Microtubules under mechanical pressure can breach dense actin networks

Abstract

The crosstalk between actin network and microtubules is key to the establishment of cell polarity. It ensures that the asymmetry of actin architec ture along cell periphery directs the organization of microtubules in cell interior. In particular, the way the two networks are physically inter-twined regulates the spatial organization and the distribution of forces in the microtubule network. While their biochemical crosstalk is getting uncovered, their mechanical crosstalk is still poorly understood. Here we designed an in vitro reconstitution assay to study the physical interaction between dynamic microtubules with various structures made of actin fil aments. We found that microtubules can align and move by their polymerization force along linear bundles of actin filaments. But they cannot enter dense and branched actin meshworks, such as those found in the lamellipodium along cell periphery. However, when microtubules are immobilized, by their crosslinking with actin structures or others means, the force of polymerization builds up pressure in the microtubules that is sufficient to allow them to breach and penetrate these dense actin meshworks. This mechanism may explain the final progression of microtubules up to cell periphery through the denser parts of the actin network.