Dual axis electron tomography of ER-DMS contacts. (A) TEM image of a stage II MK showing a tubular ER cisterna extending toward the DMS. Bar, 500 nm. (B-C) Tomographic sections from a dual axis tomogram of the area in A. Note that the membranes of the DMS and ER are closely apposed but not in continuity (arrowheads). Bars, 100 nm. (D) Minimal distance in nm between the ER and DMS, as quantified from 40 contact sites in 6 tomograms. (E-G) Selected tomographic sections (∼5 nm thick) of tubular ER cisternae (arrowheads) extending toward the DMS. Bar, 100 nm. (F-G) Selected Z-orientations from the tomogram revealing filamentous structures connecting ribosome-free ER domains with the DMS. Bars, 10 nm. er, endoplasmic reticulum.