Figure 3.

Different cell states within a migrating collective. (A) A typical small sprout with a leading tip cell (green), followed by stalk cells (blue). The structure will move to the right. The stalk cells might be pulled by the tip cell or contribute directly to movement as seen for leaders and follower cells in a flat moving cohort. (B) A free migratory group; contrary to the situation in (A) there is no intrinsic polarity in the group, and thus no obvious leader. If we assume the green cell is the dominant ‘leader’ cell at this moment and the blue ones ‘followers’, the cluster will move to the right. If the leader state is assigned by extrinsic information such as an ‘attractant’ gradient, this might be sufficient to constitute ‘collective guidance’ [13].