Fig. 4. Dorsal wing (Dlw) alleles. (A) Genomic organization of the msh gene. The msh transcript consists of 2 exons spanning approx. 10 kb. Arrows indicate breakpoints associated with Dlw alleles. Other predicted genes in the region are indicated. msh expression in the wing discs was monitored using mshlacZ89, an imprecise excision line of P{lacZ}rH96 that keeps the lacZ reporter gene. (B) Wild-type wing. AWM, anterior wing margin. PWM, posterior wing margin. The AP compartment boundary is shown by a line. (C,D) patchedGal4/uas-dLMO; Dlw1/+ wing. dLMO is overexpressed in the anterior compartment. dLMO inhibits Apterous activity. PWM', ectopic posterior wing margin induced in the dorsal surface along the AP compartment boundary. The wing is overgrown owing to ectopic expression of Wg along the patchedGal4 stripe. Dorsal and ventral surfaces do not contact normally. (D) Magnification of the dorsal side of vein L3 of the wing shown in C. In a wild-type wing, vein L3 is corrugated and has three campaniform sensillae on the dorsal surface (see Fig. 1). In the Dlw1/+ wing, campaniform sensillae (arrows in C and D) and corrugation are characteristic of the dorsal surface of vein L3. Their appearance in the Dlw1/+ wing indicates that Msh activity is present, despite the loss of Apterous activity.