FIGURE 1.

Biogenesis and secretion of exosomes. Exosome biogenesis begins in the endosome pathway. The cytoplasmic membrane invaginates to form early endosomes, parts of early endosomes are recycled by the Golgi apparatus, but the majority of them mature into late endosomes (also called MVBs). The intraluminal vesicles (ILVs) in MVBs either secrete to the extracellular environment to form exosomes or are targeted to lysosomes for degradation. The autophagy pathway is proposed to interact with the endosome pathway, and the autophagosomes and MVBs can fuse to form amphisomes, which can be degraded by lysosomes or secreted extracellularly.