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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 95 (1987), S. 136-143 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The interaction between centrosomes and kinetochores was studied in multinucleate cells induced by Colcemid treatment or by random cell fusion. Except for prematurely condensed chromosomes (PCC) of the G2-phase, PCCs do not develop their own spindle area. Perhaps the maturation promoting factor (MPF) fails to activate these centrosomes. In such PCCs, the kinetochore-centrosome interaction was found to be non-specific: sometimes only a few chromosomes of a group could establish connections with centrosomes, sometimes chromosomes from the same PCC group developed microtubule (MT) attachment with different centrosomes (not the pair), and sometimes kinetochores of PCC groups failed to interact with MTs. These findings explain the abnormal mitotic behaviour of PCCs as seen in the light microscope. These PCCs develop micronuclei or normal nuclei by nuclear re-formation in telophase. All the different PCC groups revealed kinetochores with kinetochore plates. It was shown that transformation of presumptive kinetochores to a trilaminar kinetochore does not depend on nuclear envelope breakdown or on the degree of chromosome condensation. This may be induced by the MPF which may initiate different events like chromosome condensation, nuclear envelope breakdown and kinetochore transformation by secondary factors. Other observations like establishment of connections by different chromosome groups to a common centrosome, kinetochore attachment of PCCs to different centrosomes, interaction of one kinetochore with two centrosomes, kinetochores being stretched and bent to receive microtubules and finally the failure of some kinetochores to develop MT attachment, all strongly suggest that the kinetochores serve as the point of termination rather than the nucleation sites of kinetochore MTs.
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  • 2
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The B1 cell line of rat cerebral endothelium origin exhibits several dicentric and multicentric chromosomes. These chromosomes, unlike multicentrics in mouse (Vig and Zinkowski 1986) do not show premature centromere separation. All centromeres deposit kinetochore proteins and appear to be functional. Even the centromeres which fail to migrate to the poles during anaphase and make side arm bridges bind to spindle microtubules. Some multicentric chromosomes show kinetochores spaced apart with intervening stretches of euchromatin while others are located adjacent to each other thus exhibiting tandem repeats and forming a “compound” kinetochore (Brinkeley et al. 1984). Also, unlike mouse multicentric chromosomes in which different pericentric regions and the centromeres replicate at different times, the rat chromosomes appear to replicate all pericentric and centric regions in a given multicentric simultaneously. The present studies indicate that centromeres in rat and mouse replicate during the last part of the S-phase and in continuation with the pericentric heterochromatin.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A transformed cell line, B1, of cerebral endothelial origin from the Wistar-Kyoto male rat has chromatid and chromosome type bridges in virtually every cell. It exhibits various dicentric and polycentric chromosomes. Most dicentrics are symmetric isochromosomes. Certain isodicentrics are present in a fair segment of the cell population; however, almost all cells have some newly arising isodicentrics. The live cells show a lengthened prometaphase. Anaphase is also retarded possibly due to the occurrence of bridges. At anaphase some multicentrics split at only one centromere. When pulled to the two poles the unsplit centromeres and the distal chromosome segment form a side arm bridge. Another mechanism appears to be a total lack of separation of daughter centromeres at meta-anaphase (‘meiotic-like’ behavior of mitotic chromosomes). This is realized by the pulling of each of the two unsplit centromeres to opposite poles and results in bridges with both sister chromatids running parallel to each other. A break at corresponding weak points in the two sister chromatids followed by rejoining can form a dicentric isochromosome. A third mechanism, the breakage-fusion-bridge cycle, is also operative but would not produce isodicentrics. In the case of the first two mechanisms some or all centromeres apparently split between telophase and onset of the following DNA synthesis rather than at the usual time at late metaphase. These observations may suggest some previously unknown behavior of multicentric chromosomes during mitosis.
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 15 (1976), S. 2995-2999 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0741-0581
    Keywords: Monolayer cells ; preparation for SEM ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Monolayers of PtK-1 and HeLa cells grown on glass or plastic supports are extremely susceptible to lacerations, e.g., splits and cracks caused mainly by shrinkage when prepared for scanning electron microscopy (SEM). We find that a four-step fixation procedure including glutaraldehyde, OsO4, tannic acid, and uranylacetate application, in combination with critical point drying, drastically reduces these structural damages. In addition, the conductivity of the specimens is enhanced, so that they can be investigated without gold coating. Transmission electron microscopy (TEM) investigation of perpendicular sections in the area of lacerations provides evidence that the subcortical cytoskeletal elements are of crucial importance in maintaining cell membrane stability during the preparations. Our relatively quick and simple procedure results in an improved structural appearance of the cells.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Bei Silberimprägnationsversuchen an in vitro gezüchteten menschlichen Tumorzellen (Stamm HeLa) wurden Präparate der gleichen Serie sowohl mit dem Lichtals auch mit dem Elektronenmikroskop untersucht. Hinsichtlich der spezifischen Argentaffinität der fädigen Strukturen des Nukleolus (von Estable und Sotelo als „Nucleolonema“ bezeichnet) konnte festgestellt werden: 1. Das Ergebnis der Argentaffinreaktion ist abhängig von der verwendeten Fixierung. 2. Nach OsO4-Fixierung, offenbar infolge der Extraktion von Bestandteilen des Nukleolus in den Imprägnationsbädern, lassen sich im Elektronenmikroskop einige der Komponenten des Nukleolus besonders deutlich darstellen. Infolge Anlagerung von Silberkörnern treten die chromosomalen Strukturen im Kernraum und innerhalb des Nukleolus gut hervor. 3. Bei Formaldehyd- oder Glutaraldehydfixierung werden im Lichtmikroskop perlschnurartige Strukturen innerhalb des Nukleolus sichtbar; bei dichter Lagerung der Fäden, die stellenweise stark imprägniert sind, kann der Eindruck einer kontinuierlichen Silberanlagerung an die Fadenstrukturen hervorgerufen werden. Im Elektronenmikroskop zeigt sich jedoch, daß es sich um granuläre argentaffine Bezirke handelt, welche diskontinuierlich einer fädigen Struktur zugeordnet erscheinen. 4. Das Vorkommen einer fädigen Struktur läßt sich durch Vorbehandlung der Kulturen mit Adenosin bestätigen. Durch die Wirkung des Adenosins werden die fädigen Strukturen „entfaltet“ und können sowohl im Lichtals auch im Elektronenmikroskop über längere Strecken sichtbar gemacht werden. Das „Nucleolonema“ wird als eine komplexe Struktur definiert, von deren verschiedenen Komponenten, entsprechend der angewandten Methode, jeweils nur ein Teil dargestellt wird. Im fädigen Teil des Nukleolus haben sich folgende Komponenten nachweisen lassen: Desoxyribonukleoprotein, Ribonukleoprotein und eine Komponente, welche sich durch die Argentaffinreaktion darstellen läßt und vermutlich aus Lipoprotein besteht. Diese Auffassung des „Nucleolonemas“ als komplexe Struktur würde die scheinbaren Widersprüche erklären, welche bisher in bezug auf die Natur des „Nucleolonemas“ bestehen.
    Notes: Summary A silver impregnation method was applied to human tumor cells of the HeLa strain growing in vitro. Preparations of the same series were examined with both light and electron microscopes. The following results were obtained with respect to the specific affinity for silver of the filamentous structures of the nucleoli, which have been designated “nucleolonema” by Estable and Sotelo: 1. The silver reaction depends on the particular fixative used. 2. After fixation with OsO4 some of the components of the nucleolus are clearly distinguishable with the electron microscope, apparently as a result of extraction of certain constituents of the nucleolus during the impregnation process. Silver grains are deposited on the surface of chromosomal fibrillae both inside and outside the nucleoli. 3. After formaldehyde or glutaraldehyde fixation rosary-like structures are visible within the nucleolus, when viewed with the light microscope. Dense aggregation of the filaments, which are here and there strongly impregnated with silver, gives the impression of a continuous deposition of silver along these filamentous structures. It is evident from electron microscope examination, however, that the areas with an affinity for silver, which is discontinuously distributed along the filaments, are actually parts of a filamentous structure. 4. This observation of a filamentous structure is confirmed in cultures pretreated with adenosine after which there is an “unfolding” of the filamentous structures. They thus become visible over longer distances, as shown by both light and electron microscopes. We conclude that the “nucleolonema” is a complex structure made up of different components, only part of which may be identifiable after a given technique. The following components have been demonstrated: deoxyribonucleoprotein, ribonucleoprotein, and a component reacting under special conditions with silver, which may be a lipoprotein. This interpretation of the “nucleolonema” as a complex structure reconciles certain here-to-fore seemingly-contradictory concepts of the nature of the “nucleolonema”.
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  • 7
    ISSN: 1573-6849
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung An Hand elektronenmikroskopischer Präparate werden die Struktur und die Entwicklungsgeschichte der Flügelschuppen von Ephestia kühniella aus dem Gebiet des Symmetriefeldes und der distalen Querbinde des Vorderflügels beschrieben. Die Gestalt einer Schuppe läßt sich zerlegen in eine Grundgestalt, für deren Form in erster Linie die Zellgrenzmembran verantwortlich sein dürfte, und eine größere Zahl von periodisch wiederkehrenden Strukturelementen. Es treten Gradienten auf, die die Strukturelemente verstärken oder abschwächen. Die Ausformung der periodischen Strukturelemente beginnt, sobald über den zunächst nackten Fortsatz der Schuppenbildungszelle in etwa 200 Å Abstand eine mehrschichtige Membran, die Cuticulinschicht, gebreitet worden ist. In dem (extrazellulären!) Raum zwischen der Cuticulinschicht, die das weitere Geschehen gegen den Exuvialraum abriegelt, und der Zellgrenzmembran wird die Cuticula gebildet. Die periodisch wiederkehrenden Strukturelemente werden in endgültigem Abstand voneinander unter Mitwirkung von Cuticulinschicht und Zellgrenzmembran nacheinander angelegt. Als Träger der formbildenden Prozesse ist die Zellgrenzmembran anzusehen.
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  • 9
    Publication Date: 2019-07-12
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Experimental Cell Research (ISSN 0014-4827); 166; 191-208
    Format: text
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