Purified motor proteins organise microtubules in micrometre-sized droplets

Introduction

Time course of TPX2 and chTOG stimulated microtubule nucleation.

Time course of TPX2 and chTOG stimulated microtubule nucleation in the absence (top) and presence (bottom) of importins, showing that regulation of microtubule nucleation is regulated by importin in vitro (Roostalu et al., Nat. Cell Biol., 2015)

Microtubule cytoskeleton function requires precise control of microtubule nucleation and dynamics. Compared to the regulation of microtubule growth, the molecular mechanism underlying the regulation microtubule nucleation is poorly understood.

In mitosis and meiosis, the chromatin-driven spindle assembly pathway exerts control of microtubule nucleation locally in the vicinity of chromosomes. One of the key targets is the multifunctional protein TPX2. Using a novel TIRF microscopy-based in vitro reconstitution assay, we found that TPX2 directly stabilises growing microtubule ends and stimulates microtubule nucleation by stabilising early microtubule nucleation intermediates and acts synergistically with the microtubule polymerase chTOG (XMAP215 homolog) to promote microtubule nucleation (Roostalu et al., Nat Cell Biol., 2015).

Importins control the efficiency of microtubule nucleation by selectively blocking TPX2's interaction with microtubule nucleation intermediates. Currently we are investigating role of other nucleation factor using TIRF microsopy assays.