This thesis describes and evaluates approaches to computational models of Epithelial cell interactions. It begins with a review of existing approaches and in particular includes a rational reconstruction of a model of squamous epithelial cell interactions previously described by Stekel Stekel et al., 1995 . Suggestions for improving this model are made, including methods for analysing spatial clusters of cells using Delau- nay triangulation and heterogeneity of epithelial tissue using connective component labeling. Histological images of oral epithelium are used to develop a classification of base ment membrane shape in normal and dysplastic tissues. The method combines Fourier descriptors for shape representation, Principal Component Analysis for data reduction and the closest mean and support vector machine algorithms for pattern recognition. This approach is suggested as a general technique for evaluating the output of simulation models which involve curvilinear features in a shape-based clas sification of the tissues modelled. A new model of epithelial cell interactions is proposed by extending the Glazier- Graner framework for cell sorting Graner, 1993, Graner and Sawada, 1993 . The model includes biological processes such as cell division, differentiation, adhesion and death. In particular, the roles of differential adhesion and cell division during the-development of epithelium are discussed. The typical ordered structure of a healthy epithelium is shown to arise provided differential adhesion and cell division are modelled appropriately.

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MurG is the last intracellular enzyme involved in the biosynthesis of the bacterial cell wall, it is a glycosyl transferase that catalyses the transfer of A/-acetyl glucosamine from uridine diphosphate A/-acetyl glucosamine (UDP-GlcNAc) to the 04 hydroxyl group of MurNAc(pentapeptide)-pyrophosphoryl undecaprenol.

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L’interaction d’assemblées de moteurs et de filaments du cytosquelette donne naissance à des comportements actifs qui demeurent peu compris, malgré la large caractérisation de leurs molécules individuellement. En contrôlant la géométrie de polymérisation de l’actine via des micropatrons surfaciques de nucléation, nous avons observé in vitro l’émergence de battements de faisceaux de filaments parallèles d’actine en présence de myosines en solution (myosine V ou HMM II (Heavy MeroMyosine II)). La forme du battement est similaire pour les deux types de moteurs, mais avec des oscillations un ordre de grandeur plus rapides avec la myosine II qu’avec la myosine V. Dans les deux cas, une onde de déformation transverse se propage à vitesse uniforme de la base à la pointe du faisceau d’actine. Avec la polymérisation, les faisceaux d’actine s’allongent à vitesse constante : la période croît, mais la vitesse de l’onde mécanique reste inchangée. L’utilisation de myosines-GFP a révélé un pic de concentration et un recrutement localisé des myosines au sein du faisceau d’actine, avant qu’une onde de concentration ne se propage vers la pointe de concert avec l’onde mécanique de l’actine. Ces résultats présentent une nouvelle forme de couplage entre l’affinité des myosines à l’actine et la forme du faisceau d’actine. Ce travail de thèse décrit l’émergence de battements actifs imitant ceux des flagelles comme une propriété intrinsèque de l’interaction de filaments polaires et de moteurs moléculaires. Le contrôle de la structure lors du processus d’auto-organisation fournit des informations clés pour étudier les principes physiques génériques du battement flagellaire. / The emergent active behaviors of molecular motors assemblies and cytoskeletal filaments systems remain poorly understood, though individual molecules have been extensively characterized. By controlling the geometry of actin polymerization with surface micropatterns of a nucleation promoting factor, we were able to demonstrate in vitro the emergence of flagellar-like beating of bundles of parallel actin filaments in the presence of myosin motors. We worked with both myosin V and heavy-meromyosin II. The waveform of oscillation was similar for the two types of motors, but oscillations with myosin II were one order of magnitude faster than with myosin Va. In both cases, a bending wave traveled at a uniform speed from the anchored base of the actin bundle towards the tip. As polymerization occurred, the actin bundle elongated at a constant speed, resulting in an increase of the oscillation period, but the speed of the traveling bending wave remains constant. GFP-tagged myosin V revealed the presence of a myosin concentration peak within the actin bundle. Strikingly, myosin V motors were locally recruited within the actin bundle, before a concentration wave propagated towards the bundle’s tip in concert with the actin bending wave. These results revealed a novel form of coupling between the myosin affinity for actin and the actin bundle shape. Our work demonstrates that active flagellar-like beating emerges as an intrinsic property of polar bundles of filaments in interaction with molecular motors. Structural control over the self-assembly process provides key information to clarify the underlying physical principles of flagellar-like beating.