The dynamics of microtubule stability: A reconstitution of regulated microtubule assembly under force

The microtubule cytoskeleton is an intracellular polymer network involved in cell shape, cell motility, and cell division. Microtubules are self-assembling, dynamic polymers composed of tubulin proteins that alternate between phases of growth and shrinkage, a behaviour known as “dynamic instability”. A key feature of microtubules is their ability to generate pushing and pulling forces through controlled assembly and disassembly, guiding for example cell division. The stability of microtubules is largely governed by the progressive hydrolysis of incorporated tubulin dimers. In this thesis we sought to resolve microtubule assembly under force in the presence of regulatory proteins. Through the in vitro reconstitution of microtubule growth against novel micro-fabricated barriers, we studied the biochemical changes leading up to microtubule destabilization. We found that the resulting microtubule lifetimes can be understood with a simple phenomenological 1D model based on noisy microtubule growth and a single hydrolysis rate. Additionally, we explored the implementation of light-inducible protein-protein interactions to gain spatiotemporal control over microtubule function in particular and over in vitro reconstitutions in general. As a proof-of-principle, we developed a light-inducible microtubule gliding assay based on the reversible recruitment of motor proteins to a surface.