(A,B) MC3T3 cells transfected with Cherry-HSP47, Venus-proα1(I) (A) or Venus-proα2(I) (B), and marker of ER lumen (ssCFP-KDEL). (C,D) MC3T3 cells transfected with Cherry-HSP47 (C) or TagBFP2-HSP47 (D), Venus-proα1(I) (C) or GFP-proα2(I) (D) and marker of cis-Golgi CFP-GM130 (C) or Cherry-GM130 (D). Switching of the fluorescent tag colors in different images illustrates that each of these and subsequent experiments were performed with different combinations of fluorescent tag colors, to eliminate potential tag-specific effects. Arrows mark Golgi structures containing procollagen. All images are Airyscan (A,B) or confocal (C,D) single slices; scale bars = 10 μm (full cell) and 1 μm (zoomed areas); N≥20 (≥4 experiments with different FP combinations) for each panel.