Munc13-4 regulates MVB size. (A and B) MDA-MB-231 cells stably expressing control shRNA (Ctrl) or Munc13-4 shRNA were fixed for immunofluorescence detection of endogenous CD63 (red) and LAMP1 (green) by confocal microscopy (A) or SIM (B). Bars, 5 μm. (C) Mean diameter of CD63⁺ structures in each indicated cell type imaged by confocal or SIM shown as mean values ± SE for three cells/group from three separate preparations (*, P < 0.05). (D) SIM showing orthogonal (top) and 3D reconstruction view of CD63 (red) and LAMP1 (green) in MDA-MB-231 cells stably expressing control shRNA (Ctrl) or Munc13-4. Bars, 5 μm. (E) 3D reconstruction of SIM images from Ctrl MDA-MB-231 cell in D of a single MVB labeling CD63 (red) and LAMP1 (green). Linescan of indicated channels is shown on the bottom. Bars, 1 µm.