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Biomedical subjects

N Paweletz

Publications and source records attributed to N Paweletz.

At least 91 records · Page 5Linked to original sources
PubMed1984

Synchronous DNA synthesis and mitosis in multinucleate cells with one chromosome in each nucleus.

Multinucleate cells were induced by colcemid treatment in PtK1 cells in culture. DNA synthesis and mitotic behavior of those cells in which each nucleus contained a single chromosome were studied. More than 80% of such cells showed synchronous DNA synthesis and mitosis in all nuclei. As these genetically different nuclei respond identically to the molecules that initiate DNA synthesis and mitosis, intranuclear control of initiation of DNA synthesis and induction of mitosis by genes on individual chromosomes can be excluded. The occasional occurrence of asynchronous division in multinucleate cells is assumed to result from unequal availability of the inducer molecules to the individual nuclei.

Cell Nucleus↗
PubMed1984

Events associated with the initiation of mitosis in fused multinucleate HeLa cells.

Large multinucleate (LMN) HeLa cells with more than 10-50 nuclei were produced by random fusion with polyethylene glycol. The number of nuclei in a particular stage of the cell cycle at the time of fusion was proportionate to the duration of the phase relative to the total cell cycle. The fused cells did not gain generation time. Interaction of various nuclei in these cells has been observed. The nuclei initially belonging to the G1- or S-phase required a much longer time to complete DNA synthesis than in mononucleate cells. Some of the cells reached mitosis 15 h after fusion, whereas others required 24 h. The cells dividing early, contained a larger number of initially early G1-phase nuclei than those cells dividing late. The former very often showed prematurely condensed chromosome (PCC) groups. In cells with a large number of advanced nuclei the few less advanced nuclei could enter mitosis prematurely. On the other hand, the cells having a large number of nuclei belonging initially to late S- or G2-phase took longer to reach mitosis. These nuclei have been taken out of the normal sequence and therefore failed to synthesize the mitotic factors and depended on others to supply them. Therefore the cells as a whole required a longer period to enter mitosis. Although the nuclei became synchronized at metaphase, the cells revealed a gradation in prophase progression in the different nuclei. At the ultrastructural level the effect of advanced nuclei on the less advanced ones was evident with respect to chromosome condensation and nuclear envelope breakdown. Less advanced nuclei trapped among advanced nuclei showed PCC and nuclear envelope breakdown prematurely, whereas mitotic nuclei near interphase or early prophase nuclei retained their nuclear envelopes for a much longer time. PCC is closely related to premature breakdown of the nuclear envelope. Our observations clearly indicate that chromosome condensation and nuclear envelope breakdown are two distinct events. Kinetochores with attached microtubules could be observed on prematurely condensed chromosomes. Kinetochores of fully condensed chromosomes often failed to become connected to spindle elements. This indicates that the formation of a functional spindle is distinct from the other events and may depend on different factors.

Cell Division↗
PubMed1984

On the flexibility of surface structures of tumor cells in vitro.

When HeLa cells are detached from their support by trypsin, trypsin-EDTA, or by mechanical means large zeiotic blebs are formed. After reseeding the cells onto glass these blebs shrink. Those blebs near the support collapse completely to form lobes in the neighborhood of lobopodia. By scanning and transmission electron microscopy we could show the transformation of these zeiotic blebs into true lobopodia. This implies a repair of cell surface structures and components as well as of the subcortical cytoskeleton.

Cell Membrane↗
PubMed1984

On the formation of orientated protrusions in confrontation cultures of human diploid and tumor cells.

Wi38 cells (diploid human embryonic lung fibroblasts) were cultivated for 24 h on cover slips, following which HeLa cells (a monolayer and a suspension subline) were seeded on top of the fibroblasts. Some tumor cells lay on the glass between fibroblasts and by some means induced the Wi38 cells to form protrusions orientated towards the tumor cells. By statistical methods it has been shown that the outgrowth of these protrusions is a non-random process that is not restricted to either normal or the tumor cells. This contact behavior can only be explained by the assumption of an exchange of signals and a chemotactic mechanism must be assumed.

Cell Communication↗
PubMed1984

The centrosome cycle in the mitotic cycle of sea urchin eggs.

When sea urchin eggs entering mitosis are exposed to an appropriate concentration of mercaptoethanol, the chromosome cycle is restrained while the centrosome cycle advances. The two poles of the mitotic apparatus separate into four poles, while the chromosomes remain in their metaphase arrangements until released by the removal of the mercaptoethanol. We follow the centrosomes through the stages of the generation of two poles by each original pole. In electron microscopic studies, the osmiophilic component of the centrosomes serves as an indicator of their changing forms as each pole generates two poles. In light microscopic studies, including observations of birefringence, the shapes of the polar ends of the spindles are taken as indicators of the shapes of the centrosomes. The successive stages of the centrosome cycle are (1) compact spherical centrosomes at the time of formation of the mitotic apparatus; (2) expansion and flattening of the centrosomes, leading to (3) formation of thin flat plates, perpendicular to the spindle axis. Corresponding to the extended flat shape of the centrosomes, the spindle poles are flat; microtubules 'point' to the centrosomal plate and not the centrioles. The centrioles are separated in the flattening of the centrosomes. (4) The flat plate divides into two and each of the two halves becomes more compact, defining two separate poles. Our findings resurrect and update Boveri's [5] observations and interpretations of the centrosome. Centrosomes have shapes. The shapes may be imparted to the microtubular structures that they generate. The formation of two separate centrosomes from one, in the formation of mitotic poles, is describable as a sequence of changes in shape.

Animals↗
PubMed1984

The vesicular compartment of the mitotic apparatus in mammalian cells.

Intracellular membranes might play an eminent role in regulating several events during mitosis: In this paper the appearance and changing configurations of the vesicular compartment of the mitotic apparatus of HeLa cells was studied from anaphase to telophase. In early prophase electron opaque and transparent membranous vesicles are found in the pericentriolar region outside the nucleus. During prometaphase when the nuclear envelope opens and starts to disappear, an increasing number of these vesicles appears in the mitotic apparatus near the chromosomes. During metaphase vesicles are spread all over the mitotic apparatus, the number of electron opaque vesicles decreases while the total amount of vesicles does not change significantly. Anaphase shows the same pattern of distribution in the half-spindle and in the midbody. In telophase the amount of electron opaque vesicles increases again. They are now found around vacuoles and near the newly appearing Golgi-cisternae. We assume that the electron opaque vesicles are derived from the Golgi- apparatus which disintegrates during prophase and reappears in late telophase. The change in the appearance of the different types of vesicles during metaphase coincides with drastic changes in the ionic milieu in the mitotic apparatus (Wolniak et al., 1983).

Anaphase↗
PubMed1984

Are membranes of the mitotic apparatus translocated by microtubules?

During all mitotic stages membranous structures can be found around and within the mitotic apparatus of HeLa cells. A careful ultrastructural analysis partly by means of stereo-electron microscopy of semithin (0.5 microns) sections reveals a close association of membranes and microtubules in many regions of the mitotic apparatus. The contact can be direct or via connecting structures (cross-bridges). Referring to various hypotheses concerning the translocation of membranous structures in the cytoplasm of interphase cells (see Suchard and Goode, 1982), the assumption that microtubules participate in the transport of membranous structures in the mitotic apparatus is discussed in detail.

Biological Transport↗
PubMed1984

Morphological and behavioral characteristics of two rat tumor cell lines with different metastatic capacities.

The morphological characteristics of two rat tumor cell lines were studied by means of scanning electron microscopy. While the ASML-cells (Ascites, Solid, Metastases, Lung) when spread via the lymphatic vessels form metastases in the lung, the AS-cells (Ascites, Solid) do not form secondary tumors. The ASML-cells do not attach on glass or plastic but grow in suspension; AS-cells, can be cultivated as monolayers. The ASML-cells form loosely packed clusters when they are shaken in a gyratory shaker, AS-cells produce well organized aggregates in which the intercellular contacts are very intensive. When a mixture of cells from both lines is aggregated the two types sort out and the line-specific aggregate or cluster is formed without interaction between the two types. ASML-cells remain spherical when confronted with pieces of the aortic wall and there are no signs of reaction with the underlying endothelial cells. The endothelium is drastically altered when AS-cells are seeded on top of the aortic wall: the tumor cells flatten, penetrate the endothelial layer and induce the endothelial cells to retract. These phenomena can also be seen in confrontations with the mesothelium of the diaphragm. As also cells from aggregates or clusters behave as the single cells we conclude that the newly formed heterotypic contacts are favored over homotypic ones. In addition they have proved to be more intensive.

Animals↗
PubMed1984

Nuclear asynchrony in multinucleate rat kangaroo cells.

Multinucleate (MN) cells were induced in PtK1 cells by colcemid treatment. A large percentage of cells developed nuclear asynchrony both in relation to DNA synthesis and mitosis within one cell cycle. Asynchrony could be traced even in metaphase and anaphase cells in which interphase nuclei, PCC of S-phase nuclei and less condensed prophase-like chromosomes could be observed along with normally condensed chromosomes. The occurrence of such abnormalities in these large MN cells may be explained on the basis of an uneven distribution of inducer molecules of DNA synthesis and mitosis due to cytoplasmic compartmentation. The less condensed form of all the chromosomes except chromosome 4 could be traced in asynchronous metaphase. The failure of the less condensed chromosomes to undergo complete condensation does not always appear to result from late entry of nuclei containing these chromosomes into G2 phase. It is likely that chromosome 4 carries gene(s) for chromosome condensation, as this chromosome itself never appears in a less condensed form. The inducers for chromosome condensation may not always be available at equal concentrations to all chromosomes located in separate nuclei, thus they may sometimes fail to undergo complete condensation before other nuclei reach the end of prophase, when the nuclear envelopes of all nuclei present in the cell break down simultaneously.

Animals↗
PubMed1984

Structural and functional alterations of lipid-depleted ascites tumor cells in culture.

Ascites tumor cells growth-arrested in lipid-depleted medium were modified with respect to their lipid composition, i.e. mainly cholesterol and the phospholipid fraction. These so-called lipid-depleted cells were generally smaller, had a surface area reduced by 55% compared to the control cells and had an altered cell surface architecture with large parts being smooth, interrupted by isolated bundles of microvilli and blebs as revealed by scanning electron microscopy. This deorganization process of the cells. Lectin-induced agglutination and receptor binding capacity was reduced, and also the receptor distribution was changed resulting in a cap-like formation on the surface as shown with FITC-labelled concanavalin A. The reduction in lipid content yielding a lower C/P ratio profoundly decreased the plasma membrane fluidity which was determined by fluorescence polarization measurements. Studies on fatty acid and cholesterol de novo synthesis revealed only small increases under lipid-free conditions not sufficient to meet the requirements of the lipid-depleted cells for these substances. It is therefore concluded that ascites tumor cells need exogenous preformed lipids for adequate functioning of the cell.

Animals↗
PubMed1984

Scanning electron microscopic observations on cells grown in vitro. VII. HeLa cells can penetrate Wi38 fibroblasts.

When HeLa cells are seeded on a preexisting monolayer of Wi38 fibroblasts, the HeLa cells "try" to get into direct contact with the glass substrate. Once on top of a flat fibroblast the HeLa cell can either migrate from the fibroblast to settle between two fibroblasts on glass or somehow stimulate the underlying cells to retract. In a few cases the HeLa cell directly penetrates the fibroblast, "melting" its way through the underlying cell. The mechanism of this phenomenon which has never been described before in this combination is discussed.

Cell Communication↗
PubMed1983

Studies on intravascular phagocytosis in the lung.

In this paper we have shown for the first time endocytosis by intravascular lung phagocytes. Glutaraldehyde-treated erythrocytes (discocytes) homed rapidly to the rat lung as measured by scintigraphic procedures. Transmission and scanning electron microscopy showed that the discocytes are phagocytosed by macrophages, blood monocytes and granulocytes as whole cells. This process could not be inhibited by silica treatment.

Animals↗
PubMed1983

An epithelial cell line with elongated myoid morphology derived from bovine mammary gland. Expression of cytokeratins and desmosomal plaque proteins in unusual arrays.

Cells of a clonal line (BMGE + HM) selected from bovine mammary gland epithelial cell cultures are described which, after reaching confluence, do not assume typical epithelioid morphology, but form elongated cells with long slender processes extending over the surfaces of other cells. However, cells of this line which display non-epithelioid morphology and are exceptionally rich in actin microfilaments are identified as epithelial cells by their synthesis of cytokeratins and desmosomal plaque proteins, as demonstrated by immunofluorescence and immunoelectron microscopy and by gel electrophoresis of cytoskeletal proteins. The cells do not produce vimentin and desmin filaments. The specific cytokeratin polypeptides of these myoid cells are identical to those present in normal epithelioid BMGE + H cells but are arranged in unusual arrays of meshworks of finely dispersed, non-fasciated filaments and granular structures. Desmosomal plaque proteins, notably desmoplakins, are abundant, but the electron microscopic appearance of the desmosomes is abnormal in that most of them are associated with a second accessory plaque formed at a distance of 0.1-0.15 micron from the normal desmosomal plaque. Both cytokeratin filaments and desmosomal structures are found throughout the whole cytoplasm, including the extended cell processes. The existence of an epithelial cell line with such an unusual morphology demonstrates the importance of non-morphological criteria in identifying epithelium-derived cells. Our findings also indicate that dramatic differences of cell shape and organization of epithelial cells need not necessarily be associated with changes in the expression of specific cytoskeletal proteins. The possible origin of this cell line from myoepithelial cells is discussed.

Animals↗
PubMed1983

Distinctive subcellular alterations induced by hypertonic stress in sea urchin eggs.

Sea urchin eggs continuously exposed to a hypertonic solution were ultrastructurally examined for osmotic-stress induced alterations. No fertilization membranes formed during the treatment and the surface-cortex complexes remained unaltered from the unfertilized state. However, the osmotic stress did induce a number of subcellular changes. During the first 30 minutes of the treatment the eggs formed many endoplasmic reticulum whorls and compacted Golgi body aggregations. Both of these new formations can be correlated with rapid changes in intracellular calcium, known to occur in hypertonic stressed eggs. Aggregations of mitochondria could be observed at later stages; these aggregations can also be related to subcellular stress and possible changes in internal calcium concentrations. The various morphological transitions within the cytoplasm, along with the lack of a cortical reaction in these eggs, not only supports the idea that calcium is released during parthenogenetic activation, but also suggests that this free calcium originates from stores other than the stores that are involved during fertilization or simple artificial activation.

Animals↗
PubMed1982

Transmission electron microscopic studies on the mitotic cycle of nucleolar proteins impregnated with silver.

Hela cells were impregnated with silver according to Paweletz et al. (1967). In cells in mitosis not only the nucleolar organizer regions (NORs) are strongly impregnated but also part of the nucleolar material, which accumulates in and around the chromosomes. The treatment with adenosine, which in interphase cells spreads the nucleolar material within the nucleus, also distributes the argentophilic material in and around the chromosomes. During the reconstruction phase this material reassembles around the NORs to form parts of the new nucleolus. The silver impregnation technique clearly demonstrates that two main components are responsible for the argentophily of the nucleolus. This is in agreement with the results obtained by Lischwe et al. (1979).

Cell Nucleolus↗