"Cell Motility: How Cellular Machines Generate Precise Responses in a Complex Environment"
Cell motility is a critical biological process. Axons of developing neurons crawl centimeters to make synapses in the brain. Fibroblast cells migrate and generate forces in order to heal wounds. Immune cells crawl through blood vessels to the site of infection. Regulation of cytoskeleton, molecular motors and extracellular adhesions by a protein mediated signaling network controls these processes. Our studies show that non-linear response to stimuli, periodicities and phase transitions are inherent to this network. Cells initiate attachment to a surface in an all-or-nothing manner, demonstrating a thresholded response to external chemical signals. Following initiation, spreading proceeds by one of two distinct mechanisms: isotropically, increasing its area in all directions at once or anisotropically, moving outward one step at a time. Following spreading, cells initiate a series of periodic membrane contractions creating a force-dependent positive feedback loop used to direct further motility. Fourier power spectra of membrane velocity and the scaling behavior of area growth both indicate dynamic phase transitions between these different cell states. These behaviors developed in the cellular machine to provide precise responses based on a wide variety of environmental inputs.