Directed persistent motion maintains sheet integrity during multi-cellular spreading and migration

Multi-cellular migration plays an important role in physiological processes such as embryogenesis, cancer metastasis and tissue repair. Collective cell migration involves specific single cell motility behaviour that maintains the integrity of the monolayer and the fluid-like behavior of the sheet at long time scales. We have studied the dynamics of MCF-10A, MDA-MB-231 epithelial cell monolayers and that of a NIH-3t3 fibroblast monolayer. For the case where MCF-10A cell-cell interactions are so weak that single cells can detach from the monolayer, a collective cell front can be maintained by interplay between the directed persistent motion of the monolayer and the random motion of escaping single cells. The dynamics of the MCF-10A monolayer is contrasted with the MDA-MB-231 monolayer where single cells did not detach, with non-interacting NIH-3t3 fibroblast cells that are always random walkers, and with a MCF-10A monolayer treated with a calcium chelating agent that reduces intercellular interactions.