Search PubMed⌕ Search

Biomedical subjects

J Wartiovaara

Publications and source records attributed to J Wartiovaara.

At least 19 recordsLinked to original sources
PubMed1979

Fibronectin expression is determined by the genotype of the transformed parental cells in heterokaryons between normal and transformed fibroblasts.

The expression of fibronectin, a cell surface-associated transformation-sensitive glycoprotein, was studied in hetero- and homokaryons of normal and SV40-transformed human fibroblasts. In immunofluorescence, fibroblast homokaryons had an intense surface-associated and intracelluar fibronectin fluorescence similar to that of normal fibroblasts. Transformed cells and their homokaryons had a minimal surface-associated and a weak intracellular fibronectin fluorescence. In heterokaryons formed between transformed and normal fibroblasts, the expression of fibronectin fell within 24 h to the level of the transformed cell homokaryons. The change was detectable already at 3 h after fusion and was gene-dose dependent. These results show that the transformed genotype determines fibronectin expression in the heterokaryons.

Cell Fusion↗
PubMed1978

Fibronectin and the pericellular matrix of normal and transformed adherent cells.

Fibronectin is a major glycoprotein component of normal fibroblasts in culture. External fibronectin is predominantly present in a pericellular fibrillar matrix that mediates distant cell-cell and cell-substratum contacts. A small proportion of external fibronectin is closely associated with the plasma membrane. In the matrix, fibronectin is partially disulfide bonded into complexes. Plasma transglutaminase, activated by thrombin, also cross-links external fibronectin into high-molecular-weight covalent complexes. In cultures of normal fibroblasts, pericellular matrix fibronectin displays extensive codistribution with (pro)collagens types I and III. Transformed adherent cells show decreased formation of the fibronectin-collagen matrix. The deficient synthesis of fibronectin and other matrix components and abnormal interactions with the matrix may account for several phenotypic characteristics of transformed cells. The pericellular matrix structure has been prepared by use of deoxycholate and hypotonic medium to solubilize the cells. The matrix contains glycosaminoglycans, procollagens, and fibronectin. The fibronectin codistributes with the procollagens. The matrix may be considered to be an in vitro equivalent of the connective tissue matrix and basal laminae found in vivo. Human sarcoma cells spread rapidly on the prepared matrix and assume an elongated morphology characteristic of normal fibroblasts. The prepared matrix may provide a general tool to study the effects of matrix on cellular behavior and differentiation.

Animals↗
PubMed1978

Cross-linking of erythrocyte membrane proteins by periodate and intramembrane particle distribution.

Treatment of isolated human erythrocyte membranes at pH 7.4 with 0.1-0.5 mM-sodium periodate specifically cross-linked some of the spectrin polypeptides. Treatment with 2 mM-periodate resulted in complete cross-linking of spectrin and partial cross-linking of other polypeptides. The latter treatment also caused aggregation of the intramembrane particles made visible by freeze-fracturing. When membranes that had been treated with 2 mM-periodate were depleted of spectrin by treatment with 0.1 mM-EDTA, extensive aggregation of the intramembrane particles occurred.

Amino Acids↗
PubMed1978

Distribution of glycophorin on the surface of human erythrocyte membranes and its association with intramembrane particles: an immunochemical and freeze-fracture study of normal and En(a-) erythrocytes.

Human erythrocyte membranes of the En(a-) blood group lack the major sialoglycoprotein (glycophorin). By absorption of a crude antiglycophorin antiserum with En(a-) membranes a specific antiglycophorin antiserum was obtained. By immune electron microscopy we showed that glycophorin is randomly distributed on the surface of normal erythrocytes. When polycationized ferritin, which mainly binds to glycophorin, was used as a marker a similar even labeling of normal erythrocyte membranes was seen. En(a-) membranes bound much less of this marker. In freeze-fracturing the intramembrane particles of both membrane types had a similar distribution and appeared in equal amounts. However, partial removal of spectrin from these membranes, followed by incubation at pH 6 resulted in more extensive aggregation of the particles in En(a-) membranes than in normal membranes. The results may be interpreted as glycophorin contributing by electrostatic repulsion to the random distribution of the intramembrane particles in normal cells. This repulsion is weakened in in En(a-) cells by the lack of glycophorin.

Anions↗
PubMed1978

External fibronectin of cultured human fibroblasts is predominantly a matrix protein.

The distribution of a major glycoprotein (fibronectin) of human fibroblast cultures was studied in immunoelectron microscopy with peroxidase- or ferritin-labeled antibodies. External fibronectin was visualized in pericellular structures, in some areas on the growth substratum, and to a lesser degree in close association with the upper and lower surface membranes of the cell. The pericellular fibronectin-containing structures consisted of amorphous or vaguely fibrillar material forming strands or patches, 50-500 nm in diameter; the structures appeared to mediate distant cell-to-cell and cell-to-substrate contacts. When in close association with the plasma membrane, fibronectin markers were seen as discrete patches. The exact relationship between this form of fibronectin and the plasma membrane, however, remained open. Filamentous material was commonly seen in the cortical cytoplasm under patches of membrane-associated fibronectin. The distribution that we observed is consistent with the proposed roles of fibronectin in cell interactions with neighboring structures and with its presence in vivo as an extracellular glycoprotein in connective tissue matrix and basal laminae.

Cell Adhesion↗
PubMed1978

Fluorescent antibodies and lectins stain intracellular structures in fixed cells treated with nonionic detergent.

Nonionic detergent (NP40) treatment of paraformaldehyde-fixed normal and SV40-transformed human fibroblasts resulted in intracellular penetration of two chosen fluorescent antibodies and Concanavalin A (Con A). After the detergent treatment nuclear SV40 T antigen, cytoplasmic fibronectin glycoprotein and Con A binding sites could be visualized in fluorescence microscopy. The lowest NP40 concentration which made fixed cells permeable was 0.05%. The morphology of cells was preserved better by this new method than by conventional fixation methods, such as acetone treatment. In scanning electron microscopy the surface of the fixed NP40-treated cells had only small rugosities and fine pores. The subsurface cytoskeleton especially was well preserved and had a more distinct fine structure. The improved morphology made it possible to detect a similar distribution of fibronectin and Con A binding sites in the perinuclear endoplasmic reticulum regions.

Antigens, Viral↗
PubMed1978

Lectin-binding sites are found in rat liver cell plasma membrane only on its extracellular surface.

In the present study ultrastructural localization of binding sites for 5 lectins was studied in rat liver cell surface membrane fractions. For this purpose ferritin-coupled Concanavalin A, wheat germ agglutinin, soybean agglutinin, Ricinus communis agglutinin 120 and Lotus tetragonolobus agglutinin I were used as probes for mannose, N-acetyl glucosamine, N-acetyl galactosamine, galactose and fucose moieties in glycoproteins and glycolipids. Although recent reports suggest presence of glycogroups on the cytoplasmic surface of cellular membranes ultrastructural identification of membrane surfaces in the present study indicated an asymmetric localization of lectin-binding sites exclusively on the extracellular side of the membranes.

Animals↗
PubMed1978

Lectin binding in early mouse embryos.

Lectin binding in early mouse embryos was used to explore possible changes in cell surface properties during early development. Embryos at different stages of development were stained with fluorescein-coupled Concanavalin A (FITC-Con A) or wheat germ agglutinin (FITC-WGA). In zygote to 8-cell embryos, fixed with paraformaldehyde before staining or stained at 4 degrees C before fixation, the fluorescein-coupled lectins gave a continuous ring-like labelling of cell surfaces. When unfixed embryos stained at 4 degrees C with low concentrations of FITC-Con A (10--20 microgram/ml) were incubated at 37 degrees C they showed a continuous surface labelling at zygote stage but a patch-like aggregation of Con A-binding sites in 2-cell stage and older embryos. Use of higher lectin concentrations ( greater than 100 microgram/ml) did not result in patch formation at 37 degrees C. FITC-WGA gave a spotty but unaggregated labelling pattern also at 37 degrees C. The results show that in the early stages of mouse embryogenesis developmentally associated changes occur in the binding behaviour of Con A but not of WGA.

Animals↗
PubMed1978

Metabolic inhibitors and kidney tubule induction.

The induction of kidney tubules in metanephric mesenchyme has previously been shown to require close contact between the interacting tissues. In our study we show that low concentrations of inhibitors of RNA, DNA and protein synthesis inhibit tubule induction, although they do not seem to prevent the formation of contacts between the interacting tissues. The effective concentrations were about the same as those which inhibited the synthesis of macromolecules. Cycloheximide caused an increased synthesis of RNA. Low concentrations of Mitomycin C inhibited DNA synthesis but not tubule formation. A concentration of the inhibitors which caused weakened induction also caused a marked decrease in leucine incorporation. We concluded therefore, that a decrease in protein synthesis in the inducing tissue is responsible for the inhibition of induction.

Animals↗
PubMed1977

Changes in the distribution of a major fibroblast protein, fibronectin, during mitosis and interphase.

The distribution of a major fibroblast protein, fibronectin, was studied by immunofluorescence and immunoscanning electron microscopy in cultures of human and chicken fibroblasts during different phases of the cell cycle. The main findings were: (a) In interphase cells, the intensity of surface-associated fibronectin fluorescence correlated with that of intracellular fibronectin fluorescence. (b) The intensity of the fluorescence of both surface-associated and intracellular fibronectins was not changed in cells that were synthesizing DNA. (c) Mitotic cells had reduced amounts of surface-associated but not of intracellular fibronectin. The surface fibronectin that remained on meta-, ana-, or telophase cells had a distinct punctate distribution and was also localized to strands attaching the cells to the substratum. Fibronectin strands first reappeared on the surface of flattening cytoplasmic parts of telophase cells. (d) Fibronectin was also detected in extracellular fibrillar material on the growth substratum, particularly around dividing cells. Thus, surface-associated fibrillar fibronectin was present during G(1), S, and G(2) but in cells undergoing mitosis the distribution was altered and the amount appeared to be reduced. The observations on the distribution of surface-associated fibronectin suggest that rather than being involved in growth control this fibronectin plays a structural role in interactions of cells with the environment.

Animals↗
PubMed1977

Cell contacts and polysomes in irradiated human jejunal mucosa at onset of epithelial repair.

Epithelial ultrastructure was studied in the jejunal biopsies of irradiated cancer patients at early stages of mucosal regeneration 1 to 3 days after completing treatment. Major changes in the typical atrophic areas lacking villi were the following: (1) Cell contacts were loose between surface epithelial cells lacking signs of degeneration with extracellular gaps visible between the lateral membrane interdigitations. (2) Numerous processes from such epithelial cells extended into the underlying basement membranes and sometimes, especially in crypt areas, came into close contact with processes from underlying mesenchymal cells. (3) The epithelial cells often had enlarged nucleoli with granular threads. Increased amounts of epithelial cells were also seen with numerous membrane-free polysomes. The study suggests that at the onset of jejunal epithelial regeneration in man an epitheliomesenchymal cell interaction takes place similar to that described in normal gut development in laboratory animals. The possible significance of the close contacts between epithelial and mesenchymal cells, also seen in crypt areas of regenerated epithelium, is discussed in the light of mechanisms proposed for tissue interactions. The noticed increase in polysomes is interpreted as a morphologic sign of activated protein synthesis in the differentiating cells of the epithelium.

Epithelial Cells↗