FIG. 2.

Morphology of macroautophagy. Nucleation of the phagophore occurs following induction by the ULK1/2 complex. Elongation of the phagophore is aided by the ATG12–ATG5-ATG16L1 complex, the class III PtdIns3K complex, LC3-II, and ATG9. Eventually, the expanding membrane closes around its cargo to form an autophagosome and LC3-II is cleaved from the outer membrane of this structure. The outer membrane of the autophagosome will then fuse with the lysosomal membrane to form an autolysosome. In some instances, the autophagosome may fuse with an endosome, forming an amphisome, before fusing with the lysosome. The contents of the autolysosome are then degraded and exported back into the cytoplasm for reuse by the cell. See the text for details. This figure was modified from Figure 1 in Yang and Klionsky (153). ATG, autophagy-related; PtdIns3K, phosphatidylinositol 3-kinase; ULK, unc-51-like kinase (C. elegans). To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars