Autophagosomes: biogenesis from scratch?

To survive extreme environmental conditions, and in response to certain developmental and pathological situations, eukaryotic organisms employ the catabolic process of autophagy. This degradative pathway allows cells to eliminate large portions of the cytoplasm, from aberrant protein aggregates to superfluous or damaged organelles and even entire organisms such as invading bacteria. Structures targeted for destruction are sequestered into large double-membrane vesicles called autophagosomes and then delivered into the interior of the lysosome or vacuole, where they are consumed by resident hydrolases. Autophagosome formation during selective autophagy is dependent upon the cargoes, and in all cases seems to involve expansion of the sequestering membrane.