Plenary Session III (Imaging) – Light Microscopy
Dynamic actin cycling regulates mitochondrial dynamics
Mitochondria are dynamic organelles that undergo both fission and fusion, and can be actively translocated along the microtubule cytoskeleton to sites of cellular need. The role of the actin cytoskeleton in the modulation of mitochondrial dynamics has been well-studied in yeast, but is less clear in mammalian cells. Using live-cell imaging on a spinning disk confocal microscope, we identified a cyclic assembly/disassembly process, in which actin filaments transiently assemble around subpopulations of mitochondria, leading to a localized fragmentation of the interconnected mitochondrial network. Following actin disassembly, mitochondrial fragments rapidly re-fuse to reform the steady state network. We propose that in interphase cells, this cycling promotes network remodeling to maintain homeostasis. Longer-term imaging indicates that actin cycling markedly accelerates as cells enter mitosis. As mitochondria lose their connection with the microtubule cytoskeleton in dividing cells, we find that actin cycling has a distinct effect on mitochondrial dynamics during mitosis. Active assembly of actin filaments leads to rapid bursts of mitochondrial motility that effectively drive spatial mixing. To monitor actin assembly and mitochondrial mixing, we have applied super-resolution, iSIM and lattice light sheet microscopy as well as localized photo-activation of fluorophores or local induction of reactive oxygen species. Based on these observations, we propose that dynamic actin cycling in mitosis drives spatial shuffling to promote balanced inheritance of mitochondria in the resulting daughter cells.