Lors d’une blessure, les cellules migrent et prolifèrent collectivement pour rétablir la continuité de l’épithélium. En migrant, les cellules exercent des forces entre elles ainsi que sur le substrat et de nombreuses études suggèrent un couplage mécanique entre la migration et la prolifération. Récemment découvert, le cofacteur de transcription Yap (Yes-associated protein) est régulé par des signaux mécaniques. L’activation de YAP se traduit par sa rétention nucléaire et augmente la prolifération cellulaire. D’un point de vue mécanique, l’engagement des intégrines dans les adhésions focales, l’aire d’étalement des cellules et la contractilité de l’actomyosine activent YAP. Au contraire, l’engagement des cadhérines dans les jonctions intercellulaires inhibent Yap. A ce jour, les contributions respectives des contacts cellulaires et de l’actomyosine pour la régulation de Yap de de la prolifération restent inexplorées.Au cours de cette thèse, nous nous sommes intéressés au rôle des adhésions au substrat, des jonctions cellule-cellule, du cytosquelette d’actomyosine et de la tension mécanique inter- et intracellulaire sur l’activation de YAP et sur la prolifération cellulaire pendant la cicatrisation épithéliale.D’abord, nous avons étudié le rôle de l’étalement cellulaire et des forces transmises par les contacts cellule-substrat sur la régulation de la localisation de Yap. En confinement sur des motifs adhésifs micro-fabriqués, les kératinocytes humains (HaCaT) adoptent un mouvement collectif oscillatoire. En combinant la vidéomicroscopie, la microscopie à force de traction (TFM) et l’analyse quantitative d’images, nous avons d’abord montré que la migration des cellules est alternativement divergente et convergente ce qui régule l’étalement des cellules. Nous avons ensuite montré que l’étalement d’une cellule est corrélé aux forces de traction sur le substrat et à la relocalisation nucléaire de Yap. Bien qu’ils soient encore préliminaires, ces résultats suggèrent que Yap est régulé par les forces transmises au contacts cellule-substrat pendant la migration épithéliale.Ensuite, nous nous sommes intéressés à la régulation de Yap et de la prolifération cellulaire pendant la migration épitheliale en absence de contacts cellule-substrat. Pour cela, nous avons forcé la migration de monocouches de cellules HaCaT sur des bandes adhérentes séparées de bandes cytorépulsives. Lorsqu’elles migrent sur les bandes adhérentes, les cellules HaCaT étendent une couche de cellules suspendues au-dessus des bandes cytorépulsives. Les cellules suspendues sont cohésives entre elles mais n’interagissent pas avec le substrat. Dans le feuillet de cellules suspendues, les fibres de stress d’actine se réorganisent à l’échelle du tissu grâce au renforcement des contacts cellule-cellule et la contractilité est augmentée. Ce modèle est le premier qui permet de découpler la contractilité de l’actomyosine et les adhésions cellule-substrat pendant la migration épithéliale. Malgré l’augmentation des contraintes d’étirement, l’absence de contacts cellule-substrat empêche la localisation nucléaire de YAP et inhibe la prolifération des cellules suspendues. En conclusion, l’engagement de contacts cellule-substrat sont nécessaires à la localisation nucléaire de Yap et à l’augmentation de la prolifération pendant la cicatrisation épithéliale in vitro.Ces travaux démontrent que les forces de traction sur le substrat sont associées à la localisation nucléaire de Yap et à l’augmentation de la prolifération pendant la migration épithéliale in vitro / After a wound, cells both migrate and proliferate collectively to restore epithelial continuity and to heal the wound. While migrating, cells exert forces on the substrate and pull on each other. Several previous studies suggest a mechanical coupling between collective cell migration and proliferation. Recently discovered, the transcription co-factor Yap (Yes-associated protein) is regulated by mechanical signal. Yap activation induces its nuclear retention and cell cycle progression. Integrin engagement on cell-substrate contacts, cell spreading and actin contractility are related to Yap activation. In turn, cadherin engagement and forces in cell-cell contacts induces Yap nuclear exclusion and reduce cell proliferation. Integrins and cadherins anchor actomyosin cytoskeleton and to date, and the respective contributions of cell-substrate adhesions, cell-cell junctions and actin cytoskeleton on regulation Yap and cell proliferation remain unexplored.In this thesis, we interested in the role of substrate adhesions, cell-cell junctions, actomyosin cytoskeleton and cell mechanical loading on Yap activation and cell proliferation during epithelial wound healing.First, we aim to understand the role of cell spreading and mechanical loading of cell-substrate contacts on the regulation of Yap localisation. Confined on microfabricated adhesive patterns, human keratinocytes HaCaT adopt an oscillatory collective motion. Combining videomicroscopy, traction force microscopy (TFM) and quantitative image analysis, we show that collective cell movements are alternatively divergent and convergent which regulate local cell spreading. Then, we show that cell spreading correlate with traction forces on the substrate and nuclear localisation of Yap. While it remains preliminary, our data show that forces at cell-substrate contacts and cell spreading induce nuclear localisation of Yap during collective cell movements.In the second part of the thesis, we interested on Yap localisation and proliferation during epithelial migration in absence of cell-substrate contacts. To do so, we forced migration of monolayer of HaCaT keratinocytes on micropattern comprising alternatively adherent and cytorepulsive stripes. While migrating on adherent line, cells extend a multicellular layer over the non-adherent areas. Suspended cells are cohesive with each other but do not engage cell-substrate adhesion. In the suspended cell layer, actin stress fibres reorganise at the tissue level thanks to reinforcement of cell-cell contacts and contractility is increased. This model is the first one that allow to decouple actomyosin contractility and cell-substrate contact during epithelial migration. Despite increased stretching stress, absence of cell-substrate contacts induces Yap cytoplasmic localisation and inhibits cell proliferation. To conclude, cell-substrate contact engagement is necessary to induce Yap nuclear localisation and increase cell proliferation during epithelial wound healing in vitro.This work demonstrates that traction forces through cell-substrate contacts are associated to nuclear localisation of Yap and to increased cell proliferation during epithelial wound healing in vitro

published_or_final_version / Physics / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 93-94).

Thesis (M.S.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (December 12, 2006) Includes bibliographical references.

No description available.

No description available.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

No description available.

Dans le cas des générations de transistors sub-14nm, l’intégration de contacts métalliques classiques soumis aux limitations de la lithographie optique ne permet pas d’atteindre les performances d’alignement requises par les règles de dessin (pitch de grille 64nm en FDSOI 10nm) et les rendements industriels. Dans le cadre de ce travail de thèse, une nouvelle architecture de contacts auto-alignés (Self-Aligned Contacts ou SAC) est adressée pour les technologies FDSOI CMOS. Tout d’abord, nous avons proposé et validé l’intégration d’un module SAC dans une route CMOS FDSOI 14nm. Nous avons aussi démontré morphologiquement la faisabilité de contacts SAC pour des pitchs plus agressifs (noeud technologique 10nm). Par le biais de simulations numériques (TCAD et SPICE) l’impact de l’intégration des contacts auto-alignés sur les performances du transistor et du circuit, en termes de capacités parasites notamment, a ensuite été évalué dans le cas de la technologie 10nm FDSOI. Finalement, différentes techniques de transfert de contraintes mécaniques dans le canal du transistor ont été analysées en vue d’améliorer les performances de PFET en 10nm FDSOI. La génération des contraintes mécaniques via les contacts sur source-drain a également été investiguée. / For sub-14nm transistor generations, the integration of classical metallic contacts subjected to optical lithography limitations prevents the fulfillment of alignment performance required by design rules (64nm gate pitch for the 10nm node) and industrial yields. In the frame of this PhD. work, an original transistor architecture featuring self-aligned contacts (SAC) is studied for CMOS FDSOI technologies. First, a SAC module has been integrated and validated on a CMOS 14nm FDSOI process flow. The feasibility of SAC integration at a more aggressive gate pitch (10nm node) has also been demonstrated morphologically. The impact of such integration on the transistor and circuit performance, in terms of parasitic capacitances especially, has been evaluated through numerical simulations (TCAD, SPICE) in the case of the 10nm FDSOI technology. Finally, several techniques inducing mechanical stress within the transistor channel have been analyzed in order to improve the device performance. Among those, the use of contacts on source-drain to induce such stress has been particularly investigated.

Electrical contact resistance (ECR) measurements are needed for judging the performance of electrical appliances. Understanding the behaviour of ECR at low temperature gives a unique opportunity for understanding the contact mechanism itself and controlling the contact resistance for its applications in various areas at these temperatures. In many high-end applications, sophisticated electronic devices are being operated below ambient temperature to improve their performance. The availability of cryogens, improvement in Thermo-Electrical (TE) based Peltier coolers, accelerated the development of these devices. In designing such systems, an accurate measurement of electrical contact resistance below room temperature is important. A detailed experimental investigation has been conducted on electrical contact resistance across bare and coated metal contacts at low temperatures. As a part of the experimental investigation, a test facility capable of varying the contact force, surrounding pressure and temperature, is developed. The design, construction, testing and use of this facility are described. Electrical contact resistance at different contact pressures across copper, OFHC copper and brass with and without gold coatings is measured using 4-wire technique with high accuracy. The test specimen preparation, instrumentation and data acquisition are explained in detail. The setup is standardized by comparing the experimental results obtained across copper-copper contacts in vacuum with the theoretical model. The electrical contact resistance is measured as a function of contact force at different temperatures. The effect of loading and unloading, and the existence of hysteresis are experimentally studied. The electrical properties of conductors improve at low temperature but this is not true for contact resistance. At low temperature the contact resistance increases and it depends on applied contact force, hardness and roughness of the contacting surfaces. Gold-coated contacts exhibited an increase in contact resistance at low temperatures.