bluuebunny/crossref_metadata_2025_split huggingface dataset:
Actin cytoskeleton and motility in rat sarcoma cell populations with different metastatic potential
Authors: Pokorná E. , Jordan P. W. , O'Neill C. H. , Zicha D. , Gilbert C. S. , Veselý P. 
Published: February 2005

AbstractWe have studied the organisation of the actin cytoskeleton in three related rat sarcoma cell populations of differing malignancy. They were derived by neoplastic progression from a population which had transformed spontaneously in vitro, and were distinguished by their ability to give rise to reproducibly different numbers of metastases, ranging from 10% to 80% of the animals inoculated. We found characteristic differences in the arrangement of the actin cytoskeleton. Confocal three‐dimensional microscopy showed that nearly all of the least malignant population contained conspicuous actin stress fibres lying in the lower part of the cell parallel to the substratum and no other actin structures. Actin in the intermediate population was typically situated in a diffuse layer underlying the whole plasma membrane, in which no fibres could be seen. Two thirds of the most malignant population consisted of more rounded cells filled with a three‐dimensional network of fine oblique actin fibres. There were focal contacts in all these cells; their area showed a regular decrease from 1.3 μm2 to 0.4 μm2. The differences in actin distribution were accompanied by differences in motility, which increased as malignancy increased. When individual cells were fixed after they had been tracked by time‐lapse, their cytoskeleton type correlated with the speed at which they had moved. All these differences were enhanced at low pH. These findings point to the possibility that the three‐dimensional network of fine actin fibres in acid culture could be a measure of the malignant potential of transformed cells in vitro. © 1994 Wiley‐Liss, Inc.
Are microtubules essential for the secretory process in rat parotid gland?
Authors: Robin Philippe , Rossignol Bernard , Raymond Marie‐Noëlle 
Published: February 2005

AbstractThe role of microtubules in the exocrine secretory process is not yet well established, and their disruption by anti‐microtubule drugs leads to variable effects on intracellular transit and protein secretion. We investigated the involvement of microtubules in the regulated secretory process of rat parotid glands using microscopic techniques and pulse‐chase experiments. We showed that 10 μM colchicine or nocodazole destroys the microtubule network in parotid acinar cells but only weakly reduces the release of newly synthesized proteins. The half‐effect was obtained with 0.22 μM colchicine. Moreover, this small reduction was found to be independent of the nature of the drug (colchicine, colcemid, or nocodazole) and of the nature of the stimulation (β‐adrenergic or cholinergic pathways). Using nocodazole, we have been able to determine that the steps affected by the drug are very early events in the secretory pathway. Finally, we showed by kinetic analysis that microtubule disruption slows protein release only moderately but does not reduce the total amount of secreted protein. We conclude from this study that microtubule integrity is not essential for protein secretion in rat parotid gland. © 1994 Wiley‐Liss, Inc.
Microtubule‐associated protein function: Lessons from expression in spodoptera frugiperda cells
Authors: Kosik Kenneth S. , McConlogue Lisa 
Published: February 2005

AbstractThe phenotypes induced by the expression of neuronal microtubule‐associated proteins (MAPs) in Sf9 cells have provided data on the in situ function of these proteins. Both MAP2 and tau can induce long processes in Sf9 cells, and the processes contain bundles of microtubules. In both cases the microtubules are aligned with their plus ends distal. Tau expression usually induces a single process that is unbranched and of uniform caliber. Processes can form even when the cells are grown in suspension. Microtubules do not extend all the way to the tip; instead the terminal region contains an actin‐rich meshwork. Taxol treatment of Sf9 cells also induces the assembly of microtubules into bundles but does not induce process formation in Sf9 cells. Therefore the in vitro properties of tau as a molecule capable of assembling, stabilizing, and bundling microtubules do not fully account for the in vivo ability of tau alone to transduce microtubule assembly into a change in cell shape. The morphological features of the processes induced by MAP2 differ in highly informative ways. © 1994 Wiley‐Liss, Inc.
Organization of actin and microtubules during process formation in tau‐expressing sf9 cells
Authors: Knowles Roger , Leclerc Nicole , Kosik Kenneth S. 
Published: February 2005

AbstractInsect Sf9 cells usually elaborate a highly characteristic single process when infected with a baculovirus encoding recombinant human tau. The processes are unbranched, of uniform caliber, and contain bundles of microtubules. Because taxol treatment alone does not induce process outgrowth in these cells, it is believed that tau confers properties on microtubules that permits the conversion of microtubule assembly into the formation of processes. Here we have analyzed the reorganization of both actin filaments and microtubules during process initiation. A zone of organelle exclusion representing the focal reorganization of actin at one pole of the cell anticipated process emergence. A relationship between actin organization and process emergence was also suggested by a shift from single to multiple process formation after treatment with cytochalasin D. The rate of process elongation doubled after cytochalasin treatment of tau‐expressing cells. The increase in rate was due to the inhibition of the growth arrest phases which occur in the absence of cytochalasin. In contrast, Sf9 cells treated with cytochalasin after more than 20 h of tau expression were relatively resistant to the drug's effects. We conclude that actin and microtubules are specifically reorganized during tau‐induced process outgrowth and that a dynamic relationship between actin filaments and microtubules effects process formation. © 1994 Wiley‐Liss, Inc.
Rhazinilam mimics the cellular effects of taxol by different mechanisms of action
Authors: David Bruno , Sévenet Thierry , Morgat Michel , Guénard Daniel , Moisand André , Tollon Yvette , Thoison Odile , Wright Michel 
Published: February 2005

AbstractWe have investigated the effects of the microtubule poison rhazinilam on microtubule assembly in vivo and in vitro. In mammalian cells, rhazinilam mimics the effects of taxol and leads to microtubule bundles, multiple asters, and microtubule cold stability. In vitro, rhazinilam protected preassembled microtubules from cold‐induced disassembly, but not from calcium ion‐induced disassembly. Moreover, both at 0°C and at 37°C, rhazinilam induced the formation of anomalous tubulin assemblies (spirals). This process was prevented by maytansine and vinblastine, but not by colchicine. Preferential saturable and stoichiometric binding of radioactive rhazinilam to tubulin in spirals was observed with a dissociation constant of 5 μM. This binding was abolished in the presence of vinblastine and maytansine. In contrast, specific binding of radioactive rhazinilam to tubulin assembled in microtubules was undetectable. These results demonstrate that rhazinilam alters microtubule stability differently than taxol, and that the overall similar effects of rhazinilam and taxol on the cellular cytoskeleton are the consequence of two distinct mechanisms of action at the molecular level. © 1994 Wiley‐Liss, Inc.
Dynamics of actin and alpha‐actinin in the tails of Listeria monocytogenes in Infected PtK2 Cells
Authors: Nanavati Dipali , Ashton Francis T. , Sanger Jean M. , Sanger Joseph W. 
Published: February 2005

AbstractListeria monocytogenes can penetrate and multiply within a variety of cell types, including the PtK2 kidney epithelial line. Once released within the cytoplasm, L. monocytogenes acquires the capacity for rapid movement through the host cell [Dabiri et al., 1990: Proc. Natl. Acad. Sci. 87:6068‐6072]. In the process, actin monomers are inserted in proximity to one end of the bacterium, forming a column or tail of actin filaments [Sanger et al., 1992: Infect. Immun. 60:3609‐3619]. The rate of new actin filament growth correlates closely with the speed of bacterial migration. In this study we have used fluorescently labeled actin and alpha‐actinin to monitor the movement and turnover rate of actin and alpha‐actinin molecules in the tails. The half‐lives of the actin and alpha‐actinin present in the tails are approximately the same: actin, 58.7 sec; alpha‐actinin, 55.3 sec. The half‐life of alpha‐actinin surrounding a dividing bacterium was 30 sec, whereas its half‐life in the tails that formed behind the two daughter cells was about 20‐30% longer. We discovered that the speeds of the bacteria are not constant, but show aperiodic episodes of decreased and increased speeds. There is a fluctuation also in the intensities of the fluorescent probes at the bacterium/tail interface, implying that there is a fluctuation in the number of actin filaments forming there. There was no strong correlation, however, between these fluctuating intensities and changes in speed of the bacteria. These measurements suggest that while actin polymerization at the bacterial surface is coupled to the movement of the bacterium, the periodic changes in intracellular motility are not a simple function of the number of actin filaments nucleating at the bacterial surfaces. © 1994 Wiley‐Liss, Inc.
Sequential appearance of muscle‐specific proteins in myoblasts as a function of time after cell division: Evidence for a conserved myoblast differentiation program in skeletal muscle
Authors: Lin Zhongxiang , Lu Mei‐Hua , Schultheiss Thomas , Choi John , Holtzer Sybil , Dilullo Camille , Fischman Donald A. , Holtzer Howard 
Published: February 2005

AbstractBased on the assumption that a conserved differentiation program governs the assembly of sarcomeres in skeletal muscle in a manner analogous to programs for viral capsid assembly, we have defined the temporal and spatial distribution of 10 muscle‐specific proteins in mononucleated myoblasts as a function of the time after terminal cell division. Single cells in mitosis were identified in monolayer cultures of embryonic chicken pectoralis, followed for selected time points (0–24 h postmitosis) by video time‐lapse microscopy, and then fixed for immunofluorescence staining. For convenience, the myoblasts were termed x‐h‐old to define their age relative to their mitotic “birthdate.” All 6 h myoblasts that emerged in a mitogen‐rich medium were desmin+ but only 50% were positive for a α‐actin, troponin‐I, α‐actinin, MyHC, zeugmatin, titin, or nebulin. By 15 h postmitosis, approximately 80% were positive for all of the above proteins. The up‐regulation of these 7 myofibrillar proteins appears to be stochastic, in that many myoblasts were α‐actinin+ or zeugmatin+ but MyHC− or titin− whereas others were troponin‐I+ or MyHC+ but α‐actinin− or α‐actin−. In 15‐h‐old myoblasts, these contractile proteins were organized into nonstriated myofibrils (NSMFs). In contrast to striated myofibrils (SMFs), the NSMFs exhibited variable stoichiometries of the sarcomeric proteins and these were not organized into any consistent pattern. In this phase of maturation, two other changes occurred: (1) the microtubule network was reorganized into parallel bundles, driving the myoblasts into polarized, needle‐shaped cells; and (2) the sarcolemma became fusion‐competent. A transition from NSMFs to SMFs took place between 15 and 24 h (or later) postmitosis and was correlated with the late appearance of myomesin, and particularly, MyBP‐C (C protein). The emergence of one, or a string of ∼ 2 μ long sarcomeres, was invariably characterized by the localization of myomesin and MyBP‐C to their mature positions in the developing A‐bands. The latter group of A‐band proteins may be rate‐limiting in the assembly program. The great majority of rnyoblasts stained positively for desmin and rnyofibrillar proteins prior to, rather than after, fusing to form myotubes. This sequential appearance of muscle‐specific proteins in vitro fully recapitulates myofibrillar assembly steps in rnyoblasts of the myotome and limb bud in vivo, as well as in nonrnuscle cells converted to myoblasts by MyoD. We suggest that this cell‐autonomous myoblast differentiation program may be blocked at different control points in immortalized rnyogenic cell lines. © 1994 Wiley‐Liss, Inc.
Striated fibers in trichomonads: Costa proteins represent a new class of proteins forming striated roots
Authors: Viscogliosi Eric , Brugerolle Guy 
Published: February 2005

AbstractThe production of monoclonal antibodies and the use of biochemical techniques revealed that B‐type costa proteins in trichomonads are composed of several major polypeptides with molecular weight detected between 100 and 135 kDa similar to those found in the A‐type costae. Although differences were observed between the two types in their fine structure, we tested whether proteins composing the two costa types belong to the same protein family. A polyclonal antibody produced against the 118 kDa costa protein of Trichomonas vaginalis also recognized a 118 kDa costa protein in all other trichomonad genera studied so far whether they have A‐ or B‐type costae. Moreover biochemical characteristics of costa proteins indicated that these proteins might represent a novel class of striated root‐forming proteins in addition to centrin, giardin, and assemblin. © 1994 Wiley‐Liss, Inc.
Microfilament‐associated growth cone component depends upon Tau for its intracellular localization
Authors: DiTella M. , Feiguin F. , Morfini G. , Cáceres A. 
Published: February 2005

AbstractWe report here a novel intracellular localization and function of Tau proteins in cultured cerebellar neurons. Immunofluorescence staining of detergent‐extracted cytoskeletons with antibodies specific for Tau proteins revealed intense labeling of growth cone microtubules. Besides, suppression of Tau by antisense oligonucleotide treatment results in the complete disappearance of antigen 13H9, a specific growth cone component with properties of microfilament‐ and microtubule‐associated protein [Goslin et al., 1989: J. Cell Biol. 109:1621–1631], from its normal intracellular location. This phenomenon is unique to neurite‐bearing cells, is not associated with the disappearance of microtubules from growth cones, and is not reversed by taxol, a microtubule‐stabilizing agent. In addition, Tau‐suppressed neurons display a significant reduction in growth cone area and fillopodial number; on the contrary, fillopodial length increases significantly. The alterations in growth cone morphology are accompanied by considerable changes in the phalloidin staining of assembled actin. Taken together, the present results suggest that in developing neurons Tau proteins participate in mediating interactions between elements of the growth cone cytoskeleton important for maintaining the normal structural organization of this neuritic domain. © 1994 Wiley‐Liss, Inc.
Nanometer scale vibration in mutant axonemes of Chlamydomonas
Authors: Yagi Toshiki , Kamimura Shinji , Kamiya Ritsu 
Published: February 2005

AbstractFlagellar axonemes of sea urchin sperm display high frequency (200–400 Hz) vibration with nanometer scale amplitudes in the presence of ATP [Kamimura and Kamiya, 1992: J. Cell Biol. 116:1443–1454]. To investigate how various axonemal components affect the vibration, we examined vibration in wild‐type and mutant axonemes of Chlamydomonas. At 1 mM ATP, wild‐type axonemes underwent vibration at 100–650 Hz with amplitudes of 4–40 nm. This vibration was similar to, but less regular than, that in sea urchin sperm. Axonemes of the mutants ida1 and ida4 lacking part of the inner arm dynein underwent vibrations indistinguishable from that of wild‐type. The mutant oda1 lacking the entire outer arm underwent vibration at about half the wild‐type frequency. Unexpectedly, the paralyzed mutants pf18 lacking the central pair and pf14 lacking the radial spokes displayed vibration with significantly higher frequencies and smaller amplitudes than those in the wild‐type vibration. These results indicate that the high‐frequency vibration is common to many kinds of mutant axonemes that lack various axonemal substructures, but that its manner is sensitive to the presence of outer arm dynein and the central pair/radial spoke system. Simultaneous measurements of amplitude and frequency in wild‐type and mutant axonemes suggest that the velocity of microtubule sliding in vibrating axonemes is lower than the velocity of sliding under load‐free conditions. The velocity is particularly low in pf18. A possible mechanism is proposed to explain the lower sliding velocity and vibration amplitude in the pf18 axoneme, based on an assumption that central pair/radial spoke system may work to regulate the switching of two antagonizing forces within the axoneme. © 1994 Wiley‐Liss, Inc.
Stimulation of the ATP‐dependent interaction between actin and myosin by a myosin‐binding fragment of smooth muscle caldesmon
Authors: Lin Yuan , Ishikawa Ryoki , Okagaki Tsuyoshi , Ye Li‐Hong , Kohama Kazuhiro 
Published: February 2005

AbstractWe reported previously that smooth muscle caldesmon stimulates the ATP‐de‐pendent interaction between actin and phosphorylated smooth muscle myosin, as monitored by ATPase measurment and in vitro motility assay. Furthermore, this effect changes from stimulatory to inhibitory with increasing concentrations of caldesmon [Ishikawa et al., 1991: J. Biol. Chem. 266:21784–21790]. The N‐terminal (myosin‐binding) fragment and the C‐terminal (actin‐binding) fragment were purified from digests of caldesmon. The effects of the myosin‐binding fragment and the actin‐binding fragment on the interaction were stimulatory and inhibitory, respectively, indicating that stimulatory and inhibitory domains are localized in the myosin‐binding domain and actin‐binding domain of caldesmon, respectively. The effect of the myosin‐binding fragment on the interaction was exclusively stimulatory when the interaction was challenged by caldesmon, both at lower and higher concentrations. However, the actin‐binding fragment had no effect on the interaction at lower concentrations and inhibited the interaction at higher concentrations. Thus, the stimulatory effect of caldesmon that is observed at lower concentrations can be explained by the hypothesis that the stimulatory effect of the myosin‐binding domain predominates over the inhibitory effect of the actin‐binding domain when the concentration of caldesmon is low. With uncleaved caldesmon, we also emphasized the role of the myosin‐binding domain in the stimulation as follows; the stimulatory effect of caldesmon became obscured when binding of caldesmon to myosin was competed by the exogenous caldesmon‐binding fragment of myosin. © 1994 Wiley‐Liss, Inc.
Interactions among endoplasmic reticulum, microtubules, and retrograde movements of the cell surface
Authors: Terasaki Mark , Reese Thomas S. 
Published: February 2005

AbstractRelationships among the endoplasmic reticulum (ER), microtubules, and bead movements on the cell surface were investigated in the thin peripheral region of A6 cells, a frog kidney cell line. ER tubules were often aligned with microtubules, as shown by double‐labeling with DiOC6(3) and anti‐tubulin in fixed cells. In living cells stained with DiOC6(3) and observed in time lapse, there were frequent extensions, but few retractions, of ER tubules. In addition, there was a steady retrograde (towards the cell center) movement of all of the ER at ∼0.3 μm/min. Since microtubules are often aligned with the ER, microtubules must also be moving retrogradely. By simultaneous imaging, it was found that the ER moves retrogradely at the same rate as aminated latex beads on the cell surface. This indicates that the mechanisms for ER and bead movement are closely related. Cytochalasin B stopped bead and ER movement in most of the cells, providing evidence that actin is involved in both retrograde movements. The ER retracted towards the cell center in nocodazole while both ER and microtubules retracted in taxol. Time lapse observations showed that for both drugs, the retraction of the ER is the result of retrograde movement in the absence of new ER extensions. Presumably, ER extensions do not occur in nocodazole because of the absence of microtubules, and do not occur in taxol because taxol‐stabilized microtubules move retrogradely and there is no polymerization of new microtubule tracks for ER elongation. © 1994 Wiley‐Liss, Inc.This Article is a US Government work and, as such, is in the public domain in the United States of America.
Myosin I localizes to the midbody region during mammalian cytokinesis
Authors: Breckler Jennifer , Burnside Beth 
Published: February 2005

AbstractDuring cytokinesis, daughter cells are cleaved in two by the constriction of an actin‐rich contractile ring which encircles the equator of the dividing cell. Filamentous myosin II is present in the contractile ring and necessary for constriction of the furrow, as shown in several cell types [Satterwhite and Pollard, 1992: Curr. Opin. Cell Biol. 4:43–52]. However, no functional role nor distinctive localization has been previously identified for non‐filamentous “unconventional” myosins, such as myosin I, during cytokinesis. Using antibodies to adrenal medullary myosin I, we report that myosin I is localized in 3T3 fibroblasts to the mid‐equatorial plane during late‐cytokinesis, as well as to the polar edges as previously described in ameboid cells [Fukui et al., 1989: Nature 341:328–331]. Confocal microscopy revealed that myosin I is concentrated at the midbody region in a nearly continuous transverse disk, extending from the cortical region of the furrow through the midbody itself. These findings suggest that, in addition to the accepted role of filamentous myosin II in constriction of the contractile ring, non‐filamentous myosin I might contribute to motile events occurring late in cytokinesis. © 1994 Wiley‐Liss, Inc.
PMA and calcium ionophore induce myosin and F‐actin rearrangement during histamine secretion from RBL‐2H3 cells
Authors: Ludowyke Russell I. , Kawasugi Kazuo , French Peter W. 
Published: February 2005

AbstractRat basophilic leukemia (RBL‐2H3) cells undergo morphological and cytoskeletal changes during antigen‐induced secretion of allergic mediators. The exact role these changes play in the process of secretion is unclear. Using confocal microscopy we now show that PMA + A23187 causes extensive F‐actin rearrangements during secretion of [3H] 5‐HT. We also describe for the first time the association of myosin with F‐actin during this secretory process. In unstimulated cells, myosin and F‐actin are concentrated at the plasma membrane with no evidence of stress fibres. Upon addition of PMA or A23187, both F‐actin and myosin are rearranged into membrane ruffles and discrete aggregations (foci), followed by the formation of parallel stress fibres located on the ventral membrane. This is in contrast to reports in other cell types in which PMA has been described as causing the disruption of F‐actin stress fibres. The time course of secretion coincides with the formation of the foci and ruffles whilst the stress fibres form after the majority of secretion has occurred. These changes are accompanied by a 40% decrease in cell height and a two‐fold increase in cell spreading and they occur in the absence of extracellular calcium but are inhibited by the protein kinase C inhibitor, Bisindolylmaleimide, which also inhibits secretion. The formation of myosin‐decorated stress fibres, foci, and ruffles is not sufficient to cause secretion, as PMA alone induces these changes without any secretion. The relevance of actin and myosin rearrangements for the regulation of secretion is discussed. © 1994 Wiley‐Liss, Inc.