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Kerry Bloom - One of the best experts on this subject based on the ideXlab platform.
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function and assembly of dna looping clustering and microtubule attachment complexes within a eukaryotic kinetochore
Molecular Biology of the Cell, 2009Co-Authors: Marybeth Anderson, Julian Haase, Kerry BloomAbstract:The kinetochore is a complex protein–DNA assembly that provides the Mechanical Linkage between microtubules and the centromere DNA of each chromosome. Centromere DNA in all eukaryotes is wrapped around a unique nucleosome that contains the histone H3 variant CENP-A (Cse4p in Saccharomyces cerevisiae). Here, we report that the inner kinetochore complex (CBF3) is required for pericentric DNA looping at the Cse4p-containing nucleosome. DNA within the pericentric loop occupies a spatially confined area that is radially displaced from the interpolar central spindle. Microtubule-binding kinetochore complexes are not involved in pericentric DNA looping but are required for the geometric organization of DNA loops around the spindle microtubules in metaphase. Thus, the mitotic segregation apparatus is a composite structure composed of kinetochore and interpolar microtubules, the kinetochore, and organized pericentric DNA loops. The Linkage of microtubule-binding to centromere DNA-looping complexes positions the pericentric chromatin loops and stabilizes the dynamic properties of individual kinetochore complexes in mitosis.
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function and assembly of dna looping clustering and microtubule attachment complexes within a eukaryotic kinetochore
Molecular Biology of the Cell, 2009Co-Authors: Marybeth Anderson, Julian Haase, Elaine Yeh, Kerry BloomAbstract:The kinetochore is a complex protein–DNA assembly that provides the Mechanical Linkage between microtubules and the centromere DNA of each chromosome. Centromere DNA in all eukaryotes is wrapped ar...
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persistent Mechanical Linkage between sister chromatids throughout anaphase
Chromosoma, 2009Co-Authors: Benjamin D Harrison, Margaret L Hoang, Kerry BloomAbstract:In budding yeast, we have found that sister rDNA arrays marked with fluorescent probes can be visualized as two distinguishable strands during metaphase. Upon anaphase, these arm loci are drawn into the spindle, where they adopt a cruciform-like structure and stretch 2.5-fold as they migrate to the poles. Therefore, while sister rDNA arrays appear separated in metaphase, Mechanical Linkages between sister arm loci persist throughout anaphase in yeast, as shown in grasshopper spermatocytes (Paliulis and Nicklas 2004). These Linkages are partially dependent on the protector of cohesin, SGO1. In anaphase, the spatially regulated dissolution of these Mechanical Linkages serves to prevent premature sister separation and restrain the rate of spindle elongation. Thus, sister separation is temporally controlled and Linkages between sister chromatids contribute to the regulation of anaphase spindle elongation.
Thomas P. Stossel - One of the best experts on this subject based on the ideXlab platform.
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Mechanical strain in actin networks regulates filgap and integrin binding to filamin a
Biophysical Journal, 2012Co-Authors: Allen J Ehrlicher, David A Weitz, Fumihiko Nakamura, Joh H Hartwig, Thomas P. StosselAbstract:Mechanical stresses elicit cellular reactions mediated by chemical signals. Defective responses to forces underlie human medical disorders, such as cardiac failure and pulmonary injury. Despite detailed knowledge of the cytoskeleton's structure, the specific molecular switches that convert Mechanical stimuli into chemical signals have remained elusive. Here we identify the actin-binding protein, filamin A (FLNa) as a central mechanotransduction element of the cytoskeleton by using Fluorescence Loss After photo Conversion (FLAC), a novel high-speed alternative to FRAP. We reconstituted a minimal system consisting of actin filaments, FLNa and two FLNa-binding partners: the cytoplasmic tail of s-integrin, and FilGAP. Integrins form an essential Mechanical Linkage between extracellular and intracellular environments, with s integrin tails connecting to the actin cytoskeleton by binding directly to filamin. FilGAP is a FLNa-binding GTPase-activating protein specific for Rac, which in vivo regulates cell spreading and bleb formation. We demonstrate that both externally-imposed bulk shear and myosin II driven forces differentially regulate the binding of integrin and FilGAP to FLNa. Consistent with structural predictions, strain increases s-integrin binding to FLNa, whereas it causes FilGAP to dissociate from FLNa, providing a direct and specific molecular basis for cellular mechanotransduction. These results identify the first molecular mechanotransduction element within the actin cytoskeleton, revealing that Mechanical strain of key proteins regulates the binding of signaling molecules.“Mechanical strain in actin networks regulates FilGAP and integrin binding to filamin A”A.J. Ehrlicher, F. Nakamura, J.H. Hartwig, D.A. Weitz and T.P. Stossel. Nature (2011) doi:10.1038/nature10430.
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Mechanical strain in actin networks regulates filgap and integrin binding to filamin a
Nature, 2011Co-Authors: David A Weitz, Fumihiko Nakamura, Alle Ehrliche, Joh H Hartwig, Thomas P. StosselAbstract:Living cells need to respond to Mechanical forces for many essential biological functions. This mechanosensing activity is thought to be a property of the actin cytoskeleton, but no specific mechanisms have yet been identified. In this study, Ehrlicher et al. identify the actin-binding protein filamin A (FLNa) as a central mechanotransduction element. In a minimal reconstituted system, ligand binding to filamin is affected by Mechanical forces, causing certain binding partners to dissociate and others to adhere more strongly. This selectivity may provide a direct molecular link between physical forces and biological activity. Mechanical stresses elicit cellular reactions mediated by chemical signals. Defective responses to forces underlie human medical disorders1,2,3,4 such as cardiac failure5 and pulmonary injury6. The actin cytoskeleton’s connectivity enables it to transmit forces rapidly over large distances7, implicating it in these physiological and pathological responses. Despite detailed knowledge of the cytoskeletal structure, the specific molecular switches that convert Mechanical stimuli into chemical signals have remained elusive. Here we identify the actin-binding protein filamin A (FLNA)8,9 as a central mechanotransduction element of the cytoskeleton. We reconstituted a minimal system consisting of actin filaments, FLNA and two FLNA-binding partners: the cytoplasmic tail of β-integrin, and FilGAP. Integrins form an essential Mechanical Linkage between extracellular and intracellular environments, with β-integrin tails connecting to the actin cytoskeleton by binding directly to filamin4. FilGAP is an FLNA-binding GTPase-activating protein specific for RAC, which in vivo regulates cell spreading and bleb formation10. Using fluorescence loss after photoconversion, a novel, high-speed alternative to fluorescence recovery after photobleaching11, we demonstrate that both externally imposed bulk shear and myosin-II-driven forces differentially regulate the binding of these partners to FLNA. Consistent with structural predictions, strain increases β-integrin binding to FLNA, whereas it causes FilGAP to dissociate from FLNA, providing a direct and specific molecular basis for cellular mechanotransduction. These results identify a molecular mechanotransduction element within the actin cytoskeleton, revealing that Mechanical strain of key proteins regulates the binding of signalling molecules.
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Mechanical strain in actin networks regulates filgap and integrin binding to filamin a
Nature, 2011Co-Authors: Allen J Ehrlicher, David A Weitz, Fumihiko Nakamura, Joh H Hartwig, Thomas P. StosselAbstract:Mechanical stresses elicit cellular reactions mediated by chemical signals. Defective responses to forces underlie human medical disorders such as cardiac failure and pulmonary injury. The actin cytoskeleton's connectivity enables it to transmit forces rapidly over large distances, implicating it in these physiological and pathological responses. Despite detailed knowledge of the cytoskeletal structure, the specific molecular switches that convert Mechanical stimuli into chemical signals have remained elusive. Here we identify the actin-binding protein filamin A (FLNA) as a central mechanotransduction element of the cytoskeleton. We reconstituted a minimal system consisting of actin filaments, FLNA and two FLNA-binding partners: the cytoplasmic tail of β-integrin, and FilGAP. Integrins form an essential Mechanical Linkage between extracellular and intracellular environments, with β-integrin tails connecting to the actin cytoskeleton by binding directly to filamin. FilGAP is an FLNA-binding GTPase-activating protein specific for RAC, which in vivo regulates cell spreading and bleb formation. Using fluorescence loss after photoconversion, a novel, high-speed alternative to fluorescence recovery after photobleaching, we demonstrate that both externally imposed bulk shear and myosin-II-driven forces differentially regulate the binding of these partners to FLNA. Consistent with structural predictions, strain increases β-integrin binding to FLNA, whereas it causes FilGAP to dissociate from FLNA, providing a direct and specific molecular basis for cellular mechanotransduction. These results identify a molecular mechanotransduction element within the actin cytoskeleton, revealing that Mechanical strain of key proteins regulates the binding of signalling molecules.
Julie A. Theriot - One of the best experts on this subject based on the ideXlab platform.
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material properties of actin networks from motile fish keratocytes under large deformations
Biophysical Journal, 2012Co-Authors: Mark A Tsuchida, Julie A. TheriotAbstract:In actin-based crawling motility, cells continuously build, reorganize, and disassemble an actin network in a process driven jointly by biochemical reactions and Mechanical work. A thorough understanding of how forces produced by actin and myosin contribute to whole-cell movement will thus require detailed knowledge of the material properties of the cytoskeletal network at the relevant spatial and temporal scales (micrometer-scale deformations over tens of seconds to minutes). Measurements of Mechanical properties have largely been limited to microscopic strains, whole-cell bulk measurements, or reconstituted gels that do not fully capture the cellular cytoskeletal organization.We have therefore sought to characterize the deformation of actin networks driven from motile cells under large (up to several hundred percent) applied strains. Using detergent-extracted cytoskeletons from fish epithelial keratocytes, we have applied arbitrary strains to the actin network between the cell body at the rear of the cell and the native adhesions in the lamellipodial (front) region of the cell, using a glass needle. Deformations through the cell body propagated through a significant portion of the lamellipodium, in some cases reaching the leading edge, indicating good Mechanical Linkage between the cell body and the lamellipodium. The lamellipodial actin network is surprisingly flexible and exhibits strain hardening. At rates of deformation comparable to the speeds of live, crawling cells, the network exhibited significantly elastic behavior, suggesting that elastic forces might contribute to the myosin-driven reorganization of the actin network in the rear of the cell. These results will help refine current physical models for crawling cell motility.
Marybeth Anderson - One of the best experts on this subject based on the ideXlab platform.
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function and assembly of dna looping clustering and microtubule attachment complexes within a eukaryotic kinetochore
Molecular Biology of the Cell, 2009Co-Authors: Marybeth Anderson, Julian Haase, Elaine Yeh, Kerry BloomAbstract:The kinetochore is a complex protein–DNA assembly that provides the Mechanical Linkage between microtubules and the centromere DNA of each chromosome. Centromere DNA in all eukaryotes is wrapped ar...
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function and assembly of dna looping clustering and microtubule attachment complexes within a eukaryotic kinetochore
Molecular Biology of the Cell, 2009Co-Authors: Marybeth Anderson, Julian Haase, Kerry BloomAbstract:The kinetochore is a complex protein–DNA assembly that provides the Mechanical Linkage between microtubules and the centromere DNA of each chromosome. Centromere DNA in all eukaryotes is wrapped around a unique nucleosome that contains the histone H3 variant CENP-A (Cse4p in Saccharomyces cerevisiae). Here, we report that the inner kinetochore complex (CBF3) is required for pericentric DNA looping at the Cse4p-containing nucleosome. DNA within the pericentric loop occupies a spatially confined area that is radially displaced from the interpolar central spindle. Microtubule-binding kinetochore complexes are not involved in pericentric DNA looping but are required for the geometric organization of DNA loops around the spindle microtubules in metaphase. Thus, the mitotic segregation apparatus is a composite structure composed of kinetochore and interpolar microtubules, the kinetochore, and organized pericentric DNA loops. The Linkage of microtubule-binding to centromere DNA-looping complexes positions the pericentric chromatin loops and stabilizes the dynamic properties of individual kinetochore complexes in mitosis.
Brindejonc Anne - One of the best experts on this subject based on the ideXlab platform.
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Etude d'un rotor d'hélicoptère sans plateau cyclique avec des servopaddles actives
HAL CCSD, 2009Co-Authors: Brindejonc AnneAbstract:This thesis presents the design, fabrication, testing and analytical study of a novel concept of actively controlled Hiller type servopaddle to achieve rotor primary control. The blades on the swashplateless rotor are coupled to a servopaddle equipped with a piezo electrically actuated aileron located behind the paddle trailing edge. The aileron is deflected because of the actuator and generates a lift. This leads to a variation of the paddle pitch moment, as well as of the paddle pitch and lift. Hence, a change in paddle flap and in blade pitch via a Mechanical Linkage is created. The system {blade, paddle, aileron} is independent from any other {blade, paddle, aileron} assembly. Thus, the active servopaddle can generate both cyclic and collective inputs. Such a system presents the advantage of reduced Mechanical complexity, parasitic drag and weight. The fuel consumption of the aircraft is thus expected to significantly decrease and its availability to increase. A small scale RC helicopter has been flown outdoor and served as a proof of concept. The system showed good hover capability under windy and non predictable conditions. A four degree-of-freedom analysis including aileron dynamics has been developed to predict the dynamic behavior and assess the feasibility of such a swashplateless rotor. The analysis is used to investigate the effect of system parameters on the blade control authority. Hover stand tests are performed in a more controlled environment. The aim of these tests is to validate the theory and to investigate the effects of different design variables on the blade pitch response. To this end, the system is equipped with sensors. In the case of both the outdoor and hover stand tests, the paddle actuation is achieved by a small swashplate to ensure a quick, affordable and simple design. The rest of design remains the same as described earlier. For a paddle of span equal to 40% of the blade radius, with a cyclic pitch input of 9°, a 5° blade cyclic pitch output was observed.Cette thèse présente la conception, la fabrication et l'étude analytique d'un nouveau concept basé sur la barre de Hiller pour réaliser la commande du rotor sans plateau cyclique. Les pales sont couplées à des palettes. Un aileron, commandé par des actionneurs piezo-électriques, est situé derrière le bord de fuite de chaque palette. L'aileron est incliné par l'actionneur, et génère ainsi une portance. Le moment en pas de la palette change ainsi que le pas, la portance et le battement de la palette. L'angle de battement de la palette et l'angle de pas de la pale étant couplés, ce dernier varie. Chaque ensemble {pale palette aileron} est indépendant d'un autre. La palette peut donc générer du pas collectif et cyclique en entrée de la pale. Comparé aux rotors conventionnels, un tel système présente divers avantages tels la réduction de la complexité mécanique, de la traînée et du poids. La consommation en fuel de l'hélicoptère devrait donc décroître fortement et la disponibilité de l'aéronef augmenter. Un hélicoptère de modélisme a été piloté en milieu extérieur et sert à valider le concept de couplage. Le système a pu maintenir un vol stationnaire stable malgré la présence de vent. Une analyse comprenant la dynamique de l'aileron et quatre degrés de liberté est développée pour évaluer le comportement dynamique et apprécier la faisabilité d'un tel concept de rotor sans plateau cyclique. L'analyse est utilisée pour investiguer l'effet des paramètres du système sur l'influence que la palette et l'aileron peuvent exercer sur la pale. Des tests en stationnaire ont été réalisés sur un banc rotor principal qui représente un environnement plus maîtrisé. Le but de ces tests est de valider l'étude théorique et d'évaluer l'effet de différentes variables de conception sur la réponse en pas de la pale. Pour ce faire, le système est équipé de capteurs. Dans le cas des essais en vol comme au banc rotor principal, la commande en pas de la palette est réalisée par de petits plateaux cycliques assurant une conception rapide, simple et peu coûteuse. Le reste du système est inchangé. Pour une palette d'envergure égale à 40% du rayon de la pale, avec un pas cyclique de g o, un angle de pas cyclique de pale de 5° a été obtenu
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Etude d'un rotor d'hélicoptère sans plateau cyclique avec des servopaddles actives
2009Co-Authors: Brindejonc Anne, Carmona Jean-claude, Malburet FrançoisAbstract:Cette thèse présente la conception, la fabrication et l'étude analytique d'un nouveau concept basé sur la barre de Hiller pour réaliser la commande du rotor sans plateau cyclique. Les pales sont couplées à des palettes. Un aileron, commandé par des actionneurs piezo-électriques, est situé derrière le bord de fuite de chaque palette. L'aileron est incliné par l'actionneur, et génère ainsi une portance. Le moment en pas de la palette change ainsi que le pas, la portance et le battement de la palette. L'angle de battement de la palette et l'angle de pas de la pale étant couplés, ce dernier varie. Chaque ensemble {pale palette aileron} est indépendant d'un autre. La palette peut donc générer du pas collectif et cyclique en entrée de la pale. Comparé aux rotors conventionnels, un tel système présente divers avantages tels la réduction de la complexité mécanique, de la traînée et du poids. La consommation en fuel de l'hélicoptère devrait donc décroître fortement et la disponibilité de l'aéronef augmenter. Un hélicoptère de modélisme a été piloté en milieu extérieur et sert à valider le concept de couplage. Le système a pu maintenir un vol stationnaire stable malgré la présence de vent. Une analyse comprenant la dynamique de l'aileron et quatre degrés de liberté est développée pour évaluer le comportement dynamique et apprécier la faisabilité d'un tel concept de rotor sans plateau cyclique. L'analyse est utilisée pour investiguer l'effet des paramètres du système sur l'influence que la palette et l'aileron peuvent exercer sur la pale. Des tests en stationnaire ont été réalisés sur un banc rotor principal qui représente un environnement plus maîtrisé. Le but de ces tests est de valider l'étude théorique et d'évaluer l'effet de différentes variables de conception sur la réponse en pas de la pale. Pour ce faire, le système est équipé de capteurs. Dans le cas des essais en vol comme au banc rotor principal, la commande en pas de la palette est réalisée par de petits plateaux cycliques assurant une conception rapide, simple et peu coûteuse. Le reste du système est inchangé. Pour une palette d'envergure égale à 40% du rayon de la pale, avec un pas cyclique de g o, un angle de pas cyclique de pale de 5 a été obtenu.This thesis presents the design, fabrication, testing and analytical study of a novel concept of actively controlled Hiller type servopaddle to achieve rotor primary control. The blades on the swashplateless rotor are coupled to a servopaddle equipped with a piezo electrically actuated aileron located behind the paddle trailing edge. The aileron is deflected because of the actuator and generates a lift. This leads to a variation of the paddle pitch moment, as well as of the paddle pitch and lift. Hence, a change in paddle flap and in blade pitch via a Mechanical Linkage is created. The system {blade, paddle, aileron} is independent from any other {blade, paddle, aileron} assembly. Thus, the active servopaddle can generate both cyclic and collective inputs. Such a system presents the advantage of reduced Mechanical complexity, parasitic drag and weight. The fuel consumption of the aircraft is thus expected to significantly decrease and its availability to increase. A small scale RC helicopter has been flown outdoor and served as a proof of concept. The system showed good hover capability under windy and non predictable conditions. A four degree-of-freedom analysis including aileron dynamics has been developed to predict the dynamic behavior and assess the feasibility of such a swashplateless rotor. The analysis is used to investigate the effect of system parameters on the blade control authority. Hover stand tests are performed in a more controlled environment. The aim of these tests is to validate the theory and to investigate the effects of different design variables on the blade pitch response. To this end, the system is equipped with sensors. In the case of both the outdoor and hover stand tests, the paddle actuation is achieved by a small swashplate to ensure a quick, affordable and simple design. The rest of design remains the same as described earlier. For a paddle of span equal to 40% of the blade radius, with a cyclic pitch input of 9, a 5 blade cyclic pitch output was observed.PARIS-Arts et Métiers (751132303) / SudocSudocFranceF