The microtubule cytoskeleton is a dynamic network that rapidly adapts to changes in the cellular environment. This rapid reorganization results from a tight regulation of the microtubule dynamics. Microtubules undergo phases of growing and shortening through the addition and removal of tubulin dimers at their ends. However, microtubule dynamics is not just controlled at the microtubule ends, but also depends on tubulin exchange all along the shaft of microtubules. Shaft dynamics is a powerful regulator of the microtubule lifespan: shaft damages generated by dissociation of tubulin dimers get repaired by incorporation of fresh tubulin dimers. These repair sites act as rescue sites where a depolymerizing microtubule stops shortening and starts to re-grow. Therefore, the more a microtubule is damaged/repaired, the longer is the lifetime and the length of the microtubule. Given the importance of shaft dynamics, a functional microtubule network relies on the regulation of end- and shaft-dynamics. However, the relevance of shaft dynamics within a cellular context has not been fully explored.

Molecular motors use microtubules as roads to transport cargoes within the cell. In this thesis I present that the traffic of kinesin-1 motors also modifies the microtubule tracks while walking on them. First, I demonstrate in vitro that kinesin-1 increases microtubule shaft renewal and, consequently, the microtubule rescue frequency in a concentration-dependent manner. As a result of an increased number of rescue events, microtubules are longer and have an increased lifetime. In cells, an increase in kinesin-1 activity increases the microtubule rescue frequency which ultimately results in a densification of the microtubule network. This local densification of the network changes the shape and polarity of the cell. Second, I reveal that this property of kinesin-1-induced damages along the microtubule shaft is a mean to decrease the levels of acetylation, a tubulin post-translational modification occurring within the microtubule lumen. I demonstrate that the deacetylase HDAC6 relies on microtubule shaft damages as entry sites into the lumen, whereas αTAT 1 acetylation activity is independent from these entry sites. Third, I show that the modulation of microtubule shaft damages by different proteins might be a general mechanism to tune the acetylation array within the cell.

Taken together, these results provide a new perspective on the interaction between the molecular motor kinesin-1 and the underlying microtubule network. In addition of transporting cargoes, kinesin-1 modifies the dynamics, lifetime and composition of the microtubules used as tracks. These local changes drive an overall reorganization of the microtubule network which could underlie cell polarization and migration.