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Results for “Germ Layers”

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At least 847 records · Page 47Linked to original sources
PubMed1994

Induction of erythropoiesis in the amphibian embryo.

Germ-layer formation and differentiation of specialized tissues in vertebrate embryogenesis is a multistep mechanism that is mediated by different growth factors (or growth factor-related molecules). We have investigated various differentiation factors that contribute to mesoderm formation in amphibian embryos and analyzed the formation of blood islands during embryogenesis and in ectodermal explants that have been incubated with mesoderm inducing factors. Erythropoiesis in these explants is demonstrated by whole mount in situ hybridization using an embryonic alpha-globin probe. Furthermore, we have isolated several transcription factors of the fork head family and analyzed whether they are involved in the pathway leading to hematopoietic cells. One of these factors, termed Xenopus fork head (XFD)-2, is transcribed in blastula stage embryos for a limited time period in dorsal and ventral mesoderm. Moreover, the target sequence of this factor is found to be present within the upstream sequences of many genes that are expressed in mesoderm-derived tissues.

Amino Acid Sequence↗
PubMed2003

Adult bone marrow stem cells regenerate myocardium in ischemic heart disease.

Recent studies have demonstrated the existence of several populations of primitive cells in mouse and human bone marrow that have the capacity, both in vitro and in vivo, to give rise to cells of all three germ layers. Mesenchymal/stromal stem cells and hematopoietic stem cells are the leading candidates for this activity that some believe may recapitulate the potential of embryonic stem cells. Very little is known about the molecular controls for this adult stem cell activity commonly referred to as transdifferentiation or plasticity. Regeneration of a large number of cell types and tissues has been investigated with one of the most extensively studied being the myocardium. These studies involved ligation of the left coronary artery in adult mice and the direct injection or mobilization of bone marrow stem cells. Using this protocol we, and others, have observed the generation of new cardiomyocytes and endothelial cells in the zone of ischemic myocardium. This approach has progressed to clinical trials at several academic institutions. Although the preliminary findings from these trials do not permit unequivocal conclusions, they do suggest that safety and feasibility are not significant problems that would argue against extending these trials in a large, randomized, double-blinded study. When considerations such as these are addressed, cell therapy may become a new modality in the treatment of heart patients.

Animals↗
PubMed2003

Pluripotent stem cells identified in multiple murine tissues.

Pluripotential stem cells (PSCs) have been recently described in many tissues including skeletal muscle, brain, and bone marrow. However, the true nature of these cells is still unclear, and their precise definition has yet to be determined. We hypothesized that a common, rare population of PSCs with a broad tissue differentiation potential can be identified in multiple murine tissues and that these cells are capable of transdifferentiation into cells of different primordial germ layer origins in response to diverse microenvironmental cues. To examine this hypothesis, we isolated phenotypically defined cells from murine skeletal muscle and cultured these cells under different conditions tailored to promote differentiation into several cell types including myocytes. We report here that in conditions permissive for hematopoietic differentiation, muscle-derived CD45(-)Sca-1(+)c-kit(-) cells differentiated into cells expressing hematopoietic-specific mRNA; while in conditions promoting myogenic, neuronal, and adipocytic differentiation, cells morphologically typical of these cell types expressing tissue-specific markers were identified 9-14 days in culture. When CD45(-)Sca-1(+)c-kit(-) cells from muscle or bone marrow were transplanted intracerebellarly into Purkinje cell degenerative (pcd) mice, the behavior of these mice improved 28 days after transplantation relative to mice injected with vehicle alone, suggesting that these cells contributed to the appearance of functional neuronal cells that may have improved the ataxic condition characteristic of these mice. Phenotypic analysis of single cell suspensions prepared from brain, blood, and intestinal epithelium revealed the presence of CD45(-)Sca-1(+)c-kit(-) cells in varying degrees. These studies suggest that a phenotypically common, multipotent cell can be identified in different tissues and that this cell may represent a universal pluripotent stem cell residing at different levels in multiple murine tissues.

Animals↗
PubMed2004

RETRACTED: Evidence of a pluripotent human embryonic stem cell line derived from a cloned blastocyst.

Somatic cell nuclear transfer (SCNT) technology has recently been used to generate animals with a common genetic composition. In this study, we report the derivation of a pluripotent embryonic stem (ES) cell line (SCNT-hES-1) from a cloned human blastocyst. The SCNT-hES-1 cells displayed typical ES cell morphology and cell surface markers and were capable of differentiating into embryoid bodies in vitro and of forming teratomas in vivo containing cell derivatives from all three embryonic germ layers in severe combined immunodeficient mice. After continuous proliferation for more than 70 passages, SCNT-hES-1 cells maintained normal karyotypes and were genetically identical to the somatic nuclear donor cells. Although we cannot completely exclude the possibility that the cells had a parthenogenetic origin, imprinting analyses support a SCNT origin of the derived human ES cells.

Animals↗
PubMed2005

Nuclear reprogramming of somatic cells after fusion with human embryonic stem cells.

We have explored the use of embryonic stem cells as an alternative to oocytes for reprogramming human somatic nuclei. Human embryonic stem (hES) cells were fused with human fibroblasts, resulting in hybrid cells that maintain a stable tetraploid DNA content and have morphology, growth rate, and antigen expression patterns characteristic of hES cells. Differentiation of hybrid cells in vitro and in vivo yielded cell types from each embryonic germ layer. Analysis of genome-wide transcriptional activity, reporter gene activation, allele-specific gene expression, and DNA methylation showed that the somatic genome was reprogrammed to an embryonic state. These results establish that hES cells can reprogram the transcriptional state of somatic nuclei and provide a system for investigating the underlying mechanisms.

Adult↗
PubMed1998

Mixer, a homeobox gene required for endoderm development.

An expression cloning strategy in Xenopus laevis was used to isolate a homeobox-containing gene, Mixer, that can cause embryonic cells to form endoderm. Mixer transcripts are found specifically in the prospective endoderm of gastrula, which coincides with the time and place that endodermal cells become histologically distinct and irreversibly determined. Loss-of-function studies with a dominant inhibitory mutant demonstrate that Mixer activity is required for endoderm development. In particular, the expression of Sox17alpha and Sox17beta, two previously identified endodermal determinants, require Mixer function. Together, these data suggest that Mixer is an embryonic transcription factor involved in specifying the endodermal germ layer.

Animals↗
PubMed1998

Embryonic stem cell lines derived from human blastocysts.

Human blastocyst-derived, pluripotent cell lines are described that have normal karyotypes, express high levels of telomerase activity, and express cell surface markers that characterize primate embryonic stem cells but do not characterize other early lineages. After undifferentiated proliferation in vitro for 4 to 5 months, these cells still maintained the developmental potential to form trophoblast and derivatives of all three embryonic germ layers, including gut epithelium (endoderm); cartilage, bone, smooth muscle, and striated muscle (mesoderm); and neural epithelium, embryonic ganglia, and stratified squamous epithelium (ectoderm). These cell lines should be useful in human developmental biology, drug discovery, and transplantation medicine.

Animals↗
PubMed2000

Generalized potential of adult neural stem cells.

The differentiation potential of stem cells in tissues of the adult has been thought to be limited to cell lineages present in the organ from which they were derived, but there is evidence that some stem cells may have a broader differentiation repertoire. We show here that neural stem cells from the adult mouse brain can contribute to the formation of chimeric chick and mouse embryos and give rise to cells of all germ layers. This demonstrates that an adult neural stem cell has a very broad developmental capacity and may potentially be used to generate a variety of cell types for transplantation in different diseases.

Animals↗
PubMed2005

Teaching resources. Mesodermal differentiation: signal integration during development.

This Teaching Resource provides a summary and slides derived from a lecture on the signaling cascades that mediate early embryogenesis and is part of the course "Cell Signaling Systems: A Course for Graduate Students." The lecture focuses on the mechanisms underlying germ layer formation, patterning, and suppression in the vertebrate embryo, with particular emphasis on the regulation of mesodermal development in the model organism Xenopus laevis.

Animals↗
PubMed2006

RBP-Jkappa-dependent notch signaling is dispensable for mouse early embryonic development.

The Notch signaling pathway is an evolutionarily conserved signaling system which has been shown to be essential in cell fate specification and in numerous aspects of embryonic development in all metazoans thus far studied. We recently demonstrated that several components of the Notch signaling pathway, including the four Notch receptors and their five ligands known in mammals, are expressed in mouse oocytes, in mouse preimplantation embryos, or both. This suggested a possible implication of the Notch pathway in the first cell fate specification of the dividing mouse embryo, which results in the formation of the blastocyst. To address this issue directly, we generated zygotes in which both the maternal and the zygotic expression of Rbpsuh, a key element of the core Notch signaling pathway, were abrogated. We find that such zygotes give rise to blastocysts which implant and develop normally. Nevertheless, after gastrulation, these embryos die around midgestation, similarly to Rbpsuh-null mutants. This demonstrates that the RBP-Jkappa-dependent pathway, otherwise called the canonical Notch pathway, is dispensable for blastocyst morphogenesis and the establishment of the three germ layers, ectoderm, endoderm, and mesoderm. These results are discussed in the light of recent observations which have challenged this conclusion.

Animals↗
PubMed2001

The mouse snail gene encodes a key regulator of the epithelial-mesenchymal transition.

Snail family genes encode DNA binding zinc finger proteins that act as transcriptional repressors. Mouse embryos deficient for the Snail (Sna) gene exhibit defects in the formation of the mesoderm germ layer. In Sna(-/-) mutant embryos, a mesoderm layer forms and mesodermal marker genes are induced but the mutant mesoderm is morphologically abnormal. Lacunae form within the mesoderm layer of the mutant embryos, and cells lining these lacunae retain epithelial characteristics. These cells resemble a columnar epithelium and have apical-basal polarity, with microvilli along the apical surface and intercellular electron-dense adhesive junctions that resemble adherens junctions. E-cadherin expression is retained in the mesoderm of the Sna(-/-) embryos. These defects are strikingly similar to the gastrulation defects observed in snail-deficient Drosophila embryos, suggesting that the mechanism of repression of E-cadherin transcription by Snail family proteins may have been present in the metazoan ancestor of the arthropod and mammalian lineages.

Abnormalities, Multiple↗
PubMed1989

Differential activity of a tissue-specific extinguisher locus in hepatic and nonhepatic cells.

Tissue-specific extinguisher 1 (Tse-1) is a genetic locus on mouse chromosome 11 that can repress expression of several liver genes in trans. This locus is clearly active in fibroblasts, as hepatoma cells retaining fibroblast chromosome 11 are extinguished for both tyrosine aminotransferase and phosphoenolpyruvate carboxykinase gene expression. To assess the activity of Tse-1 in other tissues, we transferred mouse chromosome 11 from several different cell types into rat hepatoma recipients. Tse-1 was active in nonhepatic cell lines derived from each primary germ layer, but Tse-1 activity was not apparent in hybrids between hepatoma cells and primary mouse hepatocytes. These differences in the genetic activity of murine Tse-1 were apparently heritable in cis.

Animals↗
PubMed2005

Upregulation of tissue kallikrein, kinin B1 receptor, and kinin B2 receptor in mast and giant cells infiltrating oesophageal squamous cell carcinoma.

BACKGROUND: The mitogenic kinin peptides formed by the serine protease, tissue kallikrein (TK1), stimulate the proliferation of tumour cells and, by increasing vascular permeability, enhance metastasis. Oesophageal mucosal epithelial cells are derived from the epithelial cell germ layer, which expresses the kallikrein-kinin cascade. AIM: To determine the cellular distribution of active TK1, prokallikrein, and the kinin B(1) and B(2) receptors in oesophageal carcinoma by immunocytochemistry and in situ hybridisation (ISH). METHODS: Fifty oesophageal specimens (33 biopsies and 17 resections) and 10 control specimens adjacent to tumour or normal oesophageal biopsies were studied. Specific antibodies were used to determine the cellular localisation of TK1, prokallikrein, and the kinin B(1) and B(2) receptors in normal and oesophageal specimens by standard immunohistochemical techniques. The intensity of immunolabelling was quantified by image analysis. Antisense probes for TK1 and the kinin B(1) and B(2) receptors were also used to localise mRNA. RESULTS: TK1 (active and prokallikrein) was expressed in the mucosa of normal and tumour oesophageal epithelium. In general, expression was highest in activated mast cells, followed by giant tumour cells. Immunolabelling results were confirmed by ISH experiments. CONCLUSIONS: This is the first demonstration that TK1 and kinin B(1) and B(2) receptors are expressed in oesophageal carcinoma. Because TK1 released from tumour cells enzymatically generates mitogenic kinins from its endogenous substrate, kininogen, it is possible that third generation kinin receptor antagonists, which have been shown to be cytotoxic to cancer cells, may be useful therapeutic agents in this disease.

Carcinoma, Squamous Cell↗
PubMed1994

Hydrocephalus in an infant with trisomy 22.

We present an infant with true trisomy 22. Mosaicism is ruled out by the finding of a 47,XX, +22 karyotype in all cells analysed originating from two embryonic germ layers. The physical findings are consistent with the previously noted features including developmental delay, ear abnormalities, micrognathia, clefting, and congenital heart disease. The patient is the first described with macrocephaly and hydrocephalus and the second with holoprosencephaly.

Abnormalities, Multiple↗
PubMed1995

Drosophila gastrulation: from pattern formation to morphogenesis.

The major morphogenetic movements during Drosophila gastrulation--germ band extension and the invagination of the mesoderm and endoderm--are driven by cell intercalation and cell shape changes, respectively. The regions of the early embryo in which these movements occur and which give rise to the germ layers are demarcated by a small number of zygotically expressed genes. These genes code for transcription factors that regulate cell behavior by controlling expression of target genes whose products modulate the cytoskeleton and other subcellular compartments.

Animals↗
PubMed1999

Vertebrate endoderm development.

Endoderm, one of the three principal germ layers, contributes to all organs of the alimentary tract. For simplicity, this review divides formation of endodermal organs into four fundamental steps: (a) formation of endoderm during gastrulation, (b) morphogenesis of a gut tube from a sheet of cells, (c) budding of organ domains from the tube, and (d) differentiation of organ-specific cell types within the growing buds. We discuss possible mechanisms that regulate how undifferentiated endoderm becomes specified into a myriad of cell types that populate the respiratory and gastrointestinal tracts.

Animals↗
PubMed2005

Molecular genetics of axis formation in zebrafish.

The basic vertebrate body plan of the zebrafish embryo is established in the first 10 hours of development. This period is characterized by the formation of the anterior-posterior and dorsal-ventral axes, the development of the three germ layers, the specification of organ progenitors, and the complex morphogenetic movements of cells. During the past 10 years a combination of genetic, embryological, and molecular analyses has provided detailed insights into the mechanisms underlying this process. Maternal determinants control the expression of transcription factors and the location of signaling centers that pattern the blastula and gastrula. Bmp, Nodal, FGF, canonical Wnt, and retinoic acid signals generate positional information that leads to the restricted expression of transcription factors that control cell type specification. Noncanonical Wnt signaling is required for the morphogenetic movements during gastrulation. We review how the coordinated interplay of these molecules determines the fate and movement of embryonic cells.

Animals↗
PubMed1995

Teratomas, dermoids, and epidermoids of the head and neck.

Dermoids and epidermoids are ectoderm-lined inclusion cysts that differ in complexity: Epidermoids have only squamous epithelium; dermoids contain hair, sebaceous and sweat glands, and squamous epithelium. Both arise from trapped pouches of ectoderm, near normal folds, or from failure of surface ectoderm to separate from the neural tube. These slowly expanding, unilocular, cystic masses may produce only mild symptoms. They commonly occur in the orbit, calvarial diploic space, and intracranially (the posterior and middle fossae). They may be complicated by rupture leading to chemical meningitis, and dermoids with a fistulous tract can become infected. Craniofacial teratomas are true neoplasms arising from misplaced embryologic germ cells. They contain a medley of heterogeneous tissues, typically reflecting more than one of the three embryonic germ layers. They are usually multiloculated masses, often large, with complex radiologic characteristics. Craniofacial teratomas may manifest prenatally with macrocrania or polyhydramnios, during a difficult delivery, or postnatally as a life-threatening mass causing brain herniation, hydrocephalus, respiratory distress, or feeding difficulty. In infancy, they can be biologically benign, even when their histologic characteristics are immature. Surgery is the treatment of choice for all three masses and may be curative.

Adolescent↗