Motor-Mediated Cortical versus Astral Microtubule Organisation in Lipid-Monolayered Droplets [Cell Biology]

June 25th, 2014 by Baumann, H., Surrey, T.

The correct spatial organisation of microtubules is of crucial importance for determining the internal architecture of eukaryotic cells. Microtubules are arranged in space by a multitude of biochemical activities and by spatial constraints imposed by the cell boundary. The principles underlying the establishment of distinct intracellular architectures are only poorly understood. Here, we have studied the effect of spatial confinement on the self-organisation of purified motors and microtubules that are encapsulated in lipid-monolayered droplets in oil, varying in diameter from five to hundred micrometres, which covers the size range of typical cell bodies. We found that droplet size alone had a major organising influence. The presence of a microtubule-crosslinking motor protein decreased the number of accessible types of microtubule organisations. Depending on the degree of spatial confinement, the presence of the motor caused either the formation of a cortical array of bent microtubule bundles or the generation of single microtubule asters in the droplets. These are two of the most prominent forms of microtubule arrangements in plant and metazoan cells. These results provide insight into the combined organising influence of spatial constraints and crosslinking motor activities determining distinct microtubule architectures in a minimal biomimetic system. In the future, this simple lipid monolayered droplet system characterised here, can be readily expanded to include further biochemical activities or used as the starting point for the investigation of motor-mediated microtubule organisation inside liposomes surrounded by a deformable lipid bilayer.