During organogenesis, the migration of epithelial tissues can be controlled by their leading edge, a region that detects external guidance cues and directs cohesive tissue movement. An example of this is the migrating primordium of the zebrafish lateral line, from which mechanosensory organs arise as a result of rosette-like structures being deposited by the trailing cells of the primordium. On , Darren Gilmour and colleagues show that, in this tissue, cells behind the leading edge become assembled into sensory organ progenitors in response to Fgf signalling. By using fgf3;fgf10 double mutant fish and by inhibiting Fgf signalling, the authors demonstrate that this pathway is necessary for organising prospective sensory organs and for driving cells towards an increasingly epithelial, non-leader fate as they fall behind the leading edge. While Fgf signalling has been shown to select `leader' cell fate in several different contexts, this new work reveals that the same signalling pathway can drive this fate transition in the reverse direction, turning leaders into followers.
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