The pixel size in xy was set to be 5 nm and the FIB-milling was done every 8 nm. The acquired raw FIB-SEM images were aligned using TrackEM2 (Cardona et al., PloS one, e38011, 2012) in ImageJ (http://rsbweb.nih.gov/ij/). After alignment, the stack was cropped, gray levels were inverted and the images were smoothened with a mean filter (kernel size: 15 × 15 nm). A small part of the nucleus is missing.