Regulation of epithelial cell organization by tuning cell–substrate adhesion

Abstract

Collective migration of cells is of fundamental importance for a number of biological functions such as tissue development and regeneration, wound healing and cancer metastasis. The movement of cell groups consisting of multiple cells connected by cell-cell junctions depends on both extracellular and intercellular contacts. Epithelial cell assemblies are thus regulated by a cross-talk between cell-substrate and cell-cell interactions. Here, we investigated the onset of collective migration in groups of cells as they expand from a few cells into large colonies as a function of extracellular matrix (ECM) protein coating. By varying the amount of ECM presented to the cells, we observe that the mode of colony expansion, as well as their overall geometry, is strongly dependent on substrate adhesiveness. On high ECM protein coated surfaces, cells at the edges of the colonies are well spread exhibiting large outward-pointing protrusive activity, whereas cellular colonies display more circular and convex shapes on less adhesive surfaces. Actin structures at the edge of the colonies also show different organizations with the formation of lamellipodial structures on highly adhesive surfaces and a pluricellular actin cable on less adhesive ones. The analysis of traction forces and cell velocities within the cellular assemblies confirm these results. By increasing ECM protein density, cells exert higher traction forces together with a higher outward motility at the edges. Furthermore, tuning cell-cell adhesion of epithelial cells modified the mode of expansion of the colonies. Finally, we used a recently developed computational model to recapitulate the emergent experimental behaviors of expanding cell colonies and extract that the main effect of the different cell-substrate interactions is on the ability of edge cells to form outward lamellipodia-driven motility. Overall, our data suggest that switching behaviors of epithelial cell assemblies result in a tug-of-war between friction forces at the cell-substrate interface and cell-cell interactions.

Contact inhibition of locomotion determines cell–cell and cell–substrate forces in tissues

“…Traction forces in larger sheets have only been measured at relatively low resolutions (6,11), but the results seem to agree with our model prediction that traction forces do not remain strictly limited to the edge in such clusters. We should also note that, although single cells are nonmotile, small colonies can move around or rotate because of CIL (Movie S1).…”

“…CIL implies that cells at the edge of a tissue exert the strongest substrate traction forces. The fact that cells at the edge might behave differently from cells in the tissue interior was observed not only in cell clusters that form supercells (7)(8)(9)(10)(11) and spreading tissues experiencing kenotaxis (16) but also, with leader cells at the tip of fingers guiding the closure of model wounds (29,47). Recently, it was shown that cell clusters consisting of nonchemotactic single cells can exhibit collective chemotaxis through CIL (33,35,48).…”

“…More recently, interest has shifted toward deciphering the forces that multiple cells that are adhered to each other, in either small clusters (6)(7)(8)(9)(10)(11) or larger sheets (12-17), exert on a substrate. Because of interaction with their neighbors, cells in a tissue can behave significantly different from single cells.…”

Emergent structures and dynamics of cell colonies by contact inhibition of locomotion

“…In experiments, the transition from a cell monolayer to a 3D aggregate can be induced in many ways (48), such as by increasing the density of cell-cell adhesion proteins (35,49). Alternatively, one can reduce the density of cell-substrate proteins (49,50), which, in our diagram, entails a decrease of the critical cell-cell adhesion for the wetting transition, Eq. 7.…”

Facile Preparation of Photoactivatable Surfaces with Tuned Substrate Adhesiveness

“…Commonly used approaches to tackle this issue are to simply change the coating concentration of fibronectin solutions and observe appropriate size and/or geometry of cell clusters that randomly attach thereon 9 or to stamp a poly(dimethylsiloxane) (PDMS) stencil onto protein-coated surfaces to rationally control cell geometries and remove it to observe cell migration. 10 However, such physically adsorbed proteins are susceptible to gradual replacement with medium or cell-producing proteins.…”