Vestigial-dependent recruitment contributes to robust patterning but is not required for wing-fate induction in Drosophila

Cell recruitment is a process by which a differentiated cell induces neighboring cells to adopt its same cell fate. In Drosophila, cells expressing the wing selector gene, vestigial (vg), drive a feed-forward recruitment signal that propagates Vg expression suggesting that the Vg pattern is established as a wavefront throughout the wing pouch. However, the dynamics of Vg pattern formation does not meet this expectation. Here we show that an induction signal may drive Vg expression without Vg feedforward recruitment several cells away from the dorsal-ventral (DV) boundary. Particularly, when Vg expression is strongly inhibited either at the DV boundary or away from it, the activation of the vg Quadrant Enhancer still occurs at a distance, although the levels and precision of the pattern are compromised. Using live imaging of a dual-fluorescent reporter system, we show that contact-dependent cell recruitment does occur in wild-type conditions suggesting that a combination of a long-range induction signal and a signal-relay recruitment establishes Vg patterning in a robust manner. Overall, our findings reveal a previously unidentified role of cell recruitment as a robustness-conferring patterning mechanism. Summary StatementRobust formation of the Vg pattern is established by two mechanisms: a fast, long-range, but noisy induction signal; and a more precise signal relay, contact-dependent, cell recruitment process.