bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for regulation of lamellipodial and tail contraction of glycerinated chicken embryonic fibroblasts by myosin light chain kinase
Authors: Cande W. Zacheus , Ezzell Robert M. 
Published: February 2005

AbstractPermeabilized cell models of muscle and nonmuscle cells have proven useful for examining the regulation of actin, myosin, and other cytoskeletal proteins during cell contraction. Upon addition of Ca2+ and ATP, glycerinated chick embryonic skin fibroblasts retract their tails and lamellipodia. Ca2+‐independent contractions are obtained by preincubation of cell models in Ca2+ ATPγS, followed by EGTA and ATP addition, or by addition of trypsin‐treated myosin light chain kinase that no longer requires Ca2+ for reactivation. By pretreating cells before glycerination with colchicine, it is possible to study lamellipodial contraction independent of tail contraction. Similar responses to ATPγS pretreatment and unregulated myosin light chain kinase are observed in cells that only contain lamellipodia. SDS‐PAGE electrophoresis of glycerinated fibroblasts incubated in ATPγ35S and Ca2+ shows that only two major proteins are thiophosphorylated, and that one of them, a band that comigrates with the 20K MW light chain of myosin, is thiophosphorylated in a Ca2+‐dependent manner. Since the rate of tail contraction is several‐fold faster after Ca2+ and ATPγS pretreatment or incubation in excess myosin light chain kinase, myosin light chain phosphorylation may be a rate‐limiting step during contraction.
Actomyosin dynamics in chemotactic amoeboid movement of Dictyostelium
Authors: Fukui Yoshio , Yumura Shigehiko 
Published: February 2005

AbstractUnder some physiological conditions, amoeboid cells are known to display a vectorial movement in response to chemotactic signals. Recent cell biological studies demonstrated the establishment of myosin filaments in Dictyostelium and indicate that the site of the motive force production is primarily localized at the posterior cortex. Furthermore, the traction force at the side body of a polarized amoeba is thought to play an essential role for the amoeboid movement. It is also suggested that certain dynamic activities of the actomyosin‐based cytoskeletal system are related to the establishment of mechanochemical transducing elements transiently organized during the chemotaxis. This review focuses on recent selective studies on the chemotactic movement of Dictyostelium, which is coupled with rapid redistribution of myosin filaments, and probably mediated by a transient phosphorylation of myosin.
Quinacrine‐induced changes in mitotic PtK1 spindle microtubule organization
Authors: Armstrong Lydia , Snyder Judith Armstrong 
Published: February 2005

AbstractQuinacrine, an acridine derivative which competitively binds to ATP binding sites, has been used to study the role of ATP requiring molecules in microtubule organization in mitotic PtK1 cells. Brief treatments of metaphase cells with concentrations of quinacrine ranging from 2 to 10 μM decreased spindle length and birefringence in a concentration‐dependent manner. With either increasing quinacrine concentrations or duration of treatment, metaphase cells demonstrated a specific reorganization of spindle microtubules. Both polarization and electron microscopy showed a substantial loss of non‐kinetochore spindle microtubules with an increase in astral microtubules: this was particularly evident in the region adjacent to the spindle domain. Addition of millimolar concentrations of dinitrophenol to quinacrine‐containing medium did not potentiate the response of metaphase cells to quinacrine treatment. Time‐lapse video analysis demonstrated that the astral microtubules are the result of reorganization of spindle microtubules. These data suggest that functional ATP binding sites are required to maintain stable interactions between microtubules and that these interactions are responsible for maintaining the bowed configuration of non‐kinetochore spindle microtubules which are under compression at metaphase.
Spindle function in the green alga Mougeotia: Absence of anaphase A correlates with postmitotic nuclear migration
Authors: Pickett‐Heaps Jeremy D. , Wetherbee Richard 
Published: February 2005

AbstractIn the filamentous green alga Mougeotia, each daughter nucleus formed by mitosis is then rapidly moved along the recently divided daughter cell to the central cleavage developing in the chloroplast. This movement is brought about by a cone‐shaped array of microtubules (MTs) that ensheath the daughter nucleus and are focused upon a small region, presumably a microtubule‐organising center (MTOC). Movement is completed when the MTOC locates and then resides in the chloroplast cleavage, drawing the nucleus into this position.The mitotic spindle is open with initially broad, ill‐defined poles. Anaphase A contributes minimally, if at all, to chromosome separation since the half spindles remain about the same length during anaphase and telophase. Thus, anaphase is accommodated and probably achieved by spindle elongation; the interzonal MTs also generate a rudimentary phragmoplast at the ingrowing cleavage furrow. The persistent polar MTs become directly transformed into the cone‐shaped array and initiate nuclear movement during early telophase. Various closely or distantly related green algae show this trait of persistent polar MTs. We conclude that this trait has allowed some species to evolve a motility system based directly on the capabilities of astral MTs, for generating the postmitotic nuclear movement essential for the restoration of the interphase cell organization.
Massive actin bundle couples macrocilia to muscles in the ctenophore Beroë
Authors: Tarmm Sidney L. , Tamm Signhild 
Published: February 2005

AbstractMacrocilia are thick compound ciliary organlles arising individually from elongated epithelial cells on the lips of beroid ctenophores. A giant wedge‐shaped bundle of microfilaments extends 25–30 μm from the base of each macrocilium to the lower end of the cell, terminating at a junction with an underlying smooth muscle cell. The broad end of the microfilament bundle is anchored to the macrocilium by striated rootlet fibers that extend from the basal bodies into the bundle and are linked to the microfilaments by periodic bridges. Fluorescence microscopy of rhodamine‐phalloidin stained intact tissue, dissociated macrociliary cells, and Triton/glycerol‐isolated bundles shows that the microfilaments contain actin. The microfilaments run generally parallel to the long axis of the bundle but are not highly ordered. Filaments decorated with myosin S1 show a uniform polarity with arrowheads pointing away from the tapered membrane‐associated end of the bundle. No variations in bundle length (nor changes in rootlet periodicity) were observed in tissue fixed under conditions of calcium activation. Isolated bundles did not contract in Mg‐ATP, even though detached macrocilia underwent reactivated beating and sliding disintegration. Macrocilia arc used to bite through food organisms or transport prey into the stomach. The actin filament bundles probably play a supporting role as a structural linker between macrocilia and subepithelial muscle fibers and may serve as intracellular tendons lo mechanically coordinate the motor activities of macrocilia and muscles during prey ingestion.
Translational control and the cytoskeleton in Physarum polycephalum
Authors: Brodeur Richard D. , Jeffery William R. 
Published: February 2005

AbstractTranslationally active plasmodia of the syncytial slime mold Physarum polycephalum develop into translationally dormant sclerotia during starvation. Although functional mRNA and ribosomes exist in sclerotia, protein synthesis is suppressed at the level of initiation. To test the possibility that alterations in the cytoskeleton may limit protein synthesis, we have examined the distribution of polysomes and actin mRNA in the cytoskeletal (CSK) and soluble (SOL) fractions of Triton X‐100‐extracted plasmodia and sclerotia. Most of the polysomes and actin mRNA were located in the CSK of plasmodia, while most of the ribosomes and actin mRNA were located in the SOL of sclerotia. The results suggest that ribosomes and mRNA shift from the CSK to the SOL as protein synthesis is suppressed during starvation. Plasmodia and sclerotia can be induced to accumulate excess polysomes by treatment with low levels of the elongation inhibitor cycloheximide. Treatment of plasmodia with cycloheximide caused excess polysomes to accumulate in the SOL, suggesting that the CSK contains a limited capacity for binding translational components and that the association of polysomes with the cytoskeleton is not required for protein synthesis. Treatment of sclerotia with cycloheximide, however, caused polysomes and actin mRNA to accumulate in the CSK, suggesting that the selcrotial cytoskeleton, although depleted in ribosomes and mRNA, is capable of binding translational components. It is concluded that alterations in the sclerotial cytoskeleton are not involved in translational control.
High time‐resolution analysis of transient bending patterns during ciliary responses following electric stimulation in sea urchin embryos
Authors: Baba Shoji A. , Mogami Yoshihiro 
Published: February 2005

AbstractTransient ciliary movement during responses to electric stimulation of embryos of the sea urchin, Hemicentrotus pulcherrimus, was analyzed in terms of angular direction with a time resolution of approximately 2 ms with high‐speed microcinematography. In the primitive response, which can be induced only in the early stages of development of the embryo, bending transients always started with a short pause in the middle of the effective stroke, irrespective of beat position on stimulation. In the reversal response, induced only in the late stages of development, bending transients occurred with a delay as short as some 10 ms from stimulation, and with a transient sharp deviation from the normal beat before the cilium took the position of the beginning of the recovery stroke of the reversed beat. The delay was significantly shorter at the base than at the tip, suggesting that some form of signal travels along the cilium; the speed was ten times higher than that of propagating bends in the normal beat. These facts indicate that the sensitivity to internal changes resulting from stimulation of the axoneme may vary with development, ciliary beat positions, and regions along the cilium.
Movements of intracellular particles in undifferentiated amebae of Dictyostelium discoideum
Authors: Roos U.‐P. , De Brabander M. , Nuydens R. 
Published: February 2005

AbstractWe recorded live, undifferentiated amebae of Dictynstelium discoideum by video microscopy and analyzed the behavior of cytoplasmic particles and granules. Cytoplasmic streaming and saltatory movements are the two major types of particle movements that occur in interphase amebae. Saltatory movements predominated in an area around the nucleus‐associated body (NAB) and many were radial toward or away from it, the velocity being very similar in both directions. Some saltations were simple forward movements, and others were complex to‐and‐fro movements with as many as seven turnabouts. For a given leg of movement the velocity was not uniform along the path. Small particles (< 1 μm) moved faster (X = 2.8 μm/s) than large (∼ 1 μm; X = 2.1 μm/s) and very large (> 1 μm; X = 1.4 μm/s) particles, but the smallest particles were visible only in the running image and could not be analyzed. Ultrastructurally, saltating particles are digestive vacuoles and vesicles of various sizes, appearances, and contents, which are numerous particularly in the vicinity of the NAB. Several lines of evidence pointed to a role of microtubules (MTs) in saltatory particle movements. Composites of particle tracks corresponded closely to MT arrays visualized by immunofluorescence. No saltations occurred in mitotic amebae that lack cytoplasmic MTs, but the movements resumed toward the end of division, concurreduced with the rebuilding of the complex of cytoplasmic MTs. Nocodazole reduced and eventually slopped saltatory movements over a period of 3 h, when aberrant MT patterns were the rule. Saltations in slime mold amebae may be an eye‐catching feature of intracellular transport functioning in endo‐ and exocytosis in the shuffling of vesicles containing factors involved in ameboid movement, and in the transduction of external signals to the cell center.
Isolation and characterization of sea urchin egg spectrin: Calcium modulation of the spectrin–actin interaction
Authors: Fishkind Douglas J. , Bonder Edward M. , Begg David A. 
Published: February 2005

AbstractSea urchin egg spectrin has been purified from a homogenate of unfertilized Strongylocentrotus purpuratus eggs using standard biochemical procedures. SDS‐PAGE analysis of the molecule revealed a closely spaced, high molecular weight doublet at 237/234 kDa (present in an equimolar ratio). Rotary shadowed images of egg spectrin revealed a double‐stranded, elongate, flexible rod‐shaped contour, measuring 210 nm in length and ∼ 4–8 nm in width. Additionally, this molecule is shown to be immunologically related to avian erythroid spectrin, since it cross‐reacts with antibodies prepared against the chicken erythrocyte α‐spectrin/240 kDa subunit. The interaction of egg spectrin with actin was examined by sedimentation and falling‐ball viscometry assays. The binding and cross linking properties of spectrin to actin demonstrate a unique Ca++‐sensitive regulation at micromolar Ca++ concentrations. This observation provides new insight into the way Ca++ may regulate spectrin–actin interactions in vitro and further suggests possible structural and modulatory roles for egg spectrin in the developing sea urchin embryo.
Organization and dynamics of a cortical fibrous network of Paramecium: The outer lattice
Authors: Cohen Jean , de Loubresse Nicole Garreau , Klotz Catherine , Ruiz Françloise , Bordes Nicole , Sandoz Daniel , Bornens Michel , Beisson Janine 
Published: February 2005

AbstractA monoclonal antibody, CC212, raised against ciliated cortices of quail oviduct cells and characterized as an antimyosin of smooth muscle and nonmuscle cells, was shown to specifically label a regular cortical network in Paramecium and to recognize two Triton X‐100–insoluble polypeptides at 130 and 50 kDa. However, no evidence was obtained that these polypeptides are related to myosin.An immunofluorescence study and ultrastructural immunogold localization allowed us to identify the CC212‐decorated material as a component of the outer lattice, a submembrane cytoskeletal network which runs along the top of the ridges visible by scanning electron microscopy and delineates the periphery of each cortical unit. The dynamics of the outer lattice during the cell cycle was studied by immunofluorescence and it was found that the outer lattice growth is achieved without disruption of the preexisting meshes by longitudinal elongation and additon of new transverse partitions. A striking disorganization of the outer lattice was observed in a thermosensitive mutant primarily altered in basal body duplication. These observations suggest possible functions of the outer lattice and demonstrate the interdependence of basal body duplication, surface growth, and outer lattice remodelling.
Frequency and orientation of pseudopod formation of Dictyostelium discoideum amebae chemotaxing in a spatial gradient: Further evidence for a temporal mechanism
Authors: Varnum‐Finney Barbara J. , Voss Edward , Soll David R. 
Published: February 2005

AbstractAmebae of Dictyostelium discoideum normally chemotax to aggregation centers by assessing the direction of outwardly moving, nondissipating waves of the chemoattractant cAMP. However, D. discoideum amebae can also assess the direction of a relatively stable spatial gradient. We demonstrate that amebae migrating towards the “source” of a stable, spatial gradient move faster, extend fewer pseudopodia, and turn less frequently than amebae migrating away from the “source” in the same spatial gradient. In addition, amebae extend lateral pseudopods in a polarized fashion from the anterior half of the cell, and do so as frequently towards the source as away from the source. However, those formed towards the source more often produce a turn than those formed away from the source. These results suggest that there may be two decision‐making systems, one localized in the pseudopods, and one along the entire cell body; they support the suggestion that Dictyostelium amebae may employ a temporal mechanism to assess the direction of a spatial gradient of chemoattractant.
Characterization of the intermediate filament apparatus in skin fibroblasts from patients with giant axonal neuropathy: Effect of trypsin
Authors: Manetti Roberto , Ceccarini Constante , Guazzi Giancarlo , Federico Antonio , Tiezzi Antonio , Bugnoli Massimo , Ceccarini Elvira Costantino 
Published: February 2005

AbstractSkin fibroblasts from two siblings with giant axonal neuropathy (GAN) were examined by both biochemical and immunocytochemical studies. The presence of intermediate filaments (IF) characteristic of these cells was affected by the growth conditions. Immediately after plating and during the following 24 hours the majority of the cells contained an IF “bundle”; however, after 4–6 days in culture only a minority of the cells retained this structure. We present evidence that trypsinization but not serum concentration is likely to influence the formation of the “bundle.” The results indicate that the formation of the “bundle” may result from a defective association or relationship between the cytoskeleton and the plasma membrane.
Motile mechanism of blue damselfish (Chrysiptera cyanea) iridophores
Authors: Oshima Noriko , Fujii Ryozo 
Published: February 2005

AbstractIridophores of the blue damselfish, Chrysiptera cyanea, responded to the sympathetic substance, norepinephrine by a shift towards longer wavelengths of the spectral peak of the light reflected by stacks of light‐reflecting platelets (“coloring response”). All antimitotic reagents tested, i.e., colchicine, vinblastine, and podophyllotoxin, inhibited the response reversibly, while an actin inhibitor, cytochalasin B, did not. Erythro‐9‐[3‐(2‐hydroxynonyl)]adenine (EHNA), a dynein ATPase inhibitor, also blocked the iridophore response effectively. These results indicate that the tubulin‐dynein system may be involved in the motility of iridophores, which is regarded as the simultaneous alteration of the distance between adjacent reflecting platelets within the cells.
Phosphorylation determines two distinct species of tau in the central nervous system
Authors: Papasozomenos Sozos Ch. , Binder Lester I. 
Published: February 2005

AbstractThe monoclonal antibody, Tau‐1, which had previously been used to localize tau to the axonal compartment in brain has been reutilized for light and electron microscopic immunohistochemistry following phosphatase treatment of tissue. We report here that a significant quantity of tau in the central nervous system is phosphorylated in situ at or near the Tau‐1 epitope, preventing the binding of the Tau‐1 antibody. Upon removal of this/these phosphate group(s), however, Tau‐1 was observed in the somatodendritic compartment of neurons as well as in axons. Furthermore, intense staining was also observed in astrocytes and in perineuronal glial cells. This immunoreactivity was present along the lengths of microtubules and on ribosomes (polysomes). Treatment of immunoblots of extracts of whole cerebral cortex with phosphatase confirmed the immunohistochemical results in that a 50–65% increase in Tau‐1 binding to the tau region of the blot was noted. Moreover, a novel monoclonal antibody, Tau‐2, was also used in these experiments. This antibody binds only to tau and localizes along microtubulesin axons, somata, dendrites, and astrocytes and on ribosomes (polysomes) without phosphatase pretreatment.
Structural and chemical characterization of isolated centrosomes
Authors: Bornens Michel , Paintrand Michel , Berges Josette , Marty Marie‐Chantal , Karsenti Eric 
Published: February 2005

AbstractA procedure adapted from that described by Mitchison and Kirschner [Nature 312:232–237, 1984] was used to isolate centrosomes from human lymphoid cells. High yields of homogeneous centrosomes (60% of the theoretical total, assuming one centrosome per cell) were obtained. Centrosomes were isolated as pairs of centrioles, plus their associated pericentriolar material. Ultrastructural investigation revealed: 1) a link between both centrioles in a centrosome formed by the gathering in of a unique bundle of thin filaments surrounding each centriole; 2) a stereotypic organization of the pericentriolar material, including a rim of constant width at the proximal end of each centriole and a disc of nine satellite arms organized according to a ninefold symmetry at the distal end and; 3) an axial hub in the lumen of each centriole at the distal end surrounded by some ill‐defined material.The total protein content was 2 to 3 × 10−2 pg per isolated centrosome, a figure that suggests that the preparations were close to homogeneity. The protein composition was complex but specific, showing proteins ranging from 180 to 300 kD, one prominent band at 130 kD, and a group of proteins between 50 and 65 kD. Actin was also present in centrosome preparations.Functional studies demonstrated that the isolated centrosomes were competent to nucleate microtubules in vitro from purified tubulin in conditions in which spontaneous assembly could not occur. They were also very effective at inducing cleavage when microinjected into unfertilized Xenopus eggs.
Association of intermediate filaments with vinculin‐containing adhesion plaques of fibroblasts
Authors: Bershadsky Alexander D. , Tint Irena S. , Svitkina Tatjana M. 
Published: February 2005

AbstractDouble immunofluorescence staining of quail embryo fibroblasts with rabbit antibody to vinculin and mouse monoclonal antibody to vimentin revealed a coincidence between fluorescence patterns for cell‐substrate focal contacts and intermediate filaments. Most of the vinculin‐containing adhesion plaques coincided with the ends of vimentin‐positive fibrils.This association was further corroborated by immunoelection microscopic observations of the cytoskeletons of quail and mouse fibroblasts using a platinum replica technique. The intermediate filaments were identified either by direct treatment with antivimentin IgM or by an indirect immunogold staining method.Colcemid treatment of the cells caused a collapse of intermediate filaments and destroyed their association with focal contacts. During the early stages of the colcemid‐induced collapse of the intermediate filaments, single vimentin fibrils appeared to retain their association with focal contacts.The possible role of the intermediate filaments in the formation and maintenance of focal contacts is discussed.