Fig. 2: CD63 and CD9 transiently co-localize in multivesicular bodies and at the plasma membrane.

a Principle of the RUSH system used to follow CD63 and CD9 intracellular trafficking. SBP streptavidin binding peptide, strept streptavidin, ER endoplasmic reticulum. b Micrographs and quantifications of live imaging of HeLa cells co-transfected with the CD63-mCherry and CD9-eGFP RUSH plasmids. Biotin at 40 μM was added at T = 0. White arrows show peripheral compartments where CD63 and CD9 co-localize. Z-projection of 11 planes. Scale bar: 5 μm. Quantification upon time of three independent experiments showing the mean ± SD eGFP and mCherry fluorescence intensity in the Golgi and in large compartments, the mean ± SD number of eGFP- or mCherry-positive small compartments and the median and range of the Pearson’s co-localization coefficient between eGFP and mCherry where automatically quantified. N = 3 independent experiments. 5 fields per experiments where imaged, for a total of at least 10 individual cells to analyze per experiment. c Representative electron microscopy images of HeLa cells co-transfected with RUSH constructs of CD63-mCherry and CD9-eGFP, 1 h or 2 h after incubation with biotin, or at steady-state, labeled with anti-eGFP gold 10 nm (red arrows) and anti-mCherry gold 15 nm (blue arrows). Relative labeling index (RLI) in each compartment quantified from 7 different fields per replicate is represented as mean (n = 2 independent biological replicates). d Confocal microscopy pictures of HeLa cells (z-projection) co-transfected with CD63-mCherry- and CD9-eGFP-RUSH plasmids, and stained with anti-Rab7 after 1 h of incubation with biotin. Scale bar: 10 μm. Mander’s coefficients representing the % of CD9 + /CD63-, CD9-/CD63 + , and CD9 + /CD63 + intracellular compartments also positive for the Rab7 signal in each cell are shown. Results from two independent experiments are shown, each dot represents one cell (23 cells from replicate 1, and 24 cells from replicate 2) and the median is represented. Ordinary one-way ANOVA with a Tukey’s multiple comparisons test was performed to compare the different categories of intracellular compartments shown on the graph.