Figure 1:

(A-B). The wing imaginal disc as a model system for studying organ growth control. The wing discs are epithelial sacs loosely attached to the tracheal system during larval growth (A). During the third instar larvae (shown in B) the wing disc assumes a folded morphology with the pouch cells prominently forming an ellipse shape in the center of the “pear”-shaped organ (B’ and B”). Red marks the nubbin expression domain (nubbin-mcherry) and green marks dad expression (dad-GFP), which a target and inhibitor of DPP signaling. The transgenic fly line was a gift from the Affolter lab. During metamorphosis, the pouch will undergo eversion and elongation to form the adult wing. The pouch is patterned by morphogen gradients that establish a Cartesian coordinate system along the anterior-posterior (AP) and dorsal-ventral (DV) axes. The Dachsous-Fat pathway forms a gradient along the proximal – distal axis. C: Hyperplastic mutants such as wts^P2 do not terminate growth and become highly folded. D: Proliferation depends on the milieu as shown