Cardiomyocyte differentiation by GATA-4-deficient embryonic stem cells

Towards Understanding the Gene-Specific Roles of GATA Factors in Heart Development: Does GATA4 Lead the Way?

Transcription factors play crucial roles in the regulation of heart induction, formation, growth and morphogenesis. Zinc finger GATA transcription factors are among the critical regulators of these processes. GATA4, 5 and 6 genes are expressed in a partially overlapping manner in developing hearts, and GATA4 and 6 continue their expression in adult cardiac myocytes. Using different experimental models, GATA4, 5 and 6 were shown to work together not only to ensure specification of cardiac cells but also during subsequent heart development. The complex involvement of these related gene family members in those processes is demonstrated through the redundancy among them and crossregulation of each other. Our recent identification at the genome-wide level of genes specifically regulated by each of the three family members and our earlier discovery that gata4 and gata6 function upstream, while gata5 functions downstream of noncanonical Wnt signalling during cardiac differentiation, clearly demonstrate the functional differences among the cardiogenic GATA factors. Such suspected functional differences are worth exploring more widely. It appears that in the past few years, significant advances have indeed been made in providing a deeper understanding of the mechanisms by which each of these molecules function during heart development. In this review, I will therefore discuss current evidence of the role of individual cardiogenic GATA factors in the process of heart development and emphasize the emerging central role of GATA4.

Transcription factor protein interactomes reveal genetic determinants in heart disease

Congenital heart disease (CHD) is present in 1% of live births, yet identification of causal mutations remains challenging. We hypothesized that genetic determinants for CHDs may lie in the protein interactomes of transcription factors whose mutations cause CHDs. Defining the interactomes of two transcription factors haplo-insufficient in CHD, GATA4 and TBX5, within human cardiac progenitors, and integrating the results with nearly 9,000 exomes from proband-parent trios revealed an enrichment of de novo missense variants associated with CHD within the interactomes. Scoring variants of interactome members based on residue, gene, and proband features identified likely CHD-causing genes, including the epigenetic reader GLYR1. GLYR1 and GATA4 widely co-occupied and co-activated cardiac developmental genes, and the identified GLYR1 missense variant disrupted interaction with GATA4, impairing in vitro and in vivo function in mice. This integrative proteomic and genetic approach provides a framework for prioritizing and interrogating genetic variants in heart disease.

Electrically conductive nanomaterials for cardiac tissue engineering

Patient deaths resulting from cardiovascular diseases are increasing across the globe, posing the greatest risk to patients in developed countries. Myocardial infarction, as a result of inadequate blood flow to the myocardium, results in irreversible loss of cardiomyocytes which can lead to heart failure. A sequela of myocardial infarction is scar formation that can alter the normal myocardial architecture and result in arrhythmias. Over the past decade, a myriad of tissue engineering approaches has been developed to fabricate engineered scaffolds for repairing cardiac tissue. This paper highlights the recent application of electrically conductive nanomaterials (carbon and gold-based nanomaterials, and electroactive polymers) to the development of scaffolds for cardiac tissue engineering. Moreover, this work summarizes the effects of these nanomaterials on cardiac cell behavior such as proliferation and migration, as well as cardiomyogenic differentiation in stem cells.

GLI1+ progenitor cells in the adrenal capsule of the adult mouse give rise to heterotopic gonadal-like tissue

As certain strains of mice age, hyperplastic lesions resembling gonadal tissue accumulate beneath the adrenal capsule. Gonadectomy (GDX) accelerates this heterotopic differentiation, resulting in the formation of wedge-shaped adrenocortical neoplasms that produce sex steroids. Stem/progenitor cells that reside in the adrenal capsule and retain properties of the adrenogonadal primordium are thought to be the source of this heterotopic tissue. Here, we demonstrate that GLI1⁺ progenitors in the adrenal capsule give rise to gonadal-like cells that accumulate in the subcapsular region. A tamoxifen-inducible Cre driver (Gli1-creER^T2) and two reporters (R26R-lacZ, R26R-confetti) were used to track the fate of GLI1⁺ cells in the adrenal glands of B6D2F2 mice, a strain that develops both GDX-induced adrenocortical neoplasms and age-dependent subcapsular cell hyperplasia. In gonadectomized B6D2F2 mice GLI1⁺ progenitors contributed to long-lived adrenal capsule cells and to adrenocortical neoplasms that expressed Gata4 and Foxl2, two prototypical gonadal markers. Pdgfra, a gene expressed in adrenocortical stromal cells, was upregulated in the GDX-induced neoplasms. In aged non-gonadectomized B6D2F2 mice GLI1⁺ progenitors gave rise to patches of subcapsular cell hyperplasia. Treatment with GANT61, a small-molecule GLI antagonist, attenuated the upregulation of gonadal-like markers (Gata4, Amhr2, Foxl2) in response to GDX. These findings support the premise that GLI1⁺ progenitor cells in the adrenal capsule of the adult mouse give rise to heterotopic tissue.

Protein tyrosine phosphatase 1B (PTP1B) is required for cardiac lineage differentiation of mouse embryonic stem cells

Protein tyrosine phosphatase 1B (PTP1B) has been shown to regulate multiple cellular events such as differentiation, cell growth, and proliferation; however, the role of PTP1B in differentiation of embryonic stem (ES) cells into cardiomyocytes remains unexplored. In the present study, we investigated the effects of PTP1B inhibition on differentiation of ES cells into cardiomyocytes. PTP1B mRNA and protein levels were increased during the differentiation of ES cells into cardiomyocytes. Accordingly, a stable ES cell line expressing PTP1B shRNA was established. In vitro, the number and size of spontaneously beating embryoid bodies were significantly decreased in PTP1B-knockdown cells, compared with the control cells. Decreased expression of cardiac-specific markers Nkx2-5, MHC-α, cTnT, and CX43, as assessed by real-time PCR analysis, was further confirmed by immunocytochemistry of the markers. The results also showed that PTP1B inhibition induced apoptosis in both differentiated and undifferentiated ES cells, as presented by increasing the level of cleaved caspase-3, cytochrome C, and cleaved PARP. Further analyses revealed that PTP1B inhibition did not change proliferation and pluripotency of undifferentiated ES cells. Taken together, the data presented here suggest that PTP1B is essential for proper differentiation of ES cells into cardiomyocytes.

GATA4 and GATA6 regulate pancreatic endoderm identity through inhibition of hedgehog signaling

GATA4 and GATA6 are zinc finger transcription factors that have important functions in several mesodermal and endodermal organs, including heart, liver and pancreas. In humans, heterozygous mutations of either factor are associated with pancreatic agenesis; however, homozygous deletion of both Gata4 and Gata6 is necessary to disrupt pancreas development in mice. In this study, we demonstrate that arrested pancreatic development in Gata4(fl/fl); Gata6(fl/fl); Pdx1:Cre (pDKO) embryos is accompanied by the transition of ventral and dorsal pancreatic fates into intestinal or stomach lineages, respectively. These results indicate that GATA4 and GATA6 play essential roles in maintaining pancreas identity by regulating foregut endodermal fates. Remarkably, pancreatic anlagen derived from pDKO embryos also display a dramatic upregulation of hedgehog pathway components, which are normally absent from the presumptive pancreatic endoderm. Consistent with the erroneous activation of hedgehog signaling, we demonstrate that GATA4 and GATA6 are able to repress transcription through the sonic hedgehog (Shh) endoderm-specific enhancer MACS1 and that GATA-binding sites within this enhancer are necessary for this repressive activity. These studies establish the importance of GATA4/6-mediated inhibition of hedgehog signaling as a major mechanism regulating pancreatic endoderm specification during patterning of the gut tube.

Oxytocin improves the expression of cardiac specific markers in porcine bone marrow stem cells differentiation

Bone marrow stem cells (BMSCs) treated with 5-azacytidine possess myogenic differentiation potential. Oxytocin (OT) induces cardiomyogenesis in murine embryonic and cardiac stem cells. We attempted to isolate, characterize, and induce OT-mediated cardiomyogenic differentiation of porcine pBMSCs. Cells were treated as: control, OT, and 5-azacytidine groups. During early passages, transcripts of Oct4, GATA4, OT receptor, and phospholamban were expressed. RT-PCR showed upregulation of GATA4 in OT and 5-azacytidine-induced groups. Immunocytochemistry revealed higher expressions of cardiac troponin T and myosin heavy chain in OT than in 5-azacytidine-induced groups (p < 0.01). Western blot analysis showed upregulation of cardiac troponin I in OT-induced pBMSCs (p < 0.01). We infer pBMSCs should be induced during early passages, when expressing transcription factors related to pluripotency and cardiomyogenesis, as well as OT receptor. The more abundant expression of cardiac specific proteins in OT-treated pBMSCs suggests OT could be a more potent cardiomyogenic inducer of pBMSC.

Combined biophysical and soluble factor modulation induces cardiomyocyte differentiation from human muscle derived stem cells

Cellular cardiomyoplasty has emerged as a novel therapy to restore contractile function of injured failing myocardium. Human multipotent muscle derived stem cells (MDSC) can be a potential abundant, autologous cell source for cardiac repair. However, robust conditions for cardiomyocyte (CM) differentiation are not well established for this cell type. We have developed a new method for CM differentiation from human MDSC that combines 3-dimensional artificial muscle tissue (AMT) culture with temporally controlled biophysical cell aggregation and delivery of 4 soluble factors (microRNA-206 inhibitor, IWR-1, Lithium Chloride, and BMP-4) (4F-AG-AMT). The 4F-AG-AMT displayed cardiac-like response to β-adrenergic stimulation and contractile properties. 4F-AG-AMT expressed major cardiac (NKX2-5, GATA4, TBX5, MEF2C) transcription factors and structural proteins. They also express cardiac gap-junction protein, connexin-43, similar to CMs and synchronized spontaneous calcium transients. These results highlight the importance of temporal control of biophysical and soluble factors for CM differentiation from MDSCs.

Simvastatin-enhanced expression of promyogenic nuclear factors and cardiomyogenesis of murine embryonic stem cells

A combination of statin and stem cell therapies has been shown to benefit in experimental models of myocardial infarction. This study tests whether treatment with simvastatin has a direct impact on the cardiomyogenic development of murine embryonic stem cells (ESCs) in embryoid bodies. In a concentration-dependent manner, simvastatin treatment enhanced expression of several promyogenic nuclear transcription factors, including GATA4, Nkx2.5, DTEF-1 and myocardin A. The statin-treated cells also displayed higher levels of cardiac proteins, including myosin, α-actinin, Ryanodine receptor-2, and atrial natriuretic peptide, and they developed synchronized contraction. The statin's promyogenic effect was partially diminished by the addition of the two isoprenoids FPP and GGPP, which are intermediates of cholesterol synthesis. Thus, simvastatin treatment enhances ESC myogenesis during early development perhaps via a mechanism inhibiting the mevalonate-FPP/GGPP pathway.

Regulation of PTEN/Akt pathway enhances cardiomyogenesis and attenuates adverse left ventricular remodeling following thymosin β4 Overexpressing embryonic stem cell transplantation in the infarcted heart

Thymosin β4 (Tβ4), a small G-actin sequestering peptide, mediates cell proliferation, migration, and angiogenesis. Whether embryonic stem (ES) cells, overexpressing Tβ4, readily differentiate into cardiac myocytes in vitro and in vivo and enhance cardioprotection following transplantation post myocardial infarction (MI) remains unknown. Accordingly, we established stable mouse ES cell lines, RFP-ESCs and Tβ4-ESCs, expressing RFP and an RFP-Tβ4 fusion protein, respectively. In vitro, the number of spontaneously beating embryoid bodies (EBs) was significantly increased in Tβ4-ESCs at day 9, 12 and 15, compared with RFP-ESCs. Enhanced expression of cardiac transcriptional factors GATA-4, Mef2c and Txb6 in Tβ4-EBs, as confirmed with real time-PCR analysis, was accompanied by the increased number of EB areas stained positive for sarcomeric α-actin in Tβ4-EBs, compared with the RFP control, suggesting a significant increase in functional cardiac myocytes. Furthermore, we transplanted Tβ4-ESCs into the infarcted mouse heart and performed morphological and functional analysis 2 weeks after MI. There was a significant increase in newly formed cardiac myocytes associated with the Notch pathway, a decrease in apoptotic nuclei mediated by an increase in Akt and a decrease in levels of PTEN. Cardiac fibrosis was significantly reduced, and left ventricular function was significantly augmented in the Tβ4-ESC transplanted group, compared with controls. It is concluded that genetically modified Tβ4-ESCs, potentiates their ability to turn into cardiac myocytes in vitro as well as in vivo. Moreover, we also demonstrate that there was a significant decrease in both cardiac apoptosis and fibrosis, thus improving cardiac function in the infarcted heart.

GATA4 is a critical regulator of gonadectomy-induced adrenocortical tumorigenesis in mice

In response to gonadectomy certain inbred mouse strains develop sex steroidogenic adrenocortical neoplasms. One of the hallmarks of neoplastic transformation is expression of GATA4, a transcription factor normally present in gonadal but not adrenal steroidogenic cells of the adult mouse. To show that GATA4 directly modulates adrenocortical tumorigenesis and is not merely a marker of gonadal-like differentiation in the neoplasms, we studied mice with germline or conditional loss-of-function mutations in the Gata4 gene. Germline Gata4 haploinsufficiency was associated with attenuated tumor growth and reduced expression of sex steroidogenic genes in the adrenal glands of ovariectomized B6D2F1 and B6AF1 mice. At 12 months after ovariectomy, wild-type B6D2F1 mice had biochemical and histological evidence of adrenocortical estrogen production, whereas Gata4(+/-) B6D2F1 mice did not. Germline Gata4 haploinsufficiency exacerbated the secondary phenotype of postovariectomy obesity in B6D2F1 mice, presumably by limiting ectopic estrogen production in the adrenal glands. Amhr2-cre-mediated deletion of floxed Gata4 (Gata4(F)) in nascent adrenocortical neoplasms of ovariectomized B6.129 mice reduced tumor growth and the expression of gonadal-like markers in a Gata4(F) dose-dependent manner. We conclude that GATA4 is a key modifier of gonadectomy-induced adrenocortical neoplasia, postovariectomy obesity, and sex steroidogenic cell differentiation.

Progress in stem cell biology in regenerative medicine for liver disease

Regenerative medicine using stem cells has attracted much attention, since stem cells are responsible for highly proliferative activity and multipotential ability of differentiation. Induced pluripotent stem cells and embryonic stem cells or the adult stem cells such as bone marrow-derived stem cells and adipose tissue-derived stem cells have been expected as a cell source of regenerative medicine. Since differentiating methods of human stem cells into the defined lineage of cells remains to be developed, we focus on the differentiating strategies of pluripotent stem cells and mesenchymal stem cells into liver lineage, especially on cytokine function and gene expression during hepatic differentiation. The survey of previously published papers discloses that the protocols that mimic the liver developmental process seem to be effective in obtaining functional hepatocytes. However, in order to develop hepatic regenerative medicine that is useful in a clinical setting, more effective and potent strategies that obtain mature hepatocytes are required.

Mechanisms of cardiogenesis in cardiovascular progenitor cells

Self-renewing cells of the vertebrate heart have become a major subject of interest in the past decade. However, many researchers had a hard time to argue against the orthodox textbook view that defines the heart as a postmitotic organ. Once the scientific community agreed on the existence of self-renewing cells in the vertebrate heart, their origin was again put on trial when transdifferentiation, dedifferentiation, and reprogramming could no longer be excluded as potential sources of self-renewal in the adult organ. Additionally, the presence of self-renewing pluripotent cells in the peripheral blood challenges the concept of tissue-specific stem and progenitor cells. Leaving these unsolved problems aside, it seems very desirable to learn about the basic biology of this unique cell type. Thus, we shall here paint a picture of cardiovascular progenitor cells including the current knowledge about their origin, basic nature, and the molecular mechanisms guiding proliferation and differentiation into somatic cells of the heart.

Increased cardiogenesis in P19-GFP teratocarcinoma cells expressing the propeptide IGF-1Ea

The mechanism implicated in differentiation of endogenous cardiac stem cells into cardiomyocytes to regenerate the heart tissue upon an insult remains elusive, limiting the therapeutical goals to exogenous cell injection and/or gene therapy. We have shown previously that cardiac specific overexpression of the insulin-like growth factor 1 propeptide IGF-1Ea induces beneficial myocardial repair after infarct. Although the mechanism is still under investigation, the possibility that this propeptide may be involved in promoting stem cell differentiation into the cardiac lineage has yet to be explored. To investigate whether IGF-1Ea promote cardiogenesis, we initially modified P19 embryonal carcinoma cells to express IGF-1Ea. Taking advantage of their cardiomyogenic nature, we analyzed whether overexpression of this propeptide affected cardiac differentiation program. The data herein presented showed for the first time that constitutively overexpressed IGF-1Ea increased cardiogenic differentiation program in both undifferentiated and DMSO-differentiated cells. In details, IGF-1Ea overexpression promoted localization of alpha-actinin in finely organized sarcomeric structure compared to control cells and upregulated the cardiac mesodermal marker NKX-2.5 and the ventricular structural protein MLC2v. Furthermore, activated IGF-1 signaling promoted cardiac mesodermal induction in undifferentiated cells independently of cell proliferation. This analysis suggests that IGF-1Ea may be a good candidate to improve both in vitro production of cardiomyocytes from pluripotent stem cells and in vivo activation of the differentiation program of cardiac progenitor cells.

Mitogen-activated protein kinase in endothelin-1-induced cardiac differentiation of mouse embryonic stem cells

Endothelin-1(ET-1) is a potent vasoconstrictor involved in the development of cardiovascular diseases and is an important regulator of heart development. However, the role of ET-1 in cardiac differentiation of mouse embryonic stem cells (mESCs) and the underlying molecular mechanisms remain poorly understood. In the present study, we showed that ET-1 significantly up-regulated gene expression of the cardiac specific transcriptional factors Nkx2.5, GATA4, and conduction system specific marker CX40, with no affect on the gene expression of α-MHC and β-MHC in cardiac differentiation of mESCs. The percentage of beating embryoid bodies (EB) and the Troponin T (TnT) positive area in total EBs was unchanged following ET-1 treatment, while the percentage of spindle cells that stained positively with TnT was increased in the presence of ET-1. Further investigation indicated that the percentage of beating EBs and the TnT positive area were decreased by the extracellular signal-related kinases (ERK)-1/2 inhibitor U0126 and the p38 inhibitor SB203580, but not by the Jun amino-terminal kinases (JNK) inhibitor SP600125. Inhibition of ERK1/2, p38, and JNK pathways also blocked the up-regulation of Nkx2.5 and GATA4 by ET-1, however only inhibition of the ERK1/2 pathway had negatively effects on the increase in CX40 expression in response to ET-1. ET-1 induced an increase in the percentage of spindle cells was also inhibited by U0126. Our results suggest that ET-1 plays a significant role in the cardiac differentiation of mESCs, especially in those cells committed to the conduction system, with the ERK1/2 pathway playing a critical role in this process.

Approaches for immunological tolerance induction to stem cell-derived cell replacement therapies

The shortage of donors for organ transplantation and also to treat degenerative diseases has led to the development of the new field of regenerative medicine. One aim of this field, in addition to in vivo induction of endogenous tissue regeneration, is to utilize stem cells as a supplementary source of cells to repair or replace tissues or organs that have ceased to function owing to ageing or autoimmunity. Embryonic stem cells hold promise in this respect because of their developmental capacity to generate all tissues within the body. More recently, the discovery of induced pluripotent stem cells, somatic cells reprogrammed to a primitive embryonic-like state by the introduction of pluripotency factors, may also act as an important cell source for cell replacement therapy. However, before cell replacement therapy can become a reality, one must consider how to overcome the potential transplant rejection of stem cell-derived products. There are several potential ways to circumvent the hurdles presented by the immune system in this setting, not least the induction of immunological tolerance in the host. In this review, we consider this and other approaches for engendering acceptance of stem cell-derived tissues.

Human embryonic fibroblasts support single cell enzymatic expansion of human embryonic stem cells in xeno-free cultures

The future application of human embryonic stem cells (hESC) for therapeutic approaches requires the development of xeno-free culture conditions to prevent the potential transmission of animal pathogens or xenobiotic substances to hESC. An important component of the majority of hESC culture systems developed is the requirement for fibroblasts to serve as feeders. For this purpose, several studies have used human foreskin fibroblasts established under xeno-free conditions. In this study we report xeno-free establishment and maintenance of human embryonic fibroblasts (XHEF) and demonstrate their ability to support long-term self-renewal of hESC under xeno-free culture conditions, using a commercially available complete medium. Importantly, our culture conditions allow enzymatic passaging of hESC. In contrast, hESC cultured on human foreskin fibroblasts (XHFF) under the same conditions were poorly maintained and rapidly subject to differentiation. Our study clearly shows that the source of human fibroblasts is essential for long-term xeno-free hESC maintenance.

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.

Xenopus explants as an experimental model system for studying heart development

Many developmental processes are highly conserved in all vertebrate organisms. This conservation has allowed developmental biologists to use numerous animal models to further our understanding of the molecular mechanisms that govern heart development and congenital heart disease. Amphibian embryos represent a useful model for such studies because their relatively large embryos are available in large numbers and survive simple microsurgery. In addition, until swimming tadpole stages, an amphibian embryo develops using nutrients stored in each of its many cells. This feature has the advantage that explants isolated from embryonic tissue will continue to survive in isolation and differentiate in culture. Furthermore, cells from the ectodermal layer of the blastula or gastrula embryos are stem cell like in that they are pluripotent and can be induced to form various tissues in vitro. Here, we will review work from recent studies in which explants from the amphibian embryos were used to further our understanding of vertebrate heart development. We will bring together the key facts needed for using Xenopus explants as experimental approaches for studying molecular pathways and gene regulatory networks in vertebrate cardiogenesis. The knowledge generated with these approaches supports the usefulness of amphibian explants, and the relevance of the findings strongly validates the conservation of molecular pathways that underlie heart development in all vertebrates.

Gata4 directs development of cardiac-inducing endoderm from ES cells

The transcription factor Gata4 is essential for normal heart morphogenesis and regulates the survival, growth, and proliferation of cardiomyocytes. We tested if Gata4 can specify cardiomyocyte fate from an uncommitted stem or progenitor cell population, by developing a system for conditional expression of Gata4 in embryonic stem cells. We find that in embryoid body cultures containing even a low ratio of these cells, expression of Gata4 is sufficient to enhance significantly the generation of cardiomyocytes, via a non-cell-autonomous mechanism. The Gata4-expressing cells do not generate cardiac or other mesoderm derivatives. Rather, Gata4 expression directs the development of two types of Sox17+ endoderm. This includes an epCam+Dpp4+ subtype of visceral endoderm. In addition, Gata4 generates similar amounts of epCam+Dpp4- definitive endoderm enriched for Cxcr4, FoxA2, FoxA3, Dlx5 and other characteristic transcripts. Both types of endoderm express cardiac-inducing factors, including WNT antagonists Dkk1 and Sfrp5, although the visceral endoderm subtype has much higher cardiac-inducing activity correlating with relatively enhanced levels of transcripts encoding BMPs. The Gata4-expressing cells eventually express differentiation markers showing commitment to liver development, even under conditions that normally support mesoderm development. The results suggest that Gata4 is capable of specifying endoderm fates that facilitate, with temporal and spatial specificity, the generation of cardiomyocyte progenitors from associated mesoderm.

Human eosinophil cationic protein enhances stress fiber formation in Balb/c 3T3 fibroblasts and differentiation of rat neonatal cardiomyocytes

We found that eosinophil cationic protein (ECP) stimulated the growth of mouse Balb/c 3T3 fibroblasts. ECP-treated 3T3 cells were more flattened and exhibited enhanced stress fiber formation. The enhancement of cytoskeleton after addition of recombinant ECP appeared stable and was able to inhibit disassembly of actin filaments that was induced by fibroblast growth factor-2. The ROCK inhibitor, Y-27632, abrogated this enhancement on stress fiber formation that was induced by ECP indicating the involvement of Rho/ROCK signaling pathway. The effect of ECP was assessed on the differentiation of primary cardiomyocytes derived from rat neonatal heart since the development of actin filaments is significantly related with organization of stress fibers. As the result, both beating rate and the expression of cardiac muscle specific markers such as atrial natriuretic factor were enhanced in the presence of ECP. Thus ECP may also function as a cardiomyocyte differentiation factor.

Neural tube defects in mice with reduced levels of inositol 1,3,4-trisphosphate 5/6-kinase

Inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) is a key regulatory enzyme at the branch point for the synthesis of inositol hexakisphosphate (IP(6)), an intracellular signaling molecule implicated in the regulation of ion channels, endocytosis, exocytosis, transcription, DNA repair, and RNA export from the nucleus. IP(6) also has been shown to be an integral structural component of several proteins. We have generated a mouse strain harboring a beta-galactosidase (betagal) gene trap cassette in the second intron of the Itpk1 gene. Animals homozygous for this gene trap are viable, fertile, and produce less ITPK1 protein than wild-type and heterozygous animals. Thus, the gene trap represents a hypomorphic rather than a null allele. Using a combination of immunohistochemistry, in situ hybridization, and betagal staining of mice heterozygous for the hypomorphic allele, we found high expression of Itpk1 in the developing central and peripheral nervous systems and in the paraxial mesoderm. Examination of embryos resulting from homozygous matings uncovered neural tube defects (NTDs) in some animals and axial skeletal defects or growth retardation in others. On a C57BL/6 x 129(P2)Ola background, 12% of mid-gestation embryos had spina bifida and/or exencephaly, whereas wild-type animals of the same genetic background had no NTDs. We conclude that ITPK1 is required for proper development of the neural tube and axial mesoderm.

Mouse androgenetic embryonic stem cells differentiated to multiple cell lineages in three embryonic germ layers in vitro

The embryos of some rodents and primates can precede early development without the process of fertilization; however, they cease to develop after implantation because of restricted expressions of imprinting genes. Asexually developed embryos are classified into parthenote/gynogenote and androgenote by their genomic origins. Embryonic stem cells (ESCs) derived from asexual origins have also been reported. To date, ESCs derived from parthenogenetic embryos (PgESCs) have been established in some species, including humans, and the possibility to be alternative sources for autologous cell transplantation in regenerative medicine has been proposed. However, some developmental characteristics, which might be important for therapeutic applications, such as multiple differentiation capacity and transplantability of the ESCs of androgenetic origin (AgESCs) are uncertain. Here, we induced differentiation of mouse AgESCs and observed derivation of neural cells, cardiomyocytes and hepatocytes in vitro. Following differentiated embryoid body (EB) transplantation in various mouse strains including the strain of origin, we found that the EBs could engraft in theoretically MHC-matched strains. Our results indicate that AgESCs possess at least two important characteristics, multiple differentiation properties in vitro and transplantability after differentiation, and suggest that they can also serve as a source of histocompatible tissues for transplantation.

Retinoic acid receptor gamma activates receptor tyrosine kinase Tie1 gene transcription through transcription factor GATA4 in F9 stem cells

OBJECTIVE

The retinoic acid receptors (RARs) alpha, beta2, and gamma regulate specific subsets of target genes during all-trans retinoic acid (RA) induced differentiation of F9 teratocarcinoma stem cells. The Tie1 gene exhibited reduced expression in RA-treated F9 RARgamma-/- cells as compared to wild-type (WT) by microarray analysis. Our goal was to analyze the Tie1 gene, which encodes a surface receptor tyrosine kinase expressed in the hematovascular system.

MATERIALS AND METHODS

We assessed Tie1, Tie2, Flk1, Runx1, Peg/Mest2, and angiopoietin-1 and 2 mRNA levels and Tie1 promoter activity.

RESULTS

We showed that RARgamma, but not RARalpha or RARbeta2, is required for Tie1 promoter activation by RA. Treatment with a RARgamma selective agonist plus a retinoid X receptor agonist (LGD1069) increased Tie1 mRNA levels by 11- +/- 2.5-fold 48 hours after RA addition in F9 WT, but not in F9 RARgamma-/- cells, by quantitative reverse transcription polymerase chain reaction. Multiple putative GATA elements were identified in the Tie1 proximal promoter. RA increased GATA4 transcripts by 12- +/- 1-fold in F9 WT at 48 hours, but not in F9 RARgamma-/- cells. In addition, transfection of a GATA4 expression vector increased Tie1 promoter/luciferase activity in both RA-treated F9 WT and RARgamma-/- cells. Tie1 promoter deletion analyses indicated that a region of the promoter that possessed multiple GATA sites mediated the RA-associated Tie1 transcriptional increase.

CONCLUSIONS

Our results indicate that GATA4 plays a role in the RA/RARgamma-associated transcriptional activation of the Tie1 promoter. An understanding of RAR specificity in RA signaling should result in insights into hematopoietic stem cell signaling and potentially in improved therapies for several human diseases.

Loss of both GATA4 and GATA6 blocks cardiac myocyte differentiation and results in acardia in mice

Despite significant advances in identifying signaling molecules that induce cardiogenesis in mammals, the transcription factors that control the onset of cardiac myocyte gene expression have remained elusive. Candidates include the zinc finger transcription factors GATA binding proteins 4 and 6 (GATA4, GATA6). The individual loss of either protein in mice results in lethality prior to the onset of heart development due to defects in the extra-embryonic endoderm; however, when this extra-embryonic deficiency is circumvented using tetraploid embryo complementation, cardiac myocyte differentiation initiates normally. Here we show that these factors have redundant roles in controlling the onset of cardiac myocyte differentiation. As a consequence, Gata4(-/-)Gata6(-/-) embryos completely lack hearts, although second heart field progenitor cells are still generated. Our data support a model whereby GATA4 or GATA6 are essential for expression of the network of transcription factors that regulate the onset of cardiac myocyte gene expression during mammalian development.

Heart field: from mesoderm to heart tube

In this review we discuss the major morphogenetic and regulative events that control myocardial progenitor cells from the time that they delaminate from the epiblast in the primitive streak to their differentiation into cardiomyocytes in the heart tube. During chick and mouse embryogenesis, myocardial progenitor cells go through four specific processes that are sequential but overlapping: specification of the cardiogenic mesoderm, determination of the bilaterally symmetric heart fields, patterning of the heart field, and finally cardiomyocyte differentiation and formation of the heart tube. We describe the morphological and molecular events that play a pivotal role in each of these four processes.

GATA-4 is required for sex steroidogenic cell development in the fetal mouse

The transcription factor GATA-4 is expressed in Sertoli cells, steroidogenic Leydig cells, and other testicular somatic cells. Previous studies have established that interaction between GATA-4 and its cofactor FOG-2 is necessary for proper Sry expression and all subsequent steps in testicular organogenesis, including testis cord formation and differentiation of both Sertoli and fetal Leydig cells. Since fetal Leydig cell differentiation depends on Sertoli cell-derived factors, it has remained unclear whether GATA-4 has a cell autonomous role in Leydig cell development. We used two experimental systems to explore the role of GATA-4 in the ontogeny of testicular steroidogenic cells. First, chimeric mice were generated by injection of Gata4-/- ES cells into Rosa26 blastocysts. Analysis of the resultant chimeras showed that in developing testis Gata4-/- cells can contribute to fetal germ cells and interstitial fibroblasts but not fetal Leydig cells. Second, wild-type or Gata4-/- ES cells were injected into the flanks of intact or gonadectomized nude mice and the resultant teratomas examined for expression of steroidogenic markers. Wild-type but not Gata4-/- ES cells were capable of differentiating into gonadal-type steroidogenic lineages in teratomas grown in gonadectomized mice. In chimeric teratomas derived from mixtures of GFP-tagged Gata4+/+ ES cells and unlabeled Gata4-/- ES cells, sex steroidogenic cell differentiation was restricted to GFP-expressing cells. Collectively these data suggest that GATA-4 plays an integral role in the development of testicular steroidogenic cells.

Inositol-1,4,5-trisphosphate-mediated spontaneous activity in mouse embryonic stem cell-derived cardiomyocytes

Embryonic stem cell-derived cardiomyocytes (ESdCs) have been proposed as a source for cardiac cell-replacement therapy. The aim of this study was to determine the Ca2+-handling mechanisms that determine the frequency and duration of spontaneous Ca2+ transients in single ESdCs. With laser scanning confocal microscopy using the Ca2+-sensitive dye Fluo-4/AM, we determined that spontaneous Ca2+ transients in ESdCs at the onset of beating (day 9) depend on Ca2+ entry across the plasma membrane (50%) whereas Ca2+-induced Ca2+ release is the major contributor to Ca2+ transients in ESdCs after 16 days (72%). Likewise, Ca2+ extrusion in 9-day-old ESdCs depends on Na+-Ca2+ exchange (50.0+/-8%) whereas Ca2+ reuptake by the sarco(endo)plasmic Ca2+ ATPase (72+/-5%) dominates in further differentiated cells. Spontaneous Ca2+ transients were suppressed by the inositol-1,4,5-trisphosphate (IP3) receptor (IP3R) blocker 2-aminoethoxydiphenyl borate (2-APB) and the phospholipase C blocker U73122 but continued in the presence of caffeine. Stimulation of IP3 production by phenylephrine or endothelin-1 had a positive chronotropic effect that could be reversed by U73122 and 2-APB. The presence of Ca2+-free solution and block of L-type Ca2+ channels by nifedipine also resulted in a cessation of spontaneous activity. Overall, IP3R-mediated Ca2+ release in ESdCs is translated into a depolarization of the plasma membrane and a whole-cell Ca2+ transient is subsequently induced by voltage-dependent Ca2+ influx. Although ryanodine receptor-mediated Ca2+ release amplifies the IP3R-induced trigger for the Ca2+ transients and modulates its frequencies, it is not a prerequisite for spontaneous activity. The results of this study offer important insight into the role of IP3R-mediated Ca2+ release for pacemaker activity in differentiating cardiomyocytes.

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.

Expression and loss of alleles in cultured mouse embryonic fibroblasts and stem cells carrying allelic fluorescent protein genes

Background

Loss of heterozygosity (LOH) contributes to many cancers, but the rate at which these events occur in normal cells of the body is not clear. LOH would be detectable in diverse cell types in the body if this event were to confer an obvious cellular phenotype. Mice that carry two different fluorescent protein genes as alleles of a locus would seem to be a useful tool for addressing this issue because LOH would change a cell's phenotype from dichromatic to monochromatic. In addition, LOH caused by mitotic crossing over might be discernable in tissues because this event produces a pair of neighboring monochromatic cells that are different colors.

Results

As a step in assessing the utility of this approach, we derived primary embryonic fibroblast populations and embryonic stem cell lines from mice that carried two different fluorescent protein genes as alleles at the chromosome 6 locus, ROSA26. Fluorescence activated cell sorting (FACS) showed that the vast majority of cells in each line expressed the two marker proteins at similar levels, and that populations exhibited expression noise similar to that seen in bacteria and yeast. Cells with a monochromatic phenotype were present at frequencies on the order of 10^-4 and appeared to be produced at a rate of approximately 10^-5 variant cells per mitosis. 45 of 45 stably monochromatic ES cell clones exhibited loss of the expected allele at the ROSA26 locus. More than half of these clones retained heterozygosity at a locus between ROSA26 and the centromere. Other clones exhibited LOH near the centromere, but were disomic for chromosome 6.

Conclusion

Allelic fluorescent markers allowed LOH at the ROSA26 locus to be detected by FACS. LOH at this locus was usually not accompanied by LOH near the centromere, suggesting that mitotic recombination was the major cause of ROSA26 LOH. Dichromatic mouse embryonic cells provide a novel system for studying genetic/karyotypic stability and factors influencing expression from allelic genes. Similar approaches will allow these phenomena to be studied in tissues.

Parietal endoderm secreted S100A4 promotes early cardiomyogenesis in embryoid bodies

Cardiomyogenesis is influenced by factors secreted by anterior-lateral and extra-embryonic endoderm. Differentiation of embryonic stem cells in embryoid bodies allows to study the influence of growth factors on cardiomyogenesis. By these means SPARC was identified as a new factor enhancing cardiomyogenesis [M. Stary, W. Pasteiner, A. Summer, A. Hrdina, A. Eger, G. Weitzer, Parietal endoderm secreted SPARC promotes early cardiomyogenesis in vitro, Exp. Cell Res. 310 (2005) 331-341]. Here we report a similar and new function for S100A4, a calcium-binding protein of the EF-hand type. S100A4 is secreted by parietal endoderm and promotes early differentiation and proliferation of cardiomyocytes. Oligomeric S100A4 supports cardiomyogenesis in a concentration-dependent manner, whereas inhibition of autocrine S100A4 severely attenuates cardiomyogenesis. S100A4 specifically influences transcription in differentiating cardiomyocytes, as evident from increased expression of cardiac transcription factor genes nkx2.5 and mef2C. These data suggest that S100A4, like SPARC, plays a supportive role in early in vitro cardiomyogenesis.

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.

GATA factors lie upstream of Nkx 2.5 in the transcriptional regulatory cascade that effects cardiogenesis

Members of the GATA-4, -5, and -6 subfamily of transcription factors are co-expressed with the homeoprotein Nkx 2.5 in the precardiac mesoderm during the earliest stages of its specification and are known to be important determinants of cardiac gene expression. Ample evidence suggests that GATA factors and Nkx 2.5 cross-regulate each other's expression; however, the temporal order of the expression of these transcription factors in vivo remains unresolved, and thus precise definition of the role of the products of the genes they transcribe in early development has been difficult to assess. We employed P19 CL6 mouse embryonic carcinoma cells as a model to investigate this problem, because these cells, like embryonic stem cells, can be induced to differentiate along multiple lineages. Here we demonstrate that when P19 CL6 cells are induced to differentiate to a cardiogenic lineage, the expression of GATA-4 and GATA-6 is up-regulated prior to the transcriptional activation of Nkx 2.5. Moreover, over-expression of GATA-4 or -6 at the time of Nkx 2.5 induction results in a significant up-regulation of endogenous Nkx 2.5 transcription. Finally, it is known that a Nkx-dependent enhancer is necessary for GATA-6 expression within cardiomyocytes of the developing mouse embryo. We demonstrate that within undifferentiated P19 CL6 cells, GATA-6 expression is subject to active repression by a novel upstream element that possesses binding sites for factors involved in transcriptional repression that are conserved between mammalian species.

Molecular analysis of cardiomyocytes derived from human embryonic stem cells

During early embryogenesis, the cardiovascular system is the first system to be established and is initiated by a process involving the hypoblastic cells of the primitive endoderm. Human embryonic stem (hES) cells provide a model to investigate the early developmental stages of this system. When removed from their feeder layer, hESC create embryoid bodies (EB) which, when plated, develop areas of beating cells in 21.5% of the EB. These spontaneously contracting cells were demonstrated using histology, immunostaining and reverse transcription-polymerase chain reaction (RT-PCR), to possess morphological and molecular characteristics consistent with cardiomyocytic phenotypes. In addition, the expression pattern of specific cardiomyocytic genes in human EB (hEB) was demonstrated and analyzed for the first time. GATA-4 is the first gene to be expressed in 6-day-old EB. Alpha cardiac actin and atrial natriuretic factor are expressed in older hEB at 10 and 20 days, respectively. Light chain ventricular myosin (MLC-2V) was expressed only in EB with beating areas and its expression increased with time. Alpha heavy chain myosin (alpha-MHC) expression declined in the pulsating hEB with time, in contrast to events in EB derived from mice. We conclude that human embryonic stem cells can provide a useful tool for research on embryogenesis in general and cardiovascular development in particular.

Gata4 regulates the formation of multiple organs

We have developed a loss-of-function model for Gata4 in zebrafish, in order to examine broadly its requirement for organogenesis. We show that the function of Gata4 in zebrafish heart development is well conserved with that in mouse, and that, in addition, Gata4 is required for development of the intestine, liver, pancreas and swim bladder. Therefore, a single transcription factor regulates the formation of many organs. Gata6 is a closely related transcription factor with an overlapping expression pattern. We show that zebrafish depleted of Gata6 show defects in liver bud growth similar to mouse Gata6 mutants and zebrafish Gata4 morphants, and that zebrafish embryos depleted of both Gata4 and Gata6 display an earlier block in liver development, and thus completely lack liver buds. Therefore, Gata4 and Gata6 have distinct non-redundant functions in cardiac morphogenesis, but are redundant for an early step of liver development. In addition, both Gata4 and Gata6 are essential and non-redundant for liver growth following initial budding.

Maternal administration of thalidomide or valproic acid causes abnormal serotonergic neurons in the offspring: implication for pathogenesis of autism

Embryonic exposure to thalidomide (THAL) or valproic acid (VPA) before neural tube closure has been demonstrated as a useful model for human autism in rats. Abnormalities of the serotonergic system which are often observed in human autism have been shown in these rats. Thus, we examined whether early serotonergic neuronal development is perturbed by THAL/VPA. When pregnant rats were exposed to THAL or VPA on embryonic day 9, a dramatic shift of the distribution of serotonergic neurons in the dorsal raphe nucleus was observed on postnatal day 50. This alteration is thought to reflect abnormality of serotonergic neuronal differentiation and migration. In vitro studies revealed that VPA retards the maturation of serotonergic neuron from ES cell-derived neuronal progenitors, whereas exogenously added Sonic hedgehog, a morphogen that has been implicated in serotonergic cell fate, partially prevented this retardation. These results indicate that disruption of early serotonergic neuronal development might be involved in the etiology of autism.

Nodal inhibits differentiation of human embryonic stem cells along the neuroectodermal default pathway

Genetic studies in fish, amphibia, and mice have shown that deficiency of Nodal signaling blocks differentiation into mesoderm and endoderm. Thus, Nodal is considered as a major inducer of mesendoderm during gastrulation. On this basis, Nodal is a candidate for controlling differentiation of pluripotent human embryonic stem cells (hESCs) into tissue lineages with potential clinical value. We have investigated the effect of Nodal, both as a recombinant protein and as a constitutively expressed transgene, on differentiation of hESCs. When control hESCs were grown in chemically defined medium, their expression of markers of pluripotency progressively decreased, while expression of neuroectoderm markers was strongly upregulated, thus revealing a neuroectodermal default mechanism for differentiation in this system. hESCs cultured in recombinant Nodal, by contrast, showed prolonged expression of pluripotency marker genes and reduced induction of neuroectoderm markers. These Nodal effects were accentuated in hESCs expressing a Nodal transgene, with striking morphogenetic consequences. Nodal-expressing hESCs developing as embryoid bodies contained an outer layer of visceral endoderm-like cells surrounding an inner layer of epiblast-like cells, each layer having distinct gene expression patterns. Markers of neuroectoderm were not upregulated during development of Nodal-expressing embryoid bodies, nor was there induction of markers for definitive mesoderm or endoderm differentiation. Moreover, the inner layer expressed markers of pluripotency, characteristic of undifferentiated hESCs and of epiblast in mouse embryos. These results could be accounted for by an inhibitory effect of Nodal-induced visceral endoderm on pluripotent cell differentiation into mesoderm and endoderm, with a concomitant inhibition of neuroectoderm differentiation by Nodal itself. There could also be a direct effect of Nodal in the maintenance of pluripotency. In summary, analysis of the Nodal-expressing phenotype suggests a function for the transforming growth factor-beta (TGF-beta) growth factor superfamily in pluripotency and in early cell fate decisions leading to primary tissue layers during in vitro development of pluripotent human stem cells. The effects of Nodal on early differentiation illustrate how hESCs can augment mouse embryos as a model for analyzing mechanisms of early mammalian development.

The roles of GATA-4, -5 and -6 in vertebrate heart development

The transcription factors GATA-4, -5 and -6 are expressed very early in heart tissue. Essential GATA sites have been detected in several cardiac genes and the cardiac GATA factors interact with a wide variety of cofactors which synergistically increase gene expression. These multi-protein transcriptional complexes confer promoter-specificity on the GATA factors and also on the more broadly expressed cofactors. Here we summarise the data on these interactions and represent the conclusions as a GATA factor-based genetic regulatory network for the heart. Of the three cardiac GATAs, GATA-4 is by far the most extensively studied, however, loss-of-function data question its presumed dominance during heart development as opposed to hypertrophy.

Transcriptional regulation of cardiac conduction system development: 2004 FASEB cardiac conduction system minimeeting, Washington, DC

The development of the complex network of specialized cells that form the atrioventricular conduction system (AVCS) during cardiac morphogenesis occurs by progressive recruitment within a multipotent cardiomyogenic lineage. Understanding the molecular control of this developmental process has been the focus of recent research. Transcription factors representative of multiple subfamilies have been identified and include members of zinc-finger subfamilies (GATA4, GATA6 HF-1b), skeletal muscle transcription factors (MyoD), T-box genes (Tbx5), and also homeodomain transcription factors (Msx2 and Nkx2.5). Mutations in some of these transcription factors cause congenital heart disease and are associated with cardiac abnormalities, including deficits within the AVCS. Mouse models that closely phenocopy known human heart disease provide powerful tools for the study of molecular effectors of AVCS development. Indeed, investigations of the Nkx2.5 haploinsufficient mouse have shown that peripheral Purkinje fibers are significantly underrepresented. This piece of data corroborates our previous work showing in chick, mouse, and humans that Nkx2.5 is elevated in the differentiating AVCS relative to adjacent working ventricular myocardial tissues. Using the chick embryo as a model, we show that this elevation of Nkx2.5 is transient in the network of conduction cells comprising the peripheral Purkinje fiber system. Functional studies using defective adenoviral constructs, which disrupt the normal variation in level of this gene, result in perturbations of Purkinje fiber phenotype. Thus, the precise spatiotemporal regulation of Nkx2.5 levels during development may be required for the progressive emergence of gene expression patterns specific to differentiated Purkinje fiber cells.

Mouse strain susceptibility to gonadectomy-induced adrenocortical tumor formation correlates with the expression of GATA-4 and luteinizing hormone receptor

Certain inbred strains of mice, including DBA/2J, develop adrenocortical tumors in response to gonadectomy. Spindle-shaped cells with limited steroidogenic capacity, termed A cells, appear in the subcapsular region of the adrenal gland, followed by sex steroid-producing cells known as B cells. These changes result from unopposed gonadotropin production by the pituitary, but the adrenocortical factors involved in tumorigenesis have not been characterized. GATA-4, a transcription factor normally expressed in fetal, but not adult, adrenocortical cells, was found in neoplastic cells that proliferate in the adrenal cortex of gonadectomized DBA/2J mice. GATA-4 mRNA was detected in the adrenal glands of female mice 0.5 months after ovariectomy and reached a maximum by 4 months. Castrated male mice developed adrenocortical tumors more slowly than gonadectomized females, and the onset of GATA-4 expression in the adrenal was delayed. In situ hybridization and immunohistochemistry revealed GATA-4 mRNA and protein in A and B cells, but not in normal adrenocortical cells. mRNA encoding another factor associated with adrenocortical tumorigenesis, LH receptor (LHR), was detected in A and B cells. In addition, transcripts for P450 17 alpha-hydroxylase/C17-C20 lyase, an enzyme essential for the production of sex steroids, and inhibin-alpha were found in B cells. Unilateral ovarian regeneration, a phenomenon known to occur in gonadectomized mice, was observed in a subset of DBA/2J mice undergoing complete ovariectomy. In these animals, adrenocortical tumor progression was arrested; A cells and GATA-4 expression were evident, but there was no expression of LHR or P450 17 alpha-hydroxylase/C17-C20 lyase. Strain susceptibility to adrenocortical tumorigenesis (DBA/2J >> FVB/N) correlated with the expression of GATA-4 and LHR, implicating these factors in the process of adrenocortical neoplasia in response to continuous gonadotropin stimulation.

Differentiation of mouse embryonic stem cells into pancreatic and hepatic cells

Here, we present efficient strategies to differentiate ES cells either into pancreatic or into hepatic cell types. We recommend a strategy to select nestin+ cells, an early progenitor cell type with high developmental plasticity, followed by differentiation induction with specific growth and extracellular matrix factors into pancreatic and hepatic cell types. Cells differentiating via nestin+ cells into the pancreatic and hepatic lineage expressed tissue-specific genes. Proteins characteristic for mature endocrine pancreatic or hepatic cells were synthesized and released. Further, a histotypic "spinner" culture system was introduced to generate mature insulin- and albumin-producing cells at high efficiency.

Tools for targeted manipulation of the mouse genome

In the postgenomic era the mouse will be central to the challenge of ascribing a function to the 40,000 or so genes that constitute our genome. In this review, we summarize some of the classic and modern approaches that have fueled the recent dramatic explosion in mouse genetics. Together with the sequencing of the mouse genome, these tools will have a profound effect on our ability to generate new and more accurate mouse models and thus provide a powerful insight into the function of human genes during the processes of both normal development and disease.

Transcription factors in cardiogenesis: the combinations that unlock the mysteries of the heart

Heart formation is one of the first signs of organogenesis within the developing embryo and this process is conserved from flies to man. Completing the genetic roadmap of the molecular mechanisms that control the cell specification and differentiation of cells that form the developing heart has been an exciting and fast-moving area of research in the fields of molecular and developmental biology. At the core of these studies is an interest in the transcription factors that are responsible for initiation of a pluripotent cell to become programmed to the cardiac lineage and the subsequent transcription factors that implement the instructions set up by the cells commitment decision. To gain a better understanding of these pathways, cardiac-expressed transcription factors have been identified, cloned, overexpressed, and mutated to try to determine function. Although results vary depending on the gene in question, it is clear that there is a striking evolutionary conservation of the cardiogenic program among species. As we move up the evolutionary ladder toward man, we encounter cases of functional redundancy and combinatorial interactions that reflect the complex networks of gene expression that orchestrate heart development. This review focuses on what is known about the transcription factors implicated in heart formation and the role they play in this intricate genetic program.

Early signals in cardiac development

The heart is the first organ to form during embryogenesis and its circulatory function is critical from early on for the viability of the mammalian embryo. Developmental abnormalities of the heart have also been widely recognized as the underlying cause of many congenital heart malformations. Hence, the developmental mechanisms that orchestrate the formation and morphogenesis of this organ have received much attention among classical and molecular embryologists. Due to the evolutionary conservation of many of these processes, major insights have been gained from the studies of a number of vertebrate and invertebrate models, including mouse, chick, amphibians, zebrafish, and Drosophila. In all of these systems, the heart precursors are generated within bilateral fields in the lateral mesoderm and then converge toward the midline to form a beating linear heart tube. The specification of heart precursors is a result of multiple tissue and cell-cell interactions that involve temporally and spatially integrated programs of inductive signaling events. In the present review, we focus on the molecular and developmental functions of signaling processes during early cardiogenesis that have been defined in both vertebrate and invertebrate models. We discuss the current knowledge on the mechanisms through which signals induce the expression of cardiogenic transcription factors and the relationships between signaling pathways and transcriptional regulators that cooperate to control cardiac induction and the formation of a linear heart tube.

Molecular embryogenesis of the heart

Development of the heart is a complex process involving primary and secondary heart fields that are set aside to generate myocardial and endocardial cell lineages. The molecular inductions that occur in the primary heart field appear to be recapitulated in induction and myocardial differentiation of the secondary heart field, which adds the conotruncal segments to the primary heart tube. While much is now known about the initial steps and factors involved in induction of myocardial differentiation, little is known about induction of endocardial development. Many of the genes expressed by nascent myocardial cells, which then become committed to a specific heart segment, have been identified and studied. In addition to the heart fields, several other "extracardiac" cell populations contribute to the fully functional mature heart. Less is known about the genetic programs of extracardiac cells as they enter the heart and take part in cardiogenesis. The molecular/genetic basis of many congenital cardiac defects has been elucidated in recent years as a result of new insights into the molecular control of developmental events.