Dynamics of mitochondrial cristae. (a) Transmission electron microscopy (TEM) of mitochondria from HeLa cells. (b) Dual-color live-cell imaging of mitochondria. HeLa cells stably expressing COX8A-SNAP fusion proteins were labeled using SNAP-Cell SiR. In addition, mtDNA was labeled with PicoGreen (red). The cristae were visualized by STED nanoscopy, the nucleoids by confocal scanning light microscopy. (c) Live-cell time-lapse STED nanoscopy of mitochondria. Mitochondria were recorded every 15 seconds. Shown are three frames out of ten. Arrows indicate the behavior of two separated groups of cristae during the fission of a mitochondrion. The whole image series is shown in Supplementary Movie S1. (b) Shows unprocessed raw data without background subtraction; in (c) photobleaching was compensated by adapting the color table. Scale bars: a: 0.5 µm; b,c: 1 µm.