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PubMed2005

Requirements for endoderm and BMP signaling in sensory neurogenesis in zebrafish.

Cranial sensory neurons largely derive from neurogenic placodes (epibranchial and dorsolateral), which are ectodermal thickenings that form the sensory ganglia associated with cranial nerves, but the molecular mechanisms of placodal development are unclear. Here, we show that the pharyngeal endoderm induces epibranchial neurogenesis in zebrafish, and that BMP signaling plays a crucial role in this process. Using a her5:egfp transgenic line to follow endodermal movements in living embryos, we show that contact between pharyngeal pouches and the surface ectoderm coincides with the onset of neurogenesis in epibranchial placodes. By genetic ablation and reintroduction of endoderm by cell transplantation, we show that these contacts promote neurogenesis. Using a genetic interference approach we further identify bmp2b and bmp5 as crucial components of the endodermal signals that induce epibranchial neurogenesis. Dorsolateral placodes (trigeminal, auditory, vestibular, lateral line) develop independently of the endoderm and BMP signaling, suggesting that these two sets of placodes are under separate genetic control. Our results show that the endoderm regulates the differentiation of cranial sensory ganglia, which coordinates the cranial nerves with the segments that they innervate.

Animals↗
PubMed2006

Sequential allocation and global pattern of movement of the definitive endoderm in the mouse embryo during gastrulation.

During mouse gastrulation, endoderm cells of the dorsal foregut are recruited ahead of the ventral foregut and move to the anterior region of the embryo via different routes. Precursors of the anterior-most part of the foregut and those of the mid- and hind-gut are allocated to the endoderm of the mid-streak-stage embryo, whereas the precursors of the rest of the foregut are recruited at later stages of gastrulation. Loss of Mixl1 function results in reduced recruitment of the definitive endoderm, and causes cells in the endoderm to remain stationary during gastrulation. The observation that the endoderm cells are inherently unable to move despite the expansion of the mesoderm in the Mixl1-null mutant suggests that the movement of the endoderm and the mesoderm is driven independently of one another.

Animals↗
PubMed1988

Pepsinogen gene transcription induced in heterologous epithelial-mesenchymal recombinations of chicken endoderms and glandular stomach mesenchyme.

Proventricular (glandular stomach) mesenchyme of chicken embryos can induce endoderms of some parts of embryonic digestive tract to produce embryonic chicken pepsinogen (ECPg), a marker protein for the differentiation of embryonic proventricular epithelium. In the present study, we investigated the production of ECPg mRNA in the course of epithelial-mesenchymal interactions between endoderms of digestive tract and proventricular mesenchyme. ECPg mRNA was detected by Northern hybridization with ECPg cDNA as a probe. In normal development of the proventriculus, ECPg mRNA was first detected at day 7 of incubation, and it ceased to be produced by day 21. Embryonic esophagus, gizzard and small intestine did not contain ECPg mRNA. When 6-day esophagus, gizzard or proventricular endoderm was associated and cultured with 6-day proventricular mesenchyme, the recombinates formed proventricular-gland-like complex glands and produced ECPg mRNA in almost equal quantity. However, 6-day small intestinal or 3.5-day allantoic endoderm did not produce pepsinogen mRNA under the same conditions, though the recombinates formed complex glands. These results indicate that the proventricular mesenchyme can induce de novo transcription of ECPg gene in esophagus, proventricular and gizzard endoderms, and that ECPg gene in small intestinal and allantoic endoderms fails to react to the inducing signal.

Animals↗
PubMed1989

Differential localization of villin and fimbrin during development of the mouse visceral endoderm and intestinal epithelium.

The apical surface of transporting epithelia is specially modified to absorb nutrients efficiently by amplifying its surface area as microvilli. Each microvillus is supported by an underlying core of bundled actin filaments. Villin and fimbrin are two actin-binding proteins that bundle actin filaments in the intestine and kidney brush border epithelium. To better understand their function in the assembly of the cytoskeleton during epithelial differentiation, we examined the pattern of villin and fimbrin expression in the developing mouse using immunofluorescence and immunoelectron microscopy. Villin is first detected at day 5 in the primitive endoderm of the postimplantation embryo and is later restricted to the visceral endoderm. By day 8.5, villin becomes redistributed to the apical surface in the visceral endoderm, appearing in the gut at day 10 and concentrating in the apical cytoplasm of the differentiating intestinal epithelium 2-3 days later. In contrast, fimbrin is found in the oocyte and in all tissues of the early embryo. In both the visceral endoderm and gut epithelium, fimbrin concentrates at the apical surface 2-3 days after villin; this redistribution occurs when the visceral endoderm microvilli first contain organized microfilament bundles and when microvilli first begin to appear in the gut. These results suggest a common mechanism of assembly of the absorptive surface of two different tissues in the embryo and identify villin as a useful marker for the visceral endoderm.

Animals↗
PubMed1998

Anterior-posterior patterning within the Caenorhabditis elegans endoderm.

The endoderm of higher organisms is extensively patterned along the anterior/posterior axis. Although the endoderm (gut or E lineage) of the nematode Caenorhabditis elegans appears to be a simple uniform tube, cells in the anterior gut show several molecular and anatomical differences from cells in the posterior gut. In particular, the gut esterase ges-1 gene, which is normally expressed in all cells of the endoderm, is expressed only in the anterior-most gut cells when certain sequences in the ges-1 promoter are deleted. Using such a deleted ges-1 transgene as a biochemical marker of differentiation, we have investigated the basis of anterior-posterior gut patterning in C. elegans. Although homeotic genes are involved in endoderm patterning in other organisms, we show that anterior gut markers are expressed normally in C. elegans embryos lacking genes of the homeotic cluster. Although signalling from the mesoderm is involved in endoderm patterning in other organisms, we show that ablation of all non-gut blastomeres from the C. elegans embryo does not affect anterior gut marker expression; furthermore, ectopic guts produced by genetic transformation express anterior gut markers generally in the expected location and in the expected number of cells. We conclude that anterior gut fate requires no specific cell-cell contact but rather is produced autonomously within the E lineage. Cytochalasin D blocking experiments fully support this conclusion. Finally, the HMG protein POP-1, a downstream component of the Wnt signalling pathway, has recently been shown to be important in many anterior/posterior fate decisions during C. elegans embryogenesis (Lin, R., Hill, R. J. and Priess, J. R. (1998) Cell 92, 229-239). When RNA-mediated interference is used to eliminate pop-1 function from the embryo, gut is still produced but anterior gut marker expression is abolished. We suggest that the C. elegans endoderm is patterned by elements of the Wnt/pop-1 signalling pathway acting autonomously within the E lineage.

Animals↗
PubMed1998

GATA transcription factors as potentiators of gut endoderm differentiation.

Gene inactivation studies have shown that members of the GATA family of transcription factors are critical for endoderm differentiation in mice, flies and worms, yet how these proteins function in such a conserved developmental context has not been understood. We use in vivo footprinting of mouse embryonic endoderm cells to show that a DNA-binding site for GATA factors is occupied on a liver-specific, transcriptional enhancer of the serum albumin gene. GATA site occupancy occurs in gut endoderm cells at their pluripotent stage: the cells have the potential to initiate tissue development but they have not yet been committed to express albumin or other tissue-specific genes. The GATA-4 isoform accounts for about half of the nuclear GATA-factor-binding activity in the endoderm. GATA site occupancy persists during hepatic development and is necessary for the activity of albumin gene enhancer. Thus, GATA factors in the endoderm are among the first to bind essential regulatory sites in chromatin. Binding occurs prior to activation of gene expression, changes in cell morphology or functional commitment that would indicate differentiation. We suggest that GATA factors at target sites in chromatin may generally help potentiate gene expression and tissue specification in metazoan endoderm development.

Animals↗
PubMed2000

The homeobox gene Hex is required in definitive endodermal tissues for normal forebrain, liver and thyroid formation.

The homeobox gene Hex is expressed in the anterior visceral endoderm (AVE) and rostral definitive endoderm of early mouse embryos. Later, Hex transcripts are detected in liver, thyroid and endothelial precursor cells. A null mutation was introduced into the Hex locus by homologous recombination in embryonic stem cells. Hex mutant embryos exhibit varying degrees of anterior truncation as well as liver and thyroid dysplasia. The liver diverticulum is formed but migration of hepatocytes into the septum transversum fails to occur. Development of the thyroid is arrested at the thyroid bud stage at 9.5 dpc. Brain defects are restricted to the rostral forebrain and have a caudal limit at the zona limitans intrathalamica, the boundary between dorsal and ventral thalamus. Analysis of Hex(-/-) mutants at early stages shows that the prospective forebrain ectoderm is correctly induced and patterned at 7.5 days post coitum (dpc), but subsequently fails to develop. AVE markers are expressed and correctly positioned but development of rostral definitive endoderm is greatly disturbed in Hex(-/-) embryos. Chimeric embryos composed of Hex(-/-) cells developing within a wild-type visceral endoderm show forebrain defects indicating that Hex is required in the definitive endoderm. All together, these results demonstrate that Hex function is essential in definitive endoderm for normal development of the forebrain, liver and thyroid gland.

Animals↗
PubMed2000

Early mouse endoderm is patterned by soluble factors from adjacent germ layers.

Endoderm that forms the respiratory and digestive tracts is a sheet of approximately 500-1000 cells around the distal cup of an E7.5 mouse embryo. Within 2 days, endoderm folds into a primitive gut tube from which numerous organs will bud. To characterize the signals involved in the developmental specification of this early endoderm, we have employed an in vitro assay using germ layer explants and show that adjacent germ layers provide soluble, temporally specific signals that induce organ-specific gene expression in endoderm. Furthermore, we show that FGF4 expressed in primitive streak-mesoderm can induce the differentiation of endoderm in a concentration-dependent manner. We conclude that the differentiation of gastrulation-stage endoderm is directed by adjacent mesoderm and ectoderm, one of the earliest reported patterning events in formation of the vertebrate gut tube.

Animals↗
PubMed2002

Interactions between Hox-negative cephalic neural crest cells and the foregut endoderm in patterning the facial skeleton in the vertebrate head.

The vertebrate face contains bones that differentiate from mesenchymal cells of neural crest origin, which colonize the median nasofrontal bud and the first branchial arches. The patterning of individual facial bones and their relative positions occurs through mechanisms that remained elusive. During the early stages of head morphogenesis, an endodermal cul-de-sac, destined to become Sessel's pouch, underlies the nasofrontal bud. Reiterative outpocketings of the foregut then form the branchial pouches. We have tested the capacity of endoderm of the avian neurula to specify the facial skeleton by performing ablations or grafts of defined endodermal regions. Neural crest cells that do not express Hox genes respond to patterning cues produced regionally in the anterior endoderm to yield distinct skeletal components of the upper face and jaws. However, Hox-expressing neural crest cells do not respond to these cues. Bone orientation is likewise dependent on the position of the endoderm relative to the embryonic axes. Our findings thus indicate that the endoderm instructs neural crest cells as to the size, shape and position of all the facial skeletal elements, whether they are cartilage or membrane bones.

Animals↗
PubMed1996

Hydra regeneration from recombined ectodermal and endodermal tissue. I. Epibolic ectodermal spreading is driven by cell intercalation.

Cell-cell interaction and cell rearrangement were examined in the process of epithelial sheet formation during regeneration from hydra cell aggregates. The ectodermal and endodermal epithelial cell layers of Hydra magnipapillata were separated by procaine treatment. Each of the separated layers was then dissociated into single cells and reaggregated to produce ectodermal or endodermal cell aggregates. When the two aggregate types were recombined, a firm adhesion was quickly established between them. This was followed by a vigorous spreading of the ectodermal epithelial cells as a thin layer over the endoderm in a manner similar to the 'epiboly' in some developing embryos. Cell movement in this spreading process was examined using fluorescent dyestaining. It revealed that cells initially located in the inside of the aggregate migrated to intercalate themselves among the cells originally present in the contact surface. This radial cell intercalation took place continuously in the contact surface of both the ectodermal and endodermal aggregates, and produced a rapid growth of the contact surface, eventually leading to complete envelopment of the entire endoderm by the ectoderm. The resulting structure was a small sphere having a two-layered epithelial organization as in normal hydra. This sphere regenerated into a complete hydra a few days later. A tryptic extract of hydra membrane fraction specifically inhibited the ectodermal spreading over the endoderm, but not the initial adhesion or the later regeneration processes. These observations suggest that radial cell intercalation at the contact surface plays a crucial role in producing ectodermal spreading and establishing epithelial sheet organization in the recombined aggregates. The intercalation is presumably activated by a signal exchange through the contact surface. The inhibitory effect of the membrane extract suggests that it contains a factor that is involved in some way in this signaling mechanism.

Animals↗
PubMed1999

Distinct roles for visceral endoderm during embryonic mouse development.

The murine visceral endoderm is an extraembryonic cell layer that appears prior to gastrulation and performs critical functions during embryogenesis. The traditional role ascribed to the visceral endoderm entails nutrient uptake and transport. Besides synthesizing a number of specialized proteins that facilitate uptake, digestion, and secretion of nutrients, the extraembryonic visceral endoderm coordinates blood cell differentiation and vessel formation in the adjoining mesoderm, thereby facilitating efficient exchange of nutrients and gases between the mother and embryo. Recent studies suggest that in addition to this nutrient exchange function the visceral endoderm overlying the egg cylinder stage embryo plays an active role in guiding early development. Cells in the anterior visceral endoderm function as an early organizer. Prior to formation of the primitive streak, these cells express specific gene products that specify the fate of underlying embryonic tissues. In this review we highlight recent investigations demonstrating this dual role for visceral endoderm as a provider of both nutrients and developmental cues for the early embryo.

Animals↗
PubMed1991

Cell lineage studies of the origin and differentiation of primary endoderm, using intraspecific chimaeras.

The origin of the primary endoderm was studied by combining experimentally eight-cell embryos and ICMs isolated by microsurgery from blastocysts homozygous for different alleles at the glucosephosphate isomerase (GPI-1) locus. The results confirm that the primary endoderm cells are derived from the ICM. The yolk sac splanchnopleure, which is composed of both extraembryonic endoderm and mesoderm, usually displayed the ICM GPI isoenzyme genotype. It must be concluded that the embryonic endoderm (visceral endoderm) and the parietal endoderm have a common origin and develop from the primitive ectoderm of the egg cylinder.

Animals↗
PubMed1984

The role of endoderm in blood cell ontogeny in the newt Pleurodeles waltl.

In order to determine the origin of blood cells we performed embryonic grafts of different portions of mesoderm from various locations between diploid and tetraploid embryos at the tail-bud stage. The tetraploid animals were the hosts. The size differences between tetraploid and diploid cells made identification possible by direct microscopic examination of blood smears. In a previous report we showed the important role of truncal anterior mesoderm in the genesis of blood cells. We now establish that this effect is brought about by the inductive capacity of the hepatic endoderm or by the fact that the environmental conditions are more appropriate for blood stem cell development, whereas in the absence of the hepatic endoderm the blood stem cells fail to appear. Grafting of hepatic anlage containing endoderm and mesoderm gives rise to numerous graft-derived blood cells which last throughout the life span of the hosts. The same result is obtained by grafting truncal posterior ventral or lateral mesoderm onto hepatic endoderm. Heterotopic grafting of truncal anterior mesoderm isolated from its underlying hepatic endoderm leads to the formation of only a few blood cells which last only during larval life. This demonstrates that the whole lateral and ventral truncal mesoderm is able to differentiate into blood cells when associated with hepatic endoderm.

Animals↗
PubMed1981

Identification and immunoprecipitation of cytoskeletal proteins from murine extra-embryonic endodermal cells.

Murine extra-embryonic endodermal cells derived from either teratocarcinomas or cultured mouse blastocysts contain two protein species of Mr = 55,000 and Mr = 50,000 endodermal cytoskeletal proteins A and B, respectively) that are insoluble in nonionic detergent and 1 M NaCl and are not found in abundance in embryonal carcinoma cells, the stem cells of teratocarcinomas. Antiserum raised against the electrophoretically purified endo B protein immunoprecipitated endo B from [35S]methionine-labeled cell lysates of three parietal endodermal cell lines, a presumptive visceral endodermal cell line, and a mouse hepatoma line. Immunoprecipitable endo B was not found in murine embryonal carcinoma cells, fibroblasts, myoblasts, keratinocytes, erythroleukemic or neuroblastoma cells. These results are consistent with the view that endo B is not tubulin, vimentin, desmin, or keratin. Amino acid composition data, partial peptide analysis of immunoprecipitated endo B, and immunoprecipitation analysis with antikeratin serum support the suggestion that endo B is not a keratin. Indirect immunofluorescent staining of parietal endodermal cells with the endo B antiserum resulted in the fluorescence of a fibrillar cytoskeletal network. The synthesis of endo B was increased dramatically when embryonal carcinoma cells were induced to differentiate by treatment with retinoic acid. Endo B appears to be a cytoskeletal protein that is synthesized when malignant embryonal carcinoma cells differentiate to benign extra-embryonic endoderm.

Amino Acids↗
PubMed1996

TGF-beta 1 regulation of laminin secretion by F9-derived primitive endoderm cells: a potential role in cell migration within the mouse blastocyst.

The first differentiation event occurring in the preimplantation mouse blastocyst is the formation of inner cell mass (ICM) derived primitive endoderm (PrE) cells, some of which migrate over the inner surface of the trophectoderm to establish the parietal endoderm layer. Reichert's membrane, a basement membrane located between the trophectoderm and the emerging endodermal layer, is implicated in this migration. In this study, F9 murine embryonal carcinoma cells were used as an in vitro model for embryonic endoderm to investigate the regulation of laminin secretion by these cells during their differentiation under serum-free culture conditions. The formation of PrE-like cells was induced using retinoic acid, and the cells were then cultured with dibutyryl cAMP (dbcAMP), forskolin, or transforming growth factor (TGF) beta 1 or beta 2, and the levels of secreted laminin were measured using ELISA. dbcAMP and forskolin stimulated (p < 0.01) laminin secretion, whereas TGF-beta 1 decreased (p < 0.01) the secretion of laminin by PrE-like cells during a 72-h culture period (without influencing laminin deposition by these cells). In contrast, TGF-beta 2 did not significantly influence (p > 0.05) laminin secretion. The results of in vitro migration experiments using mouse ICMs prepared by immunosurgery indicated that, unlike fibronectin, neither laminin nor type IV collagen supported the outward movement of differentiating PrE-like cells. These findings support a potential role for TGF-beta 1 in influencing the establishment of the parietal endoderm cell layer within the mouse blastocyst by reducing the extent of laminin deposition in Reichert's membrane during endoderm cell migration.

Animals↗
PubMed1983

Endodermal sinus tumor (yolk sac tumor) of the orbit.

The endodermal sinus tumor is a malignant germ cell neoplasm that usually arises in gonads, but on rare occasion occurs in extragonadal locations. Five tumors of the orbit, which by light microscopy displayed features characteristic of gonadal endodermal sinus tumor, were tested for the presence of alpha fetoprotein using paraffin-embedded tissue and an immunoperoxidase technique. Each tumor contained intracytoplasmic alpha fetoprotein. Review of the clinical histories revealed that orbital endodermal sinus tumors differ from other extragonadal endodermal sinus tumors in that they occur at a younger age and when treated aggressively can result in long-term survival. In children with rapidly progressive proptosis the distinction between endodermal sinus tumor and rhabdomyosarcoma poses diagnostic difficulties for both the clinician and the pathologist. When considering the diagnosis of endodermal sinus tumor, the use of immunohistochemical testing for alpha fetoprotein can be helpful.

Child, Preschool↗
PubMed1998

Notochord repression of endodermal Sonic hedgehog permits pancreas development.

Notochord signals to the endoderm are required for development of the chick dorsal pancreas. Sonic hedgehog (SHH) is normally absent from pancreatic endoderm, and we provide evidence that notochord, in contrast to its effects on adjacent neuroectoderm where SHH expression is induced, represses SHH expression in adjacent nascent pancreatic endoderm. We identify activin-betaB and FGF2 as notochord factors that can repress endodermal SHH and thereby permit expression of pancreas genes including Pdx1 and insulin. Endoderm treatment with antibodies that block hedgehog activity also results in pancreatic gene expression. Prevention of SHH expression in prepancreatic dorsal endoderm by intercellular signals, like activin and FGF, may be critical for permitting early steps of chick pancreatic development.

Activins↗
PubMed2006

Early development of zooxanthella-containing eggs of the corals Porites cylindrica and Montipora digitata: The endodermal localization of zooxanthellae.

We studied the early development of zooxanthellae-containing eggs of the scleractinian corals Porites cylindrica and Montipora digitata to elucidate how zooxanthellae become localized to the endoderm of planulae during the course of development. In both species, zooxanthellae were distributed evenly in the oocytes and delivered almost equally to the blastomeres during cleavage. In P. cylindrica, gastrulation occurred via delamination or ingression, and blastomeres containing zooxanthellae dropped into the blastocoel during gastrulation. Thus, zooxanthellae were restricted to the endodermal cells at the gastrula or early planula stage in P. cylindrica. In M. digitata, gastrulation occurred by a combination of invagination and epiboly to form a somewhat concave gastrula. Zooxanthellae were present in both endodermal and ectodermal cells of early planulae, but they disappeared from the ectoderm as the planulae matured. In our previous study on two species of Pocillopora, we found that zooxanthellae were localized in eggs as well as in embryos, and that blastomeres containing zooxanthellae later dropped into the blastocoel to become restricted to the endoderm (Hirose et al., 2000). The timing and mechanism of zooxanthella localization and types of gastrulation differed among species belonging to the three genera. These results suggest that zooxanthella localization in the embryos reflects the timing of the determination of presumptive endoderm cells and/or specificity of zooxanthellae toward presumptive endoderm cells.

Animals↗