Collective cell migration patterns: Follow the leader

Wound healing is essential to the survival of an organism. A breach in tissue composed of a continuous layer of cells provokes a very complex response intended to close, and eventually heal, the wound. In epithelial tissue, the opening of a gap induces the proliferation and movement of the surrounding intact cells, which eventually closes the gap. A multitude of chemical signals are produced when a wound occurs, and thereafter, which leads to proliferation and motility in the surrounding intact layer (1). In this issue of PNAS, Poujade et al. (2) demonstrate that cell motility that closes an open gap in a cell culture (a “wound”) can be triggered even in the absence of cell damage. A unique experimental setup allows the authors to follow the behavior of a continuous and undisturbed monolayer of cells that suddenly finds itself with a free boundary as a model of an open wound. The authors observe that the subsequent cell motility is highly nonuniform and develops distinct morphological patterns and collective motion.

The response of a cell culture to damage that mimics wounding has been analyzed previously. In previous studies (3, 4), a uniform layer of cells was grown on a substrate and then scratched (wounded) with a sharp object. Although these experiments have advanced our knowledge of the wound-healing process, they are complicated to interpret because they involve several effects. First, the sharp object breaks up the cells and releases their constituents into the solution as cellular debris (1). The surrounding cells are therefore affected by the chemical triggers released from the neighboring damaged cells. In addition, the cells at the edges of the open gap are further affected by the sudden loss of neighbors, which opens a free boundary on one of their sides. The cells at this free boundary …

*E-mail: nirgov{at}wisemail.weizmann.ac.il