Expression of mutant Idh in the fly CNS. (A) Introduction of genetic elements that modulate caspase-dependent apoptosis genes to CCAP neurons expressing Idh-R195H. (B) Idh-R195H enhances the apoptosis-driven phenotype for developing eye ectopically expressing Reaper (Rpr) under control of the Gmr-Gal4 promoter. (C) Idh-R195H enhances the apoptosis-driven phenotype for developing eye cells expressing dsRNA knocking down DIAP1 under control of the Gmr-Gal4 promoter. (D) Glucose-6-phosphate dehydrogenase (G6PD or G6PDH) and WT Idh, which are expected to increase the NADPH pool, enhanced the wing-expansion defect caused by expression of Idh-R195H in CCAP neurons. In contrast, alleles expected to lower the pool of NADPH, including a deficiency of Idh and dsRNA against Idh, suppressed the phenotype. (E) Model for Idh-R195H-induced phenotype in the fly CNS. Idh-R195H consumes NADPH and produces D-2HG, leading to ROS formation. This leads to p53-induced caspase-independent cell death. Cell death of CCAP neurons that secrete bursicon to enforce wing expansion leads to a wing-expansion defect. G6PDH and genes that produce NADPH enhance the phenotype. SOD2 scavenges ROS to suppress the phenotype. All crosses were done at 25°C unless otherwise indicated. Genotypes: (A) CCAP-Gal4, UAS-Idh-R195H/+ (control). CCAP-Gal4, UAS-Idh-R195H/UAS-DIAP1. CCAP-Gal4, UAS-Idh-R195H/Dronc[dsRNA]. CCAP-Gal4, UAS-Idh-R195H/Apaf1[dsRNA]. CCAP-Gal4, CCAP-Gal4, UAS-Idh-R195H/p53[dsRNA]. (B) Gmr-Gal4/+; UAS-Rpr/+. Gmr-Gal4/+; UAS-Rpr/UAS-Idh-WT. Gmr-Gal4/+; UAS-Rpr/UAS-Idh-R195H. (C) Gmr-Gal4/+; UAS-DIAP1/+. Gmr-Gal4/+; UAS-DIAP1/UAS-Idh-WT. Gmr-Gal4/+; UAS-DIAP1/UAS-Idh-R195H. (D) CCAP-Gal4, UAS-Idh-R195H/+ (control). CCAP-Gal4, UAS-Idh-R195H/UAS-G6PD. CCAP-Gal4, UAS-Idh-R195H/UAS-Idh-WT. CCAP-Gal4, UAS-Idh-R195H/+; IDH[nNC1]/+. CCAP-Gal4, UAS-Idh-R195H/UAS-Idh-R195H. IDH[nNC1]/+ indicates a null allele of endogenous Idh.⁸⁰  Flies were photographed with a Leica Kombistereo microscope, original magnification ×10. dsRNA, double-stranded DNA.