FIGURE 1.

Exosome biosynthesis. (1) Early endosomes are formed by inward budding of the limiting membrane of cells. Surface proteins (orange triangles) may be incorporated into the early endosomal membrane. (2) Early endosomes undergo a maturation process to form late endosomes, in which the biogenesis of exosomes occurs by continuous invagination of the limiting membrane. (3) This particular type of late endosome, which ends up accumulating numerous small intraluminal vesicles with a diameter of 40 to 150 nm is called multivesicular body (MVB). During this process, cytosolic components (eg, miRNAs) are actively packed into the vesicles. In addition, communication with the Golgi apparatus through bidirectional vesicle exchange leads to the incorporation of tetraspanins (blue rectangles) into the membrane of the vesicles. (4) Besides that, cytosolic histone‐bound DNA fragments can be transported to MVBs via the autophagosome pathway. (5) Finally, MVBs either fuse with the plasma membrane causing the release of their content into the extracellular environment, or fuse with lysosomes for degradation of their cargo.