The Influence of Microtubule Persistence Length on Their Collective Motion

Abstract

Collective motion is a self-organized phenomenon widely recognized in nature, from the macroscopic level of fish schools and bird flocks to the microscopic level of bacterial colonies, self-propelled microparticles, and rods. The collective motion has also been found to be existing within the reconstructed cytoskeleton filament-motor system in vitro, such as the microtubule (MT)-kinesin system, and actin filament-myosin system. Although previous studies proved that the collective pattern of filaments is formed through a dynamic process, including filament's collision and alignment, the formation mechanism of the collective pattern is still not clear. Notably, the persistence length of filaments, an apparent factor influencing their gliding trajectories and alignment behavior, should affect the collective motion directly. However, how the filaments’ stiffness influences their collective motion still needs to be clarified, and related experimental verifications also lack. Here, we investigated the influence of MT persistence length on the formation of their collective motion using an MT-kinesin system in the presence of the depletant agent. Based on our previous study that MT stiffness is dependent on its polymerization rate, MTs with various stiffness were prepared by modifying their growth rate via changing the tubulin concentration with the presence of GTP or GMPCPP, respectively. The whole transition process of the MT-kinesin system, from initial homogeneous state to final nematic state, was tracked and quantitatively evaluated by the nematic order parameters and skewness parameters. Moreover, the final collective patterns formed by MTs with various persistence lengths were characterized and further verified with machine learning. All the results indicate that softer MTs finally tend to form a local stream, whereas stiffer MTs prefer to form stable bundles. This work proves that the persistence length influences not only the phase transition process but also their final collective pattern.