Crowding-induced organization in cells: spontaneous alignment and sorting of filaments with physiological control points.

Under sufficiently crowded conditions, elongated particles spontaneously align along a common axis and separate from particles with dissimilar packing parameters. Clarifying the relevance of these entropy-driven phenomena to intact cells has required the development of theoretical approaches that tractably take into account daunting physiological complexities including the extreme crowding of the cytosol, the complex mixture of macromolecules present, the process of filament self-assembly, and the characteristic widths, flexibilities and charges of filaments formed by different proteins. This review summarizes the approaches taken, including their validation by observations of simpler systems, and the insights that have been gained into the means by which cells can modulate and capitalize upon spontaneous ordering.