Figure 1.

Schematic and simplified representation of the endolysosomal system showing the different organelles described in this article. Sorting endosomes (SE) are vacuolar compartments often bearing bilayered, flat clathrin coats (brown). Tubules emanate from SE that form the recycling endosomes (RE). The RE may localize to the peri-Golgi area forming the endocytic recycling compartment (ERC) or distribute to the cell periphery. The RE network is complex with multiple sorting sites, thereby the tubular sorting endosome (TSE) or tubular endosomal network (TEN) is also represented. AP1 (red) and AP3 (green) coated buds on RE (ERC/TSE/TEN) are shown. Late endosomes correspond to multivesicular bodies (MVBs) filled with intraluminal vesicles (ILVs). MVBs are fated for fusion with lysosomes. In some cells, a population of MVBs fuse with the plasma membrane, a process during which the ILVs are secreted as exosomes. Gray arrows indicate directions of transport/maturation of compartments. Blue arrows indicate invagination at the endosomal membrane of SE and MVBs required for ILV formation.