Fig. 2. Response of EE4-lacZ to bHLH transgene expression and E(spl) loss of function in third instar wing disks. (A-H) UAS transgenes (as noted on each panel) were driven by pnr-Gal4, which expresses in the proximal notum (region shaded green in A; note SC and DC proneural clusters, white and black arrowheads, respectively). (A) Wild-type pattern, which corresponds to the proneural clusters present at this stage (compare with Ac accumulation in I). (B) EE4-lacZ was abolished by UAS-E(spl)m7 expression. (C) EE4-lacZ was significantly reduced by UAS-E(spl)m expression. (D) UAS-E(spl)m7KNEQ also repressed strongly. (E) EE4-lacZ was activated when UAS-sc is present, but severely diminished when E(spl)m7 (F) or E(spl)m7KNEQ (H) were co-expressed. Note that weak patchy expression remains. (G) Co-expression of UAS-E(spl)m did not suppress EE4-lacZ activation by UAS-sc. (I) Wild-type and (J) UAS-E(spl)m7; pnr-GAL4 disk immunostained for Ac. Accumulation in proneural clusters was seen in both cases — despite E(spl)m7 expression. Over-accumulation in SOPs of the dorsocentral cluster was abolished by E(spl)m7 (arrow). Insets show the boxed region of the notum at twice the magnification. (K,L) EE4-lacZ disks developed lightly with X-gal to compare levels of expression between wild-type disks (K — compare with wild-type disk developed longer in A) and disks null for E(spl)m8 and m7 (L). Although the E(spl) mutation does not affect expression pattern, it results in a more intense signal in all proneural clusters. (M,M') A mitotic clone null for the entire E(spl)-C is visualized by absence of green nuclear Myc staining. ß-galactosidase (EE4-lacZ) is visualized in red. The clone (outlined in M'), which overlaps the distal wing margin, shows more intense EE4-lacZ staining, consistent with loss of repression due to the absence of E(spl) function. (M') Red channel only.