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  • Articles  (91)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 2 (1982), S. 287-308 
    ISSN: 0886-1544
    Keywords: actin-binding protein ; Dictyostelium ; cytoskeleton ; amoeboid movement ; calcium ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A protein from Dictyostelium discoideum with an apparent subunit molecular weight of 95,000 daltons (95K protein) was previously identified as an actin-binding protein ‘Hellewell and Taylor, 1979’. In this paper, we present a method for purifying the protein, and characterize some important aspects of its structure and function. Purification of the 95K protein is achieved by fractionation with ammonium sulfate followed by chromatography on DEAE-cellulose, gel filtration on 6% agarose, and final purification on hydroxyapatite. The 95K protein is a dimer, composed of apparently identical subunits. It is a rod-shaped molecule, 38 nm in length, with a Stokes radius of 74 Å. In these structural properties, the 95K protein is similar to muscle and nonmuscle α-actinins. The 95K protein and filamin are equally competent, when compared on a weight basis, to enhance the apparent viscosity of actin as determined by falling ball viscometry. The apparent viscosity of mixtures of the 95K protein and actin is dramatically reduced at pH greater than 7.0 or free ‘Ca2+’ greater than 10-7 M. We also examine the mechanism by which calcium regulates the interaction of the 95K protein and actin. A change in free ‘Ca2+’ induces no detectable change in the quaternary structure of the 95K protein. Our experiments indicate that the 95K protein does not dramatically alter the length distribution of actin filaments in the presence of micromolar free ‘Ca2+’. A large fraction of the 95K protein cosediments with actin in the presence of low free ‘Ca2+’ (ca. 3 × 10-8M), but not in the presence of high free ‘Ca2+’ (ca. 4 × 10-6M). We conclude that increased free ‘Ca2+’ inhibits gelation of actin by the 95K protein by reducing the affinity of the 95K protein for actin. We propose that 95K protein is an important component of the cytoskeletal/contractile system in D. discoideum amoebae.
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  • 2
    ISSN: 0886-1544
    Keywords: platelet ; platelet adhesion ; cytoskeleton ; high voltage electron microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Adhesion of platelets in vitro resulted in rapid polymerization of the amorphous cytoplasmic ground substance into an organized cytoskeletal superstructure. This cytoskeleton, characterized through the use of whole-mount and stereo (3-D), high-voltage microscopy in conjunction with morphometrics and cytochemistry, comprised four major size classes of filaments organized in distinctive zones. The central matrix, or granulomere, at the center of the cell mass, was an ill-defined meshwork of 80-100-Å filaments which enshrouded granules, dense bodies, and elements of the dense tubular system as identified through peroxidase cytochemistry. Demarcasting this central matrix was a trabecular zone containing 30-50, 80-100, and 150-170 Å filaments in an open and rigid-appearing lattice. Circumscribing the trabecular zone and extending to the margins of the hyalomere was the third region, the peripheral web, in which 70-Å filaments were arranged in a tight honeycomb lattice. This organizational pattern was retained in cytoskeletons prepared by Triton x-100 extraction of the adherent cells, and was observed in basally located cells of aggregates which formed subsequent to adhesion. Our observations are consistent with biochemical studies of cytoskeletons prepared from suspended platelets and suggest a contractile protein composition for the superstructure during adhesion.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 3 (1983), S. 657-669 
    ISSN: 0886-1544
    Keywords: Hela spectrin ; membrane ; cytoskeleton ; filamin ; actin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: From 30-40 g of Hela-S3 cells grown in suspension, 0.25-0.50 mg of spectrin has been purified by conventional biochemical procedures starting from a low ionic strength extraction at alkaline pH of crude Hela membranes. Hela spectrin consists in its native form of a tetramer α2β2 of two high molecular weight polypeptides (240,000 and 230,000 daltons). Three different populations of Hela membranes depleted of both spectrin and actin have been prepared on discontinuous sucrose gradients. Surprisingly, spectrin will reassociate with only the heavier membrane fraction. This reassociation is specific for Hela spectrin, since three other purified Hela proteins as well as human erythrocyte spectrin do not reassociate under the same conditions. This binding is not due to the presence of traces of actin still present in the membrane fraction since two Hela actin-binding proteins (filamin I and II) do not show any significant binding to this fraction. The nature of the membrane-binding site for Hela spectrin is discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 6 (1986), S. 291-304 
    ISSN: 0886-1544
    Keywords: cytoskeleton ; microtubule ; microfilament ; adult ; culture ; cardiac ; myocyte ; immunofluorescence ; antibodies ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Antitubulin, phalloidin. and antimyosin were used to study the distribution of microtubules, microfilaments, and myofibrils in cultured adult cardiomyocytes. These cells undergo a stereotypic sequence of morphological change in which myotypic features are lost and then reconstructed during a period of polymorphic growth. Microtubules, though rearranged during these events in culture, are always present in an organized network. Myosin and actin structures, on the other hand, initially degenerate. This initial degeneration is reversed when a cell attaches to the culture substratum. Upon attachment, new microtubules are laid down as a cortical network adjacent to the sarcolemma and, subsequently, as a network in the basal part of the cell. Actin and then myosin filament bundles appear next, in a pattern corresponding to the pattern of the microtubules. Finally, striated myofibrils are formed, first in the central part of the cell, and subsequently in the outgrowing processes of the cell, A mechanism is suggested by which the eventual polymorphic shape of a cell is related to the shape of its initial area of contact with the culture substratum. Finally, a model of myofibrillogenesis is proposed in which microtubules participate in the insertion of myosin among previously formed actin filament bundles to produce myofibrils.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 8 (1987), S. 284-291 
    ISSN: 0886-1544
    Keywords: tyrosination ; acetylation ; post-translational modifications ; cytoskeleton ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have examined the distribution of acetylated α-tubulin using immunofluorescence microscopy in fibroblastic cells of rat brain meaninges. Meningeal fibroblasts showed heterogenous staining patterns with a monoclonal antibody against acetylated α-tubulin ranging from staining of primary cilia or microtubule-organising centers (MTOCs) alone to extensive microtubule networks. Staining with a broad spectrum anti-α-tubulin monoclonal indicated that all cells possessed cytoplasmic microtubule networks. From double-labeling experiments using an antibody against acetylated α-tubulin (6-11B-1) and antibodies against either tyrosinated or detyrosinated α-tubulin, it was found that acetylated α-tubulin and tyrosinated α-tubulin were often segregated to different microtubules. The microtubules containing acetylated but not tyrosinated α-tubulin were cold stable. Therefore, it appeared that in general meningeal cells possessed two subset of microtubules: One subset contained detyrosinated and acetylated α-tubulin and was cold stable, and the other contained tyrosinated α-tubulin and was cold labile. These results are consistent with the idea that acetylation and detyrosination of α-tubulin are involved in the specification of stable microtubules.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 3 (1983), S. 525-534 
    ISSN: 0886-1544
    Keywords: actin ; actin-membrane interactions ; coelomocytes ; calmodulin ; cytoskeleton ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Coelomocytes from several echinoderm species undergo an actin-mediated cytoskeletal transformation once subjected to hypotonic shock. In this study, coelomocytes from the sea urchins Lytechinus variegatus and Arbacia punctulata were induced to “transform” by treatment with 〉 5 μM of the calcium ionophore A23187 in the presence of external Ca++. The dependence of ionophore transformation on external Ca++ and the lack of chlorotetracycline staining indicates that these cells rely on external Ca++ sources. NBD-phallacidin (7-Nitrobenz-2-oxa-1,3-diazole-phallacidin) staining of lysolecithin permeabilized cells and wholemount transmission electron microscopy (TEM) show that similar reorganizations of the actin cytoskeleton take place during hypotonic shock and ionophore transformation, although actin filament bundling is less apparent in A23187-treated cells. As has been shown with hypotonic shock transformation, the ionophore elicited shape change is inhibited by anticalmodulin drugs. Greater than 10 μM concentrations of W 13 inhibit filopod formation, while this drug's less active structural analogue, W 12, exhibits no effects. W 13 also appears to disrupt actin filament-membrane associations in the cells. Fluorescent localization of calmodulin using a photooxidized derivative of trifluoperazine indicates a general cytoplasmic distribution with some concentration in filopod core bundles. Coelomocyte transformation may be an example of a cellular shape change regulated by Ca++ through the action of calmodulin modulation of actin-membrane interactions.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 9 (1988), S. 140-152 
    ISSN: 0886-1544
    Keywords: cell surface ; cytoskeleton ; receptor-mediated endocytosis ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cell-surface IgM (antigen receptor) sediments with the membrane fraction following osmotic lysis and homogenization of cells of the human lymphoblastoid cell line WiL2. In nonreducing buffers, SDS PAGE analysis of membrane pellets demonstrates that “native” membrane IgM exists as a dimer. In contrast to osmotic lysis, lysis of cells with the nonionic detergent Triton X-100 releases approximately 90% of the membrane-bound IgM into the supernatant; approximately 10% of the IgM pellets with the cytoskeletal fraction on centrifugation. Ligand challenge with either m̈-chain-specific antibodies or concanavalin A induces a change in the state of membrane IgM making it refractory to detergent extraction, such that 43% of the IgM pellets during centrifugation. This ligand-induced retention of IgM is significantly diminished by the microfilament-disrupting agent cytochalasin D, whereas pretreatment of cells with sodium azide or colchicine results in no significant change in the percentage of membrane IgM retained by Triton X-100 residues. These results indicate that retention of IgM involves an association with the cortical actin-based cytoskeleton. Investigation of the structural basis for ligand-induced Triton X-100 retention of membrane IgM by using ferritin-conjugated antibodies, myosin subfragment S1, and stereo-imaging electron microscopy has revealed linkages between ligand-receptor (antigen-IgM) complexes and elements of the cortical actin-based cytoskeleton.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 8 (1987), S. 61-67 
    ISSN: 0886-1544
    Keywords: platelets ; cytoskeleton ; vimentin ; microtubules ; immunofluorescence ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Human and bovine platelets contain a 58,000-dalton vimentinlike protein that cross-reacts with antivimentin antibody. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blots indicate that this protein is present in whole platelet lysates and triton insoluble cytoskeletons. Transmission electron microscopy of platelets reveals an isotropic network of individual intermediate filaments distributed throughout the platelets. High salt, triton extracted, glutaraldehyde and tannic acid fixed platelets reveal 10-nm filaments that can be seen to form a peripheral ring, as well as an isotropic network in the body of the cells. Indirect immunofluorescence of resting and spread platelets demonstrates a circumferential staining pattern close to the cell membrane, with additional fibrillar staining throughout the platelets. Our data suggest that the 58,000-dalton vimentinlike protein may be associated with the microtuble coil and the plasma membrane, and may thus help to maintain the resting platelet's discoid shape.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 6 (1986), S. 2-14 
    ISSN: 0886-1544
    Keywords: Allogromia ; reticulopods ; cytoskeleton ; microtubules ; actin ; saltatory transport ; cell shape ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cytoskeletal inhibitors were used as probes to test the involvement of microtubules and actin microfilaments in the development, motility, and shape maintenance of the pseudopodial networks (i e, reticulopodia) of the foraminifers Allogromia sp strain NF and Allogromia laticcllaris. Agents that disassemble cytoplasmic microtubules (cold, colchicine, and nocodazole) arrest all movement but have variable effects on reticulopodial shape. Electron microscopy reveals a granulofibrillar matrix but few, if any, microtubules in these motility-arrested reticulopods. Allogromiids treated with cytochalasin B or D lose substrate adhesion and undergo dramatic changes in shape and motile behavior, highlighted by the coalescence of reticulopodial cytoplasm into irregularly shaped bodies with chaotic motility. Serial semithick sections of such preparations, viewed by high-voltage electron microscopy, document a striking rearrangement of microtubules within these cytochalasin-induced bodies. All aspects of cytochalasin-altered motility are completely inhibited by colchicine. Actin is present in reticulopodia, as determined by staining with rhodamine-phalloidin; this staining is not observed in cytochalasin-treated organisms. These data provide compelling evidence that microtubules are required for reticulopodial motility. An actin-based cytoskeleton is thought to play a role in maintaining shape, mediating pseudopod/substrate adhesion, and coordinating the various microtubule-dependent processes.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 6 (1986), S. 15-24 
    ISSN: 0886-1544
    Keywords: cytoskeleton ; keratin ; vimentin ; microtubules ; saltatory movements ; motility ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The distribution and motility of cytoplasmic particles was examined in PtK1 cells in which intermediate filament networks had been disrupted by acrylamide. In these cells, particles (mitochondria and vesicles) accumulated near the cell center although saltatory movements continued. This left a broad sheet of agranular cytoplasm at the periphery of the cell. Particles were capable of movement into this sheet. Intermediate filaments were absent in the peripheral cytoplasm although microtubules remained in a normal configuration. Particles apparently move along the microtubules. These results indicate that particle movement along microtubules is not dependent upon the normal configuration of intermediate filaments. It is suggested that intermediate filaments are necessary for normal organelle distribution and serve as a matrix with which particles can associate to maintain position.
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