The Golgi complex as a source for yeast autophagosomal membranes

Today, more than 50 years after the discovery of autophagy, the origin of the autophagosomal membranes remains for the most part elusive. Many sources for the lipid bilayers have been proposed, but no conclusive evidence has been found to support one particular origin. The lipids do not appear to be generated at the site of autophagosome formation, the phagophore assembly site (PAS), since so far no lipid synthesizing enzyme has been found at this location. The current consensus is also that the autophagosomes do not directly bud off from a pre-existing compartment, and recent evidence in mammalian cells has revealed that the nascent autophagosome could expand through a lipid transfer mechanism from an adjacent organelle. In yeast, such an event has never been observed and data from our and other laboratories suggest that the Golgi complex could be a key player in mediating the expansion of the phagophore.