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  • Life and Medical Sciences  (30,791)
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  • 1
    ISSN: 0886-1544
    Keywords: chromosome movement ; meiosis ; spermatocytes ; prophase ; nuclear envelope ; aster ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Association of bivalent chromosomes with the astral centers and nuclear envelope was analyzed in crane-fly spermatocytes during the final hours of diakinesis. In contrast to other systems in which movement of chromosomes during diakinesis correlates with the clustering of bivalents near the astral centers, such clustering is not prevalent in crane-fly spermatocytes. Polarization indices of bivalents calculated 5 to 10 minutes before the end of diakinesis provided evidence for polarization of only a fraction of all bivalents. Similar results were obtained in a large number of fixed cells in which asters and chromosomes were preferentially stained. Ultrastructural analysis of cells in late diakinesis revealed significant contact between bivalents and the nuclear envelope in all 46 cells that were analyzed. The extent of contact in some cells was greater than in others. Sites of contact included the telomeric ends of bivalents, and in some cases the distribution of contact sites suggested the possible involvement of centromeres in chromosome-nuclear envelope association. The results are consistent with the hypothesis that a dynamic interaction between chromosomes and nuclear envelope may exist during late prophase, when the movement of chromosomes is known to occur.
    Additional Material: 6 Ill.
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  • 2
    ISSN: 0886-1544
    Keywords: taxol ; microtubules ; intermediate filaments ; fibroblasts ; epithelial cells ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Taxol promotes microtubule (MT) assembly in vitro and induces the reorganization of the cytoskeleton into unusual MT arrays in cultured cells. The possibility that taxol also has an indirect effect on intermediate filaments (IF) was investigated. In baby hamster kidney (BHK-21) and human skin (ENSON) fibroblasts treated with 1-10 μM taxol for 1-24 h, the drug induces changes which are similar to those produced by colchicine. These include a loss of major cellular extensions, a redistribution of organelles to a perinuclear location, and an inhibition of locomotion. Saltatory particle movements are not inhibited, however. Ruffling and filopod formation continue, indicating that cells are viable up to 24 h.Polarized light microscopy of living fibroblasts treated with taxol reveals the presence of perinuclear birefringent material which has been examined by immunofluorescence. In control cells, IF and MT radiate from a juxtanuclear region and extend to the cell periphery. In taxol-treated cells, MT and IF are excluded from cell margins, forming large central bundles.In the epithelial cell lines PtK2 and PAM, the keratin system of IF does not become redistributed; in PtK2, however, a second fibroblastlike system of IF does become redistributed to a perinuclear position during taxol treatment.Ultrastructural analyses show that taxol-treated fibroblasts contain parallel arrays of cross-bridged MT-IF as well as bundles of MT exclusive of IF. Epithelial cells contain a predominance of IF-free MT bundles which are organized into hexagonally packed arrays. In these bundles MT frequently exhibit hooks or other incomplete MT profiles and are linked by filamentous material.
    Additional Material: 14 Ill.
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  • 3
    ISSN: 0886-1544
    Keywords: contact inhibition ; contact guidance ; growth cones ; cell-cell interactions ; neuronal contact behavior ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The outcome of contact interactions involving neurons and nonneurons varies depending on the cell types involved. When neuronal growth cones from either ciliary (motor) or dorsal root (sensory) ganglia directly contact the lamellipodium of an embryonic heart fibroblast, both neurite elongation and fibroblast locomotion are inhibited. This occurs in spite of the fact that cell-surface activity in both cells continues unabated. Such contact inhibition is not observed when homologous ganglionic nonneurons are involved in the interaction. In fact, these cells become intimately associated with growth cones and/or neuritic shafts as a result of the contact. The detailed nature of the respose to contact exhibited by nerves and nonnerves varies not only with cell type but also with the portion of the cell involved in the contact. Growth cone filopodia tend to actively palpate the fibroblast surface, whereas spread regions, termed “veils,” form areas of apposition with fibroblast lamellipodia. This latter situation resembles the “typical” contact inhibition of locomotion that occurs following embryonic heart fibroblast-fibroblast interactions. Growth cones also frequently exhibit contact guidance when interacting with nonruffling lateral surfaces of heart fibroblasts.
    Additional Material: 8 Ill.
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  • 4
    ISSN: 0886-1544
    Keywords: Caenorhabditis elegans spermatozoa ; cell motility ; electron microscopy ; cell-substrate contact ; 2-nm filaments ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The locomotion of C. elegans spermatozoa resembles, in many respects, the crawling movements of other eukaryotic cells. However, these sperm contain surprising little actin, which plays no apparent role in this cell's motility. Electron microscopy has revealed that crawling spermatozoa retain a strict morphological polarity so that the organelle-filled cell body is separated from the pseudopod by an array of cytoplasmic laminar membranes. When sperm crawl only the pseudopod contacts the substrate; the cell body is either pulled behind or carried on top of the rear portion of the pseudopod. Fingerlike projections which extend forward from the leading edge of the pseudopod initiate contact with the substrate. The underside of the pseudopod exhibits areas of close (40 nm separation) membrane-substrate association with intervening areas of wide (up to 300 nm) membrane-substrate gaps. The pseudopod cytoplasm contains 2-nm filaments but no filamentous actin has been observed. These 2-nm filaments were detected in thin sections of crawling cells and in negative-stained remnants of spermatozoa disrupted by either hypotonic buffer on Triton X-100. The filaments are found both free in the cytoplasm and closely associated with the cytoplasmic face of the plasma membrane and are usually oriented along the long axis of the cell. Neither the identity nor the function of these filaments has been established although their location and orientation suggest that they may be involved in generating propulsion.
    Additional Material: 8 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 3 (1983), S. 363-366 
    ISSN: 0886-1544
    Keywords: erythrocyte ; membranes ; spectrin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 6
    ISSN: 0886-1544
    Keywords: focal contacts ; microfilaments ; microinjection ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The role of structural elements in the organization and maintenance of focal contacts was studied by microinjecting into tissue culture cells specific probes which interfere with filamentous actin or with vinculin: actin interaction. Injection of actin capping proteins from Physarum and brain resulted in breakdown of microfilament bundles starting at their distal ends and in loss of focal contacts. This process was fully reversible. Injection of a high affinity antibody against chicken gizzard vinculin led to partial breakdown of microfilament bundles concomitant with disruption of focal contacts with vinculin remaining at the plasma membrane. This process was irreversible.
    Additional Material: 3 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 3 (1983), S. 383-390 
    ISSN: 0886-1544
    Keywords: F-actin aggregates ; actin-membrane interactions ; transformed/normal cell coculture ; F-actin/tropomyosin interaction ; temperature-sensitive viral mutant ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Observations on the role of transformation-specific F-aggregates [Carley et al, 1981] in altering morphology, adhesion and intercellular interaction in transformed cells are reported here. The appearance and disappearance of membrane- and substrate-associated F-actin aggregates (MAG and SAG, respectively) are followed in a cell line temperature-sensitive for transformation. Since MAG structures also appear near the membrane in suspension cultures of transformed cells and in transformed cells in coculture with untransformed cells, they appear to function at cell-cell contacts. Unlike microfilament bundles in untransformed cells, MAG and SAG do not contain the F-actin regulatory protein tropomyosin. The lack of tropomyosin in these structures near the membrane is reminiscent of areas of an exceptionally active actin cytoskeleton usually associated with motile processes of the normal cell membrane. Such areas of membrane-cytoskeletal interaction may be involved in the aberrant cell-cell communication as well as the aggressive behavior often seen in transformed cells.
    Additional Material: 3 Ill.
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  • 8
    ISSN: 0886-1544
    Keywords: microfilament-membrane attachments ; cell-cell contacts ; fascia adherens ; immunofluorescence microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: On the premise that the fascia adherens of cardiac muscle cell intercalated disk membranes is a structure that is closely homologous to the focal adhesions formed by fibroblasts, a fascia adherens preparation was isolated from chicken cardiac muscle, and was analyzed for its protein composition. A prominent 200-kilodalton (kd) protein was purified from the fascia preparation and shown to be antigenically unrelated to several previously characterized cytoskeletal proteins, including cardiac myosin and vinculin. With monospecific antibodies to the 200-kd protein, an identical or closely similar intracellular protein was shown to be associated with the focal adhesion plaques of fibroblasts.
    Additional Material: 6 Ill.
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  • 9
    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.
    Additional Material: 11 Ill.
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  • 10
    ISSN: 0886-1544
    Keywords: brain spectrin ; actin ; immunofluorescence ; peptide mapping ; protein phosphorylation ; syndeins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Membrane-associated mouse brain spectrin is a 972,000 Mr, 10.5S, (αβ)2 tetramer containing two ∼ 240,000 Mr subunits and two ∼ 235,000 Mr subunits. Two-dimensional [125I]tryptic peptide mapping indicates that these subunits share only limited and equivalent overlap with the α- and β-subunits of red blood cell (RBC) spectrin. Both the 220,000 Mr β-subunit of RBC spectrin and the 235,000 Mr β-subunit of brain spectrin are phosphorylated in the intact mouse. In vitro analysis suggests that both are phosphorylated by a cAMP-independent protein kinase. Antibodies against pure native mouse red blood cell spectrin cross-react with brain spectrin, and antibodies against pure brain spectrin cross-react with both the α-and β-subunits of mouse RBC spectrin. Both antibodies have been utilized to localize brain spectrin within distinct cellular entities of the mouse cerebellum. Granule cell neurons of the internal granule layer and Purkinje cell neurons demonstrated intense fluorscence of the cortical cytoplasm immediately adjacent to the plasma membrane and unstained nuclei, when either RBC or brain spectrin antibodies were utilized for staining. The molecular layer of the cerebellum stained only lightly, and oligodendrocytes and astrocytes appeared to have little fluorescence. Therefore, while brain is a tissue rich in nonerythroid spectrin, the concentration of these immunoreactive analogues is quite variable within distinct cellular entities of the cerebellum.
    Additional Material: 3 Ill.
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