Movies of bundling actin fibers

Non-Brownian vs. Brownian

Here is a movie of the bundling process for fibers of length 1 with initial mesh size 0.2 microns without thermal fluctuations. All of the motion here is driven by the cross links, and fibers of the same color are considered to be in the same bundle. When we add Brownian motion, we see how much faster the initial stages of bundling occur, as the system is being mixed so much faster.

Effect of mesh size

When the mesh size is larger, fibers can still bundle because they can still find each other by Brownian diffusion. Here are movies for initial mesh sizes 0.2 microns, 0.4 microns, and 0.8 microns.

Effect of CL concentration

Bundling can proceed at large mesh sizes only when the CL concentration is sufficiently large, since otherwise fibers that might be close to each other will not be able to attach by a CL. Here are movies showing the effect of this at initial mesh size 0.4 microns, with kon being the base value, four times the base value, and one quarter of the base value. For simulations with the smallest kon, notice how the fibers move around a lot but are unable to initially organize into small bundles, as is characteristic of the other simulations. There is instead a bias towards large bundles adding one fiber at a time.