Fig. 4: Ultrastructural analysis of nuclear envelope in dynamin TKO cells.

a–d Representative tomograms (left) of dynamin TKO cells, computational three-dimensional reconstruction (middle), and merge of the computational rendering over the tomogram (right). a–a” “Budding” of the outer nuclear membrane (ONM). b–b” Vesicle-like structures delimited by ONM, connected to the NE lumen by a long narrow membrane neck (inset) as if undergoing fission. Of note, these structures present ribosomes on their surface suggesting a link between NE remodeling and the ER. The size of small bud seen on the computational three-dimensional reconstruction is 70 nm (arrow). c–c” Irregular vesicle-like structure delimited by ONM, connected to the cytoskeleton (arrowhead) and the NE lumen by a long narrow membrane neck (inset). d–d” Double membrane vesicle-like structure containing DNA. Scale bar 300 nm; insets 205 nm. MemBrain software was used for automatic segmentation of reconstructed tomograms. Color code: yellow—outer nuclear membrane (ONM), cyan—inner nuclear membrane (INM); brown/blue—small vesicles with DNA/nuclear material present in their lumen; white—segmented membranes in the nuclear proximity with no connection to the NE (see “Methods” for the classification criteria).