Morphometric analysis of ERTGoCS. (A) Electron micrograph showing ER (white arrowhead) closely apposed (red dashed line) to the TGN (black arrowheads) in a HeLa cell expressing TGN46-HRP (visualized by the DAB reaction that produces a dark product in the lumen of the TGN). Golgi cis elements are indicated. (B) Measurement of ERTGoCS distance (left; y axis) and length (right; y axis). Mean ± SD of 40 and 22 Golgi stacks, respectively, representative of three independent experiments. (C) Percentage of Golgi stacks negative (white bar) or positive (black bar) for ERTGoCS (left part of graph). In the ERTGoCS-positive Golgi stacks, the frequency distribution of the ERTGoCS surface area was calculated and expressed as a percentage of the total TGN surface (Materials and methods). n = 130 Golgi stacks. (D) FIB-SEM images of a HepG2 cell. Four images from Video 1 taken every 60 nm representing a total depth of 240 nm. The ER is colored in red and the TGN in green. The small arrow indicates a clathrin-coated profile that identifies the trans pole of the Golgi.