Wolff K, Barrett-Freeman C, Evans M R, Goryachev A B, Marenduzzo D
Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, D-10623 Berlin, Germany. SUPA, School of Physics and Astronomy, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, UK.
Phys Biol. 2014 Feb;11(1):016005. doi: 10.1088/1478-3975/11/1/016005. Epub 2014 Jan 27.
We present a numerical simulation study of the dynamics of filopodial growth in the presence of active transport by myosin X motors. We employ both a microscopic agent-based model, which captures the stochasticity of the growth process, and a continuum mean-field theory which neglects fluctuations. We show that in the absence of motors, filopodia growth is overestimated by the continuum mean-field theory. Thus fluctuations slow down the growth, especially when the protrusions are driven by a small number (10 or less) of F-actin fibres, and when the force opposing growth (coming from membrane elasticity) is large enough. We also show that, with typical parameter values for eukaryotic cells, motors are unlikely to provide an actin transport mechanism which enhances filopodial size significantly, unless the G-actin concentration within the filopodium greatly exceeds that of the cytosol bulk. We explain these observations in terms of order-of-magnitude estimates of diffusion-induced and advection-induced growth of a bundle of Brownian ratchets.
我们展示了一项关于丝状伪足在肌球蛋白X马达主动运输存在下生长动力学的数值模拟研究。我们采用了两种模型，一种是基于微观主体的模型，它捕捉了生长过程的随机性；另一种是连续统平均场理论，它忽略了涨落。我们表明，在没有马达的情况下，连续统平均场理论高估了丝状伪足的生长。因此，涨落会减缓生长，特别是当突起由少量（10个或更少）F-肌动蛋白纤维驱动时，以及当阻碍生长的力（来自膜弹性）足够大时。我们还表明，对于真核细胞的典型参数值，除非丝状伪足内的G-肌动蛋白浓度大大超过细胞质总体浓度，否则马达不太可能提供一种能显著增加丝状伪足大小的肌动蛋白运输机制。我们根据一束布朗棘轮的扩散诱导生长和平流诱导生长的数量级估计来解释这些观察结果。
