Autophagy degrades or recycles cellular components through the formation of a double membrane vesicle, termed autophagosome, which fuses with the lysosome, where the degradation process takes place. In this Graphical Review we provide an updated and comprehensive overview on autophagosome biogenesis, a unique process consisting of three main phases: nucleation, expansion, and maturation, tightly regulated by lipid species and protein complexes.

Autophagy is an intracellular catabolic process that eliminates cytoplasmic constituents selectively by tight engulfment in an isolation membrane or recycles bulk cytoplasm by nonselective sequestration. Completion of the isolation membrane forms a double membrane vesicle, termed autophagosome, that proceeds to fusion with the lysosome, where the inner membrane and its cytoplasmic content are degraded. Autophagosome biogenesis is unique in that the newly-formed membrane, termed phagophore, is elongated by direct lipid flow from a proximal ER-associated donor membrane. Recent years mark a tremendous advancement in delineating the direct regulation of this process by different lipid species and associated protein complexes. Here we schematically summarize the current view of autophagy and autophagosome biogenesis.