bluuebunny/crossref_metadata_2025_split huggingface dataset:
A model for the molecular basis of filament contractility and sliding as demonstrated by helix models
Authors: Jarosch Robert 
Published: February 2005

AbstractThe twisting behavior of α helices has hardly been considered hitherto with regard to the function of proteins. The well‐known electrostatic repulsion between the highly charged side chains, which depends on their interaction with ions, is absolutely connected with torsional rotations of the helix as long as its hydrogen bonds hold. This means a direct transformation of chemical into mechanical energy. However, the stability of a twisted single α helix with charged side chains is low in an aqueous environment. It may easily ball up to form a globular molecule with nonhelical regions of the polypeptide chain. This corresponds to a primitive contraction that obviously occurs with spasminlike proteins that contain strongly twisted filaments as Salisbury [J. Submicrosc. Cytol. 15:105–110, 1983] has shown. Steps that increase the stability and rigidity of α helical filaments are (1) the formation of coiled‐coils, (2) self‐intertwining (“telephone cord phenomenon”) or intertwining with other coiled‐coils as shown with the intermediate filaments, and (3) association with cytoskeletal elements (microfilaments, protofilaments of microtubules) that contain globular subunits. These coarser elements are rotated by winding and unwinding of the smaller helical molecules and thus transmit the torsion produced in the α helices to the microscopic level by the sliding (screwing) motion and the shearing effect that is connected with the waves of a rotating helix. Particles are transported if connected to the helical side arms. Since the displacement of the side arms seems to occur along the single protofilaments of a microtubule, a rotation of these protofiiaments is suggested. The bidirectional transport of particles along single microtubules may be explained by the association of left‐ and right‐handed helices with the protofilaments. According to the models, parallel and antiparallel sliding of neurofilaments and neurotubules is suggested.
Intracellular particle motions (cytoplasmic streaming) in staminal hairs of Setcreasea purpurea: Effect of azide and low temperature
Authors: Tucker Edward B. , Allen Nina Stromgren 
Published: February 2005

AbstractCytoplasmic streaming and its response to azide and low temperature were examined by using high‐resolution video‐enhanced light microscopy in Setcreasea purpurea staminal hair cells of immature flowers. Particles and organelles examined moved along well‐defined pathways, in repeated and unequal saltatory steps, at different rates and sometimes against the main direction of flow (bidirectionally) in both transvacuolar strand and peripheral cytoplasm. Particle movements were reversibly inhibited with azide. Low temperatures caused transvacuolar strands to shift or break. This cytoplasm accumulated in areas outside of the vacuole where spherosomes continued to saltate, but not along well‐defined pathways. In the peripheral cytoplasm, however, the spherosomes continued to move normally, amyloplasts became swollen, and they plus the other organelles (except spherosomes) were stationary. Normal particle movements were obtained when chilled cells were rewarmed to 27°C for ca 15 min.
Effects of colcemid and taxol on microtubules and intermediate filaments in chick embryo fibroblasts
Authors: Forry‐Schaudies Suzanne , Murray John M. , Toyama Yoshiro , Holtzer Howard 
Published: February 2005

AbstractReports on how changes in microtubule (MT) distribution or polymerization affect the distribution of intermediate filaments (IFs) differ. Therefore, we have used cytoimmunofluorescence techniques and electron microscopy to systematically examine and compare the arrangements of MTs and IFs in cultures of chick embryo fibroblasts under the following conditions: at different times during the cell cycle, in the presence of Colcemid or of taxol, in the presence of both drugs in succession or simultaneously in varying ratios, and during recovery from treatment with Colcemid or taxol.We have found that depolymerization of MTs by 1 μM Colcemid resulted in the rapid formation of massive IF‐cables, structures distinct from “collapsed IFs” or “juxtanuclear coils.” Neither the rapid formation of IF‐cables nor their dispersion during recovery required protein synthesis. Cells treated with 10 μM taxol rapidly formed MT‐bundles, as well as aggregates of intertwining IFs, termed “IF‐skeins.” MT‐bundles and IF‐skeins displayed strikingly complementary distributions. This reciprocal distribution of packed MTs and IFs was also obvious in untreated anaphase and telophase cells. When 10 μM taxol and 1 μM Colcemid were applied simultaneously, the complementary distributions of MT‐bundles and IF‐skeins mimicked those in taxol alone. This ability of taxol to block Colcemid's effects was concentration dependent Decreasing the taxol:Colcemid ratio allowed the depolymerization of MTs, which correlated with the formation of IF‐cables.
Dynamic aspects of the contractile system in Physarum Plasmodium: II. Contractility of triton cell models in accordance with the contraction and relaxation phases of the plasmodia
Authors: Ishigami Mitsuo , Hatano Sadashi 
Published: February 2005

AbstractThe contractility of Physarum plasmodium was investigated using cell models that were prepared by treating thin‐spread plasmodia with ice‐cold 0.2% Triton X‐100. Cell models obtained from the anterior regions of the thin‐spread plasmodia in the contraction phase retained many birefringent cytoplasmic fibrils. The fibrils vigorously contracted on addition of ATP, inducing simultaneous contraction of the whole cell models. In contrast, cell models prepared from the anterior regions in the relaxation phase scarcely contained the birefringent fibrils and exhibited only weak contractility on addition of ATP. The posterior regions of the thinspread plasmodia, which were composed of ramified plasmodial strands, always retained many fibrils when treated with the Triton solution and showed intensive contraction on addition of ATP.SDS‐polyacrylamide gel electrophoresis showed that the model was enriched for actin and myosin. About 40% of the actin was extracted from the plasmodium by the Triton treatment, while scarcely any myosin was extracted.Fragmin, a F‐actin‐fragmenting factor, caused the birefringent fibrils to diminish in the presence of Ca2+, but more than 30 minutes was required for their complete disappearance. The birefringent fibrils weakened by 30‐minute fragmin treatment disappeared immediately on addition of ATP or AMP‐PNP.
Cytoskeletal architecture and motility in a giant freshwater amoeba, Reticulomyxa
Authors: Koonce Michael P. , Euteneuer Ursula , McDonald Kent L. , Menzel Diedrik , Schliwa Manfred 
Published: February 2005

AbstractReticulomyxa is a large, multinucleated freshwater protozoan with striking intracellular transport. Cyloplasmic streaming and saltatory movements of individual organelles (at rates of up to 25 μm/sec) are observed within the naked cell body and the extensive reticulate peripheral network of fine cytoplasmic strands. As demonstrated by video‐enhanced light microscopy, individual organelles move only when associated with cytoskeletal linear elements. The linear elements are composed of mixed colinear bundles of microtubules and actin filaments, which form the backbone of the reticulopodial network. The constant branching, sprouting, and fusion of network stands suggest unique membrane properties and an unusually dynamic cytoskeleton. The electrophoretic mobility of Reticulomyxa tubulins and the lack of crossreactivity with several antibodies known to react with many plant and animal tubulins suggest that they may differ from other tubulins more widely than might be expected. Reticulomyxa's large size, the rapidity and pervasiveness of the two forms of transport, and the simple and ordered cytoskeleton make the organism well suited for future studies on the mechanisms of intracellular transport.
Slow pulsatile movements of Schwann cells in vitro: A time‐lapse cinemicrographic study
Authors: Forman David S. , Shain William G. , Fuchs David A. 
Published: February 2005

AbstractSlow pulsatile movements of Schwann cells in vitro were studied quantitatively by using time‐lapse cinemicrography. Schwann cells from peripheral nerves of 3‐day‐old rats were cultured in serum‐free medium. Most Schwann cells showed intermittent episodes of pulsatile movement; each episode consisted of one or several contractile pulses. About half of the episodes consisted of a single pulse, and episodes with more than four pulses were rare. The average episode of activity lasted 2.6 min, while the average duration of a single pulse was 1.5 min. The mean quiescent interval between episodes of activity was 3.7 min. Some cells showed no pulsatile activity. Active cells averaged 6.6 episodes/h. The fraction of time which a Schwann cell spent in pulsatile activity varied widely, with an average of 28%. Behavior of Schwann cells in HEPES‐buffered Hanks saline was generally similar to that in the complete medium. Raising K+ to 40 mM or Ca++ to 10 mM did not markedly affect the time course of the pulsatile motility, although the contractions were more vigorous in the high Ca++. Pulsatile movement was reversibly inhibited by cytochalasin B and appeared to be potentiated by drugs that disrupt microtubules.
Theoretical analysis of radioactivity profiles during fast axonal transport: Effects of deposition and turnover
Authors: Reed M. C. , Blum J. J. 
Published: February 2005

AbstractIn a preceding study [Blum, J.J., and Reed, M.C. (1985): Cell Motil. 5:507–527], factors responsible for the shape and velocity of the leading edge of the radiolabeled organelle profile were analyzed, but processes that might influence the shape of the plateau‐like region behind the advancing wave were ignored. It is now shown that deposition of material from the fast transport system into membrane‐associated structures, degradation of such deposited material and its return to the soma by the retrograde transport system, or leakage of radiolabeled material from the axon can account for the shape of the plateau. Furthermore, these processes are compatible with the maintenance of such structural inhomogeneities as the nodes of Ranvier.
Substructure of sidearms on squid axoplasmic vesicles and microtubules visualized by negative contrast electron microscopy
Authors: Langford George M. , Allen Robert D. , Weiss Dieter G. 
Published: February 2005

AbstractWe present a high‐resolution electron microscopic study of the sidearms on microtubules and vesicles that are suggested to form the crossbridges which produce the microtubule‐based vesicle transport in squid axoplasm. The sidearms were found attached to the surfaces of the anterogradely transported vesicles in the presence of ATP. These sidearms were made of one to three filaments of uniform diameter. Each filament measured 5–6 nm in width and 30–35 nm in length. The filaments in some of the sidearms had splayed apart by pivoting at their base, thereby assuming a “V” shape. The spread configuration illustrated the independence of the individual filaments. The filaments in other sidearms were closely spaced and oriented parallel to each other, a pattern called the compact configuration. In axoplasmic buffer containing AMP‐PNP, structures indistinguishable from the filaments of the sidearms on the vesicles were observed attached to microtubules. Pairs of filaments, thought to represent the basic functional unit, were observed attached to adjacent protofilaments of the microtubules by their distal tips. These data support a model of vesicle movement in which a pair of filaments within a sidearm forms two crossbridges and moves a vesicle by “walking” along the protofilaments of the microtubule.
Polymorphic assembly of subtilisin‐cleaved tubulin
Authors: White Elizabeth A. , Burton Paul R. , Himes Richard H. 
Published: February 2005

AbstractLimited proteolysis of tubulin with subtilisin results in cleavage of both the α and β subunits, releasing small peptides from the C‐terminal ends. At 37°C the digested tubulin assembles into polymorphic structures: microtubules with attached ribbons in the presence of GTP, rings in the presence of GDP, and protofilament spirals in the presence of vinblastine. Undigested tubulin does not assemble under these conditions. Rings and Vinca‐induced spiral structures are assembled from undigested tubulin only when microtubule‐associated proteins, high Mg2+ concentrations, or polycations are present. Thus, cleavage with subtilisin affects assembly in a manner similar to the addition of these agents. It appears that binding of positively charged substances may act by neutralizing the charge on the highly acidic C‐terminal regions of the α‐ and β‐subunits, while cleavage with subtilisin produces the same effect by removing these peptides. Undigested and subtilisin‐digested tubulin form sheets of protofilaments in the presence of Zn2+, which indicates that the binding sites for the 2–3 Zn2+ ions necessary to induce sheet formation do not reside in the C‐terminal regions of the monomers.
Contractility of the spasmoneme in glycerinated Vorticella stalk induced by various divalent metal and lanthanide ions
Authors: Yokoyama Yukiko , Asai Hiroshi 
Published: February 2005

AbstractThe glycerinated stalks of the peritrich ciliate, Vorticella, can contract helically and reversibly on the addition of not only Ca2+ but also other divalent or trivalent cations having ionic radii not far from 1 Å. In order to investigate the stalk contraction quantitatively in the absence of Ca2+‐chelators, we developed a method to eliminate contaminating Ca2+ and other metal ions in KC1 and pHbuffer solutions by using a Ca2+‐and heavy metal ion‐specific ion exchange resin (Eporas MX‐2) Thus, it was possible to measure the relationship between the fractional stalk length of Vorticella and the free concentration of alkaline earth metal, transition metal, and lanthanide ions in the 0.1 M KC1 and buffer (pH 6.8) solutions. Among these ions, Ca2+, Nd3+, and Eu3+ (having ionic radii of about 1 Å) had the highest affinity for the contractile element in the spasmoneme. As the concentration of lanthanide ions (except Nd3+ and Eu3+) is increased, the Vorticella stalk contracts abruptly at a threshold level; this means that the Hill's parameter is very high, probably more than 6. The results of these experiments and of the co‐mixtures of Ca2+ and Tb3+ suggest that a contractile element in the spasmoneme contains both contractile Ca2+‐binding and regulatory Ca2+‐binding sites.
Wave of cortical actin polymerization in the sea urchin egg
Authors: Yonemura Shigenobu , Mabuchi Issei 
Published: February 2005

AbstractThe distribution of actin filaments in the cortical layer of sea urchin eggs during fertilization has been investigated by light microscopy using fluorescently labeled phallotoxins. The cortical layer of both whole eggs and cortices isolated on a glass surface was examined. In cortices of unfertilized eggs, numerous fluorescent spots were seen, which may correspond to short actin filament cores in microvilli. After insemination, one of the sperm‐attaching points on the egg surface first became strongly fluorescent. This fluorescence grew around the point of sperm penetration with the growth of the fertilization cone. Then, the cortical layer of the egg around the fertilization cone became strongly fluorescent and the fluorescence propagated in a wavelike manner over the entire cortex. The mechanism of the propagation of actin polymerization is discussed.
Role of cortical tension in fibroblast shape and movement
Authors: Albrecht‐Buehler Guenter 
Published: February 2005

AbstractIn order to analyze the cellular mechanism of shape formation, the shape of individual 3T3 cells was perturbed by micromanipulation resulting in the detachment and relaxation of a cellular extension and the bending of the extension to form an “elbow” at a variable angle β. Finally, the tip of the extension was allowed to reattach to the substrate away from the cell.The cells reacted by drawing the extension tight. If β < 90°, the elbow moved laterally for 8–15 min until the extension projected orthogonally at the cell surface. If β ≥90°, the extension remained stationary, Finally, in all cases webs formed between attachment points in the perturbed area. If the tip of the extension was allowed to touch its own cell body, thus forming a loop, the cells invariably closed the loop.The paper interprets the cellular reaction as the result of cortical tension and suggests that it is a major factor in the formation of fibroblast shape and the expressions of fibroblast motility.
Reversible inhibition of microtubuies and cell growth by the bicyclic colchicine analogue MTC
Authors: Díez José C. , Avila Jesús , Nieto Juan M. , Andreu José M. 
Published: February 2005

Abstract2‐methoxy‐5‐(2,3,4‐trimethoxyphenyl) 2,4,6‐cycloheptatrien‐1‐one (MTC) is a synthetic colchicine analogue, lacking the B ring of the alkaloid (Fitzgerald: Biochem. Pharmacol. 25:1381–1387, 1976). MTC has been shown to bind reversibly to the colchicine binding site of tubulin and to inhibit microtubule assembly in vitro (Andreu et al: Biochemistry 23:1742–1752, 1984; Bane et al: J. Biol. Chem. 259:7391–7398, 1984). Its action on different cultured cell lines (PtK2, Pk15, and SV‐3T3) has now been studied. 0.2 × 10−6 M MTC stopped Pkl5 and SV‐3T3 cell growth, inducing an accumulation of mitoses in a few hours. Removal of MTC from the culture medium rapidly restored normal mitotic index and growth rates. Partial depolymerization of the cytoplasmic microtubules of PtK2 cells was observed at concentrations ranging from 2 to 5 × 10−7 M. Maximal microtubule network depolymerization was obtained after 4 h of treatment with 2 to 5 × 10−6 M MTC or at a higher MTC concentration (2 × 10−5 M) for less than 2 h. Removal of 2 × 10−5 M MTC (the highest MTC concentration used) from the culture medium resulted in almost complete microtubule polymerization after 10 min of drug recovery and a normal microtubule network in 20–30 min.MTC constitutes an antimitotic drug directed to the colchicine site. It is water‐soluble, shows a fast and reversible action, and may therefore be employed as a convenient tool to study cellular microtubule‐dependent functions.
Patterns of tubulin isotype synthesis and usage during mitotic spindle morphogenesis in Physarum
Authors: Paul Eileen C. A. , Roobol Anne , Foster Kay E. , Gull Keith 
Published: February 2005

AbstractTubulin synthesis in the naturally synchronous plasmodium of Physarum polycephalum is a markedly periodic event restricted to the late G2 period of the cell cycle. Mitosis in the plasmodium is intranuclear, and there are no cytoplasmic microtubules at any stage of the cell cycle. We have combined a biochemical investigation of the synthesis of the plasmodial tubulin isotypes and their participation in the mitotic spindle with a microscopic study (immunofluorescence) of the development of spindle microtubules throughout the cell cycle.We have shown that all four tubulin isotypes identified in the plasmodium (α1, α2, β1 and β2) are present in the mitotic spindle. The stoichiometry of isotype usage in the mitotic spindle generally reflects the overall abundance of isotypes in the plasmodium as a whole: β2 > α1 > α2 > β1. We have also shown that tubulins synthesized in the G2 period of one cell cycle can be incorporated into the spindles of the immediately ensuing mitosis and have sufficient biological longevity to allow participation in the mitotic divisions of future cell cycles. Thus, the phenomenon of periodic tubulin synthesis does not reflect a restricted use of tubulin to the cell cycle in which it was synthesized. The major polymerization of tubulin in the nucleus occurred less than 30 min before metaphase. A novel tubulin‐containing structure was, however, present in the nucleus approximately 60 min before metaphase. Polymerized tubulin is rapidly removed from the nucleus following nucleokinesis.
Distribution of multiple centrospheres determines migration of BHK syncitia
Authors: Lewis Lindiann , Albrecht‐Buehler Guenter 
Published: February 2005

AbstractAfter fusion of BHK cells with polyethylene glycol, the resulting syncitia contained in 77% of the cases multiple microtubule organizing centers (MTOCs), which were aggregated into a common centrosphere. Based on the observation of phagokinetic tracks, we found that the syncitia were able to locomote if (1) the MTOCs aggregated into a common centrosphere cluster, and (2) the clustered centrospheres were excluded from the cluster of nuclei of the syncitium. The results suggest that each individual pair of one nucleus and one centrosphere contributes, in a process of vectorial addition, its individual polarity to the polarity of the syneitium. Thus the widely accepted idea that the centrosphere is involved in the determinatinn of cell polarity can be generalized beyond the case of single cells.
Cordycepin disrupts the microtubule networks and arrests nil 8 hamster fibroblasts at the onset of mitosis
Authors: Zieve Gary W. , Feeney Robert J. , Roemer Elizabeth J. 
Published: February 2005

AbstractThe nucleoside analogue 3′‐deoxyadenosine (cordycepin) arrests dividing cells at the onset of mitosis in prometaphase. The microtubules in the arrested prometaphase cells depolymerize to two small asters. A minimum of 80 μg/ml cordycepin or 20 μg/ml cordycepin in combination with 2 μg/ml of the deaminase inhibitor erythro‐9‐(2‐hydroxy‐3‐nonyl) adenosine (EHNA) lo inhibit its degradation is required to see these effects. Analysis of cell extracts by high‐pressure liquid chromatography indicates that cordycepin enters the cells rapidly and is phosphorylated to 3′‐dATP. The intracellular concentration rises almost linearly from 0.7 mM after 15 min to 7 mM by 210 min. Concomitantly the ATP concentration shows a rapid drop from the 4 mM present in controls. However, the direct reduction of ATP levels does not mimic the same rapid effects of cordycepin on the microtubules. In addition, similar effects are not produced by a variety of other adenosine analogues with alterations in the 2′ and 3′ ribose positions. Although other pharmacological reagents arrest cells at the onset of mitosis, cordycepin is unusual because of the collapse of the microtubule networks to two small asters that radiate from the microtubule‐organizing center. 3′‐dATP can replace the requirement for ATP or GTP in the vitro polymerization of microtubules from microtubule protein: however, at limiting concentrations of nucleotide it requires approximately two times the concentration of 3′‐dATP as ATP to support an equivalent level of microtubule polymerization. This suggests that the effects of cordycepin in vivo may be the result of the depletion of cellular ATP pools and the altered ability of 3′dATP to substitute for ATP‐dependent reactions. Current experiments are testing this hypothesis.