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A subdomain of the endoplasmic reticulum forms a cradle for autophagosome formation


Autophagy is a bulk degradation process in eukaryotic cells and has fundamental roles in cellular homeostasis.The origin and source of autophagosomal membranes are long-standing questions in the field. Using electron microscopy, we show that, in mammalian culture cells, the endoplasmic reticulum (ER) associates with early autophagic structures called isolation membranes (IMs). Overexpression of an Atg4B mutant, which causes defects in autophagosome formation, induces the accumulation of ER–IM complexes. Electron tomography revealed that the ER–IM complex appears as a subdomain of the ER that formed a cradle encircling the IM, and showed that both ER and isolation membranes are interconnected.

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Figure 1: Close association of the ER with the IM during autophagy.
Figure 2: Immunogold electron microscopy of ER–IM complexes.
Figure 3: Electron tomography of ER–IM complexes from control cells.
Figure 4: Electron tomography of two different ER–IM complexes shows a connection between the IM and the ER.
Figure 5: Possible models for autophagosome formation in mammalian cells.

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We thank H. Nishioka and N. Kajimura for technical assistance with electron tomography, K. Nishino for assistance with setting up a computer and for useful comments on figure presentations, H. Omori for technical assistance with immunoelectron microscopy and K. Matsunaga and N. Taguchi for technical assistance with plasmid construction. This study was supported by grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

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Authors and Affiliations



M.H.N., N.F., T.N., T.Y. and A.Y. designed experiments. M.H.N. performed conventional electron microscopy and electron tomography, N.F. performed cell biological and immuofluorescence experiments and A.Y. performed immunoelectron microscopy. M.H.N., T.Y. and A.Y. wrote the manuscript. T.N. and A.Y. contributed to conceptual discussions. A.Y. and T.Y. supervised the project.

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Correspondence to Tamotsu Yoshimori or Akitsugu Yamamoto.

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The authors declare no competing financial interests.

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Hayashi-Nishino, M., Fujita, N., Noda, T. et al. A subdomain of the endoplasmic reticulum forms a cradle for autophagosome formation. Nat Cell Biol 11, 1433–1437 (2009).

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