Short linear structures connect the IM and ER in the early phase of receptor-mediated mitophagy. DRP1 KO HeLa cells were treated with DFP for 16 h and fixed with a mixture of aldehyde and osmium solutions for electron tomography. EM images of 115 serial sections (∼6.5-nm thickness) were reconstructed from three resin-embedded sections (300-nm thick each). (A–D) Representative EM image of section 51 (A) and its color-segmented 3D version (B), rotated ∼100° vertically, as indicated by the arrow (C and D). See also Video 6. (E–G) Enlargements of the boxed and labeled areas in D, captured from slightly different angles. (H and I) Serial images of two representative sites indicated in the boxed areas (left), arranged from left to right and labeled with the section(s) numbers. See also Videos 7 and 8. mt (pink), mitochondria; IM (green); L, linear structure (cyan); ER (blue); Go, Golgi complex (pale yellow). Arrows in A, H, and I indicate the IM. Colored arrowheads in E–G indicate linear structures, which correspond to the same-colored arrowheads in H and I. Scale bars: 200 nm (A) and 100 nm (E–I).