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At least 523 records · Page 29Linked to original sources
PubMed2001

Rac and Cdc42 GTPases control hematopoietic stem cell shape, adhesion, migration, and mobilization.

Critical to homeostasis of blood cell production by hematopoietic stem/progenitor (HSC/P) cells is the regulation of HSC/P retention within the bone marrow microenvironment and migration between the bone marrow and the blood. Key extracellular regulatory elements for this process have been defined (cell-cell adhesion, growth factors, chemokines), but the mechanism by which HSC/P cells reconcile multiple external signals has not been elucidated. Rac and related small GTPases are candidates for this role and were studied in HSC/P deficient in Rac2, a hematopoietic cell-specific family member. Rac2 appears to be critical for HSC/P adhesion both in vitro and in vivo, whereas a compensatory increase in Cdc42 activation regulates HSC/P migration. This genetic analysis provides physiological evidence of cross-talk between GTPase proteins and suggests that a balance of these two GTPases controls HSC/P adhesion and mobilization in vivo.

Animals↗
PubMed1999

Gnarley1 is a dominant mutation in the knox4 homeobox gene affecting cell shape and identity.

Maize leaves have a stereotypical pattern of cell types organized into discrete domains. These domains are altered by mutations in knotted1 (kn1) and knox (for kn1-like homeobox) genes. Gnarley (Gn1) is a dominant maize mutant that exhibits many of the phenotypic characteristics of the kn1 family of mutants. Gn1 is unique because it changes parameters of cell growth in the basal-most region of the leaf, the sheath, resulting in dramatically altered sheath morphology. The strongly expressive allele Gn1-R also gives rise to a floral phenotype in which ectopic carpels form. Introgression studies showed that the severity of the Gn1-conferred phenotype is strongly influenced by genetic background. Gn1 maps to knox4, and knox4 is ectopically expressed in plants with the Gn1-conferred phenotype. Immunolocalization experiments showed that the KNOX protein accumulates at the base of Gn1 leaves in a pattern that is spatially and temporally correlated with appearance of the mutant phenotype. We further demonstrate that Gn1 is knox4 by correlating loss of the mutant phenotype with insertion of a Mutator transposon into knox4.

Alleles↗
PubMed1996

Early post-radiation changes of red blood cell shape in rats.

Scanning electron microscopy (SEM) of red blood cells in whole blood samples from rats was performed following acute gamma-irradiation of animals with 0.25 to 1 Gy. Increased incidence of echinocytosis was observed and found to be dose- and time-dependent. At a higher radiation dose (1 Gy), echinocytosis was revealed within 5 minutes after treatment and persisted up to 3 weeks. The data demonstrate the applicability of SEM for detecting minimal radiation-induced lesions of red blood cells.

Animals↗
PubMed1979

Hormone-induced pigment translocations in amphibian dermal iridophores, in vitro: changes in cell shape.

Hormone-induced pigment translocation studies were conducted at both the light and electron microscopic levels on cultured dermal iridophores from the Mexican leaf frog, Pachymedusa dacnicolor. Two distinct types of dermal iridophores were characterized which differed in (1) their in vivo locations, (2) their overall morphologies in vitro, (3) their responses to alpha-MSH, ACTH, c-AMP or theophylline, (4) their physical alterations of light, and (5) certain ultrastructural features. One iridophore (Type I) was found to be physiologically responsive to the above hormones or agents by a reversible retraction of cellular processes and a thickening of the cell body, an event which is inhibited by cytochalasin B. The other iridophore (Type II) appeared to be unresponsive. Type I iridophores contain cube-like pigmentary organelles, refractosomes, while Type II iridophores contain larger, bar-shaped refractosomes. In addition, both iridophore types contain 60 and 100 A microfilaments as well as microtubules. By in large, micorfilaments were found within microvilli, beneath and parallel to the plasma membrane and in the perinuclear region. Occasionally, bundles of 100 A microfilaments were found between layers of refractosomes in Type I iridophores. These results are discussed in relation to hormone-induced changes in cell shape.

Actins↗
PubMed1992

Cyclic changes of membrane conductivity in fertilized and activated eggs of teleost (Misgurnus fossilis) and their relation to the cell shape.

Oscillations of membrane ionic conductivity, with a period similar to cell cycle duration, were observed in fertilized and activated loach (Misgurnus fossilis) eggs. In cleaving eggs the decrease in conductivity coincided with mitosis. Synchronously with the oscillations of membrane conductivity in activated as well as in fertilized eggs, rhythmic changes in blastodisc shape occurred. The blastodisc rounded up during the period of increasing membrane conductivity and flattened while conductivity decreased. Scanning microscopy of fertilized and activated eggs revealed differences in the surface relief of rounded and flattened blastodiscs.

Animals↗
PubMed1998

Control of cell shape and elongation by the rodA gene in Bacillus subtilis.

The Escherichia coli rodA and ftsW genes and the spoVE gene of Bacillus subtilis encode membrane proteins that control peptidoglycan synthesis during cellular elongation, division and sporulation respectively. While rodA and ftsW are essential genes in E. coli, the B. subtilis spoVE gene is dispensable for growth and is only required for the synthesis of the spore cortex peptidoglycan. In this work, we report on the characterization of a B. subtilis gene, designated rodA, encoding a homologue of E. coli RodA. We found that the growth of a B. subtilis strain carrying a fusion of rodA to the IPTG-inducible Pspac promoter is inducer dependent. Limiting concentrations of inducer caused the formation of spherical cells, which eventually lysed. An increase in the level of IPTG induced a sphere-to-short rod transition that re-established viability. Higher levels of inducer restored normal cell length. Staining of the septal or polar cap peptidoglycan by a fluorescent lectin was unaffected during growth of the mutant under restrictive conditions. Our results suggest that rodA functions in maintaining the rod shape of the cell and that this function is essential for viability. In addition, RodA has an irreplaceable role in the extension of the lateral walls of the cell. Electron microscopy observations support these conclusions. The ultrastructural analysis further suggests that the growth arrest that accompanies loss of the rod shape is caused by the cell's inability to construct a division septum capable of spanning the enlarged cell. RodA is similar over its entire length to members of a large protein family (SEDS, for shape, elongation, division and sporulation). Members of the SEDS family are probably present in all eubacteria that synthesize peptidoglycan as part of their cell envelope.

Artificial Gene Fusion↗
PubMed2006

Surface tension influences cell shape and phagocytosis in alveolar macrophages.

The effect of surface tension on alveolar macrophage shape and phagocytosis was assessed in vivo and in vitro. Surface tension was regulated in vivo by conditionally expressing surfactant protein (SP)-B in Sftpb-/- mice. Increased surface tension and respiratory distress were produced by depletion of SP-B and were readily reversed by repletion of SP-B in vivo. Electron microscopy was used to demonstrate that alveolar macrophages were usually located beneath the surfactant film on the alveolar surfaces. Reduction of SP-B increased surface tension and resulted in flattening of alveolar macrophages on epithelial surfaces in vivo. Phagocytosis of intratracheally injected fluorescent microbeads by alveolar macrophages was decreased during SP-B deficiency and was restored by repletion of SP-B in vivo. Incubation of MH-S cells, a mouse macrophage cell line, with inactive surfactant caused cell flattening and decreased phagocytosis in vitro, findings that were reversed by the addition of sheep surfactant or phospholipid containing SP-B. SP-B controls surface tension by forming a surfactant phospholipid film that regulates shape and nonspecific phagocytic activity of alveolar macrophages on the alveolar surface.

Animals↗
PubMed2004

How do Abl family kinases regulate cell shape and movement?

Genetic analysis and studies of normal and leukemia cells in culture have shown that Abl family nonreceptor tyrosine kinases regulate cell morphogenesis and motility. Abl family kinases, which include Drosophila (D-) Abl and the vertebrate Abl and Arg proteins, relay signals from cell surface growth-factor and adhesion receptors to promote cytoskeletal rearrangements. Recent biochemical and crystallographic analyses have clarified the mechanisms by which growth-factor and adhesion receptors might regulate the activity of Abl family kinases. When activated, Abl family kinases can regulate cytoskeletal dynamics by phosphorylating several known cytoskeletal regulatory proteins. In addition, the C-terminal half of Abl family kinases has several domains that bind to cytoskeletal components. Emerging evidence suggests that Abl family kinases can use these domains to directly organize cytoskeletal structure in vivo.

Animals↗
PubMed1983

Dynamic behaviour of amphiphilic lipids to penetrate into membrane of intact human erythrocytes and to induce change in the cell shape.

Shape change (crenation, echinocyte formation) of intact human erythrocytes induced by added phosphatidylcholine or lysophosphatidylcholine species with varying acyl chain lengths was dependent only on the amount of the lipid incorporated into the membrane (determined with 14C-labelled lipids), irrespective of the chain length. The chain length appears to determine the speed and the maximal extent of the lipid transfer from the outside medium into the membrane. The altered shape gradually reverted upon incubation at 37 degrees C, not at low temperature, until the cells reassumed their normal shape. Translocation of the incorporated lipid molecules from the outer to the inner leaflet of the membrane lipid bilayer occurred to a slight extent during the incubation.

Biological Transport↗
PubMedDate not supplied

Effects of red cell shape and orientation on propagation of sound in blood.

In this paper, the red blood cell (RBC) is assumed to have an oblate spheroidal shape and the same volume (87 micrometer3) and about the same sphericity index (0.7) as a typical human RBC. The acoustic field is assumed to be either parallel or perpendicular to the axis of symmetry of the spheroid, and a wave equation is formulated for a dilute RBC suspension. Because of the small density difference between the RBC and plasma (about 5%), the assumption of spherical shape of the RBC suffices for computation of the velocity and the scattering of sound in blood. For all practical purposes, scattering of sound in blood follows Rayleigh's law of scattering. However, the viscous absorption coefficient at 1 MHz for a spheroidally shaped RBC oscillating broadside and edgewise to an acoustic field is about 40% and 136%, respectively, of that for a spherically shaped RBC. These results illustrate the significant effects of RBC shape and orientation on the viscous loss of sound energy in blood.

Erythrocytes↗
PubMed1985

Studies on the mechanism of human red cell loss of viability during storage at +4 degrees C in vitro. I. Cell shape and total adenylate concentration as determinant factors for posttransfusion survival.

Red cells stored in SAGM medium for 42 days at +4 degrees C were rejuvenated by bicarbonate, pyruvate and adenosine. Autologous 24-hour posttransfusion survival was determined in untreated as well as rejuvenated cells and showed an improvement from 77.4 +/- 4.7 to 89.2 +/- 7.2%. The erythrocyte adenylate energy charge decreased relatively more than the total adenylate concentration during storage, but the latter correlated better with posttransfusion red cell survival. Considerable deteriorations in red cell morphology (expressed as morphology index) and in deformability (measured as red cell fluidity) were observed during storage but were partly reversed by rejuvenation. The morphology index and the posttransfusion survival showed a significant correlation (r = 0.95, p less than 0.005) after, but not before, rejuvenation, indicating that the remaining changes are more permanent and decisive of survival. It is suggested that, in the proportion of stored erythrocytes which respond to rejuvenation, the capacity and time dependence of recovery of normal shape and flexibility are important.

Adenine↗
PubMed1992

Protein phosphatase inhibitors okadaic acid and calyculin A alter cell shape and F-actin distribution and inhibit stimulus-dependent increases in cytoskeletal actin of human neutrophils.

The phosphatase inhibitors okadaic acid and calyculin A were found to elicit or to modify several neutrophil responses, suggesting that dephosphorylation plays a regulatory role. The concentrations of okadaic acid (> or = 1 mumol/L) that were effective on neutrophil functions (shape changes and marginal stimulation of pinocytosis) were shown to stimulate the incorporation of 32PO4 into many neutrophil proteins several-fold. Calyculin A was effective at 50-fold lower concentrations. In the presence of the inhibitors, the cells exhibited a nonpolar shape and the polarization response induced by chemotactic peptide was inhibited. Both phosphatase inhibitors also induced the association of F-actin with the cell membrane. A steady-state phosphatase activity is thus involved in maintaining shape and F-actin localization of resting cells. Inhibitors alone had no significant effect on the amount of cytoskeleton-associated actin. The increase in cytoskeletal actin observed at 30 minutes of stimulation with phorbol ester or 5 to 30 minutes of stimulation with chemotactic peptide, however, was abolished by okadaic acid or calyculin A, suggesting an important role of a phosphatase. In contrast, the early increase in cytoskeleton-associated actin observed at 1 minute of stimulation with peptide was not affected. This finding indicates that the increased association of actin with the cytoskeleton in the early and the later stages of neutrophil activation may be mediated by different signalling pathways.

Actins↗
PubMed1973

Microtubule biogenesis and cell shape in Ochromonas. I. The distribution of cytoplasmic and mitotic microtubules.

In the first of two companion papers which attempt to correlate microtubules and their nucleating sites with developmental and cell division patterns in the unicellular flagellate, Ochromonas, the distribution of cytoplasmic and mitotic microtubules and various kinetosome-related fibers are detailed. Of the five kinetosome-related fibers, which have been found in Ochromonas, two, the kineto-beak fibers and the rhizoplast fibers are utilized as attachment sites for distinct groups of microtubules. The set of microtubules attached to the kineto-beak fibers apparently shape the anterior beak region of the cell whereas the rhizoplast microtubules appear to extend into and shape the tail in vegetative cells. In mitotic cells a rhizoplast is found at each spindle pole apparently serving as foci for the spindle microtubules. These findings are discussed in relation to the less well defined attachment sites for vegetative and mitotic microtubules in other kinds of cells. It is noted that the effects of depolymerizing microtubules in vivo might be easily quantitated in whole populations since no external wall or pellicle contributes to the maintenance or the biogenesis of the characteristic cell form of Ochromonas.

Cell Division↗
PubMed1992

Relationships between chromosome segregation, cell shape and temperature in Escherichia coli.

The partitioning of chromosomes into daughter cells during the division of Escherichia coli is non-random. As a result, the chromosome containing the older template DNA strand has a higher probability of segregating toward the old cell pole than toward the new cell pole. The numerical value of this probability is a function of the incubation temperature. It is shown here that a recent model for explaining the physiological basis for non-random chromosome segregation also explains the temperature dependence of the segregation process.

DNA Replication↗
PubMed2004

Cell shape normalization, dendrite orientation, and melanin production of normal and genetically altered (haploinsufficient NF1)-melanocytes by microstructured substrate interactions.

Little is known about how functional regulation failure in genetically altered cells is influenced by topographical confinement of cells, a situation often present in tissues in vivo. We used cultured melanocytes derived from human skin samples as a model system for such investigations. Normal melanocytes have a very well defined shape consisting of a cell body and two dendrites arranged 180 degrees relative to each other. In contrast, neurofibromin 1-melanocytes (NF1-melanocytes) have up to a 50% reduction of neurofibromin 1, which results in an altered morphology that can be easily measured. NF1-melanocytes deviate from the defined structure of normal melanocytes by forming more than two dendrites per cell. We show that morphology consequences of genetically altered melanocytes can be canceled if cells interact with substrates microstructured by stripes that apply mechanophysical signals in the form of physical topography. The strength of the mechanophysical signal was varied systematically by increasing the height of the microstructures. Melanocytes respond to surface topographical features that are larger than 50 nm and have lateral confinements smaller 4 microns. The response of normal and NF1-melanocytes to different topographies was analyzed quantitatively by determining density distributions for the number of dendrites per cell, the angles between dendrites, and the orientation imprinted in the substrate. The synthesis of melanin, a pigment produced by melanocytes, differs in the case of genetically altered NF1- and normal melanocytes. In both cases, the interaction with microstripes enhanced melanin production significantly. This enhanced melanin production is speculated to be caused by the mechanical stabilization of the dendrites by substrate guidance.

Cell Size↗
PubMed1988

Organelle distribution in the wedge-, spindle- and inverted wedge-shaped neuroepithelial cells during chick embryo neurulation.

The formation of the neural tube is a morphogenetic process involving cell-shape changes. The activity of the cytoskeletal elements of the neuroepithelial cells and the interkinetic nuclear migration affect the neuroepithelial cell shape in a way that these cells acquire three distinct conformations of wedge-shaped, spindle-shaped and inverted wedge-shaped cells. Each of them is ultrastructurally characterized in this paper with regard to the intracellular distribution of mitochondria, rough endoplasmic reticulum, yolk droplets, lipid bodies and Golgi apparatus. These distribution patterns are analyzed in relation to the role played by the neuroepithelial cells during the successive phases of neural tube formation.

Animals↗