Fig. 1.
Microscopic interaction between filaments. (A) Schematics of the system. Contrary to what happens on glass, motors on a supported membrane are incapable of pushing filaments against an obstacle as they slip on the membrane. On glass, conversely, colliding filaments can overcome obstacles and crawl over each other. (B) Example of a collision between filaments on a membrane resulting in alignment in roughly a minute. (Scale bar, 5 μm). The Inset shows a schematic of the collision and of the incoming angle θin and the outcoming angle θout. (C) Outcoming angle (θout) of collisions between filaments as a function of the incoming angle (θin). The dashed line indicates the case of no interaction. Red indicates collisions resulting in polar alignment and blue antipolar. (D) Angles between four different colliding filaments as a function of time. Insets show different phases of the collision: because of volume exclusion, filaments stop, fluctuate, and eventually align, either polarly or anti-polarly. (E) Example of a multifilament collision leading to polarity sorting. Filaments acting as an obstacle also act as accumulation sites. As all filaments accumulating are oriented in the same direction, this introduces a polar bias in the system. (Scale bar, 2 μm).