Speaker
Description
Cytoskeletal filaments are vital for various cellular processes, such as cell motility, division and shape maintenance, all of which depend on the active motion of filaments. Across evolution, two mechanisms have emerged: propulsion, in which molecular motors generate an active force; and treadmilling. In treadmilling, filaments directionally polymerize by growing on one end and shrinking on the other, resulting in active motion without any active force. The implications of this mechanism on filament behavior are largely unexplored. Here, we use minimal model simulations to systematically compare treadmilling and propelled filaments, examining their collective behavior, robustness to noise, and interaction with passive objects.
We find that treadmilling and propulsion result in different collision mechanisms: propelled filaments align by mutual pushing, whereas treadmilling depolymerize and “die” upon collision. Both of these collision types can drive collective alignment into filament bundles with nematic (treadmilling) or polar (propelled) symmetry. Treadmilling filaments suppress density fluctuations and therefore require higher density to align, but once aligned, they are far more stable. When a bundle of propelled filaments is locally perturbed, misaligned filaments push against the remaining bundle, causing it to break apart. Perturbed treadmilling filaments simply die out, the perturbation stays local and heals. This results in treadmilling alignment being significantly more robust in crowded and noisy environments. We further ask if these collective states are capable of producing work, placing a passive cogwheel in a bath of filaments. Interestingly, both classes of filaments are capable of rotating the cogwheel, even though treadmilling filaments do not possess any active force. Our findings highlight treadmilling as an alternative mechanism of active motion with robust alignment, revealing design principles of the cytoskeleton and paving the way for novel bioinspired devices.