Fig. 1. Expression of msh and ara/caup in the wing disc. Images show accumulation of Msh (green), Ara/Caup (red) and Wg (blue). (A) Late second instar disc. The border between the Msh and Ara/Caup domains is relatively sharp (arrowhead). (B) Mid-third instar discs. There is low level Msh accumulation in the dorsal wing pouch (arrow) and in the posterior notum (arrowhead). (C) Late third instar disc images. Channels showing Msh and Ara/Caup expressions are separately illustrated at bottom of the panel. Yellow lines indicate the positions of z-axis optical sections. These are shown at left (top) and right (middle) of the panel, with separate and merged red and green channels. White curved lines highlight the profiles of the disc epithelium sections. vh, ventral hinge, pl, pleura; dh, dorsal hinge; n, notum; ln, lateral notum; mn, medial notum; wp, wing pouch; a, anterior; p. posterior; white asterisks, tegula; blue asterisks, dorsal radius. msh expression is maximal in the dorsal and ventral prospective hinges (white arrowheads) and lower in the posterior notum (white arrow), while that of ara/caup is maximal at the prospective lateral notum (yellow arrowhead). Blue arrow indicates the region of decreased Iro-C expression in the lateral notum of late third instar discs. Blue horizontal line indicates the fold that approximately coincides with the notum/hinge boundary. In the notum/dorsal hinge z-section, there is strong notal expression of ara/caup that does not overlap with the strong expression of msh. This expression is also contiguous but does not overlap at the z-section through the ventral hinge and pleura (top, left). Wg marks the wing pouch epithelium (blue arrowhead) and this is contiguous with the domain of msh expression. Therefore, this should correspond to the ventral hinge and ara/caup expression should correspond to the pleura.