Controlling ‘cell’ size and shape to elucidate the mechanics of microtubule aster positioning*

The microtubule (MT) cytoskeleton plays critically important roles in numerous eukaryotic cellular functions, and it does so across a functionally diverse and morphologically disparate range of cell types. In these roles, MT assemblies must adopt distinct cell cycle-dependent morphologies and physical dimensions to perform specific functions. During interphase, the MT network takes the form of a radial astral array (aster) that functions to center the nucleus, a by proxy the mitotic spindle, which ultimately dictates the position of the cell division plane. The mechanical underpinnings of this positioning phenomenon remain elusive despite its fundamental importance to both symmetric and asymmetric vision and intensive study. To address this gap in our collective understanding, we have combined photo-labile hydrogels with cell-free extracts in a new experimental platform that affords exquisite control of “cell” shape and volume. By observing the behavior/dynamics of MT asters confined in hydrogel micro-containers of different geometries, we have elucidated the relative contribution of MT-based pushing forces to aster positioning and have begun to characterize the length scales over which they operate.