MCExtrusion · Mechanisms of Cell Extrusion controlling Tissue Homeostasis in the Intestine

The intestinal epithelium undergoes continuous self-renewal through coordination of cell proliferation in the crypt and cell removal in the villus region. The aim of this project is to elucidate the mechanisms controlling the removal of differentiated cells from the villus. Preliminary data indicate that most extruding cells are non-apoptotic suggesting alternative mechanisms regulating this key homeostatic event. Cells might either commit to extrusion through specific differentiation programs or local tissue mechanical constraints might force the extrusion of otherwise indistinguishable cells. Feedback between cell fate and mechanical constraints can be also envisaged. Here I propose to identify genes that control cell extrusion by analyzing the dynamic transcriptomic signature of the mouse intestinal epithelium using nascent mRNA sequencing (scEU-seq) and pharmacologic inhibition of candidate pathways in intestinal organoids. Target genes will be functionally validated by a CRISPR-Cas9-mediated knockout screen. This analysis will be flanked by experiments investigating a potential role of tissue-scale mechanical forces in cell extrusion. I will measure the mechanical properties of the intestinal epithelium and obtain a detailed description of the morphological dynamics characterizing cell extrusion using live imaging and 3D-shape reconstruction. Precise manipulation of cortical tension by means of laser ablation combined with subcellular optogenetics will be used to functionally perturb tissue mechanics and reveal the impact of cell contractility and tissue tension on the extrusion process. Collectively, this project will help understanding how tissue homeostasis in the intestinal epithelium is maintained and dissect the relative contribution of genetic signaling circuits and tissue mechanics in regulating cell extrusion.