Seminar

The internal organization of cells is governed by the architecture and polarity of cytoskeletal filaments, which serve as tracks for motor-driven transport. How active transport by molecular motors collectively organizes microtubule networks into structured and polarized states remains an open question.
 

In this talk, I will present a combined experimental and theoretical study of microtubules interacting with oppositely directed molecular motors bound to a fluid membrane. We show that the competition between plus- and minus-end directed motors leads to a rich range of dynamical behaviors, including sustained transport, polarity sorting, and the formation of aligned microtubule bands in which motors segregate into domains of opposite polarity. These patterns emerge from a balance of forces generated by motors walking in opposite directions, maintaining the system in a dynamic steady state.
 

To understand the observations, we propose an active Cahn-Hilliard theory for the dynamics of a new type of phase transition where the driving force is not the direct interactions between the two separating components, but their active sorting by a third polar species. This third species can transport the other two along its polarity in opposite directions, thus separating them. We predict the formation of motor domains, and further show that they can either coarsen to form macroscopic phases or reach a finite micro- or mesoscopic steady state size, these latter due to an arrest of coarsening through activity.
 

Our results uncover a new mechanism by which active transport drives phase separation and polarity organization, providing insight into the self-organization of cytoskeletal structures and, more broadly, active systems.