Fig. 7. The role of cic in the specification of Drosophila wing veins. Active genes and proteins are shown in black, whereas inactive genes and proteins are in red. EGFR and MAPK are active in vein cells and inactive in the intervein tissue from third larval instar onwards (see text). In vein cells, EGFR signalling downregulates Cic protein levels in the nucleus, thus relieving repression of vein-specific genes such as aos, vvl and dpp. In addition, EGFR signalling is required in the veins for the activation of rho and the repression of bs, in a cic-independent manner. rho expression in the veins further increases EGFR activation in a paracrine loop. Conversely, absence of EGFR signalling in the intervein territories allows these cells to maintain high levels of Cic throughout larval and pupal development, which represses the expression of vein-specific genes. In addition, these cells accumulate Bs protein that represses rho and promotes intervein differentiation.
