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  • Epithelium formation  (1)
  • Vimentin  (1)
  • pointed end  (1)
  • 1
    ISSN: 1432-0878
    Keywords: Intermediate filaments ; Vimentin ; Pigment epithelial cells ; Epithelium formation ; Immunofluorescence ; Chicken
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Retinal pigmented epithelial cells of chicken have circumferential microfilament bundles (CMBs) at the zonula adherens region. Isolated CMBs are polygons filled with a meshwork composed primarily of intermediate filaments; they show three major components of 200000, 55000, and 42000 daltons in SDS-gel electrophoresis. Here we have characterized the 55000-dalton protein immunochemically and ultrastructurally. Immunoblotting and immunofluorescence microscopy have shown that the 55000-dalton protein is an intermediate filament protein, vimentin. Vimentin filaments changed their distribution during differentiation of pigmented epithelial cells in culture. The protein in the elongated cells showed a fibroblast-type pattern of intermediate filaments. During epithelium formation, the filaments were uniformly distributed and formed a finer meshwork at the apical level. In pigmented epithelial cells that differentiated and matured in culture, vimentin and actin exhibited their characteristic behavior after treatment with colcemid. In the central to basal region of the cell, intermediate filaments formed thick perinuclear bundles. In the apical region, however, intermediate filaments changed in organization from a nonpolarized meshwork to a polarized bundle-like structure. Simultaneously, new actin bundles were formed, running parallel to the intermediate filaments. This suggests that there is some interaction between microfilaments and intermediate filaments in the apical region of these cells.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 2 (1982), S. 457-470 
    ISSN: 0886-1544
    Keywords: fragmin ; critical actin concentration ; nucleation ; filament growth ; pointed end ; barbed end ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: As reported previously, fragmin isolated form Physarum plasmodia restricts the polymerization of actin to produce short F-actin filaments in the presence of Ca2+ ions. Here it is shown that when actin is polymerized at low concentrations of salts, fragmin increases the critical concentration of actin for polymerization. This effect of fragmin on the critical concentration is independent of the molar ratio of fragmin to actin. The addition of actin monomers onto heavy meromyosin-decorated F-actin fragments treated with fragmin occurs unidirectionally at the pointed end of each fragment. These results suggest that fragmin binds to the barbed ends of F-actin filaments and inhibits association and dissociation of actin monomers at this end. Fragmin accelerates the initial stage of polymerization of actin. When a constant amount of G-actin is polymerized in the presence of small amounts of fragmin, the inverse of the half-polymerization time increases in proportion to the square root of the amount of fragmin added. This means that fragmin acts as a potent promoter of the nucleation step in actin polymerization. Both functions of fragmin-promotion of nucleation and capping at the barbed end of F-actin-require micromolar concentrations of Ca2+.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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