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PubMed2006

Dynamic organization of the actin cytoskeleton during meiosis and spore formation in budding yeast.

During sporulation in Saccharomyces cerevisiae, the four daughter cells (spores) are formed inside the boundaries of the mother cell. Here, we investigated the dynamics of spore assembly and the actin cytoskeleton during this process, as well as the requirements for filamentous actin during the different steps of spore formation. We found no evidence for a polarized actin cytoskeleton during sporulation. Instead, a highly dynamic network of non-polarized actin cables is present underneath the plasma membrane of the mother cell. We found that a fraction of prospore membrane (PSM) precursors are transported along the actin cables. The velocity of PSM precursors is diminished if Myo2p or Tpm1/2p function is impaired. Filamentous actin is not essential for meiotic progression, for shaping of the PSMs or for post-meiotic cytokinesis. However, actin is essential for spore wall formation. This requires the function of the Arp2/3p complex and involves large carbohydrate-rich compartments, which may be chitosome analogous structures.

Actin Cytoskeleton↗
PubMed1993

Mechanotransduction across the cell surface and through the cytoskeleton.

Mechanical stresses were applied directly to cell surface receptors with a magnetic twisting device. The extracellular matrix receptor, integrin beta 1, induced focal adhesion formation and supported a force-dependent stiffening response, whereas nonadhesion receptors did not. The cytoskeletal stiffness (ratio of stress to strain) increased in direct proportion to the applied stress and required intact microtubules and intermediate filaments as well as microfilaments. Tensegrity models that incorporate mechanically interdependent struts and strings that reorient globally in response to a localized stress mimicked this response. These results suggest that integrins act as mechanoreceptors and transmit mechanical signals to the cytoskeleton. Mechanotransduction, in turn, may be mediated simultaneously at multiple locations inside the cell through force-induced rearrangements within a tensionally integrated cytoskeleton.

Actin Cytoskeleton↗
PubMed1986

Progressive reorganization of the host cell cytoskeleton during adenovirus infection.

Infection of cells with adenovirus lead to a characteristic reorganization of all cytoskeleton systems, starting with alterations at the microtubuli of the cells. During this progress, the flat, extended, and polar morphology of the cytoskeleton became nonpolar and rounder. These rearrangements were initiated before the appearance of adenovirus structural proteins hexon and fiber, as well as before the shutoff of host protein synthesis. We conclude that these alterations reflect a specific reorganization rather than an unorganized breakdown of the cell during adenovirus infection.

Actin Cytoskeleton↗
PubMed1999

LPS-induced depolymerization of cytoskeleton and its role in TNF-alpha production by rat pneumocytes.

Lipopolysaccharide (LPS) polymerizes microfilaments and microtubules in macrophages and monocytes. Disrupting microfilaments or microtubules with cytochalasin D (CytoD) or colchicine can suppress LPS-induced tumor necrosis factor-alpha (TNF-alpha) gene expression and protein production from these cells. We have recently demonstrated that primary cultured rat alveolar epithelial cells can produce TNF-alpha on LPS stimulation. In the present study, we found that the LPS-induced increase in TNF-alpha mRNA level and protein production in alveolar epithelial cells was not inhibited by CytoD or colchicine (1 nM to 10 microM). In fact, LPS-induced TNF-alpha production was further enhanced by CytoD (1-10 microM) and inhibited by jasplakinolide, a polymerizing agent for microfilaments. Immunofluorescent staining and confocal microscopy showed that LPS (10 microg/ml) depolymerized microfilaments and microtubules within 15 min, which was prolonged until 24 h for microfilaments. These results suggest that the effects of LPS on the cytoskeleton and the role of the cytoskeleton in mediating TNF-alpha production in alveolar epithelial cells are opposite to those in immune cells. This disparity may reflect the different roles between nonimmune and immune cells in host defense.

Actin Cytoskeleton↗
PubMed2006

Microtubule-targeting agents inhibit angiogenesis at subtoxic concentrations, a process associated with inhibition of Rac1 and Cdc42 activity and changes in the endothelial cytoskeleton.

Conventional anticancer agents may display antiangiogenic effects, but the underlying mechanism is poorly understood. We determined the antiangiogenic properties of cisplatin, doxorubicin, and the microtubule-targeting agents docetaxel, epothilone B, and vinblastine at concentrations not affecting cell proliferation. We also assessed tubulin and actin morphology and the activity of two key molecules in cell motility, the small Rho GTPases Cdc42 and Rac1. The highest non-toxic concentration (HNTC) of each drug was defined as the concentration inhibiting a maximum of 10% human umbilical vein endothelial cell growth on a 1-hour drug exposure, being for cisplatin 10 micromol/L, doxorubicin 100 nmol/L, docetaxel 10 nmol/L, epothilone B 1 nmol/L, and vinblastine 10 nmol/L. Comparative endothelial cell functional assays using HNTCs for an exposure time of 1 hour indicated that endothelial cell migration in the wound assay, endothelial cell invasion in a transwell invasion system, and endothelial cell formation into tubelike structures on a layer of Matrigel were significantly inhibited by docetaxel, epothilone B, and vinblastine (P < 0.05), but not by cisplatin and doxorubicin. Docetaxel was slightly more efficient in the inhibition of endothelial cell motility than epothilone B and vinblastine. Fluorescence microscopy revealed that only the microtubule-targeting agents affected the integrity of the tubulin and F-actin cytoskeleton, which showed disturbed microtubule structures, less F-actin stress fiber formation, and appearance of nuclear F-actin rings. These observations were associated with early inhibition of Rac1 and Cdc42 activity. In conclusion, HNTCs of microtubule-targeting agents efficiently reduce endothelial cell motility by interference with microtubule dynamics preventing the activation of Rac1/Cdc42 and disorganizing the actin cytoskeleton.

Actin Cytoskeleton↗
PubMed2006

The endothelial cytoskeleton as a target of electroporation-based therapies.

Electroporation-based therapies, such as electrochemotherapy and electrogene therapy, result in the disruption of blood vessel networks in vivo and cause changes in blood flow and vascular permeability. The effects of electroporation on the cytoskeleton of cultured primary endothelial cells and on endothelial monolayer permeability were investigated to elucidate possible mechanisms involved. Human umbilical vein endothelial cells (HUVECs) were electroporated in situ and then immunofluorescence staining for filamentous actin, beta-tubulin, vimentin, and VE-cadherin as well as Western blotting analysis of levels of phosphorylated myosin light chain and cytoskeletal proteins were performed. Endothelial permeability was determined by monitoring the passage of FITC-coupled dextran through endothelial monolayers. Exposure of endothelial cells to electric pulses resulted in a profound disruption of microfilament and microtubule cytoskeletal networks, loss of contractility, and loss of vascular endothelial cadherin from cell-to-cell junctions immediately after electroporation. These effects were voltage dependent and reversible because cytoskeletal structures recovered within 60 min of electroporation with up to 40 V, without any significant loss of cell viability. The cytoskeletal effects of electroporation were paralleled by a rapid increase in endothelial monolayer permeability. These results suggest that the remodeling of the endothelial cytoskeleton and changes in endothelial barrier function could contribute to the vascular disrupting actions of electroporation-based therapies and provide an insight into putative mechanisms responsible for the observed increase in permeability and cessation of blood flow in vivo.

Actin Cytoskeleton↗
PubMedDate not supplied

Morphometry of axon cytoskeleton at internodal regions of rat sciatic nerve during aging.

BACKGROUND: Nerve endings undergo a lifespan morphofunctional modulation which is reported to be markedly impaired with aging. Neurone structural remodelling is in charge of processes occurring in the nerve cell soma, however the axonal transportation of organelles and molecules by cytoskeletal elements plays a very important role in the morphological rearrangements taking place at peripheral compartments. OBJECTIVE: To assess the involvement of axonal ultrastructure in the reported age-related decline of slow axoplasm flow mechanisms, we carried out a morphometric study of axon cytoskeleton in aging. METHODS: Female Wistar rats (3, 12 and 30 months of age) were anesthetized and perfused with saline followed by a fixation solution (glutaraldehyde 5% + formalin 2% in 0.1 cacodylate buffer pH 7.4). The excised sciatic nerves were processed according to conventional electron microsopic procedures. Axons sectioned perpendicularly to their longitudinal axis at the internodal region (mean axoplasm area: 18.25-26.5 microm(2)) were sampled by a systematic random procedure. The overall number of neurofilaments (No.Nfs) and microtubules (No.Mts) per total axoplasm area analysed, the numeric density (number/microm(2) of axoplasm area) of neurofilaments (NaNfs) and microtubules (NaMts), the myelin thickness, the number of myelin lamellae and the R proportion [No. Nfs/(No.Nfs + No.Mts)] were the parameters measured by computer-assisted semiautomatic methods. RESULTS: No.Nfs, NaNfs, myelin thickness and the number of myelin lamellae did not change between 12 and 30 months of age, while a significant increase of these parameters was found in a comparison with younger rats. No.Mts and NaMts were significantly increased at 12 vs. 3 as well as at 30 vs. 12 months of age, respectively. R proportion did not show any difference due to age. CONCLUSIONS: The present findings support that the dynamic condition of the axonal cytoskeleton appears to be preserved at a high extent in aging. Thus, the intra-axonal defective spacing of cytoskeletal elements (e.g. neurofilaments), rather than their number, is proposed to contribute to the decline of the slow axonal transport of organelles and molecules reported in aging.

Actin Cytoskeleton↗
PubMed1995

Cytoskeleton in myelin-basic-protein-deficient shiverer oligodendrocytes.

Production of CNS myelin by oligodendrocytes requires the regulated synthesis and assembly of cytoskeletal components. However, the molecular signals that mediate this process are not known. Here we use the shiverer mutant mouse, which is missing a large segment of the myelin basic protein (MBP) gene, to investigate the possible role in cytoskeletal assembly of an MBP gene product or of other myelin components whose expression may be linked to that of MBP. In axon-free cultures, we find that approximately half of shiverer oligodendrocytes have enlarged cell bodies, abnormal processes and fail to elaborate extensive membrane sheets. In those membrane sheets that are elaborated by shiverer oligodendrocytes, microtubular structures are abnormal in size and distribution. Additionally, 2',3'-cyclic nucleotide 3'-phosphohydrolase and microfilaments are not colocalized with microtubular structures as they would be in mature wild-type membrane sheets. These observations suggest that an MBP gene product has a direct or indirect role in regulating various aspects of cytoskeleton assembly in wild-type oligodendrocytes. In the absence of this signal, oligodendrocytes apparently do not normally assemble cytoskeleton; this may be one important basis for the abnormal morphology of intact shiverer CNS.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗
PubMed2003

Chlamydia pneumoniae affect surfactant trafficking and secretion due to changes of type II cell cytoskeleton.

Understanding the surfactant dysfunction by gram-negative bacteria pulmonary infection, the intracellular fate of Chlamydia pneumoniae (Cpn), its interaction with uptake, recycling, and secretion of surfactant and with the cytoskeleton of type II pneumocytes was investigated. Bacteria colocalized with surfactant protein (SP)-A-mediated endocytosed lipid and early endosomes (EEA1- and Rab5-positive) after 3 and 6 h of infection. No specific contact with late endosomes (Rab7- and M6PR-positive), lysosomal, or lamellar body markers (CD63, 3C9) was found after 12 h of infection. In Cpn-infected cells, SP-A-mediated lipid uptake was significantly increased. After SP-A-mediated lipid uptake followed by "re-secretion," 90% of the internalized lipid remained intracellularly. SP-A and lipid did strongly colocalize with early endosomes. Internalized SP-A cannot be resecreted rapidly to plasma membrane, and lipid is not transported toward late endosomes (Rab7- and M6PR-positive) or lamellar bodies (CD63- and 3C9-positive). These results indicate that increased surfactant internalization is caused by an inhibition in intracellular surfactant transport. Accumulation of SP-A-mediated lipid was associated with changes in beta-tubulin. Increases in surfactant secretion were associated with changes in F-actin. We postulate that Cpn infection of type II cells causes changes of the cytoskeleton, and that these effects are associated with alterations in intracellular transport and secretion of surfactant.

Actin Cytoskeleton↗
PubMed2000

Imaging of dynamic changes of the actin cytoskeleton in microextensions of live NIH3T3 cells with a GFP fusion of the F-actin binding domain of moesin.

BACKGROUND: The cell surface undergoes continuous change during cell movement. This is characterized by transient protrusion and partial or complete retraction of microspikes, filopodia, and lamellipodia. This requires a dynamic actin cytoskeleton, moesin, components of Rho-mediated signal pathways, rearrangement of membrane constituents and the formation of focal adhesion sites. While the immunofluorescence distribution of endogenous moesin is that of a membrane-bound molecule with marked enhancement in some but not all microextensions, the C-terminal fragment of moesin co-distributes with filamentous actin consistent with its actin-binding activity. By taking advantage of this property we studied the spontaneous protrusive activity of live NIH3T3 cells, expressing a fusion of GFP and the C-terminal domain of moesin. RESULTS: C-moesin-GFP localized to stress fibers and was enriched in actively protruding cellular regions such as filopodia or lamellipodia. This localization was reversibly affected by cytochalasin D. Multiple types of cytoskeletal rearrangements were observed that occurred independent of each other in adjacent regions of the cell surface. Assembly and disassembly of actin filaments occurred repeatedly within the same space and was correlated with either membrane protrusion and retraction, or no change in shape when microextensions were adherent. CONCLUSIONS: Shape alone provided an inadequate criterion for distinguishing between retraction fibers and advancing, retracting or stable filopodia. Fluorescence imaging of C-moesin-GFP, however, paralleled the rapid and dynamic changes of the actin cytoskeleton in microextensions. Regional regulatory control is implicated because opposite changes occurred in close proximity and presumably independent of each other. This new and sensitive tool should be useful for investigating mechanisms of localized actin dynamics in the cell cortex.

3T3 Cells↗
PubMed2003

Calcium regulation of actin crosslinking is important for function of the actin cytoskeleton in Dictyostelium.

The actin cytoskeleton is sensitive to changes in calcium, which affect contractility, actin-severing proteins, actin-crosslinking proteins and calmodulin-regulated enzymes. To dissect the role of calcium control on the activity of individual proteins from effects of calcium on other processes, calcium-insensitive forms of these proteins were prepared and introduced into living cells to replace a calcium-sensitive form of the same protein. Crosslinking and bundling of actin filaments by the Dictyostelium 34 kDa protein is inhibited in the presence of micromolar free calcium. A modified form of the 34 kDa protein with mutations in the calcium binding EF hand (34 kDa deltaEF2) was prepared using site-directed mutagenesis and expressed in E. coli. Equilibrium dialysis using [(45)Ca]CaCl(2) revealed that the wild-type protein is able to bind one calcium ion with a Kd of 2.4 microM. This calcium binding is absent in the 34 kDa deltaEF2 protein. The actin-binding activity of the 34 kDa deltaEF2 protein was equivalent to wildtype but calcium insensitive in vitro. The wild-type and 34 kDa deltaEF2 proteins were expressed in 34-kDa-null and 34 kDa/alpha-actinin double null mutant Dictyostelium strains to test the hypothesis that calcium regulation of actin crosslinking is important in vivo. The 34 kDa deltaEF2 failed to supply function of the 34 kDa protein important for control of cell size and for normal growth to either of these 34-kDa-null strains. Furthermore, the distribution of the 34 kDa protein and actin were abnormal in cells expressing 34 kDa deltaEF2. Thus, calcium regulation of the formation and/or dissolution of crosslinked actin structures is required for dynamic behavior of the actin cytoskeleton important for cell structure and growth.

Actin Cytoskeleton↗
PubMed1996

Three-dimensional organization of rat hepatocyte cytoskeleton: relation to the asialoglycoprotein endocytosis pathway.

Analysis by confocal microscopy has revealed features of the microtubule network of rat hepatocytes in culture, establishing the three-dimensional disposition of the microtubule-based cytoskeleton, its relation to the actin-based cytoskeleton and to ligand-containing endosomes during receptor-mediated endocytosis and the alterations in its structure and disposition by the microtubule pertubant, Taxol. By co-localization studies, we have been able to demonstrate that the microtubules have a significant role in receptor-mediated endocytosis of asialoglycoproteins in this cell. Asialoorosomucoid-containing endosomes attach to widely spaced arrays of microtubules running under the baso-lateral surface of the hepatocytes 5-15 minutes after the initiation of endocytosis and then travel along microtubule paths to become concentrated with microtubules near the centrosome and at bile canaliculi after 30-60 minutes of receptor-mediated endocytosis. Receptor-mediated endocytosis is affected, but not abolished by Taxol, which inhibits the rate of asialoorosomucoid degradation at the same concentrations as those that disrupt microtubule and cytoplasmic dynein distribution, and that prevent the concentration of endosomes centrally. The results support suggestions that asialoorosomucoid-containing endosomes are captured by microtubules just below the actin layer at the cell periphery and these are actively transported centrally along microtubules, possibly by cytoplasmic dynein, so that the concentration of endosomes near the centrosome, and the subsequent efficient lysosomal degradation of ligand, are consequences of the confluence of microtubules in this region.

Actin Cytoskeleton↗
PubMed1990

Fluorescence-mediated visualization of actin and myosin filaments in the contractile membrane-cytoskeleton complex of Dictyostelium discoideum.

An intact complex that consisted of the cell membrane and cytoskeleton was prepared from Dictyostelium amoebae by an improved version of the method previously used by CLARKE et al. (1975). Proc. Natl. Acad. Sci. USA., 72: 1758-1762. After cells had attached tightly to a polylysine-coated coverslip in the presence of a divalent cation, the upper portions of the cells were removed with a jet of microfilament-stabilizing solution squirted from a syringe. The cell membranes left on the coverslip were immediately stained with tetramethylrhodamine-conjugated phalloidin for staining of actin filaments, and with antibody against myosin from Dictyostelium and a fluorescein-conjugated second antibody for staining of myosin. Networks of actin filaments and numerous rod-like structures of myosin (myosin filaments) aligned along them were observed on the exposed cytoplasmic surfaces of the cell membranes. These networks were similar to those observed in the cortex of fixed whole cells. Addition of ATP to these intact complexes of cell membrane and cytoskeleton caused the aggregation of both actin and myosin into several dot-like structures of actin on the cell membrane. Similar dot-like structures were also seen in the cortex of fixed whole cells, and their changes in distribution correlated with the motile activity of the cells. Transmission electron microscopy showed that these dot-like structures were composed of an electron-dense structure at the center, from which numerous actin filaments radiated outwards. These observations suggest that these novel dot-like structures are organizing centers for cortical actin filaments and may possibly be related to the adhesion of cells to the substratum.

Actin Cytoskeleton↗
PubMed2004

Requirement for an intact cytoskeleton for volume regulation in boar spermatozoa.

Osmotically induced cell swelling triggers a chain of events leading to a net loss of major cell ions and water, resulting in cell volume recovery, a process known as regulatory volume decrease (RVD). In many cell types, there is an evidence that the cytoskeleton may play a role in the initial sensing and transduction of the signal of volume change. In this study, we tested the hypothesis that an intact microfilament and microtubule network is required for volume response and RVD in boar sperm before and after capacitation treatment and whether addition of cytochalasin D and colchicine to the capacitation medium would affect volumetric behaviour. Capacitation is a series of cellular and molecular alterations that enable the spermatozoon to fertilize an oocyte. Cell volume measurements of washed sperm suspensions were performed electronically in Hepes-buffered saline solutions of 300 and 180 mosmol/kg. After exposure to hypoosmotic conditions, boar sperm showed initial swelling (up to 150% of initial volume within 5 min), which was subsequently partially reversed (to about 120-130% after 20 min). Treatment with cytochalasin D led to reduced initial swelling (1 micromol/l) and loss of RVD in washed sperm (1-10 micromol/l) and at the beginning of incubation under capacitating conditions (5 micromol/l). Short treatment with 500 micromol/l colchicine affected the volume regulatory ability in sperm under capacitating conditions but not in washed sperm. No significant differences in cell volume response were observed after subsequent addition of cytochalasin D and colchicine to the suspensions of sperm incubated for 3 h under capacitating conditions. However, the incubation under capacitating conditions in the presence of cytochalasin D led to improved volume regulation at the end of the incubation period (23%). The microfilament network appears to be important for volume regulation in washed boar spermatozoa while intact microtubules do not seem to be necessary for osmotically induced RVD. The changes in cytoskeleton microfilament organization during capacitation, possibly affecting the osmotically induced volume response, appear to occur at the later stages of capacitation, whereas changes in microtubules, related to volume regulatory ability, may be programmed within the first stages of capacitation.

Actin Cytoskeleton↗
PubMed1989

Morphological study of the cytoskeleton of endothelial cells in vitro. Effects of heparin and protamine.

The relation between the cytoskeleton and multiplication of cultured endothelial cells was observed immunocytochemically and electron microscopically. Heparin and protamine were used to control the multiplication of the cells. Cytochalasin D, a microfilament synthesis inhibitor, was also used, and its effect on cytoskeletal morphology was compared with the effect of heparin or protamine. In order to quantify changes in microfilaments, the ratio of the length of microfilaments to that of intermediate filaments (M/I ratio) was measured by transmission electron microscopy of the whole mounted cells. The addition of heparin to the culture medium not only enhanced multiplication of the endothelial cells, but also induced the outgrowth of many pseudopodia. In association with these changes, microfilaments became sparse, and stress fibers became short. The addition of protamine to the culture medium suppressed multiplication of endothelial cells and made them spherical. The thickening of the cytoplasmic layer increased the apparent density of the cytoskeleton, but the M/I ratio remained unchanged. Cytochalasin D made the endothelial cells spherical, and at the same time stress fibers disappeared, and microfilaments became sparse. The M/I ratio was smaller than that of the others. Protamine may inactivate protein which forms bridges to connect microfilaments or which binds microfilaments and the cell membrane.

Actin Cytoskeleton↗
PubMed2006

Endothelial cell cortactin coordinates intercellular adhesion molecule-1 clustering and actin cytoskeleton remodeling during polymorphonuclear leukocyte adhesion and transmigration.

Endothelial cell ICAM-1 interacts with leukocyte beta(2) integrins to mediate adhesion and transmit outside-in signals that facilitate leukocyte transmigration. ICAM-1 redistribution and clustering appear necessary for leukocyte transmigration, but the mechanisms controlling ICAM-1 redistribution and clustering have not been identified. We recently reported that Src kinase phosphorylation of endothelial cortactin regulates polymorphonuclear cell (PMN) transmigration. In this study, we tested the hypotheses that the Src family kinase-cortactin pathway mediates association of ICAM-1 with the actin cytoskeleton and that this association is required for ICAM-1 clustering and leukocyte transmigration. Cross-linking ICAM-1 induced cytoskeletal remodeling and a decrease in ICAM-1 lateral mobility, as assessed by fluorescence recovery after photobleaching. Cytoskeletal remodeling after ICAM-1 cross-linking was reduced by knockdown of cortactin by small interfering RNA, by expression of a cortactin mutant deficient in Src phosphorylation sites (cortactin3F), and by the Src kinase inhibitor PP2. Pretreatment of cytokine-activated human endothelial monolayers with cortactin small interfering RNA significantly decreased both actin and ICAM-1 clustering around adherent PMN and the formation of actin-ICAM-1 clusters required for PMN transmigration. Our data suggest a model in which tyrosine phosphorylation of cortactin dynamically links ICAM-1 to the actin cytoskeleton, enabling ICAM-1 to form clusters and facilitate leukocyte transmigration.

Actin Cytoskeleton↗
PubMed1995

Involvement of the cytoskeleton in regulation of collagen synthesis and secretion.

11-day chick embryo skin fibroblasts administered in vitro with colchicine or cytochalasin B, have been investigated for collagen synthesis and secretion. The cytoskeleton, examined by confocal laser scanning immunofluorescence microscope, exibited in colchicine treated cells a clear loss of microtubules, in cytochalasin B treated cells a diffuse staining and patches of intracellular fluorescence caused by actin disassembly. Cytochalasin B treatment decreased endocellular type I collagen synthesis and the total uptake of 3H-proline, while enhanced collagen secretion. Colchicine did not interfere with the collagen secretion and the label uptake, whereas it increased endocellular collagen synthesis. In addition, both drugs induced an increase of the alpha2:alpha1 ratio of collagen chains. The results obtained suggest that the cytoskeleton controls not only the morphological organization of cell components, but also the organization of biochemical processes.

Actin Cytoskeleton↗
PubMed2001

[Alterations in actin cytoskeleton and rate of reparation of human endothelium (the wound-healing model) under the condition of clinostatting].

Effects of long-term simulation of hypogravity on actin cytoskeleton and cell migration were investigated in cultured human endothelium cells (EC). In control, F-actin resided predominantly on the periphery of cell forming an array of parallel bundles with "dense bodies" along the edge. A small number of actin cable fibers was found in the center. Already after 1-2 hrs of clinostatting at 5 RPM the cell cytoskeleton showed actin filament thinning and displacement toward the cell edges. In subsequent 6-18 hrs, almost all actin fibers had left the center part of EC and had ranged themselves in a continuous F-actin line in the intercellular contact area. In most cases, these changes resulted in the so-called "ruff-edge". Since both the disappearance of cable fibers and formation of the "ruff-edge" add to the cell migration activity, this parameter was studied with the would-healing model. According to our data, 24-48 hrs of exposure to hypogravity stimulates cell migration and expedites 2-3 times reparation of mechanically damaged monolayer. The results suggest that effects of hypogravity on cultured human EC are likely to be consequent to alterations in the activity of protein kinase C and/or adenylate cyclase involving many members of the cellular metabolism.

Actin Cytoskeleton↗