Importance of Notch activation in dorsal or ventral boundary cells for wing development.

<p>(A–D) Expression of UAS <i>psn</i> in <i>psn</i> mutant wing imaginal discs exclusively in dorsal cells with <i>ap</i>Gal4. Arrowhead points to the inner ring-like expression domain of Wg in the proximal wing anlage. (A, B) Expression of Ap (green) and Wg (red) in <i>Psn^C1</i> mutant discs. Note that the boundary of Ap expressing and non-expressing cells is irregular because the compartment boundary fails to form. In addition the diameter of the inner ring-like domain of Wg is strongly reduced and the expression domain along the D/V boundary is lost (C, D) A similar Phenotype is observed if UAS <i>psn</i> is expressed exclusively in dorsal cells with <i>ap</i>Gal4. Thus restoring a functional Notch pathway in only dorsal cells is not sufficient to rescue expression of Wg along the D/V boundary. (E) In contrast supplying psn activity simultaneously in dorsal and ventral cells by expressing UAS Psn with <i>dpp</i>Gal4 restores Wg expression (arrow in E). (F–H) Expression of UAS mib1 in <i>mib1²</i>/<i>mib1³</i> mutant wing discs with <i>ap</i>Gal4. (F) Expression of Wg in a <i>mib</i> mutant control disc. The diameter of the residual ring-like domain of Wg expression is dramatically reduced and the expression domain along the D/V boundary is lost. (G, H) Expression of UAS <i>mib1</i> exclusively in dorsal cells with <i>ap</i>Gal4 is sufficient to restore expression of Wg along the D/V boundary (arrow) and to allow wing development to occur. (I–N) Expression of UAS <i>Su(H)-RNAi</i> during wing development with <i>ap</i>Gal4 (I–M) and <i>sd</i>Gal4 (N). Expression with <i>ap</i>Gal4 results in the formation of a nearly normal looking wing anlage. However, the comparison with the expression of Ap expression revealed that the Wg domain is restricted to VBCs in early (I, J) and late (K–M) third instar discs. (N) Expression on both half of the wing results in abolishment of expression of Wg along the D/V boundary.