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  • 1
    ISSN: 0886-1544
    Keywords: coelomocytes ; cytoskelton ; calmodulin-binding proteins ; alpha-spectrin ; shape transformation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Sea urchin coelomocytes contain an actin-based cytoskeleton that undergoes major organizational changes as the cells transform from one morphology (petaloid) to another (filopodial). The molecular mechanisms directing and regulating this cytoskeletal reorganization are not well understood; Ca2+ has been implicated, but the specific targets of its action have not been identified. Since the effect of Ca2+ on a variety of cellular processes has been shown to be mediated by the Ca2+-binding protein calmodulin, we investigated the role of this protein in coelomocyte morphological transformation. The calmodulin inhibitory drugs trifluoperazine, chlorpromazine, and calmidazolium were shown to inhibit coelomocyte morphological transformation in response to hypotonic shock in a dosedependent fashion and at concentrations consistent with their reported potencies as anti-calmodulin agents. Calmodulin isolated from coelomocytes using trifluorophenothiazine affinity chromatography co-migrates with bovine brain calmodulin on 15% SDS-polyacrylamide gels and demonstrates a characteristic shift in electrophoretic mobility in the presence of Ca2+. Another diagnostic for calmodulin, Ca2+-dependent activation of exogenous 3':5' cyclic AMP phosphodiesterase, was demonstrated by whole coelomocyte homogenates, heat-treated homogenates, and the affinity purified coelomocyte protein. Localization of calmodulin in coelomocytes by indirect immunofluorescence reveals an association of calmodulin, at least in part, with the actin-based cytoskeleton. Calmodulin-binding polypeptides with estimated relative mobilities of 240,000, 195,000, 170,000, 70,000, 60,000, 30,000, and 20,000 daltons were identified using 125I-calmodulin overlay procedures. Ca2+-dependent calmodulin-binding in these preparations was demonstrated for all but the Mr 30,000 and 20,000 coelomocyte polypeptides. The majority of the calmodulin-binding proteins identified in whole petaloid coelomocyte preparations are also found in Triton X-100 insoluble cytoskeletal fractions. Immunoblotting with antiserum raised against chicken erythrocyte alpha-spectrin suggests that the 240,000 Mr calmodulin-binding polypeptide corresponds to coelomocyte alpha-spectrin. This protein was enriched in isolated coelomocyte filopodia where, we propose, it serves an analogous function to its counterpart in erythrocytes, in linking the actin-cytoskeleton to the plasma membrane. Thus, calmodulin is present in coelomocytes and possibly participates in the morphological transformation of these cells through regulation of cytoskeletal and/or membrane-cytoskeletal interactions.
    Additional Material: 11 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 26 (1993), S. 262-273 
    ISSN: 0886-1544
    Keywords: cortical flow ; coelomocytes ; cytoskeleton ; video enhanced microscopy ; cytochalasin ; colcemid ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Sea urchin coelomocytes naturally flatten on a substratum into a discoid morphology and display striking, centripetally directed cortical flow along the radii of the cell when viewed with time lapse, video enhanced microscopy. The rate of cortical flow averaged 4.5 μm/min in the peripheral most 10 μm of cytoplasm but slows considerably in the perinuclear region. Cytochalasin B causes: (1) the flow to stop, (2) the buildup of an actin filament-rich peripheral ridge of cytoskeletal material, (3) the centrifugal dissolution of a portion of the actin cytoskeleton, and (4) the contraction of other portions of the cytoskeleton into foci. Cytochalasin D (CD), on the other hand, causes the flowing actin meshwork to become severed from the edge of the cell and allows it to be drawn at least part way in towards the nucleus. A smaller peripheral ridge of actin filament buildup is also seen with CD. Colcemid induces another striking change in the cytoskeleton. The centripetal progression of the actin is not stopped by colcemid, but shortly after leaving the periphery of the cell, the linear elements within the flow become reoriented into arcs. The long axis of the arcs is roughly parallel with the cell's edge. The effects of all three drugs are reversible. The results are discussed in light of other systems and potential mechanisms for cortical flow. © 1993 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 1 (1980), S. 131-140 
    ISSN: 0886-1544
    Keywords: sea urchin coelomocytes ; motility ; filopodial formation and elongation ; ciné film analysis ; scanning electron microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Sea urchin coelomocytes were examined during their morphological transformation from petaloid to filopodial forms by scanning electron microscopy and ciné film analysis. Petaloid coelomocytes have a variable morphology but, in general, consist of numerous thin sheets of cytoplasm, the petals, arranged in three dimensions around a central nuclear region. The transition to the filopodial form can occur in either substrate-attached or suspended cells and begins with the formation of several microspikes at the edge of each petal. These become more apparent as the cytoplasm between each microspike/filopodium is retracted centripetally. Concomitantly, the diameter of the flattened cell is increased by as much as twofold as the filopodia actively lengthen at a uniform, average rate of 0.5 μm/minute. The transformation process requires ca 15 minutes and is complete when the cell diameter no longer increases. These filopodia are functionally distinct from the passively produced retraction fibers observed in cultured mammalian cells. The formation of filopodia is biphasic and includes both a cytoplasmic retraction phase and an active extension phase.
    Additional Material: 7 Ill.
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  • 4
    ISSN: 0886-1544
    Keywords: microtubules ; microfilaments ; filopodia ; cell spreading ; coelomocytes ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Sea urchin coelomocytes were used as a model system to investigate the distribution and role of microtubules and microfilaments in cell spreading and filopodial formation. By using immunoblot characterized antisera to tubulin and actin coupled with immunofluorescence techniques, cellular protrusions were seen to contain actin filaments but no microtubules. Cells depleted of MT's by cold and colcemid treatments could attach, spread, and transform to the filopodial morphology normally.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 3 (1983), S. 683-691 
    ISSN: 0886-1544
    Keywords: α-spectrin ; coelomocytes ; filopodia ; actin/membrane interactions ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have investigated the presence and localization of an α-spectrinlike protein and its potential role in the morphological transformation of sea urchin coelomocytes. In immunofluorescence images there is a diffuse fluorescence throughout the petaloid cytoplasm, indicating a random distribution of the spectrinlike protein prior to the transformation. As these cells form filopodia, there is a coincident appearance of a spectrinlike protein, as seen in fluorescent images, at the site of filopodial initiation. As the filopodia continue to form and lengthen, the spectrin localization parallels their development. There is a single polypeptide observed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels of whole coelomocyte lysates that cross-reacts with the anti-α-spectrin immunogen and comigrates with it at 240 kilodaltons.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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