Figure 2. The Drosophila NRF-2α/GABPβ homologue Delg is required for mitochondrial biogenesis.

(A) Schematic representation of the homology between human NRF-2α and Drosophila Delg. The pointed and ETS domains are 37% and 74% identical in amino acid sequence, respectively. The Q¹⁹³ to Stop codon mutation in delg⁶¹³ [21] is indicated. (B) MitoTracker and DAPI stainings of fixed fat bodies from third instar larvae. Whereas wild type cells show abundant staining throughout the cytoplasm, delg mutant cells show a strong reduction in staining. (C) Quantitation of MitoTracker staining. Mean fluorescent intensity per cell was calculated in ImageJ. Quantitation was done in blind, n≥21. (D) Nonylacridine orange (NAO; in green), which detects the mitochondrial phospholipid cardiolipin, and Hoechst³³³⁴² (specific for DNA, shown in blue) stainings in unfixed larval fat bodies. (E) Electron microscopy images of larval fat bodies. Arrows point to mitochondria, which show a strong size reduction in delg mutant cells. (F) Quantitation of electron microscopy, shown is the average mitochondrial area, n≥34. (G) Homozygous mutant clones for delg were induced using the Flp/FRT system, delg^tne/delg^tne cells are recognized by the absence of GFP (arrows), and show strong, cell-autonomous reduction in MitoTracker staining. Bar equals 20 µm, except 2 µm in E.