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  • Physics  (153)
  • Cell & Developmental Biology  (98)
  • 1980-1984  (246)
  • 1960-1964  (5)
  • 1983  (139)
  • 1980  (107)
  • 1960  (5)
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  • 1980-1984  (246)
  • 1960-1964  (5)
Year
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 1 (1980), S. 63-71 
    ISSN: 0886-1544
    Keywords: Physarum polycephalum ; myosin light chains ; polyacrylamide gel electrophoresis ; calcium ; cytoplasmic streaming ; actomyosin ATPase regulation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Myosin from the slime mold Physarum polycephalum contains three sizes of polypeptides: a heavy chain and two light chains, LC-1 and LC-2. Using a simple qualitative test for calcium binding by comparing electrophoretic migration of the polypeptides in sodium dodecy1 sulfate (SDS) acrylamide gels in the presence and absence of calcium, we have found that Physarum myosin light chain LC-2 migrates with an apparent molecular weight of 16,900 daltons in the presence of the metal ion chelator ethylene glycol bis (B-aminoethyl ether) N,N′-tetraacetic acid (EGTA). However, if calcium chloride is added to the sample prior to electrophoresis, the apparent molecular weight decreases to 16,100. Lanthanide and cadmium ions, but not magnesium, can substitute for calcium. Because the ionic radii of Ca2+, La3+, and Cd2+ are almost identical, we conclude that Physarum myosin LC-2 possesses a very size-specific binding site for calcium. Physarum myosin LC-1 and the heavy chain give no evidence for binding calcium by this test. Since cytoplasmic streaming in the plasmodium of Physarum requires calcium, our evidence indicates that the calcium-binding property of Physarum myosin LC-2 may be important in regulating the production of force by actomyosin in the ectoplasm. Unexpectedly, the myosin light chain in Physarum capable of binding calcium, LC-2, is the essential light chain, while LC-1 is a member of the regulatory class of myosin light chains [V. T. Nachmias, personal communication]. Until now, essential myosin light chains have not been shown to have high affinity divalent cation binding sites. This means a new version of the myosin-based model for actomyosin regulation by calcium may be required to explain cytoplasmic movement in Physarum, and perhaps in other motile systems involving cytoplasmic myosins as well.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 1 (1980), S. 159-162 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 3 (1983), S. 1-19 
    ISSN: 0886-1544
    Keywords: cytoplasmic transport ; Saltation ; microtubules ; keratocytes ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We report the first direct demonstration that the cytoplasmic transport of organelles and vesicles (collectively called particles) takes place along microtubules. Living keratocytes from the corneal stroma of the frog, Rana pipiens, were observed with Allen video-enhanced constrast, differential interference constrast (AVEC-DIC) microscopy [Allen et al, 1981]. In sufficiently thin regions of these cells a network of linear elements was visible. When particles were observed in motion, they always moved along these linear elements. The linear elements remained intact and in focus on the microscope when lysed in a cell lysis solution that stabilized microtubules. Preparations were then fixed in formaldehyde, washed with phosphate-buffered saline (PBS), incubated with rabbit antitubulin, washed with PBS, stained with rhodamine-conjugated goat antirabbit, and washed with PBS. The extracted cells continued to remain in place and in focus on the microscope throughout these procedures. The same cells were then observed using epifluorescence optics and a silicon-intensified target (SIT) video camera. A network of fluorescent linear elements was seen to correspond in number, form, and position to the linear elements seen in the live AVEC-DIC image. Taken together, the AVEC-DIC and fluorescence microscopy observations prove that the linear elements along which particles move are microtubules (MTLEs). The observed particle speeds, pause times, and distances moved varied widely, even for the same particle on the same microtubule. Particles were also observed to switch from one microtubule to another as they were transported. The polarity of the microtubules did not seem to affect the particle direction, since particles were observed to move in both directions on the same MTLE. When not in motion these particles behaved as if anchored to the microtubules since they showed negligible Brownian motion. Finally, it was observed that an elongate particle could move onto two intersecting linear elements such that it was deformed into an inverted “Y” shape. This indicates that there may be more than a single site of attachment between the force generator and the particle.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 177 (1983), S. 245-254 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Striking ultrastructural and hormonal parameters of premature menopause and aging are reported in female Xyleborus ferrugineus fed cholesterol, rather than 7-dehydrocholesterol, as a sole dietary sterol. The titer of free ecdysteroids in such 63-day-old females remained abnormally elevated through the period of the ovarian cycle. A similar plateauing of such elevated titer also occurred in 147-day-old, irregularly cycling females fed only cholesterol as the dietary sterol. These hormonal changes in menopausing X. ferrugineus females seem especially analogous to the maintenance of an elevated concentration of 17-β-estradiol through the estrous, as well as the proestrous, ovary of aged irregularly cycling rats. The highly abnormal ultrastructure of ovaries of X. ferrugineus females aged 216 days on a diet containing cholesterol as the sole sterol seems quite analogous to that of the nonovulatory follicles in older, irregularly cycling rats. Our new findings involving aging X. ferrugineus females indicate further the usefulness of an insect model to study aging processes.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 102 (1980), S. 175-181 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A procedure has been investigated for sorting viable cells according to their DNA content. Cells are stained with the U.V. activated fluorochromes 4′6-diamidino-2-pheylindole (DAPI), Hoechst 33258 or Hoechst 33342, and sorted with a Fluorescence Activated Cell Sorter. Hoechst 33342 is a suitable vital stain for a varietyof cell types. Hoechst 33258 and DAPI, however, are quantitative vital stains for CHO cells only. Cloning efficiency is unaffected by the sorting procedure, and these stains are not mutagenic at concentrations suitable for vital staining. Potential applications of this procedure to cell biology are discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 104 (1980), S. 153-162 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: BALB/c or DBA/2 mice were infected with Abelson murine leukemia virus (A-MuLV), pseudotype Molony murine leukemia virus (M-MuLV). Infection of these mice with 104 focus-forming units of A-MuLV (M-MuLV) induced overt leukemia, detectable grossly or microscopically in 90% of the mice at 20-38 days. However, these methods did not detect leukemia at 17 days or before. Bone marrow cells from A-MuLV-infected leukemic or preleukemic mice were placed in tissue culture in a soft agarose gel. Cells from leukemic or preleukemic BALB/c mice grew to form colonies of 103 cells or more, composed of lymphoblasts, whereas marrow cells from normal uninfected mice did not. Cells from these colonies grew to form ascitic tumors after intraperitoneal inoculation into pristane-primed BALB/c recipient. Colony-forming leukemia cells could be detected in the marrow of A-MuLV-infected mice as early as 8 days after virus incoluation. The number of colony-forming leukemia cells increased as a function of time after virus inoculation.Colony-forming leukemia cells require other cells in order to replicate in tissue culture. Normal bone marrow cells, untreated or after treatment with mitomycin-C, provide this “helper” function. Only in the presence of untreated or mitomycin-C treated helper cells was the number of colonies approximately proportional to the number of leukemia cells plated.Marrow cells from leukemic BALB/c mice form more colonies than those from leukemic DBA/2 mice. The number of colonies formed per 103 microscopically identifiable leukemia cells plated was determined to be 2-3 for leukemic BALB/c mice and 0.3 for DBA/2 mice. Cocultivation of leukemic DBA/2 marrow cells with mitomycin-C treated normal BALB/c cells did not increase the number of colonies formed by the DBA/2 leukemic cells. Thus, the decreased ability of DBA/2 leukemia cells to form colonies appears to be a property of the leukemia cell population.
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  • 7
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The effect of inhibition of the cell membrane Na+-K+ pump on the Balb/c-3T3 cell growth cycle was studied. Inhibition of the Na+-K+ pump resulted in a dose-dependent reduction of intracellular K+ concentration ({K+}i). However, inhibition of protein synthesis in G0/G1 and of subsequent entry into S phase occurred only after {K+}i fell below a critical threshold (50-60 mmoles/liter). Thus, when the {K+}i falls below a critical threshold, protein synthesis is inhibited, preventing cells from entering the S phase.The platelet-derived growth factor (PDGF) induces cells to become “competent” to traverse the cell cycle; the platelet-poor plasma component of serum allows competent cells to progress through G0/G1 and enter S phase. Inhibition of the Na+-K+ pump did not prevent the induction of competence by PDGF, but it did reversibly inhibit plasma-mediated events in early G0/G1. Similarly, cycloheximide inhibited plasma-mediated events but did not prevent PDGF-induced competence. Thus, protein synthesis may not be required for induction of competence; alternatively, the induction of the competent state may occur in these cells after removal of PDGF and protein synthesis inhibitor. Protein synthesis is required for subsequent plasma-mediated events in G0/G1.
    Additional Material: 7 Ill.
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  • 8
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The possibilities that the growth-promoting effect of the extracellular matrix (ECM) produced by cultured bovine corneal endothelial (BCE) cells could be due to: (1) adsorbed cellular factors released during the cell lysis process leading to the denudation of the ECM; (2) adsorbed serum or plasma factors: or (3) adsorbed exogenous growth factors have been examined. Exposure of confluent BCE cultures to 2 M urea in medium supplemented with 0.5% calf serum denudes the ECM without cell lysis. The ECM prepared by this procedure supports cell growth just as well as ECM prepared by denudation involving cell lysis. Thus, it is unlikely that the growth-promoting properties of ECM are due to adsorbed cellular factors. When the ECM produced by BCE cells grown in defined medium supplemented with high-density lipoprotein, transferrin, and insulin was compared to the ECMs produced by cells grown in the presence of serum- or plasma-supplemented medium, all were found to be equally potent in stimulating cell growth. It is therefore unlikely that the growth-promoting ability of the ECM is due to adsorbed plasma or serum components. When fibroblast growth factor (FGF)-coated and ECM-coated plastic dishes were submitted to a heat treatment (70°C, 30 min) which results in the inactivation of FGF, the growth-supporting ability of FGF-coated dishes was lost, while the comparable ability of ECM-coated dishes was not affected significantly. This observation tends to demonstrate that the active factor present in the ECM is not FGF. Nor is it platelet derived growth factor (PDGF), since treatment known to destroy the activity of PDGF, such as exposure to dithiothreitol (0.1 M, 30 min, 22°C) or to β-mercaptoethanol (10%) in the presence or absence of 6 M urea for 30 min at 227°C, does not affect the growth-promoting activity of ECM. It is therefore unlikely that the growth-promoting effect of ECM is due to cellular growth-promoting agents or to plasma or serum factors adsorbed onto the ECM.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 114 (1983), S. 267-278 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Liposomes made by sonication of egg yolk phosphatidyl choline support the proliferation of low-density bovine vascular and corneal endothelial cells, and vascular smooth muscle cells maintained on basement laminacoated dishes and exposed to a defined medium supplemented with transferrin. The optimal growth-promoting effect of phosphatidyl choline was observed at concentrations of 25 μg/ml for low-density cultures of vascular smooth muscle cells, and 100 μg/ml for vascular and corneal endothelial cells. The growth rate and final cell density of vascular endothelial cells exposed to a synthetic medium supplemented with transferrin and either high-density lipoproteins or phosphatidyl choline has been compared. Although cultures exposed to phosphatidyl choline reached a final cell density similar to that of cultures exposed to high-density lipoproteins, they had a longer average doubling time (17 h vs. 12 h) during their logarithmic growth phase and a shorter lifespan (17 generations vs. 30 generations). Similar observations were made in the case of vascular smooth muscle cells or bovine corneal endothelial cells maintained in medium supplemented with transferrin, fibroblast growth factor (FGF) or epidermal growth factor (EGF), and insulin and exposed to either high-density lipoproteins or phosphatidyl choline. Since phosphatidyl choline can, for the most part, replace highdensity lipoproteins in supporting the proliferation of various cell types, it is likely that the growth stimulating signal conveyed by high-density lipoproteins is associated with its polar lipid fraction, which is composed mostly of phosphatidyl cholines.
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  • 10
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The Arrhenius plot of the rate of V79 Chinese hamster cell inactivation due to hypothermia has a “break” around 7-10°C with optimum storage temperature for unprotected cells being about 10°C. Addition of the membrane lipid perturber, butylated hydroxytoluene, improves survival of cells when compared to controls at temperatures below this break but not above. Arrhenius plots of growth rates of the cells show breaks at 30 and 40°C. Measurements of membrane fluidity by electron spin resonance or membrane polarization anisotropy by fluorescence spectrophotometry techniques as a function of temperature in these cells also reveal “breaks” centered around 8 and 30°C. Hence, the changes in the rate of cell inactivation and growth as a function of temperature may be related to membrane lipid phase changes.
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