Autophagosomal Membrane Origin and Formation.

Autophagosome formation is a regulated membrane remodeling process, which involves the generation of autophagosomal membrane precursors (vesicles), the assembly of the autophagosomal membrane precursors to form the phagophore, and phagophore elongation to complete the autophagosome. The sources of the autophagosomal membrane precursors are endomembrane compartments, such as the endoplasmic reticulum (ER), the ER-Golgi intermediate compartment (ERGIC), ER-exit sites (ERES), and endosomes. In response to stress, these structures are remodeled, to generate the early autophagosomal membrane precursors. The phagophore assembly site (PAS), which mainly localizes on the ER, harbors the site for autophagosomal membrane assembly, elongation, and completion. ATG proteins, membrane remodeling factors, and autophagic membranes follow a precise choreography to complete the overall process. In this chapter, we briefly discuss our current knowledge on the membrane origins of the autophagosome, as well as autophagosomal precursor generation, assembly, and expansion.