Competition for space induces cell elimination through compaction-driven ERK downregulation
The plasticity of developing tissues relies on the adjustment of cell survival and growth rate to environmental cues. This includes the effect of mechanical cues on cell survival. Accordingly, compaction of an epithelium can lead to cell extrusion and cell death. This process was proposed to contribute to tissue homeostasis but also to facilitate the expansion of pretumoral cells through the compaction and elimination of the neighbouring healthy cells. However we know very little about the pathways than can trigger apoptosis upon tissue deformation and the contribution of compaction driven death to clone expansion was never assessed in vivo. Using the Drosophila pupal notum and a new live sensor of ERK, we show that tissue compaction induces cell elimination through the downregulation of EGFR/ERK pathway and the upregulation of the pro-apoptotic protein Hid. Those results suggest that the sensitivity of EGFR/ERK pathway to mechanics could play a more general role in the fine tuning of cell elimination during morphogenesis and tissue homeostasis. Secondly, we assessed in vivo the contribution of compaction driven death to pretumoral cell expansion. We found that the activation of the oncogene Ras in clones can also downregulate ERK and activate apoptosis in the neighbouring cells through their compaction, which contributes to Ras clone expansion. The mechanical modulation of EGFR/ERK during growth-mediated competition for space may contribute to tumour progression.