Difference in Dachsous Levels between Migrating Cells Coordinates the Direction of Collective Cell Migration

In contrast to extracellular chemotactic gradients, how cell-adhesion molecules contribute to directing cell migration remains more elusive. Here we studied the collective migration of Drosophila larval epidermal cells (LECs) along the anterior-posterior axis and propose a migrating cell group-autonomous mechanism in which an atypical cadherin Dachsous (Ds) plays a pivotal role. In each abdominal segment, the amount of Ds in each LEC varied along the axis of migration (Ds imbalance), which polarized Ds localization at cell boundaries. This Ds polarity was necessary for coordinating the migratory direction. Another atypical cadherin, Fat (Ft), and an unconventional myosin Dachs, both of which bind to Ds, also showed biased cell-boundary localizations, and both were required for the migration. Altogether, we propose that the Ds imbalance within the migrating tissue provides the directional cue and that this is decoded by Ds-Ft-mediated cell-cell contacts, which restricts lamellipodia formation to the posterior end of the cell.