Navigation within the cellular monolayer

Abstract

Confronted by a cell‐free gap, a cellular monolayer ordinarily extends its free edge until the gap is filled. Although this process is arguably the simplest of all dynamical patterning modules, governing physical principles that might explain this process remain obscure. To expose physical forces that cause constituent cells to move as they do, we placed in the path of an advancing epithelial cell sheet an island upon which cells could not adhere. The monolayer impacts but cannot cover this island, and is therefore said to become frustrated. Systematic components of the resulting nonuniform velocity field and underlying force fields reveal striking dynamical features. Far from the frustrated edge, local traction forces pull systematically along the local migration velocity vector. Near the frustrated edge, however, local traction forces veer away from the local velocity vector by angles approaching 90°. At the frustrated edge itself, traction forces pull systematically normal to that edge, but generate no normal displacements. Corresponding intercellular stresses reveal unanticipated but fundamental dynamical patterning modules that call for a new physical picture of monolayer dynamics.This work was supported by the Spanish Ministry for Science and Innovation (BFU2009–07595), the European Research Council (Grant Agreement 242993) and the National Institutes of Health (R01HL102373, R01HL107561).