Figure 1.

Schematic presentation of the biogenesis and composition of the three main classes of extracellular vesicles. Apoptotic bodies (left panel) are formed when cells enter apoptosis, and may contain nuclear material such as histones and DNA. They are heterogenous in size (50–5000 nm), irregularly shaped and harbor a variety of cellular proteins. Microvesicles (middle panel) are formed by budding and subsequent fission of the plasma membrane. Selective incorporation of membrane proteins and cytosolic proteins takes place during formation, resulting in vesicles which may be enriched in specific proteins and lipids compared to the parent cell. Microvesicles are thought to be smaller than apoptotic bodies (50–1000 nm) and more homogenously shaped. Selective enrichment of cellular content also occurs during the formation of exosomes (right panel), however exosomes originate from budding into the limiting membrane of large endosomal structures named multivesicular bodies (denoted with MVB). This process is facilitated by endosomal proteins. Subsequent fusion of MVBs with the plasma membrane results in release of the exosomes. Exosomes are small (<100 nm), relatively homogenous in size, and may contain (endosomal) proteins involved in their assembly, such as CD9, Alix and TSG101.

Abbreviation: NC, nucleus.