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G C Tucker

Publications and source records attributed to G C Tucker.

33 records · Page 2Linked to original sources
PubMed1990

Alternative patterns of mitogenesis and cell scattering induced by acidic FGF as a function of cell density in a rat bladder carcinoma cell line.

The dual function exerted by acidic fibroblast growth factor (aFGF) in a rat bladder carcinoma cell line has been explored under two different conditions of culture density. At low cell density, aFGF promotes the epithelium-to-mesenchyme transition of NBT-II cells characterized by cell dissociation, morphological changes toward a fibroblastic-like phenotype, and acquisition of cell motility. Under these conditions, NBT-II cells are unresponsive to the growth-promoting effect of aFGF. At high cell density, aFGF is a potent mitogenic factor, but its scattering activity is essentially abrogated. Slight modifications in the binding of aFGF to its specific receptors were observed at high cell density; these changes correlated with a downregulation of receptors with no apparent change in their molecular form. NBT-II cells located at the edge of artificial wounds mimicked the behavior of subconfluent cells, because they did not proliferate upon aFGF treatment. Furthermore, in large-sized NBT-II colonies, peripheral cells were the first to dissociate in response to aFGF. Altogether, our results suggest that the cellular response to multifunctional growth factors might depend on the localization within the responding cell population.

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PubMed1990

[Modulation of epithelial differentiation of cultured rat bladder carcinoma].

Epithelium-to-mesenchyme transformation plays a key role in tissue remodelling in embryos since it allows cells from the primitive epithelia to migrate to other sites where they participate in the formation of new structures. A similar phenomenon may be involved in the detachment of malignant cells from neighboring primary tumor cells, which is a prerequisite to the invasion of neighboring tissues or the development of metastases. To test this hypothesis, an in vitro model using a rat bladder carcinoma cell line was developed. Cells exhibited epithelial features under standard culture conditions. After exposure to a soluble inducer (acidic FGF) or the specific extracellular matrix components (collagens), the cells acquired a fibroblastic phenotype, separated from one another, and started to move freely on the substrate. Inducers were found to act synergistically on the fibroblastic transformation of carcinoma cells and to promote the penetration of these cells into collagen gels.

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PubMed1989

Reversible transition towards a fibroblastic phenotype in a rat carcinoma cell line.

Two distinct mechanisms by which bladder carcinoma cells of the NBT-II cell line dissociate and migrate away from an in vitro reconstituted epithelial sheet were examined as regards intercellular adhesion and cell locomotion. Scattering of NBT-II bladder carcinoma cell line was promoted by 2 distinct culture protocols: (i) deposition of some components of the extracellular matrix onto the culture substratum (glass or plastic) induced cell dispersion of the epithelial sheet of carcinoma cells, and (ii) addition of Ultroser G, a serum substitute, to the culture medium induced scattering and acquisition of motility of NBT-II cells. Under both culture conditions, NBT-II cells dissociated, lost their epithelial morphology, acquired fibroblastic shape and migrated actively. We show that, among different extracellular matrix proteins, only collagens were able to promote the transition towards fibroblastic phenotype (referred as epithelium-to-mesenchyme transition or EMT). Furthermore, the native 3-dimensional helical structure of collagens was required for their function. During induction of EMT of NBT-II cells with Ultroser G, the junctions between epithelial cells were split, polarized epithelial cell organization was lost, and the resulting individual cells became motile and assumed a spindle-like fibroblastoid appearance. Using immunofluorescence microscopy techniques, we demonstrate that this change is accompanied by redistribution of desmosomal plaque proteins (desmoplakins, desmoglein, plakoglobin) and by reorganization of the cytokeratin and the actin-fodrin filament systems. Intermediate-sized filaments of the vimentin type were formed de novo in the fibroblastoid cell form. The observed transition towards fibroblastic phenotype (epithelium-to-mesenchyme transition or EMT) was fully reversed by removing the inducing factors from the culture medium, as shown by the disappearance of vimentin filaments and the reappearance of desmosomes in the newly formed epithelial cells.

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PubMed1989

Rearrangements of desmosomal and cytoskeletal proteins during the transition from epithelial to fibroblastoid organization in cultured rat bladder carcinoma cells.

Changes of cell morphology and the state of differentiation are known to play important roles in embryogenesis as well as in carcinogenesis. Examples of particularly profound changes are the conversions of epithelial to mesenchymal cells; i.e., the dissociation of some or all polygonal, polar epithelial cells and their transformation into elongate, fibroblastoid cells of high motility. As an in vitro model system for such changes in cell morphology, we have used cell cultures of the rat bladder carcinoma-derived cell line NBT-II which, on exposure to inducing medium containing a commercial serum substitute (Ultroser G), show an extensive change in their organization (epithelial-mesenchymal transition): the junctions between the epithelial cells are split, the epithelial cell organization is lost, and the resulting individual cells become motile and assume a spindle-like fibroblastoid appearance. Using immunofluorescence microscopy and biochemical protein characterization techniques, we show that this change is accompanied by a redistribution of desmosomal plaque proteins (desmoplakins, desmoglein, plakoglobin) and by a reorganization of the cytokeratin and the actin-fodrin filament systems. Moreover, intermediate-sized filaments of the vimentin type are formed in the fibroblastoid cells. We demonstrate that the modulation of desmosomal proteins, specifically an increase in soluble desmoplakins, is a relatively early event in cell dissociation and in epithelial-mesenchymal transition. In this process, a latent period of 5 h upon addition of inducing medium precedes the removal of these desmosomal components from the plasma membrane. The transition, which is reversible, is dependent on continued protein synthesis and phosphorylation but not on the presence of the inducing medium beyond the initial 2-h period. We discuss the value of this experimental system as a physiologically relevant approach for studying the regulation of the assembly and disassembly of desmosomes and other intercellular adhesion structures, and as a model of the conversion of cells from one state of differentiation into another.

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PubMed1988

Expression of the HNK-1/NC-1 epitope in early vertebrate neurogenesis.

A family of glycoconjugates has recently been shown to share a common carbohydrate epitope recognized by the mouse monoclonal antibody HNK-1. The specificity of HNK-1 was found to be similar to that of another monoclonal antibody, NC-1. These two IgM monoclonal antibodies were raised after immunization of mice with a human T-cell line and avian neural crest-derived ganglia, respectively. The antigens recognized by these antibodies include the myelin-associated glycoprotein, MAG, a glycolipid of defined structure, and a set of molecules involved in cell adhesion. The timing and pattern of appearance of these antigens are distinct. Moreover, the epitope may be absent on an antigen at a given stage or in a given tissue. Therefore, although the molecules able to carry the NC-1/HNK-1 epitope are numerous and expressed in various tissues, the use of the monoclonal antibodies on tissue sections has proven adequate for following the migration of avian neural crest cells, the major cell lineage recognized by NC-1 and HNK-1 during early embryogenesis. Analogies in several other species have been found on the basis of HNK-1 reactivity. In this study we show that NC-1 and HNK-1 can be used successfully to label migrating neural crest cells in dog, pig and human. On the other hand, the NC-1/HNK-1 epitope was not present on migrating crest cells in amphibians or mice and was found only transiently on the neural crest of rats.

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PubMed1988

Cell-adhesion and substrate-adhesion molecules: their instructive roles in neural crest cell migration.

The individualization of crest cells from the neural folds and neural tube involves distinct mechanisms affecting both the tissue shape and the cell environment. Though these mechanisms are not fully understood at the molecular level, the analysis of the distribution of several molecules reported to promote intercellular contacts indicates a correlation between cell detachment from the neurepithelium and the decrease of cell adhesion molecule expression. During the following phase of migration, the mode of adhesion of crest cells switches preferentially to the cell-to-substratum type. Various experiments showed that among the major extracellular matrix components, fibronectins were decisive in promoting cell attachment, spreading and motility. Additional studies on receptors for fibronectins gave new insights on the differences between a motile and a stationary cell. These results will be discussed with particular reference to the migration at the cephalic level where most perturbation experiments were performed. The molecular biology of fibronectins provided a finer understanding of the interactions between a cell and these molecules. The tools derived from this technique will open new areas of investigation hopefully leading to a better understanding of (i) the regulation of the cell-fibronectins interaction and (ii) the specificity of the pathways of migration followed by migrating cells, like the descendants of the neural crest.

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PubMed1987

Heterogeneity of human anti-MAG IgM as revealed by their reactivity on avian embryonic tissues.

Monoclonal IgM from patients with peripheral neuropathies frequently have an antibody activity directed against myelin-associated glycoprotein (MAG). Reactivity of 19 of these sera with avian embryonic tissues was compared. Immunohistological studies allowed their classification into distinct groups according to the staining pattern. Both neural and non-neural cell lineages were recognized by these antibodies. The IgM specificities were also compared with those of the monoclonal antibodies HNK-1 and NC-1, which react with MAG and some cell adhesion molecules. Only one group displayed a pattern of staining similar to that observed with these monoclonals. The reactivity of these IgM paraproteins with two cell adhesion molecules, neural cell adhesion molecule and neuron-glia-cell adhesion molecule by immunoblotting confirmed the heterogeneity found in the histological study.

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PubMed1986

Pathways of avian neural crest cell migration in the developing gut.

The NC-1 and E/C8 monoclonal antibodies recognize a similar population of neural crest cells as they migrate from vagal levels of the neural tube and colonize the branchial arch region of 2- to 3-day-old chicken embryos. Some of these immunoreactive cells then appear to enter the gut mesenchyme on the third day of incubation just caudal to the third branchial cleft. After entering the gut, these cells migrate in a rostral-caudal direction, using primarily the superficial splanchnic mesodermal epithelium of the gut as a substratum. The antigen-positive cells remain preferentially associated with the splanchnopleure. Few antigenic cells enter the mesenchyme surrounding the endoderm at anterior levels whereas they are found throughout the mesenchyme when nearing the umbilicus. At postumbilical levels, immunoreactive cells are distributed on both sides of the differentiating muscle layer but not within it. Although fibronectin immunoreactivity can be found throughout the wall of the gut, there is no apparent relationship between the distribution of fibronectin and the location of the immunoreactive cells. These results suggest that a mechanism more complex than a mere interaction with fibronectin may account for migration of crest-derived cells in the gut.

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PubMed1985

How do the migratory and adhesive properties of the neural crest govern ganglia formation in the avian peripheral nervous system?

The peripheral nervous system derives mainly from the neural crest both in the head and trunk. Using markers such as fibronectin (FN), neural cell-adhesion molecule (NCAM), the nucleolar marker for quail cells in chimaeric embryos, and NC-1, a monoclonal antibody specific to crest cells and their neural derivatives, we have attempted to reconstruct the processes that lead to the formation of peripheral ganglia. Our observations allow us to propose a model of the formation of ganglia based on morphogenetic movements and on variations of crest cell adhesiveness. In most cases, crest cells migrate in morphologically defined and transient pathways that lead them to their final site of arrest; these pathways are always associated with FN, which appears necessary for crest cell attachment and movement in vitro. The directionality of crest cell migration is probably dictated by the cells' motile properties and population pressure in restricted areas suitable for cell movement. The disappearance of the pathways and of the substrate necessary for migration while the population is rapidly dividing may be responsible for the aggregation of crest cells in the case of the sensory ganglia. To the contrary, the aggregation of crest cells into autonomic ganglia (sympathetic, enteric, and ciliary ganglia) does not seem to obey the same rules, no disappearance of the substratum or of the pathways being obvious; rather, their formation seems correlated with the de novo synthesis of adhesive molecules such as NCAM.

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PubMed1984

Identical reactivity of monoclonal antibodies HNK-1 and NC-1: conservation in vertebrates on cells derived from the neural primordium and on some leukocytes.

NC-1 and HNK-1, two mouse monoclonal antibodies raised against quail ciliary ganglion and a human leukemic cell-line, respectively, were found to display the same pattern of reactivity. Species investigated included human, rodents, birds and amphibians. In 1- to 3-day-old avian embryos, migrating crest cells are stained, whereas in older animals neuroepithelial cells and neurons are labelled. Staining with fluorescein isothiocyanate-conjugated NC-1 is blocked by preincubation with HNK-1. In immunoblot analyses both antibodies recognize the same pattern of bands which are different in central and peripheral nervous systems and vary during development. Thus, HNK-1/NC-1 provides a useful tool for investigating the ontogeny of neural and lymphocytic cells carrying this determinant, which, in view of its high degree of conservation during vertebrate evolution, may play an important part within the haematopoietic and nervous systems.

Animals↗
PubMedDate not supplied

[Experimental models of angiogenesis (in vitro and in vivo)].

The multiplicity of experimental models of angiogenesis in vitro and in vivo complicates the choice of a straightforward strategy to accurately identify the anti-angiogenic potential of a natural or synthetic compound with antitumoral activity. In the absence of such consensus, it is clear that the demonstration of an activity lies in the use of several models, both in vitro and in vivo. A rapid overview of the most currently used models, especially in vitro, is presented, with an emphasis on their limitations. Several examples of research strategies for identifying antitumoral anti-angiogenic compounds are used in illustration.

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