Mechanics of crypt folding, tissue compartmentalization and collective cell migration in intestinal organoids

Abstract

[eng] The intestinal epithelium is a monolayer of cells that covers the inner surface of the gut. It protects against pathogens, absorbs nutrients, and secretes hormones and other molecules. This epithelium is folded into finger-like protrusions, called villi, composed of differentiated cells, and invaginations, called crypts, where stem cells reside. Stem cells proliferate and generate new cells that gradually differentiate and actively migrate towards the villus tip, where they finally extrude and die. The tight spatio-temporal regulation of proliferation, differentiation, migration and death in domains of extreme curvature suggests an essential role of mechanical forces in intestinal homeostasis. However, the mechanics of the intestinal epithelium is poorly understood. In part, this is due to technical limitations of quantitative measurements in vivo. Intestinal organoids have emerged as gold standard in vitro models of the intestinal epithelium. They recapitulate key physiological features of the native tissue, including the heterogeneity of cell types, the compartmentalization of those cell types into crypt-like and villus-like regions, the folding of the crypts and the dynamics of proliferation, differentiation and death. In this thesis, by combining intestinal organoids with quantitative three-dimensional force mapping, we show that intestinal organoids exhibit a non-monotonic stress distribution that mechanically compartmentalize the tissue into functional compartments. The stem cell compartment pushes the Extracellular Matrix (ECM) and folds through apical constriction of the stem cells. The transit amplifying region pulls the ECM and elongates through basal constriction, generating a mechanical boundary between the crypt and the villus. Crypt-villus boundary formation and proper tissue compartmentalization is controlled by Eph/Ephrin signaling. Finally, we show that cells are pulled out of the crypt along a gradient of increasing tension, rather than pushed by a compressive stress downstream of mitotic pressure, as previously assumed. Overall, the data presented in this thesis unveils how patterned forces enable crypt folding, tissue compartmentalization and collective cell migration in the intestinal epithelium.