Effects of microtubule length and crowding on active microtubule network organization

Active filament networks can organize into various dynamic architectures driven by cross-linking motors. Densities and kinetic properties of motors and microtu-bules have been shown previously to determine active microtubule network self-organization, but the effects of other control parameters are less under-stood. Using computer simulations, we study here how microtubule lengths and crowding effects determine active network architecture and dynamics. We find that attractive interactions mimicking crowding effects or long microtubules both promote the formation of extensile nematic networks instead of asters. When microtubules are very long and the network is highly connected, a new iso-tropically motile network state resembling a "gliding mesh"is predicted. Using in vitro reconstitutions, we confirm the existence of this gliding mesh experimen-tally. These results provide a better understanding of how active microtubule network organization can be controlled, with implications for cell biology and active materials in general.