Fig. 3. Autonomous development of anterior and posterior compartments. (A) Evolution of the P/A ratio during the second half of the larval period in control M(3)67C/+, en-M⁺ and ci-M⁺ wing discs. In the control, the ratio increases during 3rd instar, whereas in en-M⁺ discs the P/A ratio is approximately uniform. In ci-M⁺, the ratio also increases, but it is significantly smaller than control until day 6. At the end of the larval period the P/A ratio of three classes of disc becomes the same. (B,C) A 2nd instar wild-type disc shows wg expression (red) in the presumptive wing pouch (B), and a similar aged en-M⁺ disc has virtually all posterior cells transformed to M⁺, as indicated by the loss of the GFP marker (C,C'). (D-E') expression of wg and vg in en-M⁺ early third instar discs. The expression of both genes is uncoupled in the anterior and posterior compartments, being more advanced in the posterior one. (D,D') wg expression in the posterior compartment is restricted to a proximal ring and the DV region, whereas in the anterior compartment is more diffused in the wing pouch. (E,E') vg expression is already expanding to the wing pouch in the posterior compartment, whereas it is still restricted to the DV region in the anterior compartment. (F-G') Similar results observed in ci-M⁺ discs: there is a slight but detectable difference in wg expression (F,F'), and more clear difference for vg (G,G').