Fig. 3. The trans-regulatory landscape controlling rho expression diverged between D. virilis and D. melanogaster. (A,B) In D. virilis, the Dmel rho^2.2 enhancer drove expression of the reporter in a pattern resembling that of the endogenous Dvir rho^4.2 enhancer during DA formation; the V-shaped stripe at stage 10B (A) and the pattern corresponding to the four clusters of DA-forming cells at stage 12 (B) were observed. The cluster of cells forming the anterior DA is indicated by a white arrowhead (B). (C-F) Dmel rho^2.2 and Dvir rho^4.2 expressed in D. melanogaster were activated in a largely similar pattern, with some exceptions. The expression of Dmel rho^2.2-GFP was detected as the L-shaped stripe on either side of the midline from stage 10B (C) to 12 (D) in D. melanogaster. When expressed in D. melanogaster, Dvir rho^4.2-GFP showed the L-shaped expression pattern, similar to Dmel rho^2.2 in this species, but with a slightly posterior expansion (E). This extra expression of Dvir rho^4.2-GFP further expanded posteriorly until stage 12 (F). Anterior is to the left; (A,C-F) dorsal view; (B) dorso-lateral view.