Fig. 2. Ectopic Rho expression in wild-type and vn mutant discs. (A-E) Wild-type (A-C) and vn^– (D,E) discs containing clones that ectopically express Rho, monitored for the expression of Ap (B,D; red in middle panels), ap-lacZ (C; red), mirr-lacZ (B,D,E; red in middle or right panels), vgQ-lacZ (A; red), Vg (A; blue) and Wg (C; blue). The clones were induced during the first instar and are marked by absence of GFP expression (green). (A) Duplicated wing blade primordium (outlined in the right panel; the extra primordium is outlined in yellow) caused by a ventrally situated clone of Rho-expressing cells (arrowhead) which we infer has induced the formation of an ectopic D compartment. Note that expression of the vg gene (visualized by Vg protein expression, blue) is normally expressed along the DV compartment boundary (asterisks) in response to Notch signaling and in the remainder of the wing blade primordium in response to Wg emanating from the boundary. Expression of the vgQ-lacZ gene (red) depends on the vg ‘quadrant’ enhancer, which is activated by Wg signaling, but blocked by Notch signaling, thus allowing the ectopic DV boundary that forms within the duplicated wing blade primordium to be visualized (yellow asterisk). (B) Ectopic expression of mirr-lacZ and expansion of Ap expression caused by a dorsolateral clone of Rho-expressing cells. Note that ectopic mirr-lacZ is closely associated with the clone, outlined in white, in contrast to boundary of expression of Ap expression, which extends many cell diameters further ventrally. (C) Expansion of ap-lacZ expression caused by two dorsally situated clones of Rho-expressing cells located within the dorsal compartment. Wg is expressed in cells flanking the ap^ON-ap^OFF interface, indicating that the boundary has organizer activity. (D) Partial rescue of growth and patterning of a vn mutant disc by clones ectopically expressing Rho. The boundaries of mirr-lacZ expression are located close to the clone, whereas those of Ap expression are located further away. (E) Extensive rescue of a vn^– mutant disc by a single dorsally situated clone of Rho-expressing cells.