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Mol Biol Cell. 2018 Jun 1;29(11):1346-1358. doi: 10.1091/mbc.E17-11-0688. Epub 2018 Apr 10.

The contributions of the actin machinery to endocytic membrane bending and vesicle formation.

Author information

1
Department of Biochemistry and NCCR Chemical Biology, University of Geneva, 1211 Geneva, Switzerland.
2
Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.
3
Structural and Computational Biology Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.
4
Cell Biology Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
5
Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.

Abstract

Branched and cross-linked actin networks mediate cellular processes that move and shape membranes. To understand how actin contributes during the different stages of endocytic membrane reshaping, we analyzed deletion mutants of yeast actin network components using a hybrid imaging approach that combines live imaging with correlative microscopy. We could thus temporally dissect the effects of different actin network perturbations, revealing distinct stages of actin-based membrane reshaping. Our data show that initiation of membrane bending requires the actin network to be physically linked to the plasma membrane and to be optimally cross-linked. Once initiated, the membrane invagination process is driven by nucleation and polymerization of new actin filaments, independent of the degree of cross-linking and unaffected by a surplus of actin network components. A key transition occurs 2 s before scission, when the filament nucleation rate drops. From that time point on, invagination growth and vesicle scission are driven by an expansion of the actin network without a proportional increase of net actin amounts. The expansion is sensitive to the amount of filamentous actin and its cross-linking. Our results suggest that the mechanism by which actin reshapes the membrane changes during the progress of endocytosis, possibly adapting to varying force requirements.

PMID:
29851558
PMCID:
PMC5994895
DOI:
10.1091/mbc.E17-11-0688
[Indexed for MEDLINE]
Free PMC Article

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