TY - JOUR T1 - Physical Basis of Large Microtubule Aster Growth JF - bioRxiv DO - 10.1101/055939 SP - 055939 AU - Keisuke Ishihara AU - Kirill S. Korolev AU - Timothy J. Mitchison Y1 - 2016/01/01 UR - http://biorxiv.org/content/early/2016/06/26/055939.abstract N2 - Microtubule asters-radial arrays of microtubules organized by centrosomes-play a fundamental role in the spatial coordination of animal cells. The standard model of aster growth assumes a fixed number of microtubules originating from the centrosomes. This model does not scale with cell size, and we recently found evidence for microtubule nucleation away from centrosomes. Here, we combine microtubule nucleation and polymerization dynamics to develop a biophysical model of aster growth. Our model predicts that asters expand as traveling waves and recapitulates all major aspects of aster growth. Strikingly, the model predicts an explosive transition from stationary to growing asters with a discontinuous jump of the expansion velocity to a nonzero value. Experiments in frog egg extract confirm main theoretical predictions. Our results suggest that asters are a meshwork of short, shrinking microtubules maintained by autocatalytic nucleation and provide a paradigm for the assembly of robust and evolvable polymer networks. ER -