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At least 325 records · Page 18Linked to original sources
PubMed1997

The oval-shaped cell as a candidate for a liver stem cell in embryonic, neonatal and precancerous liver: identification based on morphology and immunohistochemical staining for albumin and pyruvate kinase isoenzyme expression.

Oval cells observed in some experimental models of hepatocarcinogenesis can function as stem cells capable of differentiating into hepatocytes and bile ductular cells. Using markers which characterise embryonic hepatocytes, we showed that oval cells display different patterns of gene expression, suggesting some are more mature than others. In this study we looked for oval cells in developing liver, predicting that they are abundant in embryonic liver and decline in number during development. Albumin (ALB) serves as a liver-specific marker, and the isoenzymes of pyruvate kinase, M2-PK and L-PK, are used to identify immature and mature hepatocytes, respectively. Small oval-shaped cells expressing ALB, M2-PK and L-PK are found near the vascular spaces and portal areas in 20-day gestation (E20), E21, newborn, 3-day and 1-week-old rat liver. Similar cells expressing ALB and M2-PK, but not L-PK are seen only periportally in adult liver. These are abundant in early embryonic liver and decrease in number during development until only a few, located periportally, persist in the adult. Oval cells, located periportally a few days after commencing a choline-deficient, ethionine-supplemented diet, co-express ALB and M2-PK. Their similarity with respect to markers, morphology and location suggests that oval-shaped cells may be the progenitors of oval cells.

Albumins↗
PubMed2004

Extracellular matrix controls myosin light chain phosphorylation and cell contractility through modulation of cell shape and cytoskeletal prestress.

The mechanism by which vascular smooth muscle (VSM) cells modulate their contractility in response to structural cues from extracellular matrix remains poorly understood. When pulmonary VSM cells were cultured on increasing densities of immobilized fibronectin (FN), cell spreading, myosin light chain (MLC) phosphorylation, cytoskeletal prestress (isometric tension in the cell before vasoagonist stimulation), and the active contractile response to the vasoconstrictor endothelin-1 all increased in parallel. In contrast, MLC phosphorylation did not increase when suspended cells were allowed to bind FN-coated microbeads (4.5-microm diameter) or cultured on micrometer-sized (30 x 30 microm) FN islands surrounded by nonadhesive regions that support integrin binding but prevent cell spreading. Cell spreading and MLC phosphorylation also both decreased in parallel when the mechanical compliance of flexible FN substrates was raised. MLC phosphorylation was inhibited independently of cell shape when cytoskeletal prestress was dissipated using a myosin ATPase inhibitor in fully spread cells, whereas it increased to maximal levels when microtubules were disrupted using nocodazole in cells adherent to FN but not in suspended cells. These data demonstrate that changes in cell-extracellular matrix (ECM) interactions modulate smooth muscle cell contractility at the level of biochemical signal transduction and suggest that the mechanism underlying this regulation may involve physical interplay between ECM and the cytoskeleton, such that cell spreading and generation of cytoskeletal tension feed back to promote MLC phosphorylation and further increase tension generation.

Animals↗
PubMed1980

Ultrastructural observations on changes in cell shape in chromatophores of the sea urchin Centrostephanus longispinus.

Alterations in cell shape of the light-sensitive chromatophores of the sea urchin Centrostephanus longispinus were studied by scanning- and transmission electron microscopy. Transition of the aggregated to the dispersed state is accompanied by incorporation of vesicles into the membrane of the pigment cell. During disperson a system of microtubules originating from centriole-like structures is established throughout the stellate cell. Within restricted areas of the cell, cytoplasmic differentiation and condensation is found. The possible functional significance of the findings is briefly discussed.

Animals↗
PubMed1997

GFP-moesin illuminates actin cytoskeleton dynamics in living tissue and demonstrates cell shape changes during morphogenesis in Drosophila.

Moesin, ezrin, and radixin (MER) are components of the cortical actin cytoskeleton and membrane processes such as filopodia and microvilli. Their C-terminal tails contain an extended region that is predicted to be helical, an actin binding domain, and a region(s) that participates in self-association. We engineered an in vivo fluorescent actin binding protein (GFP-moe) by joining sequences that encode the jellyfish green fluorescent protein (GFP) to sequences that encode the C-terminal end of the sole Drosophila MER homolog, moesin [Moesin-like gene product, referred to previously as the D17 MER-like protein; Edwards et al., 1994, Proc. Natl. Acad. Sci. USA 91, 4589], and Dmoesin [McCartney and Fehon, 1996, J. Cell Biol. 133, 843]. Transgenic flies expressing this fusion protein under control of the hsp70 promoter were generated and used for analysis of cell shape changes during morphogenesis of various developmental stages and tissues. Following heat shock, high levels of stable fusion protein are produced by all somatic tissues. GFP-moe localizes to the cortical actin cytoskeleton, providing a strong in vivo marker for cell shape and pattern during epithelial morphogenesis. The protein also becomes highly enriched in pseudopods, microvilli, axons, denticles, the border cell process, and other membrane projections, potentially by binding to endogenous moesin as well as actin. We show that GFP-moe can be used to examine the development and behavior of these dynamic structures in live specimens. We observe a bright green fluorescent, presumably actin-rich, polar cell proboscis that inserts itself into the forming micropyle and appears to maintain an opening for sperm passage around which the chorion is formed. We also confirm the existence of an actin-rich purse string at the leading edge of the lateral epidermis and provide a dynamic analysis of its behavior as it migrates during dorsal closure. Observations of embryos, larvae, and pupae show that GFP-moe is also useful for labeling the developing nervous system and will be a good general marker of dynamic cell behavior during morphogenesis in live tissues and demonstrate that fusion of a subcellular localization signal to GFP greatly increases its utility as a cell marker.

Amino Acid Sequence↗
PubMed2002

Inhibition of PDGF-stimulated and matrix-mediated proliferation of human vascular smooth muscle cells by SPARC is independent of changes in cell shape or cyclin-dependent kinase inhibitors.

Interactions among growth factors, cells, and extracellular matrix regulate proliferation during normal development and in pathologies such as atherosclerosis. SPARC (secreted protein, acidic, and rich in cysteine) is a matrix-associated glycoprotein that modulates the adhesion and proliferation of vascular cells. In this study, we demonstrate that SPARC inhibits human arterial smooth muscle cell proliferation stimulated by platelet-derived growth factor or by adhesion to monomeric type I collagen. Binding studies with SPARC and SPARC peptides indicate specific and saturable interaction with smooth muscle cells that involves the C-terminal Ca2+-binding region of the protein. We also report that SPARC arrests monomeric collagen-supported smooth muscle cell proliferation in the late G1-phase of the cell cycle in the absence of an effect on cell shape or on levels of cyclin-dependent kinase inhibitors. Cyclin-dependent kinase-2 activity, p107 and cyclin A levels, and retinoblastoma protein phosphorylation are markedly reduced in response to the addition of exogenous SPARC and/or peptides derived from specific domains of SPARC. Thus, SPARC, previously characterized as an inhibitor of platelet-derived growth factor binding to its receptor, also antagonizes smooth muscle cell proliferation mediated by monomeric collagen at the level of cyclin-dependent kinase-2 activity.

Amino Acid Sequence↗
PubMed1987

Media-induced departures from the usual, temperature-dependent cell shapes of Sporothrix schenckii and concomitant changes in the acid phosphatase isoenzyme patterns.

Sporothrix schenckii grew as mycelia at 20 degrees C or yeast at 35 degrees C on a common culture medium, YNG (yeast extract, neopeptone and glucose), in agreement with previous observations that standard media support the mycelial phase at the lower temperature and the yeast phase at the higher temperature. Special media, M-1 and M-2, were used to generate yeast at 20 degrees C and mycelia at 35 degrees C, respectively, i.e. the reverse of the typically-observed, temperature-dependent phases. In this context the M-1 induced (or forced) generation of yeast cells at 20 degrees C was judged to be abnormal yet these cells had a typical yeast ultrastructure including the definitive microfibrillar zone of the cell envelope. Electropherograms of extracts of these cells (M-1 at 20 degrees C) displayed the typical acid phosphatase isoenzyme pattern of yeast grown at 35 degrees C, and that is much more complicated than the typical pattern for extracts of mycelia grown at 20 degrees C on YNG. On the other hand the fungus was held in the mycelial phase on M-2 at 35 degrees C, at least for short term cultures, to complement the study and provide a departure from the cell shape which is expected at the higher temperature. These mycelia were judged to be ultrastructurally abnormal in that they had a thin microfibrillar zone not previously seen in S. schenckii mycelia produced on standard media at lower temperatures. The cell-free extract of these abnormal mycelia grown at 35 degrees C exhibited an isoenzyme pattern which was closer to that of yeast grown at 35 degrees C than to mycelia grown at 20 degrees C, although one isoenzyme showed intermediate electrophoretic mobility. The findings with M-2 medium at 35 degrees C were less meaningful because of the eventual conversion to yeast phase. Overall the results indicate an association between acid phosphatase isoenzyme pattern and cell shape, rather than simply an expression of the various acid phosphatases with growth temperature.

Acid Phosphatase↗
PubMed2005

Overexpression of a family of RPEL proteins modifies cell shape.

Proteins containing RPEL motifs (e.g., MAL) are important in the regulation of gene expression by the actin cytoskeleton. Screening the ENSEMBL database for RPEL proteins identified four additional proteins that contain RPEL motifs and nuclear localisation sequences, three of which (RPEL-A, RPEL-B and RPEL-C) are expressed in adult mouse tissues with different expression profiles. The mRNAs encoding RPEL-B and RPEL-C were subject to alternative splicing. Expression of these genes in cells indicated that they had a marked effect on cell shape. Furthermore, when expressed with a nuclear localised actin all of the different forms became restricted to the nucleus.

Actins↗
PubMed1999

Ectopic expression of constitutively activated Ral GTPase inhibits cell shape changes during Drosophila eye development.

The small GTP-binding protein Ral is activated by RalGDS, one of the effector molecules for Ras. Active Ral binds to a GTPase activating protein for CDC42 and Rac. Although previous studies suggest a role for Ral in the regulation of CDC42 and Rac, which are involved in arranging the cytoskeleton, its in vivo function is largely unknown. To examine the effect of overexpressing Ral on development, transgenic Drosophila were generated that overexpress wild-type or mutated Ral during eye development. While wild-type Ral caused no developmental defects, expression of a constitutively activated protein resulted in a rough eye phenotype. Activated Ral did not affect cell fate determination in the larval eye discs but caused severe disruption of the ommatidial organization later in pupal development. Phalloidin staining showed that activated Ral perturbed the cytoskeletal structure and cell shape changes during pupal development. This phenotype is similar to that caused by RhoA overexpression. In addition, the phenotype was synergistically enhanced by the coexpression of RhoA. These results suggest that Ral functions to control the cytoskeletal structure required for cell shape changes during Drosophila development.

Animals↗
PubMed1978

Effect of thymine concentration on cell shape in Thy- Escherichia coli B/r.

Cells of a thymineless mutant of Escherichia coli B/r are shown to change their shape when the concentration of thymine in the growth medium is reduced. Electron micrographs of whole cells and isolated sacculi were used to make quantitative measurements of the changes in cell length and width which occur as a result of such a change in thymine concentration. The results showed that there is an increase in cell volume, which is due to an increase in cell width accompanied by a decrease in cell length. These changes were compared with the predictions of models which assume that cell shape is influenced by the chromosome replication cycle.

DNA, Bacterial↗
PubMed1980

Defective and plaque-forming lambda transducing bacteriophage carrying penicillin-binding protein-cell shape genes: genetic and physical mapping and identification of gene products from the lip-dacA-rodA-pbpA-leuS region of the Escherichia coli chromosome.

A series of defective lambda transducing phage carrying genes from the lip-leuS region of the Escherichia coli chromosome (min 14 on the current linkage map) has been isolated. The phage defined the gene order as lac---lip-dacA-rodA-pbpA-leuS---gal. These included the structural genes for penicillin-binding protein 2 (pbpA) and penicillin-binding protein 5 (dacA) as well as a previously unidentified cell shape gene that we have called rodA. rodA mutants were spherical and very similar to pbpA mutants but were distinguishable from them in that they had no defects in the activity of penicillin-binding protein 2. The separation into two groups of spherical mutants with mutations that mapped close to lip was confirmed by complementation analysis. The genes dacA, rodA, and pbpA lie within a 12-kilobase region, and represent a cluster of genes involved in cell shape determination and peptidoglycan synthesis. A restriction map of the lip-leuS region was established, and restriction fragments were cloned from defective transducing phage into appropriate lambda vectors to generate plaque-forming phage that carried genes from this region. Analysis of the proteins synthesized from lambda transducing phage in ultraviolet light-irradiated cells of E. coli resulted in the identification of the leuS, pbpA, dacA, and lip gene products, but the product of the rodA gene was not identified. The nine proteins that were synthesized from the lip-leuS region accounted for 57% of its coding capacity. Phage derivatives were constructed that allowed about 50-fold amplification of the levels of penicillin-binding proteins 2 and 5 in the cytoplasmic membrane.

Bacterial Proteins↗
PubMed1988

Influence of cytochalasin D-induced changes in cell shape on proteoglycan synthesis by cultured articular chondrocytes.

There is growing evidence that cell shape regulates both proliferation and differentiated gene expression in a variety of cell types. We have explored the relationship between the morphology of articular chondrocytes in culture and the amount and type of proteoglycan they synthesize, using cytochalasin D to induce reversible cell rounding. When chondrocytes were prevented from spreading or when spread cells were induced to round up, 35SO4 incorporation into proteoglycan was stimulated. Incorporation into the cell layer was stimulated more than into the medium. When the cells were allowed to respread by removing cytochalasin D, proteoglycan synthesis returned to control levels. Cytochalasin D-induced stimulation of 35SO4 incorporation reflected an increase in core protein synthesis rather than lengthening of glycosaminoglycan chains, because [3H]serine incorporation into core protein was also stimulated. The observed stimulation of proteoglycan synthesis was not due to an overall stimulation of protein synthesis, to inhibition of DNA synthesis, or to accumulation of cells in one phase of the cell cycle. Cytochalasin D-treatment of cells in suspension caused no further stimulation of 35SO4 incorporation, suggesting that the observed effects were due to cell rounding rather than exposure to cytochalasin D per se; nevertheless, we cannot completely rule out other, nonspecific, effects of the drug. Fibroblasts and chondrocytes that had been passaged to stimulate dedifferentiation did not incorporate more 35SO4 when treated with cytochalasin D, suggesting that increased proteoglycan synthesis in response to rounding may itself be a differentiated property of chondrocytes.

Animals↗
PubMed1996

Polarity of T cell shape, motility, and sensitivity to antigen.

T cell activation requires contact with APCs. We used optical techniques to demonstrate T cell polarity on the basis of shape, motility, and localized sensitivity to antigen. An intracellular Ca2+ clamp showed that T cell shape and motility are extremely sensitive to changes in [Ca2+]i (Kd = 200 nM), with immobilization and rounding occurring via a calcineurin-independent pathway. Ca2+ dependent immobilization prolonged T cell contact with the antigen-presenting B cell; buffering the [Ca2+]i signal prevented the formation of stable cell pairs. Optical tweezers revealed spatial T cell sensitivity to antigen by controlling placement on the T cell surface of either B cells or alpha-CD3 MAb-coated beads. T cells were 4-fold more sensitive to contact made at the leading edge of the T cell compared with the tail. We conclude that motile T cells are polarized antigen sensors that respond physically to [Ca2+]i signals to stabilize their interaction with APCs.

Animals↗
PubMed2003

Automated analysis of morphometric parameters for accurate definition of erythrocyte cell shape.

BACKGROUND: Modification of erythrocyte morphology is clinically important in hematology and medicine. Its detection is routinely performed by subjective microscopic evaluation, which is difficult and strongly dependent on the operator's expertise. We developed an original automated methodology to analyze erythrocyte cell shape modification to support and improve the operator's capability and expedite measurements. METHODS: We used morphometric parameters derived from optical microscope images elaborated with an image processing software (NIH Scion Image) to construct a new application for statistical multivariate discriminant analysis. RESULTS: For each cell type the elaboration of the morphometric parameters allowed us to develop a chromogenic index, a dimension index, a biconcavity index, and a density profile. The measurements of these indexes were used to construct a statistical methodology that could discriminate among erythrocyte morphologies according to Bessis. When applied casewise, the model effectively differentiated between discocytes, target cells, ovalocytes, macrocytes, and microcytes, with an agreement of 70% between actual and predicted classifications. CONCLUSIONS: The results clearly demonstrated that a set of opportunely selected morphometric parameters derived from optical microscope images and statistically analyzed can effectively discriminate with a high degree of certainty among different shape modifications that red blood cells can undergo in various in vitro and in vivo conditions. This method represents the first attempt to automate the definition of erythrocyte morphology and may have important applications in cases in which the detection of erythrocyte cell shape changes is crucial.

Automation↗
PubMed2003

Fgd1, the Cdc42 GEF responsible for Faciogenital Dysplasia, directly interacts with cortactin and mAbp1 to modulate cell shape.

FGD1 mutations result in Faciogenital Dysplasia (FGDY), an X-linked human disease that affects skeletal formation and embryonic morphogenesis. FGD1 and Fgd1, the mouse FGD1 ortholog, encode guanine nucleotide exchange factors (GEF) that specifically activate Cdc42, a Rho GTPase that controls the organization of the actin cytoskeleton. To further understand FGD1/Fgd1 signaling and begin to elucidate the molecular pathophysiology of FGDY, we demonstrate that Fgd1 directly interacts with cortactin and mouse actin-binding protein 1 (mAbp1), actin-binding proteins that regulate actin polymerization through the Arp2/3 complex. In yeast two-hybrid studies, cortactin and mAbp1 Src homology 3 (SH3) domains interact with a single Fgd1 SH3-binding domain (SH3-BD), and biochemical studies show that the Fgd1 SH3-BD directly binds to cortactin and mAbp1 in vitro. Immunoprecipitation studies show that Fgd1 interacts with cortactin and mAbp1 in vivo and that Fgd1 SH3-BD mutations disrupt binding. Immunocytochemical studies show that Fgd1 colocalizes with cortactin and mAbp1 in lamellipodia and membrane ruffles, and that Fgd1 subcellular targeting is dynamic. By using truncated cortactin proteins, immunocytochemical studies show that the cortactin SH3 domain targets Fgd1 to the subcortical actin cytoskeleton, and that abnormal Fgd1 localization results in actin cytoskeletal abnormalities and significant changes in cell shape and viability. Thus, this study provides novel in vitro and in vivo evidence that Fgd1 specifically and directly interacts with cortactin and mAbp1, and that these interactions play an important role in regulating the actin cytoskeleton and, subsequently, cell shape.

Actin Cytoskeleton↗
PubMedDate not supplied

Changes in cell shape and actin distribution induced by constant electric fields.

The development of motility in cultured cells is usually associated with a polarization of the cell shape. In particular, the leading edge of the cell is extended into a lamella which acts as a locus for the elaboration of cell processes and for the formation of cell-substrate contacts and, at the opposite end, retraction fibres often extend beyond the trailing edge of the cell. The alignment of microfilament bundles (stress fibres) along the direction of migration and the presence of a band of actin at the leading edge of the cell suggest an involvement of this protein in the motile process. The direction of growth and orientation of various cell types in tissue culture can be influenced by externally applied d.c. electric fields but the effect of the field on cellular motile activities is unknown. Here we describe a galvanotropic response of cultured Xenopus epithelial cells. At a field strength of 5 V cm-1 these cells elongate perpendicularly with respect to the field. The anodal side of the cell retracts and both the ends and cathodal edge become active in the extension of ruffling lamellipodia. In parallel with the change in the cell axis, stress fibres are oriented perpendicularly to the field, and a band of actin is associated with the lamellae at the cathodal edge and at the ends of the cell.

Actins↗
PubMed2002

Calculation of dielectric spectra of suspensions of rod-shaped cells using boundary element method.

The boundary element method (BEM) has been applied to the calculation of dielectric spectra of suspensions of rod-shaped cells using two kinds of models: model-R consisting of a cylinder and two hemispheres and model-PU of prolate spheroid shape. Both models have an insulating shell phase of a uniform thickness. The calculations were compared with those using a conventional spheroidal model with a confocal shell (model-PC) and previous observations on rod-shaped yeast cells. The differences among the three models were not considerable and all the models succeeded in interpreting the observed data on yeast cells.

Models, Biological↗
PubMed1993

Effect of red blood cell shape on oxygen transport in capillaries.

A mathematical model of oxygen (O2) transport within a capillary utilizes axisymmetric red blood cell (RBC) shapes that were predicted theoretically by Zarda et al. in 1977. Chemical kinetics and both free and facilitated diffusion of O2 are accounted for in this time-dependent model. The finite-element method is used to solve the governing partial differential equations. It is found that the shape of RBCs, characterized by the shape parameter theta adapted from Zarda et al., affects such important O2 transport characteristics as capillary wall O2 flux and hemoglobin (Hb) saturation. At an RBC residence time (time for an RBC to travel from the capillary inlet to a given point) of 0.22 s, a change in the shape parameter theta from 0 (undeformed cell) to 26 (parachute-shaped cell) decreases the spatially averaged O2 flux by 26%. The dependence of O2 flux on RBC shape diminishes as the RBC residence time increases. The difference in Hb saturation at the RBC residence time of 0.22 s can be as large as 10% for different values of theta. The mass transfer Nusselt number, which is inversely proportional to transport resistance, decreases with increases in theta. The fractional transport resistance in the plasma region accounts for approximately 65-80% of the total intracapillary resistance. Calculations show that local chemical equilibrium in the O2-Hb chemical reaction is attained everywhere except within a thin boundary layer adjacent to the erythrocyte membrane, where significant deviation from chemical equilibrium occurs.

Animals↗
PubMed1991

Patterns of actin filaments during cell shaping in developing mesophyll of wheat (Triticum aestivum L.).

Young leaves of wheat exhibit a smooth developmental gradient with meristematic cells at the base and highly differentiated cells at the tip. During differentiation, mesophyll cells attain a lobed outline resembling tube-shaped balloons with almost regularly spaced isthmi. Microfilament patterns in developing wheat mesophyll cells were investigated using fluorescent-labeled phalloidin. Various patterns were found, including delicate arrays of transversely oriented microfilaments in the cortex of the cytoplasm. A close correlation between changes in the patterns of cortical microfilaments, microtubules, cell wall microfibrils, and cell shape was observed. The fine arrays of transversely oriented microfilaments coaligned with bands of microtubules occurring during cell elongation. These bands were found beneath sites of intense wall deposition. It has recently been proposed that the resulting hoops of wall reinforcement prevent cell expansion in the corresponding regions and thus give rise to the peculiar cell shape. When cell expansion ceased, and the typical lobed cell shape was attained, a dense network of microfilaments was retained in the cytoplasm, which was in contrast to what has been described for the microtubular arrays.

Actin Cytoskeleton↗