[Collective cell migrations].

Historically centered on the study of individual cell motility, the field of cell migration has recently moved up one level to look at cooperative behaviour within migratory cell populations. It is now well established that numerous physiological and pathological migration events involve collectively migrating cells rather than solitary cells or concomitantly migrating individual cells. In this review, we first discuss the criteria allowing a given migratory event to be classified as collective cell migration. We then summarize the main concepts that rule collective cell migration in epithelial and mesenchymal tissues with a main focus on mechanisms controlling polarity and directionality in cell collectives.