Dissertations / Theses on the topic 'Non muscle myosin II A'
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Frei, Ryan. "Regulatory Elements of Drosophila Non-Muscle Myosin II." Thesis, University of Oregon, 2013. http://hdl.handle.net/1794/12954.
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Non-muscle myosin II (NM-II) is present in every cell type and moves actin filaments to provide contraction within the cell. NM-II has a motor domain, a neck domain that binds two light chains, a long coiled-coil tail domain, and a carboxyl-terminal tailpiece. NM-II forms bipolar filaments by associating near the carboxyl-terminus of the tail. It has long been known that both the formation of bipolar filaments and enzymatic activity of the motor domain are regulated by phosphorylation of one of the neck-binding light chains, known as the regulatory light chain (RLC). This phosphorylation causes a large-scale conformational shift of both the motor domains and the tail domain. However, the mechanism of this regulation and the elements that mediate the autoinhibition remain unknown.
We have taken a deletional approach to finding the elements necessary for autoinhibition and regulation of filament assembly. We have used salt- dependent pelleting assays, cell culture, and analytical ultracentrifugation to identify two small regions in the IQ motifs of the neck and the carboxyl-terminal tailpiece that are essential for autoinhibition.
Another necessary element for autoinhibition is the fold the coiled coil of the tail back on itself by means of hinge domains. We used internal deletions, pelleting assays, and thermal stability assays to identify and characterize the flexible hinge domains within the coiled-coil tail of NM-II. These hinges consist of low-stability regions of coiled coil, and can be stiffened by introducing mutations that cause the sequence to mimic a more ideal coiled coil. By defining these essential elements of autoinhibition, this work paves the way for a mechanistic understanding of the complex regulation of NM-II in the cell.
This dissertation contains unpublished co-authored material.2015-07-11
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Swailes, Nathan. "Actin and non-muscle myosin II in pre-fusion myoblasts." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416842.
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Picariello, Hannah Stubbs. "The Diverse Roles of Non-muscle Myosin II in Tumorigenesis." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1562680454131993.
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Khan, Protiti. "The Role of Myosin Light Chain Kinase and Non Muscle Myosin II In Ras Signaling to ERK." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_theses/177.
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We have previously reported that non-muscle myosin II (NMMII) and myosin light chain kinase (MLCK) are required for oncogenic Ras signaling to ERK in Ki-Ras transformed rat fibroblsasts (Helfman and Pawlak, J. Cell Biochem. 95(5), 1069-80, 2005). Here I examine if MLCK plays a role in ERK signaling in various tumor derived human epithelial cell lines. I also determined whether genetic inhibition of NMMII isoforms IIA and IIB, or MLCK also inhibits ERK activation in the MCF 10A human breast epithelial cell line expressing oncogenic H-Ras. Inhibition of MLCK by pharmacological inhibitors such as ML-7 and ML-9 was used to determine the role of MLCK in ERK signaling in an array of H/K-Ras transformed and tumor derived cell lines: T-24 bladder carcinoma, HCT 116 colon carcinoma, and MCF 10A Ras breast cancer cells. Genetic inhibition was carried out using specific siRNA targeted towards MLCK and NMMIIA or IIB. The knock down of NMM IIA and IIB did not inhibit active ERK, which suggested either a redundant function of NMM IIC or an alternate substrate for MLCK. Inhibition of MLCK by ML-7/ML-9 reduced activated ERK in all H/K-Ras transformed, or human tumor derived cell lines we tested. The possible mechanism of how MLCK could play a role in ERK signaling was tested by co-immunoprecipitation (co-IP) of MAPK scaffolding proteins with MLCK. That the ERK scaffold KSR1 regulates ERK signaling in MCF 10A Ras, was demonstrated through inhibition of KSR1 with siRNA. Moreover, KSR was shown to interact with MLCK because it was found to co-precipitate with MLCK.
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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 adherensAdherens 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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Ricketson, Derek Lee. "Drosophila non-muscle myosin II bipolar filament formation : importance of charged residues and specific domains for self-assembly /." Connect to title online (Scholars' Bank) Connect to title online (ProQuest), 2009. http://hdl.handle.net/1794/10285.
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Ding, Siyu Serena. "Elucidating the role of non-muscle myosin II in Caenorhabditis elegans stem-like seam cell divisions." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:5b5cb805-327a-4a58-b3db-3787f5264efc.
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Caenorhabiditis elegans seam cells (SC) are multipotent neuroectodermal cells that undergo both symmetrical and asymmetrical divisions throughout larval development, thus providing a valuable model system to gain mechanistic insights into the regulation of asymmetric divisions and the switch between the symmetric and asymmetric modes of division. Reiterative SC asymmetric division typically produces a differentiative anterior daughter that moves out of the seam line and joins the hyp7 syncytium and a proliferative posterior daughter that retains seam fate and carries on dividing. Non-muscle myosin II (NMY II) has emerged as a key regulator in the asymmetric divisions of the C. elegans zygote, the C. elegans Q neuroblast, and the Drosophila neuroblast systems. In addition to being an essential player in cytokinesis, nmy-2's roles in cell adhesion and migration processes further underline its potential as a regulator of seam cell asymmetric divisions. In this thesis work, I investigated the role of NMY-2 in C. elegans seam cell divisions. I found that nmy-2 is expressed in the seam and its protein localization is dynamic during SC divisions. Post-embryonic nmy-2 knockdown using a combination of temperature sensitive mutants and RNA interference robustly reduces terminal SC number. This reduction is due to progressive SC loss after each asymmetric division as a consequence of aberrant cell fate determination. I identified three classes of cell fate transformation phenotypes following nmy-2 knockdown, and sought to dissect the cell molecular basis of these phenotypes using a dual-color fate reporter strain. Although prevalent in nmy-2 knockdown, cytokinesis defects are not the only cause of SC losses. nmy-2 also does not appear to regulate SC divisions by affecting spindle positioning. In summary, nmy-2 function is crucial to ensure the proper division and fate specification in post-embryonic SC development.
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Ricketson, Derek Lee 1980. "Drosophila non-muscle myosin II bipolar filament formation: Importance of charged residues and specific domains for self-assembly." Thesis, University of Oregon, 2009. http://hdl.handle.net/1794/10285.
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xii, 107 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.Non-muscle myosin II generates contractile forces for processes such as cytokinesis, motility, and polarity. Contractility requires assembly of myosin molecules into bipolar mini-filaments through electrostatic interactions between coiled-coil tail domains of the heavy chains. Analyses of myosin II from various organisms have revealed "assembly domains" within the C-terminal portion of the tail domain that mediate filament formation. However, it has been unclear precisely how assembly domains interact with one another, or otherwise contribute to tail-tail interactions, to form the bipolar mini-filament structure. To understand tail domain interactions, we first identified a 90-residue region (1849-1940) of the Drosophila non-muscle myosin II tail domain that was necessary and sufficient for filament formation, using salt-dependent solubility and a novel fluorescence energy transfer assay. We identified residues within this "assembly domain" that were critical for filament assembly by analyzing the effect of point mutations. We found that single point mutations in specific positively charged regions completely disrupt filament assembly. Surprisingly, none of the negatively charged regions within the assembly domain are required for assembly. Most of the mutations in positively charged residues that disrupted filament assembly clustered within a 15-residue segment (1880-1894) that appears to form a critical interaction surface. Using this information, along with known geometrical constraints and electrostatic calculations, we constructed a structural model of the bipolar mini-filament. This model features one favored anti-parallel tail overlap and multiple slightly less stable alternative overlaps. The ability of the positive segment to interact with multiple negative regions explains the lack of required negatively charged residues in the assembly domain. To our knowledge, this structural model of the non- muscle myosin II bipolar filament is consistent with all physical observations and provides a framework for understanding the detailed mechanism by which this fundamental cellular structure is generated. This dissertation contains previously published and unpublished co-authored material.
Committee in charge: Tom Stevens, Chairperson, Chemistry; Kenneth Prehoda, Advisor, Chemistry; J. Andrew Berglund, Member, Chemistry; Christopher Doe, Member, Biology; Karen Guillemin, Outside Member, Biology
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Sarkar, Saheli. "Combined Experimental and Mathematical Approach for Development of a Microfabrication-Based Model to Investigate Cell-Cell Interaction during Migration." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1301420667.
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Messineo, Stefania. "Development of a gene targeting strategy (Recombinase-Mediated CAssette Exchange) to generate cellular models of MYH9-related disease." Doctoral thesis, Università degli studi di Trieste, 2011. http://hdl.handle.net/10077/4603.
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2009/2010La malattia MYH9-correlata (MYH9-RD) è una malattia autosomica dominante, caratterizzata da trombocitopenia congenita con piastrine di grandi dimensioni, aggregati nei neutrofili, sordità progressiva, cataratta e nefropatia. La MYH9-RD è causata da mutazioni nel gene MYH9 che codifica per la catena pesante della miosina non muscolare di classe II (miosina-9). I meccanismi patogenetici che causano questa malattia non sono ancora stati chiaramente identificati e il loro studio è complicato dalla mancanza di adeguati modelli cellulari e animali. Lo scopo di questo progetto è stato di generare un modello in vitro per studiare la funzione della miosina-9 e il ruolo di due mutazioni che incorrono nel gene MYH9: la R702C e la R1933X, che correlano rispettivamente con un fenotipo grave e lieve. Per questo motivo abbiamo deciso di manipolare le cellule staminali embrionali murine (ES), che sono pluripotenti e possono essere differenziate in diversi linee cellulari, compresa la linea megacariocitica. Per ingegnerizzare queste cellule ad alta efficienza abbiamo messo a punto una strategia nota come "scambio di cassette mediato da ricombinasi" (RMCE). Dopo l'integrazione di una cassetta fiancheggiata da siti FRT (sequenze di riconoscimento per l'enzima flippasi), il sistema ci ha permesso di scambiare diverse sequenze di DNA in presenza dell'enzima flippasi. Quindi il primo esone codificante del gene Myh9 è stato distrutto dall'inserimento, mediante ricombinazione omologa, di una cassetta fiancheggiata da due siti FRT contenente il gene reporter Beta-galattosidasi. Successivamente abbiamo scambiato questa cassetta con altre tre contenenti il cDNA Myh9 murino wild-type e i due mutati, generando i cloni ES che esprimono queste sequenze esogene sotto il controllo del promotore Myh9 endogeno. La caratterizzazione a livello dell'RNA e delle proteine di questi cloni ci ha portato a stabilire che gli alleli mutati e wild-type sono espressi allo stesso livello, suggerendo che le manipolazioni genetiche non interferiscono con i corretti meccanismi fisiologici di trascrizione e traduzione del gene Myh9. Tuttavia, mediante Western Blot abbiamo mostrato che la proteina miosina-9 è espressa a livello inferiore nei cloni mutati rispetto ai wild-type. Le analisi di immunofluorescenza per indagare la presenza di aggregati di miosina-9, che sono sempre presenti nei neutrofili di pazienti, non hanno rilevato alcuna variazione nella distribuzione della miosina-9, fatta eccezione per un segnale di intensità minore. Questi risultati indicano che, nonostante l'espressione dell'allele ingegnerizzato sia normale, la proteina mutata sembra essere degradata, almeno nelle cellule ES murine, determinando un effetto di aploinsufficienza delle mutazioni R702C e R1933X. Per accertare la loro pluripotenza, abbiamo differenziato dei cloni ES in corpi embrioidi e cardiomiociti, senza rivelare alcuna differenza tra i cloni mutanti e i wild-type. Dal momento che una caratteristica congenita dei pazienti MYH9-RD è la macrotrombocitopenia, abbiamo sviluppato un protocollo per differenziare i cloni mutati ES in megacariociti per indagare come le mutazioni in MYH9 portino a una impropria produzione di piastrine. In conclusione, per studiare la MYH9-RD abbiamo sviluppato una strategia che ci ha permesso di esprimere sequenze di interesse in cellule ES di topo sotto il controllo del promotore Myh9 endogeno. La differenziazione in vitro di queste cellule ci permetterà di studiare l'effetto delle mutazioni nel corso della megacariocitopoiesi. Inoltre, poiché le cellule ES possono anche essere usate per generare modelli animali, questa strategia ci permetterà di testare diverse ipotesi patogenetiche in vitro, prima di passare a studi in vivo.
XXIII Ciclo
1982
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Adamek, Nancy. "Kinetic properties of slow isoforms of mammalian muscle and non-muscle myosin." Thesis, University of Kent, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516203.
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Hawthorne, Alicia Lynn. "The Development and Regeneration of the Serotonergic System." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1264027000.
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Thomas, Dustin G. "ROLE OF NON-MUSCLE MYOSIN IIB IN BREAST CANCER INVASION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1449156792.
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Flynn, Patrick G. "Activation of Non-Muscle Myosin IIB Helps Mediate TNF-Alpha Cell Death Signaling." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/369.
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TNF-alpha can stimulate a variety of kinases with the ability to activate non-muscle myosin II. As a result, increases in actin filament formation and actomyosin contractility (AMC) have been reported in response to TNF-alpha. These events are thought to play an important role in mediating TNF-alpha induced apoptosis but how they do so is unclear. In this study we prevented non-muscle myosin II activation in response to TNF-alpha by treating cells with the myosin light chain kinase (MLCK) inhibitor ML-7 or through isoform specific siRNA knockdown of myosin IIA and IIB. We found that treatment with ML-7 or knockdown of myosin IIB, but not IIA, impaired the cleavage of caspase 3 and caspase 8 as well as nuclear condensation in response to TNF-alpha. During this cell death process myosin II seemed to function independent of AMC since treatment of cells with blebbistatin or cytochalasin D failed to inhibit TNF-alpha induced caspase cleavage. Immunoprecipitation studies revealed associations of myosin IIB with clathrin and FADD in response to TNF-alpha suggesting a role for myosin IIB in TNFR1 endocytosis and DISC formation. Taken together these findings suggest that myosin IIB activation promotes TNF-alpha cell death signaling in a manner independent of its force generating property.
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Irvine, Andrew Francis. "Characterising the interaction between metastasis-associated protein S100A4 and non-muscle myosin IIA in vitro and in vivo." Thesis, University of Leicester, 2012. http://hdl.handle.net/2381/27622.
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S100A4 is a member of the S100 family of proteins and increases the motility of many cell types. This is also thought to explain its association with the epithelial-mesenchymal transition (EMT), a developmental program re-activated during tumourigenesis. Mechanistically, S100A4 interacts with a number of targets including Smad3 and liprin-β1; however, the best characterised is non-muscle myosin IIA (NMIIA) which regulates many aspects of the cytoskeleton. There is a large body of in vitro data indicating that S100A4 promotes the monomeric state of NMIIA; however, in vivo evidence for the interaction in cells is lacking. Accordingly, the first aim of this study was to determine if S100A4 interacts with, and promotes the monomeric state of NMIIA in A431 cells undergoing SIP1-induced EMT. Intriguingly, co-localisation analysis of S100A4 and NMIIA in A431-SIP1 cells using immunoelectron microscopy indicated that NMIIA is present in a folded, 10S state, and unfolded 6S state, and S100A4 interacts with both. This represents the first evidence of 10S and 6S states of NMIIA in non-muscle cells. In addition, FRAP analysis demonstrated that cells with attenuated expression of S100A4 turned over NMIIA with a slower rate, consistent with S100A4 promoting the monomeric state. The second part of the study explored the mechanism of the S100A4-NMMIA interaction. In vitro analysis of phosphomimetic S1916D and S1943D NMIIA showed no differences in binding affinity with S100A4 compared to WT NMIIA, contrary to the published literature. Based on the NMR structure of S100A4 and NMIIA, V77 and C81 were identified as key S100A4 residues that mediated the interaction with NMIIA. Mutation of these sites abolished the interaction with NMIIA, an effect reflected in null-phenotypes for both proteins when over-expressed in A431 cells compared to WT S100A4. In conclusion, this study suggests S100A4 is an important regulator of NMIIA dynamics in cells.
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Persson, Malin. "Characterization and optimization of the in vitro motility assay for fundamental studies of myosin II." Doctoral thesis, Linnéuniversitetet, Institutionen för kemi och biomedicin (KOB), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-25241.
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Myosin II is the molecular motor responsible for muscle contraction. It transforms the chemical energy in ATP into mechanical work while interacting with actin filaments in so called cross-bridge cycles. Myosin II or its proteolytic fragments e.g., heavy meromyosin (HMM) can be adsorbed to moderately hydrophobic surfaces in vitro, while maintaining their ability to translocate actin filaments. This enables observation of myosin-induced actin filament sliding in a microscope. This “in vitro motility assay” (IVMA) is readily used in fundamental studies of actomyosin, including studies of muscle contraction. The degree of correlation of the myosin II function in the IVMA with its function in muscle depends on how the myosin molecules are arranged on the surface. Therefore a multi-technique approach, including total internal reflection spectroscopy, fluorescence interference contrast microscopy and quartz crystal microbalance with dissipation, was applied to characterize the HMM surface configurations. Several configurations with varying distributions were identified depending on the surface property. The most favorable HMM configurations for actin binding were observed on moderately hydrophobic surfaces. The effects on actomyosin function of different cargo sizes and amount of cargo loaded on an actin filament were also investigated. No difference in sliding velocities could be observed, independent of cargo size indicating that diffusional processive runs of myosin II along an actin filament are not crucial for actomyosin function in muscle. Furthermore, a tool for accurate velocity measurements appropriate for IVMAs at low [MgATP] was developed by utilizing the actin filament capping protein CapZ. These improvements allowed an investigation of the [MgATP]-velocity relationship to study possible processivity in fast skeletal muscle myosin II. It is shown that the [MgATP]–velocity relationship is well described by a Michaelis-Menten hyperbola. In addition, statistical cross-bridge modeling showed that the experimental results are in good agreement with recent findings of actomyosin cross-bridge properties, e.g., non-linear cross-bridge elasticity. However, no effect of inter-head cooperativity could be observed. In conclusion, the described results have contributed to in-depth understanding of the actomyosin cross-bridge cycle in muscle contraction.
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Zepter, Valeria Lamounier. "Analyse der Funktion der nichtmuskulären schweren Myosinketten in glatten Muskelzellen." Doctoral thesis, Humboldt-Universität zu Berlin, Medizinische Fakultät - Universitätsklinikum Charité, 2003. http://dx.doi.org/10.18452/14837.
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Das Ziel dieser Studie war es, die Beteiligung der nichtmuskulären schweren Myosinketten an der Kontraktion der glatten Muskeln unter physiologischen Bedingungen zu untersuchen. Als Versuchsmodell wurde die Harnblase von neugeborenen Wildtyp und transgenen Mäusen verwendet, bei denen das Gen für die glattmuskelspezifischen schweren Myosinketten durch "Gene Targeting" funktionell eliminiert wurde (Knock-Out). Das Fehlen der Expression der glattmuskelspezifischen schweren Myosinketten wurde durch Elektrophorese und Immunfärbung bestätigt. Im Gegensatz dazu blieb die Expression der nichtmuskulären schweren Myosinketten unverändert. Die mechanische Analyse des glatten Muskels wurde mit intakten Muskelpräparaten aus der Harnblase durchgeführt. Das Muskelpräparat wurde in KCl-Lösung oder mit Phorbolester stimuliert. Die Aktivierung mittels depolarisierender KCl-Lösung führte bei neugeborenen Wildtyp Mäusen zuerst zu einer transienten Kontraktion (Phase 1) mit hoher Kraftentwicklung und maximaler Verkürzungsgeschwindigkeit, und danach zu einer tonischen Kontraktion (Phase 2) mit niedrigerer Kraftentwicklung und maximaler Verkürzungsgeschwindigkeit. Blasenpräparate neugeborener Knock-Out Mäuse dagegen zeigten keine Phase 1, sondern nur eine tonische Kontraktion, die mit Wildtyp Mäusen vergleichbar war. Daher scheint nichtmuskuläres Myosin an der tonischen Kontraktion des glatten Muskels beteiligt zu sein. Durch Stimulierung mit Phorbolester waren ähnliche tonische Muskelkontraktionen der Blasenpräparate sowohl bei Wildtyp als auch bei Knock-Out Mäusen zu beobachten. Vermutlich wird also das nichtmuskuläre Myosin durch Stimulierung mit Phorbolester aktiviert. Intrazelluläre Filamente wurden durch Immunfluoreszenz mit einem spezifischen Antikörper gegen nichtmuskuläre schwere Myosinketten in kultivierten primären glatten Muskelzellen untersucht. Dabei zeigten die Muskelzellen sowohl von Wildtyp als auch von Knock-Out Mäusen intrazelluläre dicke Myosinfilamente, was für die Beteiligung des nichtmuskulären Myosins an der glatten Muskelkontraktion spricht. Entsprechend wurden intrazelluläre Filamente mit einem Antikörper gegen glattmuskelspezifische schwere Myosinketten in kultivierten primären glatten Muskelzellen untersucht. Wie erwartet, konnten nur in glatten Muskelzellen von Wildtyp Mäusen intrazelluläre Filamente nachgewiesen werden, nicht aber in denen von Knock-Out Mäusen. In dieser Arbeit konnte zum ersten Mal gezeigt werden, dass nichtmuskuläres Myosin zumindest an der tonischen Kontraktion glatter Muskelzellen beteiligt sein kann.The aim of the present study was to investigate the involvement of non-muscle myosin heavy chain in smooth muscle contraction under physiological conditions. As an experimental model urinary bladder from neonatal wild-type mice as well as from neonatal mice with disrupted smooth muscle myosin heavy chain expression was used. This animal model was established through gene targeting technology, resulting in complete elimination of the expression of smooth muscle myosin heavy chains. The lack of expression of smooth muscle myosin heavy chains was confirmed by electrophoresis and immunoblotting. On the other hand, non-muscle myosin heavy chain expression remained normal, as verified by Western blot analysis. The mechanical analysis of smooth muscle was performed with intact urinary bladder preparations, stimulated using prolonged KCl depolarization or with phorbol ester. Prolonged activation by KCl depolarization of intact bladder preparations from wild-type neonatal mice produced an initial transient state (phase 1) of high force generation and maximal shortening velocity, followed by a sustained state (phase 2) with lower force generation and maximal shortening velocity. In contrast, bladder preparations from homozygous knockout neonatal mice did not exhibit phase 1, but phase 2 could be observed, i.e. a similar isometric force and maximal shortening velocity, compared to wild-type phase 2. Thus, non-muscle myosin appears to be recruited in the sustained phase of smooth muscle contraction during prolonged KCl depolarization in the animal model used. Upon stimulation with phorbol ester a similar sustained contraction was observed in both wild-type and knockout smooth muscle preparations. Therefore, non-muscle myosin may also be recruited during phorbol ester stimulation in both wild-type and knockout muscle preparations. The participation of non-muscle myosin in smooth muscle contraction was further supported by the finding of longitudinally arranged intracellular filaments in cultivated smooth muscle cells from both wild-type and knockout mice by immunofluorescence microscopy, using a specific antibody raised against non-muscle myosin heavy chain. In a similar way, smooth muscle myosin heavy chain structures were investigated in cultivated smooth muscle cells. As expected, longitudinally arranged intracellular filamentous structures of smooth muscle myosin were observed in wild-type smooth muscle cells, but not in smooth muscle cells from knockout mice. In conclusion, in neonatal smooth muscle the initial phase of contraction elicited by KCl depolarization is generated by smooth muscle myosin heavy chain recruitment. Upon prolonged KCl depolarization non-muscle myosin is recruited in the sustained phase of contraction, as well as upon stimulation with phorbol ester. Thus, it was possible, for the first time, to verify the involvement of the non-muscle myosin in smooth muscle contraction in vivo. The results of the present study contribute to the understanding of the regulatory mechanisms of smooth muscle contraction.
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Höök, Peter. "A novel single skeletal muscle cell in vitro motility assay : effects of aging and non-enzymatic glycosylation on myosin function /." Stockholm, 2001. http://diss.kib.ki.se/2001/91-628-4688-4/.
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Zehrer, Annette [Verfasser], and Barbara [Akademischer Betreuer] Walzog. "The non-muscle myosin heavy chain Myh9 is essential for neutrophil migration during acute inflammation / Annette Zehrer ; Betreuer: Barbara Walzog." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1206878126/34.
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Matsunaga, Erika Midoli. "Distribuição do tipo de fibras musculares e sua correlação genotípica na doença de Pompe." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/5/5138/tde-29042009-102848/.
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A doença de Pompe (GSDII), autossômica recessiva, é causada pela deficiência da enzima lisossomal que degrada o glicogênio, -glucosidase ácida (GAA). O quadro clínico varia de acordo com a idade de início da doença, grau de progressão e envolvimento dos tecidos: predominantemente cardíaco e muscular esquelético na forma de início-precoce (FIP) e mais restrito no músculo esquelético na forma de início-tardio (FIT). A sobrevida média na FIP é de 9-12 meses. Com avanço dos métodos histológicos, histoquímicos e imunoistoquímicos intensificou-se a análise estrutural e funcional dos tipos de fibras musculares. O estudo da vascularização também é de importância pelo aporte nutricional e funcional das fibras. O objetivo do presente trabalho é analisar a correlação da distribuição do tipo de fibras com a forma de apresentação clínica da doença de Pompe, seu genótipo correspondente e a quantidade residual da enzima GAA. Analisou-se 10 biópsias musculares de pacientes FIP e 09 de FIT comparados com o grupo controle, pareados por idade e gênero. Os pacientes foram selecionados segundo dados clínicos e laboratoriais, sendo feito o seqüenciamento de toda parte codificante do gene e Western Blotting (WB) com anticorpo monoclonal 15362-157, cedido pela Genzyme (primário 1:200 e secundário 1:10.000). A confirmação do diagnóstico foi feita através da medida da atividade residual de GAA em papel filtro, da presença de miopatia vacuolar com grânulos PAS e fosfatase ácida positivos em biópsia muscular e pela presença de mutação no gene GAA. A reação de imunoistoquímica foi realizada para fibras tipo I (lenta), tipo II (rápida) e densidade capilar (ulex), utilizando anticorpos monoclonais, respectivamente: antimiosina lenta (1:80), anti-miosina rápida (1:40) da Novocastra e ulex da Vector (1:800). A contagem das fibras foi realizada por 2 observadores em todo fragmento do corte transversal da biópsia com auxílio de um programa semi-automatizado. Observou-se predomínio de fibras tipo II em ambos os gêneros na FIP e predomínio de fibras tipo I em mulheres e tipo II em homens, na FIT. Aumento da densidade capilar, em comparação com os controles, foi notada em ambas as formas IP e IT. Verificou-se em média 90% de fibras vacuoladas nos casos FIP com completa distorção da arquitetura, enquanto na FIT, a porcentagem de fibras vacuoladas foi variável (0-88%). Como alguns genes constitutivos influenciam na distribuição das fibras musculares, como o gene ACE, o polimorfismo deste gene foi analisado quanto aos genótipos I/I, D/D e I/D. Observou-se ausência de concordância entre o genótipo do ACE e a distribuição de fibras em 60% dos casos da FIP e FIT, atribuindo-se o resultado da distribuição do tipo de fibras como parte da patologia da doença de Pompe. A gravidade da doença variou inversamente com a quantidade de enzima residual, sendo compatível com o quadro clínico do paciente. A presença de mutação deletéria em ambos os alelos foi observada em 3/10 casos de IP, sendo que todos os 3 casos apresentaram ausência total de enzima no WB. Há maior envolvimento de fibras tipo II em GSDII, sem depleção da microcirculação muscular. Estudos demonstram que a remoção do depósito de glicogênio ocorre diferencialmente nos tipos de fibra, sendo menos eficiente nas fibras tipo II. O achado do presente estudo poderá ter implicações na resposta à recente terapêutica proposta por reposição enzimática.The glycogen storage disease type II (GSDII), autosomal recessive disorder, is caused by the deficiency of GAA (acid -glucosidase) a lysossomal enzyme that degrades the glycogen. The clinical findings are in accordance to great variability of age onset, degree of disease progression and extent of tissue involvement: predominantly cardiac and skeletal muscle in the infantile form (I) and more restricted to the skeletal muscle in the late-onset form (LO). The average survival time of the infantile form is 9-12 months. With advances of the histological, histochemical and imunohistochemical methods structural and functional analysis of muscle fiber types were intensified. The study of the capillary density is also important for nutritional and functional aspects. The objective of the present work is to analyze the correlations of the fiber type distribution to clinical presentation, genotype and residual GAA enzymatic activity. We analyzed 10 muscle biopsies of infantile and 09 of late-onset patients and compared to age and gender matched controls. The patients were selected according to clinical and laboratorial data, molecular diagnosis by full gene sequencing, and Western Blotting (WB) with monoclonal antibody 15362-157, courtesy Genzyme Science Group (primary 1:200 and secondary 1:10.000). Diagnostic confirmation was made by GAA enzymatic measurement in DBS, presence of vacuolar myopathy in muscle biopsy, and presence of mutation in GAA gene. The imunohistochemical study was carried out by detection of type I (slow), type II (fast) fibers and capillaries, using monoclonal antibodies, respectively: anti-slow myosin (1:80), anti-fast myosin (1:40) (Novocastra) and ulex (1:800) (Vector). Morphometry was performed by 2 observers using a half-automatized program. Type II fiber predominance was observed in both gender in the infantile form, type I fiber predominance in women and type II predominance in men with LO. Increase of the capillary density, in comparison to controls was noticed in both forms. 90% of vacuolated fibers with complete distortion of fiber architecture were demonstrated in I cases, while in LO, the percentage of vacuolated fibers ranged from 0 to 88%. As some constitutive gene, like ACE, influence muscle fiber distribution, its polymorphisms I/I, D/D and I/D gene were analyzed. Absence of agreement was observed between ACE genotype and fiber type distribution in 60% of I and LO cases, which was attributed as consequence of Pompe disease pathology itself. The disease severity varied inversely to the amount of residual GAA enzymatic activity, being compatible with the patient clinical findings. The presence of deleterious mutation in both alleles was observed in 3/10 infantile cases, and all 3 presented total enzyme absence at WB. A greater fiber type II involvement was observed in GSDII, without decrease in muscle capillary density. Recent studies demonstrated that glycogen deposit removal occurs distinctively in different fiber types, being less efficient in type II fibers. The present findings might have implications in the reply to the recent proposed enzyme replacement therapy.
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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 pathologiesThis 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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Borges, Ricardo Moraes. "Constrição celular apical durante a invaginação do placóide do cristalino em galinhas." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/42/42134/tde-24032009-100332/.
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O cristalino de vertebrados se origina a partir da invaginação do ectoderme que recobre a vesícula óptica. A invaginação epitelial em diversos modelos é causada pela constrição celular apical, mediada pela contração apical de actina e miosina II e regulada pela GTPase RhoA. Neste trabalho nós investigamos se a invaginação do cristalino em embriões de galinha ocorre devido à constrição celular apical e se este evento é controlado por RhoA. Actina filamentosa e miosina II são expressas na porção apical do cristalino durante a invaginação. Quando a polimerização de actina é inibida por Citocalasina D, o cristalino não invagina, sugerindo que a constrição celular apical poderia contribuir para a invaginação do cristalino. RhoA também é expressa durante o desenvolvimento do cristalino, mas a inibição de RhoA, por eletroporação da forma dominante-negativo, não impediu a invaginação do placóide do cristalino, não alterou a distribuição de miosina II na porção apical do cristalino nem sua ativação, indicando que a invaginação do cristalino independe de RhoA.Vertebrate lens derives from invagination of the ectoderm that overlies optic vesicles. Epithelial invagination in many model systems is driven by apical cell constriction, mediated by actin and myosin II contraction regulated by GTPase RhoA. Here we investigate the possibility that chick lens placode invagination could also be driven by apical cell constriction and controlled by RhoA. We show that actin and myosin II are expressed at lens apical side during lens invagination. Actin polymerization inhibition by in ovo Cytochalasin D treatment prevents lens placode invagination, suggesting that lens placode invagination could be driven by apical cell constriction. RhoA GTPase is also expressed at apical portion of lens placode and during lens invagination. However, when we overexpressed by electroporation the dominant-negative RhoA in the pre-lens ectoderm invagination was not affected. Furthermore, dominant-negative RhoA didnt affect myosin II apical localization nor myosin II phosphorilation, indicating that in lens invagination this process is not regulated by GTPase RhoA.
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Schulz, Cathrin. "Tumour-selective apoptosis : identification of NMHCIIa as novel death receptor interactor regulating the response to TRAIL." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-01069133.
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The cytokine TRAIL is a promising cancer therapeutic candidate as it induces apoptosis selectively in transformed cells. TRAIL-induced clustering of its receptors (DR) is essential for the DISC complex formation, which induces cell death. The mechanism for TRAIL's tumour selective effect is largely unknown. We identified the cytoskeleton proteins non-muscle myosin heavy chain IIa, IIb (NMHCIIa, NMHCIIb), myosin regulatory light chain (MLC2) and ß-actin as novel DR-interactors. An initially weak and TRAIL-induced abrogation of NMHCII/DR interaction correlated with efficient DISC formation in tumour cells. In contrast, a robust NMHCII/DR interaction that was sustained upon TRAIL stimulus was accompanied by incomplete DISC arrangement. Weakening the NMHCII/DR interaction in normal cells using chemical inhibitors enhanced TRAIL-induced apoptosis. Intriguingly, siRNA-mediated NMHCIIa- but not NMHCIIb depletion potently released TRAIL resistance in normal cells and influenced DISC composition. Reduced NMHCII/DR interaction in transformed cells was characterised by diminished MLC2 phosphorylation and altered protein expression of upstream regulatory kinases. Our results suggest that normal cell resistance to TRAIL-apoptosis is based on the interaction of cytoskeleton components with DR that is impaired upon transformation. Since NMHCII function in cell adhesion and migration, it will be interesting to study possible roles of the interaction in cell detachment and altered TRAIL sensitivity; moreover this link may provide clues as to the cause of TRAIL resistance in some cancers.
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Rao, Yanhua. "An Atat1/Mec-17-Myosin II axis controls ciliogenesis." Diss., 2013. http://hdl.handle.net/10161/7224.
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Primary cilia are evolutionarily conserved, acetylated microtubule-based organelles that transduce mechanical and chemical signals. Primary cilium assembly is tightly controlled and its deregulation causes a spectrum of human diseases. Formation of primary cilium is a collaborative effort of multiple cellular machineries, including microtubule, actin network and membrane trafficking. How cells coordinate these components to construct the primary cilia remains unclear. In this dissertation research, we utilized a combination of cell biology, biochemistry and light microscopy technologies to tackle the enigma of primary cilia formation, with particular focus on isoform-specific roles of non-muscle myosin II family members. We found that myosin IIB (Myh10) is required for cilium formation. In contrast, myosin IIA (Myh9) suppresses cilium formation. In Myh10 deficient cells, Myh9 inactivation significantly restores cilia formation. Myh10 antagonizes Myh9 and increases actin dynamics, permitting pericentrosomal preciliary complex formation required for cilium assembly. Importantly, Myh10 is upregulated upon serum starvation-induced ciliogenesis and this induction requires Atat1/Mec-17, the microtubule acetyltransferase. Our findings suggest that Atat1/Mec17-mediated microtubule acetylation is coupled to Myh10 induction, whose accumulation overcomes the Myh9-dependent actin cytoskeleton, thereby activating cilium formation. Thus, Atat1/Mec17 and myosin II coordinate microtubules and the actin cytoskeleton to control primary cilium biogenesis.
Dissertation
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Patino, Descovich Carlos. "Characterizing cortical myosin mini-filament regulation, length and its macroscopic implications in cytokinetic dynamics." Thèse, 2013. http://hdl.handle.net/1866/11328.
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PERCARIO, VALENTINA. "A study of the mechano-kinetic parameters of different isoforms of muscle myosin II in vivo." Doctoral thesis, 2017. http://hdl.handle.net/2158/1079340.
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The performance of skeletal muscles contracting in isometric conditions or actively shortening against an external load exhibits a large variability: parameters such as speed of isometric force development, unloaded shortening velocity, maximum power output and ATPase activity vary from one muscle to the other according to the functional tasks of muscles. Muscles involved in maintenance of posture develop low power (low shortening speed for a given load) consuming ATP at low rate, while muscles involved in movement develop high power (high shortening speed for a given load) consuming ATP at high rate, whereas the efficiency of energy conversion is similar in both muscle types. The different biochemical and mechanical performances are attributed to the myosin heavy chain (MHC) isoform expressed in skeletal muscle: muscles responsible for the maintenance of posture (slow muscles) mostly contain fibres expressing the slow MHC isoform while those involved in movement (fast muscles) mostly contain fibres expressing the fast MHC isoform. The work described in this thesis is aimed at investigating in situ the mechanical and kinetic bases of the functional diversity of the isoforms of the myosin motor present in slow skeletal muscles in terms of both the properties of the single motor and of the motor ensemble in the half-sarcomere. For this the mechanical parameters of the myosin motor (force, stiffness and size and speed of the working stroke) and of the motor ensemble (number of motors attached to actin, kinetics underlying both the rate of isometric force development and the force-velocity relation) have been determined in demembranated fibres from a slow skeletal muscle of the rabbit, the soleus, and compared to those from a fast muscle, the psoas. Apart the ten time slower kinetics of both the working stroke and the motor
attachment-detachment rates, the most relevant finding is that the slow myosin isoform has a three time smaller stiffness and develops a correspondingly three time smaller force than the fast isoform. In terms of a myosin-actin interaction model with a tight coupling between mechanical and biochemical steps, in contrast to the data in the literature, this finding predicts a three times smaller efficiency in energy conversion in the slow muscle. These results suggest that the stiffness of the myosin motor is a determinant of the isoform-dependent functional diversity between skeletal muscle types and opens the question on the molecular mechanism for the high efficiency of the slow muscle.
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Santos, Marina Patrícia Fonseca. "Identification of novel non-muscle myosin IIA (NMIIA) interacting partners." Master's thesis, 2013. https://repositorio-aberto.up.pt/handle/10216/70448.
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Santos, Marina Patrícia Fonseca. "Identification of novel non-muscle myosin IIA (NMIIA) interacting partners." Dissertação, 2013. https://repositorio-aberto.up.pt/handle/10216/70448.
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Vaqueirinho, Daniela Helena da Ascenção Loureiro Geraldo. "The role of Arl13b and the non-muscle myosin IIA in cancer cell migration." Master's thesis, 2017. http://hdl.handle.net/10362/26412.
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Tsai, Hsiao-Chu, and 蔡効矩. "Using an optogenetic platform (CRY2/CIB1) to study the interaction between non-muscle myosin MYH9 and microtubules." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/hkgbda.
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碩士國立交通大學
分子醫學與生物工程研究所
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Growth cone is a highly motile structure in developing neuron. It detects different axon guidance cues, which is known to attract or repel axons growth. These guidance molecules accomplish this by changing the structure of neuronal cytoskeleton, which leads to neurite extension or retraction. Migrating cells exist similar structure called leading edge. It responds to extracellular cues to polarize and extend protrusions in the direction of migration. While the protein molecules involved in these processes have been identified, the precise mechanism remains unknown. MYH9 is an ubiquitously expressed non-muscle myosin that localizes to the leading edge and affect neurite outgrowth and cell migration. It has been shown that microtubules and F-actin transiently interact with each other in the growth cone. However, the protein mediating such interaction remains elusive. Our recent observation that MYH9 and microtubules interact with each other prompts us to investigate whether MYH9 is mediating such interaction and whether this interaction is the mechanism of neurite retraction and cell migration. To test this hypothesis, we set up a system that can artificially induce the interaction between microtubules and MYH9, and use this system to investigate whether microtubule-MYH9 interaction can affect neurite retraction and cell migration. However, we did not observe a stronger interaction between MYH9 and microtubules during neurite retraction, and the data in migration cells did not show any effect about cell migration after artificially induce the interaction between microtubules and MYH9.
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Goloborodko, Alexander. "Molecular Mechanisms of Germ Plasm Anchoring in the Early Zebrafish Embryo." Doctoral thesis, 2019. http://hdl.handle.net/21.11130/00-1735-0000-0005-145A-0.
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Solinet, Sara. "Les rôles distincts des isoformes de myosine II non-musculaire dans des processus cellulaires impliquant le cytosquelette d'actine." Thèse, 2008. http://hdl.handle.net/1866/2852.
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Le complexe actomyosine, formé de l’association de la myosine II avec les filaments d’actine, stabilise le cytosquelette d’actine et génère la contraction cellulaire nécessaire à plusieurs processus comme la motilité et l’apoptose dans les cellules non-musculaires. La myosine II est un hexamère formé d’une paire de chaînes lourdes (MHCs) et de deux paires de chaînes légères MLC20 et MLC17. La régulation de l’activité de la myosine II, c'est-à-dire son interaction avec les filaments d’actine, est directement liée à l’état de phosphorylation des MLC20, mais il reste beaucoup à découvrir sur l’implication des MHCs. Il existe trois isoformes de MHCs de myosine II, MHCIIA, MHCIIB et MHCIIC qui possèdent des fonctions à la fois communes et distinctes. Notre but est de mettre en évidence les différences de fonction entre les isoformes de myosine II, au niveau structurale, dans la stabilisation du cytosquelette d’actine, et au niveau de leur activité contractile, dans la génération des forces de tension.
Nous nous sommes intéressés au rôle des isoformes des MHCs dans l’activité du complexe actomyosine qui est sollicité durant le processus de contraction cellulaire de l’apoptose. Dans quatre lignées cellulaires différentes, le traitement conjoint au TNFα et à la cycloheximide causait la contraction et le rétrécissement des cellules suivi de leur détachement du support de culture. Par Western blot, nous avons confirmé que la phosphorylation des MLC20 est augmentée suite au clivage de ROCK1 par la caspase-3, permettant ainsi l’interaction entre la myosine II et les filaments d’actine et par conséquent, la contraction des cellules apoptotiques. Cette contraction est bloquée par l’inhibition des caspases et de ROCK1. MHCIIA est dégradée suite à l’activation de la caspase-3 alors que MHCIIB n’est pas affectée.
En utilisant une lignée cellulaire déficiente en MHCIIB, ou MHCIIB (-/-), nous avons observé que la contraction et le détachement cellulaires durant l’induction de l’apoptose se produisaient moins rapidement que dans la lignée de type sauvage (Wt) ce qui suggère que l’isoforme B est impliquée dans la contraction des cellules apoptotiques. Parallèlement, la kinase atypique PKCζ, qui phosphoryle MHCIIB et non MHCIIA, est activée durant l’apoptose. PKCζ joue un rôle important puisque son inhibition bloque la contraction des cellules apoptotiques.
Par la suite, nous nous sommes intéressés à la modulation de la morphologie cellulaire par la myosine II. Les fibroblastes MHCIIB (-/-), présentent un large lamellipode dont la formation semble dû uniquement à l’absence de l’isoforme MHCIIB, alors que les fibroblastes Wt ont une morphologie cellulaire étoilée. La formation du lamellipode dans les fibroblastes MHCIIB (-/-) est caractérisée par l’association de la cortactine avec la membrane plasmique. L’observation en microscopie confocale nous indique que MHCIIA interagit avec la cortactine dans les fibroblastes Wt mais très peu dans les fibroblastes MHCIIB (-/-). Le bFGF active la voie des MAP kinases dans les fibroblastes Wt et MHCIIB (-/-) et induit des extensions cellulaires aberrantes dans les fibroblastes MHCIIB (-/-). Nos résultats montrent que l’implication de l’isoforme B de la myosine II dans la modulation de la morphologie cellulaire.
L’ensemble de nos résultats participe à distinguer la fonction structurale et contractile de chacune des isoformes de myosine II dans la physiologie cellulaire.We are interested in studying the modulation of the actomyosin complex which is involved in different cellular processes such as cell locomotion and apoptosis. The actomyosin complex is formed by the association of actin filaments and myosin II. The non-muscle myosin II is a hexamer formed by one pair of heavy chains (MHCs) and two pairs of light chain (MLC20 and MLC17). The actomyosin activity is dependent on MLC20 and MHCs phosphorylation. There are three isoforms of MHCs (MHCIIA, MHCIIB and MHCIIC) which have common but also distinctive roles in several cellular processes. Our aim is to clarify the structural and contractile functions of each isoforme of myosin II in different cellular processes, in particular, cell contraction and cell morphology. First, we studied the implication of myosin II isoforms in cell shrinkage and detachment during apoptosis which are both dependent on actomyosin contractility. We treated four different cell lines with TNFα in combination with cycloheximide (CHX) to trigger apoptosis. We confirmed that TNFα induced caspase-3 activation, ROCK1 cleavage and increased MLC20 phosphorylation. We showed that TNFα/CHX induced the caspase-dependent MHCIIA degradation, whereas MHCIIB levels and association with the actin cytoskeleton remained virtually unchanged. Cell shrinkage and detachment were blocked by caspase and ROCK1 inhibitors. Using the MHCIIB (-/-) cell line, we observed that the absence of MHCIIB did not affect cell death rate. However, MHCIIB (-/-) fibroblasts showed more resistance to TNFα-induced actin disassembly, cell shrinkage and detachment than wild type (Wt) fibroblasts, indicating the participation of MHCIIB in these events. PKCζ, which only phosphorylates MHCIIB, was cleaved during apoptosis, co-immunoprecipitated preferentially with MHCIIB and, interestedly, PKCζ inhibition blocked TNFα-induced shrinkage and detachment. Our results demonstrate that MHCIIB, together with MLC phosphorylation and actin, constitute the actomyosin cytoskeleton that mediates contractility during apoptosis. Second, we studied the involvement of myosin II isoforms in cell shape modulation. Fibroblasts MHCIIB (-/-) spontaneously formed lamellipodia whereas Wt fibroblasts presented a stellate shape. Cortactin was associated with the leading edge of lamellipodia in MHCIIB (-/-) fibroblasts, but it localised diffusely in the cytoplasm or at the end of fine cellular projections in Wt fibroblasts. The levels of cortactin and cortactin phosphorylated in Tyr421 associated with membrane in MHCIIB (-/-) fibroblasts were higher than in Wt fibroblasts. Confocal microscopy showed cortactin/MHCIIA colocalization in wild type but not in MHCIIB (-/-) fibroblasts. bFGF activates Erk1/2 in wild type and MHCIIB (-/-) fibroblasts and induces the formation of aberrant membrane projections in MHCIIB (-/-) fibroblasts. In conclusion, our results contribute to characterize the structural and contractile role of each myosin II isoforms in the physiology of the cell.