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At least 73 records · Page 4Linked to original sources
PubMed1993

Tyrosine phosphorylation of actin in Dictyostelium associated with cell-shape changes.

When Dictyostelium cells that have initiated their developmental program upon starvation are returned to growth medium, there is a rapid and transient de novo tyrosine phosphorylation of a 43-kilodalton protein. This protein was found to be actin. Most of the phosphorylation occurred in a single, minor acidic isoform of actin. Developing cells that had been returned to growth medium lost their pseudopod extensions, became round, and had reduced adhesion to the substratum. These effects occurred with kinetics that matched the increase in tyrosine phosphorylation of actin. In mutant cell lines in which the gene for the phosphotyrosine phosphatase PTP1 had been disrupted, tyrosine phosphorylation of actin was rapid and more prolonged. These cells responded with proportionally accelerated kinetics of cell rounding. Cell lines overexpressing PTP1 had diminished amplitude and duration of actin tyrosine phosphorylation and exhibited diminished cell-shape change and an accelerated return to the extended cell-shape morphology seen in starved cells.

Actins↗
PubMed1987

Regulation of cell shape in the Cloudman melanoma cell line.

We show that Cloudman melanoma cells undergo rapid arborization in response to [Nle4,D-Phe7]alpha-melanocyte-stimulating hormone, a potent analogue of alpha-melanocyte stimulating hormone (alpha-MSH). The arbors were established by extension of processes and resembled dendrites. We used this system to study the regulation of cell shape. alpha-MSH is known to induce increases in cAMP levels, and agents such as forskolin and isobutylmethylxanthine that led to increased cAMP also caused arborization. However, equally dramatic arbors were formed after incubation with the protein kinase C inhibitor H-7 [1-(5-isoquinolinesulfonyl)-alpha-methyl-piperazine]. Phorbol diesters that activate protein kinase C led to cell rounding and antagonized alpha-MSH. The actions of protein kinase C cannot be rationalized in terms of indirect effects on cAMP: neither H-7 nor phorbol diesters alone altered cAMP levels, nor did they affect the increase in cAMP induced by MSH. We show also that MSH produced longer-term effects that cannot be mimicked by cAMP. Specifically, even in the continued presence of alpha-MSH, arborization was followed by morphological reversal to the unstimulated flattened configuration within 2 hr. (This did not occur with other agents that increase cAMP or with H-7.) Most importantly, whereas MSH-induced arborization occurred in the presence of cycloheximide, actinomycin D, or in enucleated cells, the reversal of arborization did not. Thus, MSH induced a program of rapid shape change that was dependent on new protein synthesis and gene transcription.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMedDate not supplied

[Membrane organization in the plane of the layer and cell shape. Statistical approach].

Relationship between the structure and mechanical properties of membranes and the shape of cells was analysed. Fluid-mosaic model of the membrane with several components was studied. The components could move freely in the membrane plane, interacted with each other and had different mechanical properties, such as bending rigidity and spontaneous curvature. For such a multicomponent system free energy was found, and integral-differential equations relating the distribution of membrane components and the membrane local curvature were obtained from the condition of free energy minimum. A number of consequences were obtained from the equation. With a change of intramembrane interactions phase separation or calsterization of particles is initiated. This in its turn may cause a strong change in the local curvature. The numerical solution of the system for two -- dimensional case made it possible to find the distribution of structural components along the membrane and calculate the cell shape. Some transformation of erythrocytes were described.

Biomechanical Phenomena↗
PubMedDate not supplied

Micropatterned surfaces for control of cell shape, position, and function.

The control of cell position and function is a fundamental focus in the development of applications ranging from cellular biosensors to tissue engineering. Using microcontact printing of self-assembled monolayers (SAMs) of alkanethiolates on gold, we manufactured substrates that contained micrometer-scale islands of extracellular matrix (ECM) separated by nonadhesive regions such that the pattern of islands determined the distribution and position of bovine and human endothelial cells. In addition, the size and geometry of the islands were shown to control cell shape. Traditional approaches to modulate cell shape, either by attaching suspended cells to microbeads of different sizes or by plating cells on substrates coated with different densities of ECM, suggested that cell shape may play an important role in control of apoptosis as well as growth. Data are presented which show how micropatterned substrates were used to definitively test this hypothesis. Progressively restricting bovine and human endothelial cell extension by culturing cells on smaller and smaller micropatterned adhesive islands regulated a transition from growth to apoptosis on a single continuum of cell spreading, thus confirming the central role of cell shape in cell function. The micropatterning technology is therefore essential not only for construction of biosurface devices but also for the investigation of the fundamental biology of cell-ECM interactions.

Animals↗
PubMed2003

Changes in cell shape, cytoskeletal proteins and adhesion sites of cultured cells after extracellular Ca2+ chelation.

Although much is known about the molecules involved in extracellular Ca2+ regulation, the relationship of the ion with overall cell morphology is not understood. The objective of the present study was to determine the effect of the Ca2+ chelator EGTA on the major cytoskeleton components, at integrin-containing adhesion sites, and their consequences on cell shape. Control mouse cell line C2C12 has a well-spread morphology with long stress fibers running in many different directions, as detected by fluorescence microscopy using rhodamine-phalloidin. In contrast, cells treated with EGTA (1.75 mM in culture medium) for 24 h became bipolar and showed less stress fibers running in one major direction. The adhesion plaque protein alpha 5-integrin was detected by immunofluorescence microscopy at fibrillar adhesion sites in both control and treated cells, whereas a dense labeling was seen only inside treated cells. Microtubules shifted from a radial arrangement in control cells to a longitudinal distribution in EGTA-treated cells, as analyzed by immunofluorescence microscopy. Desmin intermediate filaments were detected by immunofluorescence microscopy in a fragmented network dispersed within the entire cytoplasm in EGTA-treated cells, whereas a dense network was seen in the whole cytoplasm of control cells. The present results suggest that the role of extracellular Ca2+ in the regulation of C2C12 cell shape can be mediated by actin-containing stress fibers and microtubules and by intermediate filament reorganization, which may involve integrin adhesion sites.

Animals↗
PubMed2006

A default mechanism of spindle orientation based on cell shape is sufficient to generate cell fate diversity in polarised Xenopus blastomeres.

The process of oriented divisions of polarised cells is a recurrent mechanism of cell fate diversification in development. It is commonly assumed that a specialised mechanism of spindle alignment into the axis of polarity is a prerequisite for such systems to generate cell fate diversity. Oriented divisions also take place in the frog blastula, where orientation of the spindle into the apicobasal axis of polarised blastomeres generates inner and outer cells with different fates. Here, we show that, in this system, the spindle orients according to the shape of the cells, a mechanism often thought to be a default. We show that in the embryo, fatedifferentiative, perpendicular divisions correlate with a perpendicular long axis and a small apical surface, but the long axis rather then the size of the apical domain defines the division orientation. Mitotic spindles in rounded, yet polarised, isolated Xenopus blastula cells orient randomly, but align into an experimentally introduced long axis when cells are deformed early in the cell cycle. Unlike other systems of oriented divisions, the spindle aligns at prophase, rotation behaviour is rare and restricted to small angle adjustments. Disruption of astral microtubules leads to misalignment of the spindle. These results show that a mechanism of spindle orientation that depends on cell shape rather than cortical polarity can nevertheless generate cell fate diversity from a population of polarised cells.

Animals↗
PubMedDate not supplied

Regulation of epithelial cell shape and polarity by cell-cell adhesion (Review).

Among all cell types that exhibit a polarized phenotype, epithelial cells are unique in that their polarity depends on the integration of the cell into a tissue, the epithelium. In recent years, the analysis of epithelial cell polarity in different epithelia and organisms has contributed to an understanding of the components involved and has further demonstrated that cell polarity and cell adhesion are intimately related to each other. Therefore, processes that mediate and modulate cell adhesion and coordinate adhesion and cell shape are fundamental for the function of epithelia. Recent results obtained in Drosophila melanogaster and Caenorhabditis elegans have provided further insight into the complex circuits regulating these processes, and have laid the direction for future analysis.

Animals↗
PubMed1985

On the role of microfilaments in cell-shape-mediated growth control of lens epithelial cells.

With regard to the fact that, in anchorage-dependent lens epithelial cells, DNA synthesis can be switched on and off by cell flattening and cell rounding, respectively, the state of the microfilaments has been followed by labelling actin with FL-phalloidin during cell-shape alterations. Cell flattening proved to be accompanied by both a structural organization of actin filaments into stress fibres and an enlargement of the area of the cell nucleus. Cell rounding, on the other hand, caused the microfilament bundles to disappear and the area of the nucleus to become smaller. From the time course of the inhibition of DNA synthesis by cytochalasin B, it was inferred that functionally intact microfilaments are required for the entrance of the cells into DNA synthesis but not for the maintenance of ongoing DNA synthesis. The assumption has been made that the tension, generated by microfilaments during cell spreading, will affect the state of the plasma membrane as well as the shape and the structure of the nucleus, which in turn seems to be preparatory for cells to enter the cycle.

Actins↗
PubMed2000

Apoptosis of syncytia induced by the HIV-1-envelope glycoprotein complex: influence of cell shape and size.

Cells stably transfected with a lymphotropic HIV-1 Env gene form syncytia when cocultured with CD4(+)CXCR4(+) cells. Heterokaryons then spontaneously undergo apoptosis, while manifesting signs of mitochondrial membrane pemeabilization as well as nuclear chromatin condensation. Modulation of cellular geometry was achieved by growing syncytia on self-assembled monolayers of terminally substituted alkanethiolates designed to control the adhesive properties of the substrates. Spreading of syncytia, induced by culturing them on small circular adhesive islets (diameter 5 microm), placed at a distance that cells can bridge (10 microm), inhibited spontaneous and staurosporin-induced signs of apoptosis, both at the mitochondrial and at the nuclear levels, and allowed for the generation of larger syncytia. Transient cell spreading conferred a memory of apoptosis inhibition which was conserved upon adoption of a conventional cell shape. Limiting syncytium size by culturing them on square-shaped planar adhesive islands of defined size (400 to 2500 microm(2)), separated by nonadhesive regions, enhanced the rate of apoptotic cell death, as indicated by an accelerated permeabilization of the outer mitochondrial membrane, loss of the mitochondrial inner transmembrane potential, and an increased frequency of nuclear apoptosis. In conclusion, external constraints on syncytial size and shape strongly modulate their propensity to undergo apoptosis.

Apoptosis↗
PubMed2002

Ezrin turnover and cell shape changes catalyzed by proteasome in oxidatively stressed cells.

We find that ezrin, a cytoskeletal protein involved in anchoring actin to the cell membrane, is preferentially degraded and resynthesized after oxidative stress. Ezrin was identified using 2-dimensional gels and amino-terminal microsequencing as one of a select few [35S]methionine prelabeled proteins degraded in clone 9 rat liver cells exposed to hydrogen peroxide (H2O2). Metabolic labeling of cellular proteins with [35S]methionine after oxidative stress showed that resynthesis of ezrin rose dramatically but carboxyl terminus anti-ezrin monoclonal antibodies revealed constant intracellular ezrin levels; in other words, degradation and resynthesis were exactly matched. Ezrin degradation was blocked by selective inhibitors of the proteasome (lactacystin, NLVS, and epoxomycin) and by an antisense oligonucleotide directed against the proteasome C2 subunit. H2O2 also caused major changes in cell shape, including significant increases in cell diameter, which must require substantial cytoskeletal rearrangement. Peroxide-induced increases in cell diameter were, however, blocked by the selective proteasome inhibitor lactacystin. The degradation and resynthesis of ezrin may therefore be an underlying mechanism for overall cell shape changes observed during oxidative stress. Oxidative stress induces extensive protein oxidation and degradation and significant increases in cell blebbing, rounding-up, and overall size. Our results indicate that all these oxidant-induced changes may actually be catalyzed by the proteasome.

Acetylcysteine↗
PubMed1987

Morphometric analyses of changes in cell shape in the neuroepithelium of mammalian embryos.

During neurulation the elevation of the neural folds is accompanied by, and thought to be partly driven by, changes in the shapes of the neuroepithelial cells. This paper explores the use of form factors for the measurement of changes in cell shape during normal and perturbed neural fold elevation in rat embryos; it is the first attempt to quantify changes in the shapes of cells during neurulation in mammalian embryos. Rat embryos at 9.9 days of gestation, when the neural epithelium is a biconvex plate, and at 10.4 days of gestation, when the cervical neural epithelium has formed the neural tube and when the cephalic neural folds have elevated but not fused, were used. In addition, embryos in which the cephalic neural folds had been caused to re-open by culture in saline with low calcium were examined. Embryos were fixed and then fractured across the neural axis. A montage of the fractured edge of the neuroepithelium was prepared from a series of scanning electron micrographs. Cells of the neuroepithelium were classified according to the shapes of their profiles as rectangular, round, apically tapered, basally tapered or spindle-shaped, the last three categories being considered as 'tapered'. The outlines of the cells were digitised using a computer-linked graphics tablet to provide estimations of the perimeters (p) and areas (a) of the cell profiles, and the form factors, f. of the cell profiles were calculated by f = 4 pi a/p2. This factor is a unitless ratio which is unity for a circle and less than unity for any other shape. It provides a measure of the efficiency with which a perimeter encloses an area, and thus indicates the degree of deformation of a shape from circular. From 9.9 to 10.4 days the cervical neuroepithelium shows a decrease in the percentage of rectangular cells and an increase in the percentage of spindle-shaped cells. The mean form factors of cells in the apically tapered and spindle-shaped categories decrease, showing that these cells are more elongated and tapered in later embryos. When embryos at 10.4 days are cultured in saline with low calcium the elevated cephalic neural folds collapse. Concomitantly the percentage of round cells in the cephalic neural folds increases and the percentage of apically tapered and spindle-shaped cells decrease.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Effects of adrenergic agents and phosphodiesterase inhibitors on outflow facility and cell shape of bovine trabecular meshwork.

Changes in the outflow facility of perfused calf eyes and in the shape of cells in cultured trabecular meshwork (TM) have been studied, following exposure to adrenergic agents and phosphodiesterase inhibitors (PDE). Dobutamine caused confluent TM cells to change their usual polygonal shape to a characteristic stellate shape. Salbutamol had no effect, but PDE inhibitors, isobutylmethylxanthine (IBMX), theophylline, and caffeine were very effective in producing this shape change. Epinephrine, isoproterenol, dobutamine, and salbutamol did not increase the outflow facility, either at 22 degrees C or 36 degrees C, while theophylline, caffeine, and IBMX did increase it in a dose-dependent manner. On the other hand, the high concentrations of beta-adrenergic agents required to produce even a small change in outflow facility and cell shape argue against the involvement of adrenergic-receptor mediation and may suggest another mechanism; on the other, the enhancement of epinephrine effects by PDE inhibitors and the similar effect produced by cyclic adenosine 3',5'-cyclic phosphate (cAMP) and purines suggest that changes in the cell shape are produced by beta-receptor activation. The beta-adrenergic agents were not effective in changing outflow facility, but the PDE inhibitors were remarkably effective both in changing the shape and in increasing facility.

Administration, Topical↗
PubMed2003

Cytoskeletal control of plant cell shape: getting the fine points.

The shapes of plant cells, which are defined by their surrounding walls, are often important for cell function. The cytoskeleton plays key roles in determining plant cell shape, mainly by influencing the patterns in which wall materials are deposited in expanding cells. Studies employing cytoskeleton-disrupting drugs, together with studies of mutants with cytoskeletal defects, have demonstrated that both microtubules and actin filaments are critical for all modes of cell expansion, although their precise roles remain poorly understood. In recent years, however, significant progress has been made in understanding the contributions of a variety of proteins that influence cell shape by regulating the organization and polymerization of cytoskeletal filaments in expanding cells.

Actins↗
PubMed1992

Radiation-induced DNA unwinding is influenced by cell shape and trypsin.

Incubation of cells in high salt/alkali typically leads to denaturation and unwinding of DNA, yet DNA from Chinese hamster V79 cells grown for 1 day as spheroids stops unwinding after only 5-10 min. We previously postulated that this was a result of "constraints" to DNA unwinding present in cells in spheroids but not in monolayers, and that these constraints could be responsible for the increased resistance of spheroids of V79 cells to killing by ionizing radiation (i.e., the contact effect). However, studies reported here indicate that this limited DNA unwinding is correlated with a round cell shape and lack of cell surface fibronectin. In round cells which continue to synthesize fibronectin, demonstration of constraints requires prior exposure to trypsin in order to digest cell surface fibronectin. However, trypsin did not influence cell killing by ionizing radiation. Therefore, the increase in radiation resistance of V79 spheroids and the change in their DNA unwinding kinetics both appear contingent upon a change in cell shape; differences in DNA denaturation rates which are detected in spheroids using the unwinding assay are apparently not directly responsible for the contact effect.

Animals↗
PubMed1993

Cell shape and arrangement of cultured aortic smooth muscle cells grown on collagen gels.

Aortic smooth muscle cells (SMC) grown on conventional plastic culture dishes have morphological and functional properties of dedifferentiated cells in subculture. We examined the influence of collagen gels on the cell shape and arrangement. The cells grown on collagen gels showed a multilayered growth with formation of nodules. When the edge of the collagen gels was detached from the culture dish, the shape and arrangement of cells on the edge differed from that of the central, still attached region. The cells grown on floating collagen gels exhibited a spindle-like shape and were arranged in concentric circles. These findings suggest that the physical property of the substrate influences the cell shape and arrangement.

Animals↗
PubMed2006

Viscoelastic retraction of single living stress fibers and its impact on cell shape, cytoskeletal organization, and extracellular matrix mechanics.

Cells change their form and function by assembling actin stress fibers at their base and exerting traction forces on their extracellular matrix (ECM) adhesions. Individual stress fibers are thought to be actively tensed by the action of actomyosin motors and to function as elastic cables that structurally reinforce the basal portion of the cytoskeleton; however, these principles have not been directly tested in living cells, and their significance for overall cell shape control is poorly understood. Here we combine a laser nanoscissor, traction force microscopy, and fluorescence photobleaching methods to confirm that stress fibers in living cells behave as viscoelastic cables that are tensed through the action of actomyosin motors, to quantify their retraction kinetics in situ, and to explore their contribution to overall mechanical stability of the cell and interconnected ECM. These studies reveal that viscoelastic recoil of individual stress fibers after laser severing is partially slowed by inhibition of Rho-associated kinase and virtually abolished by direct inhibition of myosin light chain kinase. Importantly, cells cultured on stiff ECM substrates can tolerate disruption of multiple stress fibers with negligible overall change in cell shape, whereas disruption of a single stress fiber in cells anchored to compliant ECM substrates compromises the entire cellular force balance, induces cytoskeletal rearrangements, and produces ECM retraction many microns away from the site of incision; this results in large-scale changes of cell shape (> 5% elongation). In addition to revealing fundamental insight into the mechanical properties and cell shape contributions of individual stress fibers and confirming that the ECM is effectively a physical extension of the cell and cytoskeleton, the technologies described here offer a novel approach to spatially map the cytoskeletal mechanics of living cells on the nanoscale.

Animals↗
PubMedDate not supplied

The effects of tumor sera on cell shape and photosynthesis of Euglena gracilis.

Cells of Euglena gracilis treated with human sera show a marked change in cell shape: Fully elongated cells have nearly totally been transformed to disk-shaped cells. This serum-mediated contraction is followed by irreversible cytolysis. Disintegration of chloroplast membranes leads to decreased photosynthetic O2 evolution. Sera from humans suffering from tumors reveal higher lytic activities than sera from individuals not suffering from tumors. Heating sera at 56 degrees C for 10 min or addition of EDTA destroyed or inhibited, respectively, the lytic activities completely. Polysaccharides transformed in polyanions by sulphatisation like dextransulphates or heparin seem to protect Euglena against serum activities. The effects described for human sera are believed to display the role of the complement pathway in the cytolysis of Euglena gracilis.

Animals↗