Flows, Self-Organization, and Transport in Living Cells

Efficient control of mass, energy, and information flows is critical for the robust function of large complex systems. Cities, for example, can come to a standstill when power grids, transportation, or information networks are disrupted. A living organism is another -- its functioning can require the tandem operation of circulatory and nervous systems that couple disparate parts of the body, orchestrating the joint work of billions of cells. Large-scale coordination is no less essential in a single cell, particularly for events leading up to cell division or the maturation of an egg. Much of that coordination is actuated through the cell's cytoskeleton, a collection of polymers, cross-linkers, and molecular motors, that organizes itself into mesoscopic active structures to perform its various tasks. I will discuss a beautiful instance -- involving large growing egg cells -- where the cytoskeleton harnesses the surrounding fluid to coordinate its activity and execute its tasks. Modeling reveals an interplay -- across multiple time-scales -- between active forces, cell geometry, polymer mechanics, and collective hydrodynamics, with predictions being met by new experiments. I'll also discuss related self-organizational phenomena found in experiments in artificial cells filled with cellular fluids. Both involve the collective interaction of cytoskeletal polymers with motors and geometry, and understanding them has required new experiments, new models, and new methods of simulation. As mechanics problems they are also beautiful, giving rise to novel fluid-structure problems, and new instabilities to ponder.