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Biomedical subjects

N Paweletz

Publications and source records attributed to N Paweletz.

At least 109 records · Page 6Linked to original sources
PubMed1981

Cooperation of kinetochores and pole in the establishment of monopolar mitotic apparatus.

Monopolar mitotic apparatus can be produced in sea urchin eggs by a manoeuvre that distributes the four poles of the second mitosis into four separate blastomeres. The pole of the monopolar mitotic apparatus generates a half-spindle that is similar in structural details to the half-spindle of a normal bipolar mitotic apparatus, although the chromosomes are not as well aligned as in a normal metaphase plate. The chromosomes are oriented; one kinetochore faces the pole while its sister kinetochore faces away from the pole. The poleward kinetochore is connected to the pole by bundles of microtubules. No microtubules are seen on the sister kinetochore that faces away from the pole. Therefore, a single pole can direct most of the events in the establishment of a mitotic apparatus. Our interpretation examines the cooperation of kinetochores and poles in the formation of microtubules between them, stressing the half-spindle as the medium of cooperation and leaving open the question whether the kinetochores are origins or terminations of microtubules.

Animals↗
PubMed1981

Scanning electron microscopic observation on cells grown in vitro. VI. aggregate formation in confrontation cultures of human diploid and tumor cells.

Two human cell lines, HeLa carcinoma cells and Wi38 lung fibroblasts have been used in confrontation experiments to study different adhesion processes including cellular motility, sorting out and invasion by SEM and statistics. Aggregates of one cell type were co-cultured with resuspended cells of the other type for up to 96 hours and vice versa. Homotypic aggregation kinetics as a control showed a saturation of the time-dependent increase in aggregate diameter and a mirror-like decrease in single cell number for both cell lines. In the heterotypic aggregation process, dissociated HeLa cells covered the surface of Wi38 aggregates without showing any particular distribution pattern. They partially penetrated the outer fibroblast layers and invasive actions were detected. Suspended Wi38 lung cells also adhered to the tumor cell aggregates. After a period of non-coordinated, random settlement (8 to 18 h or co-cultivation), the fibroblasts sorted out to form a network around the tumor aggregates in the form of sheets of cells arranged in parallel. The underlying HeLa cells then broke through the Wi38 layers, thus performing an inside-out invasion. Finally, all the aggregates were again covered by HeLa cells.

Cell Adhesion↗
PubMed1980

Plasma membrane heterogeneity in ascites tumor cells. Isolation of a light and a heavy membrane fraction of the glycogen-free Ehrlich-Lettré substrain.

In this work we report on the isolation of two plasma membrane fractions of a glycogen-free substrain of Ehrlich-Lettré ascites cells, a light fraction sedimenting in a sucrose gradient at 1.10 g/ml, and a heavy fraction sedimenting at nuclei by a combination of short-term swelling and mild Dounce homogenization. A 12 000 X g postnuclear pellet (PII) containing major portions of the plasma membrane marker enymes, 5'-nucleotidase, ouabain-sensitive (Na+ + K+)-ATPase and the alkaline phosphatase, was prepared by differential centrifugation. The two plasma membrane fractions were obtained by centrifugation on a discontinuous sucrose gradient, from which they were further purified on a linear sucrose gradient applying sedimentation velocity conditions only. Enrichment factors for the three marker enzymes were between 5- and 14-fold for the light fraction and between 3- and 7-fold for the heavy fraction with an overall yield of 1--4% and 0.5--1.7%, respectively, of cellular protein. Contamination of both fractions with nuclear material was minor. Mitochondrial contamination was about 8% for the light material and somewhat higher for the heavy material. In the light fraction, co-sedimentation of lysosomal and Golgi marker enzymes was detected. The presence of membrane structures of these organelles could not be confirmed definitely by electron microscopy. Differences in sialic acid content and phospholipid composition within the two fractions, especially in the relative proportion of lecithin to sphingomyelin, suggests differences in membrane fluidity. The light material showed mostly unit membrane vesicles in thin-section and freeze-etch electron microscopy, whereas the heavy fraction mainly consisted of sheet-like membrane fragments.

5'-Nucleotidase↗
PubMed1980

Scanning electron microscopic observations on cells grown in vitro. V. Human diploid cells can attach also with their upper surface.

When small glass particles are seeded on top of human diploid cells in a monolayer the cells attach firmly to the glass with their upper surface. In combination with this attachment fingerlike protrusions and small leading lamellae are formed de novo from the normally completely protrusion-free upper surface. These results are in contradition to findings from Vasiliev and Gelfand [10]. Our results indicate that attachment and adhesiveness must not unequivocally be in relation to the presence and formation of cellular protrusions.

Cell Adhesion↗
PubMed1980

Membranes of the mitotic apparatus of mammalian cells.

HeLa cells in mitosis are fixed by KMnO4 to obtain a good preservation of membranes. Inside and around the mitotic apparatus a vesicular, a tubular and a cisternal type of membranes are demonstrated. Small spherical or ellipsoidal vesicles are distributed at random in the spindle area. Zones around the poles and in the midbody of telophase cells are almost free from vesicles. Elements of the tubular ER are often aggregated in parallel arrays at the periphery of the spindle region, thus resembling dictyosomes. During telophase tubular ER is most prominent at the cleavage furrow. Layers of concentrically arranged flat cisternae surround the spindle region during the middle stages of mitosis. Radiating from the poles such membranes form large asters, thereby interrupting the concentric arrangement. This pattern might act as a barrier against larger cytoplasmic organelles or as a cisternal system to bring about an oriented transport of molecules from or to the poles. Fragments of the two large indentations of the nuclear envelops in prophase are aggregated in the spindle region and later on contribute to form new envelopes around the daughter nuclei.

Fixatives↗
PubMed1979

Fine structure of the mitotic cycle of unfertilized sea urchin eggs activated by ammoniacal sea water.

Unfertilized sea urchin eggs enter a mitotic chromosome cycle after treatment with sea water containing ammonia. Centrioles cannot be found but microtubules are formed in the later stages of the cycle. The microtubules are displayed in an astral arrangement centered on clusters of osmiophilic bodies. In early stages, distinct kinetochores on the condensed chromosomes show no attachments to microtubules. Later, a few microtubules may be attached to the kinetochores. The chromosomes and microtubules are contained in a "clear zone", a large compact accumulation of membranes which displaces yolk particles and mitochondria, but not ribosomes, from that region of the cell. No bipolar spindle is formed.

Ammonia↗
PubMed1978

The formation of contacts between HeLa cells. Directed mutual outgrowth of cell surface protrusions.

The contacting behavior of HeLa cells in subconfluent monolayer cultures has been studied by phase contrast and scanning electron microscopy. We present further evidence that cells separated from each other by a cell-free space up to 20 micron width can simultaneously form directed and mutual protrusions against each other. A statistical analysis demonstrated that in more than half of the possible contact events a reciprocal outgrowth of cell surface protrusions had occurred. This suggests that contact formation is not just a random process, but may be influenced by so far unrecognized factors.

Cells, Cultured↗
PubMed1978

Mitotic asynchrony of multinucleate cells in tissue culture.

A high degree of mitotic asynchrony is reported for spontaneously arising multinucleate cells of HeLa and Pt-K1, tissue culture cell lines. Neither nuclear number, nor nuclear size nor the presence or absence of nucleoli, could be directly related to the asynchronous behaviour of the cells. Suboptimal levels of nutrients led to a higher frequency of asynchrony. A partial compartmentation of the cytoplasm could be detected in some of the multinucleate cells. The compartmentation of the cytoplasm may lead to an uneven distribution of inducer and non-inducer metabolites. All these factors together may be responsible for the high degree of mitotic asynchrony.

Animals↗
PubMed1978

[Fetal damage due to mushroom poisoning with amanita phalloides during the first trimester of pregnancy (author's transl)].

A 25-year old para II suffered of mushroom poisoning by amanita phalloides at 9 weeks gestation. When the life threatening maternal illness was overcome a therapeutic abortion was carried out at 12 weeks gestation. Prostaglandin F2 alpha was injected retro-amniotically. The damage to the fetus by the toxins of amanita phalloides is described and discussed.

Abortion, Therapeutic↗
PubMed1978

Scanning electron microscopic observations on cells grown in vitro. IV. HeLa cells do not have an upperside-underside polarity.

Small glass particles are added to HeLa monolayer cell cultures. Landing on top of a flattened cell fingerlike protrusions are surrounding the particles. Later on leading lamellae are formed on the upperside of the cell and the glass becomes more and more surrounded until it appears to be "incorporated" completely. The glass particles become attached so firmly that by detaching them the cell surface is destroyed. This speaks against the assumption that cells in monolayers are polarized.

Cell Adhesion↗
PubMed1976

Ultrastructure of aggregates of tumor and normal cells and of mixed aggregates.

Contact areas have been studied in pure aggregates of either normal and malignant cells and mixed aggregates contaning both cell types. The structures of both cell types are compared. Tumor cells form looser connections than normal cells. The contanct areas of tumor cells resemble those of embryonic and mitotic cells. In a mixed aggregate sorted out, the two cell types are arranged in two regions: the "HeLa" - and the "decidua region." The contact areas and the cells in these regions do not differ from those of the pure aggregates. If tumor and normal cells are in direct connection with each other, they show remarkable changes: the tumor cells lose their spherical appearance as well as parts of their organelles and become ameboid. The normal cells from a dense layer of filamentous material beneath the membrane in the neighborhood of the tumor cell.

Cell Aggregation↗
PubMed1976

[Morphological and biochemical investigations of hairs in inborn errors of amino acid metabolism (author's transl)].

The influence of inborn errors of metabolism on the amino acid content, the structure and growth of human hair has been studied in patients suffering from Phenylketonuria, Cystinosis, Homocystinuria and Tyrosinosis. Examiniation of hairs under the scanning electron microscope reveals defects and abnormalities such as a plicated pattern of the cuticula in patients with Phenylketonuria and Cystinosis. The amino acid content of the hydrolized hair keratin of all patients was within normal range and did not reveal significant changes of phenylalanine, cystine, homocystine, methionine or tyrosine. Disturbance in hair growth was determined by evaluation of standardized hair root samples. The results indicate an increase in hair root atrophy with increasing severity of the disorder of amino acid metabolism.

Amino Acid Metabolism, Inborn Errors↗
PubMed1976

Studies on coexistence and intercellular communication. Scanning electron microscopy for early stages of co-culturing of normal mesothelial cells and mouse ascites tumor cells in vitro.

Mouse ascites tumor cells (MAT-cells) were co-cultured with mesothelial cells of the mouse. During early stages of coexistence (30-60 min) the mesothelial cells show fingerlike protrusions formed mostly at their flanks pointing towards MAT-cells in the neighbourhood. Obviously there is a directional response of the mesothelial cells to the existence of MAT-cells. The mesothelial cells are the most active partner at the beginning of coexistence. Later on MAT-cells also develop fingerlike protrusions which grow towards the mesothelial cells. A network of fingerlike protrusions is formed in the region between MAT-cells and mesothelial cells when they come near to each other. The advantages of the system serving as a model for investigations on intercellular communication are discussed.

Animals↗
PubMed1976

Characterization of 20S component in tubulin from mammalian brain.

Tubulin from porcine brain, purified by at least two cycles of assembly and disassembly, was characerized at different pH values by sedimentation velocity analysis and turbidimetric measurements. At pH 6.4 the depolymerized material was composed of two major species sedimenting with so20,w values of 6 and 36 and a minor one of 20S. By raising the pH, the amount of the 20S component increased and that of the 36S decreased, whereas that of the 6S component was unaltered. At pH 7.6 the mixture contained 20S and 6S components but hardly any 36S. The 20S species can be separated from the 6S ones by gel filtration on agarose A-15m at pH 7.6. On electron microscopic examination this preparation contains far fewer double rings compared to the material at pH 6.4, but single rings could often be seen. Sodium dodecyl sulfate gel electrophoresis of the 20S and 36S components showed that they consist almost entirely of tubulin and some higher and lower molecular weight fractions. Turbidity measurements showed that the minimal protein concentration necessary for polymerization increases with increasing pH. The turbidity plateau reached at a given pH can be raised by decreasing the pH. From these results it is suggested that the 20S component is an intermediate of the 36S species. The results further indicate the existence of a pH-dependent equilibrium between the 20S species and the 36Soligomers.

Animals↗
PubMed1976

Observations in vitro regarding the mechanism of the cell destruction by stimulated lymphocytes.

In contrast to other cells stimulated lymphocytes release substances probably cytotoxic which are incorporated by the target cells. The cellular material is released by tearing off parts of fine processes which the lymphocytes extend on to the surface of the target cells. This explains the before mentioned observations that the cell destruction mediated by lymphocytes depends absolutely on a close contact between the lymphocytes and the target cells.

Antigen-Antibody Reactions↗