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© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.

Abstract

Autophagosome biogenesis occurs in the transient subdomains of the endoplasmic reticulum that are called omegasomes, which, in fluorescence microscopy, appear as small puncta, which then grow in diameter and finally shrink and disappear once the autophagosome is complete. Autophagosomes are formed by phagophores, which are membrane cisterns that elongate and close to form the double membrane that limits autophagosomes. Earlier electron-microscopy studies showed that, during elongation, phagophores are lined by the endoplasmic reticulum on both sides. However, the morphology of the very early phagophore precursors has not been studied at the electron-microscopy level. We used live-cell imaging of cells expressing markers of phagophore biogenesis combined with correlative light-electron microscopy, as well as electron tomography of ATG2A/B-double-deficient cells, to reveal the high-resolution morphology of phagophore precursors in three dimensions. We showed that phagophores are closed or nearly closed into autophagosomes already at the stage when the omegasome diameter is still large. We further observed that phagophore precursors emerge next to the endoplasmic reticulum as bud-like highly curved membrane cisterns with a small opening to the cytosol. The phagophore precursors then open to form more flat cisterns that elongate and curve to form the classically described crescent-shaped phagophores.

Details

Title
Morphology of Phagophore Precursors by Correlative Light-Electron Microscopy
Author
Gudmundsson, Sigurdur Runar 1 ; Kallio, Katri A 2 ; Vihinen, Helena 3   VIAFID ORCID Logo  ; Jokitalo, Eija 3   VIAFID ORCID Logo  ; Ktistakis, Nicholas 4 ; Eskelinen, Eeva-Liisa 5   VIAFID ORCID Logo 

 Molecular and Integrative Biosciences, University of Helsinki, 00790 Helsinki, Finland; Biomedical Center, School of Health Sciences, University of Iceland, 101 Reykjavik, Iceland 
 Molecular and Integrative Biosciences, University of Helsinki, 00790 Helsinki, Finland 
 Institute of Biotechnology, University of Helsinki, 00790 Helsinki, Finland 
 Babraham Institute, Cambridge CB22 3AT, UK 
 Institute of Biomedicine, University of Turku, 20520 Turku, Finland 
First page
3080
Publication year
2022
Publication date
2022
Publisher
MDPI AG
e-ISSN
20734409
Source type
Scholarly Journal
Language of publication
English
ProQuest document ID
2724215472
Copyright
© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.