Electron transport chain complex I and mitochondrial fusion regulate ROS for differentiation in Drosophila neural stem cells

Mitochondrial activity and dynamics play crucial roles in regulating neuronal differentiation. Neural stem cells (NSCs) or neuroblasts in Drosophila require the regulation of mitochondrial fusion, along with the activity of the electron transport chain (ETC), to meet the metabolic demands of differentiation. However, the mechanisms by which mitochondrial fusion and activity together regulate NSC differentiation are not well understood. We investigated the relationship between mitochondrial fusion, and ETC complex I activity during Drosophila neuroblast differentiation. We found that depletion of complex I subunits did not affect the number of type II neuroblasts but reduced their proliferation, thereby decreasing the numbers of mature intermediate precursor cells (mINPs), ganglion mother cells (GMCs), and neurons in each lineage. Complex I depletion decreased the mitochondrial membrane potential and cristae numbers, and increased mitochondrial fragmentation and ROS. Increased ROS resulting from the depletion of antioxidant enzymes also led to a decrease in mINPs, GMCs, and neurons in each type II neuroblast lineage. Both complex I and antioxidant protein depletion led to delayed G1/S transition and decreased nuclear cyclin E levels. Interestingly, the defects in proliferation, differentiation, and ROS in complex I and anti-oxidant protein depleted neuroblasts could be restored by fused mitochondrial morphology obtained through additional depletion of the fission protein Drp1. Further, overexpression of anti-oxidant proteins could alleviate the ROS and rescue the differentiation defect in complex I depleted type II neuroblasts. Together, this study reveals a role for complex I and mitochondrial fusion in restricting ROS for differentiation in Drosophila neuroblasts.