fig1

Figure 1. Structure and composition of the two vesicles; their release from the plasma membrane by exocytosis and outward budding. A comparison of the images confirms that exosome vesicles are smaller than ectosome vesicles. Plasma membranes of exosomes are in black, whereas those of vesicle membranes are different: sky blue for those of endocytic nature, i.e., the MVB (B) and its exosomes (A and B); violet for those of ectosomes (A and B), in which plasma membrane and endosome are mixed. In exosome and ectosome vesicles, the color of the lumen is substantially different: lemon yellow for exosomes (A and B) and maya blue for ectosomes (A and B). The present comparison emphasizes the moderate chemical distinction between the vesicle types (A). Several essential membrane proteins are listed below. Some (e.g., tetraspanins and integrins) predominate in exosome but are also present in ectosome. In contrast, other proteins (e.g., receptors, glycoproteins, and metalloproteinases) are present in ectosomes and are not appreciable in the exosome. In both A vesicles, nucleic acids are present (neon orange) in the depth of the lumen. B images show the release of the two vesicle types: by exocytosis of MVBs, with the subsequent release of exosomes, by outward budding of ectosomes followed by growth and then outward release from the plasma membrane. The images of the two enlarged vesicles shown in two A are reproduced with permission^[26].