A new method to measure mechanics and dynamic assembly of branched actin networks

Pierre Bauër,Thomas Pujol,Olivia Du Roure,Julien Heuvingh,Joseph Tavacoli,Jessica Planade

doi:10.1038/s41598-017-15638-5

Abstract

We measured mechanical properties and dynamic assembly of actin networks with a new method based on magnetic microscopic cylinders. Dense actin networks are grown from the cylinders’ surfaces using the biochemical Arp2/3-machinery at play in the lamellipodium extension and other force-generating processes in the cell. Under a homogenous magnetic field the magnetic cylinders self-assemble into chains in which forces are attractive and depend on the intensity of the magnetic field. We show that these forces, from piconewtons to nanonewtons, are large enough to slow down the assembly of dense actin networks and controlled enough to access to their non linear mechanical responses. Deformations are measured with nanometer-resolution, well below the optical resolution. Self-assembly of the magnetic particles into chains simplifies experiments and allows for parallel measurements. The combination of accuracy and good throughput of measurements results in a method with high potential for cell and cytoskeleton mechanics. Using this method, we observed in particular a strong non linear mechanical behavior of dense branched actin networks at low forces that has not been reported previously.

Highlights

The cell uses its cytoskeleton to resist deformation and integrate mechanical cues from its environment
The precision on the deformation - and on the mechanical properties - is achieved by measuring the displacement of the particles in bright field microscopy with nm-resolution, well below the optical resolution
We will give first results we obtained with this new method

Summary

Introduction

The cell uses its cytoskeleton to resist deformation and integrate mechanical cues from its environment. With cylinders, the actin gel is compressed between two aligned flat surfaces, giving directly access to the stress - strain relation for mechanical probing The strength of this new method relies on three ingredients: 1) Applied stresses that are externally controlled and modulated, 2) Self-assembled structures which allow simple experiments and parallel measurements to be carried out and 3) Measurements of the relative displacements of the particles with nanometer resolution. This technique has been developed for the specific characterization of dense actin networks mechanics but can be used to study other cytoskeleton meshworks, sub-cellular structures or even cells

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Conclusion