Thesis presented December 17, 2021

Abstract:
The cytoskeleton is involved in a myriad of cellular functions such as motility, division, shape-changing. Actin and Microtubules are the two main classes of biopolymers involved in the cytoskeleton organization and are heavily studied. Although our understanding of the mechanical and chemical properties of actin filaments and microtubules has largely improved over the last decade, their complex interactions and the function of this crosstalk are still not well understood. In this work, we used a combination of reconstituted in vitro assays with well-characterized biochemical compositions, coupled with microfabrication techniques, to spatially control the interaction between different actin architectures and microtubules and observe their behaviours. Our results showed that even in absence of regulatory proteins, actin filaments and microtubules could dynamically co-align in a reconstituted system. We found that, when microtubules polymerized unconstrained and perpendicularly to a branched actin network, they were able to generate enough force to propel themselves in the opposite direction of their growth, as if they were growing against a solid wall. The direction of this displacement was biased by the presence of actin bundles that directed the microtubule motion along their length. We then constrained microtubules between two close bars of branched actin networks. We could observe that the microtubule polymerization force could overcome the resistance of the actin wall and allow the microtubule to cross it. In conclusion, we revealed new general principles regulating the interaction between actin networks and microtubules, and the consequence of this interaction on the microtubule dynamics.

Keywords:
Mechanics, Actin, Microtubule

On-line thesis. ​