title: Physical basis of large microtubule aster growth.
abstract: 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. However, aster morphology in this model does not scale with cell size, and we recently found evidence for non-centrosomal microtubule nucleation. Here, we combine autocatalytic 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. With increasing nucleation rate, the model predicts an explosive transition from stationary to growing asters with a discontinuous jump of the aster velocity to a nonzero value. Experiments in frog egg extract confirm the main theoretical predictions. Our results suggest that asters observed in large fish and amphibian eggs are a meshwork of short, unstable microtubules maintained by autocatalytic nucleation and provide a paradigm for the assembly of robust and evolvable polymer networks.
authors.affiliation: Department of Systems Biology, Harvard Medical School, Boston, United States.|Cell Division Group, Marine Biological Laboratory, Woods Hole, United Sates.
authors.forename: Keisuke
authors.identifier: 0000-0002-8481-8680
authors.initials: K
authors.lastname: Ishihara
authors.affiliation: Department of Physics and Graduate Program in Bioinformatics, Boston University, Boston, United States.
authors.forename: Kirill S
authors.initials: KS
authors.lastname: Korolev
authors.affiliation: Department of Systems Biology, Harvard Medical School, Boston, United States.|Cell Division Group, Marine Biological Laboratory, Woods Hole, United Sates.
authors.forename: Timothy J
authors.identifier: 0000-0001-7781-1897
authors.initials: TJ
authors.lastname: Mitchison
mesh_terms: D055592:Biophysical Phenomena; D005057:Eukaryotic Cells; D008870:Microtubules / Q000378:metabolism*; D008954:Models, Biological; D055503:Protein Multimerization
keywords: aster; biophysics; cell biology; microtubules; nucleation; polymer networks; reaction-diffusion; structural biology; xenopus