bluuebunny/crossref_metadata_2025_split huggingface dataset:
The incorporation of actin and fascin into the cytoskeleton of filopodial sea urchin coelomocytes
Authors: Otto J. J. , Bryan J. 
Published: February 2005

AbstractEchinoderm coelomocytes transform from petaloid cells with large motile lamellipodia to filopodial forms. During this morphological transformation, actin filaments extensively reorganize from a random meshwork into tight bundles, which become the skeletons or cores of the filopodia. Antibody localization procedures show that fascin, a 58,000 dalton actin cross‐linking protein, becomes incorporated into the filament bundles as they form. Isolated filopodial cores have a pronounced transverse striping pattern, which has been previously identified with fascin crosslinks, and gel electrophoresis identifies a protein in the cores that co‐migrates with purified egg fascin. A few of the core fragments also have a distinctive “cap,” which we presume is the membrane insertion site for actin filaments.We have developed a radioimmunoassay for fascin and have used it to study the redistribution of this protein during transformation. Data from the assay indicate that fascin constitutes about 5% of the total cell protein and that substantially more fascin, approximately 1.5–2 times more, is found in the Triton‐insoluble cytoskeletons of the filopodial cells than in the petaloid cells. Actin, measured by the DNAase I inhibition assay accounts for approximately 10% of the total cell protein. Approximately 65% of this actin is in a soluble non‐filamentous form in the petaloid cells. Our results show that actin polymerization must occur during the cell shape change, since we find approximately 25% more actin in the filopodial cytoskeleton than in the petaloid cytoskeleton. The results show a preferential incorporation of fascin into the cytoskeleton as the cells form filopodia.
Does the geometric design of centrioles imply their function?
Authors: Albrecht‐Buehler Guenter 
Published: February 2005

AbstractThe paper suggests several principles of construction of a microscopically small device for locating the directions of signal sources in microscopic dimensions. It appears that the simplest and smallest device that is compatible with the scrambling influence of thermal fluctuations as are demonstrated by Brownian motion is a pair of cylinders oriented at right angles to each other. Nine equally spaced blades run in a pitched fashion along the mantle of each cylinder. The blades have a concave cross‐section and bend around the circumference of the cylinder in a certain rotational pattern. Considering the striking similarity of this hypothetical device with centrioles, the paper puts forward the conjecture that centrioles locate the direction of hypothetical signals inside cells.
Calcium‐induced change in form of demembranated sea urchin sperm flagella immobilized by vanadate
Authors: Okuno M. , Brokaw C. J. 
Published: February 2005

AbstractIncreased Ca2+ concentration causes a reversible increase in asymmetry of the flagellar bending waves of “potentially symmetric” demembranated sea urchin spermatozoa. When these flagella are immobilized with 5 μM vanadate, increased Ca2+ concentration causes a reversible increase in the total bend angle between the tip and the base of the immobilized flagella. These effects of Ca2+, and the movement which can be activated by CaATP2−, can be inhibited by vanadate, but in both cases, high concentrations of vanadate, of the order of 100 μM, are required. These observations suggest that ATP, possibly in the form of CaATP2−, is required for the Ca2+‐induced change in shape of the flagella, but other observations suggest that the magnitudes of asymmetry and total bend angle are more closely related to Ca2+ concentration than to CaATP2− concentration.
Intercellular bridges in the embryo of the atlantic squid, loligo pealei. II: Formation of the bridge
Authors: Cartwright Joiner , Arnold John M. 
Published: February 2005

AbstractIncomplete cytokinesis followed by the disappearance of the midbody and spindle remnant results in intercellular bridges between the cells of the blastoderm of the squid embryo. An electron microscope study of the morphology of the stages of development of the intercellular bridge is presented. Cytokinesis ceased as the furrow base reached a diameter slightly larger than the midbody. As furrowing stopped, a dense material accumulated to form a cylindrical sheath 50 nm thick, lining the inner surface of the furrow base. Proteolytic enzymes showed this material to have a significant protein component. As the midbody broke down, vesicles lined the inner surface of the bridge sheath. In this configuration, there was cyto‐plasmic continuity between the cells, and organelles appeared to pass through the bridge.The intercellular bridge could become temporarily closed. Vesicles entered the channel and fused with the vesicles lining the inner surface of the sheath. The vesicles enlarged until the channel became occluded with a series of transverse cisternae, the edges of which were embedded in the material of the sheath. When the bridge reopened, the transverse cisterna appeared to dissociate from the sheath, move out of the channel, and break down. Occasionally bridges were seen in which the bridge wall appeared distorted into lobes. It is suggested that such bridges might be in the porcess of breaking down, resulting in the final separation of the cells.
A calcium‐ and pH‐regulated actin binding protein from D. discoideum
Authors: Fechheimer Marcus , Brier Jonathan , Rockwell Mark , Luna Elizabeth J. , Taylor D. Lansing 
Published: February 2005

AbstractA protein from Dictyostelium discoideum with an apparent subunit molecular weight of 95,000 daltons (95K protein) was previously identified as an actin‐binding protein ‘Hellewell and Taylor, 1979’. In this paper, we present a method for purifying the protein, and characterize some important aspects of its structure and function. Purification of the 95K protein is achieved by fractionation with ammonium sulfate followed by chromatography on DEAE‐cellulose, gel filtration on 6% agarose, and final purification on hydroxyapatite. The 95K protein is a dimer, composed of apparently identical subunits. It is a rod‐shaped molecule, 38 nm in length, with a Stokes radius of 74 Å. In these structural properties, the 95K protein is similar to muscle and nonmuscle α‐actinins. The 95K protein and filamin are equally competent, when compared on a weight basis, to enhance the apparent viscosity of actin as determined by falling ball viscometry. The apparent viscosity of mixtures of the 95K protein and actin is dramatically reduced at pH greater than 7.0 or free ‘Ca2+’ greater than 10−7 M. We also examine the mechanism by which calcium regulates the interaction of the 95K protein and actin. A change in free ‘Ca2+’ induces no detectable change in the quaternary structure of the 95K protein. Our experiments indicate that the 95K protein does not dramatically alter the length distribution of actin filaments in the presence of micromolar free ‘Ca2+’. A large fraction of the 95K protein cosediments with actin in the presence of low free ‘Ca2+’ (ca. 3 × 10−8M), but not in the presence of high free ‘Ca2+’ (ca. 4 × 10−6M). We conclude that increased free ‘Ca2+’ inhibits gelation of actin by the 95K protein by reducing the affinity of the 95K protein for actin. We propose that 95K protein is an important component of the cytoskeletal/contractile system in D. discoideum amoebae.
Novel Forms of epithelial cell motility on collagen and on glass surfaces
Authors: Tchao R. 
Published: February 2005

AbstractThe motility of an epithelial cell line NBT‐II derived from a rat bladder tumor was examined on glass and on collagen. On glass the cells rotate in groups of 2–8 cells. Rotatory migration ceases as cells enter into mitosis; after mitosis, the daughter cells spread out and participate in the rotatory activity of the group. As the number of cells in a group increases the rate of rotatory migration slows, and groups with ten cells or more do not rotate consistently. On collagen NBT‐II cells migrate as single cells in a smooth gliding fashion, with the broad lamellipodia as the leading front. After mitosis, the two daughter cells separate at 180° of each other and migrate away independently. Before totally spreading out on the collagen surface, the pair of daughter cells shows a characteristic twist of about 60° from their original position at telophase. The difference in motility of NBT II cells on glass and on collagen is explained in terms of differences in cell‐to‐cell cohesion and cell‐to‐substrate adhesion.
The structural properties and contractile force of a clot
Authors: Jen Chauying J. , McIntire Larry V. 
Published: February 2005

AbstractWhen citrated plasma is recalcified, it forms a viscoelastic gel–a clot. The relationship between platelet contractility and clot rigidity was studied by using a rheological technique which simultaneously measured both the dynamic rigidity modulus and the contractile force during gel formation with platelet rich plasma (PRP). Protein network formation in a clot was accompanied by a contractile force throughout the clotting process. PRP demonstrated a maximum elastic modulus of 6,000 dynes/cm2 and a maximum contractile force/area of 1,500 dynes/cm2. The values of these parameters for a platelet‐free clot (PFP) were 700 dynes/cm2 and less than 100 dynes/cm2 respectively. Sonicated control PRP and PRP from a Glanzmann thrombasthenia patient both clotted in a manner similar to PFP. Metabolic inhibitors, 2‐deoxy‐D‐glucose and KCN (5 mM each), retarded the clotting curves of PRP. Cytochalasin B and E suppressed both structural rigidity and force generation in a concentration‐dependent manner similar to their inhibitory effect on actin polymerization in platelets. Colchicine (2.5 mM) or vinblastine (0.11 mM) did not affect these clotting curves. Thrombi‐activated, fixed platelets did not generate any force, nor did they significantly increase clot rigidity. Streptokinase induced a concurrent decrease of both rigidity and force in PRP clots. The elastic modulus of a PFP clot could be increased to 2,500 dynes/cm2 by externally straining the network with an axial force/area of 1,500 dynes/cm2. Our results indicate that clot structure formation in PRP is strongly coupled to the contractile force generated by the platelet microfilament system and that this force modulates clot rigidity.
Cytoplasmic transport in keratocytes: Direct visualization of particle translocation along microtubules
Authors: Hayden John H. , Allen Robert D. , Goldman Robert D. 
Published: February 2005

AbstractWe report the first direct demonstration that the cytoplasmic transport of organelles and vesicles (collectively called particles) takes place along microtubules. Living keratocytes from the corneal stroma of the frog, Rana pipiens, were observed with Allen video‐enhanced constrast, differential interference constrast (AVEC‐DIC) microscopy [Allen et al, 1981]. In sufficiently thin regions of these cells a network of linear elements was visible. When particles were observed in motion, they always moved along these linear elements. The linear elements remained intact and in focus on the microscope when lysed in a cell lysis solution that stabilized microtubules. Preparations were then fixed in formaldehyde, washed with phosphate‐buffered saline (PBS), incubated with rabbit antitubulin, washed with PBS, stained with rhodamine‐conjugated goat antirabbit, and washed with PBS. The extracted cells continued to remain in place and in focus on the microscope throughout these procedures. The same cells were then observed using epifluorescence optics and a silicon‐intensified target (SIT) video camera. A network of fluorescent linear elements was seen to correspond in number, form, and position to the linear elements seen in the live AVEC‐DIC image. Taken together, the AVEC‐DIC and fluorescence microscopy observations prove that the linear elements along which particles move are microtubules (MTLEs). The observed particle speeds, pause times, and distances moved varied widely, even for the same particle on the same microtubule. Particles were also observed to switch from one microtubule to another as they were transported. The polarity of the microtubules did not seem to affect the particle direction, since particles were observed to move in both directions on the same MTLE. When not in motion these particles behaved as if anchored to the microtubules since they showed negligible Brownian motion. Finally, it was observed that an elongate particle could move onto two intersecting linear elements such that it was deformed into an inverted “Y” shape. This indicates that there may be more than a single site of attachment between the force generator and the particle.
Invited review: Bacterial flagellar sheaths: Structures in search of a function
Authors: Sjoblad Roy D. , Emala Charles W. , Doetsch Raymond N. 
Published: February 2005

AbstractAlthough bacterial flagellar sheaths were observed over 30 years ago, they may still be characterized as structures in search of a function. In addition to true sheaths, bacterial flagella may possess other adornments that cause an increase in the organelle's cross‐sectional diameter. These “complex flagella” are sharply differentiated from sheathed flagella. Immunological and chemical distinctions have been found between flagellar sheaths, flagellar cores, and LPS layers inferred to be the sheath sensu stricto. Although complex flagella may serve as specific receptors for flagellotropic phages or in allowing for more efficient swimming in viscous environments, similar functions have not yet been attributed to true sheaths. It is postulated that flagellar sheaths may allow for specific interaction between a bacterium and a surface. In addition, there is a problem as to the relationship between a rapidly rotating flagellum and the sheath.
Bending patterns of chlamydomonas flagella I. Wild‐type bending patterns
Authors: Brokaw C. J. , Luck D. J. L. 
Published: February 2005

AbstractUsing a uniflagellate mutant of Chlamydomonas and flash photomicrography at 300 Hz, we have obtained detailed information on the forward and reverse beating modes of Chlamydomonas flagella and on the relationship between rotation of the uniflagellate cell and the bending cycle of the forward mode. Flagella ranging in length from 5 to 15.5 μm were photographed. There is a decrease in wavelength and an increase in curvature in the principal bends when the length of the flagellum is less than the normal length of 12–13 μm, but these changes are not sufficient to maintain similarity of the bending pattern. In the reverse mode, the flagellum propagates symmetrical, planar, undulatory waves with a shear amplitude which is the same as in the forward mode: there is a 19% increase in beat frequency and a similar decrease in wave length. The reorientation of the flagellar beat direction towards the axis of the cell in the reverse mode is caused both by the decrease in asymmetry of beat and by activation of sliding in the principal bends at an earlier time in the beat cycle, relative to the time of activation of sliding in reverse bends. There are additional rare modes of beating which may be related to intermediate stages in the transition between forward and reverse beating modes.
Cell motility and microtubules in cultured fibroblasts from patients with Kartagener syndrome
Authors: Walter Robert J. , Malech Harry L. , Oliver Janet M. 
Published: February 2005

AbstractPatients with Kartagener syndrome (KS) show defects in ciliary and flagellar movement that are usually associated with the partial or total absence of dynein side arms from axonemal microtubules. Dynein is essential for such movements, but its involvement in other cellular (particularly microtubule‐related) processes is unknown. It has recently been reported that neutrophils from KS patients show impaired motility including responses to chemotactic stimuli, suggesting that dynein‐like proteins may be generally involved in motile processes. In support of this, we have now found that spontaneous motility of cultured skin fibroblasts from KS patients is also markedly impaired. Three cell lines derived from skin explants of KS patients with deficient dynein side arms in nasal cilia and eight cell lines derived from normal volunteers were studied. Fibroblasts were seeded into dishes containing colloidal gold‐coated cover glasses [Albrecht‐Buehler, 1977], incubated for 24 h at 37°C, and the area of cell “phagokinetic” tracks determined.Each cell line studied in this manner reproducibly displayed an amount of spontaneous motility characteristic for that cell line. The mean track area (± SE) for all control cells studied was 14.6 ± 0.5 × 103μm2 whereas for KS fibroblasts was 8.7 ± 0.4 × 103μm2 (P < 0.001). Immunofluorescence microscopy using antitubulin and antihuman 210 K MAP antibodies revealed no differences in the staining patterns between control and KS fibroblasts. Pinocytic rates were identical, and the complement of tubulin and major microtubule associated proteins as seen on one‐dimensional SDS polyacrylamide gel autoradio‐graphs appeared similar for control and KS cells. Thus, the observed motility defect is probably not the result of alterations in the occurrence or distribution of microtubules or in the occurrence or binding of the major microtubule‐associated proteins. This defect in cellular motility may be related to the absence of dynein or may reflect another independent cellular defect.
Organization of interdoublet links in tetrahymena cilia
Authors: Warner Fred D. 
Published: February 2005

AbstractCiliary axonemes from Tetrahymena extracted by KCl to remove the dynein arms reveal an orderly array of interdoublet links connecting adjacent A‐B or A‐A subfibers. The links repeat every 96 nm at a stable site on the A subfiber positioned near the bases of radial spokes 2 and 3. Both links and radial spokes are in lateral register across the nine successive doublets of unbent axonemes. In contrast, bent axonemes or those reactivated by ATP to undergo partial sliding disintegration exhibit systematic displacement of the interdoublet links. The links show no evidence of having elastic or other extendable properties and, therefore, must have undergone intermittent attachment with nonstructural binding sites on the adjacent subfiber. These observations suggest a more dynamic role for the interdoublet links in ciliary motion than previously has been envisioned.
Changes in cytoskeletal proteins of polymorphonuclear leukocytes induced by chemotactic peptides
Authors: Fechheimer Marcus , Zigmond Sally H. 
Published: February 2005

AbstractChanges in the state of polymerization of actin and phosphorylation of myosin have been observed in polymorphonuclear leukocytes (PMNs) soon after the addition of the chemotactic peptide N‐formylnorleucylleucylphenylalanine. At a time when the cells are observed to extend many ruffles or lamellipodia from their surface, the fraction of the cellular actin present in a monomeric form is decreased by about 25% as assayed by the ability of the G‐actin to inhibit DNAase. These changes are temporally correlated with an increase in the staining by nitrobenzooxadiazole (NBD)‐phallacidin, a probe that binds F‐actin selectively. The NBD‐phallacidin staining is observed in the surface ruffles. When the peptide concentration is decreased by addition of a tenfold excess of buffer, cells withdraw their surface ruffles and form blebs. These changes correlate with an increase in the G‐actin levels detected with the DNAase inhibition assay. An increase in phosphorylation of the 20,000‐dalton light chain of myosin is also observed in leukocytes stimulated by addition of chemotactic peptide. These observations of changes in cytoskeletal proteins of PMNs provide a beginning for further studies on the regulation of cell motility by chemotactic factors.
Rheological properties of living cytoplasm: A preliminary investigation of squid axoplasm (Loligo pealei)
Authors: Sato Masahiko , Wong Terence Z. , Brown Douglas T. , Allen Robert D. 
Published: February 2005

AbstractA magnetic sphere viscoelastometer has been developed to peform rheological experiments in living axoplasm of Loligo pealei. The technique includes the use of a calibrated magnetic sphere viscoelastometer on surgically implanted ferro‐magnetic spheres in intact squid giant axons. The axoplasm was discerned to be “living” by the biological criterion of tubulovesicular organelle motility, which was observed before and after experimentation. From these in vivo experiments, new structural characteristics of the axoplasm have been identified. First, analysis of magnetic sphere trajectories has shown the axoplasm to be a complex viscoelastic fluid. Directional experimentation showed that this material is structurally anisotropic, with a greater elastic modulus in the direction parallel to the axon long axis. Second, both magnetic sphere and in vivo capillary experiments suggested that the axoplasm is tenaciously anchored to the axolemma. Third, it was found that axoplasm could be modelled as a linear viscoelastic material in the low shear rate range of 0.0001 to 0.004 s−1. The simplest mechanical model incorporating the discovered properties of the material in this range is Burger's model.
Induction of shape transformation in sea urchin coelomocytes by the calcium ionophore A23187
Authors: Hyatt Hilary A. , Shure Michael S. , Begg David A. 
Published: February 2005

AbstractWe have investigated the ability of the Ca+ + ionophore A23187 to induce the transformation of petaloid sea urchin coleomocytes to the filopodial form. The response of individual cells to different media was observed with time‐lapse phasecontrast video microscopy. In the presence of 1 mM CaCl2, isotonic medium containing 1–5 μM A23187 produces a similar shape transformation to that caused by hypotonic shock. Higher concentrations of ionophore (10–20 μM) induce the formation of filopodia that are thinner and less rigid than those generated by hypotonic shock or low doses of ionophore. A23187 also induces shape transformation in highly flattened cells that do not respond fully to hypotonic shock. The induction of cytoplasmic alkalinization by NH4Cl, methylamine‐HCl, or the Na+ ionophore monensin does not induce shape transformation, suggesting that increased intracellular pH is not the stimulus for this process. Ultrastructural changes in cytoskeletal organization were examined in negatively stained detergent‐extracted cells. Low doses of ionophore produce filopodia that are indistin‐guishable from those of hypotonically shocked cells, with actin filament bundles that are straight and cohesive along their entire length. High concentrations of ionophore produce filopodia with filament bundles that branch repeatedly and splay apart near their tips, forming loops and irregular curves. These results suggest that an increase in intracellular free Ca+ + concentration acts as the trigger that stimulates coelomocyte shape transformation, but that abnormally high concentrations of intracellular Ca+ +, produced by high doses of ionophore, interfere with actin filament bundling.