摘要:

AbstractSpirochetes are a group of bacteria with a unique ultrastructure and a fascinating swimming behavior. This article reviews the hydrodynamics of spirochete motility, and examines the motility of the spirocheteLeptospirain detail. Models ofLeptospiramotility are discussed, and future experiments are proposed.The outermost structure ofLeptospirais a membrane sheath, and within this sheath are a helically shaped cell cylinder and two periplasmic flagella. One periplasmic flagellum is attached subterminally at either end of the cell cylinder and extends partway down the length of the cell. In swimming cells, each end of the cell may assume either a spiral or a hook shape. Translational cells have the anterior end spiral shaped, and the posterior end hook shaped. In the model of Berg et al., the periplasmic flagella are believed to rotate between the sheath and the cell cylinder. Rotation of the anterior periplasmic flagellum causes the generation of a gyrating spiral‐shaped wave. This wave is believed sufficient to propel the cells forward in a low‐viscosity medium. The cell cylinder concomitantly rolls around the periplasmic flagella in the opposite direction—which allows the cell to literally screw through a gel‐like viscous medium without slippage. This model is presented, and it is contrasted to previous models ofLeptospiram

ISSN:0886-1544    

DOI:10.1002/cm.970090202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractDictyosteliumamoebae can migrate in several different modes. We tested for correlations of the direction of cell locomotion with the relative positions of the nucleus and microtubule‐organizing center (MTOC). Five cases were analyzed on electron micrographs with a microcomputer. Each mode of movement showed characteristic locations of the MTOC relative to the nucleus; however, they differed in the various cases. In randomly migrating interphase amoebae, the number of cells with the MTOC located behind the nucleus was twice as great as those with the MTOC located ahead of the nucleus. During chemotactic migration toward folic acid, cells with the MTOC behind the nucleus were more numerous, with a concomitant reduction of anterior MTOCs.When amoebae aggregated on agar plates, a posterior location of the MTOC was most strikingly favored, whereas in cells aggregating under submerged conditions, the MTOC was indifferently anterior or posterior to the nucleus. (It may be significant that EDTA‐resistant cell‐cell adhesion was fully expressed in the former cells, but weaker in the latter.) Finally, in the case of chemotactically migrating cells from dissociated pseudoplasmodia, which adhere by means of other molecules, the MTOC was consistently ahead of the nucleus. Thus the MTOC shows no necessary preferential position anterior or posterior to the nucleus; its position, rather, correlates with the type of migration and perhaps with the nature of cell‐cell a

ISSN:0886-1544    

DOI:10.1002/cm.970090203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractMitotic apparatuses (MAs) isolated from sea urchin metaphase eggs were chilled on ice to depolymerize microtubules, homogenized, and incubated with tubulin. This caused formation of many small asters with microtubules focusing on granules which were probably fragments of the centrosome. The aster‐forming protein components of the granules in the homogenized MAs were solubilized in 0.5 M KCl containing 50% glycerol. After dialysis against low‐ionic‐strength buffer solution, proteins congregated to form granular assembly capable of initiating aster formation. Phosphocellulose column chromatography enabled the separation of the aster‐forming protein fraction which contained a 51,000 molecular weight protein (51‐kd protein) as a major component. The protein fraction possessing the aster‐forming activity was also prepared from methaphase whole egg homogenate, and the elution profile of the 51‐kd protein on phosphocellulose column also coincided with that of the aster‐forming activity. The granular assembly reconstituted from the phosphocellulose fraction formed asters whose microtubules show the same growth rate and length distribution as those of asters reconstructed from the granules in the homogenized MAs. Anti‐51‐kd protein antibody that was raised in rabbit and affinity‐purified stained the center of asters which were reconstructed either from the granules in the homogenized MAs or from the granular assembly reconstituted from the phosphocellulose fraction. These results suggest that the 51‐kd protein is a component in the aster‐forming activity of the centr

ISSN:0886-1544    

DOI:10.1002/cm.970090204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractStudies were conducted to determine if dynein could bind to unpolymerized tubulin. Tubulin alone normally fractionated in the included volume of a molecular sieve Bio‐Gel A‐1.5m column. Incubated together, tubulin and dynein coeluted in the void volumn, suggesting that a complex had formed between the two. In addition, immunoelectron microscopy revealed preassembled microtubules were labeled with biotin antibody only when incubated in both dynein and biotinylated tubulin, evidence that dynein with bound biotinylated tubulin had decorated the microtubules. A fraction of the tubulin could be dissociated from dynein by addition of ATP and vanadate, as assayed by molecular sieve chromatography followed by densitometry of gels, suggesting that some tubulin bound to the B end of the dynein arm. Additional tubulin dissociated from the dynein under conditions of high salt. These studies, together with those indicating that tubulin blocked the A end of the dynein arm from binding to microtubules and promoted the interaction of two arms at their A ends, provide evidence that the A end of the arm also can bind tubulin. Thus, the tubulin subunits, themselves, on a microtubule rather than a particular surface lattice structure formed by adjacent protofilaments may provide the binding sites for both ends of the dynein

ISSN:0886-1544    

DOI:10.1002/cm.970090205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractCell‐surface IgM (antigen receptor) sediments with the membrane fraction following osmotic lysis and homogenization of cells of the human lymphoblastoid cell line WiL2. In nonreducing buffers, SDS PAGE analysis of membrane pellets demonstrates that “native” membrane IgM exists as a dimer. In contrast to osmotic lysis, lysis of cells with the nonionic detergent Triton X‐100 releases approximately 90% of the membrane‐bound IgM into the supernatant; approximately 10% of the IgM pellets with the cytoskeletal fraction on centrifugation. Ligand challenge with either m̈‐chain‐specific antibodies or concanavalin A induces a change in the state of membrane IgM making it refractory to detergent extraction, such that 43% of the IgM pellets during centrifugation. This ligand‐induced retention of IgM is significantly diminished by the microfilament‐disrupting agent cytochalasin D, whereas pretreatment of cells with sodium azide or colchicine results in no significant change in the percentage of membrane IgM retained by Triton X‐100 residues. These results indicate that retention of IgM involves an association with the cortical actin‐based cytoskeleton. Investigation of the structural basis for ligand‐induced Triton X‐100 retention of membrane IgM by using ferritin‐conjugated antibodies, myosin subfragment S1, and stereo‐imaging electron microscopy has revealed linkages between ligand‐receptor (antigen‐IgM) complexes and elements of the

ISSN:0886-1544    

DOI:10.1002/cm.970090206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractActin from sea urchin eggs was fluorescently labeled with fluorescein isothiocyanate (FITC), N‐(7‐dimethylamino‐4‐methylcoumarinyl)‐maleimide (DACM), or 5‐iodoacetamidofluorescein (IAF) and microinjected into sea urchin eggs and oocytes. It distributed evenly in the cytoplasm of unfertilized eggs. Upon fertilization, actin accumulated first around the sperm binding site and, soon afterwards, in the fertilization cone. The accumulation propagated all over the cortex after a latent period of 10–20 sec. In the case ofClypeaster japonicuseggs, propagation of the accumulation coincided with a shape change in the egg, suggesting that the accumulated actin in the cortex generates forces. FITC‐actin was incorporated into microvilli and retained in the cortex after cleavage. On the other hand, DACM‐ or IAF‐actin was not incorporated into microvilli and was dispersed from the cortex by cleavage. These differences may be attributable to differences in the properties of the actins labeled at different sites. After photobleaching by laser light irradiation, FITC‐ or IAF‐actin redistributed in the cortex of fertilized egg as quickly as it did before fertilization. When an unfertilized egg was injected with both actin and a calcium buffer (intracellular free Ca2+concentration 9 μM), the actin accumulation was similar to that during fertilization but without the latent period. This suggests that the accumulation depended on the increase in the intracellular free Ca2+concentration. When the unfertilized egg was injected with 0.2 M EGTA after injection of labeled actin and then inseminated, it accumulated only in the protrusion of cytoplasm where the sperm had entered, and fertilization was not completed. In immature oocytes, the accumulation was observed in the cortical region, including the huge protrusion of the cytoplasm where the sperm had entered. These results suggest that actin accumulation in the sperm binding site plays an important role in the sperm recept

ISSN:0886-1544    

DOI:10.1002/cm.970090207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractCa2+‐ATPase of the sarcoplasmic reticulum was localized in cryostat sections from three different adult canine skeletal muscles (gracilis, extensor carpi radialis, and superficial digitalis flexor) by immunofluorescence labeling with monoclonal antibodies to the Ca2+‐ATPase Type I (slow) myofibers were strongly labeled for the Ca2+‐ATPase with a monoclonal antibody (II D8) to the CA2+‐ATPase of canine cardiac sarcoplasmic reticulum; the type II (fast) myofibers were labeled at the level of the background with monoclonal antibody II D8. By contrast, type II (fast) myofibers were strongly labeled for Ca2+‐ATPase of rabbit skeletal sarcoplasmic reticulum. The subcellular distribution of the immunolabeling in type I (slow) myofibers with monoclonal antibody II D8 corresponded to that of the sarcoplasmic reticulum as previously determined by electron microscopy. The structural similarity between the canine cardiac Ca2+‐ATPase present in the sarcoplasmic reticulum of the canine slow skeletal muscle fibers was demonstrated by immunoblotting. Monoclonal antibody (II D8) to the cardiac Ca2+‐ATPase binds to only one protein band present in the extract from either cardiac or type I (slow) skeletal muscle tissue. By contrast, monoclonal antibody (II H11) to the skeletal type II (fast) Ca2+‐ATPase binds only one protein band in the extract from type II (fast) skeletal muscle tissue. These immunopositive proteins coelectrophoresed with the Ca2+‐ATPase of the canine cardiac sarcoplasmic reticulum and showed an apparent Mrof 115,000. It is concluded that the Ca2+‐ATPase of cardiac and type I (slow) skeletal sarcoplasmic reticulum have at least one epitope in common, which is not present on the Ca2+‐ATPase of sarcoplasmic reticulum in type II (fast) skeletal myofibers. It is possible that this site is related to the assumed necessity of the Ca2+‐ATPase of the sarcoplasmic reticulum in cardiac and type I (slow) skeletal myofibers to interact with phosphorylated phospholamban and thereby enhance the accumulation of Ca2+in the lumen of the sarcoplasmic reticulum following

ISSN:0886-1544    

DOI:10.1002/cm.970090208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractTubulin fromTrypanosoma bruceiwas characterized by Western blotting using well defined monoclonal antibodies reacting with α‐ or β‐tubulin and a new monoclonal antibody, 1B41, raised against a microtubule‐enriched fraction ofT. brucei, which specifically reacts with the β‐subunit of tubulin from eitherT. bruceior rat brain. This antibody has been used to examine the subcellular distribution of the corresponding antigen inT. bruceiby indirect immunofluorescence. The epitope recognized by 1B41 is restricted to a thin line extending from the basal body region to the anterior end of the cell body. To determine the relationship between the immunoreactive zone and the flagellum, double‐label immunofluorescence was performed in both interphase and mitotic cells with 1B41 and a flagellar marker, the monoclonal antibody 5E9, specific for the paraflagellar rod polypeptides of trypanosomes. These experiments revealed that the immunoreactive tubulin was contained in a part of the subpellicular cytoskeleton that remained in a constant spatial correspondence with the flagellum throughout the cell division cycle. The β‐tubulin recognized by 1B41 may be segregated into the microtubular structures associated with a cisterna of the endoplasmic reticulum forming thesubflagellar microtubule quartet(SFMQ). These results suggest that the presence of an antigenically unique β‐tubulin defines a subpopulation of microtubules possessing specfic dynamic properties that may be involved in the morphogenesis of daughter cells during the di

ISSN:0886-1544    

DOI:10.1002/cm.970090209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractChemotactic factors stimulate the rate of locomotion of polymorphonuclear leukocytes (PMNs). To investigate the importance of cytoplasmic calcium we have examined the ability of the chemotactic peptide N‐formylnorleucyl eucylphenalanine (FNLLP) to stimulate the locomotion of PMNs whose cytoplasmic calcium levels were reduced by incubation in EGTA or in EGTA plus the calcium ionophores, ionomycin or A23187. Locomotion was assayed by migration through micropore filters and by time‐lapse videomicroscopy. Cells in EGTA exhibited similar or slightly reduced rates of locomotion compared to cells in Hanks' balanced salt solution (HBSS). The peptide dose dependence for the stimulation of locomotion was similar in medium containing calcium or EGTA. The presence of 1 μM ionophore plus EGTA had no effect on the stimulation of locomotion by peptide. The presence of ionophores (1 μM) plus external calcium inhibited locom

ISSN:0886-1544    

DOI:10.1002/cm.970090210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0886-1544    

DOI:10.1002/cm.970090201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY