Journal articles on the topic 'Actif contours'
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1
Fallenbacher, Francine. "Les contours obscurs de la littérature scolaire : l’école romande à l’épreuve." Cahiers du Centre de Linguistique et des Sciences du Langage, no. 27 (April 1, 2022): 61–76. http://dx.doi.org/10.26034/la.cdclsl.2010.1342.
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LES QUALITES INHERENTES AU TEXTE LITTERAIRE et ses valeurs, entendues ici comme tout ce qui est transmis, en font un objet ambigu dans l’espace scolaire, dérangeant, d’une part, en tant que dispositif polymorphe et polyvalent, qui se dérobe aux pratiques communes, et privilégié, de l’autre, par les aspects moraux, idéologiques et patrimoniaux dont il est investi. Réconcilier les valeurs du littéraire associées au fictif qui font appel à l’émotion et à l’imagination, avec le travail scolaire, pose problème et questionne les enseignants sur leurs choix de corpus et de méthodes (entre liberté et contraintes). De plus, le jeune lecteur, enfant ou adolescent, développe des formes et des habitudes de lecture souvent très éloignées des pratiques lettrées prônées par l’école. Quelles formes scolaires de la littérature appellent un lecteur expert, idéalement visé par l’école obligatoire romande d’aujourd’hui ? Et que fait l’institution pour combler l’écart entre les champs culturels des élèves et ceux du milieu « lettré » ?
L’institution attribue au littéraire des valeurs symboliques et éducatives qui présupposent un sujet lecteur engagé et critique, participant activement à l’édification de cultures. Cette vision de l’apprenant actif et d’une école « citoyenne » qui a posé en Suisse romande de nombreux jalons, rencontre de fortes résistances comme dans le reste de la francophonie. Quelle cohérence donner, alors, aux rapports de l’institution avec la recherche et la formation, pour transformer peu à peu les représentations et produire l’impact attendu sur les actes pédagogiques ?
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Panteris, Emmanuel, and Dimitris Pappas. "F-Actin Organization and Epidermal Cell Morphogenesis in the Brown Alga Sargassum vulgare." International Journal of Molecular Sciences 24, no. 17 (August 26, 2023): 13234. http://dx.doi.org/10.3390/ijms241713234.
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The ordinary epidermal cells of various vascular plants are characterized by wavy anticlinal wall contours. This feature has not yet been reported in multicellular algal species. Here, we found that, in the leaf-like blades of the brown alga Sargassum vulgare, epidermal cells exhibit prominent waviness. Initially, the small meristodermal cells exhibit straight anticlinal contour, which during their growth becomes wavy, in a pattern highly reminiscent of that found in land plants. Waviness is restricted close to the external periclinal wall, while at inner levels the anticlinal walls become thick and even. The mechanism behind this shape relies on cortical F-actin organization. Bundles of actin filaments are organized, extending under the external periclinal wall and connecting its junctions with the anticlinal walls, constituting an interconnected network. These bundles define the sites of local thickening deposition at the anticlinal/periclinal wall junctions. These thickenings are interconnected by cellulose microfibril extensions under the external periclinal wall. Apart from the wavy anticlinal contour, outward protrusions also arise on the external periclinal wall, thus the whole epidermis exhibits a quilted appearance. Apart from highlighting a new role for F-actin in cell shaping, the comparison of this morphogenetic mechanism to that of vascular plants reveals a case of evolutionary convergence among photosynthetic organisms.
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Xu, Ting, Dimitrios Vavylonis, and Xiaolei Huang. "3D actin network centerline extraction with multiple active contours." Medical Image Analysis 18, no. 2 (February 2014): 272–84. http://dx.doi.org/10.1016/j.media.2013.10.015.
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Schindler, Daniel, Ted Moldenhawer, Carsten Beta, Wilhelm Huisinga, and Matthias Holschneider. "Three-component contour dynamics model to simulate and analyze amoeboid cell motility in two dimensions." PLOS ONE 19, no. 1 (January 26, 2024): e0297511. http://dx.doi.org/10.1371/journal.pone.0297511.
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Amoeboid cell motility is relevant in a wide variety of biomedical processes such as wound healing, cancer metastasis, and embryonic morphogenesis. It is characterized by pronounced changes of the cell shape associated with expansions and retractions of the cell membrane, which result in a crawling kind of locomotion. Despite existing computational models of amoeboid motion, the inference of expansion and retraction components of individual cells, the corresponding classification of cells, and the a priori specification of the parameter regime to achieve a specific motility behavior remain challenging open problems. We propose a novel model of the spatio-temporal evolution of two-dimensional cell contours comprising three biophysiologically motivated components: a stochastic term accounting for membrane protrusions and two deterministic terms accounting for membrane retractions by regularizing the shape and area of the contour. Mathematically, these correspond to the intensity of a self-exciting Poisson point process, the area-preserving curve-shortening flow, and an area adjustment flow. The model is used to generate contour data for a variety of qualitatively different, e.g., polarized and non-polarized, cell tracks that visually resemble experimental data very closely. In application to experimental cell tracks, we inferred the protrusion component and examined its correlation to common biomarkers: the F-actin density close to the membrane and its local motion. Due to the low model complexity, parameter estimation is fast, straightforward, and offers a simple way to classify contour dynamics based on two locomotion types: the amoeboid and a so-called fan-shaped type. For both types, we use cell tracks segmented from fluorescence imaging data of the model organism Dictyostelium discoideum. An implementation of the model is provided within the open-source software package AmoePy, a Python-based toolbox for analyzing and simulating amoeboid cell motility.
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Webb, A., P. Clark, J. Skepper, A. Compston, and A. Wood. "Guidance of oligodendrocytes and their progenitors by substratum topography." Journal of Cell Science 108, no. 8 (August 1, 1995): 2747–60. http://dx.doi.org/10.1242/jcs.108.8.2747.
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Oligodendrocyte progenitors arise in subventricular zones and migrate extensively during development before differentiating into mature oligodendrocytes, which myelinate nerve tracts in the central nervous system. We have used microfabricated substrata, containing periodic patterns of contours similar to those of central nervous system axons to assess the influence in vitro of substratum topography on oligodendrocytes isolated from 7 day rat optic nerve. Antiganglioside antibody A2B5 positive oligodendrocyte-type 2 astrocyte progenitors, and galactocerebroside positive and myelin basic protein positive oligodendrocytes, were highly aligned by surface contours as small as 100 nm depth and 260 nm repeat spacing. Rat optic nerve astrocytes also aligned on surface contours, but rat hippocampal and cerebellar neurons were unresponsive. Oligodendrocytes demonstrated enhanced parallel extension of their processes on narrow repeating topography in an arrangement similar to that found in the intact optic nerve. This is in marked contrast to the phenotype displayed by this cell type on planar substrata. Neither oligodendrocytes nor oligodendrocyte-type 2 astrocyte progenitors showed high-order F-actin cytoskeletal networks; thus their alignment on gratings is unlikely to result from deformation of actin cables and focal contacts. In contrast, aligned astrocytes showed striking arrangements of actin stress fibres. These results establish glial cells as potentially the most topographically sensitive cell types within the central nervous system. Furthermore, the topographical pattern inducing maximal alignment of oligodendrocyte lineage cells corresponds to the diameters of single axons within the 7 day optic nerve. Thus the migration of oligodendrocyte-type 2 astrocyte progenitors and axonal ensheathment by oligodendrocytes may be guided by axonal topography within the developing nerve.
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Imane, Haouam, Beladgham Mohammed, and Bouida Ahmed. "Hybrid medical image compression method using quincunx wavelet and geometric actif contour." Bulletin of Electrical Engineering and Informatics 9, no. 1 (February 1, 2020): 146–59. http://dx.doi.org/10.11591/eei.v9i1.1675.
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The purpose of this article is to find an efficient and optimal method of compression by reducing the file size while retaining the information for a good quality processing and to produce credible pathological reports, based on the extraction of the information characteristics contained in medical images. In this article, we proposed a novel medical image compression that combines geometric active contour model and quincunx wavelet transform. In this method it is necessary to localize the region of interest, where we tried to localize all the part that contain the pathological, using the level set for an optimal reduction, then we use the quincunx wavelet coupled with the set partitioning in hierarchical trees (SPIHT) algorithm. After testing several algorithms we noticed that the proposed method gives satisfactory results. The comparison of the experimental results is based on parameters of evaluation.
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Fox, Joan E. B. "The Platelet Cytoskeleton." Thrombosis and Haemostasis 70, no. 06 (1993): 0884–93. http://dx.doi.org/10.1055/s-0038-1649694.
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SummaryThe platelet cytoskeleton contains two actin filament-based components. One is the cytoplasmic actin filaments which fill the cytoplasm and mediate contractile events. The other is the membrane skeleton, which coats the plasma membrane and regulates properties of the membrane such as its contours and stability. In the unstimulated platelet, only 30-40% of the actin is polymerized into filaments; the rest is thought to be prevented from polymerizing by the association of thymosin β4 with monomeric actin and by the association of gelsolin with the barbed ends of pre-existing actin filaments. When platelets are activated, there is a rapid increase in actin polymerization; new filaments fill the extending filopodia and form a network at the periphery of the platelet. As a result of activation, myosin binds to cytoplasmic actin filaments, causing them to move towards the center of the platelet. As platelets aggregate, additional cytoskeletal reorganizations occur: GP Ilb-IIIa associates with adhesive ligand in a platelet aggregate; this results in the association of GP Ilb-IIIa, membrane skeleton proteins, and signaling molecules with cytoplasmic actin. Future studies should help to elucidate the significance of the cytoskeleton in regulating signal transduction events in platelets.
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M'Hiri, Slim, Mohamed Amine Mezghich, and Malek Sellami. "Contours actifs avec a priori de forme basé sur la transformée de Fourier-Mellin analytique." Traitement du signal 29, no. 1-2 (April 28, 2012): 123–42. http://dx.doi.org/10.3166/ts.29.123-142.
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Fox, Joan. "Cytoskeletal Proteins and Platelet Signaling." Thrombosis and Haemostasis 86, no. 07 (2001): 198–213. http://dx.doi.org/10.1055/s-0037-1616218.
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SummaryThe actin filament network fills the cytoplasm of unstimulated platelets and connects with a submembranous latticework of short cross-linked actin filaments, known as the membrane skeleton. One function of the cytoskeleton is to direct the contours of the membrane in the unstimulated platelet and the rapid changes in shape in the activated platelet. Activation-induced changes result from events such as phosphorylation or calpain-induced cleavage of cytoskeletal proteins. The specific reorganizations depend upon the combination of signals to which platelets are exposed. A second function of the cytoskeleton is to bind other cellular components; it binds signaling molecules, localizing them to specific cellular locations; it binds the plasma membrane regulating properties of the membrane, maintaining microdomains in the membrane, or regulating activities of membrane proteins. In this way, the cytoskeleton plays a critical role in regulation of spatial organizations and, thus, in the integration of cellular activities.
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Stamatoglou, S. C., K. H. Sullivan, S. Johansson, P. M. Bayley, I. D. Burdett, and R. C. Hughes. "Localization of two fibronectin-binding glycoproteins in rat liver and primary hepatocytes. Co-distribution in vitro of integrin (alpha 5 beta 1) and non-integrin (AGp110) receptors in cell-substratum adhesion sites." Journal of Cell Science 97, no. 4 (December 1, 1990): 595–606. http://dx.doi.org/10.1242/jcs.97.4.595.
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We have compared the localization of integrin alpha 5 beta 1 and AGp110 (apical glycoprotein of Mr 110 × 10(3]] in rat liver parenchyma and in primary hepatocyte cultures. Integrin alpha 5 beta 1 is a heterodimeric fibronectin receptor. AGp110 is a newly described monomeric glycoprotein of the apical (bile canalicular) membrane domain of liver parenchyma that binds in an RGD-independent manner to fibronectin and mediates spreading of hepatocytes onto fibronectin-coated substrata. Using Western blotting of fractionated liver membranes and immunocytochemistry of liver sections at light- and electron-microscope levels, we have confirmed that AGp110 is a canalicular glycoprotein and have established that integrin is located in approximately equal proportions in the sinusoidal, lateral and canalicular membrane domains. In the canalicular surface domain both glycoproteins are associated with microvilli. Examination of immunolabelled primary hepatocytes spread on fibronectin-coated substrata by light and laser scanning confocal microscopy revealed colocalization of AGp110, integrin, actin and vinculin in substratum-attached microextensions at the periphery of the basal cell surface. Actin filaments that terminated at these cell processes originated from circular sub-cortical actin fibres. Interference reflection microscopy revealed focal adhesive contacts at the edge of the basal cell periphery at the same location where AGp110 and integrin were observed by immunofluorescence. In vitro, a proportion of the primary hepatocytes seeded onto fibronectin-coated substrata aggregated into colonies of several cells with intercellular contacts between neighbouring cells. Cell-substratum contacts containing integrin, AGp110, actin and vinculin followed the contours of these colonies in the same manner as they delineated the basal periphery of single, substratum-attached cells. We conclude that both integrin and AGp110 contribute to hepatocyte-fibronectin adhesive interactions and that intercellular adhesion and cooperation among hepatocytes in their response to fibronectin matrices leads to colony formation and morphological differentiation of parenchymal cell monolayers in vitro.
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Chiotaki, Rena, Hara Polioudaki, and Panayiotis A. Theodoropoulos. "Differential nuclear shape dynamics of invasive andnon-invasive breast cancer cells are associated with actin cytoskeleton organization and stability." Biochemistry and Cell Biology 92, no. 4 (August 2014): 287–95. http://dx.doi.org/10.1139/bcb-2013-0120.
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Cancer cells often exhibit characteristic aberrations in their nuclear architecture, which are indicative of their malignant potential. In this study, we have examined the nuclear and cytoskeletal composition, attachment configuration dynamics, and osmotic or drug treatment response of invasive (Hs578T and MDA-MB-231) and non-invasive (MCF-10A and MCF-7) breast cancer cell lines. Unlike MCF-10A and MCF-7, Hs578T and MDA-MB-231 cells showed extensive nuclear elasticity and deformability and displayed distinct kinetic profiles during substrate attachment. The nuclear shape of MCF-10A and MCF-7 cells remained almost unaffected upon detachment, hyperosmotic shock, or cytoskeleton depolymerization, while Hs578T and MDA-MB-231 revealed dramatic nuclear contour malformations following actin reorganization.
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Murofushi, H., S. Kotani, H. Aizawa, S. Hisanaga, N. Hirokawa, and H. Sakai. "Purification and characterization of a 190-kD microtubule-associated protein from bovine adrenal cortex." Journal of Cell Biology 103, no. 5 (November 1, 1986): 1911–19. http://dx.doi.org/10.1083/jcb.103.5.1911.
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A heat-stable microtubule-associated protein (MAP) with molecular weight of 190,000, termed 190-kD MAP, was purified from bovine adrenal cortex. This MAP showed the same level of ability to promote tubulin polymerization as did MAP2 and tau from mammalian brains. Relatively high amounts of 190-kD MAP could bind to microtubules reconstituted in the presence of taxol. At maximum 1 mol of 190-kD MAP could bind to 2.3 mol of tubulin. 190-kD MAP was phosphorylated by a cAMP-dependent protein kinase prepared from sea urchin spermatozoa and by protein kinase(s) present in the microtubule protein fraction prepared from mammalian brains. The maximal numbers of incorporated phosphate were approximately 0.2 and approximately 0.4 mol per mole of 190-kD MAP, respectively. These values were lower than that of MAP2, which could be heavily phosphorylated by the endogenous protein kinase(s) up to 5 mol per mole of MAP2 under the same assay condition. 190-kD MAP had no effects on the low-shear viscosity of actin and did not induce an increase in turbidity of the actin solution. It was also revealed that 190-kD MAP does not cosediment with actin filaments. These data clearly show that, distinct from MAP2 and tau, this MAP does not interact with actin. Electron microscopic observation of the rotary-shadowed images of 190-kD MAP showed the molecular shape to be a long, thin, flexible rod with a contour length of approximately 100 nm. Quick-freeze, deep-etch replicas of the microtubules reconstituted from 190-kD MAP and brain tubulin revealed many cross-bridges connecting microtubules with each other.
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Ahmed, Zubair M., Thomas J. Jaworek, Gowri N. Sarangdhar, Lili Zheng, Khitab Gul, Shaheen N. Khan, Thomas B. Friedman, et al. "Inframe deletion of human ESPN is associated with deafness, vestibulopathy and vision impairment." Journal of Medical Genetics 55, no. 7 (March 23, 2018): 479–88. http://dx.doi.org/10.1136/jmedgenet-2017-105221.
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BackgroundUsher syndrome (USH) is a neurosensory disorder characterised by deafness, variable vestibular areflexia and vision loss. The aim of the study was to identify the genetic defect in a Pakistani family (PKDF1051) segregating USH.MethodsGenome-wide linkage analysis was performed by using an Illumina linkage array followed by Sanger and exome sequencing. Heterologous cells and mouse organ of Corti explant-based transfection assays were used for functional evaluations. Detailed clinical evaluations were performed to characterise the USH phenotype.ResultsThrough homozygosity mapping, we genetically linked the USH phenotype segregating in family PKDF1051 to markers on chromosome 1p36.32-p36.22. The locus was designated USH1M. Using a combination of Sanger sequencing and exome sequencing, we identified a novel homozygous 18 base pair inframe deletion in ESPN. Variants of ESPN, encoding the actin-bundling protein espin, have been previously associated with deafness and vestibular areflexia in humans with no apparent visual deficits. Our functional studies in heterologous cells and in mouse organ of Corti explant cultures revealed that the six deleted residues in affected individuals of family PKDF1051 are essential for the actin bundling function of espin demonstrated by ultracentrifugation actin binding and bundling assays. Funduscopic examination of the affected individuals of family PKDF1051 revealed irregular retinal contour, temporal flecks and disc pallor in both eyes. ERG revealed diminished rod photoreceptor function among affected individuals.ConclusionOur study uncovers an additional USH gene, assigns the USH1 phenotype to a variant of ESPN and provides a 12th molecular component to the USH proteome.
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Tang, Xiaoqiong, Yan Zhang, Jiangbing Mao, Yuhua Wang, Zhenghong Zhang, Zhengchao Wang, and Hongqin Yang. "Effects of substrate stiffness on the viscoelasticity and migration of prostate cancer cells examined by atomic force microscopy." Beilstein Journal of Nanotechnology 13 (June 28, 2022): 560–69. http://dx.doi.org/10.3762/bjnano.13.47.
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The stiffness of the extracellular matrix of tumour cells plays a key role in tumour cell metastasis. However, it is unclear how mechanical properties regulate the cellular response to the environmental matrix. In this study, atomic force microscopy (AFM) and laser confocal imaging were used to qualitatively evaluate the relationship between substrate stiffness and migration of prostate cancer (PCa) cells. Cells cultured on stiff substrates (35 kPa) undergone several interesting phenomena compared to those on soft substrates (3 kPa). Here, the stimulation generated by the stiff substrates triggered the F-actin skeleton to bundle its filaments, increasing the polarity index of the external contour of PCa cells. Analysis of AFM force–distance curves indicated that the elasticity of the cells cultured on 35 kPa substrates increased while the viscosity decreased. Wound-healing experiments showed that PCa cells cultured on 35 kPa substrates have higher migration potential. These phenomena suggested that the mechanical properties may be correlated with the migration of PCa cells. After actin depolymerisation, the elasticity of the PCa cells decreased while the viscosity increased, and the migration ability was correspondingly decreased. In conclusion, this study clearly demonstrated the relationship between substrate stiffness and the mechanical properties of cells in prostate tumour metastasis, providing a basis for understanding the changes in the biomechanical properties at a single-cell level.
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Dubreuil, R., T. J. Byers, D. Branton, L. S. Goldstein, and D. P. Kiehart. "Drosophilia spectrin. I. Characterization of the purified protein." Journal of Cell Biology 105, no. 5 (November 1, 1987): 2095–102. http://dx.doi.org/10.1083/jcb.105.5.2095.
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We purified a protein from Drosophila S3 tissue culture cells that has many of the diagnostic features of spectrin from vertebrate organisms: (a) The protein consists of two equimolar subunits (Mr = 234 and 226 kD) that can be reversibly cross-linked into a complex composed of equal amounts of the two subunits. (b) Electron microscopy of the native molecule reveals two intertwined, elongated strands with a contour length of 180 nm. (c) Antibodies directed against vertebrate spectrin react with the Drosophila protein and, similarly, antibodies to the Drosophila protein react with vertebrate spectrins. One monoclonal antibody has been found to react with both of the Drosophila subunits and with both subunits of vertebrate brain spectrin. (d) The Drosophila protein exhibits both actin-binding and calcium-dependent calmodulin-binding activities. Based on the above criteria, this protein appears to be a bona fide member of the spectrin family of proteins.
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Fenyves, A. M., J. Behrens, and K. Spanel-Borowski. "Cultured microvascular endothelial cells (MVEC) differ in cytoskeleton, expression of cadherins and fibronectin matrix. A study under the influence of interferon-gamma." Journal of Cell Science 106, no. 3 (November 1, 1993): 879–90. http://dx.doi.org/10.1242/jcs.106.3.879.
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Endothelial cells are known to undergo transitions in cell shape during long-term culture. Thus, the assumption that the separate phenotypes of microvascular endothelial cells (MVEC) recently isolated from bovine corpus luteum represent constitutively different cell strains cannot automatically be made. For this reason, particular morphological qualities from four of five reported MVEC types were studied. Confluent cultures of MVEC types 1, 3, 4 and 5 were either left untreated or exposed to recombinant bovine interferon-gamma (IFN-gamma; 200 units/0.5 ml culture medium) for 3 days. Paraformaldehyde-fixed monolayers were permeabilized with Triton X-100 prior to the detection of filamentous actin, using phalloidin-FITC. Vimentin filaments, cytokeratin filaments, microtubules, E- and N-cadherins as molecules of cell adhesion plaques, and fibronectin filaments were localized by the application of specific antibodies in combination with epifluorescence microscopy. Cells from untreated single cultures uniformly and reproducibly showed an actin cytoskeleton that distinguished the particular MVEC type. MVEC type 1 presented a circular band of fine actin filaments. MVEC type 3 preferentially had developed a starburst-like actin pattern. MVEC type 4 mainly exhibited a polygonal network. MVEC type 5 showed a prominent circular band of thick microfilament bundles from which short filaments radiated. Cytokeratin filaments were noted in MVEC type 1 only. Vimentin filaments occurred as a dense network constricted to the central area in MVEC type 1, while they were spread out in MVEC types 3 and 4. A wavy path comparable to the course of microtubules was apparent in MVEC type 5. Fibronectin assembled into two differently shaped layers at the basal cell side of each MVEC type. Under IFN-gamma treatment, cytoskeletal diversities were maintained between the MVEC types, yet each MVEC type showed specific modulations to its cytoskeleton and to its fibronectin matrix. Upregulation of anti-E-cadherin labelling was detected in MVEC type 1, showing a fluorescent cell border of linear contour. The upregulation of E-cadherin by IFN-gamma treatment could also be demonstrated by western blotting, which revealed a 135 kDa full-sized molecule and a 95 kDa tryptic fragment characteristic of cadherins. Anti-N-cadherin labelling was evident for MVEC type 5, giving rise to a fluorescent punctate cell margin. Our investigations support the existence of truly separate MVEC types.
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Zhang, Hui, Andrey V. Cybulsky, Lamine Aoudjit, Jianxin Zhu, Hongping Li, Nathalie Lamarche-Vane, and Tomoko Takano. "Role of Rho-GTPases in complement-mediated glomerular epithelial cell injury." American Journal of Physiology-Renal Physiology 293, no. 1 (July 2007): F148—F156. http://dx.doi.org/10.1152/ajprenal.00294.2006.
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Visceral glomerular epithelial cells (GEC) are essential for maintenance of normal glomerular permselectivity. The actin cytoskeleton is a key determinant of GEC morphology and function. In the rat passive Heymann nephritis (PHN) model of membranous nephropathy, complement C5b-9 induces nonlytic GEC injury associated with morphological changes of GEC and proteinuria. The current study addresses the role of Rho family of small GTPases in complement-mediated GEC injury. When cultured rat GEC were stimulated with complement C5b-9 for 18 h, RhoA activity increased, whereas Rac1/Cdc42 activities decreased, compared with control cells. Similar changes in Rho-GTPase activities were observed in glomeruli from rats with PHN. The amount of active p190RhoGAP, a negative upstream regulator of RhoA, was decreased in complement-stimulated GEC, potentially contributing to increased RhoA activity. To address the functional effects of Rho-GTPases, GEC were transfected with constitutively active (CA) or dominant negative (DN) Rho-GTPase mutants. GEC transfected with CA-RhoA showed a smaller and round contour and prominent cortical F-actin. In contrast, GEC transfected with CA-Rac1 demonstrated morphological changes that resembled process formation. In addition, expression of CA-RhoA attenuated complement-mediated cytotoxicity, whereas cytotoxicity was augmented by DN-RhoA. Thus exposure of GEC to complement alters the balance of RhoA, Rac1, and Cdc42 activities. The activity of Rac1 may contribute to process formation, while activation of RhoA (e.g., in the setting of complement attack), with or without blunting of Rac1 activity, may have an opposite effect, i.e., contribute to foot process effacement. Activation of RhoA increases the resistance of GEC to complement-mediated injury.
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Weber, I., E. Wallraff, R. Albrecht, and G. Gerisch. "Motility and substratum adhesion of Dictyostelium wild-type and cytoskeletal mutant cells: a study by RICM/bright-field double-view image analysis." Journal of Cell Science 108, no. 4 (April 1, 1995): 1519–30. http://dx.doi.org/10.1242/jcs.108.4.1519.
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To investigate the dynamics of cell-substratum adhesion during locomotion, a double-view optical technique and computer-assisted image analysis has been developed which combines reflection interference contrast microscopy (RICM) with bright-field imaging. The simultaneous recording of cell-substratum contact and cell body contour has been applied to aggregation-competent cells of Dictyostelium discoideum. These cells are distinguished from cells at earlier stages of development by small areas of contact to a substratum. Three questions have been addressed in analysing the locomotion of aggregation-competent cells. (1) What is the relationship between changes in the shape of cells and their contact to a substratum during a chemotactic response? (2) What is the relationship between protrusion and retraction of the cell body, and between local attachment and detachment? (3) Are there differences between wild-type and mutant cells that lack certain cytoskeletal proteins? During a chemotactic response the front region of the amoeba can bend towards the gradient of attractant without being supported by its contact with a surface, which excludes the necessity for gradients of adhesion for the response. The finding that in locomoting cells protrusion of the leading edge often precedes retraction establishes a pioneer role for the front region. The finding that gain of contact area precedes loss provides evidence for the coordination of interactions between the cell surface and a substratum. For comparison with wild-type, aggregation-competent triple mutant cells have been used that lack two F-actin crosslinking proteins, alpha-actinin and 120 kDa gelation factor, and an actin filament fragmenting protein, severin. Disturbances in the spatial and temporal control of cytoskeletal activities have been unravelled in the mutant by RICM and quantified by cross-correlation analysis of attachment and detachment vectors. In order to detect these disturbances, it was essential to analyse cell locomotion on the weakly adhesive surface of freshly cleaved mica.
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Gandhi, Harjeet Singh. "Hyalite Sol-Gel Amoeba: A Physiology-Based Biophysical Model for Segmentation and Biotransformation of Medical Images To 3D Solid-State Characterizing Native Tissue Properties for Patient-Specific and Patient-Appropriate Analysis for Surgical Applications." INTERNATIONAL JOURNAL OF COMPUTERS & TECHNOLOGY 22 (May 27, 2022): 64–85. http://dx.doi.org/10.24297/ijct.v22i.9228.
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Introduction: The endeavour to improve medical image segmentation techniques for higher analysis in surgical planning and medical therapeutics is far from becoming a standard of care in clinical practice. Hyalite Sol-Gel Amoeba model based on biophysical sciences apart from performing image segmentation is designed to extract real-world tissue densities for patient-specific and patient-appropriate analysis. Objectives: Amoeba Proteus is a unicellular independent entity, with a nucleus and sol-gel protoplasm enclosed in a membrane. The study presents versatile restructuring anatomy and physiology of the Amoeba Proteus for segmentation of 2D, and 3D medical images based on well-established principles of energy minimization and active contour. It demonstrates how the animalcule glides and advances by throwing pseudopodia driven by phenomenal actin-myosin activity that can segment a region-of-interest, and finally, at the time of apoptosis, its protoplasm and organelles acquire distribution of original image intensities to characterize tissue densities. Methods: This seminal study following a brief review of computer vision science discusses the relationship between optical density and tissue density, and the theory of sol-gel fluid mechanics. The framework of the HSG-Amoeba is described with the segmentation of various skeletal components of the thoracic cage. Results: This being a foundational study to describe the concept of the HSG-Amoeba model it requires the development of a mathematical algorithm to demonstrate its worthiness as a tool for surgical applications. Conclusion: The focus of the study is to present the design and framework of the newly conceived HSG-Amoeba model to segment a medical image and extract tissue densities without altering the original image intensities.
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Andre, P., A. M. Benoliel, C. Capo, C. Foa, M. Buferne, C. Boyer, A. M. Schmitt-Verhulst, and P. Bongrand. "Use of conjugates made between a cytolytic T cell clone and target cells to study the redistribution of membrane molecules in cell contact areas." Journal of Cell Science 97, no. 2 (October 1, 1990): 335–47. http://dx.doi.org/10.1242/jcs.97.2.335.
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In many models of cell-cell adhesion, it was reported that some cell membrane molecules might be redistributed into contact areas. However, this phenomenon was not subjected to precise quantification. In the present work, fluorescence microscopy, immunolabelling and digital image processing were combined to analyse quantitatively the spatial organization of specific or nonspecific conjugates made with a cytolytic T (CTL) lymphocyte clone (BM3.3) and target cells (EL4 or RDM4). Binding was achieved under calcium-free conditions to study the earliest steps of cell interaction, preceding CTL activation. Fluorescent antibodies were used to label class I histocompatibility molecules on both killer and target cells, and T cell receptor, CD3, CD8 and LFA-1 (CD18/CD11a) on the killer cells. Membrane bilayers were stained with a fluorescent phospholipid, glycoconjugates were labelled with periodic oxidation and Lucifer Yellow uptake, and polymerized actin was revealed with a fluorescent phallacidin derivative. Also, the fine geometry of killer-target interaction area was studied with electron microscopy and computer-assisted contour analysis. It is concluded that: (1) qualitative examination of fluorescence photomicrographs cannot permit accurate comparison between different fluorescence densities. (2) The cell-cell contact area was about fourfold higher in specific conjugates than in non-specific ones. (3) The surface density of adhesion molecules exhibited similar increases (between 30 and 80%) in the contact areas of both specific and nonspecific conjugates. (4) However, the amount of redistributed surface molecules was higher when cell-cell interaction was enhanced either by specific immunological recognition (in specific conjugates) or periodate oxidation. (5) Since redistribution did not require extracellular calcium and it was detected on nonspecific conjugates, this did not require full lymphocyte activation. Spatial reorganization of cell surface molecules may thus be a general consequence of adhesion, cell surface mobility and intermolecular forces.
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Nikitina, Nina, Nurbanu Bursa, Matthew Goelzer, Madison Goldfeldt, Chase Crandall, Sean Howard, Janet Rubin, Anamaria Zavala, Aykut Satici, and Gunes Uzer. "Data‐Driven and Cell‐Specific Determination of Nuclei‐Associated Actin Structure." Small Structures, February 16, 2024. http://dx.doi.org/10.1002/sstr.202300204.
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Quantitative volumetric assessment of filamentous actin (F‐actin) fibers remains challenging due to their interconnected nature, leading researchers to utilize threshold‐based or qualitative measurement methods with poor reproducibility. Herein, a novel machine learning‐based methodology is introduced for accurate quantification and reconstruction of nuclei‐associated F‐actin. Utilizing a convolutional neural network (CNN), actin filaments and nuclei from 3D confocal microscopy images are segmented and then each fiber is reconstructed by connecting intersecting contours on cross‐sectional slices. This allows measurement of the total number of actin filaments and individual actin filament length and volume in a reproducible fashion. Focusing on the role of F‐actin in supporting nucleocytoskeletal connectivity, apical F‐actin, basal F‐actin, and nuclear architecture in mesenchymal stem cells (MSCs) are quantified following the disruption of the linker of nucleoskeleton and cytoskeleton (LINC) complexes. Disabling LINC in MSCs generates F‐actin disorganization at the nuclear envelope characterized by shorter length and volume of actin fibers contributing a less elongated nuclear shape. The findings not only present a new tool for mechanobiology but introduce a novel pipeline for developing realistic computational models based on quantitative measures of F‐actin.
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Previs, Michael J., Ji Young Mun, Arthur J. Michalek, Samantha Beck Previs, James Gulick, Jeffrey Robbins, David M. Warshaw, and Roger Craig. "Phosphorylation and Calcium Antagonistically Tune Myosin‐binding Protein C's Molecular Structure and Function." FASEB Journal 30, S1 (April 2016). http://dx.doi.org/10.1096/fasebj.30.1_supplement.1012.2.
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During each heartbeat, calcium activates the sliding of actin‐thin filaments towards the centers of myosin‐thick filaments to shorten the overall length of cardiac muscle cells. Cardiac myosin binding protein C (cMyBP‐C) tunes these interactions throughout the contractile cycle. cMyBP‐C's C terminus is strongly bound to the thick filament backbone and its N‐terminal domains extend away and transiently interact with actin and/or the myosin S2 domain, sensitizing thin filaments to calcium and governing maximal sliding velocities. Both mechanisms are tunable by phosphorylation of 4 serines within an extensible, intrinsically disordered region of cMyBP‐C's N‐terminus, the M‐domain. Does phosphorylation impact the structure and molecular mechanics of cMyBP‐C's N terminus to tune it's function? Atomic force spectroscopy studies of N‐terminal fragments (domains C1–C2), showed that phosphorylation reduced the M‐domain's contour length and extensibility. Rotary shadowing electron microscopy showed that M‐domain phosphorylation caused N‐terminal fragments (C0–C3) to shift from an extended, rod‐like structure to a compact conformation. Taken together, M‐domain phosphorylation and its impact on cMyBP‐C's N‐terminal structure suggest a mechanism for tuning cMyBP‐C's function in motility assays. Interestingly, we found that free calcium (0.1 mM), necessary to fully activate the thin‐filament, mitigated the structural effects of phosphorylation by increasing the free‐extensibility of the phosphorylated M‐domain and shifting the phosphorylated N‐terminal fragments back to the extended, rod‐like state, as if unphosphorylated. Functionally, even though phosphorylation reduced cMyBP‐C's ability to inhibit actin filament sliding velocity in the motility assay (24% vs. 40% inhibition), addition of calcium ablated the impact of phosphorylation, fully restoring cMyBP‐C's inhibitory capacity. We conclude that phosphorylation of MyBP‐C's M‐domain may have its greatest effect on cardiac contractility by tuning cMyBP‐C's ability to sensitize actin‐thin filaments to calcium at the low levels present during the onset of contraction. Importantly, calcium levels at the peak contraction would allow cMyBP‐C to remain a potent contractile modulator, regardless of the cMyBP‐C's phosphorylation state.Support or Funding InformationNIH grants HL124041 and HL059408 supported these studies.
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Kreplak, Laurent. "The contribution of the N- and C- terminal domains to the stretching properties of intermediate filaments." MRS Proceedings 1274 (2010). http://dx.doi.org/10.1557/proc-1274-qq02-06.
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AbstractThe animal cell cytoskeleton consists of three interconnected filament systems: actin containing microfilaments (MFs), microtubules (MTs), and intermediate filaments (IFs). Among these three filaments systems, IFs are the only one that show high extensibility at both the single filament and network levels. In this work, I am presenting a simple model of IFs extensibility based on the current structural knowledge of the filaments. The only extra information added to this model compared to previous ones is the fact that the unfolded N- and C-termini of IF proteins are sandwiched between adjacent coiled-coil rod domains within the filaments. Since we know the contour length and typical persistence length of these unfolded termini, it is possible to predict the persistence length of a single filament, its maximal extensibility and the onset of coiled-coil unfolding. The predictions of the model are in good agreement with experiments on single desmin IFs stretched on a surface by AFM and on vimentin and desmin networks probed by rheology.
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Patel, Meet H., Guy Perkins, and Anna Lysakowski. "Cristae Align Across Mitochondrial Membranes in Vestibular Hair Cells to Possibly Increase ATP Output." FASEB Journal 31, S1 (April 2017). http://dx.doi.org/10.1096/fasebj.31.1_supplement.740.20.
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The main objective of this research is to study mitochondria in inner ear hair cells from a functional and structural perspective. Mitochondria are divided into three different sub‐types, according to size: large, medium, and small. Our focus is mitochondria near the cuticular plate (CP) in vestibular Type 1 hair cells. Since these mitochondria are adjacent to the CP, we also see stereociliar rootlets (SRs) in close proximity. In addition, we hypothesized that the side facing the CP has a significantly larger amount of cristae junctions (CJs) compared to the opposite side in order to satisfy energy demand of rapidly regenerating SRs. This suggests a polarization of CJs towards one side, so that they can transport ATP and Ca2+ to points of interest, such as SRs and the CP (Perkins et al. 2010). Using IMOD software created by Univ. of Colorado, we examined and accurately traced individual contours that, when meshed, gave a very detailed structure of the mitochondria. By counting CJs on either side of the mitochondria, we can determine their density relative to the CP. Using the “Get info” feature of IMOD we obtained accurate surface area measurements. Interestingly, lamellar cristae in one mitochondrion were seen to curve in the direction of the stereociliar rootlets and three mitochondria were observed to form a type of “super‐mitochondrion” by alignment of their CJs and tethering of the outer mitochondrial membranes. Stereocilia are known to construct their actin from tip to base using myosin and rate‐regulating proteins (Naoz et al. 2008). We hypothesize that mitochondria provide ATP for reconstitution of actin filaments and for maintaining the structure of the cuticular plate. The alignment of cristae between mitochondria may be able to increase ATP production. In conclusion, our results support the hypothesis that CJs are asymmetrically distributed in favor of structures of interest that require more ATP.Support or Funding InformationSupported by NIH R21‐DC013181 (AL) and P41‐RR004050 (GP, ME).
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Will, Melissa L., Andrew P. Landstrom, J. Martijn Bos, Bernard J. Gersh, Steve R. Ommen, and Michael J. Ackerman. "Abstract 371: Prevalence and Spectrum of Thin Filament Mutations in 1025 Patients with Hypertrophic Cardiomyopathy." Circulation 116, suppl_16 (October 16, 2007). http://dx.doi.org/10.1161/circ.116.suppl_16.ii_57-d.
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Background Recently, genetic testing for sarcomeric hypertrophic cardiomyopathy (HCM) became a commercially available diagnostic test involving analysis of 8 HCM-associated myofilament genes, four of which encode thin filament proteins - TNNT2- encoded cardiac troponin T, TPM1 -encoded alpha tropomyosin, TNNI3- encoded cardiac troponin I, and ACTC- encoded cardiac actin. Compared to the two most common subtypes of sarcomeric HCM, much less is known about the prevalence and spectrum of thin filament HCM. Methods Comprehensive open reading frame/splice site mutational analysis of these 4 thin filament-encoding genes was performed, using polymerase chain reaction, denaturing high performance liquid chromatography, and direct DNA sequencing, on the largest assembled cohort of unrelated patients (N = 1025, 61% male, 49 ± 18 years at diagnosis, maximal left ventricular wall thickness, LVWT, 22.3 ± 7 mm) with clinically diagnosed HCM that were seen at the Mayo Clinic. Results Nineteen distinct missense mutations, involving conserved residues and absent in 600 reference alleles, were identified in 36 of 1025 patients (3.5%) including TNNT2 (16 patients), TNNI3 (12), TPM1 (7) and ACTC (1). Among these 36 patients with thin filament-HCM, their average age at diagnosis was 33.2 ± 16 years and the average LVWT was 21 ± 8 mm. Eighteen patients (50%) had evidence for familial HCM and 13% had a positive history for sudden cardiac death. Only 13 patients (36%) had a reverse septal curvature by echocardiography. Instead, 12 patients (34%) had either sigmoidal or neutral septal contours and 9 patients (25%) had apical variant-HCM. Conclusion Here, we present the largest cohort analysis of thin filament HCM to date and detail the prevalence and spectrum of HCM-associated mutations in these 4 genes. Compared to the strong association between reverse septal curvature and thick filament HCM, the septal morphology associated with thin filament HCM was quite varied. Contrary to published estimates of the frequency of troponin T-HCM (5 – 10%) and the other subtypes of thin filament HCM, the prevalence of thin filament HCM was very low in this cohort. If confirmed in other cohorts, a revised cascade for HCM genetic testing should be considered.
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Zhang, Hualing, Yanlan Xie, Hongmei Chen, Qiqian Su, Jun He, Xiangyu Su, Danyuan Wu, Huiming Zhou, Longfeng Yu, and Wanzhong Tan. "First report of large-berry coffee (Coffea liberica) anthracnose caused by Colletotrichum kahawae in China." Plant Disease, May 8, 2024. http://dx.doi.org/10.1094/pdis-01-24-0039-pdn.
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Large-berry coffee (Coffea liberica) is one of the three cultivated coffee species and a precious breeding germplasm in China (Yan et al, 2019). Anthracnose is a damaging epidemic disease on coffee worldwide (Mohammed et al. 2015). Between June and September 2022, anthracnose was observed on coffee plants in Puer area, Yunnan, China and disease incidence (% plants diseased) of 8.5%-28.2% was recorded in the field. The disease symptoms were observed at all growth stages. Lesions on leaves were circular or oval, with a white to gray central zone outlined by a brown margin and surrounded by a chlorotic halo, Φ5.1-18.5 mm; some lesions extended and coalesced later to form large, blighted areas, leading to complete leaf senescence, defoliation and bare blighted branches on heavily infected trees. The spots on coffee berries were oval or fusiform, sunken and brown-black; diseased berries became gray-black and dried-out but remained on the tree. Leaves with typical anthracnose lesions were collected from fields in Simao ( 22.07°E,100.98°N) to isolate the pathogen. Leaf pieces (5×5mm) from the lesion margin were cut, surface-sterilized with 75% ethanol and 2% NaClO, and cultured on PDA at 25°C. Three isolates with the same colony morphology were obtained by hyphal tip purification. Detached and intact leaves of 6-month coffee seedlings were inoculated with Φ5mm mycelial discs of the isolates. Anthracnose lesions developed on the inoculated leaves, with all 3 isolates, 7d after incubation in a growth chamber (25°C, > 90% RH and lighting 8 h/d at 11000 lux). Pathogens with the same colony morphology as those of the original isolates were re-isolated from the infected tissues of inoculated leaves, thus fulfilling Koch’s Postulates. The ITS sequence (PP550861) for the isolate was PCR-amplified and Blast-n analyses showed 100 % (554/554bp) identity to Colletotrichum kahawae LWTJ01; so they were the same population and coded as KFTJ02. The actin (ACT), calmodulin(CAL), glyceraldehydes-3-phosphate dehydrogenase (GAPHD) and histone 3 (HIS3) genes (Qiu et al. 2020) were amplified from one of KFTJ02 isolates, sequenced and deposited in NCBI GenBank (OR842543, OR842544, OR842545 & OR842546). A phylogenetic tree was generated based on the concatenated sequences of the four genes and those of related Colletotrichum spp. using MEGA 6.0 and KFTJ02 clustered in the same clade with C. kahawae IMI319418 on the tree (Bootstrap sup.=88%). When cultured at 25°C on PDA for 7 days, its colonies were near round or ovoid, gray-white, contoured, Φ73.2-80.1 (76.2±2.3)mm or growth rate 10.2-11.1(8.1) mm/d (n=10). The hyphae were hyaline, septated, branching at near right angles. Conidial masses formed 14 days after incubation. The conidia were elliptical, hyaline, monocellular, 10.2-15.5 (12.7±1.06)×3.8-5.2 (4.3±0.52) µm (n=50). The appressoria were black-brown, oval or irregular, 7.8-9.3 (8.5±0.81)μm (n= 50). These morphological characteristics were consistent with those of C. kahawae (Bridge et al, 2008). Therefore, KFTJ02 was identified as C. kahawae, which has been found to infect Camellia oleifera, Areca catechu and Ficus microcarpa (Wei et al, 2023; Zhang et al, 2020; Lin 2023). The coffee berry disease pathogen (C. kahawae) is a quarantine species which has not been recorded and so it is first reported on coffee crops in China. Results of the present study provide important references for further studies on this disease.