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1.
Summary. The mechanism of cytokinesis was investigated during the first asymmetric division in fucoid zygotes. A plate of actin assembled midway between daughter nuclei where microtubules interdigitated and defined the cytokinetic plane. A membrane was then deposited in islands throughout the cytokinetic plane; the islands eventually fused into a continuous partition membrane and cell plate material was deposited in the intermembrane space. All of these structures matured from the center of the cell outward (centrifugal maturation). Pharmacological agents were used to investigate the roles of microtubules, actin, and secretion in cytokinesis. The findings indicate a mechanism of cytokinesis that may be unique to the brown algae.Correspondence and reprints: Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112-0840, U.S.A. 相似文献
2.
Summary. Effects on morphology and microfilament structure caused by phalloidin, phallacidin, and some semisynthetic phalloidin derivatives
were studied in vegetative cells of the green alga Acetabularia acetabulum (L.) Silva. All phalloidin derivatives (except for phalloidin itself) caused growth stop of the alga after 1 day and (except
for the fluorescein-labeled phalloidin) death of the cells after 4–7 days. Hair whorl tip growth and morphology as screened
by light microscopy, as well as microfilament structure in tips, suggested that growth stop is correlated with a disorganization
of actin filaments similar to that recently described for jasplakinolide (H. Sawitzky, S. Liebe, J. Willingale-Theune, D.
Menzel, European Journal of Cell Biology 78: 424–433, 1999). Using rabbit muscle actin as a model target protein, we found
that the toxic effects in vivo did not correlate with actin affinity values, suggesting that permeation through membranes
must play a role. Indeed, the most lipophilic phalloidin derivatives benzoylphalloidin and dithiolanophalloidin were the most
active in causing growth stop at ca. 100 μM. In comparison to the concentration of jasplakinolide required to cause similar
effects (<3 μM), the two most active phalloidin derivatives exhibited an activity ca. 30 times lower. Nonetheless, lipophilic
phalloidin derivatives can be used in algae, and probably also other cells, to modulate actin dynamics in vivo. In addition,
we found that the fluorescent fluorescein isothiocyanate-phalloidin is able to enter living algal cells and stains actin structures
brightly. Since it does not suppress actin dynamics, we suggest fluorescein isothiocyanate-phalloidin as a tool for studying
rearrangements of actin structures in live cells, e.g., by confocal laser scanning microscopy.
Received November 5, 2001; accepted August 8, 2002; published online November 29, 2002 相似文献
3.
Jasplakinolide reversibly disrupts actin filaments in suspension-cultured tobacco BY-2 cells 总被引:3,自引:0,他引:3
Summary. Jasplakinolide is potentially a useful pharmacological tool for the study of actin organization and dynamics in living cells,
since it induces actin polymerization in vitro and, unlike phalloidin, is membrane permeative. In the present work, the effect
of jasplakinolide on the actin cytoskeleton of living suspension-cultured Nicotiana tabacum ‘Bright Yellow 2’ cells was investigated. Actin filaments in the living cells were disrupted by jasplakinolide. The effect
of jasplakionlide on the actin cytoskeleton was concentration and time dependent. When cells were treated with a moderate
concentration (150 nM) of jasplakinolide, cortical actin filaments were disrupted preferentially, whereas actin aggregated
at the perinuclear region. With concentrations higher than 400 nM and exposure times longer than 30 min, actin filaments in
the cell disappeared completely. The effect of jasplakinolide on the actin cytoskeleton was reversible even at high concentration.
Actin bundles appeared first in the perinuclear region within 5 min, and the cortical actin array was reestablished in 15 min,
suggesting that actin filaments might be organized at this region.
Received July 31, 2001 Accepted December 14, 2001 相似文献
4.
Filamentous actin localized to polar cytoplasmic areas between chloroplasts of the prymnesiophyte Pleurochrysis sp. Phalloidin staining of cells, confocal laser scanning microscopy, and previous electron microscopy (E. K. Hawkins and
J. J. Lee, Protoplasma 216: 227–238, 2001) indicate that the location of phalloidin staining coincides with the cellular location
of the Golgi apparatus. The results are consistent with the hypothesis that filamentous actin may be involved in biogenesis
and polarized secretion of scales.
Received February 28, 2002; accepted July 1, 2002; published online November 29, 2002 相似文献
5.
Reversible protein phosphorylation regulates the dynamic organization of the pollen tube cytoskeleton: effects of calyculin A and okadaic acid 总被引:7,自引:0,他引:7
We investigated the cytoskeleton of Lilium longiflorum pollen tubes and examined the effects of the type 2A protein phosphatase (PP2A) inhibitors calyculin A and okadaic acid. An improved method for actin visualization, the simultaneous fixation and staining with rhodamine-labelled phalloidin during microscopical observation, revealed abundant actin filaments of no preferential orientation in the apical clear zone. Microtubules, visualized by indirect immunofluorescence, were mostly absent from the apices of straight-growing pollen tubes but present in those with irregular shape. Double labelling showed that both actin bundles and microtubules had a similar longitudinal or slightly helical orientation in the pollen tube shaft. In the presence of 30 nM calyculin A or okadaic acid, pollen tubes grew very slowly, branched frequently, and contained isolated, randomly oriented, curved actin bundles and microtubules. Treating pollen tubes with calyculin A or okadaic acid after germination arrested growth immediately, reversibly altered the alignment of actin bundles from axial to transverse, and disassembled microtubules. The changes in actin organization caused by the PP2A inhibitors were similar to those observed upon overexpression of AtRop1 (Y. Fu, G. Wu, Z. Yang, Journal of Cell Biology 152: 1019-1032, 2001), suggesting that hyperphosphorylation interferes with the signalling pathway of small GTPases. The effects of the PP2A inhibitors could be ameliorated with nanomolar concentrations of latrunculin B. 相似文献
6.
To understand the unusual polar body formation in the androgenetic clam, Corbicula leana, whole-mount eggs stained with monoclonal antibodies against α-tubulin, γ-tubulin, and 4’-6’-diamidino-2-phenylindole were
examined. The meiotic spindle was located at the peripheral region of the egg at metaphase I, and its axis was parallel to
the egg surface. After segregation of chromosomes at anaphase I, cytoplasmic bulges formed at both meiotic spindle pole sites.
Centrosomes were located at the apical portion of the each bulge. From the apical portion of the bulge a bundle of astral
microtubules radiated toward the bulge base in late anaphase resembling a half spindle. Maternal chromosomes and both centrosomes
were all distributed in two ”first polar bodies” and were eventually discarded. After the polar body formation only one male
pronucleus existed in the egg cytoplasm. The present study showed that the anaphase microtubules originating from a single
aster can induce the polar body formation without overlapping of microtubules from the opposing aster.
Received: 29 September 1999 / Accepted: 24 November 1999 相似文献
7.
Lentil root statoliths reach a stable state in microgravity 总被引:3,自引:0,他引:3
The kinetics of the movement of statoliths in gravity-perceiving root cap cells of Lens culinaris L. and the force responsible for it have been analysed under 1 g and under microgravity conditions (S/MM-03 mission of Spacehab 1996). At the beginning of the experiment in space, the amyloplasts
were grouped at the distal pole of the statocytes by a root-tip-directed 1-g centrifugal acceleration. The seedlings were then placed in microgravity for increasing periods of time (13, 29, 46 or 122 min)
and chemically fixed. During the first 29 min of microgravity there were local displacements (mean velocity: 0.154 μm min−1) of some amyloplasts (first at the front of the group and then at the rear). Nevertheless, the group of amyloplasts tended
to reconstitute. After 122 min in microgravity the bulk of amyloplasts had almost reached the proximal pole where further
movement was blocked by the nucleus. After a longer period in microgravity (4 h; experiment carried out 1994 during the IML
2 mission) the statoliths reached a stable position due to the fact that they were stopped by the nucleus. The position was
similar to that observed in roots grown continuously in microgravity. Treatment with cytochalasin D (CD) did not stop the
movement of the amyloplasts but slowed down the velocity of their displacement (0.019 μm min−1). Initial movement patterns were the same as in control roots in water. Comparisons of mean velocities of amyloplast movements
in roots in space and in inverted roots on earth showed that the force responsible for the movement in microgravity (Fc) was about 86% less (Fc = 0.016 pN) than the gravity force (Fg = 0.11 pN). Treatment with CD reduced Fc by two-thirds. The apparent viscosity of the statocyte cytoplasm was found to be 1 Pa s or 3.3 Pa s for control roots or
CD treated roots, respectively. Brownian motion or elastic forces due to endoplasmic reticulum membranes do not cause the
movement of the amyloplasts in microgravity. It is concluded that the force transporting the statoliths is caused by the actomyosin
system.
Received: 22 March 1999 / Accepted: 18 December 1999 相似文献
8.
Changes in actin organization in the living egg apparatus of Torenia fournieri during fertilization 总被引:3,自引:3,他引:0
Ying Fu Ming Yuan B.-Q. Huang Hong-Yuan Yang Sze-Yong Zee T. P. O’Brien 《Sexual plant reproduction》2000,12(6):315-322
Changes in actin organization in the living egg apparatus of Torenia fournieri from anthesis to post-fertilization have been investigated using microinjection and confocal microscopy. Our results revealed
that the actin cytoskeleton displays dramatic changes in the egg apparatus and appears to coordinate the events of synergid
degeneration, pollen tube arrival and gametic fusion during fertilization. Synergid degeneration occurs after anthesis and
is accompanied by actin fragmentation and degradation. The actin cytoskeleton becomes organized with numerous aggregates in
the chalazal end of the degenerating synergid, and some of the actin infiltrates into the intercellular gap between synergids,
egg and central cell, forming a distinct actin band. An actin cap is present near the filiform apparatus after anthesis and
disappears after pollen tube arrival. In the egg cell, actin filaments initially organize into a network and after pollination
become fragmented into numerous patches in the cortex. These structures, along with the actin in the degenerating synergid
and intercellular spaces form two distinct actin coronas during fertilization. The actin coronas vanish after gametic fusion.
This is the first report of changes in actin organization in the living egg apparatus. The reorganization of the actin cytoskeleton
in the egg apparatus and the presence of the actin coronas during fertilization suggest these events may be a necessary prelude
to reception of the pollen tube and fusion of the male and female gametes.
Received: 11 November 1999 / Accepted: 31 January 2000 相似文献
9.
Stomatal opening by fusicoccin is accompanied by depolymerization of actin filaments in guard cells 总被引:6,自引:0,他引:6
Actin in guard cells is assembled in a radial pattern when stomata are induced to open under light, but the filaments are
disassembled when stomata are closed under darkness or by abscisic acid (S.-O. Eun and Y. Lee, 1997, Plant Physiol. 115: 1491–1498).
To test if signals that open stomata commonly generate the polymerized form of actin in guard cells, leaves of Commelina communis L. were treated with a potent stomatal opening agent, fusicoccin, and the actin organization examined by immunolocalization
techniques. When stomata were induced to open by fusicoccin, hardly any of the filamentous form of actin was detected; instead,
the actin resembled that present in guard cells that had been treated with an antagonist to actin filaments, cytochalasin
D, and showed a sharp contrast to the long filaments developed in illuminated guard cells. Furthermore, treatment of illuminated
leaves with fusicoccin disintegrated actin filaments that had already been formed in the guard cells. Preincubation of leaves
with phalloidin, which interferes with fusicoccin-induced actin depolymerization, delayed fusicoccin-induced opening during
the early phase. These observations suggest that the prevention of actin filament formation and/or depolymerization of actin
filaments may accelerate the stomatal opening process in response to fusicoccin.
Received: 1 October 1999 / Accepted: 29 November 1999 相似文献
10.
Seed mass and seedling dimensions in relation to seedling establishment 总被引:10,自引:0,他引:10
Several experiments have shown that seedlings from larger-seeded species are better able to survive various hazards during
establishment. Previous work has suggested a general mechanism might underpin this outcome. Larger-seeded species might tend
to mobilize their metabolic resources over a longer period into the autotrophically functioning structures of the seedling.
Consequently relatively more resources would remain uncommitted at any given time during the early period of the seedling’s
growth, and available to support respiration during carbon deficit. An important aspect of this larger-seed-later-commitment
mechanism would be that at a given time, larger-seeded species would hold more resources uncommitted not just absolutely,
but relative to the functional seedling structures that needed to be supported. Here we quantify, across a wide range of phanerocotylar
species, an allometric pattern that supports the generality of a larger-seed-later-commitment mechanism as an explanation
for superior performance by larger-seeded species in face of the hazards of seedling establishment. Larger-seeded species
allocate relatively less to cotyledon area, reflecting the initial functional size of the seedling, and relatively more to
dry mass per unit area of cotyledon, reflecting stored metabolic reserves. The shift in relative allocation is progressive,
rather than seedlings falling into discrete morphological types. The allometry is similar whether considered as correlated
evolutionary divergences (phylogenetically independent contrasts) or as correlation across present-day species.
Received: 7 April 1999 / Accepted: 29 March 2000 相似文献
11.
Myosin and actin are necessary for polar lobe formation and resorption in Ilyanassa obsoleta embryos
During the first mitotic divisions many spiralian embryos form a cytoplasmic protrusion at the vegetal pole called the polar
lobe. In the gastropod Ilyanassa obsoleta the polar lobe is constricted by a contractile ring composed of filamentous actin, myosin, and associated proteins, similar
to the contractile ring of the cleavage furrow. To resolve the role of myosin and actin in polar lobe formation and resorption,
we have applied 2,3-butanedione monoxime and Latrunculin B at different stages of the first cleavage to inhibit myosin and
F-actin, respectively. Our results show that myosin is important for both cytokinesis and polar lobe formation. Additionally,
we have found that the resorption of the polar lobe is a two-step process: the first step is passive, driven by the tension
of the actin-cortex and the second step is active, in which the ATP-hydrolysis of myosin/actin interaction supplies the force
to complete the resorption of the polar lobe. We have summarized our results in a scheme of the first cleavage of Ilyanassa obsoleta.
Received: 6 November 1997 / Accepted:15 March 1998 相似文献
12.
In many types of plant cell, bundles of actin filaments (AFs) are generally involved in cytoplasmic streaming and the organization
of transvacuolar strands. Actin cross-linking proteins are believed to arrange AFs into the bundles. In root hair cells of
Hydrocharis dubia (Blume) Baker, a 135-kDa polypeptide cross-reacted with an antiserum against a 135-kDa actin-bundling protein (135-ABP),
a villin homologue, isolated from lily pollen tubes. Immunofluorescence microscopy revealed that the 135-kDa polypeptide co-localized
with AF bundles in the transvacuolar strand and in the sub-cortical region of the cells. Microinjection of antiserum against
135-ABP into living root hair cells induced the disappearance of the transvacuolar strand. Concomitantly, thick AF bundles
in the transvacuolar strand dispersed into thin bundles. In the root hair cells, AFs showed uniform polarity in the bundles,
which is consistent with the in-vitro activity of 135-ABP. These results suggest that villin is a factor responsible for bundling
AFs in root hair cells as well as in pollen tubes, and that it plays a key role in determining the direction of cytoplasmic
streaming in these cells.
Received: 16 September 1999 / Accepted: 3 December 1999 相似文献
13.
The involvement of actin filaments (AFs) in vesicle trafficking, cell wall construction and tip growth was investigated during pollen tube development of Picea meyeri. Pollen germination and tube elongation were inhibited in a dose-dependent manner by the latrunculin B (LatB) treatment. The fine AFs were broken down into disorganized fragments showing a tendency to aggregate. FM4-64 labeling revealed that the dynamic balance of vesicle trafficking was perturbed due to F-actin disruption and the fountain-like cytoplasmic pattern changed into disorganized Brownian movement. The configuration and/or distribution of cell wall components, such as pectins, callose and cellulose, as well as arabinogalactan proteins changed in obvious ways after the LatB application. Fourier transform infrared (FTIR) analysis further established significant changes in the chemical composition of the wall material. Our results indicate that depolymerization of AFs affects the distribution and configuration of cell wall components in Picea meyeri pollen tube by disturbing vesicle trafficking. 相似文献
14.
We describe an evolutionary comparison of expression of the actin gene families of two congeneric sea urchins. Heliocidaris tuberculata develops indirectly via a planktonic feeding pluteus that forms a juvenile rudiment after a long period of larval development.
H. erythrogramma is a direct developer that initiates formation of a juvenile rudiment immediately following gastrulation. The developmental
expression of each actin isoform of both species was determined by in situ hybridization. The observed expression patterns
are compared with known expression patterns in a related indirect-developing sea urchin, Strongylocentrotus purpuratus. Comparisons reveal unexpected patterns of conserved and divergent expression. Cytoplasmic actin, CyIII, is expressed in
the aboral ectoderm cells of the indirect developers, but is an unexpressed pseudogene in H. erythrogramma, which lacks aboral ectoderm. This change is correlated with developmental mode. Two CyII actins are expressed in S. purpuratus, and one in H. erythrogramma, but no CyII is expressed in H. tuberculata despite its great developmental similarity to S. purpuratus. CyI expression differs slightly between Heliocidaris and Strongylocentrotus with more ectodermal expression in Heliocidaris. Evolutionary changes in actin gene expression reflect both evolution of developmental mode as well as a surprising flexibility
in gene expression within a developmental mode.
Received: 27 July 1997 / Accepted: 30 December 1997 相似文献
15.
Voigt B Timmers AC Samaj J Müller J Baluska F Menzel D 《European journal of cell biology》2005,84(6):595-608
In vivo visualization of filamentous actin in all cells of Arabidopsis thaliana seedlings is essential for understanding the numerous roles of the actin cytoskeleton in diverse processes of cell differentiation. A previously introduced reporter construct based on the actin-binding domain of mouse talin proved to be useful for unravelling some of these aspects in cell layers close to the organ surface. However, cells more deeply embedded, especially stelar cells active in polar transport of auxin, show either diffuse or no fluorescence at all due to the lack of expression of the fusion protein. The same problem is encountered in the root meristem. Recently introduced actin reporters based on fusions between A. thaliana fimbrin 1 and GFP gave brilliant results in organs from the root differentiation zone upwards to the leaves, however failed to depict the filamentous actin cytoskeleton in the transition zone of the root, in the apical meristem and the root cap. To overcome these problems, we have prepared new transgenic lines for the visualization of F-actin in vivo. We report here that a construct consisting of GFP fused to the C-terminal half of A. thaliana fimbrin 1 reveals dynamic arrays of F-actin in all cells of stably transformed A. thaliana seedlings. 相似文献
16.
Summary. The leaf cells of Chlorophytum comosum seem to have the ability to regulate their protoplast volume and shape during the plasmolytic cycle. This phenomenon was
morphologically expressed by the stabilization of the plasmolyzed protoplast volume and shape within 1–5 min after the immersion
of the leaf segments in the plasmolytic fluid and temporarily at the onset of deplasmolysis. During the latter stage the plasmolyzed
protoplast rounded up and assumed a perfectly convex shape and glided into the cell lumen along the cell axis. This gliding
movement was active, nonsaltatory, and conducted with a constant velocity and lasted for a short time. During this movement
the protoplast volume did not change appreciably. As far as we know, this movement has not been described so far. Deplasmolysis
proceeded and was rapidly completed when the protoplast stopped moving. Leaf cells which have been affected by an antiactin
filament drug or myosin inhibitors lost their ability to regulate the volume and shape of the plasmolyzing protoplast. In
addition, the gliding protoplast movement was also inhibited in the treated cells. These data show for the first time that
the actomyosin system is involved in the mechanism of volume regulation during the plasmolytic cycle and that it underlies
the gliding movement of the deplasmolyzing protoplast.
Received June 3, 2002; accepted September 26, 2002; published online April 2, 2003
RID="*"
ID="*" Correspondence and reprints: Department of Botany, Faculty of Biology, University of Athens, Athens 15784, Greece.
E-mail: bgalatis@biol.uoa.gr 相似文献
17.
Pyrus pyrifolia stylar S-RNase induces alterations in the actin cytoskeleton in self-pollen and tubes in vitro 总被引:1,自引:0,他引:1
Summary. Pears (Pyrus pyrifolia L.) have an S-RNase-based gametophytic self-incompatibility system, and S-RNases have also been implicated in self-pollen
or genetically identical pollen rejection. Tip growth of the pollen tube is dependent on a functioning actin cytoskeleton.
In this study, configurations of the actin cytoskeleton in P. pyrifolia pollen and effects of stylar S-RNases on its dynamics were investigated by fluorescence and confocal microscopy. Results
show that actin filaments in normal pollen grains exist in fusiform or circular structures. When the pollen germinates, actin
filaments assembled around one of the germination pores, and then actin bundles oriented axially throughout the shank of the
growing tube. There was a lack of actin filaments 5–15 μm from the tube tip. When self-stylar S-RNase was added to the basal
medium, pollen germination and tube growth were inhibited. The configuration of the actin cytoskeleton changed throughout
the culturing time: during the first 20 min, the actin configurations in the self-pollen and tube were similar to the control;
after 20 min of treatment, the actin filaments in the pollen tube gradually moved into a network running from the shank to
the tip; finally, there was punctate actin present throughout the whole tube. Although the actin filaments of the self-pollen
grain also disintegrated into punctate foci, the change was slower than in the tube. Furthermore, the alterations to the actin
cytoskeleton occurred prior to the arrest of pollen tube growth. These results suggest that P. pyrifolia stylar S-RNase induces alterations in the actin cytoskeleton in self-pollen grains and tubes.
Correspondence: Shao-ling Zhang, College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu 210095, People’s
Republic of China. 相似文献
18.
Summary. In root hair cells of Limnobium stoloniferum, transvacuolar strands disperse and cytoplasmic spherical bodies (CSBs) emerge upon treatment with a protein phosphatase
inhibitor, calyculin A (CA), whose effects were previously shown to be canceled by simultaneous treatment of the cells with
a nonselective protein kinase inhibitor, K-252a. CSB formation is also suppressed by latrunculin B (LB) or cytochalasin D,
actin filament depolymerization drugs, or 2,3-butanedione monoxime, an inhibitor of myosin activity. To confirm the involvement
of myosin activity in CSB formation induced by CA, we examined the effect of an inhibitor of energy metabolism, NaN3, on CSB formation in root hair cells pretreated simultaneously with CA and LB. In the presence of CA-LB, CSB formation was
suppressed due to the depolymerization of actin filaments. When these drugs were removed, the actin filaments recovered and
CSBs emerged even in the presence of K-252a. These results indicated that the phosphorylation level in the cells is elevated
during the CA-LB treatment and that a phosphorylation level sufficient for the CSB formation was sustained even after CA removal.
On the other hand, CSB formation after simultaneous treatment with CA and LB was significantly suppressed in the presence
of NaN3. In such cells, actin filament bundles recovered, although their organization was random. The present and previous results
suggested that myosin activity is necessary for CSB formation induced by CA, and that myosin regulated by phosphorylation-dephosphorylation
is implicated in the organization of the actin cytoskeleton in root hair cells.
Received June 26, 2002; accepted October 18, 2002; published online April 2, 2003
RID="*"
ID="*" Correspondence and reprints: Department of Life Science, Graduate School of Science, Himeji Institute of Technology,
Harima Science Park City, Hyogo 678-1297, Japan. 相似文献
19.
Copidosoma floridanum is a polyembryonic wasp that undergoes total cleavage of the egg followed by proliferation of blastomeres to produce up to
2,000 embryos from a single egg. This unusual mode of development raises several questions about how axial polarity is established
in individual embryonic primordia. By examining embryonic development of larvae with duplicated structures (conjoined larvae),
we determined that conjoined larvae form by mislocalization of two embryonic primordia to a common chamber of the extraembryonic
membrane that surrounds individual embryos. Analysis of an anterior marker, Distalless, in mislocalized early embryos indicated
that anterior structures form independently of one another. This suggests each embryonic primordium has some intrinsic polarity.
However, during germband extension embryos usually fuse in register with each other, resulting in conjoined larvae with heads
facing each other. Analysis of the posterior segmental marker, Engrailed, in conjoined embryos suggested that fusion in register
initiates during germband extension. Thus, even though embryonic primordia initially have a random axial orientation, conjoined
larvae usually possess a common orientation due to reorientation during germband extension. These observations suggest that
differential cellular affinities during segmentation play an important role in embryo fusion.
Received: 13 June 1996 / Accepted: 15 August 1996 相似文献
20.
T.L. Herring C.S. Cohan E.A. Welnhofer L.R. Mills C.E. Morris 《The Journal of membrane biology》1999,171(2):151-169
Neuronal shape and volume changes require accompanying cell surface adjustments. In response to osmotic perturbations, neurons
show evidence of surface area regulation; shrinking neurons invaginate membrane at the substratum, pinch off vacuoles, and
lower their membrane capacitance. F-actin is implicated in reprocessing newly invaginated membrane because cytochalasin causes
the transient shrinking-induced invaginations, vacuole-like dilations (VLDs), to persist indefinitely instead of undergoing
recovery. To help determine if cortical F-actin indeed contributes to cell surface area regulation, we test, here, the following
hypothesis: invaginating VLD membrane rapidly establishes an association with F-actin and this association contributes to
VLD recovery. Cultured molluscan (Lymnaea) neurons, whose large size facilitates three-dimensional imaging, were used. In fixed neurons, fluorescent F-actin stains
were imaged. In live neurons, VLD membrane was monitored by brightfield microscopies and actin was monitored via a fluorescent
tag. VLD formation (unlike VLD recovery) is cytochalasin insensitive and consistent with this, VLDs formed readily in cytochalasin-treated
neurons but showed no association with F-actin. Normally, however (i.e., no cytochalasin), VLDs were foci for rapid reorganization
of F-actin. At earliest detection (1–2 min), nascent VLDs were entirely coated with F-actin and by 5 min, VLD mouths (i.e.,
at the substratum) had become annuli of F-actin-rich motile leading edge. Time lapse images from live neurons showed these
rings to be motile filopodia and lamellipodia. The retrieval of VLD membrane (vacuolization) occurred via actin-associated
constriction of VLD mouths. The interplay of surface membrane and cortical cytoskeleton in osmotically perturbed neurons suggests
that cell surface area and volume adjustments are coordinated in part via mechanosensitive F-actin dynamics.
Received: 25 March 1999/Revised: 15 June 1999 相似文献