The gene encoding the mitogen-responsive phosphoprotein Dab2 is differentially regulated by GATA-6 and GATA-4 in the visceral endoderm

In vitro models of human hypoblast and mouse primitive endoderm

The primitive endoderm (PrE, also named hypoblast), a predominantly extraembryonic epithelium that arises from the inner cell mass (ICM) of the mammalian pre-implantation blastocyst, plays a fundamental role in embryonic development, giving rise to the yolk sac, establishing the anterior-posterior axis and contributing to the gut. PrE is specified from the ICM at the same time as the epiblast (Epi) that will form the embryo proper. While in vitro cell lines resembling the pluripotent Epi have been derived from a variety of conditions, only one model system currently exists for the PrE, naïve extraembryonic endoderm (nEnd). As a result, considerably more is known about the gene regulatory networks and signalling requirements of pluripotent stem cells than nEnd. In this review, we describe the ontogeny and differentiation of the PrE or hypoblast in mouse and primate and then discuss in vitro cell culture models for different extraembryonic endodermal cell types.

Integrative analysis reveals early epigenetic alterations in high-grade serous ovarian carcinomas

High-grade serous ovarian carcinoma (HGSOC) is the most lethal gynecological malignancy. To date, the profiles of gene mutations and copy number alterations in HGSOC have been well characterized. However, the patterns of epigenetic alterations and transcription factor dysregulation in HGSOC have not yet been fully elucidated. In this study, we performed integrative omics analyses of a series of stepwise HGSOC model cells originating from human fallopian tube secretory epithelial cells (HFTSECs) to investigate early epigenetic alterations in HGSOC tumorigenesis. Assay for transposase-accessible chromatin using sequencing (ATAC-seq), chromatin immunoprecipitation sequencing (ChIP-seq), and RNA sequencing (RNA-seq) methods were used to analyze HGSOC samples. Additionally, protein expression changes in target genes were confirmed using normal HFTSECs, serous tubal intraepithelial carcinomas (STICs), and HGSOC tissues. Transcription factor motif analysis revealed that the DNA-binding activity of the AP-1 complex and GATA family proteins was dysregulated during early tumorigenesis. The protein expression levels of JUN and FOSL2 were increased, and those of GATA6 and DAB2 were decreased in STIC lesions, which were associated with epithelial-mesenchymal transition (EMT) and proteasome downregulation. The genomic region around the FRA16D site, containing a cadherin cluster region, was epigenetically suppressed by oncogenic signaling. Proteasome inhibition caused the upregulation of chemokine genes, which may facilitate immune evasion during HGSOC tumorigenesis. Importantly, MEK inhibitor treatment reversed these oncogenic alterations, indicating its clinical effectiveness in a subgroup of patients with HGSOC. This result suggests that MEK inhibitor therapy may be an effective treatment option for chemotherapy-resistant HGSOC.

Journey of the mouse primitive endoderm: from specification to maturation

The blastocyst is a conserved stage and distinct milestone in the development of the mammalian embryo. Blastocyst stage embryos comprise three cell lineages which arise through two sequential binary cell fate specification steps. In the first, extra-embryonic trophectoderm (TE) cells segregate from inner cell mass (ICM) cells. Subsequently, ICM cells acquire a pluripotent epiblast (Epi) or extra-embryonic primitive endoderm (PrE, also referred to as hypoblast) identity. In the mouse, nascent Epi and PrE cells emerge in a salt-and-pepper distribution in the early blastocyst and are subsequently sorted into adjacent tissue layers by the late blastocyst stage. Epi cells cluster at the interior of the ICM, while PrE cells are positioned on its surface interfacing the blastocyst cavity, where they display apicobasal polarity. As the embryo implants into the maternal uterus, cells at the periphery of the PrE epithelium, at the intersection with the TE, break away and migrate along the TE as they mature into parietal endoderm (ParE). PrE cells remaining in association with the Epi mature into visceral endoderm. In this review, we discuss our current understanding of the PrE from its specification to its maturation. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.

A p300/GATA6 axis determines differentiation and Wnt dependency in pancreatic cancer models

Wnt signaling regulates the balance between stemness and differentiation in multiple tissues and in cancer. RNF43-mutant pancreatic cancers are dependent on Wnt production, and pharmacologic blockade of the pathway, e.g., by PORCN inhibitors, leads to tumor differentiation. However, primary resistance to these inhibitors has been observed. To elucidate potential mechanisms, we performed in vivo CRISPR screens in PORCN inhibitor-sensitive RNF43-mutant pancreatic cancer xenografts. As expected, genes in the Wnt pathway whose loss conferred drug resistance were identified, including APC, AXIN1, and CTNNBIP1. Unexpectedly, the screen also identified the histone acetyltransferase EP300 (p300), but not its paralog, CREBBP (CBP). We found that EP300 is silenced due to genetic alterations in all the existing RNF43-mutant pancreatic cancer cell lines that are resistant to PORCN inhibitors. Mechanistically, loss of EP300 directly downregulated GATA6 expression, thereby silencing the GATA6-regulated differentiation program and leading to a phenotypic transition from the classical subtype to the dedifferentiated basal-like/squamous subtype of pancreatic cancer. EP300 mutation and loss of GATA6 function bypassed the antidifferentiation activity of Wnt signaling, rendering these cancer cells resistant to Wnt inhibition.

Specification and role of extraembryonic endoderm lineages in the periimplantation mouse embryo

During mammalian embryo development, the correct formation of the first extraembryonic endoderm lineages is fundamental for successful development. In the periimplantation blastocyst, the primitive endoderm (PrE) is formed, which gives rise to the parietal endoderm (PE) and visceral endoderm (VE) during further developmental stages. These PrE-derived lineages show significant differences in both their formation and roles. Whereas differentiation of the PE as a migratory lineage has been suggested to represent the first epithelial-to-mesenchymal transition (EMT) in development, organisation of the epithelial VE is of utmost importance for the correct axis definition and patterning of the embryo. Despite sharing a common origin, the striking differences between the VE and PE are indicative of their distinct roles in early development. However, there is a significant disparity in the current knowledge of each lineage, which reflects the need for a deeper understanding of their respective specification processes. In this review, we will discuss the origin and maturation of the PrE, PE, and VE during the periimplantation period using the mouse model as an example. Additionally, we consider the latest findings regarding the role of the PrE-derived lineages and early embryo morphogenesis, as obtained from the most recent in vitro models.

New era of trophoblast research: integrating morphological and molecular approaches

Many pregnancy complications are the result of dysfunction in the placenta. The pathogenic mechanisms of placenta-mediated pregnancy complications, however, are unclear. Abnormal placental development in these conditions begins in the first trimester, but no symptoms are observed during this period. To elucidate effective preventative treatments, understanding the differentiation and development of human placenta is crucial. This review elucidates the uniqueness of the human placenta in early development from the aspect of structural characteristics and molecular markers. We summarise the morphogenesis of human placenta based on human specimens and then compile molecular markers that have been clarified by immunostaining and RNA-sequencing data across species. Relevant studies were identified using the PubMed database and Google Scholar search engines up to March 2020. All articles were independently screened for eligibility by the authors based on titles and abstracts. In particular, the authors carefully examined literature on human placentation. This review integrates the development of human placentation from morphological approaches in comparison with other species and provides new insights into trophoblast molecular markers. The morphological features of human early placentation are described in Carnegie stages (CS), from CS3 (floating blastocyst) to CS9 (emerging point of tertiary villi). Molecular markers are described for each type of trophoblast involved in human placental development. We summarise the character of human trophoblast cell lines and explain how long-term culture system of human cytotrophoblast, both monolayer and spheroid, established in recent studies allows for the generation of human trophoblast cell lines. Due to differences in developmental features among species, it is desirable to understand early placentation in humans. In addition, reliable molecular markers that reflect normal human trophoblast are needed to advance trophoblast research. In the clinical setting, these markers can be valuable means for morphologically and functionally assessing placenta-mediated pregnancy complications and provide early prediction and management of these diseases.

GATA6 phosphorylation by Erk1/2 propels exit from pluripotency and commitment to primitive endoderm

The transcription factor GATA6 and the Fgf/Ras/MAPK signaling pathway are essential for the development of the primitive endoderm (PrE), one of the two lineages derived from the pluripotent inner cell mass (ICM) of mammalian blastocysts. A mutant mouse line in which Gata6-coding exons are replaced with H2BGFP (histone H2B Green Fluorescence Protein fusion protein) was developed to monitor Gata6 promoter activity. In the Gata6-H2BGFP heterozygous blastocysts, the ICM cells that initially had uniform GFP fluorescence signal at E3.5 diverged into two populations by the 64-cell stage, either as the GFP-high PrE or the GFP-low epiblasts (Epi). However in the GATA6-null blastocysts, the originally moderate GFP expression subsided in all ICM cells, indicating that the GATA6 protein is required to maintain its own promoter activity during PrE linage commitment. In embryonic stem cells, expressed GATA6 was shown to bind and activate the Gata6 promoter in PrE differentiation. Mutations of a conserved serine residue (S264) for Erk1/2 phosphorylation in GATA6 protein drastically impacted its ability to activate its own promoter. We conclude that phosphorylation of GATA6 by Erk1/2 compels exit from pluripotent state, and the phosphorylation propels a GATA6 positive feedback regulatory circuit to compel PrE differentiation. Our findings resolve the longstanding question on the dual requirements of GATA6 and Ras/MAPK pathway for PrE commitment of the pluripotent ICM.

Epigenetic regulation of histone modifications and Gata6 gene expression induced by maternal diet in mouse embryoid bodies in a model of developmental programming

Background

Dietary interventions during pregnancy alter offspring fitness. We have shown mouse maternal low protein diet fed exclusively for the preimplantation period (Emb-LPD) before return to normal protein diet (NPD) for the rest of gestation, is sufficient to cause adult offspring cardiovascular and metabolic disease. Moreover, Emb-LPD blastocysts sense altered nutrition within the uterus and activate compensatory cellular responses including stimulated endocytosis within extra-embryonic trophectoderm and primitive endoderm (PE) lineages to protect fetal growth rate. However, these responses associate with later disease. Here, we investigate epigenetic mechanisms underlying nutritional programming of PE that may contribute to its altered phenotype, stabilised during subsequent development. We use embryonic stem (ES) cell lines established previously from Emb-LPD and NPD blastocysts that were differentiated into embryoid bodies (EBs) with outer PE-like layer.

Results

Emb-LPD EBs grow to a larger size than NPD EBs and express reduced Gata6 transcription factor (regulator of PE differentiation) at mRNA and protein levels, similar to Emb-LPD PE derivative visceral yolk sac tissue in vivo in later gestation. We analysed histone modifications at the Gata6 promoter in Emb-LPD EBs using chromatin immunoprecipitation assay. We found significant reduction in histone H3 and H4 acetylation and RNA polymerase II binding compared with NPD EBs, all markers of reduced transcription. Other histone modifications, H3K4Me2, H3K9Me3 and H3K27Me3, were unaltered. A similar but generally non-significant histone modification pattern was found on the Gata4 promoter. Consistent with these changes, histone deacetylase Hdac-1, but not Hdac-3, gene expression was upregulated in Emb-LPD EBs.

Conclusions

First, these data demonstrate ES cells and EBs retain and propagate nutritional programming adaptations in vitro, suitable for molecular analysis of mechanisms, reducing animal use. Second, they reveal maternal diet induces persistent changes in histone modifications to regulate Gata6 expression and PE growth and differentiation that may affect lifetime health.

Formation of a polarised primitive endoderm layer in embryoid bodies requires fgfr/erk signalling

The primitive endoderm arises from the inner cell mass during mammalian pre-implantation development. It faces the blastocoel cavity and later gives rise to the extraembryonic parietal and visceral endoderm. Here, we investigate a key step in primitive endoderm development, the acquisition of apico-basolateral polarity and epithelial characteristics by the non-epithelial inner cell mass cells. Embryoid bodies, formed from mouse embryonic stem cells, were used as a model to study this transition. The outer cells of these embryoid bodies were found to gradually acquire the hallmarks of polarised epithelial cells and express markers of primitive endoderm cell fate. Fgf receptor/Erk signalling is known to be required for specification of the primitive endoderm, but its role in polarisation of this tissue is less well understood. To investigate the function of this pathway in the primitive endoderm, embryoid bodies were cultured in the presence of a small molecule inhibitor of Mek. This inhibitor caused a loss of expression of markers of primitive endoderm cell fate and maintenance of the pluripotency marker Nanog. In addition, a mislocalisation of apico-basolateral markers and disruption of the epithelial barrier, which normally blocks free diffusion across the epithelial cell layer, occurred. Two inhibitors of the Fgf receptor elicited similar phenotypes, suggesting that Fgf receptor signalling promotes Erk-mediated polarisation. This data shows that primitive endoderm cells of the outer layer of embryoid bodies gradually polarise, and formation of a polarised primitive endoderm layer requires the Fgf receptor/Erk signalling pathway.

Role of GATA factors in development, differentiation, and homeostasis of the small intestinal epithelium

The small intestinal epithelium develops from embryonic endoderm into a highly specialized layer of cells perfectly suited for the digestion and absorption of nutrients. The development, differentiation, and regeneration of the small intestinal epithelium require complex gene regulatory networks involving multiple context-specific transcription factors. The evolutionarily conserved GATA family of transcription factors, well known for its role in hematopoiesis, is essential for the development of endoderm during embryogenesis and the renewal of the differentiated epithelium in the mature gut. We review the role of GATA factors in the evolution and development of endoderm and summarize our current understanding of the function of GATA factors in the mature small intestine. We offer perspective on the application of epigenetics approaches to define the mechanisms underlying context-specific GATA gene regulation during intestinal development.

Atypical protein kinase C couples cell sorting with primitive endoderm maturation in the mouse blastocyst

During mouse pre-implantation development, extra-embryonic primitive endoderm (PrE) and pluripotent epiblast precursors are specified in the inner cell mass (ICM) of the early blastocyst in a ‘salt and pepper’ manner, and are subsequently sorted into two distinct layers. Positional cues provided by the blastocyst cavity are thought to be instrumental for cell sorting; however, the sequence of events and the mechanisms that control this segregation remain unknown. Here, we show that atypical protein kinase C (aPKC), a protein associated with apicobasal polarity, is specifically enriched in PrE precursors in the ICM prior to cell sorting and prior to overt signs of cell polarisation. aPKC adopts a polarised localisation in PrE cells only after they reach the blastocyst cavity and form a mature epithelium, in a process that is dependent on FGF signalling. To assess the role of aPKC in PrE formation, we interfered with its activity using either chemical inhibition or RNAi knockdown. We show that inhibition of aPKC from the mid blastocyst stage not only prevents sorting of PrE precursors into a polarised monolayer but concomitantly affects the maturation of PrE precursors. Our results suggest that the processes of PrE and epiblast segregation, and cell fate progression are interdependent, and place aPKC as a central player in the segregation of epiblast and PrE progenitors in the mouse blastocyst.

Functional evaluation of ES cell-derived endodermal populations reveals differences between Nodal and Activin A-guided differentiation

Embryonic stem (ES) cells hold great promise with respect to their potential to be differentiated into desired cell types. Of interest are organs derived from the definitive endoderm, such as the pancreas and liver, and animal studies have revealed an essential role for Nodal in development of the definitive endoderm. Activin A is a related TGFβ member that acts through many of the same downstream signaling effectors as Nodal and is thought to mimic Nodal activity. Detailed characterization of ES cell-derived endodermal cell types by gene expression analysis in vitro and functional analysis in vivo reveal that, despite their similarity in gene expression, Nodal and Activin-derived endodermal cells exhibit a distinct difference in functional competence following transplantation into the developing mouse embryo. Pdx1-expressing cells arising from the respective endoderm populations exhibit extended differences in their competence to mature into insulin/c-peptide-expressing cells in vivo. Our findings underscore the importance of functional cell-type evaluation during stepwise differentiation of stem cells.

Early cell fate decisions in the mouse embryo

During mammalian preimplantation development, the fertilised egg gives rise to a group of pluripotent embryonic cells, the epiblast, and to the extraembryonic lineages that support the development of the foetus during subsequent phases of development. This preimplantation period not only accommodates the first cell fate decisions in a mammal's life but also the transition from a totipotent cell, the zygote, capable of producing any cell type in the animal, to cells with a restricted developmental potential. The cellular and molecular mechanisms governing the balance between developmental potential and lineage specification have intrigued developmental biologists for decades. The preimplantation mouse embryo offers an invaluable system to study cell differentiation as well as the emergence and maintenance of pluripotency in the embryo. Here we review the most recent findings on the mechanisms controlling these early cell fate decisions. The model that emerges from the current evidence indicates that cell differentiation in the preimplantation embryo depends on cellular interaction and intercellular communication. This strategy underlies the plasticity of the early mouse embryo and ensures the correct specification of the first mammalian cell lineages.

Comparative proteomic analysis of differentiation of mouse F9 embryonic carcinoma cells induced by retinoic acid

The multipotent mouse F9 embryonic carcinoma cell is an ideal model system to investigate the mechanism of retinoic acid (RA) in cell differentiation and cell growth control and the biochemical basis of early embryonic development. We reported here a proteomics approach to study protein expression changes during the differentiation of F9 cells into the visceral endoderm. F9 cells were incubated with or without RA at 0, 24, 48, and 72 h. Total proteins extracted were separated by two-dimensional electrophoresis (2-DE) and the protein patterns on the gels were comparatively analyzed by computer. Approximately 1,100 protein spots were detected in the F9 proteome, within the pH 3-10 range. Fourteen protein spots which the levels of expression were found to be altered dramatically during the F9 cells differentiating, and were identified by MALDI-TOF MS or ESI-MS/MS. These proteins included metabolism enzymes, HSP60s, RAN, hnRNP K, FUBP1, VDAC1, STI1, and prohibitin. These proteins are involved in cellar metabolism, gene expression regulation, stress response, and apoptosis, respectively. The data from proteomic analyze are consistent with the result obtained from Western blot analysis. This study increases our understanding of the proteomics changes during F9 cells differentiation induced by RA.

Conversion from mouse embryonic to extra-embryonic endoderm stem cells reveals distinct differentiation capacities of pluripotent stem cell states

The inner cell mass of the mouse pre-implantation blastocyst comprises epiblast progenitor and primitive endoderm cells of which cognate embryonic (mESCs) or extra-embryonic (XEN) stem cell lines can be derived. Importantly, each stem cell type retains the defining properties and lineage restriction of their in vivo tissue of origin. Recently, we demonstrated that XEN-like cells arise within mESC cultures. This raises the possibility that mESCs can generate self-renewing XEN cells without the requirement for gene manipulation. We have developed a novel approach to convert mESCs to XEN cells (cXEN) using growth factors. We confirm that the downregulation of the pluripotency transcription factor Nanog and the expression of primitive endoderm-associated genes Gata6, Gata4, Sox17 and Pdgfra are necessary for cXEN cell derivation. This approach highlights an important function for Fgf4 in cXEN cell derivation. Paracrine FGF signalling compensates for the loss of endogenous Fgf4, which is necessary to exit mESC self-renewal, but not for XEN cell maintenance. Our cXEN protocol also reveals that distinct pluripotent stem cells respond uniquely to differentiation promoting signals. cXEN cells can be derived from mESCs cultured with Erk and Gsk3 inhibitors (2i), and LIF, similar to conventional mESCs. However, we find that epiblast stem cells (EpiSCs) derived from the post-implantation embryo are refractory to cXEN cell establishment, consistent with the hypothesis that EpiSCs represent a pluripotent state distinct from mESCs. In all, these findings suggest that the potential of mESCs includes the capacity to give rise to both extra-embryonic and embryonic lineages.

GATA6 and FOXA2 regulate Wnt6 expression during extraembryonic endoderm formation

One of the earliest epithelial-to-mesenchymal transitions in mouse embryogenesis involves the differentiation of inner cell mass cells into primitive and then into parietal endoderm. These processes can be recapitulated in vitro using F9 teratocarcinoma cells, which differentiate into primitive endoderm when treated with retinoic acid (RA) and into parietal endoderm with subsequent treatment with dibutyryl cyclic adenosine monophosphate (db-cAMP). Our previous work on how primitive endoderm develops revealed that the Wnt6 gene is upregulated by RA, leading to the activation of the canonical WNT-β-catenin pathway. The mechanism by which Wnt6 is regulated was not determined, but in silico analysis of the human WNT6 promoter region had suggested that the GATA6 and FOXA2 transcription factors might be involved [1]. Subsequent analysis determined that both Gata6 and Foxa2 mRNA are upregulated in F9 cells treated with RA or RA and db-cAMP. More specifically, overexpression of Gata6 or Foxa2 alone induced molecular and morphological markers of primitive endoderm, which occurred concomitantly with the upregulation of the Wnt6 gene. Gata6- or Foxa2-overexpressing cells were also found to have increased levels in T-cell factor (TCF)-dependent transcription, and when these cells were treated with db-cAMP, they developed into parietal endoderm. Chromatin immunoprecipitation analysis revealed that GATA6 and FOXA2 were bound to the Wnt6 promoter, and overexpression studies showed that these transcription factors were sufficient to switch on the gene expression of a Wnt6 reporter construct. Together, these results provide evidence for the direct regulation of Wnt6 that leads to the activation of the canonical WNT-β-catenin pathway and subsequent induction of primitive extraembryonic endoderm.

Feed-back regulation of disabled-2 (Dab2) p96 isoform for GATA-4 during differentiation of F9 cells

F9 embryonic carcinoma (EC) cells undergo extra-embryonic endodermal (ExE) differentiation in response to retinoic acid (RA) treatment, which induces the expression of two isoforms (p96 and p67) of the adaptor protein, Disabled-2 (Dab2). In the current study, constitutive and ectopic expression of the p96 isoform induced ExE differentiation in F9 EC cells in the absence of RA treatment via the activation of GATA-4 by p96. During the RA-induced differentiation process, Dab2 expression is induced by the GATA factors in a coherent feed-forward loop; on the other hand, we showed that p96 regulates GATA-4 in a positive feed-back manner in this study. Our results indicate that p96 Dab2 plays a key role in the ExE differentiation process.

Rewind to recover: dedifferentiation after cardiac injury

In adult mammals, cardiomyocytes are known to reactivate an embryonic gene-expression program after injury. In this issue of Cell Stem Cell, Kubin et al. (2011) show that oncostatin M regulates this dedifferentiation which, while beneficial for recovery from acute injury, if persistent results in heart failure in both rodents and humans.

GATA6 promotes colon cancer cell invasion by regulating urokinase plasminogen activator gene expression

GATA6 is a zinc finger transcription factor expressed in the colorectal epithelium. We have examined the expression of GATA6 in colon cancers and investigated the mechanisms by which GATA6 regulates colon cancer cell invasion. GATA6 was overexpressed in colorectal polyps and primary and metastatic tumors. GATA6 was strongly expressed in both the nuclear and cytoplasmic compartments of the colon cancer cells. GATA6 expression was upregulated in invasive HT29 and KM12L4 cells compared with the parental HT29 and KM12 cells and positively correlated with urokinase-type plasminogen activator (uPA) gene expression. Small interfering RNA (siRNA) knockdown of GATA6 resulted in reduced uPA gene expression and cell invasion. GATA6 bound to the uPA gene regulatory sequences in vivo and activated uPA promoter activity in vitro. uPA promoter deletion analysis indicated that the promoter proximal Sp1 sites were required for GATA6 activation of the uPA promoter. Accordingly, GATA6 physically associated with Sp1 and siRNA knockdown of Sp1 decreased GATA6 activation of the uPA promoter activity suggesting that Sp1 recruits GATA6 to the uPA promoter and mediates GATA6 induced activation of the uPA promoter activity. On the basis of our results, we conclude that GATA6 is an important regulator of uPA gene expression, and the dysregulated expression of GATA6 contributes to colorectal tumorigenesis and tumor invasion.

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.

Smad4-dependent pathways control basement membrane deposition and endodermal cell migration at early stages of mouse development

Background

Smad4 mutant embryos arrest shortly after implantation and display a characteristic shortened proximodistal axis, a significantly reduced epiblast, as well as a thickened visceral endoderm layer. Conditional rescue experiments demonstrate that bypassing the primary requirement for Smad4 in the extra-embryonic endoderm allows the epiblast to gastrulate. Smad4-independent TGF-β signals are thus sufficient to promote mesoderm formation and patterning. To further analyse essential Smad4 activities contributed by the extra-embryonic tissues, and characterise Smad4 dependent pathways in the early embryo, here we performed transcriptional profiling of Smad4 null embryonic stem (ES) cells and day 4 embryoid bodies (EBs).

Results

Transcripts from wild-type versus Smad4 null ES cells and day 4 EBs were analysed using Illumina arrays. In addition to several known TGF-β/BMP target genes, we identified numerous Smad4-dependent transcripts that are mis-expressed in the mutants. As expected, mesodermal cell markers were dramatically down-regulated. We also observed an increase in non-canonical potency markers (Pramel7, Tbx3, Zscan4), germ cell markers (Aire, Tuba3a, Dnmt3l) as well as early endoderm markers (Dpp4, H19, Dcn). Additionally, expression of the extracellular matrix (ECM) remodelling enzymes Mmp14 and Mmp9 was decreased in Smad4 mutant ES and EB populations. These changes, in combination with increased levels of laminin alpha1, cause excessive basement membrane deposition. Similarly, in the context of the Smad4 null E6.5 embryos we observed an expanded basement membrane (BM) associated with the thickened endoderm layer.

Conclusion

Smad4 functional loss results in a dramatic shift in gene expression patterns and in the endodermal cell lineage causes an excess deposition of, or an inability to breakdown and remodel, the underlying BM layer. These structural abnormalities probably disrupt reciprocal signalling between the epiblast and overlying visceral endoderm required for gastrulation.

Loss of GATA4 and GATA6 expression specifies ovarian cancer histological subtypes and precedes neoplastic transformation of ovarian surface epithelia

BACKGROUND

The family of zinc finger-containing GATA transcription factors plays critical roles in cell lineage specification during early embryonic development and organ formation. GATA4 and GATA6 were found to be frequently lost in ovarian cancer, and the loss is proposed to account for dedifferentiation of the cancer cells.

METHODOLOGY/PRINCIPAL FINDINGS

We further investigated the expression of GATA4 and GATA6 in ovarian surface epithelial lesions and histological subtypes of ovarian carcinomas by immunostaining. GATA4 and GATA6 were found to be absent in high percentages (80 to 90%) of serous, clear cell, and endometrioid ovarian cancer examined. In contrast, both were found positive in 11 out of 12 cases of mucinous carcinomas, suggesting the expression of the GATA factors can distinguish mucinous cancer from other histological subtypes. GATA4 was frequently lost in preneoplastic lesions such as morphologically normal inclusion cysts and epithelial hyperplasia adjacent to malignant cells. The loss of GATA6 correlates closely with neoplastic morphological transformation of ovarian surface epithelia. In culture, GATA4 expression was progressively reduced upon passaging primary ovarian surface epithelial cells, which correlated with changes in histone modification of the GATA4 locus. A reduced GATA6 gene dosage as in GATA6 (+/-) mice led to an increased pre-neoplastic changes and inclusion cysts in the ovaries, suggesting the loss of GATA6 contributes to ovarian cancer development.

CONCLUSIONS/SIGNIFICANCE

This study suggests that the expression status of GATA4 and GATA6 may dictate distinct pathologic pathways leading to serous or mucinous ovarian carcinomas. The readily loss of GATA4 expression through changes in chromatin conformation suggests a potential non-phenotypic initiating event, leading to subsequent loss of GATA6, morphological transformation, and ultimate tumorigenesis.

Dab2 regulates clathrin assembly and cell spreading

The recruitment of clathrin to the membrane and its assembly into coated pits results from its interaction with endocytic adaptors and other regulatory proteins in the context of a specific lipid microenvironment. Dab2 (disabled 2) is a mitotic phosphoprotein and a monomeric adaptor for clathrin-mediated endocytosis. In the present study, we employed GFP (green fluorescent protein) fusion constructs of different isoforms and mutants of rat Dab2 and characterized their effect on the size, distribution and dynamics of clathrin assemblies. Enhanced levels of expression of the p82 isoform of Dab2 in COS7 cells induced enlarged clathrin assemblies at the plasma membrane. p82-clathrin assemblies, which concentrate additional endocytic proteins, such as AP2 (adaptor protein 2) and epsin, are dynamic structures in which both p82 and clathrin exchange actively between the membrane-bound and cytosolic sub-populations. The ability of p82 to induce enlarged clathrin assemblies is dependent on the presence of a functional PTB domain (phosphotyrosine-binding domain), on binding to clathrin and phospholipids, and on a newly identified and evolutionarily conserved poly-lysine stretch which precedes the PTB domain. These same molecular features are required for Dab2 to enhance the spreading of COS7 cells on fibronectin. The ability of the p82 isoform of Dab2 to enhance cell spreading was confirmed in both HeLa cells and HBL cells (human breast epithelial cells). COS7 cells expressing GFP-p82 and plated on to fibronectin concentrate the beta1 integrin into clathrin-p82 assemblies. Furthermore, during cell spreading, p82-clathrin assemblies concentrate at the site of the initial cell-matrix contact and are absent from regions of intense membrane ruffling. We propose a role for Dab2 and clathrin in integrin-mediated cell spreading.

Integrins are required for the differentiation of visceral endoderm

Integrins of the beta1 subfamily are highly expressed in the early mouse embryo and are essential for the formation of primitive germ layers from the inner cell mass (ICM). We investigated the mechanisms by which alphabeta1 integrins regulate ICM morphogenesis by using the embryonic-stem-cell-derived embryoid body (EB), a model for peri-implantation development. Ablation of integrin beta1 in EBs resulted in endoderm detachment and in maturation defects, which were manifested by the mislocalization of GATA4 in the cytoplasm and the markedly reduced synthesis of basement membrane (BM) components and the lineage marker disabled homolog 2. The mutant endoderm cells failed to spread on BM substrates, but could spread on vitronectin, which induced upregulation of alphavbeta3 integrin and integrin-dependent GATA4 nuclear translocation. Forced expression of integrin beta3 in the mutant EBs completely rescued endoderm morphogenesis, suggesting that integrin beta3 can substitute for integrin beta1 in the endoderm. Furthermore, the mitogen-activated protein kinases (MAPKs) ERK1 and ERK2 (ERK1/2) and p38 were activated in endoderm in an integrin-dependent fashion. Pharmacological inhibition of ERK1/2 or p38 MAPK blocked vitronectin-induced GATA4 nuclear translocation and endoderm maturation, whereas expression of a constitutively active ERK kinase (MEK1) or p38 MAPK in the mutant cells rescued endoderm maturation in integrin-beta1-null endoderm cells. Collectively, these results suggest that integrins are required for both the stable adhesion and maturation of visceral endoderm, the latter being mediated through the activation of ERK1/2 and p38 MAPK.

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

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

Dickkopf (Dkk) 1 promotes the differentiation of mouse embryonic stem cells toward neuroectoderm

Wnt signaling has been demonstrated to have extensive roles during embryogenesis. The Wnt family is highly conserved. In mice, there are 19 Wnt genes. Dickkopf (Dkk), through its interactions with Wnt co-receptors, low-density lipoprotein receptor-related protein (LRP), Frizzled and Kremen, can act as a negative regulator to block the Wnt-signaling pathway. There are four Dkk genes in the human genome, and three in that of the mouse. Dkk1 is involved in a variety of craniofacial developmental processes and behaves as a strong head inducer and limb regulator. Dkk1 mutant mice are embryonic-lethal. Here, we investigated the effects of Dkk1 on the differentiation of murine ESCs in both the ESC and embryoid body (EB) states. The results demonstrate that Dkk1 overexpression can initiate the differentiation program of ESCs toward neuroectoderm. We believe this finding can augment our understanding of mouse ESC differentiation.

Dynamic expression of Dab2 in the mouse embryonic central nervous system

BACKGROUND

Dab2, one of two mammalian orthologs of Drosophila Disabled, has been shown to be involved in cell positioning and formation of visceral endoderm during mouse embryogenesis, but its role in neuronal development is not yet fully understood. In this report, we have examined the localization of the Dab2 protein in the mouse embryonic central nervous system (CNS) at different developmental stages.

RESULTS

Dab2 protein was transiently expressed in rhombomeres 5 and 6 of the developing hindbrain between E8.5 and E11.5, and in the floor plate of the neural tube from E9.5 to E12.5, following which it was no longer detectable within these regions. Dab2 protein was also identified within circumventricular organs including the choroid plexus, subcommissural organ and pineal gland during their early development. While Dab2 was still strongly expressed in the adult choroid plexus, immunoreactivity within the subcommissural organ and pineal gland was lost after birth. In addition, Dab2 was transiently expressed within a subpopulation of Iba1-positive mononuclear phagocytes (including presumed microglial progenitors) within the neural tube from E10.0 and was lost by E14.5. Dab2 was separately localized to Iba1 positive cells from E9.5 and subsequently to F4/80 positive cells (mature macrophage/myeloid-derived dendritic cells) positioned outside the neural tube from E12.5 onwards, implicating Dab2 expression in early cells of the mononuclear phagocyte lineage. Dab2 did not co-localize with the pan-neuronal marker PGP9.5 at any developmental stage, suggesting that Dab2 positive cells in the developing CNS are unlikely to be differentiating neurons.

CONCLUSION

This is the first study to demonstrate the dynamic spatiotemporal expression of Dab2 protein within the CNS during development.

Promoter-dependent EGFP expression during embryonic stem cell propagation and differentiation

Genetic modification is an important tool in embryonic stem (ES) cell research and requires efficient promoter systems. Here, we have compared the transcriptional activities of three ubiquitous promoters, elongation factor-1alpha (EF1alpha), phosphoglycerate kinase-1 (PGK), and cytomegalovirus (CMV), during propagation and differentiation of mouse (m) ES cells by using stable mES cell lines expressing enhanced green fluorescent protein (EGFP) under each of these promoters. In undifferentiated ES cells, the EGFP expression driven by the EF1alpha was most stable, followed by the PGK, whereas the down-regulation of EGFP expression driven by the CMV promoter was most significant during propagation up to passage 35. A similar pattern for the activities of these promoters was observed in embryoid bodies (EBs) during 14 days of differentiation, with brighter EGFP signals driven by the EF1alpha promoter versus the other two. Moreover, the EF1alpha and PGK promoters, but not CMV, were effective in almost all mES cell-differentiated neuronal cells, cardiomyocytes, and visceral endoderm cells, with the fluorescent signal intensity higher for EF1alpha and even for PGK. The CMV promoter yielded a weak fluorescent signal in about 60-80% of these differentiated cells, while a few differentiated cells with the CMV promoter showed bright EGFP expression like that with the EF1alpha promoter. These results extend previous observations for the activities of these promoters in mES cells and provide new information for choosing appropriate promoters to facilitate genetic modification of mES cells.

Retinoic acid maintains self-renewal of murine embryonic stem cells via a feedback mechanism

Embryonic stem cells (ESCs) are pluripotent cells derived from the inner cell mass (ICM) that are able to self-renew or undergo differentiation depending on a complex interplay of extracellular signals and intracellular factors. However, the feedback regulation of differentiation-dependent ESC self-renewal is poorly understood. Retinoic acid (RA), a derivative of vitamin A, plays a critical role in ESC differentiation and embryogenesis. In the present study, we demonstrate that short-term treatment of murine (m) ESCs with RA during the early differentiation stage prevented spontaneous differentiation of mESCs. The RA-treated cells maintained self-renewal capacity and could differentiate into neuronal cells, cardiomyocytes, and visceral endoderm cells derived from three germ layers. The differentiation-inhibitory effect of RA was mimicked by conditioned medium from RA-treated ESCs and was accompanied with up-regulated expression of leukemia inhibitory factor (LIF), Wnt3a, Wnt5a, and Wnt6. Such RA-induced prevention of ESC differentiation was attenuated by a neutralizing antibody against LIF or by a specific Wnt antagonist Fz8-Fc and was totally reversed in the presence of both of them. Furthermore, knock-down of beta-catenin, a component of the Wnt signaling pathway, by small interfering RNA counteracted the effect of RA. In addition, RA treatment enhanced expression of endodermal markers GATA4 and AFP but inhibited expression of primitive ectodermal marker Fgf-5 and mesodermal marker Brachyury. These findings reveal a novel role of RA in ESC self-renewal and provide new insight into the regulatory mechanism of differentiation-dependent self-renewal of ESCs, in which Wnt proteins and LIF induced by RA have the synergistic action. The short-term treatment of ESCs with RA also offers a unique model system for study of the regulatory mechanism that controls self-renewal and specific germ-layer differentiation of ESCs.

Comparative transcriptome analysis of embryonic and adult stem cells with extended and limited differentiation capacity

Comparison of the transcriptomes of pluripotent embryonic stem cells, multipotent adult progenitor cells and lineage restricted mesenchymal stem cells identified a unique gene expression profile of multipotent adult progenitor cells.

Background

Recently, several populations of postnatal stem cells, such as multipotent adult progenitor cells (MAPCs), have been described that have broader differentiation ability than classical adult stem cells. Here we compare the transcriptome of pluripotent embryonic stem cells (ESCs), MAPCs, and lineage-restricted mesenchymal stem cells (MSCs) to determine their relationship.

Results

Applying principal component analysis, non-negative matrix factorization and k-means clustering algorithms to the gene-expression data, we identified a unique gene-expression profile for MAPCs. Apart from the ESC-specific transcription factor Oct4 and other ESC transcripts, some of them associated with maintaining ESC pluripotency, MAPCs also express transcripts characteristic of early endoderm and mesoderm. MAPCs do not, however, express Nanog or Sox2, two other key transcription factors involved in maintaining ESC properties. This unique molecular signature was seen irrespective of the microarray platform used and was very similar for both mouse and rat MAPCs. As MSC-like cells isolated under MAPC conditions are virtually identical to MSCs, and MSCs cultured in MAPC conditions do not upregulate MAPC-expressed transcripts, the MAPC signature is cell-type specific and not merely the result of differing culture conditions.

Conclusion

Multivariate analysis techniques clustered stem cells on the basis of their expressed gene profile, and the genes determining this clustering reflected the stem cells' differentiation potential in vitro. This comparative transcriptome analysis should significantly aid the isolation and culture of MAPCs and MAPC-like cells, and form the basis for studies to gain insights into genes that confer on these cells their greater developmental potency.

GATA factors induce mouse embryonic stem cell differentiation toward extraembryonic endoderm

The GATA family of transcription factors are implicated in early embryonic development. There are six factors in this family in vertebrates. GATA4 and GATA6 have been demonstrated to induce mouse embryonic stem (mES) cells differentiation toward extraembryonic endoderm (ExE). We investigated the effect of GATA3 on the differentiation of mES cells both in the ES cell and in the embryoid body (EB) states. The results demonstrate that GATA3 overexpression can initiate the ES cell differentiation program toward ExE. Furthermore, overexpression of GATA1 and GATA2 in ES cells and EBs resulted in similar effects. We believe this finding can augment our understanding of mouse ES cell differentiation.

GATA-6 mediates human bladder smooth muscle differentiation: involvement of a novel enhancer element in regulating alpha-smooth muscle actin gene expression

Hollow organs exposed to pathological stimuli undergo phenotypic modulation characterized by altered expression of smooth muscle contractile proteins and loss of normal function. The molecular mechanisms that regulate smooth muscle differentiation, especially in organs other than the vasculature, are poorly understood. In this study, we describe a role for the GATA-6 transcription factor in regulation of human bladder smooth muscle differentiation. Knockdown of endogenous GATA-6 in primary human bladder smooth muscle cells (pBSMC) led to decreased mRNA levels of the differentiation markers alpha-smooth muscle actin (alpha-SMA), calponin, and smooth muscle myosin heavy chain. Similar effects were obtained following downregulation of GATA-6 by forskolin-induced elevation of intracellular cAMP levels. Forskolin treatment of pBSMC abolished recruitment of GATA-6 to the alpha-SMA promoter in vivo and reduced activity of human alpha-SMA promoter-directed gene expression by >60%. This inhibitory effect was rescued by enforced expression of wild-type GATA-6 but not by a zinc-finger-deleted mutant, GATA-6-DeltaZF, which lacks DNA-binding ability. In silico analysis of a region of the human alpha-SMA promoter, described previously as a transcriptional enhancer, identified a putative GATA-binding site at position -919/-913. Point mutation of this site in SMA-Luc abrogated GATA-6-induced activation of promoter activity. Together, these results provide the first evidence for a functional role for GATA-6 in regulation of bladder smooth muscle differentiation. In addition, these findings demonstrate that GATA-6 regulates human alpha-SMA expression via a novel regulatory cis element in the alpha-SMA promoter-enhancer.

Gene function in mouse embryogenesis: get set for gastrulation

During early mouse embryogenesis, temporal and spatial regulation of gene expression and cell signalling influences lineage specification, embryonic polarity, the patterning of tissue progenitors and the morphogenetic movement of cells and tissues. Uniquely in mammals, the extraembryonic tissues are the source of signals for lineage specification and tissue patterning. Here we discuss recent discoveries about the lead up to gastrulation, including early manifestations of asymmetry, coordination of cell and tissue movements and the interactions of transcription factors and signalling activity for lineage allocation and germ-layer specification.

Isolation and characterization of porcine visceral endoderm cell lines derived from in vivo 11-day blastocysts

Two porcine cell lines of yolk-sac visceral endoderm, designated as PE-1 and PE-2, were derived from in vivo 11-d porcine blastocysts that were either ovoid (PE-1) or at the early tubular stage of elongation (PE-2). Primary and secondary culture of the cell lines was done on STO feeder cells. The PE-1 and PE-2 cells morphologically resembled visceral endoderm previously cultured from in vivo-derived ovine and equine blastocysts and from in vitro-derived bovine blastocysts. Analysis of the PE-1- and PE-2-conditioned medium by 2D-gel electrophoresis and matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry demonstrated that they produced serum proteins. Reverse transcriptase polymerase chain reaction analysis showed that the cells expressed several genes typical for yolk-sac endoderm differentiation and function including GATA-6, DAB-2, REX-1, HNF-1, transthyretin, alpha-fetoprotein, and albumin. Unlike a porcine liver cell line, the PE-1 and PE-2 cell lines had relatively low inducible P-450 content and EROD activity, and, while they cleared ammonia from the cell culture medium, they did not produce urea. Transmission electron microscopy revealed that the cells were a polarized epithelium connected by complex junctions resembling tight junctions and by lateral desmosomes. Rough endoplasmic reticulum was prominent within the cells. Immunocytochemistry indicated that the PE-1 cells expressed cytokeratin 18 and had robust microtubule networks similar to those observed in in vivo porcine yolk-sac endoderm. Metaphase spreads prepared at passage 26 of the PE-1 cell line indicated a diploid porcine karyotype of 38 chromosomes. The cells have been grown for over 1 yr for multiple passages at 1:10 or 1:20 split ratios on STO feeder cells. The cell lines will be of interest as an in vitro model of the porcine preimplantation yolk-sac tissue.

Gene expression pattern and progression of embryogenesis in the immediate post-implantation period of mouse development

During development of the mouse conceptus from implantation to the early gastrula stage, a multitude of genes encoding structural proteins, transcription factors and components of signalling pathways are expressed in the extraembryonic and embryonic tissues derived from the trophectoderm and the inner cell mass. Some genes are expressed widely in the extraembryonic ectoderm, the visceral endoderm or the epiblast, while others display more restricted expression domains in these tissues or are expressed upon the specification of the germ layers at gastrulation. Overall, the developmental changes in gene expression mirror key events of embryogenesis, and reveal the regionalization of signalling activity and the emergence of tissue patterning.

Frequent loss of Dab2 protein and infrequent promoter hypermethylation in breast cancer

Disabled-2 (Dab2), a putative tumor suppressor protein, is lost in 80-90% ovarian tumors and ovarian/breast cancer cell lines. The clinical significance of Dab2 protein in breast cancer remains yet unknown. Immunohistochemical analysis of Dab2 protein showed no detectable expression in 67/91 (74%) breast tumors, while all 10 normal tissues showed presence of Dab2 protein. We hypothesized that epigenetic silencing of Dab2 may account for loss of protein in breast cancer. Methylation of Dab2 exon 1, a putative promoter, was analyzed in six breast cancer cell lines and in 54 primary breast tumors by methylation specific PCR. Methylation was observed in MDA-MB-231 and MDA-MB-157 cells and in 6 of 54 (11%) primary breast tumors that also showed loss of Dab2 protein. Expression of Dab2 transcripts was detected in all cell lines except MDA-MB-157. However, none of these six cell lines showed detectable levels of Dab2 protein by western blotting, while non-malignant mammary epithelial cell line MCF 10A showed Dab2 protein expression. To our knowledge this is the first report showing low frequency of Dab2 (putative) promoter methylation (11%) in primary breast tumors. Frequent loss of Dab2 protein (74%) suggest that hypermethylation of Dab2 promoter may only be one of the mechanisms accounting for its loss in breast cancer. Further, in silico analysis of Dab2 3'-UTR revealed existence of miRNA complimentary to this region of the gene, suggesting microRNA mediated targeting of Dab2 mRNA might account for loss of the protein in breast cancer.

Gene expression profiling of differentiating embryonic stem cells expressing dominant negative fibroblast growth factor receptor 2

Embryonic stem (ES) cells are derived from the inner cell mass of the blastocyst and can be cultured as three-dimensional embryoid bodies (EBs) in which embryonic pregastrulation stages are faithfully mimicked. Fibroblast growth factor receptors (mainly FGFR2) are involved in the first differentiation events during early mammalian embryogenesis. It has been demonstrated that the presence of FGFR2 is a prerequisite for laminin-111 and collagen type IV synthesis and subsequently basement membrane formation in EBs. To identify genes that are influenced by FGFR signalling, we performed global gene expression profiling of differentiating EBs expressing dominant negative FGFR2 (dnFGFR2), acquiring an extensive catalogue of down- and up-regulated genes. We show a strong down-regulation of endodermal and basement membrane related genes, which strengthen the view that the FGFR signalling pathway is a main stimulator of basement membrane synthesis in EBs. We further present down-regulation of genes previously not linked to FGFR signalling, and in addition an active transcription of some mesodermal related genes in differentiating dnFGFR2 EBs.

Histone modifications silence the GATA transcription factor genes in ovarian cancer

Altered expression of GATA factors was found and proposed as the underlying mechanism for dedifferentiation in ovarian carcinogenesis. In particular, GATA6 is lost or excluded from the nucleus in 85% of ovarian tumors and GATA4 expression is absent in majority of ovarian cancer cell lines. Here, we evaluated their DNA and histone epigenetic modifications in five ovarian epithelial and carcinoma cell lines (human 'immortalized' ovarian surface epithelium (HIO)-117, HIO-114, A2780, SKOV3 and ES2). GATA4 and GATA6 gene silencing was found to correlate with hypoacetylation of histones H3 and H4 and loss of histone H3/lysine K4 tri-methylation at their promoters in all lines. Conversely, histone H3/lysine K9 di-methylation and HP1gamma association were not observed, excluding reorganization of GATA genes into heterochromatic structures. The histone deacetylase inhibitor trichostatin A, but not the DNA methylation inhibitor 5'-aza-2'-deoxycytidine, re-established the expression of GATA4 and/or GATA6 in A2780 and HIO-114 cells, correlating with increased histone H3 and H4 acetylation, histone H3 lysine K4 methylation and DNase I sensitivity at the promoters. Therefore, altered histone modification of the promoter loci is one mechanism responsible for the silencing of GATA transcription factors and the subsequent loss of a target gene, the tumor suppressor Disabled-2, in ovarian carcinogenesis.

Early Lineage Segregation between Epiblast and Primitive Endoderm in Mouse Blastocysts through the Grb2-MAPK Pathway

It has been thought that early inner cell mass (ICM) is a homogeneous population and that cell position in the ICM leads to the formation of two lineages, epiblast (EPI) and primitive endoderm (PE), by E4.5. Here, however, we show that the ICM at E3.5 is already heterogeneous. The EPI- and PE-specific transcription factors, Nanog and Gata6, were expressed in the ICM in a random "salt and pepper" pattern, as early as E3.5, in a mutually exclusive manner. Lineage tracing showed predominant lineage restriction of single ICM cells at E3.5 to either lineage. In embryos lacking Grb2 where no PE forms, Gata6 expression was lost and all ICM cells were Nanog positive. We propose a model in which the ICM develops as a mosaic of EPI and PE progenitors at E3.5, dependent on Grb2-Ras-MAP kinase signaling, followed by later segregation of the progenitors into the appropriate cell layers.

GATA-6 regulates semaphorin 3C and is required in cardiac neural crest for cardiovascular morphogenesis

GATA transcription factors play critical roles in restricting cell lineage differentiation during development. Here, we show that conditional inactivation of GATA-6 in VSMCs results in perinatal mortality from a spectrum of cardiovascular defects, including interrupted aortic arch and persistent truncus arteriosus. Inactivation of GATA-6 in neural crest recapitulates these abnormalities, demonstrating a cell-autonomous requirement for GATA-6 in neural crest-derived SMCs. Surprisingly, the observed defects do not result from impaired SMC differentiation but rather are associated with severely attenuated expression of semaphorin 3C, a signaling molecule critical for both neuronal and vascular patterning. Thus, the primary function of GATA-6 during cardiovascular development is to regulate morphogenetic patterning of the cardiac outflow tract and aortic arch. These findings provide new insights into the conserved functions of the GATA-4, -5, and -6 subfamily members and identify GATA-6 and GATA-6-regulated genes as candidates involved in the pathogenesis of congenital heart disease.

Cell and molecular regulation of the mouse blastocyst

Animals use diverse strategies to specify tissue lineages during development. A common strategy is to partition maternally supplied and localized lineage determinants into progenitor cells. The mouse embryo appears to use a different, more regulative strategy to specify the first three lineages: the epiblast (EPI: future embryo), the trophectoderm (TE: future placenta), and the primitive endoderm (PE: future yolk sac). These lineages are specified during two successive differentiation steps leading to formation of the blastocyst. Here, we review classic and contemporary models of early lineage specification in the mouse, and describe recent efforts to understand the molecular regulation of these events. We describe evidence that trophectoderm differentiation bears resemblance to the process of epithelialization and describe the importance of apical/basal protein complexes in regulating this process. Next, we present a revised model of PE specification, and describe evidence that PE cells in the inner cell mass sort out to occupy their ultimate position on the surface of the EPI. Finally, we describe factors that reinforce these lineages and three distinct stem cell types that can be isolated from them. Together, these mechanisms guide the differentiation of the first lineages of the mouse and thereby set up tissues that will be important for the first steps of embryonic body patterning.

Involvement of GATA-4/-5 transcription factors in ovarian carcinogenesis

To clarify the role of GATA transcription factors in ovarian carcinogenesis, we analyzed the expression and methylation states of GATA-4/-5/-6 in eight human ovarian cancer cell lines. GATA-4/-5 were methylated in three and two cell lines without their expression, respectively. Methylation of GATA-4/-5 was also detected in nine and five of 15 primary ovarian cancers, respectively. GATA-6 was not methylated in any cases. We transiently over-expressed GATA-5 in the JHOC-5 cell line using an adenovirus system, resulting in that apoptosis was induced and apoptosis-related genes, such as Apaf-1, were up-regulated. These data suggest that GATA-4/-5 may be involved in ovarian carcinogenesis.

Further extension of mammalian GATA-6

Mammalian GATA-6, which has conserved tandem zinc fingers (CVNC-X(17)-CNAC)-X(29)-(CXNC-X(17)-CNAC), is essential for the development and specific gene regulation of the heart, gastrointestinal tract and other tissues. GATA-6 recognizes the (A/T/C)GAT(A/T)(A) sequence, and interacts with other transcriptional regulators through its zinc-finger region. The mRNA of GATA-6 uses two Met codons in frame as translational initiation codons, and produces L- and S-type GATA-6 through leaky ribosome scanning. GATA-6 is subjected to cAMP-dependent proteolysis by a proteasome in a heterologous expression system. These protein-based characteristics of GATA-6 will be helpful for the identification of target genes, together with determination of the in vivo binding sites for GATA-6 and understanding of the complex network of gene regulation mediated by GATA-6.

Molecular evidence for a critical period in mural trophoblast development in bovine blastocysts

Embryonic and extra-embryonic lineages are separated at the blastocyst stage in the mouse at the onset of implantation but well ahead of implantation in most mammals. To provide information on the development of the trophoblast lineage in late-implanting bovine embryos, we combined the use of molecular markers defining embryonic and extra-embryonic lineages in the mouse with a transcriptomic approach dedicated to the early steps of the elongation process, a characteristic feature of blastocyst development in ruminants. In this study, we present molecular evidence for differences between the cow and the mouse in the programming of trophoblast differentiation. This different programming encompasses: (i) the expression of epiblast specifying genes (Oct-4, Nanog) in bovine trophoblast cells at the onset of elongation, (ii) the transcription of proliferation markers in early elongating blastocysts, (iii) the early detection of trophoblast-specific transcripts related to extra-embryonic tissue's differentiation (Hand1, Ets2, IFN-tau) and (iv) the identification of a new transcript (c12) which displays a reciprocal pattern to that of Oct-4 and Nanog genes in the embryonic cells and for which no equivalent has thus far been found in the mouse. Altogether, these results tended to show that early elongation is a critical transition in bovine trophoblast development.

Endocytosis of megalin by visceral endoderm cells requires the Dab2 adaptor protein

Rapid endocytosis of lipoprotein receptors involves NPxY signals contained in their cytoplasmic tails. Several proteins, including ARH and Dab2, can bind these sequences, but their importance for endocytosis may vary in different cell types. The lipoprotein receptor megalin is expressed in the visceral endoderm (VE), a polarized epithelium that supplies maternal nutrients to the early mammalian embryo. Dab2 is also expressed in the VE, and is required for embryo growth and gastrulation. Here, we show that ARH is absent from the VE, and Dab2 is required for uptake of megalin, its co-receptor cubilin, and a cubilin ligand, transferrin, from the brush border of the VE into intracellular vesicles. By making isoform-specific knock-in mice, we show that the p96 splice form of Dab2, which binds endocytic proteins, can fully rescue endocytosis. The more abundant p67 isoform, which lacks some endocytic protein binding sites, only partly rescues endocytosis. Endocytosis of cubilin is also impaired in VE and in mid-gestation visceral yolk sac when p96 is absent. These studies suggest that Dab2 p96 mediates endocytosis of megalin in the VE. In addition, rescue of embryonic viability correlates with endocytosis, suggesting that endocytosis mediated by Dab2 is important for normal development.