Developmental coordination of mitochondrial dynamics and membrane remodeling drives organelle morphogenesis

Cellular morphogenesis involves the dynamic remodeling of mitochondria. For example, during spermatogenesis, mitochondria undergo distinct morphological changes as the cells transition from stem cells to mature sperms. However, how distinct processes regulating mitochondrial dynamics are developmentally coordinated to sculpt organelle morphology remains unclear. Using expansion microscopy to study Drosophila spermatogenesis, we first document a transition of tubular mitochondria into multilayered sheets organized in a sphere known as nebenkern, which then divides and remodels into two very long mitochondrial derivatives. We then show that the transition to organized multilayered structures is marked by membrane tubulation in the middle forming a division plane, the assembly of OPA1 and DRP1 rings along the division plane and a temporally synchronized downregulation of the fusion protein Mitofusin/Marf. We further show that Marf downregulation is mediated by the PINK1-PARK pathway, revealing an active suppression of fusion of mitochondrial derivatives during their segregation. Our study elucidates a developmentally programmed mechanism coupling membrane tubulation, fission, fusion, and membrane remodeling to drive mitochondrial morphogenesis during differentiation.