Focus: Autophagosome biogenesis

Autophagy allows cells to respond to adverse conditions, such as nutrient starvation, damage and pathogen invasion, and is crucial for maintaining cellular homeostasis. Formation of autophagosomes is an early step in the pathway; however, although the factors involved in this step are fairly well characterised, key questions remain, with the origin of the autophagosome membrane in particular being highly debated. In this Issue, we present a collection of three articles that examine important aspects of autophagosome biogenesis. First, the Hypothesis by Jana Sanchez-Wandelmer, Nicholas Ktistakis and Fulvio Reggiori (p. 185) addresses the possible role of ER exit sites (ERES) in the formation of autophagosomes as suggested by recent studies. On the basis of these data, the authors propose two models for how this ER compartment could affect autophagosome biogenesis and at which steps. Then, in the first Commentary, Sven Carlsson and Anne Simonsen (p. 193) turn their attention to the membrane and the lipid composition of the forming autophagosomes and discuss the recent progress in understanding membrane shaping and remodelling events required to accommodate the growing autophagosome. Finally, in our second Commentary, Tassula Proikas-Cezanne and colleagues (p. 207) focus on the role of the human WD-repeat protein interacting with phosphoinositides (WIPI) family, members of which recognise and decode the PtdIns3P signal at the nascent autophagosome, thereby functioning as autophagy-specific PtdIns3P-binding effectors.