Fig. 4. vg and rn mediate the activation of the IR. (A-F) Clones of vg-expressing cells. Clone cells are labelled green (GFP), Wg is labelled in blue (wg antibody) and Rn in red (rn-lacZ). When we examine the expression of wg in these clones we found three distinct results: (1) wg is expressed in a narrow ring of cells that abuts the clone border (A); (2) wg is expressed in a broader ring of cells that still abuts the clone border (B); and (3) wg is expressed in a ring that stands several cells away from the clone border (C). We infer that these three distinct results represent three stages and reproduce the process of activation of the IR throughout normal development. (D-F) vg-expressing clones activate rn expression within the cells of the clone and in surrounding cells. This activation is restricted to the Nub domain. (D) Non-autonomous activation of rn in a vg-expressing clone. The arrow indicates the fold that delimits the expression of nub. (E) Two clones out of the Nub domain (arrowheads) and a clone within the Nub domain (arrow). Owing to different planes of focus, not all the cells of the clone show rn expression. (F) vg-expressing clones that do not activate rn expression in cells out of the clone do not express wg (arrowhead). (G,H) Clones of rn-expressing cells: clone cells are red (GFP) and Wg is blue. Rn autonomously activates wg expression, but only in the Nub domain and in cells that are close to the Vg domain. (I) wg expression in ap-GAL4/UAS-vg wing disc. Note the lack of dorsal wg expression (arrow).