Fig. 4. Analysis of SOP development in Su(H)⁴⁷; Psn¹² double mutant wing imaginal discs. Anterior is towards the left, ventral towards the bottom. Expression of Sens and 22C10 is detected by antibody staining. (A) Sens expression is lost in all clusters with the exception of some cells of the PNP cluster that have residual expression (arrowhead). (B) Expression of the SOP-E in the same disc as shown in A. The cells of the notal proneural clusters of the double mutant discs still express the SOP-E (arrows), indicating that the absence of Sens expression is not caused by the loss of the cells. (C) Merge of the pictures A and B, showing Sens expression in red and expression of the SOP-E in green. (D) Similar to Su(H) mutants, Su(H)⁴⁷; Psn¹² double mutants have lost the expression of 22C10, indicating that the cells of the proneural clusters fail to differentiate neurone-specific traits. (E) Expression of a weak UASSu(H) line in the proneural clusters of Su(H) Psn double mutant wing imaginal discs with scaGal4. The expression of UASSu(H) re-establishes the expression of Sens and 22C10 in the cells of the proneural clusters.