Fig. 5. Overexpression of UAS-chn stimulates the expression of sc and of constructs bearing ASC enhancers specific for individual proneural clusters. (A-C) Sc accumulation is shown in the green channel and that of Sens in the red one. (A) Wild-type late third instar disk shows the distribution of Sc in proneural clusters and that of Sens in SOPs and additional cells flanking the prospective wing margin (WM). Proneural clusters: T/TSM, twin sensilla of the WM; L, vein L3; D/DC, dorsocentral. (B) Overexpression in the wing pouch (MS1096-Gal4 driver) induces ectopic expression of sc and of sens, but largely eliminates expression of these genes at the prospective wing margin. (C) Overexpression in the medial and central notum territory (MS248-Gal4 driver) leads to strong, almost generalized expression of sc and the emergence of many ectopic SOPs. (D) Generalized UAS-chn expression (C765-Gal4 driver) stimulated Sc accumulation (green) at many sites of the wing disk, but it did not enhance atonal expression, which remained confined to its wild-type sites (Jarman et al., 1993b), like a few cells in the prospective ventral radius (red, arrowhead). (E-O) ß-galactosidase accumulation is shown in green. (E,F) Expression of the 2.3-lacZ construct (Culí, 1998), which bears the L3 + TSM enhancer, in a wild-type disk and in a disk overexpressing UAS-chn with the MS1096-Gal4 driver, respectively. (G,H) Expression of the AS1.4DC-lacZ=DC-lacZ construct, which bears the DC enhancer, in a wild-type disk and in a disk overexpressing UAS-chn with the C765-Gal4 driver. (I,J) DC-lacZ expression in disks devoid of functional ac and sc genes (In(1)sc^10.1 allele). The construct is still expressed (I) and it is greatly stimulated by UAS-chn (J; C765-Gal4 driver). (K,L) Expression of the DC-lacZ construct in the presence of UAS-chn driven by pnr-Gal4 [a hypomorphic allele of pnr (Heitzler et al., 1996)] in the presence of a wild-type allele of pnr (K) or the null allele pnr^VX6 (L). (M) This construct is not expressed in the pnr-Gal4/pnr^VX6 genetic background (the green channel background has been enhanced to better appreciate the absence of expression). (N,O) Overexpression of UAS-chn with the C734-Gal4 driver, whose pattern of expression is revealed by the accumulation of Chn protein (red), stimulates expression of the SOP-specific enhancer SRV-lacZ (green) in a background wild-type for the ASC (N), but fails to do so in an In(1)sc^10.1 mutant disk (O). The green channel is also shown separately.