Abstract

Microtubules are stiff, dynamic protein polymers that provide a mechanical framework (cytoskeleton) to living cells. Their growth and shrinkage generates pushing and pulling forces in the piconewton range that play a role in a variety of cellular motility processes. I will present in vivo as well as in vitro experimental techniques that we use to study force generation by single microtubules. In fission yeast cells, we use automated image analysis techniques to show how force generation regulates the dynamics of microtubules in interaction with the cell ends. In vitro, we use an optical-tweezers based technique to study directly the molecular details of the microtubule growth process, as well as the forces that are generated at the dynamic microtubule end. Specifically, I will show recent results on the interaction of dynamic microtubule ends with purified dynein motor proteins that are immobilized on microfabricated barriers. In cells, pulling forces generated on microtubule ends by the minus-end directed motor protein dynein play an important role in the positioning of the mitotic spindle, for example in budding yeast and C elegans embryos. Our results suggest that, on its own, dynein attached to a surface can capture dynamic microtubule plus ends and generate pulling forces on shrinking microtubules in an ATP -dependent way.