Fig. 7.
Ultrastructure of ERESs engulfed by lysosomes. (A and C) Correlative single-slice Airyscan and transmission electron microscopy images of MC3T3 cells transfected with GFP-proα2G610C(I), TagBFP2-LC3, Apple-Sec23, and LAMP1-Halo and treated with 100 µM leupeptin for 6 h to prevent Sec23 degradation. Autophagic procollagen ERES that appears to be only partially engulfed by lysosomal membrane is labeled 1. Lysosomes with internalized procollagen, LC3, and Sec23 are labeled 2 and 3. Lysosomes with internalized degradation products, procollagen, LC3, Sec23, and LAMP1 membranes are labeled 4 and 5. The asterisk in lysosome 5 (C) marks an apparent large clump of internalized lysosomal membranes. The arrow marks rough ER filled with procollagen, which is adjacent to lysosome 5. White outlines of lysosomes 4 and 5 are projected onto the fluorescent channels. Individual blue channels are displayed in cyan. (Scale bars: 0.5 µm.) (B and D) Line plots of relative fluorescence intensities (RFU) along the yellow dashed lines (top to bottom) shown in the corresponding fluorescence channels (A and C) above the plots.