摘要:

AbstractThe amoeboflagellate transformation inPhysarum polycephaluminvolves a series of dramatic changes in cell shape and motile behavior. This report describes the morphological and behavioral changes through which a synchronously transforming population of cells passes, stressing that, although there are a series of distinguishable stages, cells at all stages display striking plasticity. Our previous studies showed that amoeboflagellates transiently display a flattened motile extension—the ridge—that projects from a specific location on the cell surface and contains a laminar core densely packed with a series of crisscrossing arrays of actin microfilaments. Details are presented here concerning the movements of the ridge as well as the dynamics of ridge formation and disassembly in relation to other morphogenetic events of the transformation. The ridge forms at about the same time as transforming cells begin to elongate, propagates undulations parallel to the long axis of the cell as the transformation proceeds, and disassembles late in the transformation. Staining of fixed cells with the fluorescent probe rhodaminephalloidin shows that the actin of amoeboid cells is strikingly redistributed as the transformation proceeds. Amoeboflagellates contain most of the stainable actin in the ridge and in a ventral‐posterior spot that may be a site of cell‐substratum adhesion. These results provide additional insights into the possible functions of the ridge and the roles of actin during the amoeboflagellate transfo

ISSN:0886-1544    

DOI:10.1002/cm.970110402

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

年代:1988

数据来源: WILEY

摘要:

AbstractWound healing in Swiss 3T3 cultures was investigated with video‐enhanced contrast (VEC) microscopy. The formation of protrusions at the leading edge of cells along wounds was investigated in detail during the spreading stage, which usually lasted from 1 to 4 hr postwounding. Lamellipodia exhibited a continuous rearward, or centripetal, transport of a variety of cellular constituents at rates of ∼0.26 μm/sec from the leading edge. The lamellipodia were also the sites of lateral migration as well as extension and retraction of actin microspikes. Actin fibers oriented transversely to the direction of movement were also observed to transport centripetally at similar rates. These fibers may in part give rise to large actin fibers forming at the interface between the base of the lamellipodia and the lamellae. Beads 0.5 μm in diameter attached to the dorsal surfaces of lamellipodia also transported centripetally at rates of ∼0.21 μm/sec. Thus there is an apparent correlation between transport of a variety of structures within lamellipodia and with surface movements of lame

ISSN:0886-1544    

DOI:10.1002/cm.970110403

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

年代:1988

数据来源: WILEY

摘要:

AbstractCentrosomes undergo cell cycle‐dependent changes in shape and separations, changes that govern the organization of the cytoskeleton. The cytoskeleton is largely organized by the centrosome; however, this investigation explores the importance of cytoskeletal elements in directing centrosome shape. Since the sea urchin egg during fertilization and mitosis displays dramatic and synchronous changes in centrosome shape, the effects of cytoskeletal inhibitors on centrosome compaction, expansion, and separation were explored by the use of anticentrosome immunofluorescence microscopy. Centrosome expansion and separation was studied during two phases: the transition after sperm incorporation, when the compact sperm centrosome enlarges and the sperm aster develops, and from prometaphase to telophase, when the compact spindle poles enlarge. Compaction was investigated when the dispersed centrosome at interphase condenses into the two spindle poles at prometaphase. Although centrosome expansion and separation typically occur concurrently, β‐mercaptoethanol results in centrosome separation independent of expansion. Microtubule inhibitors prevent centrosome expansion and separation, and expanded centrosomes collapse. Since pronuclear union is arrested by microtubule inhibitors, this treatment also affords the opportunity to explore the relative attractiveness of the male and female pronuclei for these centrosomal antigens. Both pronuclei acquire centrosomal material; though only the male centrosome is capable of organizing a functional bipolar mitotic apparatus at first division, the female centrosome nucleates a monaster. Microfilament inhibition (cytochalasin D) prevents centrosome separation but not expansion or compaction. These results demonstrate that as the centrosome shapes the cytoskeleton, the cytoskeleton alters centrosome s

ISSN:0886-1544    

DOI:10.1002/cm.970110404

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe distribution of smooth muscle (SM) and non muscle myosins was compared with that of α‐SM actin in various normal and pathological tissues and in cultured cells by means of indirect immunofluorescence using a monoclonal antibody specific for α‐SM actin [anti‐αsm‐1, Skalli et al., 1986b] and two polyclonal antibodies raised against bovine aortic myosin (ABAM) and human platelet myosin (AHPM), respectively.In normal tissues ABAM stained vascular and parenchymal smooth muscle cells (SMC), myoepithelial cells and myoid cells of the testis in a pattern similar to that reported by other authors with antisera raised against non vascular SM myosin. Cells stained with ABAM were always positive for anti‐αsm‐1. In human and experimental atheromatous plaques, most cells were positive for AHPM; a variable proportion was also stained for ABAM plus anti‐αsm‐1. Myofibroblasts from rat granulation tissue, Dupuytren's nodule and stroma from breast carcinoma were constantly positive for AHPM and negative for ABAM; however, myofibroblasts from Dupuytren's nodule and breast carcinoma were anti‐αsm‐1 positive. Early primary cultures of rat aortic SMC were positive for ABAM and anti‐αsm‐1 and became negative for ABAM and positive for AHPM after a few days in culture. They remained positive for AHPM and anti‐αsm‐1 after passages; the staining of AHPM and anti‐αsm‐1 appeared to be colocalized along the same stress fibers.These results may be relevant for the understanding of SMC function and adaptation, and show that in non malignant SMC proliferation, α‐SM actin represents a more

ISSN:0886-1544    

DOI:10.1002/cm.970110405

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

年代:1988

数据来源: WILEY

摘要:

AbstractMotor responses of the frontal cirri of the ciliateStylonychiawere recorded at the axial view of the ciliary base with high‐speed cinematography. Voltage‐clamp applying sustained hyperpolarizing voltage steps was used to explore the properties of the ciliary cycle modulated by the membrane potential. Upon hyperpolarization between – 1 and – 13 mV, a previously inactive frontal cirrus reoriented from a neutral posture and started beating so that the axis of the beating cone of a proximal cirral segment assumed an orientation near 100° (proceeding counterclockwise from posterior = 0°) and inclination near 60° (0° = perpendicular to the cell surface). The major beating amplitude was limited to about 150°. Increasing hyperpolarization increased the spatial polarity of the cycle (ratio of major over minor amplitude, from 2 to 2.4). Rates of the power stroke increased with hyperpolarizations up to – 4 mV but were consistently smaller than those of the return stroke during the ciliary cycle (ratio: 0.4 to 0.6; = temporal polarity). Comparison of different hypothetical beat forms (0‐shape, D‐shape, and egg‐shape) showed that the orientation‐time data are the major determinants of the angular velocity and rate of reorientation of the cilium during the cycle. Geometric transformation of these data led to descriptions of the cycle of a proximal ciliary segment in terms of active sliding velocities and rates of unidirectional sliding translocation between identified doublets. Three voltage‐sensitive functional parameters of the cilium—theinclination(which is noncyclic) and the rates ofactive slidingandsliding translocation(both of which are cyclic in nature)—are discussed as generating the spatial and temporal pr

ISSN:0886-1544    

DOI:10.1002/cm.970110406

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

年代:1988

数据来源: WILEY

摘要:

AbstractHyperosmotic sucrose treatment of metaphase PtK‐1 cells has been shown to produce a reversible concentration‐dependent effect on spindle elongation linked to a functional alteration in the connection of the chromosome to the spindle (Pover et al.:European Journal of Cell Biology39:366–372, 1985). Spindle elongation, similar to that which occurs at anaphase B, is thought to be driven by the compression stored in the form of microtubule curvature in the nonkinetochore (nkMT) population of microtubules at metaphase (Snyder et al.:European Journal of Cell Biology35:62–69, 1984 and 39:373–379, 1985). Addition of metabolic inhibitors to Ham's F‐12 salts with deoxyglucose (D/F‐12 medium) containing 0.4 M sucrose and 1 mM DNP does not within statistical error affect the rate and extent of sucrose‐induced spindle elongation; rates and extents are 60–75% of normal anaphase B motions. Electron microscopic analysis of metaphase cells treated with D/F‐12 medium and 0.4 M sucrose with 1 mM DNP demonstrates that spindle microtubules lose curvature and become straight in appearance, typical of microtubule organization in untreated anaphase cells. Sucrose‐treated cells released into D/F‐12 medium show a rapid reduction in spindle length; however, cells treated with either 0.4 M sucrose or 0.4 M sucrose and 1 mM DNP‐containing D/F‐12 medium and released into DNP‐containing D/F‐12 medium do not exhibit a significant reduction in spindle length. Electron microscopic analysis links changes in spindle length with microtubule/kinetochore associations. These data suggest that energy required for the initial phases of spindle elongation during anaphase is preloaded into the mitotic spindle by metaphase and does not require additional energy to be expressed as examined by sucrose‐induced spindle elongation in the presence of metabolic inhibitors. Second, energy is required to make or maintain (or both) functional chromosome associations with the spindle as measured by reduction in spindle

ISSN:0886-1544    

DOI:10.1002/cm.970110407

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

年代:1988

数据来源: WILEY

摘要:

AbstractWe have used a polyclonal affinity‐purified antibody made against chicken brain fodrin (both 240 and 235 Kd subunits) as a probe to determine if a fodrinlike protein exists in amoebae ofDictyostelium discoideum. In Western blots of whole cells and the isolated cell cortex, polypeptides measuring 220 and 70 Kd are recognized by the fodrin antibodies. In situ localization by indirect immunofluorescence with antifodrin indicates that the immunoreactive polypeptides are cortical. The immunoreactive analogues copatch and cocap with concanavalin A. At the level of resolution of the electron microscope, immunocytochemistry with antifodrin and colloidal gold confirms that the immunoreactive analogues are cortical proteins associated with microfilaments on the cytoplasmic side of the plasma membrane. We have isolated and characterized the 220 Kd protein to determine if it is similar to fodrin and to investigate its relationship to the 70 Kd polypeptide. The 220 Kd protein can be extracted from the cortex in the absence of detergent and isolated by gel filtration and sucrose density gradient sedimentation. The 220 Kd is a rod‐shaped protein 118 ± 17.8 nm (N = 37) in length. It has a sedimentation coefficient of 9.3 S and Stokes' radius of 13 nm and exists as a dimer of approximately 500,000 daltons (Mr). Isolated 220 Kd binds to actin filaments in vitro when assayed by rotary shadowing. Morphological criteria distinguish 220 Kd fromDictyosteliummyosin II heavy chain (215 Kd) and the filaminlike protein at 240 Kd. The 70 Kd polypeptide appears to be a cleavage fragment of the 220 Kd, since it is found after prolonged storage when formerly only the 220 Kd was present. Furthermore, the 220 and 70 Kd polypeptides exhibit similar one‐dimensional peptide maps when treated with TPCK trypsin. On the basis of its physical and immunoreactive characteristics, and location in the cell, the 220 Kd may be a fodrinlike p

ISSN:0886-1544    

DOI:10.1002/cm.970110408

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe mammalian genome contains 20–30 genes encoding a family of actins. To date, however, only six proteins (four muscle and two nonmuscle isoforms) encoded by this multigene complex have been identified. We have isolated two actins from the brush border of rat intestinal epithelial cells that have isoelectric points and N‐terminal peptides characteristic of the cytoplasmic β‐ and γ‐actins. However, using a panel of actin‐specific monoclonal antibodies, we show that these actins contain a set of epitopes that distinguishes them from any of the known cytoplasmic or muscle isoforms. These unique actins share features of both the nonmuscle and muscle isoforms, suggesting that they represent an intermediate in the evolution of the specialized mu

ISSN:0886-1544    

DOI:10.1002/cm.970110409

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.970110410

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.970110401

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

年代:1988

数据来源: WILEY