Fig. 4. ash2 is required for net activation. (A-C) Expression of net mRNA in third instar wing discs. (A) Wild-type discs showing net transcripts in intervein regions. The position of veins (lacking net mRNA) is indicated. (B) net expression is reduced in discs ash2¹¹²⁴¹¹/ash2¹¹²⁴¹¹. However, the central domain of the wing pouch shows expression of net. (C) Absence of net mRNA in ash2^I1 wing discs. (D) Wing of net¹ homozygous mutant with ectopic vein tissue. (E) net¹/net¹; ash2^I1 heterozygous flies show posterior wing blistering and enhanced ectopic vein connections, especially between L2-L3. (F) Wings of net¹; ash2¹¹²⁴¹¹ homozygous flies exhibit a total fusion of L2-L3 and L4-L5 with the corresponding loss of intervein regions B and D. The size of the wing is also reduced and the posterior margin is partially lost. (G) High magnification of L2 and L3 fusion, which is mostly associated with L2 thickening, as L5 is for L4-L5 fusion. Note the ventral pattern of corrugation in L2 and the sensillia campaniforme, and dorsal corrugation in L3.