We managed to characterise a new function of the EGFR/ERK pathway in cell deformation sensing and cell death induction which is also essential for cell elimination near oncogenic clones. This is one of the first characterisation of a pathway invovlved in mechanical cell competition in vivo (Current Biology, 2019).
We also started to dissect the mechanism of mechanosensing by screening for EGFR interactors and test their impact on deformation sensing in the notum. We developed several tools, including KI lines of EGFR and sensors of the pathway combined with optogenetics tool to modulate local tissue mechanics (activation or inhibition of Rho). This confirmed that ERK can be downregulated by tension release which seems to be associated with a transient relocalisation of EGFR. Importantly, the sensitivity to cell compaction/tension release is abolished upon depletion of the E3 ubiquitin ligase Cbl. This points to a potential mechanism based on EGFR trafficking modulation by cell mechanics.
We also found that every dying cell activates transiently ERK in the direct neighbours through their stretching. This modulates the spatiotemporal distribution of cell elimination and helps to maintain tissue integrity. This conserved mechanism is essential to maintain tissue sealing in context of high rates of cell elimination (Dev Cell 2021).
We also characterised the pattern of cell death in the wing imaginal disc and its contribution to clone dynamics and shape of the adult wing. This works shows that subtle spatial bias of apoptosis can significantly alter local growth and tissue shape even in fast growing tissues (bioRxiv 2022).
We are also characterising the conditions in which fast growing clones can deform and kill neighbouring cells. Using quantitative live imaging in the pupal notum combined with vertex simuatios, we found that different modes of compaction can coexist and have distinctive signatures : compaction driven by growth or compaction driven by increased line tension at clone boundaries. This project is close to completion and should be submited by the end of 2023.
Lastly, we also studied how cells engage in apoptosis and how caspases ochestrate cell extrusion. Doing so, we found an unexpected contributions of microtubules which through their depletion by caspases increase cell deformability and initiates cell extrusion without modulations of actomyosin dynamics (Nat. Comm 2022).
Along the way, we have also developed several pipelines for image analysis which have shared through accessible plugins and python procedures, including tools for local projection and tissue reconstruction (Herbert &Valon L et al., BMC Biol 2021) and more recently machine learning tools to automatically recognize cellular events in movies, including extrusion and cell division (Villars & Letort et al., Development 2023).
Overall, this project have led to several publications (Moreno et al. Curr. Biol. 2019, Valon et al., Dev Cell. 2021, Villars et al., Nat. Comm 2022, Matamoro-Vidal et al., BiorXiv 2021, in revision in Curr. Biol., Herbert et al., BMC Biol 2021, Villars et al. Development 2023) and reviews (Valon et al., Bio Cell 1019, Matamoro-Vidal A & Levayer R, Curr. Biol. 2019, Levayer R, Semin. Cancer Biol 2020, Villars & Levayer Curr. Opin Genet Dev 2023, Staneva and Levayer R, Curr Top Dev Biol 2023, Cumming & Levayer, Semin Cell Dev Biol 2023). The results of these projects were also disseminated through many conferences and symposium and discussed every year in front of high school students in Paris area throught the Declics intiative. We have also made several press releases related to the articles which for some were then also disclosed in general public scientific journals (Pour la science, Science et avenir, The scientist). We also describe part of the project in the radio show CQFD on "France Culture". The project also heped to mentor and train many students for long and short internships that were all instrumental for their training (many of them are now pursuing a PhD or following a science master program).
We have now a better understanding of epithelial cell death orchestration and the role of mechanics on cell elimination during competition and in physiologial contexts. It opens many avenues of research related to the self-organisation of tissues and the emerging properties that module the distribution and number of dying cell in a tissue and point to new players of mechanosensing. As mentioned above, this project have also led to the creation of many new tools (new fly lines and sensors, new optogenetic tools, image analysis pipelines) that were all shared widely thus promoting many other aspect of basic research.
