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  • 1
    Electronic Resource
    Electronic Resource
    Identification of frog photoreceptor plasma and disk membrane proteins by radioiodination (1987)
    s.l. : American Chemical Society
    Biochemistry 26 (1987), S. 1769-1776 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00380a040
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  • 2
    Electronic Resource
    Electronic Resource
    Origin of kinetochore microtubules in Chinese hamster ovary cells (1980)
    Springer
    Chromosoma 81 (1980), S. 483-505 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We have attempted to determine whether chromosomal microtubules arise by kinetochore nucleation or by attachment of pre-existing microtubules. The appearance of new microtubules was investigated in vivo on kinetochores to which microtubules had not previously been attached. The mitotic apparatus of Chinese hamster ovary cells was reconstructed in three dimensions from 0.25 μm thick serial sections, and the location of chromosomes, kinetochore outer disks, centrioles, virus-like particles and microtubules determined. Central to the interpretation of these data is a synchronization scheme in which cells entered Colcemid arrest without forming mitotic microtubules. Cells were synchronized by the excess thymidine method and exposed to 0.3 μg/ml Colcemid for 8 h. Electron microscopic examination showed that this Colcemid concentration eliminated all microtubules. Mitotic cells were collected by shaking off, and cell counts showed that over 95% of the cells were in interphase when treatment began and thus were arrested without the kinetochores having been previously attached to microtubules. Cells were then incubated in fresh medium and fixed for high voltage electron microscopy at intervals during recovery. — In early stages of recovery, short microtubules were observed near and in contact with kinetochores and surrounding centrioles. Microtubules were associated with kinetochores facing away from centrosomes and far from any centrosomal microtubules, and thus were not of centrosomal origin. At a later stage of recovery, long parallel bundles of microtubules, terminating in the kinetochore outer disk, extended from kinetochores both toward and away from centrosomes. Because microtubules had never been attached to kinetochores, the possibility that kinetochore microtubles were initiated by microtubule stubs resistant to Colcemid was eliminated. Therefore we conclude that mammalian kinetochores can initiate microtubules in vivo, thus serving as microtubule organizing centers for the mitotic spindle, and that formation of kinetochore-microtubule bundles is not dependent on centrosomal activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368158
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of kinetochore fibers: Microtubule continuity and inter-microtubule bridges (1981)
    Springer
    Chromosoma 83 (1981), S. 523-540 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract To understand how microtubules interact in forming the mitotic apparatus and orienting and moving chromosomes, the precise arrangement of microtubules in kinetochore fibers in Chinese hamster ovary cells was examined. Individual microtubules were traced, using high voltage electron microscopy of serial 0.25 μm sections, from the kinetochore toward the pole. Microtubule arrangement in kinetochore fibers in untreated mitotic cells and in cells recovering from Colcemid arrest were similar in two respects: the number of microtubules per kinetochore (mean 14 and 12, respectively) and the nearest neighbor intermicrotubule distance (mean∼90 nm). In Colcemid recovered cells, over 90% of the microtubules in kinetochore fibers were attached to the kinetochore (i.e. kinetochore microtubules) and extended most or all of the distance to the pole. Few free microtubules were present in the kinetochore fibers; most non-kinetochore microtubles terminated in the pole. Since kinetochores in this Colcemid-recovered system have been demonstrated to nucleate microtubules (Witt et al., 1980), it seems likely that most if not all of these kinetochore microtubules originated at the kinetochore. Some of the reconstructed kinetochore fibers were attached to chromosomes with bipolar orientation, suggesting that kinetochore microtubules need not interact with many polar microtubules for orientation to occur. In Colcemid recovered cells lysed to reduce cytoplasmic background, microtubules in kinetochore fibers were preferentially preserved. The parallel and near-hexagonal order typical of microtubules in kinetochore fibers was maintained, as was the number of kinetochore microtubules (mean, 13). The intermicrotubule distance was slightly reduced in lysed cells (mean, 60 nm). Crossbridges about 5 nm wide and 30–40 nm long were visible in kinetochore fibers of lysed cells. Such crossbridges probably contribute to the stabilization and parallel order of microtubules in kinetochore fibers, and may have a functional role as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328277
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  • 4
    Electronic Resource
    Electronic Resource
    Unequal distribution of DNA in the macronuclear division of the ciliate Euplotes eurystomus (1977)
    Springer
    Chromosoma 60 (1977), S. 59-67 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract During asexual fission in the ciliate Euplotes eurystomus, the macronucleus divides amitotically. The macronucleus was found to divide unequally, yielding sister pairs having a mean difference in DNA content of 11.6%. DNA content was determined by the Feulgen reaction using a fluorescent Schiffs reagent, and measuring fluorescence by cytophotometry. Variability in macronuclear DNA content was also examined in randomly-paired non-sister cells, and found to be greater than in sister cells. This greater variability could be due to accumulation of differences over a number of divisions, or to interclonal differences in equality of division. Two categories of non-sister cells were examined: recently divided, and “parents” constructed by averaging the DNA contents of progeny. Both showed similar variability in quantity of macronuclear DNA. The fact that cells surviving to divide showed no less variability in amount of DNA than cells immediately after division suggests that extremes in amounts of DNA resulting from unequal division are not selected against.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330411
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  • 5
    Electronic Resource
    Electronic Resource
    Structure of the mammalian kinetochore (1981)
    Springer
    Chromosoma 82 (1981), S. 153-170 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The structure of the mammalian trilaminar kinetocnore was investigated using stereo electron microscopy of chromosomes in hypotonie solutions which unraveled the chromosome but maintained microtubules. Mouse and Chinese hamster ovary cells were arrested in Colcemid and allowed to reform microtubules after Colcemid was removed. Recovered cells were then swelled, lysed or spread in hypotonic solutions which contained D2O to preserve microtubules. The chromosomes were observed in thin and thick sections and as whole mounts using high voltage electron microscopy. Bundles of microtubules were seen directly attached to chromatin, indicating that the kinetochore outer layer represents a differential arrangement of chromatin, continuous with the body of the chromosome. In cells fixed without pretreatment, the outer layer could be seen to be composed of hairpin loops of chromatin stacked together to form a solid layer. The hypotonically-induced unraveling of the outer layer was found to be reversible, and the typical 300 nm thick disk reformed when cells were returned to isotonic solutions. Short microtubules, newly nucleated after Colcemid removal, were found not to be attached to the kinetochore outer layer, but were situated in the fibrous corona on the external surface of the outer layer. This was verified by observations of thick sections in stereo which made it possible to identify microtubule ends within the section. Thus, kinetochore microtubules are nucleated within the fibrous corona, and subsequently become attached to the outer layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00286101
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  • 6
    Electronic Resource
    Electronic Resource
    Inhibition of hormone-dependent and independent breast cancer cell growthin vivo andin vitro with the antiestrogen toremifene and recombinant human interferon-α2 (1990)
    Springer
    Breast cancer research and treatment 15 (1990), S. 95-101 
    Details
    ISSN: 1573-7217
    Keywords: interferon ; toremifene ; antiestrogen ; athymic mice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The antiproliferative action of the antiestrogen toremifene and recombinant human interferon-α2a (IFN-α2a) were examined on human breast cancer cell lines grown in culture and in the athymic mouse. Solid tumors grew from an inoculation of a 99:1 ratio of hormone dependent (MCF-7) and hormone independent (MDA-MB-231) breast cancer cells without estrogen administration. However, estradiol supplementation significantly increased the rate of tumor growth. The daily administration of 1.35 × 106 U of recombinant human IFN-α2a resulted in a marked reduction of tumor growth in both estradiol-treated and non-treated mice. Toremifene administration (130 µg/day from a sustained release preparation) markedly inhibited estradiol stimulation of mouse uterine weight and partially reduced estradiol-stimulated tumor growth. The combination of IFN-α2a (1.35 × 106 u/day) with toremifene (130 µg/day) reduced estradiol-stimulated growth much below that of toremifene alone but not below that seen with interferon alone. Toremifene (10−10-10−6M) did not inhibit the growth of hormone-independent MDA-MB-231 breast cancer cellsin vitro whereas it did inhibit the growth of hormone-dependent MCF-7 cells in phenol red containing media. IFN-α2a (1–10,000 u) inhibited the growth of both MCF-7 and MDA-MB-231 cells in culture; however, MCF-7 cells were approximately 10-fold more sensitive to interferon inhibition. This was consistent with the MCF-7 cells showing a greater sensitivity to interferon than MDA-MB-231 cells in the induction of 2′5′-oligoadenylate synthetase. The heterogeneous tumor model in the athymic mouse suggests that differential sensitivities of breast cancer cells to the antiproliferative actions of interferon may influence the effectiveness of combination therapies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01810781
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