Fig. 7. Early EGFR/Ras-mediated signaling is required for establishing the D compartment. (A,B) Examples of large Egfr^– clones that preferentially populate the ventral compartment. The clones were generated during first larval instar using the Minute technique and are marked by the absence of GFP (green). Ap protein is shown in red (A), Wg protein in blue (B,C). Black arrows in A indicate small mutant clones located within the dorsal compartment. The white arrow in B indicates a small cluster of mutant cells that appear to have been left behind in the D compartment when the remainder of the clone sorted into the V compartment. Note that cells within this cluster do not express Wg, indicating that they are of D, rather than V type. (C,D) Example (C) and schematic representation (D) of a disc containing a dorsally situated clone of Egfr^– cells that has developed as an ectopic V compartment. The wing blade primordium (all cells located within the outer ring of Wg expression) is shown in color: V compartment cells are represented in yellow, and D compartment cells in blue. Egfr⁺ cells are indicated by hatching. The dorsoventral compartment boundary, which correlates with the inner ring of Wg expression, is outlined in red.