Fusion and fission of mitochondria and mtDNA foci. (A-C) Four pairs of frames (collected at 10 s intervals) from three movies of living cells (made as in Figure 4A,4B) showing YFP and ethidium fluorescence (marking mitochondria and mtDNA, respectively) are illustrated. Arrows mark a mtDNA focus that splits (A), two foci that fuse (B), and the point where a mitochondrion splits next to one mtDNA focus to give two separate tips (C). Bar: 1 μm. (D-F) Cells with YFP-tagged mitochondria were fixed, DNA and Drp1 immunolabelled with Cy5 and Cy3, and imaged; two views of one cell are shown in (D) and (E). In the merge (E), mtDNA often lies next to Drp1, which is also found in the cytoplasm . Bar: 1 μm. A cross-correlation analysis of the distribution of mtDNA and Drp1 (data from 15 images like those in (D,E)); Pearson's coefficient (r
) indicates that Drp1 is excluded from ~0.3 μm to each side of mtDNA foci (F).