A three-dimensional study of organelle interrelationships in regenerating rat liver. 5. Autophagy

ER, mature Golgi, plasma and lysosomal membranes are all able to sequester bits of cytosol and eventually some organelles. These four modes to provide in autophagy are complementary to each other. Apart from the digestion of the sequestered material, the implicated membranes (respectively ER, Golgi, plasma or lysosomal membranes) are partially degraded. This may counterbalance the continuous new formation of these membranes. It is proposed that the thin outer membrane of ER-derived autophagosomes is gradually converted into thick lysosomal membrane through consecutive fusions with different types of Golgi vesicles and with small dense bodies.