac development.

Loss of GATA-6 and GATA-4 in granulosa cells blocks folliculogenesis, ovulation, and follicle stimulating hormone receptor expression leading to female infertility

Single GATA-6 (G6(gcko)), GATA-4 (G4(gcko)), and double GATA-4/6 (G4/6(gcko)) granulosa cell-specific knockout mice were generated to further investigate the role of GATA transcription factors in ovarian function in vivo. No reproductive defects were found in G6(gcko) animals. G4(gcko) animals were subfertile as indicated by the reduced number of pups per litter and the release of significantly fewer oocytes at ovulation. In marked contrast, G4/6(gcko) females fail to ovulate and are infertile. Furthermore, G4/6(gcko) females had irregular estrous cycles, which correlate with the abnormal ovarian histology found in unstimulated adult G4/6(gcko) females showing lack of follicular development and increased follicular atresia. Moreover, treatment with exogenous gonadotropins did not rescue folliculogenesis or ovulation in double-knockout G4/6(gcko) mice. In addition, ovary weight and estradiol levels were significantly reduced in G4(gcko) and G4/6(gcko) animals when compared with control and G6(gcko) mice. Aromatase, P450scc, and LH receptor expression was significantly lower in G4(gcko) and G4/6(gcko) mice when compared with control animals. Most prominently, FSH receptor (FSHR) protein was undetectable in granulosa cells of G4(gcko) and G4/6(gcko). Accordingly, gel shift and reporter assays revealed that GATA-4 binds and stimulates the activity of the FSHR promoter. These results demonstrate that GATA-4 and GATA-6 are needed for normal ovarian function. Our data are consistent with a role for GATA-4 in the regulation of the FSHR gene and provide a possible molecular mechanism to explain the fertility defects observed in animals with deficient GATA expression in the ovary.

Master regulatory GATA transcription factors: mechanistic principles and emerging links to hematologic malignancies

Numerous examples exist of how disrupting the actions of physiological regulators of blood cell development yields hematologic malignancies. The master regulator of hematopoietic stem/progenitor cells GATA-2 was cloned almost 20 years ago, and elegant genetic analyses demonstrated its essential function to promote hematopoiesis. While certain GATA-2 target genes are implicated in leukemogenesis, only recently have definitive insights emerged linking GATA-2 to human hematologic pathophysiologies. These pathophysiologies include myelodysplastic syndrome, acute myeloid leukemia and an immunodeficiency syndrome with complex phenotypes including leukemia. As GATA-2 has a pivotal role in the etiology of human cancer, it is instructive to consider mechanisms underlying normal GATA factor function/regulation and how dissecting such mechanisms may reveal unique opportunities for thwarting GATA-2-dependent processes in a therapeutic context. This article highlights GATA factor mechanistic principles, with a heavy emphasis on GATA-1 and GATA-2 functions in the hematopoietic system, and new links between GATA-2 dysregulation and human pathophysiologies.

Retinoic acid signaling plays a restrictive role in zebrafish primitive myelopoiesis

Retinoic acid (RA) is known to regulate definitive myelopoiesis but its role in vertebrate primitive myelopoiesis remains unclear. Here we report that zebrafish primitive myelopoiesis is restricted by RA in a dose dependent manner mainly before 11 hpf (hours post fertilization) when anterior hemangioblasts are initiated to form. RA treatment significantly reduces expressions of anterior hemangioblast markers scl, lmo2, gata2 and etsrp in the rostral end of ALPM (anterior lateral plate mesoderm) of the embryos. The result indicates that RA restricts primitive myelopoiesis by suppressing formation of anterior hemangioblasts. Analyses of ALPM formation suggest that the defective primitive myelopoiesis resulting from RA treatment before late gastrulation may be secondary to global loss of cells for ALPM fate whereas the developmental defect resulting from RA treatment during 10–11 hpf should be due to ALPM patterning shift. Overexpressions of scl and lmo2 partially rescue the block of primitive myelopoiesis in the embryos treated with 250 nM RA during 10–11 hpf, suggesting RA acts upstream of scl to control primitive myelopoiesis. However, the RA treatment blocks the increased primitive myelopoiesis caused by overexpressing gata4/6 whereas the abolished primitive myelopoiesis in gata4/5/6 depleted embryos is well rescued by 4-diethylamino-benzaldehyde, a retinal dehydrogenase inhibitor, or partially rescued by knocking down aldh1a2, the major retinal dehydrogenase gene that is responsible for RA synthesis during early development. Consistently, overexpressing gata4/6 inhibits aldh1a2 expression whereas depleting gata4/5/6 increases aldh1a2 expression. The results reveal that RA signaling acts downstream of gata4/5/6 to control primitive myelopoiesis. But, 4-diethylamino-benzaldehyde fails to rescue the defective primitive myelopoiesis in either cloche embryos or lycat morphants. Taken together, our results demonstrate that RA signaling restricts zebrafish primitive myelopoiesis through acting downstream of gata4/5/6, upstream of, or parallel to, cloche, and upstream of scl.

Pioneer transcription factors: establishing competence for gene expression

Transcription factors are adaptor molecules that detect regulatory sequences in the DNA and target the assembly of protein complexes that control gene expression. Yet much of the DNA in the eukaryotic cell is in nucleosomes and thereby occluded by histones, and can be further occluded by higher-order chromatin structures and repressor complexes. Indeed, genome-wide location analyses have revealed that, for all transcription factors tested, the vast majority of potential DNA-binding sites are unoccupied, demonstrating the inaccessibility of most of the nuclear DNA. This raises the question of how target sites at silent genes become bound de novo by transcription factors, thereby initiating regulatory events in chromatin. Binding cooperativity can be sufficient for many kinds of factors to simultaneously engage a target site in chromatin and activate gene expression. However, in cases in which the binding of a series of factors is sequential in time and thus not initially cooperative, special "pioneer transcription factors" can be the first to engage target sites in chromatin. Such initial binding can passively enhance transcription by reducing the number of additional factors that are needed to bind the DNA, culminating in activation. In addition, pioneer factor binding can actively open up the local chromatin and directly make it competent for other factors to bind. Passive and active roles for the pioneer factor FoxA occur in embryonic development, steroid hormone induction, and human cancers. Herein we review the field and describe how pioneer factors may enable cellular reprogramming.

ETS-dependent regulation of a distal Gata4 cardiac enhancer

The developing heart contains an inner tube of specialized endothelium known as endocardium, which performs multiple essential functions. In spite of the essential role of the endocardium in heart development and function, the transcriptional pathways that regulate its development remain largely undefined. GATA4 is a zinc finger transcription factor that is expressed in multiple cardiovascular lineages and is required for endocardial cushion development and embryonic viability, but the transcriptional pathways upstream of Gata4 in the endocardium and its derivatives in the endocardial cushions are unknown. Here, we describe a distal enhancer from the mouse Gata4 gene that is briefly active in multiple cardiac lineages early in cardiac development but restricts to the endocardium where it remains active through cardiogenesis. The activity of this Gata4 cardiac enhancer in transgenic embryos and in cultured aortic endothelial cells is dependent on four ETS sites. To identify which ETS transcription factors might be involved in Gata4 regulation via the ETS sites in the enhancer, we determined the expression profile of 24 distinct ETS factors in embryonic mouse hearts. Among multiple ETS transcripts present, ETS1, FLI1, ETV1, ETV5, ERG, and ETV6 were the most abundant in the early embryonic heart. We found that ETS1, FLI1, and ERG were strongly expressed in the heart at embryonic day 8.5 and that ETS1 and ERG bound to the endogenous Gata4 enhancer in cultured endothelial cells. Thus, these studies define the ETS expression profile in the early embryonic heart and identify an ETS-dependent enhancer from the Gata4 locus.

Combined mutation screening of NKX2-5, GATA4, and TBX5 in congenital heart disease: multiple heterozygosity and novel mutations

Background.  Variants of several genes encoding transcription modulators, signal transduction, and structural proteins are known to cause Mendelian congenital heart disease (CHD). NKX2-5 and GATA4 were the first CHD-causing genes identified by linkage analysis in large affected families. Mutations of TBX5 cause Holt-Oram syndrome, which includes CHD as a clinical feature. All three genes have a well-established role in cardiac development. Design.  In order to investigate the possible role of multiple mutations in CHD, a combined mutation screening was performed in NKX2-5, GATA4, and TBX5 in the same patient cohort. Samples from a cohort of 331 CHD patients were analyzed by polymerase chain reaction, double high-performance liquid chromatography and sequencing in order to identify changes in the NKX2-5, GATA4, and TBX5 genes. Results.  Two cases of multiple heterozygosity of putative disease-causing mutations were identified. One patient was found with a novel L122P NKX2-5 mutation in combination with the private A1443D mutation of MYH6. A patient heterozygote for a D425N GATA4 mutation carries also a private mutation of the MYH6 gene (V700M). Conclusions.  In addition to reporting two novel mutations of NKX2-5 in CHD, we describe families where multiple individual mutations seem to have an additive effect over the pathogenesis of CHD. Our findings highlight the usefulness of multiple gene mutational analysis of large CHD cohorts.

Regeneration of cardiomyocytes from bone marrow: Use of mesenchymal stem cell for cardiovascular tissue engineering

We have isolated a cardiomyogenic cell line (CMG cell) from murine bone marrow mesenchymal stem cells. The cells showed a fibroblast-like morphology, but the morphology changed after 5-azacytidine exposure. They began spontaneous beating after 2 weeks, and expressed ANP and BNP. Electron microscopy revealed a cardiomyocyte-like ultrastructure. These cells had several types of action potentials; sinus node-like and ventricular cell-like action potentials. The isoform of contractile protein genes indicated that their muscle phenotype was similar to fetal ventricular cardiomyocytes. They expressed alpha(1A), alpha(1B), alpha(1D), beta(1), and beta(2) adrenergic and M(1) and M(2) muscarinic receptors. Stimulation with phenylephrine, isoproterenol and carbachol increased ERK phosphorylation and second messengers. Isoproterenol increased the beating rate, which was blocked with CGP20712A (beta(1)-selective blocker). These findings indicated that cell transplantation therapy for the patients with heart failure might possibly be achieved using the regenerated cardiomyocytes from autologous bone marrow cells in the near future.

Cell signaling pathways for the regulation of GATA4 transcription factor: Implications for cell growth and apoptosis

GATA4 is a member of the GATA family of zinc finger transcription factor, which regulates gene transcription by binding to GATA elements. GATA4 was originally discovered as a regulator of cardiac development and subsequently identified as a major regulator of adult cardiac hypertrophy. GATA4 regulates gene expression of various genes, which are involved in cardiac development and cardiac hypertrophy and heart failure. In addition to the heart, GATA4 plays important roles in the reproductive system, gastrointestinal system, respiratory system and cancer. Positive and negative regulations of GATA4 therefore are important components of biologic functions. The activation of GATA4 occurs via various cell signaling events. Earlier studies have identified protein-protein interactions of GATA4 with other factors. The discovery of interactions of GATA4 with nuclear factor for activated T cells (NFAT) revealed the importance of calcium signaling in the activation of GATA4. GATA4 can also be phosphorylated by mitogen activated protein kinases and protein kinase A. Lysine modifications also occur on the GATA4 molecule including acetylation and sumoylation. Both reactive oxygen-dependent and -independent antioxidant-sensitive pathways for GATA4 activation have also been demonstrated. The GATA4 activity is also regulated by modulating the level of GATA4 expression via transcriptional as well as translational mechanisms. This work summarizes the current understanding of regulatory mechanisms for modulating GATA4 activity.

GATA4 regulates estrogen receptor-alpha-mediated osteoblast transcription

Estrogens regulate osteoblast differentiation and mineralization. We identified GATA4 as a transcription factor expressed in osteoblasts and directly regulated by 17β-estradiol in this cell type but not in breast cancer cells, another estrogen-responsive tissue. Chromatin immunoprecipitation sequencing (chromatin immunoprecipitation sequencing) reveals that estrogen receptor α (ERα) binds to chromatin near GATA4 at five different enhancers. GATA4 and ERα are both recruited to ERα binding sites near genes that are specifically expressed in osteoblasts and control osteoblast differentiation. Maximal binding of GATA4 precedes ERα binding, and GATA4 is necessary for histone 3 lysine 4 dimethylation at ERα binding sites, suggesting that GATA4 is a pioneer factor for ERα. As such, knockdown of GATA4 reduced recruitment of ERα to DNA. Our study illustrates that GATA4 is a pioneer factor for ERα recruitment to osteoblast-specific enhancers.

Ectopic expression of GATA6 bypasses requirement for Grb2 in primitive endoderm formation

Gene knockouts in mice have showed that Grb2 and GATA6 are essential for the formation of primitive endoderm in blastocysts. Here, we confirmed that implanted Grb2-null blastocysts lack primitive or extraembryonic endoderm cells either at E4.5 or E5.5 stages. We analyzed the relationship between Grb2 and GATA6 in the differentiation of embryonic stem (ES) cells to primitive endoderm in embryoid body models. Upon transfection with GATA6 expression vector, Grb2-null ES cells underwent endoderm differentiation as indicated by the expression of the extraembryonic endoderm markers Dab2 and GATA4. Transfection of GATA4 expression vector also had the same differentiation potency. When GATA6- or GATA4-transfected Grb2-null ES cells were allowed to aggregate, fragments of an endoderm layer formed on the surface of the spheroids. The results suggest that GATA6 is downstream of Grb2 in the inductive signaling pathway and the expression of GATA6 is sufficient to compensate for the defects caused by Grb2 deficiency in the development of the primitive and extraembryonic endoderm.

The mammalian class 3 PI3K (PIK3C3) is required for early embryogenesis and cell proliferation

The Pik3c3 gene encodes an 887 amino acid lipid kinase, phosphoinositide-3-kinase class 3 (PIK3C3). PIK3C3 is known to regulate various intracellular membrane trafficking events. However, little is known about its functions during early embryogenesis in mammals. To investigate the function of PIK3C3 in vivo, we generated Pik3c3 null mice. We show here that Pik3c3 heterozygous are normal and fertile. In contrast, Pik3c3 homozygous mutants are embryonic lethal and die between E7.5 and E8.5 of embryogenesis. Mutant embryos are poorly developed with no evidence of mesoderm formation, and suffer from severely reduced cell proliferations. Cell proliferation defect is also evident in vitro, where mutant blastocysts in culture fail to give rise to typical colonies formed by inner cell mass. Electron microscopic analysis revealed that epiblast cells in mutant embryos appear normal, whereas the visceral endoderm cells contain larger vesicles inside the lipid droplets. Finally, we provide evidence that mTOR signaling is drastically reduced in Pik3c3 null embryos, which could be a major contributor to the observed proliferation and embryogenesis defects.

Expression of Transcription Factor GATA-6 in Alveolar Epithelial Cells Is Linked to Neonatal Lung Disease

BACKGROUND

Premature birth and respiratory distress syndrome (RDS) are risk factors for disturbed lung development and bronchopulmonary dysplasia (BPD). The molecular mechanisms related to prematurity and BPD remain largely unknown. Epithelial expression of the transcription factor GATA-6 has been implicated in normal and abnormal murine lung development.

OBJECTIVES

The possible involvement of GATA-6 in the normal development and in RDS and BPD was investigated in the human and baboon lung.

METHODS

Immunohistochemistry was used to study the expression of GATA-6 and thyroid transcription factor 1 in lung specimens from different age groups of human and baboon fetuses and newborns with lung disease. Furthermore, the regulatory role of TGF-β₁ in GATA-6 expression was investigated in human pulmonary epithelial cell lines using RT-PCR.

RESULTS

GATA-6 expression increased in the developing human airway epithelium along with advancing gestation, but diminished to negligible at birth. In RDS, GATA-6 expression was enhanced at 5-7 days after birth, and decreased thereafter. In BPD, the expression of GATA-6 in alveolar epithelial cells was low. These results were confirmed and extended using an established baboon model of prematurity. The in vitro experiments revealed that TGF-β₁ induces GATA-6 and thyroid transcription factor 1 expression in lung epithelial cells.

CONCLUSIONS

Our results suggest that the expression of GATA-6 at the early stages of the preterm lung may be related to impaired postnatal alveolar development.

Beta-catenin signaling in hepatic development and progenitors: which way does the WNT blow?

The Wnt/β-catenin pathway is an evolutionarily conserved signaling cascade that plays key roles in development and adult tissue homeostasis and is aberrantly activated in many tumors. Over a decade of work in mouse, chick, xenopus, and zebrafish models has uncovered multiple functions of this pathway in hepatic pathophysiology. Specifically, beta-catenin, the central component of the canonical Wnt pathway, is implicated in the regulation of liver regeneration, development, and carcinogenesis. Wnt-independent activation of beta-catenin by receptor tyrosine kinases has also been observed in the liver. In liver development across various species, through regulation of cell proliferation, differentiation, and maturation, beta-catenin directs foregut endoderm specification, hepatic specification of the foregut, and hepatic morphogenesis. Its role has also been defined in adult hepatic progenitors or oval cells especially in their expansion and differentiation. Thus, beta-catenin undergoes tight temporal regulation to exhibit pleiotropic effects during hepatic development and in hepatic progenitor biology.

Hyaluronan esters drive Smad gene expression and signaling enhancing cardiogenesis in mouse embryonic and human mesenchymal stem cells

Background

Development of molecules chemically modifying the expression of crucial orchestrator(s) of stem cell commitment may have significant biomedical impact. We have recently developed hyaluronan mixed esters of butyric and retinoic acids (HBR), turning cardiovascular stem cell fate into a high-yield process. The HBR mechanism(s) remain still largely undefined.

Methodology/Principal Findings

We show that in both mouse embryonic stem (ES) cells and human mesenchymal stem cells from fetal membranes of term placenta (FMhMSCs), HBR differentially affected the patterning of Smad proteins, one of the major conductors of stem cell cardiogenesis. Real-time RT-PCR and Western blot analyses revealed that in both cell types HBR enhanced gene and protein expression of Smad1,3, and 4, while down-regulating Smad7. HBR acted at the transcriptional level, as shown by nuclear run-off experiments in isolated nuclei. Immunofluorescence analysis indicated that HBR increased the fluorescent staining for Smad1,3, and 4, confirming that the transcriptional action of HBR encompassed the upregulation of the encoded Smad proteins. Chromatin immune precipitation and transcriptional analyses showed that HBR increased the transcription of the cardiogenic gene Nkx-2.5 through Smad4 binding to its own consensus Smad site. Treatment of mouse ES cells and FMhMSCs with HBR led to the concomitant overexpression of both Smad4 and α-sarcomeric actinin. Smad4 silencing by the aid of lentiviral-mediated Smad4 shRNA confirmed a dominant role of Smad4 in HBR-induced cardiogenesis.

Conclusions/Significance

The use of HBR may pave the way to novel combinatorial strategies of molecular and stem cell therapy based on fine tuning of targeted Smad transciption and signaling leading to a high-throughput of cardiogenesis without the needs of gene transfer technologies.

Hopx and Hdac2 interact to modulate Gata4 acetylation and embryonic cardiac myocyte proliferation

Regulation of chromatin structure via histone modification has recently received intense attention. Here, we demonstrate that the chromatin-modifying enzyme histone deacetylase 2 (Hdac2) functions with a small homeodomain factor, Hopx, to mediate deacetylation of Gata4, which is expressed by cardiac progenitor cells and plays critical roles in the regulation of cardiogenesis. In the absence of Hopx and Hdac2 in mouse embryos, Gata4 hyperacetylation is associated with a marked increase in cardiac myocyte proliferation, upregulation of Gata4 target genes, and perinatal lethality. Hdac2 physically interacts with Gata4, and this interaction is stabilized by Hopx. The ability of Gata4 to transactivate cell cycle genes is impaired by Hopx/Hdac2-mediated deacetylation, and this effect is abrogated by loss of Hdac2-Gata4 interaction. These results suggest that Gata4 is a nonhistone target of Hdac2-mediated deacetylation and that Hdac2, Hopx, and Gata4 coordinately regulate cardiac myocyte proliferation during embryonic development.

Direct transcriptional regulation of Gata4 during early endoderm specification is controlled by FoxA2 binding to an intronic enhancer

The embryonic endoderm is a multipotent progenitor cell population that gives rise to the epithelia of the digestive and respiratory tracts, the liver and the pancreas. Among the transcription factors that have been shown to be important for endoderm development and gut morphogenesis is GATA4. Despite the important role of GATA4 in endoderm development, its transcriptional regulation is not well understood. In this study, we identified an intronic enhancer from the mouse Gata4 gene that directs expression to the definitive endoderm in the early embryo. The activity of this enhancer is initially broad in all endodermal progenitors, as demonstrated by fate mapping analysis using the Cre/loxP system, but becomes restricted to the dorsal foregut and midgut, and associated organs such as dorsal pancreas and stomach. The function of the intronic Gata4 enhancer is dependent upon a conserved Forkhead transcription factor-binding site, which is bound by recombinant FoxA2 in vitro. These studies identify Gata4 as a direct transcriptional target of FoxA2 in the hierarchy of the transcriptional regulatory network that controls the development of the definitive endoderm.

Alteration of Differentiation Potentials by Modulating GATA Transcription Factors in Murine Embryonic Stem Cells

Background. Mouse embryonic stem (ES) cells can be differentiated in vitro by aggregation and/or retinoic acid (RA) treatment. The principal differentiation lineage in vitro is extraembryonic primitive endoderm. Dab2, Laminin, GATA4, GATA5, and GATA6 are expressed in embryonic primitive endoderm and play critical roles in its lineage commitment. Results. We found that in the absence of GATA4 or GATA5, RA-induced primitive endoderm differentiation of ES cells was reduced. GATA4 (-/-) ES cells express higher level of GATA5, GATA6, and hepatocyte nuclear factor 4 alpha marker of visceral endoderm lineage. GATA5 (-/-) ES cells express higher level of alpha fetoprotein marker of early liver development. GATA6 (-/-) ES cells express higher level of GATA5 as well as mesoderm and cardiomyocyte markers which are collagen III alpha-1 and tropomyosin1 alpha. Thus, deletion of GATA6 precluded endoderm differentiation but promoted mesoderm lineages. Conclusions. GATA4, GATA5, and GATA6 each convey a unique gene expression pattern and influences ES cell differentiation. We showed that ES cells can be directed to avoid differentiating into primitive endoderm and to adopt unique lineages in vitro by modulating GATA factors. The finding offers a potential approach to produce desirable cell types from ES cells, useful for regenerative cell therapy.

Retinoic acid regulates differentiation of the secondary heart field and TGFbeta-mediated outflow tract septation

In many experimental models and clinical examples, defects in the differentiation of the second heart field (SHF) and heart outflow tract septation defects are combined, although the mechanistic basis for this relationship has been unclear. We found that as the initial SHF population incorporates into the outflow tract, it is replenished from the surrounding progenitor territory. In retinoic acid (RA) receptor mutant mice, this latter process fails, and the outflow tract is shortened and misaligned as a result. As an additional consequence, the outflow tract is misspecified along its proximal-distal axis, which results in ectopic expression of TGFbeta2 and ectopic mesenchymal transformation of the endocardium. Reduction of TGFbeta2 gene dosage in the RA receptor-deficient background restores septation but does not rescue alignment defects, indicating that excess TGFbeta causes septation defects. This may be a common pathogenic pathway when second heart field and septation defects are coupled.

An endoderm-specific transcriptional enhancer from the mouse Gata4 gene requires GATA and homeodomain protein-binding sites for function in vivo

Several transcription factors function in the specification and differentiation of the endoderm, including the zinc finger transcription factor GATA4. Despite its essential role in endoderm development, the transcriptional control of the Gata4 gene in the developing endoderm and its derivatives remains incompletely understood. Here, we identify a distal enhancer from the Gata4 gene, which directs expression exclusively to the visceral and definitive endoderm of transgenic mouse embryos. The activity of this enhancer is initially broad within the definitive endoderm but later restricts to developing endoderm-derived tissues, including pancreas, glandular stomach, and duodenum. The activity of this enhancer in vivo is dependent on evolutionarily-conserved HOX- and GATA-binding sites, which are bound by PDX-1 and GATA4, respectively. These studies establish Gata4 as a direct transcriptional target of homeodomain and GATA transcription factors in the endoderm and support a model in which GATA4 functions in the transcriptional network for pancreas formation.

Conserved usage of alternative 5' untranslated exons of the GATA4 gene

BACKGROUND

GATA4 is an essential transcription factor required for the development and function of multiple organs. Despite this important role, our knowledge of how the GATA4 gene is regulated remains limited. To better understand this regulation, we characterized the 5' region of the mouse, rat, and human GATA4 genes.

METHODOLOGY/PRINCIPAL FINDINGS

Using 5' RACE, we identified novel transcription start sites in all three species. GATA4 is expressed as multiple transcripts with varying 5' ends encoded by alternative untranslated first exons. Two of these non-coding first exons are conserved between species: exon 1a located 3.5 kb upstream of the GATA4 ATG site in exon 2, and a second first exon (exon 1b) located 28 kb further upstream. Expression of both mRNA variants was found in all GATA4-expressing organs but with a preference for the exon 1a-containing transcript. The exception was the testis where exon 1a- and 1b-containing transcripts were similarly expressed. In some tissues such as the intestine, alternative transcript expression appears to be regionally regulated. Polysome analysis suggests that both mRNA variants contribute to GATA4 protein synthesis.

CONCLUSIONS/SIGNIFICANCE

Taken together, our results indicate that the GATA4 gene closely resembles the other GATA family members in terms of gene structure where alternative first exon usage appears to be an important mechanism for regulating its tissue- and cell-specific expression.

Gata4 and Gata5 cooperatively regulate cardiac myocyte proliferation in mice

GATA5 is a member of the zinc finger transcription factor GATA family (GATA1-6) that plays a wide variety of roles in embryonic and adult development. Experiments in multiple model systems have emphasized the importance of the GATA family members 4-6 in the development of the endoderm and mesoderm. Yet despite overlapping expression patterns, there is little evidence of an important role for GATA5 in mammalian cardiac development. We have generated a new Gata5 mutant allele lacking exons 2 and 3 that encodes both zinc finger domains (Gata5(tm)(2)(Eem)), and we show that although Gata5(-/-) mice are viable, Gata4(+/-)5(-/-) mutants die at mid-gestation and exhibit profound cardiovascular defects, including abnormalities of cardiomyocyte proliferation and cardiac chamber maturation. These results demonstrate functional redundancy between Gata4 and Gata5 during cardiac development and implicate Gata5 as a candidate modifier gene for congenital heart disease.

VEGF and IHH rescue definitive hematopoiesis in Gata-4 and Gata-6-deficient murine embryoid bodies

OBJECTIVE

Murine embryonic stem cells can be differentiated into embryoid bodies (EBs), which serve as an in vitro model recapitulating many aspects of embryonic yolk sac hematopoiesis. Differentiation of embryonic stem cells deficient in either Gata-4 or Gata-6 results in EBs with disrupted visceral endoderm (VE). While lack of VE has detrimental effects on hematopoiesis in vivo, it is unclear whether lack of VE affects hematopoiesis in EBs. Therefore, we compared Gata-4 null (G4N) and Gata-6 null (G6N) EBs with wild-type EBs to assess their ability to commit to hematopoietic cells.

MATERIALS AND METHODS

EB VE formation was examined using cell-sorting techniques and analysis visceral endoderm gene expression. Hematopoietic progenitor potential of EBs cultured under various conditions was assessed using colony-forming assays.

RESULTS

Definitive erythroid, granulocyte-macrophage, and mixed colonies were significantly reduced in G4N and G6N EBs compared to wild-type EBs. Vascular endothelial growth factor (VEGF) expression and secretion were also reduced in both G4N and G6N EBs, consistent with VE serving as a site of VEGF production. Addition of exogenous VEGF(165), to EB cultures completely rescued definitive colony-forming cells in G4N and G6N EBs. This rescue response could be blocked by addition of soluble Flk-1 Fc to EB cultures. Similarly, addition of exogenous Indian hedgehog to EB cultures also recovers the diminishment in definitive hematopoiesis in a reversible manner.

CONCLUSION

These results suggest that the absence of VE in G4N and G6N EBs does not prevent emergence of definitive progenitors from EBs. However, the decreased level of VEGF and Indian hedgehog production in VE devoid G4N and G6N EBs attenuates definitive hematopoietic progenitor cell expansion.

Retinoic acid receptors and GATA transcription factors activate the transcription of the human lecithin:retinol acyltransferase gene

Lecithin:retinol acyltransferase (LRAT) catalyzes the esterification of retinol (vitamin A). Retinyl esters and LRAT protein levels are reduced in many types of cancer cells. We present data that both the LRAT and retinoic acid receptor beta(2) (RARbeta(2)) mRNA levels in the human prostate cancer cell line PC-3 are lower than those in cultured normal human prostate epithelial cells (PrEC). The activity of the human LRAT promoter (2.0 kb) driving a luciferase reporter gene in PC-3 cells is less than 40% of that in PrEC cells. Retinoic acid (RA) treatment increased this LRAT promoter-luciferase activity in PrEC cells, but not in PC-3 cells. Deletion of various regions of the human LRAT promoter demonstrated that a 172-bp proximal promoter region is essential for LRAT transcription and confers RA responsiveness in PrEC cells. This 172-bp region, contained within the 186 bp pLRAT/luciferase construct, has five putative GATA binding sites. Cotransfection of RARbeta(2) or RARgamma and the transcription factor GATA-4 increased LRAT (pLRAT186) promoter activity in both PrEC and PC-3 cells. In addition, we found that both retinoic acid and retinol induced transcripts for the STRA6 gene, which encodes a membrane receptor involved in retinol (vitamin A) uptake, in PrEC cells but not in PC-3 cells. In summary, our data show that the transcriptional regulation of the human LRAT gene is aberrant in human prostate cancer cells and that GATA transcription factors are involved in the transcriptional activation of LRAT in PrEC cells.

Dynamic GATA6 expression in primitive endoderm formation and maturation in early mouse embryogenesis

The derivation of the primitive endoderm layer from the pluripotent cells of the inner cell mass is one of the earliest differentiation and morphogenic events in embryonic development. GATA4 and GATA6 are the key transcription factors in the formation of extraembryonic endoderms, but their specific contribution to the derivation of each endoderm lineage needs clarification. We further analyzed the dynamic expression and mutant phenotypes of GATA6 in early mouse embryos. GATA6 and GATA4 are both expressed in primitive endoderm cells initially. At embryonic day (E) 5.0, parietal endoderm cells continue to express both GATA4 and GATA6; however, visceral endoderm cells express GATA4 but exhibit a reduced expression of GATA6. By and after E5.5, visceral endoderm cells no longer express GATA6. We also found that GATA6 null embryos did not form a morphologically recognizable primitive endoderm layer, and subsequently failed to form visceral and parietal endoderms. Thus, the current study establishes that GATA6 is essential for the formation of primitive endoderm, at a much earlier stage then previously recognized, and expression of GATA6 discriminates parietal endoderm from visceral endoderm lineages.

Cardiogenic differentiation and transdifferentiation of progenitor cells

In recent years, cell transplantation has drawn tremendous interest as a novel approach to preserving or even restoring contractile function to infarcted hearts. A typical human infarct involves the loss of approximately 1 billion cardiomyocytes, and, therefore, many investigators have sought to identify endogenous or exogenous stem cells with the capacity to differentiate into committed cardiomyocytes and repopulate lost myocardium. As a result of these efforts, dozens of stem cell types have been reported to have cardiac potential. These include pluripotent embryonic stem cells, as well various adult stem cells resident in compartments including bone marrow, peripheral tissues, and the heart itself. Some of these cardiogenic progenitors have been reported to contribute replacement muscle through endogenous reparative processes or via cell transplantation in preclinical cardiac injury models. However, considerable disagreement exists regarding the efficiency and even the reality of cardiac differentiation by many of these stem cell types, making these issues a continuing source of controversy in the field. In this review, we consider approaches to cell fate mapping and establishing the cardiac phenotype, as well as the present state of the evidence for the cardiogenic and regenerative potential of the major candidate stem cell types.

Myocardin marks the earliest cardiac gene expression and plays an important role in heart development

Myocardin belongs to the SAP domain family of transcription factors and is expressed specifically in cardiac and smooth muscle during embryogenesis and in adulthood. Myocardin functions as a transcriptional coactivator of SRF and is sufficient and necessary for smooth muscle gene expression. However, the in vivo function of myocardin during cardiogenesis is not completely understood. Here we clone myocardin from chick embryonic hearts and show that myocardin protein sequences are highly conserved cross species. Detailed studies of chick myocardin expression reveal that myocardin is expressed in cardiac and smooth muscle lineage during early embryogenesis, similar to that found in mouse. Interestingly, the expression of myocardin in the heart was found enriched in the outflow tract and the sinoatrial segments shortly after the formation of linear heart tube. Such expression pattern is also maintained in later developing embryos, suggesting that myocardin may play a unique role in the formation of those cardiac modules. Similar to its mouse counterpart, chick myocardin is able to activate cardiac and smooth muscle promoter reporter genes and induce smooth muscle gene expression in nonmuscle cells. Ectopic overexpression of myocardin enlarged the embryonic chick heart. Conversely, repression of the endogenous chick myocardin using antisense oligonucleotides or a dominant negative mutant form of myocardin inhibited cardiogenesis. Together, our data place myocardin as one of the earliest cardiac marker genes for cardiogenesis and support the idea that myocardin plays an essential role in cardiac gene expression and cardiogenesis.

AMP-activated protein kinase-regulated activation of the PGC-1alpha promoter in skeletal muscle cells

The mechanisms by which PGC-1α gene expression is controlled in skeletal muscle remains largely undefined. Thus, we sought to investigate the transcriptional regulation of PGC-1α using AICAR, an activator of AMPK, that is known to increase PGC-1α expression. A 2.2 kb fragment of the human PGC-1α promoter was cloned and sequence analysis revealed that this TATA-less sequence houses putative consensus sites including a GC-box, a CRE, several IRSs, a SRE, binding sites for GATA, MEF2, p 53, NF-κB, and EBox binding proteins. AMPK activation for 24 hours increased PGC-1α promoter activity with concomitant increases in mRNA expression. The effect of AICAR on transcriptional activation was mediated by an overlapping GATA/EBox binding site at −495 within the PGC-1α promoter based on gel shift analyses that revealed increases in GATA/EBox DNA binding. Mutation of the EBox within the GATA/EBox binding site in the promoter reduced basal promoter activity and completely abolished the AICAR effect. Supershift analyses identified USF-1 as a DNA binding transcription factor potentially involved in regulating PGC-1α promoter activity, which was confirmed in vivo by ChIP. Overexpression of either GATA-4 or USF-1 alone increased the p851 PGC-1α promoter activity by 1.7- and 2.0-fold respectively, while co-expression of GATA-4 and USF-1 led to an additive increase in PGC-1α promoter activity. The USF-1-mediated increase in PGC-1α promoter activation led to similar increases at the mRNA level. Our data identify a novel AMPK-mediated regulatory pathway that regulates PGC-1α gene expression. This could represent a potential therapeutic target to control PGC-1α expression in skeletal muscle.

Reassessment of Isl1 and Nkx2-5 cardiac fate maps using a Gata4-based reporter of Cre activity

Isl1 and Nkx2-5-expressing cardiovascular progenitors play pivotal roles in cardiogenesis. Previously reported Cre-based fate-mapping studies showed that Isl1 progenitors contribute predominantly to the derivatives of the second heart field, and Nkx2-5 progenitors contributed mainly to the cardiomyocyte lineage. However, partial recombination of Cre reporter genes can complicate interpretation of Cre fate-mapping experiments. We found that a Gata4-based Cre-activated reporter was recombined by Isl1(Cre) and Nkx2-5(Cre) in a substantially broader domain than previously reported using standard Cre-activated reporters. The expanded Isl1 and Nkx2-5 cardiac fate maps were remarkably similar, and included extensive contributions to cardiomyocyte, endocardial, and smooth muscle lineages in all four cardiac chambers. These data indicate that Isl1 is expressed in progenitors of both primary and secondary heart fields, and that Nkx2-5 is expressed in progenitors of cardiac endothelium and smooth muscle, in addition to cardiomyocytes. These results have important implications for our understanding of cardiac lineage diversification in vivo, and for the interpretation of Cre-based fate maps.

GATA4 is a direct transcriptional activator of cyclin D2 and Cdk4 and is required for cardiomyocyte proliferation in anterior heart field-derived myocardium

The anterior heart field (AHF) comprises a population of mesodermal progenitor cells that are added to the nascent linear heart to give rise to the majority of the right ventricle, interventricular septum, and outflow tract in mammals and birds. The zinc finger transcription factor GATA4 functions as an integral member of the cardiac transcription factor network in the derivatives of the AHF. In addition to its role in cardiac differentiation, GATA4 is also required for cardiomyocyte replication, although the transcriptional targets of GATA4 required for proliferation have not been previously identified. In the present study, we disrupted Gata4 function exclusively in the AHF and its derivatives. Gata4 AHF knockout mice die by embryonic day 13.5 and exhibit hypoplasia of the right ventricular myocardium and interventricular septum and display profound ventricular septal defects. Loss of Gata4 function in the AHF results in decreased myocyte proliferation in the right ventricle, and we identified numerous cell cycle genes that are dependent on Gata4 by microarray analysis. We show that GATA4 is required for cyclin D2, cyclin A2, and Cdk4 expression in the right ventricle and that the Cyclin D2 and Cdk4 promoters are bound and activated by GATA4 via multiple consensus GATA binding sites in each gene's proximal promoter. These findings establish Cyclin D2 and Cdk4 as direct transcriptional targets of GATA4 and support a model in which GATA4 controls cardiomyocyte proliferation by coordinately regulating numerous cell cycle genes.

Isolation, characterization and genetic analysis of canine GATA4 gene in a family of Doberman Pinschers with an atrial septal defect

GATA4 is expressed early in the developing heart where it plays a key role in regulating the expression of genes encoding myocardial contractile proteins. Gene mutations in the human GATA4 have been implicated in various congenital heart defects (CHD), including atrial septal defect (ASD). Although ASD is the third most common CHD in humans, it is generally rare in dogs and cats. There is also no obvious predilection for ASD in dogs and cats, based on sex or breed. However, among dogs, the incidence rate of ASD is relatively high in Samoyeds and Doberman Pinschers, where its inheritance and genetic aetiology are not well understood. In this study, we identified and investigated the genetic aetiology of an ASD affected family in a pure breed dog population. Although the GATA4 gene was screened, we did not find any mutations that would result in the alteration of the coding sequence and hence, the predicted GATA4 structure and function. Although the aetiology of ASD is multifactorial, our findings indicate that GATA4 may not be responsible for the ASD in the dogs used in this study. However, this does not eliminate GATA4 as a candidate for ASD in other dog breeds.

Rex1/Zfp42 is dispensable for pluripotency in mouse ES cells

Background

Rex1/Zfp42 has been extensively used as a marker for the undifferentiated state of pluripotent stem cells. However, its function in pluripotent stem cells including embryonic stem (ES) cells remained unclear although its involvement in visceral endoderm differentiation in F9 embryonal carcinoma (EC) cells was reported.

Results

We showed the function of Rex1 in mouse ES cells as well as in embryos using the conventional gene targeting strategy. Our results clearly indicated that Rex1 function is dispensable for both the maintenance of pluripotency in ES cells and the development of embryos. However, Rex1-/- ES cells showed the defect to induce a subset of the marker genes of visceral endoderm, when differentiated as embryoid body, as found in EC cells.

Conclusion

Rex1 should be regarded just as a marker of pluripotency without functional significance like the activity of alkaline phosphatase.

Hepatocyte nuclear factor 4alpha contributes to thyroid hormone homeostasis by cooperatively regulating the type 1 iodothyronine deiodinase gene with GATA4 and Kruppel-like transcription factor 9

Type 1 iodothyronine deiodinase (Dio1), a selenoenzyme catalyzing the bioactivation of thyroid hormone, is highly expressed in the liver. Dio1 mRNA and enzyme activity levels are markedly reduced in the livers of hepatocyte nuclear factor 4alpha (HNF4alpha)-null mice, thus accounting for its liver-specific expression. Consistent with this deficiency, serum T4 and rT3 concentrations are elevated in these mice compared with those in HNF4alpha-floxed control littermates; however, serum T3 levels are unchanged. Promoter analysis of the mouse Dio1 gene demonstrated that HNF4alpha plays a key role in the transactivation of the mouse Dio1 gene. Deletion and substitution mutation analyses demonstrated that a proximal HNF4alpha site (direct repeat 1 [TGGACAAAGGTGC]; HNF4alpha-RE) is crucial for transactivation of the mouse Dio1 gene by HNF4alpha. Mouse Dio1 is also stimulated by thyroid hormone signaling, but a direct role for thyroid hormone receptor action has not been reported. We also showed that thyroid hormone-inducible Krüppel-like factor 9 (KLF9) stimulates the mouse Dio1 promoter very efficiently through two CACCC sequences that are located on either side of HNF4alpha-RE. Furthermore, KLF9 functions together with HNF4alpha and GATA4 to synergistically activate the mouse Dio1 promoter, suggesting that Dio1 is regulated by thyroid hormone in the mouse through an indirect mechanism requiring prior KLF9 induction. In addition, we showed that physical interactions between the C-terminal zinc finger domain (Cf) of GATA4 and activation function 2 of HNF4alpha and between the basic domain adjacent to Cf of GATA4 and a C-terminal domain of KLF9 are both required for this synergistic response. Taken together, these results suggest that HNF4alpha regulates thyroid hormone homeostasis through transcriptional regulation of the mouse Dio1 gene with GATA4 and KLF9.

Maternal cocaine administration in mice alters DNA methylation and gene expression in hippocampal neurons of neonatal and prepubertal offspring

Previous studies documented significant behavioral changes in the offspring of cocaine-exposed mothers. We now explore the hypothesis that maternal cocaine exposure could alter the fetal epigenetic machinery sufficiently to cause lasting neurochemical and functional changes in the offspring. Pregnant CD1 mice were administered either saline or 20 mg/kg cocaine twice daily on gestational days 8–19. Male pups from each of ten litters of the cocaine and control groups were analyzed at 3 (P3) or 30 (P30) days postnatum. Global DNA methylation, methylated DNA immunoprecipitation followed by CGI² microarray profiling and bisulfite sequencing, as well as quantitative real-time RT-PCR gene expression analysis, were evaluated in hippocampal pyramidal neurons excised by laser capture microdissection. Following maternal cocaine exposure, global DNA methylation was significantly decreased at P3 and increased at P30. Among the 492 CGIs whose methylation was significantly altered by cocaine at P3, 34% were hypermethylated while 66% were hypomethylated. Several of these CGIs contained promoter regions for genes implicated in crucial cellular functions. Endogenous expression of selected genes linked to the abnormally methylated CGIs was correspondingly decreased or increased by as much as 4–19-fold. By P30, some of the cocaine-associated effects at P3 endured, reversed to opposite directions, or disappeared. Further, additional sets of abnormally methylated targets emerged at P30 that were not observed at P3. Taken together, these observations indicate that maternal cocaine exposure during the second and third trimesters of gestation could produce potentially profound structural and functional modifications in the epigenomic programs of neonatal and prepubertal mice.

GATA factors and androgen receptor collaborate to transcriptionally activate the Rhox5 homeobox gene in Sertoli cells

How Sertoli-specific expression is initiated is poorly understood. Here, we address this issue using the proximal promoter (Pp) from the Rhox5 homeobox gene. Its Sertoli cell-specific expression is achieved, in part, through a negative regulatory element that inhibits Pp transcription in non-Sertoli cell lines. Complementing this negative regulation is positive regulation conferred by four androgen-response elements (AREs) that interact with the androgen receptor (AR), a nuclear hormone receptor expressed at high levels in Sertoli cells. A third control mechanism is provided by a consensus GATA-binding site that is crucial for Pp transcription both in vitro and in vivo. Several lines of evidence suggested that GATA factors and AR act cooperatively to activate Pp transcription: (i) the GATA-binding site crucial for Pp transcription is in close proximity to two of the AREs, (ii) GATA and AR form a complex with the Pp in vitro, (iii) overexpression of GATA factors rescued expression from mutant Pp constructs harboring defective AREs, and (iv) incubation of a Sertoli cell line with testosterone triggered corecruitment of AR and GATA4 to the Pp. Collectively, our results suggest that the Rhox5 gene achieves Sertoli cell-specific transcription using a combinatorial strategy involving negative and cooperative positive regulation.

Extra-embryonic endoderm cells derived from ES cells induced by GATA factors acquire the character of XEN cells

Background

Three types of cell lines have been established from mouse blastocysts: embryonic stem (ES) cells, trophoblast stem (TS) cells, and extra-embryonic endoderm (XEN) cells, which have the potential to differentiate into their respective cognate lineages. ES cells can differentiate in vitro not only into somatic cell lineages but into extra-embryonic lineages, including trophectoderm and extra-embryonic endoderm (ExEn) as well. TS cells can be established from ES cells by the artificial repression of Oct3/4 or the upregulation of Cdx2 in the presence of FGF4 on feeder cells. The relationship between these embryo-derived XEN cells and ES cell-derived ExEn cell lines remains unclear, although we have previously reported that overexpression of Gata4 or Gata6 induces differentiation of mouse ES cells into extra-embryonic endoderm in vitro.

Results

A system in which GATA factors were conditionally activated revealed that the cells continue to proliferate while expressing a set of extra-embryonic endoderm markers, and, following injection into blastocysts, contribute only to the extra-embryonic endoderm lineage in vivo. Although the in vivo contribution is limited to cells of parietal endoderm lineage, Gata-induced extra-embryonic endoderm cells (gExEn) can be induced to differentiate into visceral endoderm-like cells in vitro by repression of Gata6. During early passage, the propagation of gExEn cells is dependent on the expression of the Gata6 transgene. These cells, however, lose this dependency following establishment of endogenous Gata6 expression.

Conclusion

We show here that Gata-induced extra-embryonic endoderm cells derived from ES cells mimic the character of XEN cells. These findings indicate that Gata transcription factors are sufficient for the derivation and propagation of XEN-like extra-embryonic endoderm cells from ES cells.

Genetic factors in congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a relatively common birth defect associated with high mortality and morbidity. Although the exact etiology of most cases of CDH remains unknown, there is a growing body of evidence that genetic factors play an important role in the development of CDH. In this review, we examine key findings that are likely to form the basis for future research in this field. Specific topics include a short overview of normal and abnormal diaphragm development, a discussion of syndromic forms of CDH, a detailed review of chromosomal regions recurrently altered in CDH, a description of the retinoid hypothesis of CDH, and evidence of the roles of specific genes in the development of CDH.

Cooperative interaction between hepatocyte nuclear factor 4 alpha and GATA transcription factors regulates ATP-binding cassette sterol transporters ABCG5 and ABCG8

Cholesterol homeostasis is maintained by coordinate regulation of cholesterol synthesis and its conversion to bile acids in the liver. The excretion of cholesterol from liver and intestine is regulated by ATP-binding cassette half-transporters ABCG5 and ABCG8. The genes for these two proteins are closely linked and divergently transcribed from a common intergenic promoter region. Here, we identified a binding site for hepatocyte nuclear factor 4alpha (HNF4alpha) in the ABCG5/ABCG8 intergenic promoter, through which HNF4alpha strongly activated the expression of a reporter gene in both directions. The HNF4alpha-responsive element is flanked by two conserved GATA boxes that were also required for stimulation by HNF4alpha. GATA4 and GATA6 bind to the GATA boxes, coexpression of GATA4 and HNF4alpha leads to a striking synergistic activation of both the ABCG5 and the ABCG8 promoters, and binding sites for HNF4alpha and GATA were essential for maximal synergism. We also show that HNF4alpha, GATA4, and GATA6 colocalize in the nuclei of HepG2 cells and that a physical interaction between HNF4alpha and GATA4 is critical for the synergistic response. This is the first demonstration that HNF4alpha acts synergistically with GATA factors to activate gene expression in a bidirectional fashion.

Impaired mesenchymal cell function in Gata4 mutant mice leads to diaphragmatic hernias and primary lung defects

Congenital diaphragmatic hernia (CDH) is an often fatal birth defect that is commonly associated with pulmonary hypoplasia and cardiac malformations. Some investigators hypothesize that this constellation of defects results from genetic or environmental triggers that disrupt mesenchymal cell function in not only the primordial diaphragm but also the thoracic organs. The alternative hypothesis is that the displacement of the abdominal viscera in the chest secondarily perturbs the development of the heart and lungs. Recently, loss-of-function mutations in the gene encoding FOG-2, a transcriptional co-regulator, have been linked to CDH and pulmonary hypoplasia in humans and mice. Here we show that mutagenesis of the gene for GATA-4, a transcription factor known to functionally interact with FOG-2, predisposes inbred mice to a similar set of birth defects. Analysis of wild-type mouse embryos demonstrated co-expression of Gata4 and Fog2 in mesenchymal cells of the developing diaphragm, lungs, and heart. A significant fraction of C57Bl/6 mice heterozygous for a Gata4 deletion mutation died within 1 day of birth. Developmental defects in the heterozygotes included midline diaphragmatic hernias, dilated distal airways, and cardiac malformations. Heterozygotes had any combination of these defects or none. In chimeric mice, Gata4(-/-) cells retained the capacity to contribute to cells in the diaphragmatic central tendon and lung mesenchyme, indicating that GATA-4 is not required for differentiation of these lineages. We conclude that GATA-4, like its co-regulator FOG-2, is required for proper mesenchymal cell function in the developing diaphragm, lungs, and heart.

Gata6 is an important regulator of mouse pancreas development

Gata4, Gata5, and Gata6 represent a subfamily of zinc-finger transcriptional regulators that are important in the development and differentiation of numerous tissues, including many endodermally-derived organs. We demonstrate that Gata4 and Gata6 have overlapping expression patterns in the early pancreatic epithelium. Later, Gata4 becomes restricted to exocrine tissue and Gata6 becomes restricted to a subset of endocrine cells. In addition, we show Gata6, but not Gata4, physically interacts with Nkx2.2, an essential islet transcription factor. To begin determining the roles that Gata4 and Gata6 play during pancreatic development, we expressed Gata4-Engrailed and Gata6-Engrailed dominant repressor fusion proteins in the pancreatic epithelium and in the islet. At e17.5, transgenic Gata6-Engrailed embryos exhibit two distinct phenotypes: a complete absence of pancreas or a reduction in pancreatic tissue. In the embryos that do form pancreas, there is a significant reduction of all pancreatic cell types, with the few differentiated endocrine cells clustered within, or in close proximity to, enlarged ductal structures. Conversely, the majority of transgenic Gata4-Engrailed embryos do not have a pancreatic phenotype. This study suggests that Gata6 is an important regulator of pancreas specification.

A neurosphere-derived factor, cystatin C, supports differentiation of ES cells into neural stem cells

Although embryonic stem (ES) cells are capable of unlimited proliferation and pluripotent differentiation, effective preparation of neural stem cells from ES cells are not achieved. Here, we have directly generated under the coculture with dissociated primary neurosphere cells in serum-free medium and the same effect was observed when ES cells were cultured with conditioned medium of primary neurosphere culture (CMPNC). ES-neural stem cells (NSCs) could proliferate for more than seven times and differentiate into neurons, astrocytes, and oligodendrocytes in vitro and in vivo. The responsible molecule in CMPNC was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, which turned out to be cystatin C. Purified cystatin C in place of the CMPNC could generate ES-NSCs efficiently with self-renewal and multidifferentiation potentials. These results reveal the validity of cystatin C for generating NSCs from ES cells.

An improved single-cell cDNA amplification method for efficient high-density oligonucleotide microarray analysis

A systems-level understanding of a small but essential population of cells in development or adulthood (e.g. somatic stem cells) requires accurate quantitative monitoring of genome-wide gene expression, ideally from single cells. We report here a strategy to globally amplify mRNAs from single cells for highly quantitative high-density oligonucleotide microarray analysis that combines a small number of directional PCR cycles with subsequent linear amplification. Using this strategy, both the representation of gene expression profiles and reproducibility between individual experiments are unambiguously improved from the original method, along with high coverage and accuracy. The immediate application of this method to single cells in the undifferentiated inner cell masses of mouse blastocysts at embryonic day (E) 3.5 revealed the presence of two populations of cells, one with primitive endoderm (PE) expression and the other with pluripotent epiblast-like gene expression. The genes expressed differentially between these two populations were well preserved in morphologically differentiated PE and epiblast in the embryos one day later (E4.5), demonstrating that the method successfully detects subtle but essential differences in gene expression at the single-cell level among seemingly homogeneous cell populations. This study provides a strategy to analyze biophysical events in medicine as well as in neural, stem cell and developmental biology, where small numbers of distinctive or diseased cells play critical roles.

Cardiovascular genomics: a current overview of in vivo and in vitro studies

The cardiovascular system is the first system that is developed in the embryo. The cardiovascular development is a complex process involving the coordination, differentiation, and interaction of distinct cell lineages to form the heart and the diverse array of arteries, veins, and capillaries required to supply oxygen and nutrients to all tissues. Embryonic stem cells have been proposed as an interesting model system to investigate molecular and cellular mechanisms involved in mammalian development. The present review is focused on extrinsic soluble factors, intrinsic transcription factors, receptors, signal transduction pathways, and genes regulating the development of cardiovascular system in vivo and in vitro. Special emphasis has been given to cardiovascular genomics including gene expression studies on the cardiovascular system under developmental and pathophysiological conditions.

Assessing self-renewal and differentiation in human embryonic stem cell lines

Like other cell populations, undifferentiated human embryonic stem cells (hESCs) express a characteristic set of proteins and mRNA that is unique to the cells regardless of culture conditions, number of passages, and methods of propagation. We sought to identify a small set of markers that would serve as a reliable indicator of the balance of undifferentiated and differentiated cells in hESC populations. Markers of undifferentiated cells should be rapidly downregulated as the cells differentiate to form embryoid bodies (EBs), whereas markers that are absent or low during the undifferentiated state but that are induced as hESCs differentiate could be used to assess the presence of differentiated cells in the cultures. In this paper, we describe a list of markers that reliably distinguish undifferentiated and differentiated cells. An initial list of approximately 150 genes was generated by scanning published massively parallel signature sequencing, expressed sequence tag scan, and microarray datasets. From this list, a subset of 109 genes was selected that included 55 candidate markers of undifferentiated cells, 46 markers of hESC derivatives, four germ cell markers, and four trophoblast markers. Expression of these candidate marker genes was analyzed in undifferentiated hESCs and differentiating EB populations in four different lines by immunocytochemistry, reverse transcription-polymer-ase chain reaction (RT-PCR), microarray analysis, and quantitative RT-PCR (qPCR). We show that qPCR, with as few as 12 selected genes, can reliably distinguish differentiated cells from undifferentiated hESC populations.

Epithelial lineages of the small intestine have unique patterns of GATA expression

The ability of the GATA family of factors to interact with numerous other factors, co-factors, and repressors suggests that they may play key roles in tissues and cells where they are expressed. Adult mouse small intestine has been shown to express GATA-4, GATA-5, and GATA-6, where they have been implicated in the activation of a number of intestinal genes. Determination of which GATA factor(s) are involved in a specific function in tissues expressing multiple family members has proven difficult. The immunohistochemical analysis presented here demonstrate that within the mouse small intestine GATA-4/-5/-6 are found to be uniquely distributed among the various differentiated lineages of the intestinal epithelium. Among differentiated cells GATA-4 is found only in the villous enterocytes. GATA-5 is absent from enterocytes, but was found in the remaining lineages: goblet, Paneth and enteroendocrine. Additionally, high levels of GATA-6 are found in only one of these differentiated cell types, the enteroendocrine lineage. The observed distribution suggests that the GATA factors may have distinct roles in lineage allocation, lineage maintenance, and/or terminal differentiation events in small intestine.

Characterization of Pisrt1/Foxl2 in Ellobius lutescens and exclusion as sex-determining genes

The rodent Ellobius lutescens is an exceptional mammal which determines male sex constitutively without the SRY gene and, therefore, may serve as an animal model for human 46,XX female-to-male sex reversal. It was suggested that other factors of the network of sex-determining genes determine maleness in these animals. However, some sex-determining genes like SOX9 and SF1 have already been excluded by segregation analysis as primary sex-determining factors in E. lutescens. In this work, we have cloned and characterized two genes of the PIS (polled intersex syndrome) gene interval, which were reported as candidates in female-to-male sex reversal in hornless goats recently. The genes Foxl2 and Pisrt1 from that interval were identified in E. lutescens DNA and mapped to Chromosome 8. We have excluded linkage of Foxl2 and Pisrt1 loci with the sex of the animals. Hence, the involvement of this gene region in sex determination may be specific for goats and is not a general mechanism of XX sex reversal or XX male sex determination.

Derivation of germ-line-competent embryonic stem cell lines from preblastocyst mouse embryos

The first differentiation event of the mammalian embryo is thought to occur during blastulation and results in two populations of cells, the inner cell mass (ICM) and the trophectoderm. Most embryonic stem (ES) cell lines have been derived from the ICM or a further subset of ICM cells known as the epiblast. There appears to be a limited period of embryonic development during which pluripotent ES cells can be adapted from the cells of the blastocyst to culture. A method is presented here that allows ES cell lines to be isolated from preblastocyst mouse embryos. These lines were derived from 129S2/SvHsd mouse morulae and earlier cleavage stages with high efficiency. The lines expressed genes and antigens characteristic of pluripotent ES cells. XY cell lines remained karyotypically stable through extensive passaging and produced germ-line-competent chimeras upon blastocyst injection. These results suggest that true ES cells can be derived from embryos explanted at any stage of preimplantation development in the mouse. This finding raises the interesting question of whether ES cell lines derived from embryos at different stages of preimplantation development possess the same potential.

Silencing of Fshr occurs through a conserved, hypersensitive site in the first intron

Expression of the FSH receptor (Fshr) is restricted to testicular Sertoli cells and ovarian granulosa cells, thereby limiting the direct targets of FSH action to these somatic cells of the gonads. Earlier studies indicate that transcription of Fshr in the gonads requires elements outside the gene's immediate 5' flanking sequence. To help uncover candidate regulatory sequences, comparative genomics and deoxyribonuclease I hypersensitivity mapping were employed. A total of 156 evolutionarily conserved sequences were found, and partial deoxyribonuclease I hypersensitivity mapping across 45 kb of 5' flanking sequence and the first intron identified four hypersensitive sites, DHS1-4. Notably, DHS1 and DHS2 localized to conserved sites in the promoter region and exon 1 and correlated with the active state of the gene. DHS3 also corresponded to a conserved site (site 7) but was more pronounced in nonexpressing myoid cells, suggesting a role in gene silencing. Transient transfection analysis of DHS3 confirmed its role in gene silencing, a function that was promoter, cell type, and position dependent. Protein-DNA binding studies on DHS3 revealed that octamer transcription factor 1 (OCT-1) and GATA-4 bound site 7, in vitro, and transient transfection analysis showed that their binding sites were required for silencing activity. Furthermore, chromatin immunoprecipitation revealed that OCT-1 bound to site 7 in the endogenous gene, but only in myoid cells. In contrast, GATA-1 bound site 7 predominantly in Sertoli cells, suggesting that it attenuates silencer activity. The findings reveal that OCT-1 binds within DHS3 to silence Fshr transcription and implicate members of the GATA family in the modulation of this activity.