Fig. 10. One or more members of the E(spl)-C encode for the repressor activity that arrests SOP development in cells of Su(H) mutant proneural clusters. (A) Organization of the E(spl)-C. The diagram is based on previous work (Schrons et al., 1992; Bailey and Posakony, 1995; deCelis et al., 1996; Lai et al., 2000a; Lai et al., 2000b). Blue boxes label the genes that encode bearded-like genes; red labels the genes that encode bHLH repressors. The Df(3R)E(spl)^b32.2 uncovers all genes of the complex. The diagram reveals that six genes of the complex are expressed in the notal region of the wing imaginal disc. The expression of three of these genes [m, m4 and E(spl)m8] is upregulated in cells of Su(H) mutant proneural clusters. Overexpression of m and m4 causes neurogenic and E(spl)m8 anti-neurogenic phenotypes. (B,C) Expression of Sens (B) and Hnt (C) in Su(H) mutant wing imaginal discs, which carry one copy of the deficiency Df(3R)E(spl)^b32.2 in their genome. The expression of the markers is revealed by antibody staining. (B,C) A reduction of the number of the genes of the E(spl)-C by half is sufficient to regain expression of hnt and sens in cells of Su(H) mutant proneural clusters. This suggests that the repressor function that is repressed by Su(H) is encoded by one or more members of the complex. (D) Expression of E(spl)m8-lacZ in Psn^C1 mutant wing imaginal discs. Arrows indicate the proneural clusters. The cells of the clusters express high levels of E(spl)m8-lacZ. (D,E) Expression of E(spl)mß-CD2 in wild-type (D), Su(H)⁴⁷ mutant wing imaginal discs (E). Expression of E(spl)mß-CD2 is reduced in the Su(H) mutant wing imaginal discs. A similar reduction is observed in Psn mutant discs (not shown)

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