Fig. 4: Dual-colour 3D-MP-SIM visualized intra-organelle and inter-organelle interactions.

a, Dual-colour image (x–y cross-section) of the inner (PKmito Orange, magenta) and outer membranes (TOM20-mStayGold, green) of mitochondria in a live COS-7 cell, where the axial depth is 0.61 μm. Scale bar, 5 µm. b, Top: magnified x–y cross-sections at the indicated time points (for the region highlighted by the dashed box in a); the axial depth is 0.58 μm. These show the cristae dynamics in the lateral plane. Bottom: magnified y–z cross-sections (along the dashed line shown in the x–y view) at the indicated time points, showing the cristae dynamics in the axial plane. White arrowheads indicate dynamics in the inner mitochondrial membrane. Scale bars, 1 µm. c, Magnified x–y (main images) and the corresponding x–z and y–z cross-sections (smaller images) along the line indicated by two the arrows in the corresponding x–y view at the indicated time points (for the region highlighted by the dashed box in a), where the axial depth ranges from 0.71 to 1.16 μm. These show the mitochondrial nanotunnel extending from its existing structure at 41.40 s and retracting at 48.99 s, with white arrowheads indicating the tip of mitochondrial nanotunnel. Scale bars, 2 µm. d, Dual-colour image (x–y cross-section) of the outer mitochondrial membrane (TOM20-mStayGold, green) and the ER (HaloTag-Sec61β, magenta) in a live COS-7 cell, there the axial depth is 0.61 μm. Scale bar, 5 µm. e, Magnified x–y (top) and corresponding x–z (bottom) cross-sections along the dashed line in the x–y view at the indicated time points (for the region highlighted by the dashed box in d), where the axial depth ranges from 0.61 to 0.68 μm. White arrowheads indicate the contact sites and the coordinated motion of the ER and mitochondria. These show the ER extending through the central hole of the doughnut-shaped mitochondrion. Scale bars, 1 µm. f, Magnified 3D views and x–y cross-sections at the indicated time points (for the region highlighted by the dashed box in d), where the axial depth is 0.42 μm. These show that the ER wraps around the mitochondrial branch junctions. Scale bars, 1 µm. g, Magnified 3D views together with the x–y and corresponding x–z cross-sections obtained along the dashed line of the x–y view at the indicated time points (for the region highlighted by the dashed box in d), where the axial depth is 0.52 μm. These show interactions with the ER during sprouting, elongation, stabilization and retraction of the mitochondrial nanotunnels, and white arrowheads indicate the dynamics of mitochondrial nanotunnle surrounded by ER. Scale bars, 1 µm. All cross-section slices are 32.3 nm thick.