ASSEMBLY AND POSITIONING OF MICROTUBULE ASTERS IN MICROFABRICATED CHAMBERS

Intracellular organization depends on a variety of molecular assembly processes; while some of these have been studied in simplified cell-fr ee systems, others depend on the confined geometry of cells and cannot be reconstructed using bulk techniques. To study the latter processes in vitro, we fabricated microscopic chambers that simulate the closed environment of cells. We used these chambers to study the positioning of microtubule asters, Microtubule assembly alone, without the action of molecular motors, is sufficient to position asters, Asters with sh ort microtubules move toward the position expected from symmetry; howe ver, once the microtubules become long enough to buckle, symmetry is b roken, Calculations and experiments show that the bending-energy lands cape has multiple minima. Microtubule dynamic instability modifies the landscape over time and allows asters to explore otherwise inaccessib le configurations.