Ishihara Keisuke, Korolev Kirill S, Mitchison Timothy J
Department of Systems Biology, Harvard Medical School, Boston, United States.
Cell Division Group, Marine Biological Laboratory, Woods Hole, United Sates.
Elife. 2016 Nov 28;5:e19145. doi: 10.7554/eLife.19145.
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.
微管星状体——由中心体组织形成的微管径向阵列——在动物细胞的空间协调中发挥着重要作用。星状体生长的标准模型假定源自中心体的微管数量是固定的。然而，该模型中的星状体形态并不随细胞大小而变化，并且我们最近发现了非中心体微管成核的证据。在此，我们结合自催化成核和聚合动力学来建立一个星状体生长的生物物理模型。我们的模型预测星状体以行波形式扩展，并概括了星状体生长的所有主要方面。随着成核速率的增加，该模型预测会出现从静止星状体到生长星状体的爆发性转变，星状体速度会以不连续的跳跃变为非零值。在蛙卵提取物中的实验证实了主要的理论预测。我们的结果表明，在大型鱼类和两栖类卵中观察到的星状体是由自催化成核维持的短而不稳定的微管网络，并为稳健且可进化的聚合物网络的组装提供了一个范例。
