Fig. 6. Tou regulates proneural expression through the DC-specific enhancer of the ac-sc complex. Late third instar thoracic imaginal discs show lacZ expression at the DC site (Garcia-Garcia et al., 1999). In each case, the reaction was left for one hour at 22°C. (A) Wild-type pattern with lacZ expression in the DC area (arrow) (w¹¹¹⁸/+; DC: ac-lacZ/+). (B,C) Decrease of tou function results in a reduction in lacZ activity at the DC site (B: tou²; DC: ac-lacZ/+; C: tou^E44.1; DC: ac-lacZ/+). (D,E) pnr^D1 behave as constitutive activator of proneural expression (pnr^D1/DC: ac-lacZ/+) and causes increased lacZ activity. Reducing tou function in pnr^D1 suppresses excess lacZ activity at the DC site (tou²/tou²; pnr^D1/DC: ac-lacZ/+), demonstrating that Pnr and Tou regulate ac-sc expression through the DC enhancer. (F) Reduced Iswi function leads to a severe decrease of lacZ activity at the DC site (Iswi¹/Iswi²; DC: ac-lacZ/+). (G,H,I) Overexpressed Tou activates lacZ expression driven by the DC enhancer (ap^Gal4/EP622; DC: ac-lacZ/+) whereas overexpression of the dominant-negative Iswi (Iswi^K159R) is associated with a decrease in lacZ activity (ap^Gal4/Iswi^K159R; DC: aclacZ/+).