When cells are starved, are invaded by foreign bodies such as bacteria, and contain damaged organelles or aggregated proteins, double-membrane organelles called autophagosomes are formed within the cytoplasm to surround, isolate and deliver these materials to lysosomes for degradation. This pathway, called 'autophagy', is conserved from yeast to mammalian cells. Unlike other organelles, the autophagosome forms de novo, thus raising unique questions regarding its membrane biogenesis. Here we highlight a number of recent findings related to autophagosome formation and possible involvement of autophagy-specific vesicles originating from other organelles, but with particular attention on the formation sites and the relationship of the autophagosome to other organelles.
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