bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell surface displacement during euglenoid movement and its computer simulation
Authors: Suzaki Toshinobu , Williamson Richard E. 
Published: February 2005

AbstractWe recently showed by videomicroscopy that adjacent pellicular strips slide relative to each other without contraction during S‐shaped bending movement in Euglena fusca (Suzaki and Williamson, 1985). In order to validate this sliding strip mechanism for other species and other shape changes, a theoretical analysis and a computer simulation were carried out. Some of the commonly observed euglenoid cell shapes (rounded. S‐shaped, and embryo‐like shapes) were generated. Our results suggest that Euglena probably achieves a variety of cell shape changes by means of locally regulated sliding between adjacent pellicular strips of constant length and width.
Calcium‐modulated contractile proteins associated with the eucaryotic centrosome
Authors: Salisbury J. L. , Baron A. T. , Coling D. E. , Martindale V. E. , Sanders M. A. 
Published: February 2005

AbstractAffinity‐purified antibodies that recognize the 20,000‐dalton molecular weight (20 kd) striated flagellar root protein of Tetraselmis striata have been used to identify antigenic homologs in other eucaryotic organisms of diverse evolutionary origins. Among the green algae, Tetraselmis and Chlamydomonas, and their colorless relative, Polytomella, the 20‐kd homologs appear associated with basal bodies. This occurs most prominnently in the form of flagellar roots of both striated and microtubule subtended types. Among cultured mammalian cells (PtK2 and primary mouse macrophage cell lines), flagellar root protein homologs appear as basal feet, pericentriolar fibrils, and pericentriolar satellites. Mammalian sperm cells also show flagellar root protein homologs associated with their basal bodies. We envisage a functional role for these fibrous calcium‐sensitive contractile proteins in altering the orientation of centrioles or basal bodies with their associated MTOCs by responding to topological calcium fluxes.
Motility mechanisms in the actinopods (Protozoa): A review with particular attention to axopodial contraction/extension, and movement of nonactin filament systems
Authors: Febvre‐Chevalier Colette , Febvre Jean 
Published: February 2005

AbstractSeveral motility phenomena displayed by members of the Heliozoa, Radiolaria, and Acantharia (Protozoa, Actinopoda) are reviewed. These phenomena include (1) cytoplasmic streaming, internal saltatory motion, and transport of particles at the cell surface; (2) axopod contraction and extension; and (3) contraction of nonactin filament systems.Cytoplasmic streaming and saltatory motion require energy derived from oxidative phosphorylation. In addition, calcium appears to be involved in the regulation of these movements, and a role for calmodulin is suggested. At present, the molecular basis for these motility phenomena remains obscure.We have focused our attention on the rapid contraction of axopods and stalk in the marine heliozoan Actinocoryne contractilis (Febvre‐Chevalier: J. Marine Biol. Assoc. U.K. 60:901‐928, 1980). Contraction is accompanied by the cataclysmic breakdown of microtubules. For this species, a Na+ and Ca2+‐dependent action potential precedes axopod contraction. A lack of contraction in Ca2+‐free media (10−7 M Ca2+) suggests that Ca2+ fluxes across the cell membrane are required.Motile phenomena associated with nonactin filaments of fibrous systems in actinopods, especially in the myonemes of the acantharians (Febvre and Febvre‐Chevalier: Biol. Cell. 44:283–304, 1982) are also examined. In vitro contraction of these filaments is CA2+ dependent and ATP independent' cycles of contraction and extension are caused by Ca2+‐dependent conformational changes in pairs of twisted filaments. In vivo, the Ca2+ dependent contraction of these myonemes may be independent of direct mitochondrial control, but metabolic ATP and calmodulin may be required to regulate the level of free cytoplasmic calcium.
The stabilization of microtubules in isolated spindles by tubulin‐colchicine complex
Authors: Hays T. S. , Salmon E. D. 
Published: February 2005

AbstractWe have analyzed the effect of colchicine and tubulin dimer‐colchicine complex (T‐C) on microtubule assembly in mitotic spindles. Cold‐ and calcium‐labile mitotic spindles were isolated from embryos of the sea urchin Lytechinus variegatus employing EGTA/glycerol stabilization buffers. Polarization microscopy and measurements of spindle birefringent retardation (BR) were used to record the kinetics of microtubule assembly‐disassembly in single spindles. When isolated spindles were perfused out of glycerol stabilizing buffer into a standard in vitro microtubule reassembly buffer (0.1 M Pipes, pH 6.8, 1 mM EGTA, 0.5 mM MgCl2, and 0.5 mM GTP) lacking glycerol, spindle BR decreased with a halftime of 120 s. Colchicine at 1 mM in this buffer had no effect on the rate of spindle microtubule disassembly. Inclusion of 20 μM tubulin or microtubule protein, purified from porcine brain, in this buffer resulted in an augmentation of spindle BR. Interestingly, in the presence of 20 μM T‐C, spindle BR did not increase, but was reversibly stabilized; subsequent perfusion with reassembly buffer without T‐C resulted in depolymerization. This behavior is striking in contrast to the rapid depolymerization of spindle microtubules induced by colchicine and T‐C in vivo. These results support the current view that colchicine does not directly promote microlubule depolymerization. Rather, it is T‐C complex that alters microtubule assembly, by reversibly binding to microtubules and inhibiting elongation.In vivo, colchicine can induce depolymerization of nonkinetochore spindle microtubules within 20 s. In vitro, colchicine blocks further microtubule assembly, but does not induce rapid disassembly. The rate of tubulin dissociation from spindle microtubules in vitro in reassembly buffer without soluble tubulin is about 20 times slower than the rate of dissociation in vivo when assembly is blocked abruptly by T‐C. The rate of tubulin dissociation from the spindle microtubules may determine their response to T‐C, since the tubulin dissociation rate in vivo is about 12 times faster than the rate measured here for spindle microtubules in standard microtubule reassembly buffer at physiological temperature.
Effects of vanadate on the assembly and disassembly of purified tubulin
Authors: Kirazov Evgeni P. , Weiss Dieter G. 
Published: February 2005

AbstractSodium‐orthovanadate (100–700 μM) added to purified pig brain microtubule protein (molar ratios 13–90 moles vanadate/mole tubulin) inhibits to a considerable extent the assembly (up to 65%) and the disassembly rates (up to 60%) of microtubules, as determined by turbidimetry. Vanadate added to preformed microtubules did not appreciably alter the turbidity level of the samples, however, the disassembly rates were decreased in the same manner as when vanadate was added prior to polymerization. Microtubule protein kept on ice for 3–6 hours became more susceptible to vanadate than freshly prepared protein. The effect of vanadate was independent of the GTP concentration at which the polymerization assays were performed (0.025 to 1 mM GTP). In the presence of taxol, which increases the rate and extent of microtubule formation, vanadate had no effect on assembly rates. Disassembly was inhibited, however, much less than in the presence of vanadate alone. Electron microscopy and polyacrylamide gel electrophoresis did not reveal differences between microtubules prepared in the presence or in the absence of vanadate. This is consistent with the notion that vanadate does not interfere with the interaction between tubulin and the high‐molecular weight microtubule‐associated proteins. Apparently vanadate brings about an allosteric change of the microtubule protein(s) resulting in the abnormal polymerization kinetics of tubulin found in our study. The above results may be relevant for studies where the effects of vanadate on intracellular motility are interpreted as being solely due to a specific inhibition of ATPases.
Computer simulation of bend propagation by axoplasmic microtubules
Authors: Brokaw Charles J. 
Published: February 2005

AbstractThe generation of bending waves by microtubules in squid nerve axoplasm has been modelled using appropriately modified versions of computer programs developed previously for simulation of flagellar bending waves. The results confirm that a constant longitudinal force directed along the axis of the microtubule is sufficient to cause the generation of regular oscillations and propagated bending waves when the forward gliding movement of the microtubule is obstructed. No control mechanism is required to modulate the active force‐generating system. In order to obtain bending waves similar to those observed experimentally, it was necessary to use a model for the force‐generating system in which the active force decreases with increasing sliding velocity. If the elastic bending resistance of axoplasmic microtubules is similar to that of microtubules in sperm terminal filaments, the longitudinal force per unit length generated by the axoplasmic microtubules must be of the same order of magnitude as the force generated by dynein arms along the doublet microtubules of eukaryotic flagella.
Malorientation and abnormal segregation of chromosomes during recovery from Colcemid and Nocodazole
Authors: Ladrach Kenneth S. , LaFountain James R. 
Published: February 2005

AbstractReversal of meiotic arrest in crane‐fly spermatocytes by U.V. irradiation of Colcemid‐arrested cells or by rinsing Nocodazole‐arrested cells in fresh buffer results in the induction of chromosome malorientation. Malorientations observed among Colcemid‐recovering and Nocodazole‐recovering spermatocytes at frequencies higher than normally observed in untreated cells included associations of sister kinetochores of half‐bivalents with both spindle poles (amphitely), in contrast with associations of sisters with only one pole (syntely) as is usually found during the first meiotic division. In several cases, prior to anaphase onset, maloriented bivalents appeared unusually tilted with respect to the spindle axis, and during anaphase they gave rise to laggard half‐bivalents that did not segregate during anaphase along with half‐bivalents having proper syntelic orientation. The results parallel previous findings obtained during cold recovery, and the properties of the drugs used here suggest that their action on microtubules, although reversible, induces malorientation during recovery from meiotic arrest.
Kinetochore microtubules in crane‐fly spermatocytes: Untreated, 2°C‐treated and 6°C‐grown spindles
Authors: Scarcello Lisa A. , Janicke Marie A. , LaFountain James R. 
Published: February 2005

AbstractWe investigated the involvement of kinetochore microtubules (kMTs) in mediating chromosome‐to‐pole connections in crane‐fly (Nephrotoma suturalis and Nephrotoma ferruginea) spermatocytes. Two experimental treatments were used to yield spindles with reduced numbers of nonkinetochore microtubules (nkMTs). Short‐term (10–15 min) exposure of spermatocytes to 2°C caused depolymerization of the majority of nkMTs, resulting in a kMT:(kMT + nkMT) ratio of 0.76. Long‐term (24h) exposure to 2°C followed by recovery at 6°C resulted in a kMT:(kMT + nkMT) ratio of 0.55, the spindle having more nkMTs than a 2°C‐treated spindle but fewer than an untreated spindle, in which the kMT:(kMT + nkMT) ratio was 0.27. The numbers and lengths of kMTs in 6°C‐grown spindles were similar to those in untreated cells, suggesting that the overall inhibition of MT assembly at 6°C apparently did not affect the mechanism by which kMTs are formed. We observed most kMTs of early anaphase spindles to be long (>3 μm), and many extended to the polar regions of the spindle. Thus, the crane‐fly spindle appears not to be as atypical as it was previously suggested to be.
Dynamic aspects of the contractile system in Physarum Plasmodium: I. Changes in spatial organization of the cytoplasmic fibrils according to the contraction‐relaxation cycle
Authors: Ishigami Mitsuo 
Published: February 2005

AbstractDynamic changes in the spatial organizations of cytoplasmic fibrils (microfilament bundles) related to the contraction‐relaxation cycle in thin‐spread plasmodia of Physarum polycephalum were investigated by fluorescence microscopy, where NBD‐phallacidin was used to stain the fibrils, combined with polarizing light microscopy.The fibrillar organization in the anterior region, which consists of a fanlike spreading plasmodial sheet, strikingly changed according to the phase of the cycle. In the early stage of the contraction, as the endoplasm began to stream backward, the fibrils developed into a number of slender and flabby fibrils emanating from the inside of the cell membrane and the nodes. They became thicker and more straightforward fibrils running parallel to each other at the middle stage, and finally formed a thick framework consisting of a “polygonal network” near the tip of the migrating front and a “parallel array” in the inner part. In the relaxation phase, as the endoplasm streamed forward, the fibrillar framework disintegrated gradually and finally disappeared almost completely, remaining only around the nodes in some cases.The fibrillar patterns in the posterior region, which consists of ramified strands, showed no conspicuous rhythmic change with alternation of the streaming direction.
Cytoskeletal architecture of reactivated crayfish axons, with special reference to crossbridges among microtubules and between microtubules and membrane organelles
Authors: Hirokawa Nobutaka , Yorifuji Hiroshi 
Published: February 2005

AbstractBidirectional organelle movements were observed in fresh and permeabilizedreactivated (0.02% saponin, 5 mM Mg++ ATP) walking leg axons of crayfish with video‐enhanced contrast, differential interference contrast (AVEC‐DIC) microscopy; and the cytoskeletal organization of those axons was studied with quickfreeze, deep‐etch electron microscopy (QF,DE) to understand the structure of the microtubule (MT) domain and to determine the basic cytoskeletal structures necessary for organelle transport in vivo. Vesicles and mitochondria moved bidirectionally in the central parts of fresh or permeabilized‐reactivated axons. Although the axoplasm of the fresh axon was composed of longitudinally oriented microtubules and granular materials in which membrane organelles were embedded, a network of fine strands existed in the core of the granular materials. Crossbridges between membrane organelles and microtubules were present. In the central part of reactivated axons, the cytoskeleton consisted of microtubules, highly anastomosing networks of fine strands (6.6 ± 1.4 nm in width) that crosslinked the microtubules with each other, and relatively short, straight crossbridges (25 ± 3.9 nm in length, 5.5 ± 2.1 nm in width) crosslinking membrane organelles with microtubules. It has been shown that a 270KD microtubule associated protein (MAP) could be a main component of crossbridges between MTs [Hirokawa, 1986]. Hence the dynamic conformational change of crossbridges between membrane organelles and microtubules could play an important role when membrane organelles are transported.
Effects of taxol on microtubule arrays in cultured higher plant cells
Authors: Weerdenburg Carol , Falconer Marcia M. , Setterfield George , Seagull Robert W. 
Published: February 2005

AbstractTreatment with 10 μm taxol disrupted mitotic and cytoplasmic arrays of microtubules (MT) in cultured cells of two higher plants, Vicia hajastana (vetch) and Zinnia elegans. When treated for 1, 24, and 48 h, cells in both cultures showed similar effects. After 1 h, multipolar arrays of MT were noted in prophase, large aster‐like arrays of MT appeared in metaphase, and extra MT shared poles with otherwise normal‐appearing metaphase and anaphase configurations. After 24 and 48 h, some phragmoplasts were multipartite or misplaced. In interphase cells, micronuclei and multinucleate cells were evidence of irregular mitosis and cytokinesis. Cytoplasmic MT in elongated cells were oriented parallel to, instead of at right angles to the long axis of the cell. Some interphase cells lost asymmetry while maintaining organized arrays of MT. Taxol appears to disrupt mitotic and cytoplasmic arrays of MT, seemingly overriding the mechanism(s) regulating MT polymerization and orientation.
Video analysis of chemotactic locomotion of stored human polymorphonuclear leukocytes
Authors: Burton Jarrett L. , Law Ping , Bank Harvey L. 
Published: February 2005

AbstractPrevious studies of the storage of polymorphonuclear leukocytes (PMNs) have used an empirical approach to define “optimal” conditions. To date, no storage conditions have been described which satisfactorily preserve the chemotactic function of PMNs beyond 24 h. In an effort to define the precise nature of the storage lesion, we studied the chemotactic locomotion of freshly isolated PMNs and PMNs which had been suspended in citrate‐phosphate‐dextrose‐adenine (CPD‐Al) plasma and stored in PVC bags, at 20–22°C for 24 h. We used time‐lapse video recording and computer image analysis to quantitate the motion of PMNs migrating under agarose. The positions of individual motile cells were traced at 1‐min intervals for 5 min. The following parameters were used to quantitate migration: (1) speed (distance/min), (2)) persistence of locomotion index (velocity/speed), (3) orientation angle (the angle of the vector describing the next displacement of a cell relative lo a direct line toward the chemoattractant), and (4) chemotropic index (cosine of the orientation angle). After 24 h of storage, the following changes were observed: (1) fewer cells migrated, (2) (he speed of migrating cells was reduced by 25%, (3) the persistence of locomotion index decreased by 7%, which indicates that migrating cells made slightly more/wider turns, and (4) the chemotropic index was decreased by 30%, which indicates that migrating cells were less accurate in their orientation toward the chemoattractant. Apparently, the storage of PMNs selectively impairs the ability of some cells to orient accurately in a chemotactic gradient and changes the distribution of these locomotor parameters within the population.
Protein‐protein interactions in the 18S ATPase of Chlamydomonas outer dynein arms
Authors: Mitchell David R. , Rosenbaum Joel L. 
Published: February 2005

AbstractWhen outer‐row dynein arms are extracted from Chlamydomonas flagellar axonemes, they dissociate into two ATPase complexes with sedimentation coefficients of 12S and 18S. We immunized mice with 18S dynein and generated a library of monoclonal antibodies against the polypeptides in this complex. Antibodies were selected which specifically recognize the 18S α‐ and β‐heavy chains and the 83,000‐dalton and 70,000‐dalton intermediate chains. These antibodies were isolated and characterized for their ability to recognize determinants on both denatured antigens and native 18S dynein; 18S dynein was dissociated in stepwise fashion into smaller aggregates with ionic and nonionic detergents and the resulting subcomplexes were isolated by precipitation with specific monoclonal antibodies. The smallest aggregates isolated were heterodimers between the α‐chain and a 16,000‐dalton light chain and between the two intermediate chains. Additional close associations of the β‐heavy chain with an 18,000‐dalton light chain and 70,000‐dalton intermediate chain, and a weaker interaction between the intermediate chain heterodimer and light chains of 21,000 daltons and 12,500 daltons, were also observed. We present a model of 18S dynein substructure based upon this information.
Comparison of the beating of cis‐ and trans‐flagella of Chlamydomonas cells held on micropipettes
Authors: Rüffer Ursula , Nultsch Wilhelm 
Published: February 2005

AbstractChlamydomonas cells sucked onto micropipettes were filmed at 500 frames/sec and analyzed as to their forward beating mode. A comparison with freely swimming cells revealed that the flagella of the sucked cells beat in a normal threedimensional manner, with beat frequencies that correspond to those of freely swimming cells. Most beats were synchronous. but not symmetrical; cis‐ and trans‐flagellum appear to beat in a slightly different manner. Some cells beat synchronously throughout, but mostly synchrony was interrupted by a single asynchrony or up to incessant asynchronies, caused by transient accelerations of the trans‐ (fo‐) flagellum. Only rarely did cis‐ and trans‐flagella have different but constant beat frequencies. Helical swimming of Chlamydomonas more likely is due to the beat asymmetries of the two flagella than to differences of beat frequencies. In our records, the stigma is on the inside of the helical swimming path.
A unique tubulin antibody which disrupts particle movement in squid axoplasm
Authors: Johnston Karen M. , Brady Scott T. , van der Kooy Derek , Connolly Joe A. 
Published: February 2005

AbstractMicrotubules have been demonstrated to be a substrate for organelle transport and particle translocation in vitro and in vivo. Subsequent to a previous report of inhibition of axonal transport of exogenous tracers in vivo using antiserum NS‐20 against tubulin (Johnston et al: Brain Res. 1986), we now show disruption of particle movement in extruded squid axoplnsm using this unique immunological probe. Using video‐enhanced contract‐differential interference contrast (AVEC‐DIC) microscopy, we examined the properties of particle movement along microtubules and demonstrated that bolh the velocity of particle movement and the numbers of particles moving are decreased in the presence of NS‐20 antiserum or NS‐20 affinity‐purified antibodies but. not in the presence of another antiserum against tubulin. The amount of microtubule substrate does not change in the presence of any of the antisera. In conclusion, we suggest that NS‐20 antibodies bind near or at a site on the tubulin molecule which is critical in the mechanism of particle transport, and provide a direct immunological probe to examine the mechanism of microtubule involvement in axonal transport.
cAMP‐mediated inhibitory effect of calmodulin antagonists on ciliary reversal of Paramecium
Authors: Izumi Akemi , Nakaoka Yasuo 
Published: February 2005

AbstractTo explore possible roles of calmodulin in Ca2+‐induced ciliary reversal, we tested the effects of calmodulin antagonists on Triton‐extracted models of Paramecium. In the extracted models prepared by the method of Naitoh and Kaneko [Science 176:523–524, 1972], the Ca2+ ‐induced ciliary reversal was not inhibited by calmodulin antagonists, trifluoperazine (TFP), or 5‐chloro‐l‐naphthalenesulphone amide (W‐7). However, in the presence of adenosine 3′,5′‐cyclic mono‐phosphate (cAMP), whose concentration is below the one that alters the ciliary direction, TFP inhibited ciliary reversal and the models swam forward at 10−5 M Ca2+. When the washing medium in the preparation of the extracted models was replaced with one containing MgCl2, the extracted model showed sensitivity to calmodulin antagonists without addition of cAMP; at 10−5 M Ca2+, 40 μM TFP or 100 μM W‐7 inhibited the ciliary reversal and the models swam forward. Such effect of antagonists was abolished by an inhibitor of cAMP‐dependent protein kinase. On the other hand, addition of cAMP enhanced the inhibitory effect of antagonists. These results suggest that calmodulin antagonists act to increase the extent of cAMP‐dependent protein phosphorylation that inhibits the Ca2+ ‐induced ciliary reversal.