Cells communicate with neighboring cells and condition their local environment by secreting soluble factors into the extracellular space. These well-studied facets of cell biology are essential for the establishment and maintenance of physiological homeostasis. However, accumulating evidence has revealed that specific ligands, enzymes, and macromolecules are distributed into the extracellular space by virtue of their association with small vesicles, which are released by a variety of cell types. Although the biological significance of such vesicles was initially debated, purification and subsequent functional studies have shown that these extracellular vesicles are bioactive organelles carrying a wide range of protein and nucleic acid cargoes. In many cases these vesicles are laden with molecules that are involved in cell signaling, although other diverse functions are being revealed at a rapid pace. In this Perspective, we discuss recent developments in the understanding of the major pathways of extracellular vesicle biogenesis and how these vesicles contribute to the maintenance of physiological homeostasis.
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