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Scaling behaviour in steady-state contracting actomyosin networks

Abstract

Contractile actomyosin network flows are crucial for many cellular processes including cell division and motility, morphogenesis and transport. How local remodelling of actin architecture tunes stress production and dissipation and regulates large-scale network flows remains poorly understood. Here, we generate contracting actomyosin networks with rapid turnover in vitro, by encapsulating cytoplasmic Xenopus egg extracts into cell-sized ‘water-in-oil’ droplets. Within minutes, the networks reach a dynamic steady-state with continuous inward flow. The networks exhibit homogeneous, density-independent contraction for a wide range of physiological conditions, implying that the myosin-generated stress driving contraction and the effective network viscosity have similar density dependence. We further find that the contraction rate is roughly proportional to the network turnover rate, but this relation breaks down in the presence of excessive crosslinking or branching. Our findings suggest that cells use diverse biochemical mechanisms to generate robust, yet tunable, actin flows by regulating two parameters: turnover rate and network geometry.

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Fig. 1: Quantitative analysis of actin network flow and turnover.
Fig. 2: Influence of assembly and disassembly factors on actin network architecture, flow and turnover.
Fig. 3: Influence of crosslinking on actin network dynamics.
Fig. 4: Characteristics of contracting actin networks with turnover.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon request.

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Acknowledgements

We thank Y. Kafri, E. Braun and members of our laboratories for useful discussions and comments on the manuscript. We thank N. Fakhri, T. H. Tan, A. Solon, R. Voituriez, G. Bunin and C. Schmidt for useful discussions. We thank C. Field and J. Pelletier for advice on extracts and for the GFP–Lifeact construct. We thank G. Ben-Yoseph for excellent technical support. We thank J. Eskin for assistance with cartoon models.This work was supported by a grant from the Israel Science Foundation (grant no. 957/15) to K.K., a grant from the United States–Israel Binational Science Foundation (grant no. 2013275) to K.K. and A.M., a grant from the United States–Israel Binational Science Foundation to K.K. and B.L.G. (grant no. 2017158), by US Army Research Office grant W911NF-17-1-0417 to A.M., and by grants from the Brandeis NSF MRSEC DMR-1420382 and the National Institutes of Health (R01-GM063691) to B.L.G.

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Authors and Affiliations

Authors

Contributions

M.M.-G., E.A.-S. and K.K. designed the experiments. M.M.-G., N.I., S.J. and K.K. performed the experiments. M.M.-G., E.A.-S., S.J., B.L.G., N.I. and K.K. provided reagents for the experiments. M.M.-G. and K.K. analysed the data. A.M., M.M.-G. and K.K. developed the model. M.M.-G., A.M. and K.K. wrote the paper. All co-authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Kinneret Keren.

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Supplementary information

Supplementary Information

Supplementary Text, Supplementary Figures 1–9, Supplementary References 1–12.

Reporting Summary

Supplementary Video 1

Steady-state dynamics in a confined contracting actomyosin network. This video shows spinning disc confocal images at the equatorial plane of a contracting actomyosin network labelled with GFP-Lifeact within a water-in-oil droplet. The field of view is 105 µm wide, and the elapsed time is indicated.

Supplementary Video 2

Contracting actomyosin network supplemented with Cofilin, Coronin and Aip1. This video shows spinning disc confocal images at the equatorial plane of a contracting actomyosin network labelled with GFP-Lifeact formed with extract supplemented with 12.5 µM Cofilin, 1.3 µM Coronin and 1.3 µM Aip1. The field of view is 105 µm wide, and the elapsed time is indicated.

Supplementary Video 3

Contracting actomyosin network supplemented with ActA. This video shows spinning disc confocal images at the equatorial plane of a contracting actomyosin network labelled with GFP-Lifeact formed with extract supplemented with 0.75 µM ActA. The field of view is 105 µm wide, and the elapsed time is indicated.

Supplementary Video 4

Contracting actomyosin network supplemented with α–actinin. This video shows spinning disc confocal images at the equatorial plane of a contracting actomyosin network labelled with GFP-Lifeact formed with extract supplemented with 10 µM α–Actinin. The field of view is 105 µm wide and the elapsed time is indicated.

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Malik-Garbi, M., Ierushalmi, N., Jansen, S. et al. Scaling behaviour in steady-state contracting actomyosin networks. Nat. Phys. 15, 509–516 (2019). https://doi.org/10.1038/s41567-018-0413-4

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