Non-specific adhesive forces reorganize the cytoskeleton around membrane-less organelles

Phase-separation of biomolecules in cells takes place in a complex environment crossed by multiple filaments of the cytoskeleton or chromatin. Here, we study the interactions of stress granules, a phase-separated protein-RNA droplet in the cytosol, with the heterogeneous networks of the cytoskeleton. In the case of the microtubule network, for example, statistical tools similar to the radial distribution function allow for us to quantify long-ranged enhancement in filament density in the vicinity of stress granules. When microtubules are depolymerized, the molecular subunits partition to the surface of the droplet. We interpret the data using a thermodynamic model, revealing a weak non-specific affinity of the subunits to the surface of about 0.1 kT. As filaments polymerize, the adhesion is amplified leading to significant adhesion of filaments to the granule surface, making microtubule rich regions of the cell energetically favorable for stress granules.