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PubMed2001

Notochord patterning of the endoderm.

Endodermally derived organs of the gastrointestinal and respiratory system form at distinct anterioposterior and dorsoventral locations along the vertebrate body axis. This stereotyped program of organ formation depends on the correct patterning of the endodermal epithelium so that organ differentiation and morphogenesis occur at appropriate positions along the gut tube. Whereas some initial patterning of the endoderm is known to occur early, during germ-layer formation and gastrulation, later signaling events, originating from a number of adjacent tissue layers, are essential for the development of endodermal organs. Previous studies have shown that signals arising from the notochord are important for patterning of the ectodermally derived floor plate of the neural tube and the mesodermally derived somites. This review will discuss recent evidence indicating that signals arising from the notochord also play a role in regulating endoderm development.

Body Patterning↗

PubMed2001

VegT activation of Sox17 at the midblastula transition alters the response to nodal signals in the vegetal endoderm domain.

In Xenopus, the prospective endoderm and mesoderm are localized to discrete, adjacent domains at the beginning of gastrulation, and this is made evident by the expression of Sox17 in vegetal blastomeres and Brachyury (Xbra) in marginal blastomeres. Here, we examine the regulation of Sox17alpha expression and the role of Sox17alpha in establishing the vegetal endodermal gene expression domain. Injection of specific inhibitors of VegT or Nodal resulted in a loss of Sox17alpha expression in the gastrula. However, the onset of Sox17alpha expression at the midblastula transition was dependent on VegT, but not on Nodal function, indicating that Sox17alpha expression is initiated by VegT and then maintained by Nodal signals. Consistent with these results, VegT, but not Xenopus Nodal-related-1 (Xnr1), can activate Sox17alpha expression at the midblastula stage in animal explants. In addition, VegT activates Sox17alpha in the presence of cycloheximide or a Nodal antagonist, suggesting that Sox17alpha is an immediate-early target of VegT in vegetal blastomeres. Given that Nodal signals are necessary and sufficient for both mesodermal and endodermal gene expression, we propose that VegT activation of Sox17alpha at the midblastula transition prevents mesodermal gene expression in response to Nodal signals, thus establishing the vegetal endodermal gene expression domain. Supporting this idea, Sox17alpha misexpression in the marginal zone inhibits the expression of multiple mesodermal genes. Furthermore, in animal explants, Sox17alpha prevents the induction of Xbra and MyoD, but not Sox17beta or Mixer, in response to Xnr1. Therefore, VegT activation of Sox17alpha plays an important role in establishing a region of endoderm-specific gene expression in vegetal blastomeres.

Animals↗

PubMed2002

Molecular regulation of vertebrate early endoderm development.

Detailed study of the ectoderm and mesoderm has led to increasingly refined understanding of molecular mechanisms that operate early in development to generate cellular diversity. More recently, a number of powerful studies have begun to characterize the molecular determinants of the endoderm, a germ layer previously neglected in developmental biology. Work in diverse model systems has converged on an integrated transcriptional and signaling pathway that serves to establish the vertebrate endoderm. A T-box transcription factor identified in Xenopus embryos, VegT, appears to function near the top of an endoderm-specifying transcriptional hierarchy. VegT activates and reinforces Nodal-related TGFbeta signaling and also induces expression of essential downstream transcriptional regulators, Mix-like paired-homeodomain and GATA factors. These proteins cooperate to regulate expression of a relay of HMG-box Sox-family transcription factors culminating with Sox 17, which may be an obligate mediator of vertebrate endoderm development. This review synthesizes findings in three vertebrate model organisms and discusses these genetic interactions in the context of the progressive acquisition of endodermal identity early in vertebrate development.

Animals↗

PubMed1994

The tyrosine hydroxylase gene is expressed in endoderm and pancreas of early quail embryos.

The initial expression of the gene encoding tyrosine hydroxylase (TH) was studied in the trunk of quail embryos by in situ hybridization. We detected the presence of quail TH mRNA on embryonic day 3.5 (E3.5) in the sympathetic ganglia and aortic plexus, both neural crest derived structures. In contrast, the TH gene was expressed much earlier in the endodermal layer of E2 embryos, i.e. from the 8-somite stage onwards. TH mRNA was found also in the pancreatic bud, an endoderm-derived structure. The TH protein and catecholamines were subsequently looked for in these structures. TH immunoreactivity was found in cells of E2 explanted endoderm, but no catecholamine histofluorescence was observed before or after a few days in culture. TH-positive cells were also detected in cultures of pancreatic rudiments, explanted from E3 to E6 quail embryos. We suggest that the TH-positive cells of the endoderm are the progenitors of the catecholaminergic cells of the pancreas and of the enterochromaffin cells of the gut. The hypothesis that the TH-positive cells of the endoderm are involved in the expression of the catecholaminergic phenotype by neural crest cells is discussed.

Animals↗

PubMed1987

The lining of the gut in the developing rat embryo. Its relation to the hypoblast (primary endoderm) and the notochord.

A light microscopical study of the morphogenesis of the gut in the rat embryo was undertaken to provide a careful map of temporal changes in the topographical relations of the (definitive) endoderm, the notochord and the hypoblast (primary endoderm). The borderline between the (definitive) endoderm and the hypoblast that appears upon gastrulation defines the lateral extension of the future gut epithelium. Within this initially semiglobular disk, the foregut and hindgut originate sequentially as blind, rapidly growing pouches. Upon the turning of the embryo, the hardly growing peripheral part of the disk becomes located in the vitelline duct. Within the head process, endodermal and notochordal cells could not be separately identified. However, slightly more posteriorly notochordal cells are seen to become embedded into the endoderm of the foregut during gastrulation. This process is not seen over the hindgut and may explain why the detachment of the notochord from the (fore)gut begins caudally.

Animals↗

PubMed2005

Distinct populations of endoderm cells converge to generate the embryonic liver bud and ventral foregut tissues.

The location and movement of mammalian gut tissue progenitors, prior to the expression of tissue-specific genes, has been unknown, but this knowledge is essential to identify transitions that lead to cell type specification. To address this, we used vital dyes to label exposed anterior endoderm cells of early somite stage mouse embryos, cultured the embryos into the tissue bud phase of development, and determined the tissue fate of the dye labeled cells. This approach was performed at three embryonic stages that are prior to, or coincident with, foregut tissue patterning (1-3 somites, 4-6 somites, and 7-10 somites). Short-term labeling experiments tracked the movement of tissue progenitor cells during foregut closure. Surprisingly, we found that two distinct types of endoderm-progenitor cells, lateral and medial, arising from three spatially separated embryonic domains, converge to generate the epithelial cells of the liver bud. Whereas the lateral endoderm-progenitors give rise to descendants that are constrained in tissue fate and position along the anterior-posterior axis of the gut, the medial gut endoderm-progenitors give rise to descendants that stream along the anterior-posterior axis at the ventral midline and contribute to multiple gut tissues. The fate map reveals extensive morphogenetic movement of progenitors prior to tissue specification, it permits a detailed analysis of endoderm tissue patterning, and it illustrates that diverse progenitor domains can give rise to individual tissue cell types.

Animals↗

PubMed2005

Hex homeobox gene controls the transition of the endoderm to a pseudostratified, cell emergent epithelium for liver bud development.

Little is known about the mechanism by which embryonic liver, lung, and pancreas progenitor cells emerge from the endodermal epithelium to initiate organogenesis. Understanding this process and its genetic control provides insight into ontogeny, developmental abnormalities, and tissue regeneration. We find that shortly after hepatic endoderm cells are specified, they undergo a transition from a columnar, gut morphology to a pseudostratified morphology, with concomitant "interkinetic nuclear migration" (INM) during cell division. INM is a hallmark of pseudostratified epithelia and the process used by neural progenitors to emerge from the neural epithelium. We find that the transition of the hepatic endoderm, but not the neural epithelium, to a pseudostratified epithelium is dependent upon the cell-autonomous activity of the homeobox gene Hex. In the absence of Hex, hepatic endoderm cells survive but maintain a columnar, simple epithelial phenotype and ectopically express Shh and other genes characteristic of the midgut epithelium. Thus, Hex promotes endoderm organogenesis by promoting the transition to a pseudostratified epithelium, which in turn allows hepatoblasts to emerge into the stromal environment and continue differentiating.

Animals↗

PubMed2006

Animal pole determinants define oral-aboral axis polarity and endodermal cell-fate in hydrozoan jellyfish Podocoryne carnea.

Cnidarians, in contrast with bilaterians, are generally considered to exhibit radial symmetry around a single body axis (oral-aboral) throughout their life-cycles. We have investigated how the oral-aboral axis is established in the hydrozoan jellyfish Podocoryne carnea. Vital labeling experiments showed that the oral end of the blastula derives from the animal pole region of the egg as has been demonstrated for other cnidarian species. Gastrulation is restricted to the oral pole such that the oral 20% of blastula cells give rise to endoderm. Unexpectedly, bisection experiments at the 8-cell stage showed that animal regions are able to develop into normally polarized larvae, but that vegetal (aboral) blastomeres completely fail to develop endoderm or to elongate. These vegetal-derived larvae also failed to polarize, as indicated by a lack of oral-specific RFamide-positive nerve cells and a disorganized tyrosinated tubulin-positive nerve net. A different result was obtained following bisection of the late blastula stage: aboral halves still lacked the capacity to develop endoderm but retained features of axial polarity including elongation of the larva and directional swimming. These results demonstrate for the first time in a cnidarian the presence of localized determinants responsible for axis determination and endoderm formation at the animal pole of the egg. They also show that axial polarity and endoderm formation are controlled by separable pathways after the blastula stage.

Alkaline Phosphatase↗

PubMed2003

Signals from lateral plate mesoderm instruct endoderm toward a pancreatic fate.

During embryonic development, organs arise along the gut tube as a series of buds in a stereotyped anterior-posterior (A-P) pattern. Using chick-quail chimeras and in vitro tissue recombination, we studied the interactions governing the induction and maintenance of endodermal organ identify focusing on the pancreas. Though several permissive signals in pancreatic development have been previously identified, here we provide evidence that lateral plate mesoderm sends instructive signals to the endoderm, signals that induce expression of the pancreatic genes Pdx1, p48, Nkx6.1, glucagon, and insulin. Moreover, this instructive signal directs cells to form ectopic insulin-positive islet-like clusters in endoderm that would otherwise form more rostral organs. Once generated, endocrine cells no longer require interaction with mesoderm, but nonendocrine cells continue to require permissive signals from the mesoderm. Stimulation of activin, BMP, or retinoic acid signaling is sufficient to induce Pdx1 expression in endoderm anterior to the pancreas. Lateral plate mesoderm appears to pattern the endoderm in a posterior-dominant fashion as first noted in the patterning of the neural tube at the same embryonic stage. These findings argue for a central role of the mesoderm in coordinating the A-P pattern of all three primary germ layers.

Activins↗

PubMed2003

Endodermal growth factors promote endocardial precursor cell formation from precardiac mesoderm.

We previously demonstrated that the initial emergence of endocardial precursor cells (endocardial angioblasts) occurred within the precardiac mesoderm and that the endodermal secretory products promoted delamination of cells from the precardiac mesoderm and expression of endothelial lineage markers [Dev. Biol. 175 (1996), 66]. In this study, we sought to extend our original study to the identification of candidate molecules derived from the endoderm that might have induced endocardial precursor cell formation. We have detected expression of transforming growth factors beta (TGFbeta) 2, 3, and 4 in anterior endoderm at Hamburger and Hamilton (H-H) stage 5 by RT-PCR. To address the role of growth factors known to be present in the endoderm, precardiac mesodermal explants were isolated from H-H stage 5 quail embryos and cultured on the surface of collagen gels with serum-free defined medium 199. Similar to the effect of explants cocultured with anterior endoderm, when cultured with TGFbetas 1-3 (3 ng/ml each), explants formed QH-1 (anti-quail endothelial marker)-positive mesenchymal cells, which invaded the gel and expressed the extracellular marker, cytotactin (tenascin). Another member of the TGFbeta superfamily, bone morphogenetic protein-2 (BMP-2; 100 ng/ml), did not induce QH-1-positive mesenchymal cell formation but promoted formation of an epithelial monolayer on the surface of the collagen gel; this monolayer did not express QH-1. Explants treated with vascular endothelial growth factor (VEGF(165), 100 ng/ml) also did not invade the gel but formed an epithelial-like outgrowth on the surface of the gel. However, this monolayer did express the QH-1 marker. Fibroblast growth factor-2 (FGF-2; 250 ng/ml)-treated explants expressed QH-1 and exhibited separation of the cells on the surface of the gel. Finally, a combination of TGFbetas and VEGF enhanced formation of QH-1-positive cord-like structures within the gel from mesenchyme that had previously invaded the gel. Luminization of the cords, however, was not clearly evident. These findings suggest that TGFbetas, among the growth factors tested, mediate the initial step of endocardial formation, i.e., delamination of endothelial precursor cells from precardiac mesoderm, whereas VEGF may primarily effect early vasculogenesis (cord-like structure formation).

Animals↗

PubMed2001

Endodermal cyst of the quadrigeminal cistern: case report.

BACKGROUND: Endodermal cysts usually develop in the subdural space in the anterior spinal cord and rarely occur inside the cranium. Most intracranial endodermal cysts develop in the posterior fossa. We report the first case of an endodermal cyst in the quadrigeminal cistern. CASE DESCRIPTION: The patient was a 71-year-old man who suffered from gait disturbance for 6 months. Although head computed tomography (CT) scanning 4 years previously did not show any cystic lesion, CT and magnetic resonance imaging (MRI) on admission showed a cystic lesion extending from the quadrigeminal cistern to the right ambient cistern. The cyst was subtotally removed via a suboccipital transtentorial approach. The cyst wall consisted of a layer of columnar epithelium and connective tissue. Based on the results of immunostaining, it was diagnosed as an endodermal cyst. CONCLUSIONS: It is possible that the increase of secretion from the cells lining the cyst may have caused a difference in osmotic pressure between the cerebrospinal fluid and the cyst contents, leading to rapid enlargement of the cyst. An endodermal cyst should be removed as completely as possible because its cells have the ability to grow and produce secretions.

Aged↗

PubMed2002

Cititf1 and endoderm differentiation in Ciona intestinalis.

Studies on the initial formation of the endoderm have lead to the identification, mostly in Xenopus, of numerous genes relevant for the formation of this tissue during early embryogenesis (reviewed by Date, Curr. Biol. 9 (1999) R812-R815 and by Yasuo and Lemaire, Curr. Biol. 9 (1999) 869-879). In ascidians, the most primitive chordates, endoderm differentiation is an autonomous process which is almost complete at 64 cells stage. Cititf1, a gene homologous to mammalian Titf1, is the first specific endodermal marker isolated from the ascidian Ciona intestinalis (Ristatore et al., Development 126 (1999) 5149-5159). Here we study the in vivo role of Cititf1 by using two different approaches: interference and ectopic expression. The results presented here show that interference with Cititf1 function seems to affect gastrulation movements, while ectopic expression of Cititf1 mRNA into the notochord alters differentiation of this tissue probably by recruiting notochord blastomeres to an endodermal fate. These data together with studies, still in progress in our laboratory, on the transcriptional regulation of Cititf1, strongly indicate that Cititf1 plays an important role in the process of endoderm formation in Ciona embryogenesis.

Animals↗

PubMed2000

Indian hedgehog signaling in extraembryonic endoderm and ectoderm differentiation in ES embryoid bodies.

We previously demonstrated that a member of the Hedgehog gene family, Indian hedgehog (Ihh), is expressed in the visceral endoderm of EC and ES cell embryoid bodies and mouse embryos. Overexpression studies suggested that Ihh was involved in visceral endoderm differentiation. We now provide evidence for a Hh response in the embryoid body core and in the mesothelial layer of the visceral yolk sac. We also demonstrate that treatment of ES embryoid bodies with the Hh antagonists cAMP and forskolin results in downregulation of the Hh response and altered embryoid body differentiation. The outer endoderm layer undergoes a transition to parietal endoderm while formation of an embryonic ectoderm layer surrounding a cavity is inhibited. These treatments also result in a decrease in the expression of markers for the mesoderm derivatives, blood and endothelial cells. We present a model to explain how Ihh and BMP signaling may regulate extraembryonic endoderm and embryonic ectoderm differentiation.

Animals↗

PubMed2002

Prox1 is an early specific marker for the developing liver and pancreas in the mammalian foregut endoderm.

Although important progress has been made recently in the elucidation of the molecular mechanisms that regulate differentiation and morphogenesis of endoderm-derived tissues such as pancreas and liver, less is known about the preliminary steps of early regional specification. Recent evidence supports the proposal that the early endoderm contains a bipotential precursor cell type for pancreas and liver. We have also previously shown that the activity of the homeobox gene Prox1 controls hepatocyte migration during liver morphogenesis. Using detailed comparative analysis of whole embryos and reverse transcriptase polymerase chain reaction of dissected embryonic endoderm, we have now determined that in the early endoderm, Prox1 expression is restricted to regions giving rise to the mammalian pancreas and liver. This finding indicates that Prox1 is one of the earliest specific markers of this commonly fated region of the mammalian endoderm.

Activin Receptors, Type I↗

PubMed2002

BMP signalling regulates anteroposterior endoderm patterning in zebrafish.

In vertebrates, the embryonic dorsoventral asymmetry is regulated by the bone morphogenetic proteins (Bmp) activity gradient. In the present study, we have used dorsalized swirl (bmp2b) and ventralized chordino (chordin) zebrafish mutants to investigate the effects of dorsoventral signalling on endoderm patterning and on the differentiation and positioning of its derivatives. Alterations of dorsoventral Bmp signalling do not perturb the induction of endodermal precursors, as shown by normal amounts of cells expressing cas and sox17 in swirl and chordino gastrulae, but affect dramatically the expression pattern of her5, a regulator of endoderm anteroposterior patterning in zebrafish. In particular, increased levels of Bmp signalling in chordino gastrulae are associated with a markedly reduced her5 expression domain, that may be abolished by injecting bmp2b mRNA. Conversely, in swirl mutants, lacking Bmp2b, the her5 expression domain is expanded. Thus, a gradient of Bmp2b signalling defines the extension of the her5 expression domain at gastrulation and the allocation of anterior endodermal precursors. A balanced Bmp2b signalling is also required for the normal development of the pancreas, as shown by the sharp reduction of the pancreatic primordium in swirl embryos and its expansion in chordino mutants. In the latter, at 3 days post-fertilization, the increased Bmp signalling does not compromise the endocrine/exocrine pancreas compartmentalization, but the right/left positioning of the pancreas and liver is randomized. Our results suggest that by regulating the expression of her5, the Bmp2b/Chordin gradient directs the anteroposterior patterning of endoderm in zebrafish embryos.

Animals↗

PubMed1997

Cerberus-like is a secreted factor with neutralizing activity expressed in the anterior primitive endoderm of the mouse gastrula.

We report the isolation of mouse cerberus-like (cer-l), a gene encoding a novel secreted protein that is specifically expressed in the anterior visceral endoderm during early gastrulation. Expression in the primitive endoderm starts before the appearance of the primitive streak and lasts until the head-fold stage. In later stages, a second region of expression is found in newly formed somites. Mouse cer-l shares some sequence similarity with Xenopus cerberus (Xcer). In Xenopus assays cer-l, like Xcer, mRNA acts as a potent neuralizing factor that induces forebrain markers and endoderm, but is unable to induce ectopic head-like structures as Xcer does. In addition to cer-l, anterior visceral endoderm was found to express the transcription factors Lim1, goosecoid and HNF-3beta that are also present in trunk organizer cells. A model of how head and trunk development might be regulated is discussed. Given its neuralizing activity, the secreted protein Cer-l is a candidate for mediating inductive activities of anterior visceral endoderm.

Amino Acid Sequence↗

PubMed2003

Early endoderm development in vertebrates: lineage differentiation and morphogenetic function.

Gastrulation of the vertebrate embryo culminates in the formation of three primary germ layers: ectoderm, mesoderm and endoderm. The endoderm contributes to the lining of the gut and the associated organs. New components of the molecular pathway for endoderm specification have been identified in the zebrafish and Xenopus. In the mouse, the activity of orthologous factors is involved with the allocation and differentiation of the definitive endoderm. Morphogenetic interactions between the endoderm and the other germ layer derivatives are critical for the morphogenesis of head structures and organogenesis of gut derivatives.

Animals↗

PubMed2002

Formation of multiple hearts in mice following deletion of beta-catenin in the embryonic endoderm.

Using Cre/loxP, we conditionally inactivated the beta-catenin gene in cells of structures that exhibit important embryonic organizer functions: the visceral endoderm, the node, the notochord, and the definitive endoderm. Mesoderm formation was not affected in the mutant embryos, but the node was missing, patterning of the head and trunk was affected, and no notochord or somites were formed. Surprisingly, deletion of beta-catenin in the definitive endoderm led to the formation of multiple hearts all along the anterior-posterior (A/P) axis of the embryo. Ectopic hearts developed in parallel with the normal heart in regions of ectopic Bmp2 expression. We provide evidence that ablation of beta-catenin in embryonic endoderm changes cell fate from endoderm to precardiac mesoderm, consistent with the existence of bipotential mesendodermal progenitors in mouse embryos.

Animals↗