Figure 1.

The biogenesis of extracellular vesicles (EVs). Exosomes and ectosomes are two types of EVs secreted by cells. Exosomes (~30–200 nm in diameter) originate from the endosomal pathway and are secreted by the fusion of multivesicular bodies (MVBs) with the plasma membrane. Ectosomes (size range ~50–500 nm) are generated by the direct outward budding of the plasma membrane. The budding of EVs involves a variety of mechanisms, and is a combination of one or more of the following mechanisms: endosomal sorting complexes required for transport (ESCRT) complex, neutral sphingomyelinase 2 (nSMase2) generating ceramide, GTPase Ral, and the Rho family. However, specific biogenesis mechanisms are not yet clearly known. EVs are highly heterogeneous population. The cargos of EVs contain different types of cell surface proteins, intracellular protein, genetic materials [such as DNAs, messenger RNAs (mRNAs), and miRNAs], and lipid.