摘要:

AbstractThe latrunculins are architecturally novel marine compounds isolated from the Red Sea spongeLatrunculia magnifica. In vivo, they alter cell shape, disrupt microfilament organization, and inhibit the microfilament‐mediated processes of fertilization and early development. In vitro, latrunculin A was recently found to affect the polymerization of pure actin in a manner consistent with the formation of a 1:1 molar complex with G‐actin. These in vitro effects as well as previous indications that the latrunculins are more potent than the cytochalasins suggest differences in the in vivo mode of action of the two clases of drugs. To elucidate these differences we have compared the short‐ and long‐term effects of latrunculins on cell shape and actin organization to those of cytochalasin D. Exposure of hamster fibroblast NIL8 cells for 1–3 hr to latrunculin A, latrunculin B, and cytochalasin D causes concentration‐dependent changes in cell shape and actin organization. However, the latrunculin‐induced changes were strikingly different from those induced by cytochalasin D. Furthermore, while initial effects were manifest with both latrunculin A and cytochalasin D already at concentrations of about 0.03 μg/ml, latrunculin A caused complete rounding up of all cells at 0.2 μg/ml, whereas with cytochalasin D maximum contraction was reached at concentrations 10–20 times higher. The short‐term effects of latrunculin B were similar to those of latrunculin A although latrunculin B was slightly less potent. All three drugs inhibited cytokinesis in synchronized cells, but their long‐term effects were markedly different. NIL8 cells treated with latrunculin A maintained their altered state for extended periods. In contrast, the effects of cytochalasin D progressed with time in culture, and the latrunculin B‐induced changes were transient in the continued presence of the drug. These transient effects were found to be due to a gradual inactivation of latrunculin B by serum and were used to compare recovery patterns of cell shape and actin organization in two different cell lines. This comparison showed that the transient effects of latrunculin B were fully reversible for the NIL8 cells and not for the mouse neur

ISSN:0886-1544    

DOI:10.1002/cm.970130302

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe cytoskeleton ofCrithidia fasciculataconsists of a corset of paralle microtubules enclosing the cell body and closely underlying the plasma membrane. Distinct sets of crosslinks appear to connect tubules to each other and to membrane. Our objective is to determine the composition of these crosslinks and to elucidate the basis of this spectacular example of membrane‐microtubule interaction. We purified three proteins (designated COP‐33, ‐41, and ‐61 by their subunit Mr), which were consistently abundant in highly purified cytoskeletons. All three bound strongly to microtubules in vitro, and the first two induced bundles through periodic crosslinking. Polyclonal antibodies against each have been used to try to localize these proteins in thin sections of cells or whole mounts of cytoskeletons. Antibodies to COP‐41 bound sepcifically to glycosomes, organelles that encapsulate many glycolytic enzymes in these protozoa, and COP‐41 has been identified as glyceraldehyde 3‐P

ISSN:0886-1544    

DOI:10.1002/cm.970130303

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe distribution of myosin was studied in amebae of the Ax‐3 and NC‐4 strains ofDictyosteliummigrating at room temperature, using indirect immunofluorescence of aggregation‐competent amebae and the agar‐overlay technique. Amebae were fixed in methanol‐formaldehyde or absolute acetone at −15°C before or after stimulation with micromolar cyclic AMP at room temperature (20–25°C). Myosin was detected by monoclonal antibodies toDictyosteliummyosin heavy chain followed by a fluorescent secondary antibody that had been preabsorbed to remove nonspecific staining. In both strains there was a striking increase in intensity of anti‐myosin immunofluorescence in the cortex where it appeared as a continuous ring 30 seconds after addition of cyclic AMP. This correlated with a rounding up of the cell body. Sixty seconds after stimulation there was a clear reduction of cytoplasmic myosin rods in conjunction with the increased cortical localization. At this time extensions of largely hyaline cytoplasm were observed that extended beyond the cortical shell of myosin. Two minutes after the stimulus the immunofluorescence remained as a distinct line at the cortex, but the cells began to resume in elongated shape. By 3 minutes (NC‐4 strain) or 5 minutes (Ax‐3 strain) the amebae had largely returned to the control shape, and myosin had returned to its control distribution. Counts of the treated cells at different time points substantiated the observations of individual cells. The time course of translocation of myosin in the Ax‐3 strain parallels the time course of myosin phosphorylation reported in previous studies. The results are interpreted in terms of a working hypothesis for the mec

ISSN:0886-1544    

DOI:10.1002/cm.970130304

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

年代:1989

数据来源: WILEY

摘要:

AbstractChanges in microtubule organization were monitored in the stomatal complexes ofAvena sativausing tubulin immunocytochemistry. Radial arrays of cortical microtubules, previously thought to be characteristic of guard cells, also appear in adjacent subsidiary cells early in development. The subsidiary cell arrays are evident even before guard cells form via division of precursor guard mother cells. Thus, before the stomatal pore opens between sister guard cells, each complex contains four similar microtubule arrays. As the pore opens, however, the subsidiary cell system is reorganized into a network of microtubules distributed along the length of the cell. A similar change is effected in the guard cells after the pore opens. Subsidiary cells and guard cells elongate during later stages of differentiation, and a thickened wall is deposited int he narrow midzone of the latter. At the same time, microtubules in both cells assume a more axial orientation. The results are discussed in terms of developmental symmetry and the control of microtubule organization and cell wall deposition.

ISSN:0886-1544    

DOI:10.1002/cm.970130305

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn cultured human keratinocytes (NHEK) maintained in medium containing low levels of Ca2+(0.04 mM) desmoplakin is a component of certain electron‐dense bodies in the cytoplasm. These bodies are associated with bundles of intermediate filaments. Upon elevation of the level of Ca2+in the culture medium to 1.2 mM, desmoplakin first appears at sites of cell—cell contact in association with bundles of intermediate filaments. Subsequently, desmoplakin becomes incorporated into desmosomes in a manner comparable to that seen in mouse keratinocytes (Jones and Goldman:Journal of Cell Biology101:506–517, 1985). NHEK cells maintained for 24 hr at Ca2+concentrations between 0.04 mM and 0.18 mM were processed for immunofluorescence, immunoelectron, and conventional electron microscopical analysis. In NHEK cells grown at Ca2+concentrations of 0.11 mM, desmoplakin appears to be localized in electron‐dense bodies associated with intermediate filaments at sites of cell—cell contact in the absence of formed desmosomes. At a Ca2+concentration of 0.13 mM desmoplakin is arrayed like beads on a “string” of intermediate filaments at areas of cell—cell association. At 0.15 mM, desmosome formation occurs, and desmoplakin is associated with the desmosomal plaque. In basal cell carcinoma cells desmoplakin is not restricted to desmosomes but also occurs in certain electron‐dense bodies morphologically similar to those seen in NHEK maintained in low levels of Ca2+and during early stages of desmosome assembly. We discuss the possibility of “cycling” of desmoplakin through these bodies i

ISSN:0886-1544    

DOI:10.1002/cm.970130306

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe outline of cells in sparse cultures consists prediminantly of concave and convex segments; straight segments are rare and ephemeral. The convex segments are areas of active cell expansion. The concave segments are stationary and web‐shaped, similar in profile to the cables of a suspension bridge. In 3T3 fibroblasts, we have found a single microfilament bundle following the outline of every webbed edge and have called it the actin edge‐bundle (AEB). While the AEB is composed predominantly of actin, α‐actinin and myosin are also present. In contrast to normal stress fibers, AEBs are more resistant to several treatments that depolymerize F‐actin. Once an AEB disassembles, however, the webbed edge collapses and retracts, suggesting that the actin edge‐bundle is a specialized cytoskeletal structure that supports the webbed edges of interphase 3T3 fibroblasts. The stability of AEBs is independent of microtubules. We suggest that the microfilament bundles that frequently line the lateral contacts between epithelial cells in vivo may be related to the actin e

ISSN:0886-1544    

DOI:10.1002/cm.970130307

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

年代:1989

数据来源: WILEY

摘要:

AbstractChromosome movements inMesostoma ehrenbergiispermatocytes were studied using conventional video light microscopy. Kinetochore regions of the three bipolarly oriented bivalents displayed periodic back and forth movements directed to both poles at metaphase I, leading to periodic lenght changes of the bivalents. Velocity was 8–10 μm/min (maximum 17 μ/min), about one order of magnitude higher than the normal meiotic or mitotic chromosome movements of other species. One cycle of movement lasted for about 100 seconds. The movement of kinetochore regions implies that the antagonistic chromosome fibres periodically grow (assemble) and shorten (disassemble) at comparable rates. Poleward movements must be caused by forces generated in disassembling fibres, whereas movements away from the poles, accompanied by fibre growth, are probably brought about by the internal elastic force of the chromosomes. Antagonistic fibres of a bivalent can operate in or out of phase. The movements of the three kinetochore regions are coordinated insofar as growing and shortening fibres coexist in a half‐spindle at almost any time [Fuge, H. (1987):European Journal of Cell Biology44:294–298]. These observations are discussed in terms of microtubule d

ISSN:0886-1544    

DOI:10.1002/cm.970130308

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

年代:1989

数据来源: WILEY

ISSN:0886-1544    

DOI:10.1002/cm.970130301

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

年代:1989

数据来源: WILEY