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Abstract
Rapid freezing and freeze substitution were used in conjunction with immunofluorescence, whole mount EM, and immunoelectron microscopy to study the organization of myosin and actin in growth cones of cultured rat superior cervical ganglion neurons. The general cytoplasmic organization was determined by whole mount EM; tight microfilament bundles formed the core of filopodia while a dense meshwork formed the underlying structure of lamellipodia. Although the central microtubule and organelle-rich region of the growth cone had fewer microfilaments, dense foci and bundles of microfilaments were usually observed. Anti-actin immunofluorescence and rhodamine phalloidin staining of f-actin both showed intense staining of filopodia and lamellipodia. In addition, staining of bundles and foci were observed in central regions suggesting that the majority of the microfilaments seen by whole mount EM are actin filaments. Anti-myosin immunofluorescence was brightest in the central region and usually had a punctate pattern. Although less intense, anti-myosin staining was also seen in peripheral regions; it was most prominent at the border with the central region, in portions of lamellipodia undergoing ruffling, and in spots along the shaft and at the base of filopodia. Immunoelectron microscopy of myosin using postembedment labeling with colloidal gold showed a similar distribution to that seen by immunofluorescence. Label was scattered throughout the growth cone, but present as distinct aggregates in the peripheral region mainly along the border with the central region. Less frequently, aggregates were also seen centrally and along the shaft and at the base of filopodia. This distribution is consistent with myosins involvement in the production of tension and movements of growth cone filopodia and lamellipodia that occur during active neurite elongation.
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Li ZY, Streeten BW, Wallace RN. Association of elastin with pseudoexfoliative material: an immunoelectron microscopic study. Curr Eye Res 1988; 7:1163-72. [PMID: 3229128 DOI: 10.3109/02713688809033220] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Using immunoelectron microscopy, the presence of elastin and tropoelastin was demonstrated in pseudoexfoliative (PSX) material in all its classical sites on the lens capsule, ciliary non-pigment epithelium, iris epithelium and stroma, and conjunctiva. Some variability in binding affinity was seen in different sites, and labelling was more often on the periphery than the center of the PSX fibers. The elastin epitope on PSX material was more sensitive to processing than the remarkably stable epitope on mature elastic fibers. Since neither elastin nor a related component of PSX fibers, elastic microfibrillar protein, is a circulating protein, both are likely to be secreted by local ocular cells. Most of these local cells are not involved in elastogenesis normally, suggesting that an abnormal stimulus or defective regulation of matrix synthesis exists in this disease.
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Ohta M, Marceau N, French SW. Changes in the organization and antigenic determinants of intermediate filaments of rat hepatocytes after infusion of cytochalasin B in vivo. THE AMERICAN JOURNAL OF PATHOLOGY 1988; 133:578-88. [PMID: 2462355 PMCID: PMC1880806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The changes in cytokeratin intermedial filaments (IFs) after cytochalasin B (CB) infusion of rat liver in vivo were studied by light and electron microscopy, immunofluorescent staining (IMF), and immunoelectron microscopy (IEM). The CB treatment caused a change in the IFs at the cell border associated with a change in the distribution of microfilaments. The IFs at the cell border were partially disrupted. Actin aggregates were localized at points where IFs had condensed together. The pericanalicular sheath was intact but very dilated. These results indicated that the CB treatment caused an irregular distribution of the microfilaments at the cell periphery but spared the actin at the bile canaliculus. Cytokeratin staining by IMF was markedly decreased or absent; however, IEM clearly showed the presence of nonstaining IFs after CB treatment. These results indicated that the antigenic determinant of normal cytokeratin IFs became masked after CB treatment. The results indicate that F-actin disassembly induced by CB affects both the organization and conformation of cytokeratins associated with loss of integrity of the plasma membrane and vesicular uptake of plasma proteins by hepatocytes.
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29
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Vanderpuye OA, Carraway CA, Carraway KL. Microfilament association of ASGP-2, the concanavalin A-binding glycoprotein of the cell-surface sialomucin complex of 13,762 rat mammary ascites tumor cells. Exp Cell Res 1988; 178:211-23. [PMID: 3049120 DOI: 10.1016/0014-4827(88)90392-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Microfilament-associated proteins and membrane-microfilament interactions are being investigated in microvilli isolated from 13,762 rat mammary ascites tumor cells. "Phalloidin shift" analyses on velocity sedimentation gradients of Triton X-100 extracts of [3H]-glucosamine-labeled microvilli identified a 120-kDa cell-surface glycoprotein associated with the microvillar microfilament core. The identification was verified by concanavalin A (Con A) blots of one- and two-dimensional (2D) electrophoresis gels of sedimented microfilament cores. By 2D-electrophoresis and lectin analyses the 120-kDa protein appeared to be a fraction of ASGP-2, the major Con A-binding glycoprotein of the sialomucin complex of the 13,762 cells. This identity was confirmed by immunoblot analyses using immunoblot-purified anti-ASGP-2 from anti-membrane serum prepared against microvillar membranes. Proteolysis of the microvilli with subtilisin or trypsin resulted in an increase in the amount of ASGP-2 associated with the microfilament cores. An increase was also observed with sialidase treatment of the microvilli, suggesting that negative charges, probably present on the highly sialated sialomucin ASGP-1 of the ASGP-1/ASGP-2 sialomucin complex, reduce ASGP-2 association with the microfilament core. Proteolysis of isolated microvillar membranes, which contain actin but not microfilaments, also increased the association of ASGP-2 with a Triton-insoluble, actin-containing membrane fraction. Purified ASGP-2 does not bind to microfilaments in sedimentation assays. Since the Triton-insoluble membrane residue is enriched in an actin-containing transmembrane complex, which contains a different glycoprotein, we suggest that the ASGP-2 is binding indirectly via this complex to the microfilament core in the intact microvilli.
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30
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Fath KR, Lasek RJ. Two classes of actin microfilaments are associated with the inner cytoskeleton of axons. J Biophys Biochem Cytol 1988; 107:613-21. [PMID: 3417765 PMCID: PMC2115200 DOI: 10.1083/jcb.107.2.613] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The distribution and length of actin microfilaments (MF) was determined in axoplasm extruded from the giant axons of the squid (Loligo pealeii). Extruded axoplasm that was separated from the axonal cortex contains approximately 92% of the total axonal actin, and 60% of this actin is polymerized (Morris, J., and R. Lasek. 1984. J. Cell Biol. 98:2064-2076). Localization of MF with rhodamine-phalloidin indicated that the MF were organized in fine columns oriented longitudinally within the axoplasm. In the electron microscope, MF were surrounded by a dense matrix and they were associated with the microtubule domains of the axoplasm. The surrounding matrix tended to obscure the MF which may explain why MF have rarely been recognized before in the inner regions of the axon. The axoplasmic MF are relatively short (number average length of 0.55 micron). Length measurements of MF prepared either in the presence or absence of the actin-filament stabilizing drug phalloidin indicate that axoplasm contains two populations of MF: stable MF (number average length of 0.79 micron) and metastable MF (number average length of 0.41 micron). Although individual axonal MF are much shorter than axonal microtubules, the combined length of the total MF is twice that of the total microtubules. Apparently, these numerous short MF have an important structural role in the architecture of the inner axonal cytoskeleton.
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31
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Squire JM, Harford JJ. Actin filament organization and myosin head labelling patterns in vertebrate skeletal muscles in the rigor and weak binding states. J Muscle Res Cell Motil 1988; 9:344-58. [PMID: 3065359 DOI: 10.1007/bf01773878] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The structures of vertebrate skeletal muscles (particularly from frog and fish) in the rigor state are analysed in terms of the concept of target areas on actin filaments. Assuming that 100% of the heads are to be attached to actin in rigor, then satisfactory qualitative low-resolution modelling of observed X-ray diffraction data is obtained if the outer ends of these myosin heads can move axially (total range about 200A) and azimuthally (total range less than 60 degrees) from their original lattice sites on the myosin filament surface to attach in defined target areas on the actin filaments. On this basis, each actin target area comprises about four actin monomers along one of the two long-pitched helical strands of the actin filament (about 200 A) or an azimuthal range of actin binding sites of about 100 degrees around the thin filament axis. If myosin heads simply label in a non-specific way the nearest actin monomers to them, as could occur with non-specific transient attachment in a 'weak binding' state, then the predicted X-ray diffraction pattern would comprise layer lines at the same axial spacings (orders of 429 A) as those seen in patterns from resting muscle. It is shown that actin target areas in vertebrate skeletal muscles are probably arranged on an approximate 62 (right-handed) helix of pitch (P) of about 720 A, subunit translation P/6 and near repeat P/2. Troponin position need not be considered in defining the labelling pattern of cross-bridges on this 62 helix of target areas; the target areas appear to be defined solely by the azimuthal position of the actin binding sites. The distribution of actin filament labelling patterns could be regular in fish muscle which has a 'crystalline' A-band, but will be irregular in higher vertebrate muscles such as frog sartorius muscle.
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32
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Lehtonen E, Ordónez G, Reima I. Cytoskeleton in preimplantation mouse development. CELL DIFFERENTIATION 1988; 24:165-77. [PMID: 3061662 DOI: 10.1016/0045-6039(88)90048-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
This paper reviews the constituents of the cytoskeleton in the cells of the preimplantation mouse embryo and how they change as the development proceeds. The cytoskeleton can be divided into two distinct groups, that in the cytosplasm and that associated with the membrane. The first and better-known group contains microfilaments, microtubules and intermediate filaments, the second such components of the cell and nuclear membrane as spectrin-like protein and nuclear lamin. The filamentous components of the cytoplasmic cytoskeleton adhere to the nuclear and cell membrane at attachment points where specific proteins such as vinculin may mediate the interaction. Each cell of the early embryo has all of these components, but their morphological organization and molecular constitution alter as the embryo develops. These modifications are especially pronounced when the cleavage-stage embryo compacts and when the blastocysts forms and differentiates. These events represent the most critical stages of morphogenesis and cytodifferentiation in the preimplantation embryo. The cytoskeleton may thus have an important role in the control of the early mammalian development.
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33
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Bullitt ES, DeRosier DJ, Coluccio LM, Tilney LG. Three-dimensional reconstruction of an actin bundle. J Cell Biol 1988; 107:597-611. [PMID: 3417764 PMCID: PMC2115194 DOI: 10.1083/jcb.107.2.597] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
We present the three-dimensional structure of an actin filament bundle from the sperm of Limulus. The bundle is a motile structure which by changing its twist, converts from a coiled to an extended form. The bundle is composed of actin plus two auxiliary proteins of molecular masses 50 and 60 kD. Fraying the bundle with potassium thiocyanate created three classes of filaments: actin, actin plus the 60-kD protein, and actin plus both the auxiliary proteins. We examined these filaments by transmission electron microscopy and scanning transmission electron microscopy (STEM). Three-dimensional reconstructions from electron micrographs allowed us to visualize the actin subunit and the 60- and 50-kD subunits bound to it. The actin subunit appears to be bilobed with dimensions 70 X 40 X 35 A. The inner lobe of the actin subunit, located at 20 A radius, is a prolate ellipsoid, 50 X 25 A; the outer actin lobe, at 30 A radius, is a 35-A-diam spheroid. Attached to the inner lobe of actin is the 60-kD protein, an oblate spheroid, 55 X 40 A, at 50 A radius. The armlike 50-kD protein, at 55 A radius, links the 60-kD protein on one of actin's twin strands to the outer lobe of the actin subunit on the opposite strand. We speculate that the 60-kD protein may be a bundling protein and that the 50-kD protein may be responsible for the change in twist of the filaments which causes extension of the bundle.
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34
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Sherman P, Soni R, Yeger H. Characterization of flagella purified from enterohemorrhagic, vero-cytotoxin-producing Escherichia coli serotype O157:H7. J Clin Microbiol 1988; 26:1367-72. [PMID: 3045153 PMCID: PMC266611 DOI: 10.1128/jcm.26.7.1367-1372.1988] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Escherichia coli of the serotype O157:H7 has recently been isolated in human fecal specimens in association with sporadic cases and outbreaks of hemorrhagic colitis and with the hemolytic uremic syndrome. The aim of this study was to characterize the flagellin protein subunit constituents of flagellar filaments from E. coli O157:H7 strain CL-56. Flagellin isolated from a reference Salmonella enteritidis strain was used for comparison. Flagella were dissociated by incubation of bacteria under acidic conditions, centrifugation, and differential ammonium sulfate precipitation. Reconstituted flagellar filaments were demonstrated by three complementary methods: transmission electron microscopy, antigenic reactivity with H7 antiserum by a dot blot immunoassay, and immunogold localization of antiserum raised to the purified antigen to intact flagella on whole E. coli O157:H7. On sodium dodecyl sulfate-polyacrylamide gels flagellin proteins from E. coli O157:H7 demonstrated an apparent Mr of 66,000. The isoelectric point of E. coli O157:H7 flagellin was 5.42. By immunoblotting, H7 flagellin proteins were shown to be immunogenic. They induced a systemic immune response both in rabbits challenged with whole bacteria and in a human previously infected with E. coli O157:H7.
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35
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Shapland C, Lowings P, Lawson D. Identification of new actin-associated polypeptides that are modified by viral transformation and changes in cell shape. J Biophys Biochem Cytol 1988; 107:153-61. [PMID: 2839517 PMCID: PMC2115168 DOI: 10.1083/jcb.107.1.153] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
By using a monoclonal antibody we have identified a new polypeptide doublet (C4h and C4l) of Mr approximately 21 kD and pI 8 and 7, respectively, that is associated with and (at the immunofluorescence level) uniformly distributed on actin filament bundles in rat, mouse, and other vertebrate species. C4 is absent in neurones, erythrocytes, and skeletal muscle but the epitope is evolutionarily conserved as it is present in invertebrates such as molluscs and crustaceans. C4h is not found in cells such as lymphocytes and oncogenically transformed mesenchymal cells where actin stress fiber bundles are reduced in number or absent. C4l, on the other hand, is always present. C4h expression can also be blocked by switching normal nontransformed mesenchymal cells from adherent to suspension culture. Reexpression of C4h occurs 24 h after these cells are returned to normal adherent culture conditions, but can be blocked by either actinomycin D or cycloheximide, suggesting that the expression of this epitope is regulated at the transcriptional level.
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36
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Lin JJ, Lin JL, Davis-Nanthakumar EJ, Lourim D. Monoclonal antibodies against caldesmon, a Ca++/calmodulin- and actin-binding protein of smooth muscle and nonmuscle cells. Hybridoma (Larchmt) 1988; 7:273-88. [PMID: 3294163 DOI: 10.1089/hyb.1988.7.273] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Monoclonal antibodies, C2, C9, C18, C21 and C23, against chicken gizzard caldesmon have been prepared and characterized. These antibodies reacted with gizzard caldesmon (150 KDa) by enzyme-linked immunosorbent assay and protein immunoblotting. Immunofluorescence microscopy with these antibodies on cultured gizzard cells showed strong stress fiber and membrane ruffle stainings. Surprisingly, in addition to these cytoplasmic staining patterns, the C23 antibody also stained nuclei in these cells. Preabsorption of C23 with purified caldesmon abolished the staining of stress fibers and membrane ruffles as well as the staining of nuclei, suggesting that a common epitope existed in both gizzard caldesmon and the nuclear protein. Western blot analysis on the cell extract of chicken embryo fibroblast (CEF) showed that antibodies C2, C9, C18 and C21 recognized a nonmuscle caldesmon (66 KDa), whereas C23 reacted with a protein (60 KDa) different from nonmuscle caldesmon. Antibody C21 also crossreacted with a nonmuscle caldesmon (80 KDa) in normal rat kidney (NRK) cells, with a nonmuscle caldesmon (78 KDa) in human cells, and with a nonmuscle caldesmon (72 KDa) in gerbil fibroma cells. This antibody had broad-species specificity. Immunofluorescent staining of CEF cells with antibodies C2, C9, C18 and C21 showed some stress fibers and ruffles, but mostly diffuse staining. Antibody C23 crossreacted with 62 KDa and 55 KDa proteins in NRK cells, 63 KDa and 55 KDa proteins in gerbil fibroma cells and 66 KDa and 56 KDa proteins in human bladder carcinoma cells. These polypeptides were identified as nuclear lamins A and C by an anti-lamin antibody in immunoblots and two-dimensional gel analysis. Like the nuclear lamins, the C23 antigens also underwent a reversible disassembly during mitosis, as detected by double-label immunofluorescence with C23 antibody and a polyclonal anti-tubulin antibody. Tropomyosin-enriched microfilaments isolated from fibroblastic and epithelial types of NRK cells by monoclonal anti-tropomyosin antibody contained an 80 KDa protein, which had the heat-resistant property of caldesmon. The polyclonal antiserum generated against this 80 KDa protein showed a crossreactivity with purified gizzard caldesmon and vice versa. The amount of this nonmuscle caldesmon associated with the microfilaments of Kirstein virus-transformed NRK cells was greatly decreased.
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37
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Marchisio PC, D'Urso N, Comoglio PM, Giancotti FG, Tarone G. Vanadate-treated baby hamster kidney fibroblasts show cytoskeleton and adhesion patterns similar to their Rous sarcoma virus-transformed counterparts. J Cell Biochem 1988; 37:151-9. [PMID: 2456294 DOI: 10.1002/jcb.240370203] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Rous sarcoma virus-transformed baby hamster kidney fibroblasts (RSV/B4-BHK) adhere to a fibronectin-coated substratum by means of dot-like adhesion sites called podosomes in view of their shape and function as cellular feet (Tarone et al.: Exp Cell Res 159:141, 1985). Podosomes concentrate tyrosine-phosphorylated proteins, including pp60v-src, and appear in many cells transformed by oncogenes coding for tyrosine kinases. In this paper we used orthovanadate, an inhibitor of phosphotyrosine phosphatases, in order to increase the cellular concentration of phosphotyrosine and to study whether this treatment induced the cytoskeleton remodeling leading to the formation of podosomes. Indeed, orthovanadate (10-100 microM) induced in a time- and dose-dependent manner the redistribution of F-actin and the formation of podosomes in BHK cells. Cytoskeleton remodeling occurred along with a marked increase of tyrosine phosphorylated proteins. The vanadate effect on the cytoskeletal phenotype was enhanced by the simultaneous treatment of cells with a phorbol ester. Under the latter conditions almost all BHK cells showed podosomes. The vanadate effect was reversible insofar as podosomes and tyrosine-phosphorylated proteins disappeared. Then, vanadate treatment of normal cells induced the cascade of events leading to the cytoskeletal changes typical of transformation and suggested that the transformed cytoskeletal phenotype may be primarily induced by the tyrosine phosphorylation of unknown target(s) operated by endogenous kinases.
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38
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Fauvel-Lafeve F, Legrand YJ. Immunochemical identification of a thrombospondin-like structure in an arterial microfibrillar extract. Thromb Res 1988; 50:305-16. [PMID: 2839911 DOI: 10.1016/0049-3848(88)90231-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Arterial microfibrils contain a 128 Kd collagenase and pepsin resistant glycoprotein (GP 128) essential for their ability to induce platelet aggregation. A previous report (Fauvel F. et al, (1984) Biochem. Biophys. Res. Comm., 123, 114-120) showed that GP 128 and thrombospondin (TSP) synthetized by endothelial cells each inhibited the aggregation of platelets by microfibrils and not by collagen. We used a monospecific antiplatelet TSP IgG in an immunoblotting assay for the identification of a TSP-like structure in untreated, collagenase-treated and pepsin-treated arterial microfibrils. The only constituent recognized in the three samples of microfibrils was GP 128. Fab fragments of this IgG provoked a dose dependent inhibition of the microfibril induced platelet aggregation (50% inhibition with 0.25 mg, 100% inhibition with 1 mg); in contrast, they did not affect collagen induced aggregation. The results indicate that a glycoprotein constituent with a thrombospondin-like antigenicity is involved in the thrombogenic properties of arterial microfibrils.
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39
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Diesbourg L, Swatland HJ, Millman BM. X-ray diffraction measurements of postmortem changes in the myofilament lattice of pork. J Anim Sci 1988; 66:1048-54. [PMID: 3378943 DOI: 10.2527/jas1988.6641048x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Postmortem changes in the lateral spacing between filaments of the longissimus muscle in pork were examined by small-angle x-ray diffraction. Samples that were fixed in glutaraldehyde as soon as they were collected showed a rapid decrease in filament spacing from 1 h to 3 h and then a further, slower decrease to 24 h. Samples that were examined immediately or were kept prior to examination in buffered Ringer's solutions at pH values similar to those expected in the carcass showed a rapid decrease in filament spacing from 1 h to 3 h and then little further change to 24 h. In contrast, samples taken at various times postmortem and stored in Ringer's solutions at pH 7.2 for several hours before examination showed little postmortem change in lattice spacing. Fixed samples showed similar changes to those of unfixed samples, but the lattice spacing always was less in fixed than in unfixed samples. These results support the classic theory that much of the water that may be lost by drip and evaporation from meat originates from the spaces between the filaments. The major factor that caused shrinkage of the filament lattice and loss of water from the fibrils was pH.
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40
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Gupta RS, Dudani AK. Mitochondrial binding of a protein affected in mutants resistant to the microtubule inhibitor podophyllotoxin. Eur J Cell Biol 1987; 44:278-85. [PMID: 3319627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Specific antibodies to a protein P1 Mr approximately equal to 63,000) from Chinese hamster ovary cells, which is affected in mutants resistant to the microtubule inhibitor, podophyllotoxin, and behaves like a microtubule-related protein by certain criteria [14], have been raised. The antibody reacts specifically with the P1 protein in one- and two-dimensional immunoblots, and a cross-reacting protein of similar molecular mass and electrophoretic mobility is also found in cells from various vertebrate and invertebrate species. The observed similarity in the peptide maps of the cross-reacting protein from human, mouse, Chinese hamster and chicken cells indicates that the structure of this protein should be highly conserved. However, no P1-antibody cross-reacting protein was observed in plants (corn, mung), fungus (Neurospora crassa), yeast (Saccharomyces cerevisiae) and bacteria (Escherichia coli and Salmonella typhimurium). Immunofluorescence studies with the P1-antibody show that, in interphase cells of various cross-reacting species, it bound specifically to mitochondria which were associated and distributed on and along the length of microtubules. Similar association and codistribution of mitochondria and microtubules were not observed in mitotic cells. Some implications of the mitochondrial localization of the protein P1 and the observed association between microtubules and mitochondria are discussed.
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41
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Fox JE, Reynolds CC, Johnson MM. Identification of glycoprotein Ib beta as one of the major proteins phosphorylated during exposure of intact platelets to agents that activate cyclic AMP-dependent protein kinase. J Biol Chem 1987; 262:12627-31. [PMID: 3040761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Platelet function is inhibited by prostaglandin E1, prostaglandin I2, or forskolin, agents that increase the intracellular concentration of cyclic AMP. The inhibition appears to result from cyclic AMP-stimulated phosphorylation of specific intracellular proteins. One of the major increases in phosphorylation occurs in a polypeptide of Mr = 24,000 (P24). In this study, an effort was made to identify P24. Platelets prelabeled with [32P]phosphate were incubated with prostaglandin E1, prostaglandin I2, or forskolin. Proteins that became phosphorylated were detected by autoradiography of sodium dodecyl sulfate-polyacrylamide gels. Several lines of evidence indicated that P24 was the beta-subunit of the plasma membrane glycoprotein (GP) Ib, a glycoprotein that is essential for the adhesion of platelets to damaged subendothelium, for the rapid response of platelets to thrombin, and for the attachment of the membrane skeleton to the cytoplasmic face of the plasma membrane. P24 co-migrated with GP Ib beta on reduced gels (Mr = 24,000) and also on nonreduced gels (when GP Ib beta is disulfide-linked to GP Ib alpha and migrates with Mr = 170,000). Like GP Ib beta, P24 was associated with actin filaments in Triton X-100 lysates. Like GP Ib beta, it was selectively associated with filaments of the membrane skeleton and was released from filaments when the Ca2+-dependent protease was active. Antibodies against GP Ib immunoprecipitated P24 from platelet lysates. Finally, exposure of Bernard-Soulier platelets (which lack GP Ib) to prostaglandin E1 resulted in phosphorylation of other polypeptides, but not of P24. These studies show that P24, one of the major polypeptides phosphorylated when platelets are exposed to agents that inhibit platelet function by increasing the concentration of cyclic AMP, is the beta-subunit of GP Ib.
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42
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Fowler VM. Identification and purification of a novel Mr 43,000 tropomyosin-binding protein from human erythrocyte membranes. J Biol Chem 1987; 262:12792-800. [PMID: 3624279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
A new Mr 43,000 tropomyosin-binding protein (TMBP) has been identified in erythrocyte membranes by binding of 125I-labeled Bolton-Hunter tropomyosin to nitrocellulose blots of membrane proteins separated by sodium dodecyl sulfate-gel electrophoresis. This protein is not actin, because 125I-tropomyosin does not bind to purified actin on blots. Binding of 125I-tropomyosin to this protein is specific because it is inhibited by excess unlabeled tropomyosin but not by F-actin or muscle troponins. This protein has been purified to 95% homogeneity from a 1 M Tris extract of tropomyosin-depleted erythrocyte membranes by DEAE-cellulose and hydroxylapatite chromatography, followed by gel filtration on Ultrogel AcA 44. The purified protein has a Stokes radius of 3.9 nm and a sedimentation coefficient of 2.8 S, corresponding to a native molecular weight of 43,000. Binding of 125I-tropomyosin to the purified TMBP saturates at one tropomyosin molecule (Mr 60,000) to two Mr 43,000 TMBPs, with an affinity of about 5 X 10(-7) M. The TMBP is associated with the membrane skeleton after extraction of membranes with the non-ionic detergent, Triton X-100, and is present with respect to tropomyosin at a ratio of about one for every two tropomyosin molecules. Because there is enough tropomyosin for two tropomyosin molecules to be associated with each of the short actin filaments in the membrane skeleton, the erythrocyte membrane TMBP, together with tropomyosin, could function to restrict the number of spectrin molecules attached to each of the short actin filaments and thus specify the hexagonal symmetry of the spectrin-actin lattice. Alternatively, this TMBP could be homologous to one of the muscle troponins and might function with tropomyosin to regulate erythrocyte actomyosin-ATPase activity and influence erythrocyte shape.
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43
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Bowden DS, Pedersen JS, Toh BH, Westaway EG. Distribution by immunofluorescence of viral products and actin-containing cytoskeletal filaments in rubella virus-infected cells. Arch Virol 1987; 92:211-9. [PMID: 3545151 DOI: 10.1007/bf01317478] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Rubella virus (RV)-host cell interactions were examined by indirect immunofluorescence staining using antibodies to viral products and cytoskeletal components as probes. The patterns of immunofluorescence observed with human convalescent sera indicated that in infected Vero cells RV-specified proteins were distributed throughout the rough endoplasmic reticulum with some possible accumulation in the region of the Golgi complex. Viral RNA synthesis, detected with anti-double stranded RNA, appeared to be confined to small, intensely stained foci irregularly distributed in the cytoplasm. When cells were infected at a higher multiplicity, these foci appeared to aggregate into linear arrays. Infection with RV had a profound effect on the organization of actin in both Vero and BHK 21 cells, as shown by anti-actin antibodies. Actin microfilaments were observed to disintegrate progressively into amorphous aggregates of apparently monomeric actin as the infection proceeded. Because of the role actin microfilaments may play in cell mitosis it is postulated that this effect may be related to the inhibition of cell division reported to be associated with the congenital rubella syndrome.
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Koo EW, Hayes MA, Wong MK, Gotlieb AI. Aflatoxin B1 and acetaminophen induce different cytoskeletal responses during prelethal hepatocyte injury. Exp Mol Pathol 1987; 47:37-47. [PMID: 3111878 DOI: 10.1016/0014-4800(87)90005-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Primary monolayer cultures of adult rat hepatocytes exposed to the hepatocarcinogen aflatoxin B1 (AFB1) undergo a characteristic prelethal cytomorphological change that is distinct from their response to the necrogenic noncarcinogenic hepatotoxin, acetaminophen (AAP). Since changes in cell shape are mediated, at least in part, by the F-actin cytoskeleton, we designed experiments to study early prelethal alterations in the distribution of actin microfilaments in monolayer rat hepatocytes exposed to AFB1 (100 microM) or AAP (16 mM). Using rhodamine-phalloidin fluorescence microscopy, we observed that normal hepatocytes showed a submembranous F-actin distribution with focal short microfilaments extending into filopodia along the periphery of the cell. Hepatocytes exposed to AFB1 for several hours exhibited retraction of their cytoplasm within a prominent circumferential peripheral band of F-actin microfilament bundles. Retraction of focal areas of peripheral cytoplasm was associated with an increased prominence of the radial F-actin-containing filopodia. Subsequently, there appeared peripheral blebs containing very little F-actin. Hepatocytes exposed to equivalently lethal concentrations of AAP initially remained structurally normal. After several hours, the cells exhibited a prominent polar aggregate of short microfilament bundles without the formation of blebs. Both the blebbing and the polar aggregation of F-actin bundles occurred prior to cell death as shown by lactate dehydrogenase release and trypan blue exclusion. These studies support the hypothesis that the lethal effects of these two agents may occur by different biological mechanisms that are associated with remarkably distinct prelethal cytoskeletal responses.
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Milligan RA, Flicker PF. Structural relationships of actin, myosin, and tropomyosin revealed by cryo-electron microscopy. J Cell Biol 1987; 105:29-39. [PMID: 3611188 PMCID: PMC2114877 DOI: 10.1083/jcb.105.1.29] [Citation(s) in RCA: 215] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
We have calculated three-dimensional maps from images of myosin subfragment-1 (S1)-decorated thin filaments and S1-decorated actin filaments preserved in frozen solution. By averaging many data sets we obtained highly reproducible maps that can be interpreted simply to provide a model for the native structure of decorated filaments. From our results we have made the following conclusions. The bulk of the actin monomer is approximately 65 X 40 X 40 A and is composed of two domains. In the filaments the monomers are strongly connected along the genetic helix with weaker connections following the long pitch helix. The long axis of the monomer lies roughly perpendicular to the filament axis. The myosin head (S1) approaches the actin filament tangentially and binds to a single actin, the major interaction being with the outermost domain of actin. In the map the longest chord of S1 is approximately 130 A. The region of S1 closest to actin is of high density, whereas the part furthest away is poorly defined and may be disordered. By comparing maps from decorated thin filaments with those from decorated actin, we demonstrate that tropomyosin is bound to the inner domain of actin just in front of the myosin binding site at a radius of approximately 40 A. A small change in the azimuthal position of tropomyosin, as has been suggested by others to occur during Ca2+-mediated regulation in vertebrate striated muscle, appears to be insufficient to eclipse totally the major site of interaction between actin and myosin.
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Casella JF, Craig SW, Maack DJ, Brown AE. Cap Z(36/32), a barbed end actin-capping protein, is a component of the Z-line of skeletal muscle. J Cell Biol 1987; 105:371-9. [PMID: 3301868 PMCID: PMC2114938 DOI: 10.1083/jcb.105.1.371] [Citation(s) in RCA: 131] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Various biological activities have been attributed to actin-capping proteins based on their in vitro effects on actin filaments. However, there is little direct evidence for their in vivo activities. In this paper, we show that Cap Z(36/32), a barbed end, actin-capping protein isolated from muscle (Casella, J. F., D. J. Maack, and S. Lin, 1986, J. Biol. Chem., 261:10915-10921) is localized to the barbed ends of actin filaments by electron microscopy and to the Z-line of chicken skeletal muscle by indirect immunofluorescence and electron microscopy. Since actin filaments associate with the Z-line at their barbed ends, these findings suggest that Cap Z(36/32) may play a role in regulating length, orienting, or attaching actin filaments to Z-discs.
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Abstract
We have employed fluorescent analogue cytochemistry and fluorescence photobleaching to study the mobility of actin and alpha-actin along stress fibers. Rhodamine-labeled actin or alpha-actinin microinjected into embryonic chick cardiac fibroblasts soon became incorporated into stress fibers. A pulse of a laser microbeam was used to photobleach small spots on the fluorescent stress fibers. Images of the bleached fiber were recorded with an intensified image processing system at 2-3 min intervals. The distance between the bleached spot and the terminus of the stress fiber, which remained stationary throughout the experiment, was then measured in the successive images. Movement of bleached spots was detected along stress fibers located in the apparently trailing processes of polygonal fibroblasts, and only occurred in one direction: away from the distal tip of the stress fiber. The rate of movement calculated for alpha-actinin-injected cells was 0.24 +/- 0.12 micron/min, for actin-injected cells, 0.29 +/- 0.11 micron/min. The rate did not seem to be affected by the location of the spot relative to the distal end of the stress fiber unless the spot was located within the most distal 5 microns of the stress fiber. Anti-myosin antibody staining indicated that stress fibers which demonstrated translocation were relatively depleted of myosin. The apparent translocation of proteins along stress fibers, possibly generated by stretching, may be related to the retraction of cell processes during locomotion.
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Loesser KE, Doane KJ, Wilson FJ, Roisen FJ, Malamed S. Improved immunoelectron microscopic method for localizing cytoskeletal proteins in Lowicryl K4M embedded tissues. J Histochem Cytochem 1986; 34:1477-85. [PMID: 3534078 DOI: 10.1177/34.11.3534078] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
We have modified the Lowicryl K4M low-temperature dehydration and embedding procedure for immunoelectron microscopy to provide improved ultrastructural detail and facilitate the localization of actin and tubulin in isolated rat adrenocortical cells, chick spinal cord with attached dorsal root ganglia (SC-DRG), and cultured dorsal root ganglia (DRG). Cells and tissues were fixed for immunocytochemistry either in a mixture of 2% paraformaldehyde and 0.25% glutaraldehyde (0.1 M PIPES buffer, pH 7.3) or in a mixture of 0.3% glutaraldehyde and 1.0% ethyldimethylaminopropylcarbodiimide (0.1 M phosphate buffered saline, pH 7.3). Dehydration was in ethanol at progressively lower temperatures to -35 degrees C. Infiltration at -35 degrees C was followed by ultraviolet polymerization at -20 degrees C. Comparable samples were fixed in glutaraldehyde and osmium tetroxide and embedded in Epon 812 or Epon-Araldite. Post-embedding immunostaining of thin sections utilized commercially available monoclonal antibodies to tubulin and actin followed by the protein A-gold technique (Roth et al., Endocrinology 108:247, 1981). Actin immunoreactivity was observed at the periphery of mitochondria and between mitochondria and lipid droplets in rat adrenocortical cells and at the periphery of neuronal cell processes of SC-DRG. Tubulin immunoreactivity was associated with microtubules throughout neurites of cultured DRG. Our modified technique allows preservation of ultrastructural details as well as localization of antigens by immunoelectron microscopy.
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Boden P, Johnson A, Weinberger JM, Hawke M, Gotlieb AI. In situ localization of F-actin in the normal and injured guinea-pig tympanic membrane. Acta Otolaryngol 1986; 101:278-85. [PMID: 2422873 DOI: 10.3109/00016488609132838] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Although cell migration is an important function of the epithelial cells of the tympanic membrane (TM), little is known about the distribution of the F-actin cytoskeleton, a contractile protein important in cell motility. The purpose of this experiment was to study the in situ localization of F-actin in the epithelial cells of the TM. F-actin, localized using Rhodamine-phalloidin, was present as a thin cortical band at the margin of both the mucosal cells on the inner side of the drum, and the suprabasal cells of the epidermis. The basal cells showed diffuse circumferential F-actin staining sometimes appearing as short microfilaments. Following a full thickness injury, changes in the distribution of F-actin could be observed with in situ localization. While the diffuse F-actin staining of the basal cells was reduced, both long F-actin microfilament bundles extending parallel to the long axis of the cell and focal aggregates of F-actin were prominent. The suprabasal cells became elongated, and while the F-actin remained localized to the cell margin, faint central F-actin microfilaments were observed. The staining of the mucosal cells remained unchanged. This study showed that the guinea pig TM is a useful model to study the distribution of epithelial F-actin in situ under normal and repair conditions, and that the basal cell layer may be important in regulating migration in the epidermis.
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Abstract
Actin filaments capped at the barbed ends were formed by polymerizing monomeric actin onto a gelsolin-actin complex. The rate of depolymerization and polymerization of the pointed ends was determined by diluting gelsolin-capped actin filaments into various concentrations of monomeric actin. Under the conditions of the experiments (100 mM-KCl, 2 mM-MgCl2 at 37 degrees C) the rate constant of dissociation of subunits both from a shortening and a lengthening filament was found to be 0.21 s-1. As the rate of dissociation of subunits from the slow pointed end determines the rate of treadmilling, it is concluded that actin filaments treadmill with a rate of about 2 micron/h.
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