Fig. 9. The three major stages of wing development: (1) repression of Tsh by Wg and Dpp signaling; (2) Loss of Tsh allows Notch-dependent activation of Wg and Vestigial (Vg) boundary enhancer expression at the DV boundary; and (3) long-range Wg gradient induces several genes required for wing growth and patterning, e.g. Vg.