共查询到20条相似文献,搜索用时 46 毫秒
1.
In this paper we describe an experimental investigation of the mechanism of motility of vertebrate cells. Human glioma cells were treated with neomycin, an inhibitor of the phosphatidylinositol cycle; and changes in cell motility and the cytoskeleton were examined by video, fluorescence, and scanning electron microscopy and by cytofluorometry. Neomycin stimulates a single protrusion of lamellipodia from the cell margin, which is correlated with an initial rapid decrease in the amount of F-actin throughout the cell, especially at the cell edge; the fragmentation of actin filaments within the lamellipodia; and the subsequent de novo polymerization of F-actin in a marginal band at the leading edge of lamellipodia. Changes in F-actin are paralleled by changes in the distribution and amount of gelsolin. These results support the hypothesis that protrusion is initiated by the gelsolin-mediated severing and subsequent depolymerization of cortical actin filaments, which weakens the cell cortex, allowing hydrostatic or gel osmotic pressure to force the cell margin to protrude. The accompanying polymerization of filaments actin at the leading edge of the protrusion may stabilize the protrusion and support its expansion. 相似文献
2.
Some simple indications of the presence of pressure in hyphaltips have been used to investigate osmotic relationships. Theseare (1) cytoplasmic flow due to pressure loss through the apexcaused by janus green solutions, (2) extrusion of cell contentson damaging the cell wall with dilute acetic acid, and (3) continuationof apical extension growth. The osmotic equivalent of growingtips is considerably in excess of that of the growth medium,resulting in the presence of a hydrostatic pressure differentialbetween the interior of the tip and its environment. Normalextension growth is dependent upon this differential. Hyphaltips are able rapidly to equilibrate osmotically to appliedhyper- and hypotonic solutions so as to re-establish a pressuredifferential consistent with the rate of synthesis of wall materialat the apex. Apices that are caused to cease extension growthby applied hypertonic solutions enter upon a sequence of slightbut significant morphological changes leading to progressiveocclusion of the apex by continued formation of wall substancein the absence of a sufficiently high pressure differential.The subsequent behaviour of such apices depends upon the stagein this sequence reached at the re-establishment of a pressuredifferential sufficient for extension growth. 相似文献
3.
Keratocytes derived from the epidermis of aquatic vertebrates are now widely used for investigation of the mechanism of cell locomotion. One of the main topics under discussion is the question of driving force development and concomitantly subcellular force distribution. Do cells move by actin polymerization-driven extension of the lamella, or is the lamella edge extended at regions of weakness by a flow of cytoplasm generated by hydrostatic pressure? Thus, elasticity changes were followed and the stiffness of the leading front of the lamella was manipulated by local application of phalloidin and cytochalasin D (CD). In scanning acoustic microscopy (SAM), elasticity is revealed from the propagation velocity of longitudinal sound waves (1 GHz). The lateral resolution of SAM is in the micrometer range. Using this method, subcellular tension fields with different stiffnesses (elasticity) can be determined. A typical pattern of subcellular stiffness distribution is related to the direction of migration. Cells forced to change their direction of movement by exposure to DC electric fields of varying polarity alter their pattern of subcellular stiffness in relationship to the new direction. The cells spread into the direction of low stiffness and retract at zones of high stiffness. The pattern of subcellular stiffness distribution reveals force distribution in migrating cells; i.e., if a cell moves exactly in a direction perpendicular to its long axis, then the contractile forces are largest along the long axis and decrease toward the short axis. Locomotion in any angle oblique to this axis requires an asymmetric stiffness distribution. Inhibition of actomyosin contractions by La3+ (2 mM), which inhibits Ca2+ influx, reduces cytoplasmic stiffness accompanied by an immediate cessation of locomotion and a change of cell shape. Local release of CD in front of a progressing lamella activates a cell to follow the CD gradient: The lamella thickens locally and is extended toward the tip of the microcapillary. Release of phalloidin stops extension of the lamella, and the cell turns away from the releasing microcapillary. The response to CD is assumed to be the result of local weakening of the cytoplasm due to severing of the actin fibrils. Phalloidin is supposed to stabilize the leading front by inhibition of F-actin depolymerization. These observations are in favor of the assumption that migration is due to an extension of the cell into the direction of minimum stiffness, and they are consistent with the hypothesis that local release of hydrostatic pressure provides the driving force for the flux of cytoplasm. 相似文献
4.
5.
A. Grębecki 《Protoplasma》1990,154(2-3):98-111
Summary Behaviour of the membrane and contractile system was directly recorded in the advancing and retracting frontal zones of spontaneously locomoting or stimulated amoebae. The advancing pseudopodial tips alternately slow down and accelerate. In the slowing phase the frontal hyaline caps are flat and compressed by countercontraction of the cortical actin network beneath the leading edge. At this stage the membrane-cytoskeleton complex splits: the detached contractile layer is retracted inwards, and the membrane lifted outwards. The fluid endoplasm fraction is filtered forward through the detached actin network. This results in a local hydrostatic pressure drop, immediately restores the forward flow of endoplasm and initiates the acceleration phase of the leading edge progression. The frontal membrane, temporarily disconnected from the cytoskeletal layer, is free to slide and extend forward, but the new submembrane contractile network is soon repolymerized. In this way, after making one step forward, the frontal zone recovers its former state, and the cycle is then repeated. The cortex disassembly-reassembly cycles at the leading edge are produced every 2 s, on average. Retraction of the frontal contractile layers is part of the general centripetal cortex flow observed during motor functions of amoebae and many other cells, and is therefore associated with various other backward movements observed within and on the surface of advancing frontal zones of amoebae. The backward movement of the contractile cortex is also responsible for the withdrawal of previously advancing pseudopodia, if the detachment of successive contractile sheets from the frontal membrane ceases. It was demonstrated that the action of attractants and repellents is based on the activation or inhibition, respectively, of rhythmic disassembly of the membrane-cytoskeleton complex at the leading edge. 相似文献
6.
The structure of the disc is both complex and inhomogeneous, and it functions as a successful load-bearing organ by virtue of the integration of its various structural regions. These same features also render it impossible to assess the failure strength of the disc from isolated tissue samples, which at best can only yield material properties. This study investigated the intrinsic failure strength of the intact bovine caudal disc under a simple mode of internal hydrostatic pressure. Using a hydraulic actuator, coloured hydrogel was injected under monitored pressure into the nucleus through a hollow screw insert which passed longitudinally through one of the attached vertebrae. Failure did not involve vertebra/endplate structures. Rather, failure of the disc annulus was indicated by the simultaneous manifestation of a sudden loss of gel pressure, a flood of gel colouration appearing in the outer annulus and audible fibrous tearing. A mean hydrostatic failure pressure of 18+/-3 MPa was observed which was approximated as a thick-wall hoop stress of 45+/-7 MPa. The experiment provides a measurement of the intrinsic strength of the disc using a method of internal hydrostatic loading which avoids any disruption of the complex architecture of the annular wall. Although the disc in vivo is subjected to a much more complex pattern of loading than is achieved using simple hydrostatic pressurization, this latter mode provides a useful tool for investigating alterations in intrinsic disc strength associated with prior loading history or degeneration. 相似文献
7.
Under pressure: biomechanical limitations of developing pneumatocysts in the bull kelp (Nereocystis luetkeana,Phaeophyceae)
下载免费PDF全文
![点击此处可从《Journal of phycology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Maintaining buoyancy with gas‐filled floats (pneumatocysts) is essential for some subtidal kelps to achieve an upright stature and compete for light . However, as these kelps grow up through the water column, pneumatocysts are exposed to substantial changes in hydrostatic pressure, which could cause complications as internal gases may expand or contract, potentially causing them to rupture, flood, and lose buoyancy. In this study, we investigate how pneumatocysts of Nereocystis luetkeana resist biomechanical stress and maintain buoyancy as they develop across a hydrostatic gradient. We measured internal pressure, material properties, and pneumatocyst geometry across a range of thallus sizes and collection depths to identify strategies used to resist pressure‐induced mechanical failure. Contrary to expectations, all pneumatocysts had internal pressures less than atmospheric pressure, ensuring that thalli are always exposed to a positive pressure gradient and compressional loads, indicating that they are more likely to buckle than rupture at all depths. Small pneumatocysts collected from depths between 1 and 9 m (inner radius = 0.4–1.0 cm) were demonstrated to have elevated wall stresses under high compressive loads and are at greatest risk of buckling. Although small kelps do not adjust pneumatocyst material properties or geometry to reduce wall stress as they grow, they are ~3.4 times stronger than they need to be to resist hydrostatic buckling. When tested, pneumatocysts buckled around 35 m depth, which agrees with previous measures of lower limits due to light attenuation, suggesting that hydrostatic pressure may also define the lower limit of Nereocystis in the field. 相似文献
8.
R. S. Wilson 《Zoomorphology》1970,68(4):308-322
An anatomical study of five spider types has shown that the musculi laterales of the prosoma, together with the subcuticular muscle sheet of the opisthosoma, may be jointly responsible for generating the internal hydrostatic pressures which control the leg extension mechanism. 相似文献
9.
Early in molluscan evolution, the development of a conical shell with shell or pedal retractor muscles led to the need of a mechanism for the extension of the foot or the raising of the shell. The forces generated during pedal retraction and extension have been studied in Haliotis midae , an easily obtainable and conveniently large archaeogastropod. In the mantle cavity, cephalopedal venous sinus and ventricle pressure pulses were observed during pedal retraction elicited by the shadow withdrawal reflex, but were never present during extension. However, pressure pulses were recorded in the proximal region of the columellar (or shell) muscle, both during retraction and pedal extension. Sections of this region of the muscle show a three dimensional network of muscle fibres, consisting of retractor fibres passing down to the foot and circumferential and radial fibres. Contraction of the two latter sets of fibres would bring about extension of the retractors, without the use of a discrete hydrostatic skeleton, and appears to be the principal mechanism of pedal extension. Similar muscular structures, here termed the muscular antagonistic system, have been observed in the columellar muscle of other gastropods and in the cephalopod mantle. In contrast, this system has not been observed in the proximal region of the pedal retractors of bivalves or scaphopods, for the pedal haemocoel, which allows muscular antagonism in the manner of a classical hydrostatic skeleton, has developed in association with the burrowing habit. The significance of the muscular antagonistic system in molluscan evolution is discussed. 相似文献
10.
In cell stress research, there is still a need to apply long-term hydrostatic pressure without changing any other environmental condition. We present here a new, open, pressurized chamber system allowing long-term sustained and dynamic application of hydrostatic pressure with the option of additional tension. Based on the computer-controlled Flexcell Strain Unit, we designed a pressurized chamber with a dynamic airflow and a defined membrane extension, which can be regulated by spacers. During operation up to 26.6kPa, O(2) partial pressures and pH in the cell-culture medium do not change compared to control cultures kept at normal atmosphere. 相似文献
11.
In the trap bladder ofUtricularia vulgaris, a sudden expansion (convex bladder) by opening of the entrance door upon stimulus was followed by slow decreases in bladder
width and internal hydrostatic pressure. The decreases were caused by continuous water outflow from bladder lumen. The bladder
reached initial resetting state (concave bladder) in about 30 min. The internal pressure reduced to 0.86 bar. This reduction
was inhibited by application of sodium azide in the bladder lumen. The total water outflow for 30 min from a bladder, measured
using a glass capillary inserted in the bladder, was 630 nl: the rate was 21 nl/min. This rate was also inhibited by sodium azide. In bladder resetting under paraffin oil, it was observed that water emerges
from near the free edge of the trap door. From light and electron microscopic observations of the entrance region, it is concluded
that the inlet of water outflow is the bifid trichomes which stand on the inner surface of the bladder near the entrance,
and the outlet is the outer and middle zones of the pavement epithelium, or threshold, against which the free edge of the
door rests. 相似文献
12.
Chemotaxis is a cellular sensing mechanism that guides immune cells to sites of infection and leads fibroblasts to sites of injury. Here, we show in migrating primary dendritic cells and fibroblasts that the leading edge is not a uniform signaling entity, but instead consists of independent coupling units in which transient activation of PI3-kinase links to local lamellipod extension and small discrete turns in the direction of migration. These findings led to a model in which global cell polarization is independent from the chemotaxis mechanism. In this model, chemotaxis does not require spatial integration but is instead a stochastic process in which each receptor binding event within the leading edge triggers a local lamellipod extension and a small turn in the direction of migration. We show that this model and a derived "compass parameter" are sufficient to simulate the observed random migration, biased random walk, and persistent chemotactic behaviors of eukaryotic cells. 相似文献
13.
Skinfolds and feathers form the profile of the avian airfoil. The wing of birds has a nearly flat profile from shoulder to carpus, without the presence of the propatagium. The propatagium is the largest skinfold of the wing; it fills the angle formed by the partially flexed elbow, and with its feathers forms a rounded leading edge and dorsally cambered profile added to the cranial aspect of the wing. The propatagium is variably deployed, relative to elbow extension, in flight; support for its cambered shape is maintained by multilayered collagenous and elastic tissue networks suspended between leading edge and dorsal antebrachium. The leading edge ligament (Lig. propatagiale) courses from deltopectoral crest to carpus and, with its highly distensible center section, supports the leading edge of the propatagium across a range of wing extensions. The elbow extension limiting ligament (Lig. limitans cubiti) courses from deltopectoral crest to proximal antebrachium and limits maximum elbow extension. M. deltoideus, pars propatagialis inserts on the proximal end of the common origin of the propatagial ligaments and, by way of the insertions of the two ligaments, coordinates (1) automatic flexion / extension actions of the elbow and wrist, (2) propatagial deployment, and (3) tension along the length of Lig. propatagiale supporting the leading edge. © 1994 Wiley-Liss, Inc. 相似文献
14.
Effects of hydrostatic pressure on the ultrastructure and leakage of internal substances in the yeast Saccharomyces cerevisiae 总被引:2,自引:0,他引:2
Shoji Shimada Masayasu Andou Nobuko Naito Naoko Yamada Masako Osumi Rikimaru Hayashi 《Applied microbiology and biotechnology》1993,40(1):123-131
The structural damage to and leakage of internal substances from Saccharomyces cerevisiae 0–39 cells induced by hydrostatic pressure were investigated. By scanning electron microscopy, yeast cells treated at room temperature with pressuresbellw 400 MPa for 10 min showed a slight alteration in outer shape. Transmission electron microscopy, however, showed that the inner structure of the cell began to be affected, especially the nuclear membrane, when treated with hydrostatic pressure around 100 MPa at room temperature for 10 min; at more than 400–600 MPa, further alterations appeared in the mitochondria and cytoplasm. Furthermore, when high pressure treatment was carried out at — 20° C, the inner structure of the cells was severely damaged even at 200 MPa, and almost all of the nuclear membrane disappeared, although the fluorescent nucleus in the cytoplasm was visible by 4,6-diamidino-2-phenylindole (DAPI) staining. The structural damage of pressure-treated cells was accompanied by the leakage of internal substances. The efflux of UV-absorbing substances including amino acid pools, peptides, and metal ions increased with increase in pressure up to 600 MPa. In particular, amounts of individual metal ion release varied with the magnitude of hydrostatic pressures over 300 MPa, which suggests that the ions can be removed from the yeast cells separately by hydrostatic pressure treatment.
Correspondence to: S. Shimada 相似文献
15.
Lentle RG Janssen PW Asvarujanon P Chambers P Stafford KJ Hemar Y 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(5):543-556
Longitudinal and radial movements during spontaneous contractions of isolated segments of terminal ileum of the brushtail
possum, a species of arboreal folivore, were studied using high definition spatiotemporal maps. Segments obtained from specimens
were continuously perfused with solutions of various apparent viscosities at 3 cm and 5 cm hydrostatic pressure. A series
of sustained tetrodotoxin-sensitive peristaltic events occurred during perfusion. The leading edge of each peristaltic event
progressed by a succession of rhythmic surges of circular contraction with concerted concurrent phasic longitudinal contractions.
Three types of peristaltic event were observed, with differing durations of occlusion and patterns of cyclic, in phase, circular
and longitudinal contractions. Each peristaltic event was preceded by a change of shade on the D map that indicated circumferential dilatation. Differences in the slopes of these phasic shade changes from those occurring
during peristalsis indicate that this distension is passive and likely results from aboral displacement of fluid. Tetradotoxin
insensitive longitudinal contraction waves of frequency 9.2 min−1 occurred during and in the absence of peristalsis, originating at a variety of sites, and propagating either in an orad or
aborad direction but predominantly in the latter. Perfusion with 1% guar gum, at 5 cm hydrostatic pressure caused the lumen
to become distended and the generation of peristaltic events to cease pending reduction of the hydrostatic head to 3 cm but
longitudinal contractile activity was preserved. Neither the frequencies nor the rates of progression of circular and longitudinal
contractile events, nor the temporal coordination between these events, varied with the apparent viscosity of the perfusate
or altered in a manner that could facilitate mixing. 相似文献
16.
Liquid water, underwater volcanoes and possibly life forms have been suggested to be present beneath the estimated 10 km-thick ice shell of Europa the Jovian satellite J2. Europa's possible ocean is estimated to be 100-200km deep. Despite the great depth of the Europa's ocean, hydrostatic pressure at the seafloor would be 130-260 MPa, corresponding to 13-26 km depth of a theoretical Earth's ocean. The hydrostatic pressure is not beyond the edge of existing deep-sea technology. Here we propose exploration of Europa's deep-sea by the use of current technologies, taking a symbolic example of a deep submergence vehicle Shinkai 6500 which dives to a depth of 6.5 km deep (50 km depth of Europa's ocean). Shinkai 6500 is embarkable in the payload bay of the Space Shuttles in terms of size and weight for the transportation to a Low Earth Orbit (LEO). Secondary boost is needed for interplanetary flight from the LEO. On-orbit assembly of the secondary booster is a technological challenge. The International Space Station (ISS) and ISS-related technologies will facilitate the secondary boost. Also, ice shell drilling is a challenge and is needed before the dive into Europa's ocean. These challenges should be overcome during a certain leading time for matured experience in the ISS operation. 相似文献
17.
Neuronal migration. 总被引:2,自引:0,他引:2
Like other motile cells, neurons migrate in three schematic steps, namely leading edge extension, nuclear translocation or nucleokinesis, and retraction of the trailing process. In addition, neurons are ordered into architectonic patterns at the end of migration. Leading edge extension can proceed at the extremity of the axon, by growth cone formation, or from the dendrites, by formation of dendritic tips. Among both categories of leading edges, variation seems to be related to the rate of extension of the leading process. Leading edge extension is directed by microfilament polymerization following integration of extracellular cues and is regulated by Rho-type small GTPases. In humans, mutations of filamin, an actin-associated protein, result in heterotopic neurons, probably due to defective leading edge extension. The second event in neuron migration is nucleokinesis, a process which is critically dependent on the microtubule network, as shown in many cell types, from slime molds to vertebrates. In humans, mutations in the PAFAH1B1 gene (more commonly called LIS1) or in the doublecortin (DCX) gene result in type 1 lissencephalies that are most probably due to defective nucleokinesis. Both the Lis1 and doublecortin proteins interact with microtubules, and two Lis1-interacting proteins, Nudel and mammalian NudE, are components of the dynein motor complex and of microtubule organizing centers. In mice, mutations of Cdk5 or of its activators p35 and p39 result in a migration phenotype compatible with defective nucleokinesis, although an effect on leading edge formation is also likely. The formation of architectonic patterns at the end of migration requires the integrity of the Reelin signalling pathway. Other known components of the pathway include members of the lipoprotein receptor family, the intracellular adaptor Dab1, and possibly integrin alpha 3 beta 1. Defective Reelin leads to poor lamination and, in humans, to a lissencephaly phenotype different from type 1 lissencephaly. Although the action of Reelin is unknown, it may trigger some recognition-adhesion among target neurons. Finally, pattern formation requires the integrity of the external limiting membrane, defects of which lead to overmigration of neurons in meninges and to human type 2 lissencephaly. 相似文献
18.
Macdonald AG Fraser PJ 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》1999,122(1):13-36
This paper reviews experiments in which cells, subjected to hydrostatic pressures of 20 kPa or less, (micro-pressures), demonstrate a perturbation in growth and or metabolism. Similarly, the behavioural responses of aquatic animals (lacking an obvious compressible gas phase) to comparable pressures are reviewed. It may be shown that in both cases the effect of such very low hydrostatic pressures cannot be mediated through the thermodynamic mechanisms which are invoked for the effects of high hydrostatic pressure. The general conclusion is that cells probably respond to micro-pressures through a mechanical process. Differential compression of cellular structures is likely to cause shear and strain, leading to changes in enzyme and/or ion channel activity. If this conclusion is true then it raises a novel question about the involvement of 'micro-mechanical' effects in cells subjected to high hydrostatic pressure. The responses of aquatic animals to micro-pressures may be accounted for, using the model case of the crab, by the mechanical, bulk, compression of hair cells in the statocysts, the organ of balance. If this is true, it raises the interesting question of why the putative cellular mechanisms of micro-pressure transduction appear to have been superseded by the statocyst. 相似文献
19.
Tomonobu M. Watanabe Hiroshi Tokuo Kohsuke Gonda Hideo Higuchi Mitsuo Ikebe 《The Journal of biological chemistry》2010,285(25):19605-19614
Filopodia are actin-rich finger-like cytoplasmic projections extending from the leading edge of cells. Unconventional myosin-X is involved in the protrusion of filopodia. However, the underlying mechanism of myosin-X-induced filopodia formation is obscure. Here, we studied the movements of myosin-X during filopodia protrusion using a total internal reflection microscope to clarify the mechanism of myosin-X-induced filopodia formation. Myosin-X was recruited to the discrete site at the leading edge where it assembles with exponential kinetics before the filopodia extension. The myosin-X-induced filopodia showed repeated extension-retraction cycles with each extension of 2.4 μm, which was critical to produce long filopodia. Myosin-X, lacking the FERM domain, could move to the tip as does the wild type. However, it was transported toward the cell body during filopodia retraction, did not undergo multiple extension-retraction cycles, and failed to produce long filopodia. During the filopodia protrusion, the single molecules of full-length myosin-X moved within filopodia. The majority of the fluorescence spots showed two-step photobleaching, suggesting that the moving myosin-X is a dimer. Deletion of the FERM domain did not change the movement at the single molecule level with the same velocity of ∼600 nm/s as wild-type, suggesting that the myosin-X in filopodia moves without interaction with the attached membrane via the FERM domain. Based upon these results, we have proposed a model of myosin-X-induced filopodia protrusion. 相似文献
20.
Role of cofilin in epidermal growth factor-stimulated actin polymerization and lamellipod protrusion 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Stimulation of metastatic MTLn3 cells with epidermal growth factor (EGF) causes a rapid and transient increase in actin nucleation activity resulting from the appearance of free barbed ends at the extreme leading edge of extending lamellipods. To investigate the role of cofilin in EGF-stimulated actin polymerization and lamellipod extension in MTLn3 cells, we examined in detail the temporal and spatial distribution of cofilin relative to free barbed ends and characterized the actin dynamics by measuring the changes in the number of actin filaments. EGF stimulation triggers a transient increase in cofilin in the leading edge near the membrane, which is precisely cotemporal with the appearance of free barbed ends there. A deoxyribonuclease I binding assay shows that the number of filaments per cell increases by 1.5-fold after EGF stimulation. Detection of pointed ends in situ using deoxyribonuclease I binding demonstrates that this increase in the number of pointed ends is confined to the leading edge compartment, and does not occur within stress fibers or in the general cytoplasm. Using a light microscope severing assay, cofilin's severing activity was observed directly in cell extracts and shown to be activated after stimulation of the cells with EGF. Microinjection of function-blocking antibodies against cofilin inhibits the appearance of free barbed ends at the leading edge and lamellipod protrusion after EGF stimulation. These results support a model in which EGF stimulation recruits cofilin to the leading edge where its severing activity is activated, leading to the generation of short actin filaments with free barbed ends that participate in the nucleation of actin polymerization. 相似文献