The team tracked two distinct migration phases—a quick start and a later, slower phase—by the border cell cluster in developing fly egg chambers. They found that the phases required different growth factor–induced signaling pathways; only the latter was controlled by MAPK and PLCγ.
While early signals were restricted to the front of the cluster's leader, the later MAPK signal was uniform throughout leading cells. How this signal could direct movement puzzled the group until they considered that the cluster might be guided as a unit. Movies revealed that, in the late phase, the cluster slowed to a tumbling, shuffling motion in which the leading cell or two—ones with the most MAPK signaling—often changed identity.
The shuffling means that cells are constantly in competition for who is “seeing” growth factor best at any given moment by being closest to the ligand source and sensing it best. This group mentality, which can assess a larger environment than individual cells, may boost migration precision.