bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of fibrinogen derivatives in the triton‐insoluble residue of human blood platelets
Authors: Casella J. F. , Masiello N. C. , Lin S. , Bell W. , Zucker M. B. 
Published: February 2005

AbstractSeveral proteins (eg, actin, myosin, and actin‐binding protein) in the Tritoninsoluble residue of thrombin‐stimulated platelets are important in the formation of cytoskeletal structures. Electrophoretic analyses have shown that unidentified protein bands of 68,000, 55,000, and 48–50,000 daltons are also present in larger amounts after thrombin stimulation. Since these molecular weights correspond roughly to those of the α, β, and γ chains of fibrin, and since fibrinogen is found in platelet α‐granules, these bands were compared to those obtained when purified fibrinogen was treated with thrombin, exposed to 1% Triton X‐100‐5 mM EGTA, and the resultant Triton‐insoluble residue sedimented. Identification of the 68,000‐, 55,000‐, and 48‐‐50,000‐dalton bands as fibrinogen derivatives was confirmed by identifying them in comigration studies and in autoradiographs of Triton‐insoluble residues of platelets that were electrophoretically transferred to nitrocellulose paper and treated with antifibrinogen antibody and 125I‐protein A. Furthermore, if the platelet suspension was treated with thrombin in the presence of calcium ions, protein bands characteristic of the action of Factor XIII on fibrin were observed, active platelet Factor XIII apparently having been made available by lysis of platelets during preparation. Making use of the electrophoretic properties of tubulin recently described by Best et al [1981], comigration studies using hog brain tubulin indicated that tubulin is not present in significant amounts in the Triton‐insoluble residue of platelets as previously suggested. The identification of these proteins as fibrinogen derivatives does not demonstrate a physiological interaction between fibrin and the platelet cytoskeleton, since fibrin is Tritoninsoluble and can be pelleted even in the absence of platelet cytoskeletons.
Flagellar rootlets as myonemal elements for pusule contractility in dinoflagellates
Authors: Cachon Jean , Cachon Monique , Boillot Annie 
Published: February 2005

AbstractFlagellar rootlets play an important role in “primitive motile systems.” They are made of filaments able to contract by twisting and Ca+2 binding. The pusules of Dinoflagellates appear to be under the control of large bundles of 2.4 nm nonactin filaments that correspond to the striated rootlets of their two flagella.
Nocodazole pretreatment in anaphase selectively reduces anaphase B in PtK1 cells
Authors: Snyder Judith A. , Vogt Sandra I. , McLelland Sandra L. 
Published: February 2005

AbstractDuring early anaphase PtK1 cells were briefly treated with the rapidly reversible microtubule (MT) poison nocodazole. This treatment abruptly stopped chromosome motion and effected a large decrease in spindle birefringence. On removal of the drug, chromosome to pole motion (anaphase A) returned, though at a lesser rate but not extent than untreated cells. In most cases elongation of the pole‐pole distance (anaphase B) also occured, at both a rate and to an extent less than in untreated cells. During the recovery period following drug arrest spindle birefringence did not return to pretreatment levels. Electron microscopic analysis of nocodazole arrested, or arrested and released, cells revealed extensive disassembly of the nonkinetochore class of MTs (nkMTs), particularly evident in the astral region. Microtubules seen in the interzone region were largely fragments of midbody precursors. Kinetochore MTs (kMTs) appeared to be unaffected by the brief drug treatment chosen for these experiments. Analysis of MT profiles seen in transverse sections of the interzone region indicated in treated and released cells approximately 60% fewer MTs. This may suggest that chromosome motion during anaphase is not dependent on interactions between kMTs and nkMTs and separation of the spindle poles can occur in the presence of disrupted interzonal MTs.
Effects of villin on the polymerization and subunit exchange of actin
Authors: Wang Yu‐Li , Bonder Edward M. , Mooseker Mark S. , Taylor D. Lansing 
Published: February 2005

AbstractWe have investigated the Ca2+‐dependent interactions of villin, a protein of the intestinal microvillar core, with actin by monitoring resonance energy tranfer between fluorescently labeled actin subunits. In the presence of elevated free Ca2+(∼20 μM), villin affects both the nucleation and the elongation phases of actin polymerization. Consistent with previous reports, villin stimulates the nucleation process and will form stable nuclei under depolymerization conditions. Compared to the control, the net rate of polymerization is slightly inhibited at low con‐centrations of villin (villin/actin ∼ 1:400) but is stimulated at higher concentrations (villin/actin > 1:100). Villin also significantly increases the critical concentration of actin polymerization. Addition of either villin or villin‐actin complexes induces depolymerization of preassembled actin filaments. This villin‐induced depolymerization is reversible upon removal of free Ca2+ or upon the addition of phalloidin. The exchange of actin subunits at steady state is inhibited at low concentrations of villin (villin/actin ∼ 1:200) but is stimulated at higher concentrations (villin/actin ∼ 1:50). None of the above effects is observed at < 10−8 M free [Ca2+].
Quantitative analysis of axonemal bends and twists in the quiescent state of ciona sperm flagella
Authors: Omoto C. K. , Brokaw C. J. 
Published: February 2005

AbstractA simple planar model of sliding can predict the amount of sliding required to form a certain degree of bend. The accuracy of this prediction relies on the assumptions that no twists occur in the axoneme and that no sliding occurs at the base. However, previous studies indicated that twists may occur.This paper explores a new method for quantitating and analyzing twists. Preliminary results using this method showed that there were twists. In order to control for possible artifacts due to fixation and other preparative procedures, the characteristic S‐shaped quiescent state of Ciona spermatozoa was studied.Analyses of platinum replicas of those flagella in which this waveform is well preserved suggest that most, if not all, of the twists observed are due to the artifact of a curved shape settling onto a surface. Detailed analyses indicate that if twists do occur in quiescent sperm, they are probably less than 0.4 radian. Since axonemes are evidently easily twisted in rigor, and even after fixation, caution should be exercised in interpretation of axonemal twists.
Effects of folic acid upon filopodia of Dictyostelium discoideum vegetative amoebae
Authors: Rifkin Jared L. , Isik Ferda 
Published: February 2005

AbstractLiving vegetative D. discoideum amoebae were studied to determine whether their filopodia respond to folic acid, a chemoattractant for these cells. Exponentially growing amoebae (ca. 10 μm diameter) exhibit 5–30 μm long filopodia; at stationary phase, aggregation competent amoebae have numerous multibranched filopodia up to 100 μm long. Folic acid was observed to stimulate production, elongation, and branching of filopodia with its effects progressively changing as the amoebae approach aggregation. Filopodial construction was also found to be dependent upon Mg2+ levels. The significance of these results is discussed with respect to progressive changes within the vegetative phase as well as to the mechanisms of amoeboid movement, pseudopodial activity, and chemotaxis.
Light microscopic observations on the release of vesicles by isolated chromaffin cells
Authors: Edwards Charles , Englert David , Lotshaw David , Ye Han Zhang 
Published: February 2005

AbstractCultured bovine adrenal medullary chromaffin cells were stimulated with the secretogogues Ba2+ or carbamyl choline plus Ca2+. With video‐enhanced contrast, differential interference contrast microscopy, small vesicles were found to appear on the cell surface during stimulation. The structures were of lower refractive index than the cytoplasm, and their appearance required several tenths of a second. The vesicles are thought to correspond to omega figures seen with electron microscopy due to exocytosis. Many of the structures disappeared within a few seconds, but some appeared to coalesce into larger structures. The large structures may lead to the vacuoles that have been demonstrated to be present following stimulation. The nature of the cellular elements responsible for the vesicle which appeared on the surface was not found with either differential interference or interference reflection microscopy. The simplest explanation is that the refractive index of the elements is similar to that of the cell, and therefore the elements cannot be seen.
Microtubule crossbridging by Chlamydomonas dynein
Authors: Haimo Leah T. , Fenton Raymond D. 
Published: February 2005

AbstractDynein, obtained from axonemes of Chlamydomonas, binds by both its A and B ends to microtubules assembled from twice cycled (2 ×) and purified (6S) brain tubulin as well as to microtubules in native spindles, thereby inducing microtubule crossbridging. The two ends of the dynein arm exhibit distinct binding characteristics for the different microtubule preparations. Greater than 99% of the dynein arms are bound exclusively by their B ends to microtubules assembled from 6S tubulin in the presence of dynein and decorated to saturation. In contrast, greater than 80% of the dynein arms are bound by both their A and B ends to and, therefore, crossbridge 6S microtubules that are only partially dynein decorated. Binding of the A end of the dynein arm to saturated 6S microtubules can be enhanced by destabilizing the binding of the B end upon addition of ATP and vanadate. These observations suggest that Chlamydomonas dynein arms can bind by their A ends to microtubules assembled from 6S tubulin only when the B ends of the arms either are not bound or are bound but do not occupy all available dynein binding sites. Dynein exhibits a slight preference for binding by its A end to microtubules assembled from 2 × tubulin and containing microtubule associated proteins (MAPs). Approximately 90% of the dynein arms crossbridge adjacent 2 × microtubles that are only partially decorated. But as saturation of these microtubules with dynein is approached, the majority of the arms are bound solely by their A ends, while a smaller percentage are bound by their B ends or by both their A and B ends. These studies indicate that the type of microtubule as well as the degree of saturation of the microtubule with dynein can determine whether microtubule crossbridging occurs.
Time course of the motion of bull sperm flagella
Authors: Mulready Deborah E. , Rikmenspoel Robert 
Published: February 2005

AbstractDetailed measurements were made of the time course of the motion of bull spermatozoa. Fourier analysis of the data showed the time course to be basically sinusoidal within 2% to 3%. An asymmetry in the motion was present, resulting in a second harmonic component in the Fourier spectra of normal sperm of approximately 11% of the main component. When the energy metabolism of the sperm was inhibited or when the external viscosity of the medium was raised, the asymmetry was reduced. When the internal Mg2+ content of the sperm was lowered, the asymmetry was increased. The asymmetries and the corresponding second harmonic components in the Fourier spectra were correlated with the overall bend shape of the sperm and with the curvature of the path in which the sperm were swimming. Model calculations showed that the asymmetry could reside in either the internal active moments in the sperms or in the stiffness of the sperm fiagella.
Automated methods for estimation of sperm flagellar bending parameters
Authors: Brokaw Charles J. 
Published: February 2005

AbstractParameters to describe flagellar bending patterns can be obtained by a microcomputer procedure that uses a set of parameters to synthesize model bending patterns, compares the model bending patterns with digitized and filtered data from flagellar photographs, and uses the Simplex method to vary the parameters until a solution with minimum root mean square differences between the model and the data is found. Parameters for Chlamydomonas bending patterns have been obtained from comparison of shear angle curves for the model and the data. To avoid the determination of the orientation of the basal end of the flagellum, which is required for calculation of shear angles, parameters for sperm flagella have been obtained by comparison of curves of curvature as a function of length for the model and for the data. A constant curvature model, modified from that originally used for Chlamydomonas flagella, has been used for obtaining parameters from sperm flagella, but the methods can be applied using other models for synthesizing the model bending patterns.
Reorientation of the golgi apparatus and the microtubule‐organizing center inside macrophages subjected to a chemotactic gradient
Authors: Nemere Ilka , Kupfer Abraham , Singer S. J. 
Published: February 2005

AbstractMouse peritoneal macrophages subjected to gradients of activated mouse serum were found by immunofluorescence observations to have their Golgi apparatus and their microtubule‐organizing center largely oriented in the direction of the gradient. By analogy with similar results obtained with motile fibroblasts, it is proposed that these two organelles are rapidly and coordinately reoriented inside the macrophages in order to direct the insertion of new membrane mass, via vesicles derived from the Golgi apparatus, into the leading edge of the cell. Consistent with the importance of such membrane insertion to cell migration, we found that the ionophore monensin, an inhibitor of Golgi functions, inhibited cell motility in the chemostactic gradient. It was further shown that several inhibitors of chemotaxis (monensin, cytochalasin D, cycloheximide) did not inhibit the reorientation of the Golgi apparatus/microtubule‐organizing center in cells exposed to a chemotactic gradient, and that the reorientation required extracellular Ca+2.
An EHNA‐senstive ATPase in unfertilized sea urchin eggs
Authors: Penningroth Stephen M. , Rose Patricia , Cheung Anne , Peterson Dolores D. , Rothacker Dana Q. , Bershak Patricia 
Published: February 2005

AbstractIn current purification strategies, affinity for microtubules or calmodulin is used to identify and purify cytoplasmic dynein‐like ATPase from cell‐free extracts of unfertilized sea urchin eggs. However, affinity purification procedures, though they define dynein‐like ATPase activity, have not yet proven to be quantitative. An alternative purification strategy capable of producing a high yield of enzyme would require a specific assay in order to monitor cytoplasmic dynein purity at each step.In this study, we make a detailed comparison of the effects of EHNA on 22 different ATP‐metabolizing enzyme activities, including 13 Mg++‐ATPases. We isolate cytoplasmic dynein‐like ATPase activity from three species of sea urchin eggs and sperm and show by means of dose‐response curves that their sensitivities to inhibition by EHNA are very similar to one another. We demonstrate further that the EHNA dose‐response characteristics of fourteen other ATP‐metabolizing enzyme activities, including seven nondynein Mg++‐ATPases, differ quantitatively from those of dynein‐like ATPases.In studies of three other agents (vanadate, Ca++/calmodulin, and Triton X‐100), we find that dynein‐like ATPases vary by two orders of magnitude in their sensitivities to inhibition by vanadate, and little or no stimulation by either Ca++/calmodulin or Triton X‐100 is seen. Our results suggest that inhibition by EHNA is a universal and specific property of dynein‐like ATPases, which ultimately should prove useful in the quantitative purification and characterization of cytoplasmic dynein‐like ATPase (s).
An investigation of the involvement of cytoskeletal structures and secretion in gliding motility of the marine diatom, Amphora coffeaeformis
Authors: Webster Daniel R. , Cooksey Keith E. , Rubin Robert W. 
Published: February 2005

AbstractGliding motility was investigated in the marine diatom, Amphora coffeaeformis. Ultrastructural, biochemical, and pharmacological protocols were employed to probe the possible involvement of cytoskeletal proteins and a secretory process in gliding motility. Motility rate was measured using a video recording apparatus, and the effects of various cytoskeleton‐disrupting drugs on motility were tested. Cytochalasins D and E, podophyllotoxin, and vinblastine (all at 25 μUg/ml) reversibly inhibited motility, as did monensin (10 μUM) and pronase (25 μUg/ml). Biochemical protein analysis of whole‐cell extracts by one‐ and two‐dimensional polyacrylamide gel electrophoresis revealed polypeptides comigrating with rabbit skeletal muscle actin and bovine brain tubulin; however, specific assays used to separate actin from whole‐cell preparations gave ambiguous results. Ultrastructural studies revealed the presence of extracellular material between the raphe canal and the substratum in motile cultures. An assay was devised for the detection of radioactively labeled material (MW > 1800 Daltons) released by motile cultures into the culture medium. When cultures were treated with either an anticytoskeletal drug or monensin, motility was inhibited while the amount of measured radioactivity increased over solvent‐treated control groups. The results from this study indicate possible roles for both actin‐ and tubulin‐based structures in gliding motility of Amphora. Though secretion may be necessary for gliding to occur, its exact relationship to motility was not deduced. The data obtained in this study are compatible with a theory for the mechanism of gliding which involves the surface translocation of externally exposed membrane proteins against an immobile matrix of substratum‐attached secreted material to generate the force required for movement.
Ionic control of locomotion and shape of epithelial cells: I. Role of calcium influx
Authors: Mittal Ajay Kumar , Bereiter‐Hahn Jürgen 
Published: February 2005

AbstractThe role of calcium in the induction of locomotion, control of direction of locomotion, and modulation of shape of epithelial cells derived from Xenopus laevis tadpole epidermis is investigated. Local influx of calcium is achieved by electrophoretic release of small amounts of calcium from a micropipette (tip diameter 0.1–0.5 μUm) closely apposed to the cell body or lamella. The cells are made permeable for calcium by calcium ionophore A23187, and they are kept in Ca++‐free, Mg++‐rich EGTA Ringer. Another method used to induce Ca++ influx is local application of A23187 while cells move in normal culture medium.Influx of Ca++ into the lamella induces a localised increase in thickness and enlargement of the lamella. Stationary cells become active and show movement in the direction of the Ca++ gradient. Fried‐egg‐shaped cells tend to acquire a semicircular shape and start moving. Moving cells change the direction of their locomotion, following the direction of Ca++ release. Influx of Ca++ in the cell body region induces its contraction concomitant with an increase in lamellar area.These observations suggest the presence of two different Ca++‐sensitive components: an actomyosin meshwork in the cell body and an actin gel in the lamella. Influx of Ca++ induces contraction of actomyosin and solation of actin gel. Interaction of these two systems would explain modulation of shape and generation of locomotion in epithelial cells.
High‐speed cinematographic analysis of the movement of Chlamydomonas
Authors: Rüffer U. , Nultsch W. 
Published: February 2005

AbstractUsing high‐speed microcinematography (100–500 f/s) the movement of Chlamydomonas reinhardtii mutant 622 E has been studied with frame‐by‐frame analysis. The stigma lies in the cell equator, displaced out of the flagellar plane anticlockwise by an angle of about 45°. During forward movement the cells rotate anticlockwise about their long axis with a frequency of 1.4–2 Hz (maximum 2.5 Hz). The rotation is caused by a lateral component of 3‐dimensional beating of the flagella during the effective strokes. The helical swimming path is a result of an unequal flagellar beating. This is normally synchronous, but synchrony is interrupted from time to time by an additional beat of the outward directed flagellum, in our study one after about every twenty beats on average. These results are discussed and compared with the results published by other groups.
A versatile and quantitative computer‐assisted photoelectronic technique used for the analysis of ciliary beat cycles
Authors: Sanderson Michael J. , Dirksen Ellen R. 
Published: February 2005

AbstractThe beat cycles of rabbit tracheal cilia in culture and Mytilus laterofrontal cirri were recorded using a phototransistor, transillumination, video, and phase‐contrast microscopy. The photoelectronic signal and video image of the ciliary activity were simultaneously recorded as a composite image. The photoelectronic signal was converted into a digital signal by a data acquisition system for further computer processing.By the selection of a small detector area and accurate detector alignment, a simple, repetitive photoelectronic signal representing ciliary activity was obtained. This signal records the ciliary beat frequency and demonstrates the triphasic nature of the beat cycle. The photoelectronic signal can be precisely correlated with the ciliary activity by analysis of the composite video recordings to provide the duration of the effective, recovery, and rest phases of the beat cycle. The videophotoelectronic signal correlations were verified by high‐speed cinematography. High‐speed films of ciliary activity were digitized, and the image density of selected pixels was analyzed by computer with respect to time and ciliary motion.These studies indicate that duration of the phages of the beat cycle are differentially reduced with increased beat frequency; the effective phase duration was quickly reduced to a minimum. This was followed by the reduction of the duration of the recovery phase to a minimum. The rest phase continues to be reduced without reaching a minimum, over the range of beat frequencies observed. These results suggest that ciliary beat frequency may be regulated either by modifying the rates of dynein‐microtubule interactions or the rate of transition from one beat phase to the next.