Generation of stress fibers through myosin-driven re-organization of the actin cortex

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Abstract

Contractile actomyosin bundles, stress fibers, govern key cellular processes including migration, adhesion, and mechanosensing. Stress fibers are thus critical for developmental morphogenesis. The most prominent actomyosin bundles, ventral stress fibers, generated through coalescence of pre-existing stress fiber precursors. However, whether stress fibers can assemble through other mechanisms has remained elusive. We report that stress fibers can also form without requirement of pre-existing actomyosin bundles. These structures, which we named cortical stress fibers, are embedded in the cell cortex and assemble preferentially underneath the nucleus. In this process, non-muscle myosin II pulses orchestrate the reorganization of cortical actin meshwork into regular bundles, which promote reinforcement of nascent focal adhesions, and subsequent stabilization of the cortical stress fibers. These results identify a new mechanism by which stress fibers can be generated de novo from the actin cortex, and establish role for stochastic myosin pulses in the assembly of functional actomyosin bundles.

Data availability

All data generated or analysed during this study are included in the manuscript and supporting files. Source data files for pulse quantification are provided in GitHub (https://github.com/UH-LMU/lmu-users/tree/master/jaakko/NMIIA_pulses).

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Jaakko I Lehtimäki

Institute of Biotechnology, University of Helsinki, Helsinki, Finland

For correspondence
jaakko.lehtimaki@helsinki.fi

Competing interests
No competing interests declared.
Eeva Kaisa Rajakylä

Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland

For correspondence
kaisa.rajakyla@helsinki.fi

Competing interests
No competing interests declared.
Sari Tojkander

Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland

For correspondence
sari.tojkander@helsinki.fi

Competing interests
No competing interests declared.
Pekka Lappalainen

Program in Cell and Molecular Biology, Institute of Biotechnology, University of Helsinki, Helsinki, Finland

For correspondence
pekka.lappalainen@helsinki.fi

Competing interests
Pekka Lappalainen, Reviewing editor, eLife.

"This ORCID iD identifies the author of this article:" 0000-0001-6227-0354

Funding

Sigrid Juselius Foundation (4708344)

Pekka Lappalainen

Aatos Erkko Foundation (4704407)

Pekka Lappalainen

Academy of Finland (294174)

Sari Tojkander

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.