Thèse de doctorat en Modèles et instruments en médecine et en biologie
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= Dynamique spatio-temporelle des déformations membranaires et de la migration cellulaire : caractérisation à partir de séquences d'images et de modélisation théorique
This thesis concerns the study of cell deformations and is interested in two complementary approaches, an experimental one and another theoretical one. The experimental approach is motivated by the demonstration from previous works of the existence of a certain auto-organization of the deformation patterns. This auto-organization consists of the appearance of recurring protrusive patterns in space and time. This has been shown, in particular, for round-shaped cells (leukocytes or keratinocytes) which present a relatively simple organization of theactin cytoskeleton. We have chosen to study murin fibroblasts (L929 line). The fibroblasts exhibit long membrane extensions such as filopods. This time, this type of protrusion is related to a more complex organization of the actin cytoskeleton, where the filaments tend to form bundles. Our aim has been to determine if there exists a similar self-organized componentof these fibroblasts membrane deformations. Experimental characterization has been performed from image sequences where the cells were observed by phase contrast videomicroscopy. The morphodynamical data of the cells have been extracted from the images with two different methods:(i) a classical segmentation of the cell boundaries for the individual study of each protrusive zone of the cell and (ii) an optical flow method for a global characterizationof the movement of the whole cell. The results obtained show that the cells exhibit mainly symmetrical morphologies with 2 to 4 protrusions. The 4-protrusion state (cross morphology), observed for the most isolated cells, is dynamically characterized by a synchronized pulsating movement between the two perpendicular protrusive directions, where the extension in one direction is accompanied by the simultaneous retraction in the other direction (. . . ) In conclusion, we defined how the work realized experimentally allows us to propose the possibility to use the morphodynamical parameters obtained from the characterization as criteria to identify the cell phenotypes. We also discuss how theoretical modelling can orientate the choice of new experimental protocols.