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  • Cell & Developmental Biology  (2,509)
  • 1995-1999  (2,509)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 30 (1995), S. 17-25 
    ISSN: 0886-1544
    Keywords: rotation ; twisting ; microtubule-dynein complex ; 22S dynein ; dynein-track ; ATP ; sliding ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Applying a new in vitro motility assay system for microtubules and 22S dynein, we recently reported on an ATP-induced extrusion of microtubules from microtubule-dynein α- and β-complexes [Mimori and Miki-Noumura, 1994:Cell Motil. Cytoskeleton 27:180-191]. In the present study, we prepared a γ-complex by copolymerizing porcine brain tubulin and Tetrahymena ciliary 22S dynein, and examined the ATP-induced microtubule movement from the γ-complex. The extrusion process appeared quite similar to that of the β-complex. The sliding velocity was 18.39 ± 2.20 m̈m/sec, which was a value comparable to that of trypsin-digested flagellar axonemes [Yano and Miki-Noumura, 1980:J. Cell Sci. 44:169-186]. Higher velocity may be due to a densely arranged dynein-track with the same polarity, which was detached from the γ-complex and absorbed in rows on a glass surface of the slide. Sometimes a free-floating microtubule in the perfusion chamber was observed riding and sliding on the dynein-track remaining on the slide after extrusion.Unexpectedly, we found that when the front part of the microtubule was fixed to a glass surface, a continuous sliding microtubule at the rear part on the dyneintrack often transformed into a left-handed helix, and subsequently a twisted helix with several turns. The helix formation may be due to some rigidity in the microtubule and a right-handed torque component in the sliding force of 22S dynein. The addition of ATP may release some distortion accumulated in the complex structure during copolymerization of tubulin and 22S dynein, inducing reverse rotation of the microtubule. © 1995 Wiley-Liss, Inc.
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  • 2
    ISSN: 0886-1544
    Keywords: trout ; spermatozoa ; ATP ; cAMP ; axoneme ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Live trout spermatozoa initiate flagellar motility for only a short period (30 sec at 18°C) during which their mean beat frequency decreases steadily from 60 to 20 Hz. Motility then stops abruptly. Investigations of the activation of movement in demembranated sperm points to cyclic-AMP being necessary for reactivation (half effect at 0.5μm) in some conditions. cAMP acts mainly by increasing the percentage of motile cells and not the beat frequency (BF) of the flagellar axoneme. Dibutyryl cAMP does not initiate movement or prolong motility of live sperm.The initiation of movement of demembranted trout sperm was investigated in various incubation conditions relative to previous phases of in vivo movement and to ATP concentration. In the absence of cAMP and in the presence of ATP lower than 25 μM, all sperm celi models were active with BF up to 15-20 Hz whatever their previous physiological condition. In contrast, at ATP concentrations above 100 μM, the fraction of active spermatozoa decreased proportionally but the BF of the active ones increased so that, at 1 mM ATP up to 20 μM restored activity to 100% sperm models with a similar BF of 65 Hz.At ATP concentrations higher than 25 μM, cAMP was necessary in a concentration dependent manner in the reactivation, but not in the demembranation meduim. This dependence was found to be unrelated to a previous in vivo phase of movement. The antagonistic effects of ATP vs. cAMP were tested at various concentrations of both nucleotides: the apparent affinity for cAMP, measured as the concentration restoring movement of 50% cell models, was decreased from 15 nM at 0.1 mM ATP to 0.5 μM at 1 mM ATP; conversely, the affinity for ATP, measured as the concentration giving rise to the half maximal beat frequency, was not significautly affected when the concentration of cAMP was raised to 0.5 mM. Preincubation with phosphodiesterase (PDE) resulted in motility of 100% of sperm models even at low ATP concentration. This tends to show that cAMP must be constantly present to sustain motility.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 31 (1995), S. 147-158 
    ISSN: 0886-1544
    Keywords: actin ; contact guidance ; microfilaments ; microtubules ; orientation ; cytochalasin ; colcemid ; taxol ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The role of the cytoskeleton and cell attachments in the alignment of baby hamster kidney fibroblasts to ridge and groove substratum topography was investigated using confocal scanning microscopy. This was carried out with normal cells and cells treated with the cytoskeleton modifiers cytochalasin D, colcemid, and taxol. Actin was localised with fluorescent phalloidin. Tubulin, Vinculin, and intracellular adhesion molecule-1 were visualised by indirect immunofluoresence. The spreading, elongation, and orientation of the cells after 24 h of culture in these conditions were measured on grooves of 5, 10, and 25 μm width and 0.5, 1, 2, and 5 μm depth. We have also observed events over the first 30 min of cell attachment. Five minutes after cell attachment, F-actin condensations were seen close to the intersection of groove wall and ridge top, that is, at a topographic discontinuity. The condensations were often at right angles to the groove edge and showed a periodicity of 0.6 μm. Vinculin arrangement at the early stages of cell spreading was similar to that of actin. Organisation of the microtubule system followed later, becoming obvious at about 30 min after cell plating. The Curtis and Clark theory (that cell react to topography primarily at lines of discontinuity in the substratum by actin nucleation) is supported by these results. The use of cytoskeletal poisons did not entirely abolish cell reaction to grooves. Colocemid increased cell spreading and reduced cell orientation and elongation. Cytochalasin D reduced cell spreading, orientation, and elongation. Taxol reduced cell elongation but did not affect cell spreading and orientation. We conclude that the aggregation of actin along groove/ridge boundaries is a primary driving event in determining fibroblast orientation on microgrooved substrata.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 30 (1995) 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 30 (1995), S. 108-121 
    ISSN: 0886-1544
    Keywords: intercellular junctions ; desmosome ; assembly ; kinase ; phosphatase ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Desmosomes are one component of the intercellular junctional complex in epithelia. In cultures of epithelial cells, desmosome assembly can be regulated by modulating the calcium concentrations of the growth media. At present, very little is known about the intracellular signal transduction mechanisms that regulate desmosome assembly and disassembly in response to changing extracellular calcium concentrations. We have used inhibitors of protein kinases and phosphatases in a combined biochemical and morphological approach to analyze the role of protein phosphorylation in the assembly and disassembly of desmosomes in Madin-Darby canine kidney epithelial cells. Our results suggest that desmosomal proteins (desmoplakins I/II and desmoglein 1) are primarily phosphorylared on serine residues. Electron microscopic analyses of desmosome assembly upon induction of cell-cell contact, in the presence of protein kinase inhibitor, H-7, revealed an apparently normal assembly of desmosomes. However, complete disassembly of desmosomes was inhibited by H-7 upon removal of extracellular calcium. Under these conditions, although desmosomes split, desmosomal plaques and their associated cytokeratin filaments can not be internalized. In contrast, treatment of the cultures with okadaic acid (OA), an inhibitor of protein phosphatases, inhibited desmosome assembly but had no effect on disassembly. In addition, the inhibitory effect of okadaic acid on desmosome assembly was specific to this junction since we observed apparently normal tight junction and adherens junction in okadaic acid-treated cultures. These results suggest that via reversible protein phosphorylation involving both protein kinase and protein phosphatases. © 1995 Wiley-Liss, Inc.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 31 (1995), S. 196-206 
    ISSN: 0886-1544
    Keywords: gelsolin ; actin ; myofibrils ; immunofluorescence ; nebulin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have investigated the binding of gelsolin to thin myofilaments in situ and their stability against severing. Differentiated myotubes from chicken skeletal muscle containing cross-striated myofibrils were permeabilized with Triton X-100 and incubated with gelsolin. Immunoflurorescence microcopy localized both endogenous and exogenous gelsolin in the I-Z-I-regions of the sarcomers. The staining pattern suggested a binding of the exogenous gelsolin along the entire length of the thin filaments. This binding was Ca2+ dependent, but gelsolin was not removed after subsequent addition of EGTA. The fluorescence staining for actin remained unchanged after gelsolin incubation, indicating that thin filaments in cross-striated myofibrils were resistant to the severing action of gelsolin, in contrast to the microfilaments in stress fibers. After extraction of the permeabilized cells with high ionic strength to remove tropomyosin and myosin, gelsolin stell bound along the entire thin filament and the actin pattern also remained unchanged. After Triton X-100 permeabilization and high ionic strength extraction, the giant protein nebulin was found to be still present as a myofibrillar component. Gelsolin treatment after high salt extraction affected neither actin nor nebulin in the thin filaments. We therefore conclude that nebulin confers the gelsolin resistance to the sarcomeric actin filaments.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 31 (1995), S. 207-214 
    ISSN: 0886-1544
    Keywords: flagella ; Chlamydomonas ; mutant ; high-frequency vibration ; nanometer-scale measurement ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The flageliar axoneme of the mutant pf18 lacking the central pair does not beat, but undergoes a nanometer-scale, high-frequency oscillation (hyper-oscillation) in the presence of ATP [Yagi et al., 1994: Cell Motil, Cytoskeleton 29:177-185]. The present study demonstrates that the amplitude of the hyper-oscillation increases significantly in the simultaneous presence of ATP and ADP. In addition, the hyper-oscillation under these conditions sometimes takes on an exceptionally simple asymmetric pattern, in which the maximal shearing velocity exceeds 50 μm/sec, much higher than the maximal velocity of ordinary dynein-microtubule sliding. The asymmetric oscillation thus appears to be at least partly driven by an internal elastic force. Its amplitude suggests that the axoneme has an elastic component that can be stretched by as long as 0.1 μm. Analyses of the asymmetric pattern further suggests that the axonemal dyneins have a tendency to attach to and detach from the doublets cooperatively and that the mechanochemical cycle of dynein has an inherent refractory period of about 2 msec, during which dynein cannot interact with microtubules.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 31 (1995), S. 225-240 
    ISSN: 0886-1544
    Keywords: cell-substratum adhesion ; lamellar contractility ; locomotion ; silicone rubber ; traction forces ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A means of determining quantitative maps of the tractions exerted by locomoting cells on a substratum has been developed. This method is similar to the Harris silicone substratum assay [Harris et al., 1980: Science 208:177-179], but uses an improved non-wrinkling film that deforms more predictably in response to traction forces. The method also utilizes a mathematical analysis of rubber deformation to produce the final map of the distribution of tractions. The resulting maps consistently showed that fish keratocytes exert a steady-state “pinching” on the substratum, perpendicular to the cell's direction of locomotion. No significant rearward tractions were detected at or near the front edge of the cell. Likewise, no significant forward tractions associated with peeling of adhesions were found at the back of the cell. A second assay uses deflection of a lightly attached glass microneedle to measure the total force exerted by locomoting cells. Forces of approximately 4.5 × 10-3 dyn were required to “stall” locomoting keratocytes. The implications of these findings for cell movement are discussed.
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  • 9
    ISSN: 0886-1544
    Keywords: microfilamentous cytoskeleton ; actin binding proteins ; actin polymerization ; annealing ; non-muscle cells ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Gelsolin, a Ca++ activated, 90 kd actin binding protein, can regulate actin polymerization in polymorphonuclear leukocytes (PMNs) via severing of filaments to dissolve gels or by capping of filament ends to limit polymerization. In Triton-lysed PMNs, 30% of gelsolin is bound to the Triton-soluble F-actin (TSF) pool and none is bound to the Triton-insoluble F-actin (TIF) pool. Calcium-activated PMNs exhibit concurrent temporal and quantitative TIF growth and TSF and total F-actin loss. To determine if gelsolin plays a role in regulating TSF pool size, we monitored gelsolin-actin interactions and TIF, TSF and G-actin content at 5 second intervals in PMNs activated with the calcium ionophore, ionomycin. Actin pools were measured by NBDphallacidin binding and by gel scans and expressed relative to basal; gelsolin-actin interactions were measured as change in the amount of EGTA-resistant gelsolin:actin (G:A) complexes and by immunoblot quantification of gelsolin in actin pools. In basal PMNs, 33% of PMN gelsolin is bound in 1:1 EGTA-resistant G:A complexes and TSF and TIF retain 30% and 0% of PMN gelsolin, respectively. By 20 seconds after ionomycin addition, TSF decreases, TIF increases and a fraction of gelsolin repartitions from the TSF to the TIF pool. At maximum change (60 seconds), total F-actin (TIF + TSF) and TSF decrease and TIF increases by 25%; gelsolin is bound to both TSF and TIF (35% of total gelsolin in each pool), and 1:1 EGTA-resistant G:A complexes increase from 33% to 70%. No changes occur in cells activated by ionomycin in the absence of Ca++. The data show Ca++ activated TIF growth and TSF loss are temporally and quantitatively associated with an increase in the percent of gelsolin bound to actin and the translocation of gelsolin from TSF to TIF. This is unique, since no other PMN activator is known to repartition gelsolin into TIF actin. Further, the Ca++ activated initial increase in TIF concurrent with a fall in TSF without a change in total F-actin or G-actin content suggest that TIF grows initially only by TSF annealing/cross-linking to TIF. Gelsolin may regulate these events. © 1995 Wiley-Liss, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 30 (1995), S. 146-152 
    ISSN: 0886-1544
    Keywords: zinc-sheets ; macrotubes ; kinesin ; electron microscopy ; microtubules ; tubulin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Moving along a microtubule, kinesin follows a course parallel to the protofilaments; but it is not known whether kinesin binds exclusively on a single protofilament. The presence of zinc during tubulin polymerization induces sheets where neighboring protofilaments are antiparallel. If kinesin could support the motility of these zinc-sheets, then the binding site for a kinesin molecule would be limited to a single protofilament.Kamimura and Mandelkow [1992: J. Cell Biol. 118:865-75] reported that kinesin moves along zinc-sheets. We found that zinc-sheets grown under their conditions often had a microtubule-like structure along one edge. We confirmed the possibility that the motility observed by Kamimura and Mandelkow [1992: J. Cell Biol. 118:865-75] is attributed to the microtubule-like structure rather than the zinc-sheet.To resolve the question of whether kinesin can recognize an antiparallel protofilament lattice, we investigated the kinesin-mediated motility of zinc-macrotubes. At higher free zinc concentrations, zinc-sheets roll up as macrotubes, free of edges. In the presence of 10 m̈M taxol and 100 nM free Zn2+ at pH 6.8, the samples were shown by electron microscopy to contain only macrotubes. Under these buffer conditions, kinesin could bind strongly to axonemal doublets in the presence of AMP-PNP, and generate motility in the presence of ATP, but kinesin did not bind to nor move the macrotubes. This shows that kinesin cannot bind efficiently to nor move on the anti-parallel lattice; it is possible (though not necessary) that the groove between two parallel protofilaments is required for kinesin's motility. © 1995 Wiley-Liss, Inc.
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