Abstract
The mitochondrial inner membrane can reshape under different physiological conditions. How, at which frequency this occurs in living cells, and the molecular players involved are unknown. Here, we show using state-of-the-art live-cell stimulated emission depletion (STED) super-resolution nanoscopy that neighbouring crista junctions (CJs) dynamically appose and separate from each other in a reversible and balanced manner in human cells. Staining of cristae membranes (CM), using various protein markers or two lipophilic inner membrane-specific dyes, further revealed that cristae undergo continuous cycles of membrane remodelling. These events are accompanied by fluctuations of the membrane potential within distinct cristae over time. Both CJ and CM dynamics depended on MIC13 and occurred at similar timescales in the range of seconds. Our data further suggest that MIC60 acts as a docking platform promoting CJ and contact site formation. Overall, by employing advanced imaging techniques including fluorescence recovery after photobleaching (FRAP), single-particle tracking (SPT), live-cell STED and high-resolution Airyscan microscopy, we propose a model of CJ dynamics being mechanistically linked to CM remodelling representing cristae membrane fission and fusion events occurring within individual mitochondria.