Vesicular trafficking and autophagosome formation.

The source of the autophagosome membrane, and the formation of the autophagosome remain the most important questions for understanding autophagy. Fundamentally, the process of autophagosome formation is similar between yeast and mammalian cells and many of the proteins involved (called the autophagy-related (Atg) proteins) are known, having been first discovered in yeast. However, both in yeast and mammalian cells, the molecular details are missing to explain how the double-membrane autophagosome is formed. Important advances in our understanding of the formation process have recently been obtained, and here, we review and interpret these data in the context of well-known paradigms of membrane trafficking to develop some hypothetical models for how an autophagosome forms in mammalian cells.