Fig. 4

Super-resolution microscopy reveals that endosomes can carry both exogenous and endogenous exosomes. Culture performed according to Model 2, with neuron A-derived exosomes being labeled with the CellVue® Claret far-red fluorescent membrane dye (pseudocolored in green), neuron B labeled with Dendra2-CD9 (natively green but red when photoconverted) and neuron C containing no label (no color). a Conventional and (b) super-resolution images of a dendrite expressing Dendra2-labeled CD9. In the high-resolution image, structural features such as the plasma membrane become visible (scale bar 2 μm). c Magnification of the outlined rectangular region in (b). d Cross-section along the yellow line in (c) where the width of the dendrite and the thickness of the plasma membrane were measured. e-j Examples of colocalized endogenous endosomes and exogenous exosomes. e, f and g) showing events detected in axons. Panels h, i and j illustrate fusion events in soma and dendrites. In (h) and (i) exogenous exosomes are found close to the center of endosomal structures. Endosomal intraluminal nanovesicles cannot be resolved in red endosomal structures, but they contribute to the broader red fluorescence in the structure (ie: f, h and i). Scale bar 500 nm