Régulation Biophysique de l’Apoptose Epitheliale

L’apoptose est une forme de mort cellulaire programmée qui joue un rôle clé lors de la morphogenèse (acquisition de formes et structures pendant le développement), dans l’homéostasie des tissus adultes, ainsi que dans certaines maladies telles que les cancers. Alors que les signaux moléculaires responsables du déclenchement de l’apoptose ont été l’objet de multiples recherches, le rôle de facteurs biophysiques dans le contrôle de la mort cellulaire reste peu connu. Durant ma thèse qui avait pour modèle d’étude le thorax dorsal (ou notum) de la pupe de drosophile, j’ai développé des techniques d’analyse quantitative de données vidéo-microscopiques qui, combinées à l’utilisation d’outils génétiques de pointe, visaient à comprendre la régulation biophysique de l’apoptose. Tout d’abord, j’ai cherché à caractériser les caractéristiques précoces des futures cellules apoptotiques et ai découvert deux caractéristiques géométriques prédictives de ces cellules : des petites aires apicales absolue et relative. Ensuite, j’ai étudié en détail ces deux facteurs géométriques et ai montré que leurs actions dans le contrôle de la mort faisaient intervenir deux voies de signalisation génétiques différentes, voies que j’ai identifiées. Ce faisant, j’ai également découvert une connexion inédite entre prolifération et mort cellulaire dans le contrôle du développement tissulaire. En conclusion, mon travail apporte un éclairage nouveau à notre compréhension de l’apoptose épithéliale en identifiant des facteurs géométriques impliqués de façon très précoce dans la régulation de la mort cellulaire.Apoptosis is a form of programmed cell death which plays a key role in shaping multicellular organisms during development, in adult tissue homeostasis, as well as in pathological conditions such as cancer. While the molecular pathways triggering apoptosis have been extensively studied, the role of biophysical factors in driving cell death is far less understood. In particular, cell size and geometry impact a variety of cell processes, yet their possible interplay with apoptotic pathways remains unknown. Using the developing dorsal thorax (or notum) of the Drosophila as a model, I developed during my PhD advanced quantitative analyses of time-lapse microscopy data that, combined with the powerful genetic tools available in Drosophila, aimed at uncovering the biophysical mechanisms regulating apoptosis. First, I investigated the early characteristics of apoptotic cells and discovered two predictive geometrical features of these cells: small absolute and relative apical areas. Second, I studied in detail these two geometrical parameters and showed that their actions were linked to distinct genetic pathways, which I identified. By doing so, I also uncovered a novel coupling between cell proliferation and cell death in the control of tissue development. Overall, this work provides a new perspective to the understanding of epithelial apoptosis by identifying geometrical parameters that play an early role in the regulation of cell survival

Applying mechanical forces on Drosophila tissues in vivo using the StretchCo, a 3D-printable device

Summary: Applying mechanical forces to tissues helps to understand morphogenesis and homeostasis. Additionally, recording the dynamics of living tissues under mechanical constraints is needed to explore tissue biomechanics. Here, we present a protocol to 3D-print a StretchCo device and use it to apply uniaxial mechanical stress on the Drosophila pupal dorsal thorax epithelium. We describe steps for 3D printing, polydimethylsiloxane (PDMS) strip cutting, and glue preparation. We detail procedures for PDMS strip mounting, tissue compaction, and live imaging upon force application. For additional details on the use and execution of this protocol, please refer to Cachoux et al. (2023)1 from which the StretchCo machine has been derived. : Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics

The role of single-cell mechanical behaviour and polarity in driving collective cell migration

International audienceThe directed migration of cell collectives is essential in various physiological processes, such as epiboly, intestinal epithelial turnover, and convergent extension during morphogenesis as well as during pathological events like wound healing and cancer metastasis 1,2 . Collective cell migration leads to the emergence of coordinated movements over multiple cells. Our current understanding emphasizes that these movements are mainly driven by large-scale transmission of signals through adherens junctions 3,4 . In this study, we show that collective movements of epithelial cells can be triggered by polarity signals at the single cell level through the establishment of coordinated lamellipodial protrusions. We designed a minimalistic model system to generate one-dimensional epithelial trains confined in ring shaped patterns that recapitulate rotational movements observed in vitro in cellular monolayers and in vivo in genitalia or follicular cell rotation 5–7 . Using our system, we demonstrated that cells follow coordinated rotational movements after the establishment of directed Rac1-dependent polarity over the entire monolayer. Our experimental and numerical approaches show that the maintenance of coordinated migration requires the acquisition of a front-back polarity within each single cell but does not require the maintenance of cell-cell junctions. Taken together, these unexpected findings demonstrate that collective cell dynamics in closed environments as observed in multiple in vitro and in vivo situations 5,6,8,9 can arise from single cell behavior through a sustained memory of cell polarity