Physical basis of spindle self-organization

The cytoskeleton forms a variety of steady-state, subcellular structures that are maintained by continuous fluxes of molecules and energy. Understanding such self-organizing structures is not only crucial for cell biology but also poses a fundamental challenge for physics, since these systems are active materials that behave drastically differently from matter at or near equilibrium. Active liquid crystal theories have been developed to study the self-organization of cytoskeletal filaments in in vitro systems of purified components. However, it has been unclear how relevant these simplified approaches are for understanding biological structures, which can be composed of hundreds of distinct proteins. Here we show that a suitably constructed active liquid crystal theory produces remarkably accurate predictions of the behaviors of metaphase spindles-the cytoskeletal structure, composed largely of microtubules and associated proteins, that segregates chromosomes during cell division.