Abstract
Key to collective cell migration is the ability of cells to rearrange their position with respect to their neighbors. Recent theory and experiments demonstrated that cellular rearrangements are facilitated by cell shape, with cells having more elongated shapes and greater perimeters more easily sliding past their neighbors within the cell layer. Though it is thought that cell perimeter is controlled primarily by cortical tension and adhesion at each cell's periphery, experimental testing of this hypothesis has produced conflicting results. Here we studied collective cell migration in an epithelial monolayer by measuring forces, cell perimeters, and motion, and found all three to decrease with either increased cell density or inhibition of cell contraction. In contrast to previous understanding, the data suggest that cell shape and rearrangements are controlled not by cortical tension or adhesion at the cell periphery but rather by the stress fibers that produce tractions at the cell-substrate interface. This finding is confirmed by an experiment showing that increasing tractions reverses the effect of density on cell shape and rearrangements. Our study therefore reduces the focus on the cell periphery by establishing cell-substrate traction as a major physical factor controlling cell shape and motion in collective cell migration.
Highlights
In numerous cases in human health and disease, epithelial cells transition from a static, motionless state to an active, migratory state
By analogy with the effect of density on jamming of rigid particles [9,10], one might expect the transition from migratory to motionless in a cell collective to result from an increase in cell number density, and this prediction has been observed in experiments [4,5,7, 11,12,13,14]
We begin with the well-established observation that cell density affects collective cell migration, with higher density tending to arrest rearrangements within a cell monolayer [4,5,7,11,12,13,14]
Summary
In numerous cases in human health and disease, epithelial cells transition from a static, motionless state to an active, migratory state. A critical step is the transition from motionless to migratory Experiments have observed this transition [3,4,5,6,7,8] and demonstrated that it is akin to the jamming transition that occurs in particulate matter [9,10]. By analogy with the effect of density on jamming of rigid particles [9,10], one might expect the transition from migratory to motionless in a cell collective to result from an increase in cell number density, and this prediction has been observed in experiments [4,5,7, 11,12,13,14]. How the cell density affects the collective cell migration remains unclear, because the analogy between granular materials and cells is imperfect
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