Dissertations / Theses: 'Myosin mechanics'

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Ökten, Zeynep. "Single molecule mechanics and the myosin family of molecular motors." [S.l.] : [s.n.], 2006. http://www.diss.fu-berlin.de/2006/6/index.html.

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Pertici, Irene. "The power output of a myosin II-based nanomachine mimicking the striated muscle." Doctoral thesis, Università di Siena, 2018. http://hdl.handle.net/11365/1041106.

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This thesis reports the realization and first application of a synthetic nanomachine, able to reproduce in vitro the performance emerging from the array arrangement of myosin II motors in the sarcomere of the striated muscle. The nanomachine consists of an ensemble of less than ten myosin dimers from fast skeletal muscle disposed on a functionalized support carried by a piezoelectric nanopositioner and brought to interact with an actin filament attached with the correct polarity via gelsolin to a bead (Bead Tailed Actin, BTA) trapped into the focus of a Dual Laser Optical Tweezers (DLOT). In solution with [ATP] = 2 mM the nanomachine is able to produce steady force and shortening, delivering a maximum power of 5 aW. The nanomachine performances are interpreted with a kinetic model based on mechanics and energetics of fast skeletal muscle. In this way it is possible to define the minimal conditions that allow an actomyosin system in vitro to produce force and power with the efficiency of the striated muscle, in the absence of the confusing contribution of the other sarcomeric proteins. In turn, since the system is assembled one piece at a time, it allows different degrees of reconstitution of the sarcomeric assembly. Therefore it will be possible to characterize the function of native and engineered contractile, regulatory and accessory proteins. For future investigations on the Ca2+-dependent thin filament activation, the preparation of BTA has been implemented using a Ca2+-independent gelsolin fragment and the procedure for thin filament reconstitution has been established during my visit to the Institute for Biophysical Chemistry, MHH, Germany.

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Erzberger, Anna. "Actomyosin mechanics at the cell level." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-197642.

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Almost all animal cells maintain a thin layer of actin filaments and associated proteins underneath the cell membrane. The actomyosin cortex is subject to internal stress patterns which result from the spatiotemporally regulated activity of non-muscle myosin II motors in the actin network. We study how these active stresses drive changes in cell shape and flows within the cortical layer, and how these cytoskeletal deformations and flows govern processes such as cell migration, cell division and organelle transport. Following a continuum mechanics approach, we develop theoretical descriptions for three different cellular processes, to obtain - in collaboration with experimental groups - a detailed and quantitative understanding of the underlying cytoskeletal mechanics. We investigate the forces and cortex flows involved in adhesion-independent cell migration in confinement. Many types of cell migration rely on the extension of protrusions at the leading edge, where the cells attach to the substrate with specific focal adhesions, and pull themselves forward, exerting stresses in the kPa range. In confined environments however, cells exhibit migration modes which are independent of specific adhesions. Combining hydrodynamic theory, microfluidics and quantitative imaging of motile, non-adherent carcinosarcoma cells, we analyze the mechanical behavior of cells during adhesion-independent migration. We find that the accumulation of active myosin motors in the rear part of these cells results in a retrograde cortical flow as well as the contraction of the cell body in the rear and expansion in the front, and we describe how both processes contribute to the translocation of the cells, depending on the geometric and mechanical parameters of the system. Importantly, we find that the involved propulsive forces are several orders of magnitude lower than during adhesive motility while the achieved migration velocities are similar. Moreover, the distribution of forces on the substrate during non-adhesive migration is fundamentally different, giving rise to a positive force dipole. In contrast to adhesive migration modes, non-adhesive cells move by exerting pushing forces at the rear, acting to expand rather than contract their substrate as they move. These differences may strongly affect hydrodynamic and/or deformational interactions between collectively migrating cells. In addition to the work outlined above, we study contractile ring formation in the actin cytoskeleton before and during cell division. While in disordered actin networks, myosin motor activity gives rise to isotropic stresses, the alignment of actin filaments in the cortex during cell division introduces a preferred direction for motor-filament interactions, resulting in anisotropies in the cortical stress. Actin filaments align in myosin-dependent shear flows, resulting in possible feedback between motor activity, cortical flows and actin organization. We investigate how the mechanical interplay of these different cortical properties gives rise to the formation of a cleavage furrow during cell division, describing the level of actin filament alignment at different points on the cortex with a nematic order parameter, in analogy to liquid crystal physics. We show that cortical anisotropies arising from shear-flow induced alignment patterns are sufficient to drive the ingression of cellular furrows, even in the absence of localized biochemical myosin up-regulation. This mechanism explains the characteristic appearance of pseudocleavage furrows in polarizing cells. Finally, we study the characteristic nuclear movements in pseudostratified epithelia during development. These tissues consist of highly proliferative, tightly packed and elongated cells, with nuclei actively travelling to the apical side of the epithelium before each cell division. We explore how cytoskeletal properties act together with the mechanics of the surrounding tissue to control the shape of single cells embedded in the epithelium, and investigate potential mechanisms underlying the observed nuclear movements. These findings form a theoretical basis for a more detailed characterization of processes in pseudostratified epithelia. Taken together, we present a continuum mechanics description of the actomyosin cell cortex, and successfully apply it to several different cell biological processes. Combining our theory with experimental work from collaborating groups, we provide new insights into different aspects of cell mechanics.

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Bates, Genevieve. "Molecular mechanics of diaphragmatic myosin from a mouse model of Duchenne muscular dystrophy." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97145.

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Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by the absence of dystrophin in the muscle cell membranes, rendering them susceptible to mechanical damage. DMD leads to respiratory or cardiac muscle failure and death. We hypothesized that alterations in contractile protein function contribute to DMD muscle weakness. We measured muscle strip stress, myosin heavy chain (MHC) isoform composition, velocity (ʋmax) of actin propulsion by myosin, and relative myosin force in control and mdx mouse (C57Bl/10) diaphragms. Stress was statistically smaller for mdx (0.23kg/cm2±0.11; mean±SE) than control (0.69kg/cm2±0.01) whereas the MHC isoform composition was not statistically different (type I: p=0.423, type IIa/IIx: p=0.804, type IIb: p=0.401). υmax of mdx myosin (1.24µm/s±0.07) was not statistically different from control (1.37µm/s±0.12; p=0.353). Relative myosin force was not statistically different between control and mdx myosin (p=0.932). Thus, alterations in myosin molecular function do not contribute to the weakness of the mdx mouse diaphragm.
La dystrophie musculaire de Duchenne (DMD) est une maladie génétique caracterisée par un manque de dystrophine dans la membrane des cellules musculaires, les rendant susceptibles au dommage mécanique. La mort survient suite à l'insuffisance des muscles cardiaques ou respiratoires. Notre hypothèse est que des altérations au niveau des protéines contractiles jouent un rôle dans la faiblesse musculaire de la DMD. Dans cette étude, nous avons mesuré le stress généré par des faisceaux musculaires, la composition des isoformes de la chaîne lourde de myosine (MHC), la vélocité (υmax) de propulsion de l'actine par la myosine, et la force relative de la myosine de diaphragme de souris control et mdx (C57Bl/10). Nous avons observé que le stress est statistiquement plus petit pour la souris mdx (0.23±0.11; moyenne±SE) que pour le control (0.69±0.01), mais que la composition de MHC n'est pas statistiquement différente (type I: p=0.423, type IIa/IIx: p=0.804, type IIb: p=0.401). υmax de la myosine mdx (1.24µm/s±0.07) n'est pas statistiquement différente du control (1.37µm/s±0.12; p=0.353). La force relative n'est pas statistiquement différente entre la myosine control et mdx (p=0.932). Donc des altérations de la fonction moléculaire de la myosine ne contribuent pas à la faiblesse du diaphragme de la souris mdx.

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Iliffe, Cathryn Ann. "The kinetics and mechanics of myosin and subfragment-1 from insect flight muscle." Thesis, University of York, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251800.

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Léguillette, Renaud. "Expression of smooth muscle myosin heavy chain isoforms in asthma and their molecular mechanics." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103169.

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Two smooth muscle (SM) myosin heavy chain isoforms, generated by alternative mRNA splicing, differ by the presence (SM-B) or absence (SM-A) of a 7 amino acid insert in the motor domain. The rate of actin filament propulsion (nu max) of SM-B, as measured in the in vitro motility assay, is 2-fold greater than that of SM-A. I investigated the expression and function of these isoforms in healthy SM and in asthma. First, I determined the sequence of the SM-B isoform in human SM and quantified its expression at the mRNA and protein levels in several human organs. The SM-B isoform was mostly expressed in rapidly contracting phasic SM. I then purified myosin from multiple rat organs and found a rank correlation between SM-B content and numax.
I then quantified the expression of SM-B and several other contractile protein genes in endobronchial biopsies from normal and asthmatic subjects. SM-B, myosin light chain kinase (MLCK), which is responsible for myosin activation, and transgelin, a ubiquitously expressed actin binding protein but whose function is unknown, were overexpressed in the asthmatic biopsies. The increased SM-B expression and myosin activation, due to the increased MLCK expression, both contribute to the increased rate of shortening of the asthmatic airway SM. In addition, I showed that beyond its enzymatic effects, MLCK mechanically enhances numax. The binding of SM22 to actin, however, did not alter numax.
Finally, I addressed the mechanisms behind the unique capacity of SM to maintain force at low energy cost, namely the latch-state. This property is mostly observed in SM-A containing, tonic muscle. Using a laser trap, I measured the binding force of unphosphorylated (non-active) SM-A and SM-B myosin isoforms and found that they can both attach to actin and maintain force. I also measured numax at different MgADP concentrations and found that SM-A has a greater affinity for MgADP. Because MgADP must be released before myosin can detach from actin, these results suggest that the SMA isoform remains attached longer to actin, allowing it to get into the latch-state. These findings explain the greater propensity of tonic muscle to get into the latch-state.

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Patel, Sejal. "Myosin regulatory light chain phosphorylation and its role in active mechanics and force generation of the heart." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p1462361.

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Thesis (M.S.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed May 4, 2009). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 43-48).

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Düttmann, Markus [Verfasser], and Alexander S. [Akademischer Betreuer] Mikhailov. "Elastic Network Models of Proteins - Uncovering the Internal Mechanics of Actin and Myosin / Markus Düttmann. Betreuer: Alexander S. Mikhailov." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2012. http://d-nb.info/1028912919/34.

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9

Pontén, Eva. "Tendon transfer mechanics and donor muscle properties : implications in surgical correction of upper limb muscle imbalance." Doctoral thesis, Umeå universitet, Institutionen för integrativ medicinsk biologi (IMB), 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-167.

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Tendon transfer surgery is used to improve the hand function of patients with nerve injuries, spinal cord lesions, cerebral palsy (CP), stroke, or muscle injuries. The tendon of a muscle, usually with function opposite that of the lost muscle function, is transferred to the tendon of the deficient muscle. The aim is to balance the wrist and fingers to achieve better hand function. The position, function, and length at which the donor muscle is sutured is essential for the outcome for the procedure. In these studies the significance of the transferred muscle’s morphology, length and apillarization was investigated using both animal and human models. Immunohistochemical, biochemical, and laser diffraction techniques were used to examine muscle structure. In animal studies (rabbit), the effects of immobilization and of tendon transfers at different muscle lengths were analyzed. Immobilization of highly stretched muscles resulted in fibrosis and aberrant regeneration. A greater pull on the tendon while suturing a tendon transfer resulted in larger sarcomere lengths as measured in vivo. On examination of the number of sarcomeres per muscle fiber and the sarcomere lengths after 3 weeks of immobilization and healing time, we found a cut-off point up to which the sarcomerogenesis was optimal. Transfer at too long sarcomere lengths inhibited adaptation of the muscle to its new length, probably resulting in diminished function. In human studies we defined the sarcomere lengths of a normal human flexor carpi ulnaris muscle through the range of motion, and then again after a routinely performed tendon transfer to the finger extensor. A calculated model illustrated that after a transfer the largest force was predicted to occur with the wrist in extension. Morphological studies of spastic biceps brachii muscle showed, compared with control muscle, smaller fiber areas and higher variability in fiber size. Similar changes were also found in the more spastic wrist flexors comparing with wrist extensors in children with CP. In flexors, more type 2B fibers were found. These observations could all be due to the decreased use in the spastic limb, but might also represent a specific effect of the spasticity. In children and adults with spasticity very small fibers containing developmental myosin were present in all specimens, while none were found in controls. These fibers probably represent newly formed fibers originating from activated satellite cells. Impaired supraspinal control of active motion as well as of spinal reflexes, both typical of upper motor syndrome, could result in minor eccentric injuries of the muscle, causing activation of satellite cells. Spastic biceps muscles had fewer capillaries per cross-sectional area compared to age-matched controls, and also a smaller number of capillaries around each fiber. Nevertheless, the number of capillaries related to the specific fiber area was normal, and hence the spastic fibers are sufficiently supplied with capillaries. This study shows that the length of the muscle during tendon transfer is crucial for optimization of force output. Laser diffraction can be used for accurate measurement of sarcomere length during tendon transfer surgery. Wrist flexor muscles have more morphological alterations typical of spasticity compared to extensors.

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10

Streppa, Laura. "Characterizing mechanical properties of living C2C12 myoblasts with single cell indentation experiments : application to Duchenne muscular dystrophy." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN008/document.

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Cette thèse interdisciplinaire a été dédiée à la caractérisation des propriétés mécaniques de myoblastes (murins et humains) et de myotubes (murins) à l'aide de la microscopie à force atomique (AFM). En modifiant ou en inhibant la dynamique du cytosquelette (CSK) d’actine de ces cellules, nous avons pu montrer que ces propriétés mécaniques variaient. L’enregistrement de courbes de force indentation nous a permis de montrer que la présence de cellules adhérentes introduisait sur les leviers d’AFM un amortissement visqueux supplémentaire à celui d’une paroi solide, et que cet amortissement visqueux dépendait de sa vitesse d’approche et que celui-ci restait non négligeable pour les plus faibles vitesses (1μm/s). Nous avons observé que les propriétés mécaniques des précurseurs de muscles devenaient non linéaires (comportement plastiques) pour des grandes déformations (>1μm) et qu’elles dépendaient de l’état, du type de cellule et de leur environnement. En combinant des expériences d’AFM, des modèles visco-élastiques et des méthodes d'analyse multi-échelle basées sur la transformation en ondelettes, nous avons illustré la variabilité des réponses mécaniques de ces cellules (de visco-élastiques à visco-plastiques). À l'aide de courbes de force-indentation, de l’imagerie morpho-structurale (DIC, microscopie à fluorescence) et de traitements pharmacologiques, nous avons éclairé le rôle essentiel des processus actifs (dépendants de l’ATP) dans la mécanique de myoblastes, en discutant tout particulièrement ceux des moteurs moléculaires (myosine II) couplés aux filaments d’actine. En particulier, nous avons montré que les fibres de stress du cytosquelette d’actine situées autour du noyau pouvaient présenter des évènements de remodelage soudains (ruptures) et que ces ruptures étaient une mesure indirecte de l’aptitude de ces cellules à tendre leur CSK. Nous avons enfin montré qu’il était possible de généraliser cette approche à des cas cliniques humains, en l’occurrence des myoblastes primaires de porteurs sains et de patients atteints de dystrophie musculaire de Duchenne, ouvrant la voie à des études plus larges sur d’autres types cellulaires et pathologies
This interdisciplinary thesis was dedicated to the atomic force microscopy (AFM) characterization of the mechanical properties of myoblasts (murine and human) and myotubes (murine). We reported that the mechanical properties of these cells were modified when their actin cytoskeleton (CSK) dynamics was inhibited or altered. Recording single AFM force indentation curves, we showed that adherent layers of myoblasts and myotubes introduced on the AFM cantilever an extra hydrodynamic drag as compared to a solid wall. This phenomenon was dependent on the cantilever scan speed and not negligible even at low scan velocities (1μm/s). We observed that the mechanical properties of the muscle precursor cells became non-linear (plastic behaviour) for large local deformations (>1μm) and that they varied depending on the state, type and environment of the cells. Combining AFM experiments, viscoelastic modeling and multi-scale analyzing methods based on the wavelet transform, we illustrated the variability of the mechanical responses of these cells (from viscoelastic to viscoplastic). Through AFM force indentation curves analysis, morpho-structural imaging (DIC, fluorescence microscopy) and pharmacological treatments, we enlightened the important role of active (ATP-dependent) processes in myoblast mechanics, focusing especially on those related to the molecular motors (myosin II) coupled to the actin filaments. In particular, we showed that the perinuclear actin stress fibers could exhibit some abrupt remodelling events (ruptures), which are characteristic of the ability of these cells to tense their CSK. Finally, we showed that this approach can be generalized to some human clinical cases, namely primary human myoblasts from healthy donors and patients affected by Duchenne muscular dystrophy, paving the way for broader studies on different cell types and diseases

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Batters, Christopher. "Single molecule mechanical studies of acto-myosin." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414015.

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Jackson, Andrew Paul. "The mechanism of the scallop myosin ATPase." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/35258.

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Molluscan adductor muscles display thick filament regulation. A calcium binding site (regulatory domain) near the neck of the myosin molecule is responsible for controlling the ATPase activity, hence the rate of contraction. In the absence of calcium, the ATPase activity is highly suppressed. When calcium binds to the regulatory domain the inhibition is relieved allowing contraction to occur. Steady-state measurements are insufficient to characterise the ATPase activity in detail because of the dominant contribution from unregulated myosin molecules. Therefore spectoscopic techniques, allied to transient kinetic analysis were used to determine the effect of calcium on the various steps of the HMM ATPase mechanism. ATP, ADP and calcium binding to HMM caused small, but measurable, enhancements (upto 8%) in the proteins tryptophan fluorescence. Stopped-flow fluorescence spectroscopy allowed the kinetics of binding and dissociation to be elucidated. Calcium bound to, and dissociated from, HMM rapidly (108 M-1 S-1 and 25 S-1 respectively). When calcium was bound to the regulatory domain the affinity of the active site for nucleotide was reduced, an effect seen as an increase in the rate constant for nucleotide dissociation. Fluorescent ATP analogues, based on formycin were synthesised. These nucleotides displayed large fluorescence enhancements on binding to HMM (upto 500%). Turnover of FTP by HMM was suppressed 100-fold by the removal of calcium, as determined by transient kinetic measurements. The large fluorescence enhancements seen on binding of various formycin nucleotides allowd the effect of calcium on the association and dissociation processes to be examined in great detail. Binding was found to be a complex, multistep process in which the presence of calcium increased the rate of interconversion of the various HMM/nucleotide complexes by several orders of magnitude.

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Blanc, Florian. "Exploring chemo-mechanical transduction in the myosin molecular motor through computer simulations." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF066/document.

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La vie repose sur des conversions d’énergie libre assurées par des machines moléculaires. Parmi elles, la myosine couple l’hydrolyse de l’ATP à la production de force sur l’actine par basculement d’un « bras de levier ». Compléter le cycle requiert une étape de régénération, ou recovery stroke, où le moteur retourne dans sa configuration armée et hydrolyse l’ATP. Comprendre ce couplage chimio-mécanique est critique pour révéler les principes de fonctionnement des moteurs moléculaires. Cette thèse aborde la question via des simulations moléculaires. Partant d’une nouvelle structure cristallographique de la myosine VI, nous proposons un mécanisme original pour le recovery stroke dans lequel la remise en place du bras de levier est déclenchée par les fluctuations thermiques et précède la fermeture du site actif, au contraire des modèles précédemment acceptés
Life relies on free energy conversions performed by molecular machines. Among them, myosin couples the hydrolysis of ATP to force production on actin through a swing of a « lever-arm ». Completing the cycle requires a regeneration step, the recovery stroke, in which the motor returns to its armed configuration and hydrolyzes ATP. Understanding this chemo-mechanical coupling is critical to unravel the functioning principles of molecular motors. In this thesis, we tackle the problem using molecular simulations. Capitalizing on a new crystal structure of myosin VI, we propose an original mechanism for the recovery stroke in which the re-priming of the lever arm is driven by thermal fluctuations and precedes the closure of the active site, unlike previously accepted models

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14

Vasquez, Claudia G. (Claudia Gabriela). "Mechanisms of myosin regulation and function during tissue folding." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101504.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2015.
Cataloged from PDF version of thesis. "September 2015."
Includes bibliographical references.
Throughout organismal development, precise three-dimensional organization of tissues is required for proper tissue function. These three-dimensional forms are generated by coordinated cell shape changes that induce global tissue shape changes, such as the transformation of an epithelial sheet into a tube. A model for this transformation occurs early in Drosophila development where approximately 1,000 cells on the ventral side of the embryo constrict their apical sides. Apical constriction drives the formation of a furrow that invaginates, forming a tube, and consequently, a new cell layer in the embryo. Constriction of ventral cells is driven by cycles of assembly and disassembly of actin-myosin networks at the cell apex, called pulses. Pulsatile myosin leads to phases of cellular contraction and cell shape stabilization that result in step-wise apical constriction. While many of the key components of the pathway have been identified, how pulsatile myosin is regulated was previously not well understood. The results presented in this thesis identify mechanisms of regulation of these myosin pulses. First, we demonstrated that cycles of phosphorylation and dephosphorylation of the myosin regulatory light chain are required for myosin pulsing and step-wise apical constriction. Uncoupling myosin from its upstream regulators resulted in loss of pulsatile myosin behavior and continuous, instead of incremental, apical constriction. A consequence of persistent, non-pulsatile myosin is a loss of myosin network integrity as the tissue invaginated. Thus, pulsatile myosin requires tight coordination between its activator and inactivator to generate cycles of myosin assembly, coupled to cellular constriction, and myosin disassembly, associated with cell shape stabilization. Second, we demonstrated that myosin motor activity is required for efficient apical constriction and for effective generation of tissue tension. This work defines essential molecular mechanisms that are required for proper cellular constriction and tissue invagination.
by Claudia G. Vasquez.
Ph. D.

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Schwarzl, Sonja M. "Understanding the ATP hydrolysis mechanism in myosin using computer simulation techniques." [S.l. : s.n.], 2005. http://nbn-resolving.de/urn:nbn:de:bsz:16-opus-63890.

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Heidelberg, Univ., Diss., 2005.
Aus: S.M. Schwarzl, Understanding the ATP hydrolysis mechanism in myosin using computer simulation techniques, Mensch und Buch Verlag Berlin 2006, ISBN 3-86664-044-7.

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Barbier, Lucie. "Study of cellular mechanisms allowing dendritic cell migration in restricted spaces." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASL028.

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En cas d'infection, les cellules dendritiques matures (CDm) migrent des tissus périphériques vers les ganglions lymphatiques où ils déclenchent la réponse immunitaire adaptative. Ce déplacement impose une série de contraintes physiques sur les CDm. Au niveau cellulaire, la migration des CDm repose sur la contractilité du cytosquelette d’actine et de myosine. Toutefois, la réponse mécanique spécifique qui permet aux CDm d'adapter leur mode de migration aux contraintes physiques n'a pas été entièrement caractérisée. Dans ce travail, nous avons combiné une série d'approches, des outils microfluidiques aux modèles ex vivo, pour disséquer les réarrangements du cytosquelette nécessaires à l’adaptation du mode de migration des cellules dendritiques aux propriétés physiques de leur microenvironnement. Nous avons montré que les CDm sont capables de maintenir une vitesse constante tout en migrant à différents niveaux de confinement. Cela révèle la capacité des CDm à adapter leur mode de migration en réponse aux changements dans la géométrie de leur microenvironnement. Au niveau cellulaire, le confinement dans les microcanaux induit un remodelage rapide et spécifique du cytosquelette d’actine et de myosine. Il est essentiel à la plasticité migratoire des CDm et optimise le déplacement de ces cellules dans des environnements 3D complexes. Ces travaux conduisent à une meilleure compréhension des mécanismes permettant aux CDm d’adapter leur motilité face à des structures tissulaires spécifiques. Ils permettront de mieux appréhender le contrôle de la migration des leucocytes dans des espaces confinés et pouvoir ainsi la moduler avec précision afin de favoriser ou de prévenir les réponses immunitaire
Upon infection, mature dendritic cells (mDCs) migrate from peripheral tissue to lymph nodes and initiate the adaptive immune response. This fast and tightly regulated process imposes a series of physical constraints and is tuned by different microenvironmental factors, such as the physical properties of the tissue. Mechanistically, mDCs migration relies on actomyosin flow and contractility, which are dependent on non‐muscular Myosin IIA activity. However, the specific mechanoresponse that allows mDCs to adapt their migration machinery to irregular 3D landscapes has not been fully characterized. In this work, we combined a series of approaches, from micro‐fabricated devices to ex vivo skin models, to dissect the cytoskeleton rearrangements used by mDCs to overcome the physical barriers imposed by the tissue. We have shown mDCs are able to maintain a constant speed while migrating at different levels of confinement. This reveals the extreme capacity of mDCs to adapt their migration machinery in response to changes in the geometry of their microenvironment. At the cellular level, confinement in microchannels induces a fast and specific actomyosin remodelling in mDCs. This reveals a complete actomyosin rearrangement triggered by confinement, which is essential for mDCs migratory plasticity that allows these cells to move in intricate 3D geometries. The full understanding of how mDCs and other leukocytes adapt their motility to specific tissue structures will provide better knowledge on how cell migration is controlled in confined spaces and new insight to finely tune their migration to promote or prevent immune responses

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Burns, Ronald Ian Scott. "Kinetic investigation of the mechanism underlying muscle contraction in myofibrils using T.I.R.F. microscopy." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313991.

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Qin, Xiang. "Controlling mechanism of basal myosin oscillation in epithelial cells during Drosophila tissue elongation." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30006.

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La morphogenèse des tissus dans les organismes multicellulaires est très importante pour le développement et certaines pathologies. La morphogenèse tissulaire est dirigée par des forces bio-mécaniques générées par des moteurs moléculaires tels que la myosine et transmis via le cytosquelette et les structures d'adhésion à l'intérieur et entre les cellules. La contractilité de la myosine, souvent en mode oscillatoire, a été étudiée principalement au niveau du domaine apical des cellules épithéliales au cours du développement mais très peu au niveau de leur domaine basal. L'oscillation de la myosine basale est importante pour le contrôle de l'élongation du tissu durant l'oogenèse chez la Drosophile. Bien que la voie Rho1-ROCK-myosin-MBS soit connue pour contrôler l'activité de la myosine, le mécanisme précis de ce contrôle n'a pas été élucidé. Le but de mon projet de thèse est de répondre à deux questions : Quels sont les facteurs en amont de cette voie ? Comment cette voie de signalisation crée et maintient l'oscillation de la myosine ? 1) Contrairement à ce qui est déjà connu, Je me suis intéressé à l'effet des adhésions cellule-cellule et cellule-matrice dans le contrôle des voies de signalisation gouvernant l'oscillation de la myosine basale. Les adhésions cellule-matrice, mais pas les adhésions cellule-cellule, sont positivement corrélées avec l'intensité et la polarité dorso-ventrale de la myosine, indiquant que les adhésions cellule-matrice pourraient être les facteurs en amont de la voie Rho1-myosine. Les adhésions cellule-matrice régulent positivement l'activité de Rho1 près des jonctions et gouvernent les flux de ROCK et myosine à l'intérieur du domaine median, contrôlant ainsi l'élongation du tissu. D'une autre manière, les adhésions cellule-cellule affectent indirectement les flux de ROCK and myosine en contrôlant la distribution subcellulaire de ROCK et du réseau d'actomyosine. L'inhibition des adhésions cellule-cellule, qui a un effet mineur sur l'élongation du tissu, provoque la redistribution des adhésions cellule-matrice et des filaments F-actin entrainant le chargement de la myosine à différentes positions. 2) J'ai montré que l'oscillation de la myosine basale dépend peu de la tension corticale de l'actomyosine : l'inhibition du chargement de la myosine sur les filaments d'actine n'affecte pas le flux de myosine alors qu'il bloque fortement le cycle périodique des contractions/relaxations de la cellule indiquant que l'oscillation est principalement due à une réaction biochimique plutôt qu'à une tension corticale. Au cours de l'oscillation de la myosine, les protéines Rho1 et leur activité sont principalement distribuées et enrichies au niveau et près des jonctions basales, et le contrôle majeur de cette oscillation est le flux des signaux ROCK qui diffusent des jonctions basales au cortex medio-basal. Ce mouvement de ROCK est initié grâce à une interaction transitoire entre ROCK et Rho1 actif au niveau et près des jonctions basales, conduisant ainsi à l'ouverture et activation de la kinase ROCK. Au cours de ce mouvement, l'activation de ROCK permet l'accumulation et l'amplification des signaux ROCK; Cette amplification entraîne la phosphorylation de la myosine, qui ensuite génère la redistribution dynamique de la phosphatase MBS. Enfin, l'enrichissement des signaux MBS arrête les signaux ROCK et myosine. Dans ces deux études, nous avons construit un outil optogénétique confirmant les différentes étapes de l'oscillation de la myosine basale. L'ensemble de ces résultats démontrent que le mécanisme contrôlant l'oscillation de la myosine basale nécessite une réaction biochimique, et met en évidence deux contrôles diffèrent de cette oscillation par les adhésions cellule-cellule et les adhésions cellule-matrice
Tissue morphogenesis in multicellular organisms is very important in both development and human disease. Tissue morphogenesis is driven by bio-mechanic force that is normally generated by molecular motors such as myosin and transmitted via cytoskeleton and adhesion structures within and between cells. Myosin contractility, often as an oscillatory pattern, has been studied mainly in apical but less in basal domains of epithelial cells during development. Basal myosin oscillation is important in control of tissue elongation during Drosophila oogenesis. Although a signal cascade (Rho1-ROCK-myosin-MBS) has been known to regulate myosin activity, the detailed controlling mechanism is unclear. My project is aimed to address two questions: first, what is the upstream factor of this signal cascade? Second, how does this signal cascade create and maintain basal myosin oscillation? For this first question, I am interested in the effect of cell-cell and cell-matrix adhesion in control of this signal cascade governing basal myosin oscillation. Cell-matrix adhesion (Integrin and Talin), but not cell-cell adhesion (E-cadherin), is positively correlated with the intensity and Dorsal-ventral (DV) axis polarity of basal myosin oscillation, indicating that cell-matrix adhesion might be the upstream control of Rho1-myosin signal cascade. Cell-matrix adhesion positively regulates the Rho1 activity near junction and governs the pulsed ROCK and myosin signals within basal-medial domain, thus strongly controlling tissue elongation. Differently, cell-cell adhesion indirectly affects the ROCK and myosin pulses through controlling the subcellular distribution of ROCK and actomyosin network. Inhibition of cell-cell adhesion results in the redistribution of cell-matrix adhesion and F-actin filaments leading to different position of myosin loading, which plays minor effect on tissue elongation. For the second question, I unraveled that basal myosin oscillation is barely dependent on actomyosin cortical tension: inhibition of myosin loading to F-actin filament seems not to affect basal pulsatile myosin flows, while it strongly blocks the periodic cycle of cell contraction and relaxation at basal surface, thus indicating that oscillation is mainly from biochemical reaction rather than cortical tension. This observation highlighted that biochemical reaction is the main control of oscillation occurrence. During basal myosin oscillation, Rho1 proteins and Rho1 activity are mainly distributed and enriched at and near basal junction and the major control of basal myosin oscillation is the flow movement of oscillatory ROCK signals from basal junction to medio-basal cortex. This ROCK flow movement is initiated from the transient interaction of ROCK with active Rho1 at and near basal junction, thus leading to the opening and activation of ROCK kinase capability. During the membrane-medial flow movement, ROCK kinase activity mediates the accumulation and thus the amplification of ROCK signals; this positive signal amplification turns on the phosphorylation of myosin regulatory light chain (MRLC), which governs the dynamic redistribution of MBS. Finally, enriched MBS signals shut off both ROCK and myosin signals. In both study, an optogenetic tool named as LARIAT was built up in vivo to confirm the various status of basal myosin oscillation. Altogether, these results demonstrated two different controls of basal actomyosin signals by cell-matrix adhesion and cell-cell adhesion, and further demonstrated the underlying mechanism of basal myosin oscillation at the biochemical levels

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19

Tyreman, Matthew James Allanson. "Single molecule mechanical studies on the head and neck regions of myosin II." Thesis, University of York, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411476.

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20

Sladewski, Thomas Edward. "Molecular Mechanisms Of Mrna Transport By A Class V Myosin And Cytoplasmic Dynein." ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/689.

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mRNA localization ensures correct spatial and temporal control of protein synthesis in the cell. Using a single molecule in vitro approach, we provide insight into the mechanisms by which localizing mRNAs are carried by molecular motors on cytoskeletal tracks to their destination. Budding yeast serves as a model system for studying the mechanisms of mRNA transport because localizing mRNAs are moved on actin tracks in the cell by a single class V myosin motor, Myo4p. Molecular motors that specialize in cargo transport are generally double-headed so that they can "walk" for many microns without dissociating, a feature known as processivity. Thus, is was surprising when Myo4p purified from yeast was shown by in vitro assays to be non-processive. The reason for its inability to move processively is that the Myo4p heavy chain does not dimerize with itself, but instead binds tightly to the adapter protein She3p to form a single-headed motor complex. The mRNA-binding adapter protein She2p links Myo4p to mRNA cargo by binding She3p. To understand the molecular mechanisms of mRNA transport in budding yeast, we fully reconstituted a messenger ribonucleoprotein (mRNP) complex from purified proteins and a localizing mRNA (ASH1) found in budding yeast. Using single molecule in vitro assays, we find that She2p recruits two Myo4p-She3p complexes, forming a processive double-headed motor complex that is stabilized by mRNA at physiological ionic strength. Thus, only in the presence of mRNA is Myo4p capable of continuous mRNA transport, an elegant mechanism that ensures that only cargo bound motors are motile. We next wished to understand if the principles of mRNA transport in budding yeast are conserved in higher eukaryotes. In Drosophila, mRNA is transported on microtubule tracks by cytoplasmic dynein, and the adapters that link the motor to localizing transcripts are well-defined. The adapter protein bicaudal D (BicD) coordinates dynein motor activity with mRNA cargo binding. The N-terminus of BicD binds dynein, and the C-terminus interacts with the mRNA-binding protein Egalitarian. Unlike mammalian dynein alone, it was recently shown that an N-terminal fragment of BicD (BicD2CC1), in combination with a large 1.2MDa multi-subunit accessory complex called dynactin, forms a complex (DDBCC1) that is activated for long processive runs. But unlike the constitutively activated BicD2CC1 fragment, the full-length BicD molecule fails to recruit dynein-dynactin because it is auto-inhibited by interactions between the N-terminal dynein binding domain and the C-terminal cargo binding domain. To understand how dynein is activated by native cargo and full-length adapters, we fully reconstituted a mRNP complex in vitro from tissue-purified dynein and dynactin, expressed full-length adapters BicD and Egalitarian, and a synthesized localizing mRNA found in Drosophila. We find that only mRNA-bound Egalitarian is capable of relieving BicD auto-inhibition for the recruitment of dynein-dynactin, and activation of mRNA transport in vitro. Thus, the presence of an mRNA cargo for activation of motor complexes is a conserved mechanism in both budding yeast and higher eukaryotes to ensure that motor activity is tightly coupled to cargo selection.

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21

Shanely, R. Andrew. "Protein synthesis and myosin heavy chain mRNA in the rat diaphragm during mechanical ventilation." [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE0000607.

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22

Aslam, Muhammad. "Effect of cAMP-PKA signaling mechanism on barrier function of cultured endothelial cells : role of myosin light chain phosphatase /." Giessen : VVB Laufersweiler, 2007. http://d-nb.info/987804200/04.

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23

Khoury, Ziad. "Application of dynamic oscillatory rheology and Fourier transform infrared spectroscopy in the study of the mechanism of myosin gelation." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80301.

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Variable-temperature Fourier transform infrared (VT-FTIR) and circular dichroism (far-UV CD) spectroscopy were employed to investigate the sequence of structural changes responsible for the thermally induced formation of myosin gels with various rheological properties, as measured by dynamic oscillatory rheology, as well as the effects of prior high-pressure processing (HPP) on thermally induced gel formation. The viscoelastic properties of the protein gels were monitored as a function of temperature and were also measured at three fixed temperatures (44, 48, and 68°C). Examination was done of changes in the secondary structure-sensitive amide l'band in the FTIR spectra of the protein in D2O buffer (0.6M KCl, pH 6.4) as a function of temperature, as well as far-UV CD spectra. Myosin solutions were exposed to increasing hydrostatic pressure (100--400 MPa for 10 min at 16°C). The extent of unfolding of the tail was shown to be proportional to the pressure treatment, suggesting that the slight increase of gel strength may partly originate from the facilitated tail-tail interaction. (Abstract shortened by UMI.)

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24

Babcock, Joseph M. (Joseph Michel). "Effects of cross-link and myosin motor concentrations on active muscle gel contraction time and extent." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112565.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 26).
The cytoskeleton is a crucial network of actin filaments that gives the cell its shape, assists in organelle organization, and allows for cell movement. Active muscle gels are a class of materials that that mimic the functionality of the cytoskeleton. Utilizing myosin II motor proteins to initiate contraction events in actin networks, active muscle gels have the unique potential of acting as microscopic actuators. Two challenges currently faced by active muscle gels are their slow contraction time and weak contraction forces. This thesis seeks to achieve contraction events in a lab setting and observe how contraction speed and extent varies with the concentration of myosin motors and alpha-actinin crosslinks.
by Joseph M. Babcock.
S.B.

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25

Fischer, Andy J. "Muscarinic mechanisms in myopia and ocular growth." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0018/NQ38467.pdf.

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26

Lindqvist, Johan. "Cellular and Molecular Mechanisms Underlying Congenital Myopathy-related Weakness." Doctoral thesis, Uppsala universitet, Klinisk neurofysiologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-219460.

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Congenital myopathies are a rare and heterogeneous group of diseases. They are primarily characterised by skeletal muscle weakness and disease-specific pathological features. They harshly limit ordinary life and in severe cases, these myopathies are associated with early death of the affected individuals. The congenital myopathies investigated in this thesis are nemaline myopathy and myofibrillar myopathy. These diseases are usually caused by missense mutations in genes encoding myofibrillar proteins, but the exact mechanisms by which the point mutations in these proteins cause the overall weakness remain mysterious. Hence, in this thesis two different nemaline myopathy-causing actin mutations and one myofibrillar myopathy-causing myosin-mutation found in both human patients and mouse models were used to investigate the cascades of molecular and cellular events leading to weakness. I performed a broad range of functional and structural experiments including skinned muscle fibre mechanics, small-angle X-ray scattering as well as immunoblotting and histochemical techniques. Interestingly, according to my results, point mutations in myosin and actin differently modify myosin binding to actin, cross-bridge formation and muscle fibre force production revealing divergent mechanisms, that is, gain versus loss of function (papers I, II and IV). In addition, one point mutation in actin appears to have muscle-specific effects. The presence of that mutant protein in respiratory muscles, i.e. diaphragm, has indeed more damaging consequences on myofibrillar structure than in limb muscles complexifying the pathophysiological mechanisms (paper II). As numerous atrophic muscle fibres can be seen in congenital myopathies, I also considered this phenomenon as a contributing factor to weakness and characterised the underlying causes in presence of one actin mutation. My results highlighted a direct muscle-specific up-regulation of the ubiquitin-proteasome system (paper III). All together, my research work demonstrates that mutation- and muscle-specific mechanisms trigger the muscle weakness in congenital myopathies. This gives important insights into the pathophysiology of congenital myopathies and will undoubtedly help in designing future therapies.

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Arboleda-Estudillo, Yoana. "Mechanical cell properties in germ layer progenitor migration during zebrafish gastrulation." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-27725.

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Gastrulation leads to the formation of the embryonic germ layers, ectoderm, mesoderm and endoderm, and is the first key morphogenetic process that occurs in development. Gastrulation provides a unique developmental assay system in which to study cellular movements and rearrangements in vivo. The different cell movements occurring during gastrulation take place in a highly coordinated spatial and temporal manner, indicating that they must be controlled by a complex interplay of morphogenetic and inductive events. Generally, cell movement constitutes a highly integrated program of different cellular behaviors including sensing, polarization, cytoskeletal reorganization, and changes in adhesion and cell shape. During migration, these different behaviors require a continuous regulation and feedback control to direct and coordinate them. In this work, we analyze the cellular and molecular mechanisms underlying the different types of cell behaviors during gastrulation in zebrafish. Specifically, we focus on the role of the adhesive and mechanical properties of germ layer progenitors in the regulation of gastrulation movements. In the first part of the project, we investigated the role of the adhesive and mechanical properties of the different germ layer progenitor cell types for germ layer separation and stratification. In the second part of this study, we applied the same methodology to determine the function of germ layer progenitor cell adhesion in collective cell migration. Tissue organization is thought to depend on the adhesive and mechanical properties of the constituent cells. However, it has been difficult to determine the precise contribution of these different properties due to the lack of tools to measure them. Here we use atomic force microscopy (AFM) to quantify the adhesive and mechanical properties of the different germ layer progenitor cell types. Applying this methodology, we demonstrate that mesoderm and endoderm progenitors are more adhesive than ectoderm cells and that E-cadherin is the main adhesion molecule regulating this differential adhesion. In contrast, ectoderm progenitors exhibit a higher actomyosin-dependent cell cortex tension than mesoderm and endoderm progenitors. Combining these data with tissue self-assembly in vitro and in vivo, we provide evidence that the combinatorial activities of cell adhesion and cell cortex tension direct germ layer separation and stratification. It has been hypothesized that the directionality of cell movement during collective migration results from a collective property. Using a single cell transplantation assay, we show that individual progenitor cells are capable of normal directed migration when moving as single cells, but require cell-cell adhesion to participate in coordinated and directed migration when moving collectively. These findings contribute to the understanding of the gastrulation process. Cell-cell adhesion is required for collective germ layer progenitor cell migration, and cell cortex tension is critical for germ layer separation and stratification. However, many questions still have to be solved. Future studies will have to explore the interaction between the adhesive and mechanical progenitor cell properties, as well as the role of these properties for cell protrusion formation, cell polarization, interaction with extracellular matrix, and their regulation by different signaling pathways.

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28

Norman, Holly. "Cellular and Molecular Mechanisms Underlying Acute Quadriplegic Myopathy : Studies in Experimental Animal Models and Intensive Care Unit Patients." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7133.

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29

Caruel, Matthieu. "Mechanics of Fast Force Recovery in striated muscles." Phd thesis, Ecole Polytechnique X, 2011. http://pastel.archives-ouvertes.fr/pastel-00668301.

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Cette thèse est consacrée à la modélisation de la réponse transitoire d'une fibre musculaire squelettique soumise à des sollicitations mécaniques rapides. A l'échelle du nanomètre, la fibre musculaire contient des filaments d'actine et de myosine regroupés en unités contractiles appelées "sarcomères". Le filament de myosine est un assemblage de moteurs mol ́eculaires qui, en présence d'ATP, s'attachent et se d ́etachent p ́eriodiquement au filament d'actine. Au cours de ce processus d'attachement-détachement, la myosine génère une force lors d'un changement de conformation appelé "power-stroke". Ses caractéristiques peuvent être étudiées lors de la réponse transitoire de la fibre soumise à des sollicitations mécaniques rapides. Nous proposons un modèle mécanique innovant du demi-sarcomere permettant de relier les caractéristiques de la myosine à la réponse de la fibre complète. A la différence des modèles existants, privilégiant une approche discrète, ce modèle s'appuie sur la définition d'un potentiel d'énergie continu qui prend en compte une interaction de champ moyen entre les moteurs moléculaires. Ce système présente des réponses radicallement différentes à longueur imposée et à force imposée. Nous proposons en particulier une explication à la différence de cinétique observée expérimentalement. Nous montrons également que le demi-sarcomere est m ́ecaniquement instable ce qui explique les inhomogénéités de longueurs observées dans une myofibrille.

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30

Ip, Kelvin. "Mechanical integrity of myosin thick filaments of airway smooth muscle in vitro: effects of phosphoryation of the regulatory light chain." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/4131.

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Background and aims: It is known that smooth muscle possesses substantial mechanical plasticity in that it is able to adapt to large changes in length without compromising its ability to generate force. It is believed that structural malleability of the contractile apparatus underlies this plasticity. There is strong evidence suggesting that myosin thick filaments of the muscle are relatively labile and their length in vivo is determined by the equilibrium between monomeric and filamentous myosin. The equilibrium in turn is governed by the state of phosphorylation of the 20-kD regulatory myosin light chain (MLC20, or RLC). It is known that phosphorylation of the myosin light chain favors formation of the filaments; it is not known how the light chain phosphorylation affects the lability of the filaments. The major aim of this thesis was to measure the mechanical integrity of the filaments formed from purified myosin molecules from bovine airway smooth muscle, and to determine whether the integrity was influenced by phosphorylation of the myosin light chain. Methods: Myosin was purified from bovine trachealis to form filaments, in ATP containing zero-calcium solution during a slow dialysis that gradually reduced the ionic strength. Sufficient myosin light chain kinase and phosphatase, as well as calmodulin, were retained after the myosin purification and this enabled phosphorylation of RLC within 20-40 s after addition of calcium to the filament suspension. The phosphorylated and non-phosphorylated filaments were then partially disassembled by ultrasonification. The extent of filament disintegration was visualized and quantified by atomic force microscopy. Results: RLC phosphorylation reduced the diameter of the filaments and rendered the filaments more resistant to ultrasonic agitation. Electron microscopy revealed a similar reduction in filament diameter in intact smooth muscle when the cells were activated. Conclusion: Our results suggest that RLC phosphorylation is a key regulatory step in modifying the structural properties of myosin filaments in smooth muscle, where formation and dissolution of the filaments are required in the cells’ adaptation to different cell length.

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31

Arboleda-Estudillo, Yoana. "Mechanical cell properties in germ layer progenitor migration during zebrafish gastrulation." Doctoral thesis, Max-Planck-Institut für Molekulare Zellbiologie und Genetik, 2009. https://tud.qucosa.de/id/qucosa%3A25271.

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Gastrulation leads to the formation of the embryonic germ layers, ectoderm, mesoderm and endoderm, and is the first key morphogenetic process that occurs in development. Gastrulation provides a unique developmental assay system in which to study cellular movements and rearrangements in vivo. The different cell movements occurring during gastrulation take place in a highly coordinated spatial and temporal manner, indicating that they must be controlled by a complex interplay of morphogenetic and inductive events. Generally, cell movement constitutes a highly integrated program of different cellular behaviors including sensing, polarization, cytoskeletal reorganization, and changes in adhesion and cell shape. During migration, these different behaviors require a continuous regulation and feedback control to direct and coordinate them. In this work, we analyze the cellular and molecular mechanisms underlying the different types of cell behaviors during gastrulation in zebrafish. Specifically, we focus on the role of the adhesive and mechanical properties of germ layer progenitors in the regulation of gastrulation movements. In the first part of the project, we investigated the role of the adhesive and mechanical properties of the different germ layer progenitor cell types for germ layer separation and stratification. In the second part of this study, we applied the same methodology to determine the function of germ layer progenitor cell adhesion in collective cell migration. Tissue organization is thought to depend on the adhesive and mechanical properties of the constituent cells. However, it has been difficult to determine the precise contribution of these different properties due to the lack of tools to measure them. Here we use atomic force microscopy (AFM) to quantify the adhesive and mechanical properties of the different germ layer progenitor cell types. Applying this methodology, we demonstrate that mesoderm and endoderm progenitors are more adhesive than ectoderm cells and that E-cadherin is the main adhesion molecule regulating this differential adhesion. In contrast, ectoderm progenitors exhibit a higher actomyosin-dependent cell cortex tension than mesoderm and endoderm progenitors. Combining these data with tissue self-assembly in vitro and in vivo, we provide evidence that the combinatorial activities of cell adhesion and cell cortex tension direct germ layer separation and stratification. It has been hypothesized that the directionality of cell movement during collective migration results from a collective property. Using a single cell transplantation assay, we show that individual progenitor cells are capable of normal directed migration when moving as single cells, but require cell-cell adhesion to participate in coordinated and directed migration when moving collectively. These findings contribute to the understanding of the gastrulation process. Cell-cell adhesion is required for collective germ layer progenitor cell migration, and cell cortex tension is critical for germ layer separation and stratification. However, many questions still have to be solved. Future studies will have to explore the interaction between the adhesive and mechanical progenitor cell properties, as well as the role of these properties for cell protrusion formation, cell polarization, interaction with extracellular matrix, and their regulation by different signaling pathways.

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32

Miyake, Masahiro. "Identification of myopia-associated WNT7B polymorphisms provides insights into the mechanism underlying the development of myopia." Kyoto University, 2015. http://hdl.handle.net/2433/202669.

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33

Aranjuez, George Gil Fajardo. "Cellular Mechanisms that Promote the Collective Migratory Behavior of Drosophila Border Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1436369488.

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34

Sankara, Narayana Gautham Hari Narayana. "Role of non-muscle myosin-II isoforms in adherens junction biogenesis and collective migration." Thesis, Université de Paris (2019-....), 2019. https://theses.md.univ-paris-diderot.fr/SANKARA_NARAYANA_Gautham_Hari_Naryana_va.pdf.

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La formation et le remodelage des jonctions intercellulaires sont essentiels pour de nombreux processus biologiques tels que la compaction et la morphogenèse de l’embryon, la formation et la cicatrisation des tissus, le maintien de l’homéostasie tissulaire. Il est maintenant bien décrit que la myosine II non musculaire (NMII) agit comme un générateur de force et un support mécanique pour les jonctions adherens (E-cadhérine-dépendantes) lors de la migration collective et de la morphogenèse. Cependant, la contribution de NMII pendant les premières étapes de la formation de jonctions adherens reste mal connue, probablement en raison de la difficulté technique à capter un tel évènement transitoire mais complexe. Dans ce travail, nous avons étudié le rôle des isoformes non musculaires de la myosine II (NMIIA et NMIIB) au cours de la biogenèse des jonctions adherens dans les cellules MDCK, en utilisant une approche réductionniste in vitro. Cette approche, basée sur l’utilisation de substrats de culture micropatternés, chimiquement activables, mais permit un contrôle spatio-temporel de la formation des contacts intercellulaires. Mes travaux montrent que les cellules forment des contacts irréversibles base de E-cadhérine. L’élongation de ces contacts est accompagnée de la repolarisation du cytosquelette d’actine et de l’axe noyau-centrosome. En utilisant des shRNA spécifiques aux isoformes NMIIA et IIB, j’ai montré que ces deux isoformes ont contributions distinctes la formation et la dynamique des jonctions. NMIIA et NMIIB régulent différemment la biogenèse des jonctions par association avec des réseaux d'actine distincts. L'analyse de la dynamique des jonctions, de l'organisation de l'actine et des forces mécaniques a révélé que NMIIA fournit la force de traction mécanique nécessaire au renforcement et la maintenance des jonctions cellulaires. Le NMIIB est impliquée dans le clustering de la E-cadhérine, le maintien d'une couche d'actine branchée reliant les complexes de cadhérine et les fibres d'actine péri-jonctionnelles conduisant la création d'un stress mécanique anisotrope. Ces données révèlent des fonctions complémentaires imprévues de NMIIA et NMIIB dans la biogenèse et l'intégrité des jonctions adherens
Adherens junction formation and remodeling is essential for many biological processes like embryo compaction, tissue morphogenesis and wound healing. It is now well described that non-muscle myosin II (NMII) acts as a mechanical support and force-generator for E-cadherin junctions during collective migration and morphogenesis. However, the contribution of NMII during early steps of junction formation remains obscure, probably because of the technical difficulty to catch such a transient event. In this work, we investigate the role of non-muscle myosin II isoforms (NMIIA and NMIIB) during adherens junction biogenesis in MDCK cells, using an in vitro reductionist approach. This system, based on chemically switchable micropatterns allows a spatio-temporal control of adherens junction formation. Our observations on MDCK cells show that the cells form irreversible E-cadherin based contacts, junction elongation is accompanied by the repolarization of actin cytoskeleton and nucleus-centrosome axis. Using isoform-specific ShRNA for NMIIA and IIB, we show that they have distinct contributions to junction formation and dynamics. NMIIA and NMIIB differentially regulate biogenesis of AJ through association with distinct actin networks. Analysis of junction dynamics, actin organization, and mechanical forces of control and knockdown cells for myosins revealed that NMIIA provides the mechanical tugging force necessary for cell-cell junction reinforcement and maintenance. NMIIB is involved in E-cadherin clustering, maintenance of a branched actin layer connecting E-cadherin complexes and perijunctional actin fibres leading to the building-up of anisotropic stress. These data reveal unanticipated complementary functions of NMIIA and NMIIB in the biogenesis and integrity of AJ

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35

Li, Mingxin. "Celluar and Molecular Mechanisms Underlying Regulation of Skeletal Muscle Contraction in Health and Disease." Doctoral thesis, Uppsala universitet, Klinisk neurofysiologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-123005.

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Morphological changes, genetic modifications, and cell functional alterations are not always parallel. Therefore, assessment of skeletal muscle function is an integral part of the etiological approach. The general objective of this thesis was to look into the cellular and molecular events occurring in skeletal muscle contraction in healthy and diseased condition, using a single fiber preparation and a single fiber in vitro motility assay, in an attempt to approach the underlying mechanisms from different physiological angles. In a body size related muscle contractility study, scaling of actin filament sliding speed and its temperature sensitivity has been investigated in mammals covering a 5,500-fold difference in body mass. A profound temperature dependence of actin filament sliding speed over myosin head was demonstrated irrespective of MyHC isoform expression and species. However, the expected body size related scaling within orthologus myosin isoforms between species failed to be maintained at any temperature over 5,500-fold range in body mass, with the larger species frequently having faster in vitro motility speeds than the smaller species. This suggest that apart from the MyHC iso-form expression, other factors such as thin filament proteins and myofilament lattice spacing, may contribute to the scaling related regulation of skeletal muscle contractility. A study of a novel R133W β-tropomyosin mutation on regulation of skeletal muscle contraction in the skinned single fiber prepration and single fiber in vitro motility assay suggested that the mutation induced alteration in myosin-actin kinetics causing a reduced number of myosin molecules in the strong actin binding state, resulting in overall muscle weakness in the absence of muscle wasting. A study on a type IIa MyHC isoform missense mutation at the motor protein level demonstrated a significant negative effect on the function of the IIa MyHC isoform while other myosin isoforms had normal function. This provides evidence that the pathogenesis of the MyHC IIa E706K myopathy involves defective function of the mutated myosin as well as alterations in the structural integrity of all muscle irrespective of MyHC isoform expression.

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Aare, Sudhakar Reddy. "Intensive Care Unit Muscle Wasting : Skeletal Muscle Phenotype and Underlying Molecular Mechanisms." Doctoral thesis, Uppsala universitet, Klinisk neurofysiologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-180374.

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Acute quadriplegic myopathy (AQM), or critical illness myopathy, is a common debilitating acquired disorder in critically ill intensive care unit (ICU) patients characterized by generalized muscle wasting and weakness of limb and trunk muscles. A preferential loss of the thick filament protein myosin is considered pathognomonic of this disorder, but the myosin loss is observed relatively late during the disease progression. In attempt to explore the potential role of factors considered triggering AQM in sedated mechanically ventilated (MV) ICU patients, we have studied the early effects, prior to the myosin loss, of neuromuscular blockade (NMB), corticosteroids (CS) and sepsis separate or in combination in a porcine experimental ICU model. Specific interest has been focused on skeletal muscle gene/protein expression and regulation of muscle contraction at the muscle fiber level. This project aims at improving our understanding of the molecular mechanisms underlying muscle specific differences in response to the ICU intervention and the role played by the different triggering factors. The sparing of masticatory muscle fiber function was coupled to an up-regulation of heat shock protein genes and down-regulation of myostatin are suggested to be key factors in the relative sparing of masticatory muscles. Up-regulation of chemokine activity genes and down-regulation of heat shock protein genes play a significant role in the limb muscle dysfunction associated with sepsis. The effects of corticosteroids in the development of limb muscle weakness reveals up-regulation of kinase activity and transcriptional regulation genes and the down-regulation of heat shock protein, sarcomeric, cytoskeletal and oxidative stress responsive genes. In contrast to limb and craniofacial muscles, the respiratory diaphragm muscle responded differently to the different triggering factors. MV itself appears to play a major role for the diaphragm muscle dysfunction. By targeting these genes, future experiments can give an insight into the development of innovative treatments expected at protecting muscle mass and function in critically ill ICU patients.

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Seitz, Laurent B. "Mechanisms affecting post-activation potentiation following voluntary isokinetic knee extension." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2014. https://ro.ecu.edu.au/theses/1557.

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The present research was designed to: 1) determine whether the voluntary PAP effects commonly observed after conditioning activity (CA; i.e. muscular contraction prior to a ‘test’ contraction) are a consequence of acute neuromuscular alterations relating to the CA itself, or whether they simply reflect warm-up and/or familiarisation effects; 2) clarify the influence of the contraction velocity, duration and total work characteristics of the CA on voluntary PAP; 3) determine the factors allowing stronger individuals to express higher level of voluntary PAP; and 4) determine the peripheral and central mechanisms of voluntary PAP in human skeletal muscle. In Study 1, the effects of different contraction velocity, duration and total work characteristics on PAP were examined after a complete warm-up. The contributions of peripheral and central mechanisms to PAP were also examined. Voluntary and electrically-evoked torques and electromyogram (EMG) data were captured before and after five different dynamic (isokinetic) CAs, after the participants had completed an extensive warm-up including extensive task-specific practice to the point where maximal voluntary contractile capacity was achieved. Vastus lateralis (VL) EMG amplitude normalised to the muscle compound action potentiation (M-wave) amplitude (EMG:M), was taken as a measure of central drive whereas twitch peak torque and M-wave amplitude were recorded to assess peripheral function. Even after a plateau in voluntary contractile capacity was achieved after the complete warm-up, the imposition of CAs elicited significant increases in both voluntary and twitch torques (i.e., PAP). CAs with longer total contraction duration (6s) and a minimum total work of ~750-900 J produced PAP, regardless of the velocity of the CA. No changes in EMG:M were detected after any CA suggesting that central drive was not a major factor influencing PAP under the present experimental conditions. However, the increases in twitch peak torques with lack of change in Mwave amplitude suggest that peripheral function, possibly including changes in myosin regulatory light chain (RLC) phosphorylation and increased intracellular Ca2+ release and sensitivity may have contributed to the observed PAP. It is clear from the literature and the results of Study 1 that there is a significant inter-individual variability in the PAP phenomenon. Typically, stronger individuals are able to express higher levels of PAP but it is unclear why this occurs. Therefore, in Study 2 peak knee extensor torque at 60o·s-1, quadriceps and VL crosssectional area (CSA) and volume, and the type II myosin heavy chain (MHC) isoform percentage (VL) were measured to determine their relative contribution to PAP elicited under voluntary conditions. There were large to very large correlations between PAP magnitude and peak knee extensor torque at 60o·s-1 (r=0.62), quadriceps (r=0.68) and VL (r=0.62) CSA, and quadriceps (r=0.63) and VL (r=0.65) volume. Nonetheless, these correlations were not statistically significant after adjusting for the influence of type II MHC percentage (using partial correlation analysis). By contrast, the strongest correlation was observed for type II MHC percentage (r=0.77), and this correlation remained significant (r=0.56-0.66) after adjusting for other variables. This finding suggests that PAP magnitude is most clearly associated with the type II MHC isoform percentage in the human quadriceps femoris. This might be explained by the fact that myosin RLC phosphorylation, one proposed mechanism responsible for PAP, has been shown to be greater in type II MHC isoforms. The results of Study 1 and Study 2 suggest that changes at the peripheral level, possibly including changes in myosin RLC phosphorylation (and increased intracellular Ca2+ release and sensitivity) may be a primary candidate mechanism of PAP induced by a voluntary CA, although more direct measurements are required to test this assumption. Therefore, tetanic stimulations and maximal isokinetic knee extensions at 180o·s-1 were used in Study 3 to provide a more detailed investigation of the role of changes in the excitation-contraction (E-C) coupling process (i.e. changes in myosin RLC phosphorylation or increased intracellular Ca2+ release and sensitivity) to the PAP response induced by a voluntary CA. Torques produced during voluntary knee extensions, 20 Hz and catch-inducing (20-Hz train preceded by a double pulse with 5-ms interval) stimulation trains, the 20- vs. 80-Hz torque ratio (20:80) as well as the force-augmenting effect of the catch-inducing train were recorded before and after a voluntary CA or a control condition (no CA, rest). Statistically significant increases in voluntary torque, torques elicited by 20-Hz and catch-inducing trains, and 20:80 were observed 1, 4 and 7 min after the CA. Moreover, the force-augmenting effects of the catch-inducing train diminished as the magnitude of PAP increased and then increased as the magnitude of PAP diminished. Statistically significant correlations (r=0.50-0.81) were also found between the changes in voluntary torque production (i.e. PAP) and the changes in these variables. These results suggest that increases in PAP following a voluntary CA are strongly associated with changes in peripheral function, most probably changes in the E-C coupling efficiency..

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Mouton, Jacoba Martina. "The role of novel protein-protein interactions in the function and mechanism of the sarcomeric protein, myosin binding protein H (MyBPH)." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86751.

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Thesis (PhD)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Left ventricular hypertrophy (LVH) is a major risk factor for cardiovascular morbidity and mortality, and is a feature of common diseases, such as hypertension and diabetes. It is therefore vital to understand the underlying mechanisms influencing its development. However, investigating the mechanisms underlying LVH in such complex disorders can be challenging. For this reason, many researchers have focused their attention on the autosomal dominant cardiac muscle disorder, hypertrophic cardiomyopathy (HCM), since it is considered a model disease in which to study the causal molecular factors underlying isolated cardiac hypertrophy. HCM is a heterogeneous disease that manifests with various phenotypes and clinical symptoms, even in families with the same genetic defects, suggesting that additional factors contribute to the disease phenotype. Despite the identification of several HCM-causing genes, the genetic factors that modify the extent of hypertrophy in HCM patients remain relatively unknown. The gene encoding the sarcomeric protein, cardiac myosin binding protein C, cMyBPC (MyBPC3) is one of the most frequently implicated genes in HCM. Identification of proteins that interact with cMyBPC has led to improved insights into the function of this protein and its role in cardiac hypertrophy. However, very little is known about another member of the myosin binding protein family, myosin binding protein H (MyBPH). Given the sequence homology and similarity in structure between cMyBPC and MyBPH, we propose that MyBPH, like cMyBPC, may play a critical role in the structure and functionality of the cardiac sarcomere and could therefore be involved in HCM pathogenesis. The present study aimed to identify MyBPH-interacting proteins by using yeast two-hybrid (Y2H) analysis and to verify these interactions using three-dimensional (3D) co-localisation and co-immunoprecipitation (Co-IP) analyses. We further hypothesized that both MyBPH and cMyBPC may be involved in autophagy. To test this hypothesis, both MyBPH and cMyBPC were analysed for co-localisation with a marker for autophagy, LC3b-II. The role of MyBPH and cMyBPC in cardiac cell contractility were analysed by measuring the planar cell surface area of differentiated H9c2 rat cardiomyocytes in response to β-adrenergic stress after individual and concurrent siRNA-mediated knockdown of MyBPH and cMyBPC. In the present study we employed a family-based genetic association analysis approach to investigate the contribution of genes encoding the novel MyBPH-interacting proteins in modifying the hypertrophy phenotype. This study investigated the hypertrophy modifying effects of 38 SNPs and haplotypes in four candidate HCM modifier genes, in 388 individuals from 27 HCM families, in which three unique South African HCM-causing founder mutations segregate. Yeast two-hybrid analysis identified three putative MyBPH-interacting proteins namely, cardiac β-myosin heavy chain (MYH7), cardiac α-actin (ACTC1) and the SUMO-conjugating enzyme UBC9 (UBC9). These interactions were verified using both 3D co-localisation and Co-IP analyses. Furthermore, MyBPH and cMyBPC were implicated in autophagy, since both these proteins were being recruited to the membrane of autophagosomes. In addition, a cardiac contractility assay demonstrated that the concurrent siRNA-mediated knockdown of MyBPH and cMyBPC resulted in a significant reduction in cardiomyocyte contractility, compared to individual protein and control knockdowns under conditions of β-adrenergic stress. These results indicated that MyBPH could compensate for cMyBPC, and vice versa, further confirming that both these proteins are required for efficient sarcomere contraction. Results from genetic association analyses found a number of SNPs and haplotypes that had a significant effect on HCM hypertrophy. Single SNP and haplotype analyses identified SNPs and haplotypes within genes encoding MyBPH, MYH7, ACTC1 and UBC9, which contribute to the extent of hypertrophy in HCM. In addition, we found that several variants and haplotypes had markedly different statistical significant effects in the presence of each of the three HCM founder mutations. The results of this study ascribe novel functions to MyBPH. Cardiac MyBPC and MyBPH play a critical role in sarcomere contraction and have been implicated in autophagy. This has further implications for understanding the patho-etiology of HCM-causing mutations in the gene encoding MyBPH and its interacting proteins. This is to our knowledge the first genetic association analysis to investigate the modifying effect of interactors of MyBPH, as indication of the risk for developing LVH in the context of HCM. Our findings suggest that the hypertrophic phenotype of HCM is modulated by the compound effect of a number of variants and haplotypes in MyBPH, and genes encoding protein interactors of MyBPH. These results provide a basis for future studies to investigate the risk profile of hypertrophy development in the context of HCM, which could consequently lead to improved risk stratification and patient management.
AFRIKAANSE OPSOMMING: Linker ventrikulêre hipertrofie (LVH) is 'n primêre risikofaktor vir kardiovaskulêre morbiditeit en mortaliteit asook 'n kenmerk van algemene siektes soos hipertensie en diabetes. Daarom is dit van kardinale belang om te verstaan wat die onderliggende meganismes is wat die ontwikkeling van LVH beïnvloed. Die ondersoek na die onderliggende meganismes wat lei tot LVH in sulke komplekse siektes is ‟n uitdaging. Om hierdie rede fokus baie navorsers hul aandag op die autosomaal dominante hartspier siekte, hipertrofiese kardiomiopatie (HKM), wat beskou word as 'n model siekte om die molekulêre oorsake onderliggend tot geïsoleerde kardiovaskulêre hipertrofie te ondersoek. HKM is 'n heterogene siekte wat manifesteer met verskeie fenotipes en kliniese simptome, selfs in families met dieselfde genetiese defekte, wat impliseer dat addisionele faktore bydra tot die modifisering van die siekte fenotipe. Ten spyte van die identifisering van verskeie HKM-versoorsakende gene, bly die genetiese faktore wat die mate van hipertrofie in HKM pasiente modifiseer relatief onbekend. Die geen wat kodeer vir die sarkomeriese proteïen, kardiale miosien-bindingsproteïen C (kMyBPC) is die algemeenste betrokke in HKM. Die identifisering van proteïene wat bind met kMyBPC het gelei tot verbeterde insigte tot die funksie van hierdie proteïen en die rol wat hierdie proteïen in hipertrofie speel. Ten spyte hiervan, is daar baie min inligting beskikbaar oor 'n ander lid van die miosien-bindingsproteïen families, miosien-bindingsproteïen H (MyBPH). Gegewe die ooreenstemming tussen die DNA basispaar-volgorde en struktuur tussen hierdie twee proteïene, stel ons voor dat MyBPH, net soos kMyBPC, 'n kritiese rol in die struktuur en funksie van die kardiale sarkomeer speel en kan daarom betrokke wees in die patogenese van HKM. Die huidige studie het beoog om proteïene wat met MyBPH bind te identifiseer deur die gebruik van gis-twee-hibried (G2H) kardiale biblioteek sifting en om hierdie interaksies te verifieer met behulp van drie-dimensionele (3D) ko-lokalisering en ko-immunopresipitasie eksperimente. Ons het verder gehipotiseer dat beide MyBPH and kMyBPC betrokke kan wees in outofagie. Om hierdie hipotese te toets is beide MyBPH en kMyBPC geanaliseer vir ko-lokalisering met 'n merker vir outofagie, LC3b-II. Verder het ons beplan om die rol van MyBPH en kMyBPC in kardiale spiersel-sametrekking te ondersoek deur die oppervlak van gedifferensieerde H9c2 rot kardiomiosiete in reaksie op β-adrenergiese stres te meet, na individuele en gesamentlike siRNA-bemiddelde uitklopping van MyBPH en kMyBPC. In hierdie studie het ons 'n familie-gebaseerde genetiese assosiasie analise benadering gevolg om vas te stel of MyBPH en gene wat kodeer vir die geverifieerde bindingsgenote van MyBPH bydra tot die modifisering van die hipertrofiese fenotipe. Die doel van hierdie studie was om die hipertrofiese effek van 38 enkel nukleotied polimorfismes (SNPs) en haplotipes in vier kandidaat HKM modifiserende gene in 388 individue van 27 HCM families te toets, waarin drie unieke Suid-Afrikaanse HKM-stigters mutasies segregeer. G2H analise het drie verneemde MyBPH bindingsgenote geidentifiseer, naamlik miosien (MYH7), alfa kardiale aktien (ACTC1) en die SUMO-konjugerende ensiem UBC9 (UBC9). Hierdie interaksies is geverifieer deur middel van 3D ko-lokalisering en ko-immunopresipitasie analises. Verder is bewys dat MyBPH en kMyBPC betrokke is in outofagie, siende dat beide proteïene gewerf is tot die membraan van die outofagosoom. 'n Kardiale sametrekkings eksperiment het gevind dat die gesamentlike siRNA-bemiddelde uitklopping van MyBPH en kMyBPC 'n merkwaardige vermindering in die kardiomiosiet sametrekking veroorsaak het in reaksie op β-adrenergiese stres kondisies, in vergelyking met die individuele proteïen en kontrole uitkloppings eksperimente. Hierdie resultate bevestig dat MyBPH vir kMyBPC kan instaan en ook andersom, wat verder bevestig dat beide proteïene benodig word vir effektiewe sarkomeer sametrekking. Resultate van die genetiese assosiasie studie het gevind dat 'n aantal SNPs en haplotipes 'n beduidende effek of HKM hipertrofie het. Enkel SNP en haplotipe analises in gene wat kodeer vir MyBPH, MYH7, ACTC1 en UBC9 het SNPs en haplotipes geidentifiseer wat bydra tot die omvang van hipertrofie in HKM. Verder het ons gevind dat sekere SNPs en haplotipes kenmerkend verskillende statisties beduidende effekte in die teenwoordigheid van elk van die drie HKM-stigter mutasies gehad het. Die resultate van hierdie studie skryf twee nuwe funksies aan MyBPH toe. Kardiale MyBPC en MyBPH speel 'n kritiese rol in sarkomeer sametrekking en is betrokke in outofagie. Hierdie resultate het verdere implikasies vir die verstaan van die pato-etiologie van die HKM-veroorsakende mutasies in die MyBPH, MYH7, ACTC1 en UBC9 gene. So vêr dit ons kennis strek is dit die eerste genetiese assosiasie studie wat die modifiserende effek van bindingsgenote van MyBPH ondersoek as risiko aanduiding vir die ontwikkeling van LVH in die konteks van HKM. Ons bevindinge bewys dat die hipertrofiese fenotipe van HKM gemoduleer word deur die komplekse effekte van SNPs en haplotipes in die MyBPH geen en gene wat MyBPH proteïen-bindingsgenote enkodeer. Hierdie resultate verskaf dus 'n basis vir toekomstige studies om die risiko profiel van hipertrofie ontwikkeling met betrekking tot HKM te ondersoek, wat gevolglik kan bydra tot die verbeterde risiko stratifikasie en pasiënte bestuur.

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39

Shelton, Setareh Lillian. "Characterization of mechanisms regulating scleral extracellular matrix remodeling to promote myopia development." Oklahoma City : [s.n.], 2009.

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40

Holmes, Craig. "Myopia, retirement planning and commitment." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:980da095-60ab-47b5-a4e2-3962085d56ca.

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Decisions made by individuals planning for retirement may be myopic. One way of capturing this myopia is with quasi-hyperbolic discounting. It is well known that such preferences may explain why individuals fail to provide an adequate retirement income for themselves. In this thesis, the quasi-hyperbolic discounting model is applied to a number of other decisions and outcomes related to planning for retirement. There are three main focuses. Firstly, the thesis considers a model where individuals are quasi-hyperbolic discounters over both retirement and saving, and extends the results of Diamond and Köszegi (2003). It argues that mechanisms designed to overcome myopic saving decisions may lead to unplanned early retirement. This may depend on the form of income in retirement -- regular income options such as annuities offer commitment over overconsuming early in retirement, which makes early retirement less desirable to myopic retirees. Secondly, it tests these predictions using a new laboratory experiment. Over a two-month period, participants were asked to attend weekly sessions, and could leave the experiment (or "retire") in any week of their choosing. Part of their payment for attending these sessions was put aside and paid only after they had left. The results indicated that more impulsive individuals left the experiment earlier, both overall and relative to plans made in the first week of the experiment. Finally, this thesis presents a model of rising wages as a forced saving mechanism. Assuming individuals face some borrowing constraints, deferred wages implicitly place some earnings aside until much closer to retirement, when quasi-hyperbolic discounters save a greater fraction of their income, increasing total retirement wealth. It also shows that demand for rising wages should disappear for people with access to more direct saving commitment mechanisms, although when these schemes offer less commitment (due to early withdrawal or early retirement options), a combination of both mechanisms is preferred.

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komariza, Seyed Omid. "ANALYSIS AND MODELING OF THE ROLES OF ACTIN-MYOSIN INTERACTIONS IN BLADDER SMOOTH MUSCLE BIOMECHANICS." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3651.

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Muscle mechanical behavior potentially plays an important role in some of the most common bladder disorders. These include overactive bladder, which can involve involuntary contractions during bladder filling, and impaired contractility or underactive bladder, which may involve weak or incomplete contractions during voiding. Actin-myosin cross-bridges in detrusor smooth muscle (DSM) are responsible for contracting and emptying the bladder. The total tension produced by muscle is the sum of its preload and active tensions. Studies suggest that actin-myosin cross-links are involved in adjustable preload stiffness (APS), which is characterized by a preload tension curve that can be shifted along the length axis as a function of strain history and activation history. DSM also exhibits length adaptation in which the active tension curve can exhibit a similar shift. Actin-myosin cross-bridges are also responsible for myogenic contractions in response to quick stretch of DSM strips and spontaneous rhythmic contractions (SRC) that may occur during bladder filling. Studies show that SRC may participate in the mechanical regulation of both APS and length adaptation. However, the mechanical mechanisms by which actin-myosin interactions enable this interrelated combination of behaviors remain to be determined and were the primary focus of this dissertation. The objectives of this study were to: 1) provide evidence to support the hypothesis that a common mechanism is responsible for SRC and myogenic contraction, 2) develop a sensor-based mechanical model to demonstrate that SRC in one cell is sufficient to trigger stretch-induced myogenic contraction in surrounding cells and propagate the contraction, and 3) develop a conceptual model with actin-myosin cross-bridges and cross-links that produces the coupled mechanical behaviors of APS, SRC, and length adaptation in DSM. Improved understanding of bladder biomechanics may enable the identification of specific targets for the development of new treatments for overactive and underactive bladder.

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Llano-Diez, Monica. "Mechanisms Underlying Intensive Care Unit Muscle Wasting : Intervention Strategies in an Experimental Animal Model and in Intensive Care Unit Patients." Doctoral thesis, Uppsala universitet, Klinisk neurofysiologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-173466.

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Critically ill patients admitted to the intensive care unit (ICU) commonly develop severe muscle wasting and weakness and consequently impaired muscle function. This not only delays respirator weaning and ICU discharge, but has deleterious effects on morbidity, mortality, financial costs, and quality of life of survivors. Acute Quadriplegic Myopathy (AQM) is one of the most common neuromuscular disorders underlying ICU muscle wasting and paralysis, and is a consequence of modern intensive care interventions, although the exact causes remain unclear. Muscle gene/protein expression, intracellular signalling, post-translational modifications, muscle membrane excitability, and contractile properties at the single muscle fibre level were explored in order to unravel the mechanisms underlying the muscle wasting and weakness associated with AQM and how this can be counteracted by specific intervention strategies. A unique experimental rat ICU model was used to address the mechanistic and therapeutic aspects of this condition, allowing time-resolved studies for a period of two weeks. Subsequently, the findings obtained from this model were translated into a clinical study. The obtained results showed that the mechanical silencing of skeletal muscle, i.e., absence of external strain (weight bearing) and internal strain (myosin-actin activation) due to the pharmacological paralysis or sedation associated with the ICU intervention, is likely to be the primary mechanism triggering the preferential myosin loss and muscle wasting, features specifically characteristic of AQM. Moreover, mechanical silencing induces a specific gene expression pattern as well as post-translational modifications in the motor domain of myosin that may be critical for both function and for triggering proteolysis. The higher nNOS expression found in the ICU patients and its cytoplasmic dislocation are indicated as a probable mechanism underlying these highly specific modifications. This work also demonstrated that passive mechanical loading is able to attenuate the oxidative stress associated with the mechanical silencing and induces positive effects on muscle function, i.e., alleviates the loss of force-generating capacity that underlie the ICU intervention, supporting the importance of early physical therapy in immobilized, sedated, and mechanically ventilated ICU patients.

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Aslam, Muhammad [Verfasser]. "Effect of cAMP-PKA signaling mechanism on barrier function of cultured endothelial cells : role of myosin light chain phosphatase / vorgelegt von Muhammad Aslam." Giessen : VVB Laufersweiler, 2007. http://d-nb.info/988757508/34.

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PENNESTRI, MATTEO. "The Mechanism of Myosin Light Chain IQ-motif interaction and its role in the regulation of vesicle traffic in cytokinesis: a structural study." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/439.

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Calmodulina, catene leggere della miosina essenziali e regolatorie sono proteine evolutive che, attraverso il legame con gli IQ motif di proteine bersaglio, regolano processi intracellulari essenziali come il rilascio di vescicole secretorie alle sinapsi, segnali intracellulari e regolazione della divisione cellulare. La calmodulina di lievito Cmd1 e la catena leggera della miosina Mlc1p condividono la capacità di interagire con la miosina di classe V Myo2p e Myo4p e la miosina di classe II Myo1p. Queste miosine sono necessarie per il trasporto di vescicole, organelli e mRNA, orientazione del fuso mitotico e citochinesi. Studi strutturali tramite risonanza magnetica nucleare della forma non complessata di Mlc1p e studi di interazione con defferenti IQ motif di Myo2p mostrano ristrette similitudini strutturali tra Mlc1p ed altre proteine "calmodulin-like" della superfamiglia delle EF-hand per il solo lobo C. Il lobo N di Mlc1p presenta un struttura stabile e compatta che è mantenuta sia nella forma libera che nello stato complessato. Il lobo N di Mlc1p interagisce con gli IQ motif in una maniera che è regolata sia dalla sequenza degli IQ motif sia dalle caratteristiche della catena leggera. Queste caratteristiche permettono una interazione caratteristica di Mlc1p con il primo IQ motif di Myo2p se confrontato con la calmodulina. Questa scoperta fornisce una nuova visione di come calmodulina e catene leggere essenziali, attraverso deversi modi di legare con gli IQ motif regolano l'attività di crescita vegetativa e di citochinesi.
Calmodulin, regulatory, and essential myosin light chain are evolutionary conserved proteins that, by binding to IQ motifs of target proteins, regulate essential intracellular processes among which are efficiency of secretory vesicles release at synapsis, intracellular signaling, and regulation of cell division. The yeast Saccharomyces cerevisiae calmodulin Cmd1 and the essential myosin light chain Mlc1p share the ability to interact with the class V myosin Myo2p and Myo4 and the class II myosin Myo1p. These myosins are required for vesicle, organelle, and mRNA transport, spindle orientation, and cytokinesis. We have used the budding yeast model system to study how calmodulin and essential myosin light chain selectively regulate class V myosin function. NMR structural analysis of uncomplexed Mlc1p and interaction studies with the first three IQ motifs of Myo2p show that the structural similarities between Mlc1p and the other members of the EF-hand superfamily of calmodulin-like proteins are mainly restricted to the C-lobe of these proteins. The N-lobe of Mlc1p presents a significantly compact and stable structure that is maintained both in the free and complexed states. The Mlc1p N-lobe interacts with the IQ motif in a manner that is regulated both by the IQ motifs sequence as well as by light chain structural features. These characteristic allows a distinctive interaction of Mlc1p with the first IQ motif of Myo2p when compared with calmodulin. This finding gives us a novel view of how calmodulin and essential light chain, through a differential binding to IQ1 of class V myosin motor, regulate this activity during vegetative growth and cytokinesis.

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Sheshka, Raman. "Le rôle mécanique de " power stroke " dans la contraction musculaire." Phd thesis, Ecole Polytechnique X, 2012. http://pastel.archives-ouvertes.fr/pastel-00784006.

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Cette thèse est consacrée à la modélisation du fonctionnement mécanique de l'interaction myosine II / actine, qui est responsable de la génération de force active dans les muscles squelettiques à l'échelle nanomérique. Les unités contractiles du muscle contiennent les filaments d'actine et de myosine, les derniers sont formés par un assemblage des myosines II. La myosine II est un moteur moléculaire qui s'attache et se détache périodiquement au filament d'actine en présence d'ATP. Afin de comprendre le phénomène de la contraction musculaire d'un point de vue mécanique, nous suivons l'approche développée par la communauté de cliquets Browniens, qui remplace l'interprétation chimique traditionnelle de génération de force active par une étude de la dynamique de Langevin des systèmes mécaniques avec des paysages énergétiques bien définis. Nous mettons l'accent sur le rôle du changement conformationnel, ou " power stroke ", dans le fonctionnement de la myosine II. Nous identifions le "power stroke" comme le principal moteur de la contractilité, ce qui reflète la réalité biologique. Nous proposons un modèle mécanique innovant et, en mettant l'accent sur le rôle actif de " power stroke ", nous établissons un lien entre les moteurs processifs et nonprocessifs. Dans cette thèse, nous présentons les premiers exemples de modèles de moteur moléculaire nonprocessif actionnés exclusivement par "power stroke " et exploitant le phénomène de la résonance stochastique.

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Kreutziger, Kareen L. "Investigating the molecular mechanisms of cooperative tension generation in skeletal and cardiac muscle by altering acto-myosin interactions and engineering troponin C calcium binding kinetics /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8060.

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Welz, Tobias [Verfasser], and Eugen [Akademischer Betreuer] Kerkhoff. "Mechanisms of force generation for vesicle transport processes: identification and characterisation of the Spir actin nucleator - myosin V motor protein complex / Tobias Welz ; Betreuer: Eugen Kerkhoff." Regensburg : Universitätsbibliothek Regensburg, 2018. http://d-nb.info/1155359461/34.

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McKillop, Daniel F. A. "Studies on the mechanism of regulation of the interaction of actin and myosin subfragment 1 in solution and on the pressure sensitivity of the actomyosin subfragment 1 ATPase." Thesis, University of Bristol, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303879.

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Frey, Margo Tilley. "Development of a Substrate with Photo-Modulatable Rigidity for Probing Spatial and Temporal Responses of Cells to Mechanical Signals: A Dissertation." Digital WPI, 2008. https://digitalcommons.wpi.edu/etd-dissertations/337.

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"Topographical and mechanical properties of adhesive substrates provide important biological cues that affect cell spreading, migration, growth, and differentiation. The phenomenon has led to the increased use of topographically patterned and flexible substrates in studying cultured cells. However, these studies may be complicated by various limitations. For example, the effects of ligand distribution and porosity are affected by topographical features of 3D biological constructs. Similarly, many studies of mechanical cues are compounded with cellular deformation from external forces, or limited by comparative studies of separate cells on different substrates. Furthermore, understanding cell responses to mechanical input is dependent upon reliable measurements of mechanical properties. This work addresses each of these issues. To determine how substrate topography and focal adhesion kinase (FAK) affect cell shape and movement, I studied FAK-null (FAK -/-) and wild type mouse 3T3 fibroblasts on chemically identical polystyrene substrates with either flat surfaces or micron-sized pillars, I found that, compared to cells on flat surfaces, those on pillar substrates showed a more branched shape, an increased linear speed, and a decreased directional stability, which were dependent on both myosin-II and FAK. To study the dynamic responses to changes in substrate stiffness without other confounding effects, I developed a UV-modulatable substrate that softens upon UV irradiation. As atomic force microscopy (AFM) proved inadequate to detect microscale changes in stiffness, I first developed and validated a microsphere indentation method that is compatible with fluorescence microscopy. The results obtained with this method were comparable to those obtained with AFM. The UV-modulatable substrates softened by ~20-30% with an intensity of irradiation that has no detectable effect on 3T3 cells on control surfaces. Cells responded to global softening of the substrate with an initial retraction followed by a gradual reduction in spread area. Precise spatial control of softening is also possible - while there was little response to posterior softening, anterior softening elicited a pronounced retraction and either a reversal of cell polarity or a significant decrease in spread area if the cells move into the softened region. In conclusion, these techniques provide advances in gaining mechanistic insight into cellular responses to topographical and mechanical cues. Additionally, there are various other potential applications of the novel UV-softening substrate, particularly in regenerative medicine and tissue engineering. "

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Rayer, Mégane. "Mécanisme de génération de forces par les cellules apoptotiques lors de la morphogenèse de la drosophile." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30169.

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Chaque espèce vivante acquiert une forme qui lui est propre. La génération de forces mécaniques est l'une des stratégies utilisées par les cellules pour sculpter les organes. Lors du développement animal, les forces mécaniques générées dans le plan des jonctions adhérentes sont importantes pour le remodelage des tissus épithéliaux. Ces forces planaires ont été particulièrement étudiées ces dernières années. C'est le cas notamment de la constriction apicale des cellules lors de l'invagination du mésoderme de l'embryon de drosophile. La réduction de l'apex des cellules est considérée comme un processus fondamental pour la formation de la pliure initiale de cet épithélium. Toutefois, il a été découvert récemment que des forces peuvent aussi être générées dans l'axe apico-basal des cellules. L'équipe dans laquelle j'ai effectué ma thèse a montré que de telles forces sont requises pour la formation de plis dans la patte de la drosophile lors de son développement. Dans ce processus, avant de disparaitre par apoptose (ou mort programmée), les cellules vont former une structure apico-basale appelé "câble de myosine" qui, en se contractant, va induire une déformation des cellules voisines, aboutissant progressivement à la formation de plis. Cependant, les mécanismes requis pour la génération de la force apico-basale restaient inconnus. L'objectif de ma thèse était donc de chercher comment ces cellules destinées à mourir pouvaient générer une force efficace. L'hypothèse de travail était que ce câble de myosine devait être ancré au pôle apical et au pôle basal de la cellule afin de fournir une résistance permettant la génération d'une force efficace pouvant être transmise aux cellules voisines. J'ai donc cherché à identifier ces points d'ancrage grâce à des techniques d'imagerie et de génétique. Dans un premier temps, j'ai identifié le point d'ancrage apical du câble. En effet, les cellules apoptotiques réduisent leur apex mais conservent leurs jonctions adhérentes au niveau desquelles co-localise l'extrémité apicale du câble de myosine. Dans un deuxième temps, j'ai cherché quel pourrait être le point d'ancrage basal du câble de myosine. Une observation surprenante montre que le noyau des cellules apoptotiques est systématiquement relocalisé au pôle basal et que le câble de myosine rentre en contact avec lui. J'ai testé si le noyau joue un rôle dans l'ancrage du câble de myosine en perturbant sa localisation basale. La perte de fonction de Klarsicht, une protéine du complexe LINC, empêche la cellule d'induire une déformation des cellules voisines, montrant que dans ce contexte où le noyau n'est pas relocalisé au pôle basal de la cellule, la force n'est pas ou peu produite. Finalement, j'ai pu montrer que le noyau est lui-même ancré au pôle basal de la cellule afin de fournir un point de résistance lors de la contraction du câble. En effet, j'ai étudié la mobilité des noyaux, montrant d'une part que les noyaux apoptotiques sont moins mobiles que ceux des cellules non-apoptotiques et, d'autre part, que l'actine et la Taline, un composant des adhésions basales, sont requises pour la stabilisation du noyau apoptotique. De plus, j'ai observé que, lors de la contraction du câble, le noyau remonte simultanément et que celui-ci se déforme localement. Finalement, des expériences d'ablation laser du câble de myosine montrent un relâchement de la surface apicale et un recul du noyau. Ainsi, la force émise par les cellules apoptotiques est transmise dans l'axe apico-basal par une liaison adhérence apicale-câble-noyau. Mon travail met en lumière un mécanisme original de génération de force. Ce nouveau mécanisme de force apico-basale pourrait être conservé dans d'autres types cellulaires engagés dans des processus d'invagination au cours de la morphogenèse. Mes résultats montrent également que le noyau joue un rôle nouveau, au-delà de son rôle de protection du génome, en participant activement à la génération d'une force
Each animal species acquires a specific shape during development. The generation of mechanical forces is one of the strategies used by cells to sculpt organs. During animal development, the mechanical forces generated in the plane of adherens junctions are important for epithelium remodeling. These planar forces have been extensively studied over the last years. This is particularly the case during apical constriction of mesodermal cells during drosophila embryo gastrulation. The reduction of the cell's apex is considered a fundamental process to trigger invagination of this tissue. However, recently, it has been shown that forces can also be generated along the cell apico-basal axis. The team in which I did my thesis has shown that these forces are important for the formation of folds during drosophila leg development. In this process, before their disappearance, cells form an apico-basal myosin structure, called "myosin cable". The force created by the contraction of the cable is transmitted to the cell's neighbors, inducing cell shape changes progressively resulting in fold formation. However, the mechanisms required for apico-basal force generation remained unknown. The goal of my thesis was to study in detail how the cells destined to die could generate an effective force. We made the hypothesis that the myosin cable should be anchored at the apical and basal cell poles in order to promote a resistance to the cable contraction, and to allow force transmission to the neighbors. Therefore, my aim was to identify these anchoring points thanks to imaging and genetics technics. First, I had identified apical anchor point. Indeed, apoptotic cells reduce their apex but maintain their adherens junctions. The apical extremity of the myosin cable colocalizes to this adhesion structure. Secondly, I searched for the basal anchor point of myosin cable. Surprisingly, I observed that the nucleus of apoptotic cells is systematically relocated on the basal cell half and that the myosin cable contacts it. I tested whether the nucleus plays a role in myosin cable anchorage by perturbing its basal localization. The loss of function of Klarsicht, a LINC complex protein, prevents the cell to deform its neighbors, showing that, in this context the force is strongly or totally abolished. Finally, I have shown that the apoptotic nucleus itself is anchored to the basal side in order to promote a resistance during cable contraction. Indeed, I studied nuclei mobility and showed that apoptotic nuclei are less mobile than non-apoptotic nuclei. I also showed that F-actin and Talin, a basal adhesion component, are required for apoptotic nucleus stability. Furthermore, I have observed that, during cable contraction, the nucleus moves back apically and that it deforms locally. Finally, laser ablation experiments of the myosin cable show an apical recoil of apical surface and a basal recoil of the nucleus. Thus, the force generated by the apoptotic cells is transmitted in the apico-basal axis thanks to the link between apical adherence, cable and nucleus. My work highlights a new mechanism of force generation. This new mechanism of apico-basal force could be conserved in other cell types in additional invagination processes during morphogenesis. My results also show that the nucleus plays a new role, beyond the protection of the genome, by participating actively in force generation

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Dissertations / Theses on the topic 'Myosin mechanics'

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