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At least 685 records · Page 38Linked to original sources
PubMed1979

Interferon enhances 2-5A synthetase in embryonal carcinoma cells.

Mouse teratocarcinomas provide a useful model of mammalian differentiation, because the malignant embryonal carcinoma (EC) stem cells of such tumours may produce various differential cell types in vivo or in vitro. Many EC cell lines have now been established and classified on the basis of their ability to differentiate in vivo into cell types characteristically derived from any of the three germ layers. There is convincing evidence that EC cells can neither produce interferon, nor respond to it by becoming resistant to virus, whereas differentiated cells derived from EC lines behave normally in both respects. We investigated the lack of responsiveness of EC cells towards interferon by measuring the levels of two double-stranded RNA-dependent enzyme activities recently shown to be enhanced by interferon. We report here that on treatment with interferon, EC cells show increased 2-5A synthetase levels comparable to those found in differentiated cells, while there is little or no effect on kinase activity in EC cells, in contrast to their differentiated counterparts.

Adenine Nucleotides↗
PubMedDate not supplied

Prevention of gastrulation but not neurulation by antibodies to fibronectin in amphibian embryos.

Gastrulation and formation of the neural plate are major steps in early vertebrate embryogenesis. Although morphogenetic movements leading to the formation of the primary germ layers have been extensively described, the mechanisms governing migration of mesodermal cells and their interactions with ectoderm remain ill-defined. A large body of evidence indicates that fibronectin (FN), a high molecular weight cell-surface-associated glycoprotein, promotes cell adhesion and cell migration throughout embryogenesis. FN has been detected at an early blastula stage in Pleurodeles waltlii. We now show that FN is a component of a dense fibrillar matrix underlying the blastocoel roof; in contrast, the exterior surface of the embryo is devoid of FN. Microsurgical inversion of part of the blastocoel roof does not prevent mesodermal cell migration except at the site of inversion where no FN matrix is available. Perturbation experiments using antibodies to FN demonstrate that the invagination of presumptive mesodermal cells does not occur when the monovalent antibodies are injected before or at the onset of gastrulation; on the other hand, the formation of a neural plate is not prevented when late gastrula stage embryos are treated with antibodies to FN. We conclude that the presence of FN is required for cell migration during gastrulation.

Animals↗
PubMedDate not supplied

Homoeobox gene expression in mouse embryos varies with position by the primitive streak stage.

Pattern formation in animal development requires that genes be expressed differentially according to position in the sheets of cells that make up the early embryo. The homoeobox-containing genes of Drosophila are control genes active both in the establishment of a segmentation pattern and in the specification of segment identity. In situ hybridization experiments confirm that these genes are expressed in a segmentally-restricted manner and that their expression presages morphological differentiation of segmental structures. Homoeobox genes have recently been isolated from the mouse and have been shown to be expressed during mouse development. Using in situ hybridization, we show here that expression of the mouse homoeobox gene Mo-10 (ref. 7) is spatially restricted in the developing embryo and that localization of expression is already evident within the germ layers before their morphological differentiation. These findings support the suggestion that the homoeobox genes of mammals, like those of Drosophila, may be important in pattern formation.

Animals↗
PubMed1989

Mutant Drosophila embryos in which all cells adopt a neural fate.

In the Drosophila embryo, early developmental decisions lead to all cells adopting one of several initial fates, such as those characteristic of the germ layers. The central nervous system is formed subsequently from the neurogenic region of the ectoderm, in which progenitor cells of the neuroblasts and ventral epidermis are intermingled. Two classes of genes govern the segregation of neuroblasts and peripheral sensory organs. The pro-neural class of genes, for example, the achaete-scute complex, participates in the initial decision to make each uniquely positioned neuroblast or sensory organ, but are initially expressed in groups of cells. The segregation of a neuroblast or sensory organ from an equivalent group of equipotential cells involves a mechanism of lateral inhibition whereby the future epidermal cells are prevented from engaging in the primary dominant neural fate. In the absence of this inhibitory signal, all cells of the group will become neural by default. The neurogenic class of genes is thought to mediate these cell interactions. Here we report that cells in embryos mutant for shaggy which are unable to adopt any of the early initial fates, instead develop neural characteristics.

Animals↗
PubMed2000

Silberblick/Wnt11 mediates convergent extension movements during zebrafish gastrulation.

Vertebrate gastrulation involves the specification and coordinated movement of large populations of cells that give rise to the ectodermal, mesodermal and endodermal germ layers. Although many of the genes involved in the specification of cell identity during this process have been identified, little is known of the genes that coordinate cell movement. Here we show that the zebrafish silberblick (slb) locus encodes Wnt11 and that Slb/Wnt11 activity is required for cells to undergo correct convergent extension movements during gastrulation. In the absence of Slb/Wnt11 function, abnormal extension of axial tissue results in cyclopia and other midline defects in the head. The requirement for Slb/Wnt11 is cell non-autonomous, and our results indicate that the correct extension of axial tissue is at least partly dependent on medio-lateral cell intercalation in paraxial tissue. We also show that the slb phenotype is rescued by a truncated form of Dishevelled that does not signal through the canonical Wnt pathway, suggesting that, as in flies, Wnt signalling might mediate morphogenetic events through a divergent signal transduction cascade. Our results provide genetic and experimental evidence that Wnt activity in lateral tissues has a crucial role in driving the convergent extension movements underlying vertebrate gastrulation.

Animals↗
PubMedDate not supplied

Mitotic domains in the early embryo of the zebrafish.

At the midblastula transition in the zebrafish, three, and only three, spatially separate mitotic domains arise with distinctive cycle lengths and rhythms. As in Drosophila and at about the equivalent stage, the mitotic domains reflect the fate map, but they do so only very crudely: two are extraembryonic and the third forms the entire embryo. The domains appear not to subdivide during gastrulation, when the germ layers form and when cells probably commit to their eventual fates. The domains may signal specification of morphogenesis rather than cell fate, because, shortly after they appear, each assumes a different role during epiboly, the first morphogenetic movement of the embryo. During meroblastic cleavage, and continuing in the early blastula, zebrafish blastomeres divide rapidly and synchronously. At the time of the tenth cleavage, the beginning of the midblastula transition, the cell cycle lengthens, and, as in Xenopus and Drosophila, cycle length comes under nucleocytoplasmic control (D.A.K. and C.B.K., manuscript in preparation). This nucleocytoplasmic control seems to be maintained during cycle lengthening in the next 2 or 3 cycles, comprising a midblastula transition period. We now show that functionally distinct subsets of cells that arise during this period have reproducibly different mitotic cycle lengths.

Animals↗
PubMed1993

Nodal is a novel TGF-beta-like gene expressed in the mouse node during gastrulation.

During gastrulation, the three germ layers of the embryo are formed and organized along the anterior-posterior body axis. In the mouse, gastrulation involves the delamination of ectodermal cells through the primitive streak and their differentiation into mesoderm. These processes do not occur in embryos homozygous for a retrovirally induced recessive prenatal lethal mutation, the strain 413-d insertional mutation. Instead of giving rise to mesoderm, embryonic ectoderm in 413-d mutants overproliferates and then rapidly degenerates, although extraembryonic lineages remain viable. Here we isolate a candidate for the mutated gene which encodes a new member of the transforming growth factor-beta (TGF-beta) superfamily. Expression is first detected in primitive streak-stage embryos at about the time of mesoderm formation. It then becomes highly localized in the node at the anterior of the primitive streak. This region is analogous to chick Hensen's node and Xenopus dorsal lip (Spemann's organizer), which can induce secondary body axes when grafted into host embryos (reviewed in refs 5 and 6). Our findings suggest that this gene, named nodal, encodes a signalling molecule essential for mesoderm formation and subsequent organization of axial structures in early mouse development.

Amino Acid Sequence↗
PubMed1994

Inactivation of the N-CAM gene in mice results in size reduction of the olfactory bulb and deficits in spatial learning.

Neural-cell adhesion molecules (N-CAMs) are members of the immunoglobulin superfamily mediating homo- and heterophilic cell-cell interactions. N-CAM exists in various isoforms which are generated by alternative splicing. During embryonic development, N-CAMs are expressed in derivatives of all three germ layers, whereas in the adult animal they are predominantly present in neural tissue. Processes like neurulation, axonal outgrowth, histogenesis of the retina and development of the olfactory system are correlated with the regulated expression of N-CAMs. We show here that N-CAM-deficient mice generated by gene targeting appear healthy and fertile, but adult mutants show a 10% reduction in overall brain weight and a 36% decline in size of the olfactory bulb. N-CAM deficiency coincides with almost total loss of protein-bound alpha-(2,8)-linked polysialic acid, a carbohydrate structure thought to be correlated with neural development and plasticity. The animals showed deficits in spatial learning when tested in the Morris water maze, whereas activity and motor abilities appeared normal.

Animals↗
PubMedDate not supplied

dpp induces mesodermal gene expression in Drosophila.

Inductive interactions between germ layers are an essential feature of the development of many organisms. In several species these interactions are mediated by members of the transforming growth factor-beta (TGF beta) family. In amphibians, different concentrations of activin can induce different types of mesoderm in the animal cap assay. In Drosophila, a member of the TGF beta family, decapentaplegic (dpp), acts as an inductive signal. Midway through embryogenesis, dpp is expressed in the visceral mesoderm, and enhances the expression of the homeotic gene labial in the underlying midgut endoderm. Earlier in development, however, dpp expression is limited to the dorsal ectoderm. At this stage in development, thickveins, a dpp receptor, is expressed in the mesoderm, and this suggests that ectodermal dpp might not only be required for development of dorsal ectoderm, but could also act inductively to mediate pattern formation in the underlying mesoderm. Here we show, by expressing dpp ectopically in the ectoderm and mesoderm and by examining dpp null mutant embryos, that dpp regulates expression of mesodermal genes.

Animals↗
PubMed2000

Embryonic stem cell lines from human blastocysts: somatic differentiation in vitro.

We describe the derivation of pluripotent embryonic stem (ES) cells from human blastocysts. Two diploid ES cell lines have been cultivated in vitro for extended periods while maintaining expression of markers characteristic of pluripotent primate cells. Human ES cells express the transcription factor Oct-4, essential for development of pluripotential cells in the mouse. When grafted into SCID mice, both lines give rise to teratomas containing derivatives of all three embryonic germ layers. Both cell lines differentiate in vitro into extraembryonic and somatic cell lineages. Neural progenitor cells may be isolated from differentiating ES cell cultures and induced to form mature neurons. Embryonic stem cells provide a model to study early human embryology, an investigational tool for discovery of novel growth factors and medicines, and a potential source of cells for use in transplantation therapy.

Animals↗
PubMed2000

Skeletal myogenic potential of human and mouse neural stem cells.

Distinct cell lineages established early in development are usually maintained throughout adulthood. Thus, adult stem cells have been thought to generate differentiated cells specific to the tissue in which they reside. This view has been challenged; for example, neural stem cells can generate cells that normally originate from a different germ layer. Here we show that acutely isolated and clonally derived neural stem cells from mice and humans could produce skeletal myotubes in vitro and in vivo, the latter following transplantation into adult animals. Myogenic conversion in vitro required direct exposure to myoblasts, and was blocked if neural cells were clustered. Thus, a community effect between neural cells may override such myogenic induction. We conclude that neural stem cells, which generate neurons, glia and blood cells, can also produce skeletal muscle cells, and can undergo various patterns of differentiation depending on exposure to appropriate epigenetic signals in mature tissues.

Age Factors↗
PubMed2000

Purified hematopoietic stem cells can differentiate into hepatocytes in vivo.

The characterization of hepatic progenitor cells is of great scientific and clinical interest. Here we report that intravenous injection of adult bone marrow cells in the FAH(-/-) mouse, an animal model of tyrosinemia type I, rescued the mouse and restored the biochemical function of its liver. Moreover, within bone marrow, only rigorously purified hematopoietic stem cells gave rise to donor-derived hematopoietic and hepatic regeneration. This result seems to contradict the conventional assumptions of the germ layer origins of tissues such as the liver, and raises the question of whether the cells of the hematopoietic stem cell phenotype are pluripotent hematopoietic cells that retain the ability to transdifferentiate, or whether they are more primitive multipotent cells.

Animals↗
PubMed1984

Growth and differentiation of pluripotent embryonal carcinoma cells in the Snell dwarf mouse.

To investigate the influence of hormones on the process of cellular differentiation the growth and differentiation of a transplantable tumour, induced by inoculation of pluripotent mouse embryonal carcinoma (EC) cells have been studied in athymic nude mice and, normal and hypopituitary Snell dwarf mice. All athymic nude mice developed tumours independent of the numbers of cells inoculated. In contrast, the tumour percentage in normal Snell mice was lower, showing a dose-dependent increase of takes. In dwarfs tumour percentage was comparable with that observed in normal Snell mice. The morphological differentiation of teratocarcinomas grown in athymic nude mice, normal and dwarfed Snell mice shows derivatives of all three germ layers next to undifferentiated embryonal carcinoma cells. This suggests that the pituitary hormonal deficiencies of the dwarfs (growth hormone, thyroid stimulating hormone and prolactin) did not influence the tumour induction nor the development of the different tissues present in this type of tumour.

Animals↗
PubMed1989

Pattern of expression of c-erbB-2 oncoprotein in human fetuses.

The pattern of expression of the c-erbB-2 oncoprotein was investigated in whole mount preparations of 11 human fetuses by immunocytochemistry using two polyclonal antibodies, 20N and 21N. c-erbB-2 was widely expressed within all three germ layers. Expression remained relatively constant in epithelial, mesodermal and extraembryonic tissues, but varied over time during the development of the fetal skeleton. Western blotting failed to detect c-erbB-2 in normal fetal tissues but did confirm expression in a microvillous membrane preparation of placenta. c-erbB-2 expression is widespread in the human fetus and occurs at an earlier stage than epidermal growth factor receptor.

Biomarkers, Tumor↗
PubMed2006

Pluripotency of spermatogonial stem cells from adult mouse testis.

Embryonic germ cells as well as germline stem cells from neonatal mouse testis are pluripotent and have differentiation potential similar to embryonic stem cells, suggesting that the germline lineage may retain the ability to generate pluripotent cells. However, until now there has been no evidence for the pluripotency and plasticity of adult spermatogonial stem cells (SSCs), which are responsible for maintaining spermatogenesis throughout life in the male. Here we show the isolation of SSCs from adult mouse testis using genetic selection, with a success rate of 27%. These isolated SSCs respond to culture conditions and acquire embryonic stem cell properties. We name these cells multipotent adult germline stem cells (maGSCs). They are able to spontaneously differentiate into derivatives of the three embryonic germ layers in vitro and generate teratomas in immunodeficient mice. When injected into an early blastocyst, SSCs contribute to the development of various organs and show germline transmission. Thus, the capacity to form multipotent cells persists in adult mouse testis. Establishment of human maGSCs from testicular biopsies may allow individual cell-based therapy without the ethical and immunological problems associated with human embryonic stem cells. Furthermore, these cells may provide new opportunities to study genetic diseases in various cell lineages.

Age Factors↗
PubMed2006

Clonal analysis reveals a common progenitor for thymic cortical and medullary epithelium.

The thymus provides an essential environment for the development of T cells from haemopoietic progenitors. This environment is separated into cortical and medullary regions, each containing functionally distinct epithelial populations that are important at successive stages of T-cell development and selection. However, the developmental origin and lineage relationships between cortical and medullary epithelial cell types remain controversial. Here we describe a clonal assay to investigate the developmental potential of single, individually selected, thymic epithelial progenitors (marked with enhanced yellow fluorescent protein) developing within the normal architecture of the thymus. Using this approach, we show that cortical and medullary epithelial cells share a common origin in bipotent precursors, providing definitive evidence that they have a single rather than dual germ layer origin during embryogenesis. Our findings resolve a long-standing issue in thymus development, and are important in relation to the development of cell-based strategies for thymus disorders and the possibility of restoring function of the atrophied adult thymus.

Animals↗
PubMed2006

Human embryonic stem cell lines derived from single blastomeres.

The derivation of human embryonic stem (hES) cells currently requires the destruction of ex utero embryos. A previous study in mice indicates that it might be possible to generate embryonic stem (ES) cells using a single-cell biopsy similar to that used in preimplantation genetic diagnosis (PGD), which does not interfere with the embryo's developmental potential. By growing the single blastomere overnight, the resulting cells could be used for both genetic testing and stem cell derivation without affecting the clinical outcome of the procedure. Here we report a series of ten separate experiments demonstrating that hES cells can be derived from single blastomeres. In this proof-of-principle study, multiple biopsies were taken from each embryo using micromanipulation techniques and none of the biopsied embryos were allowed to develop in culture. Nineteen ES-cell-like outgrowths and two stable hES cell lines were obtained. The latter hES cell lines maintained undifferentiated proliferation for more than eight months, and showed normal karyotype and expression of markers of pluripotency, including Oct-4, SSEA-3, SSEA-4, TRA-1-60, TRA-1-81, nanog and alkaline phosphatase. These cells retained the potential to form derivatives of all three embryonic germ layers both in vitro and in teratomas. The ability to create new stem cell lines and therapies without destroying embryos would address the ethical concerns of many, and allow the generation of matched tissue for children and siblings born from transferred PGD embryos.

Blastomeres↗
PubMed1998

Transgenic bovine chimeric offspring produced from somatic cell-derived stem-like cells.

We have developed a method, using nuclear transplantation, to produce transgenic embryonic stem (ES)-like cells from fetal bovine fibroblasts. These cells, when reintroduced into preimplantation embryos, differentiated into derivatives from the three embryonic germ layers, ectoderm, mesoderm, and endoderm, in 5-month-old animals. Six out of seven (86%) calves born were found to be chimeric for at least one tissue. These experiments demonstrate that somatic cells can be genetically modified and then de-differentiated by nuclear transfer into ES-like cells, opening the possibility of using them in differentiation studies and human cell therapy.

Animals↗