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Crawling cells of various morphologies displace themselves in their biological environments by a similar overall mechanism of protrusion through actin assembly at the front coordinated with retraction at the rear. Different cell types organize very distinct protruding structures, yet they do so through conserved biochemical mechanisms to regulate actin polymerization dynamics and vary the mechanical properties of these structures. The moving cell must spatially and temporally regulate the biochemical interactions of its protein components to exert control over higher-order dynamic structures created by these proteins and global cellular responses four or more orders of magnitude larger in scale and longer in time than the individual protein-protein interactions that comprise them. To fulfill its biological role, a cell globally responds with high sensitivity to a local perturbation or signal and coordinates its many intracellular actin-based functional structures with the physical environment it experiences to produce directed movement. This review attempts to codify some unifying principles for cell motility that span organizational scales from single protein polymer filaments to whole crawling cells.
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Movie 1. Phase contrast videomicroscopy of keratocytes cultured from the scales of Hypsophrys nicaraguensis (Nicaraguan Cichlid) shows the cells extending lamellipodia as they glide rapidly across a glass surface. These cells are approximately 50—60 μm wide. Movie is sped up 100-fold over real time. Courtesy of Patricia Yam and Julie Theriot, Stanford University. Download Movie 1 (MOV)
Movie 2. Differential interference contrast videomicroscopy of differentiated neutrophil-like HL60 cells shows the cells extending pseudopods migrating toward a pipet releasing chemoattractant. These cells are approximately 10—15 μm long. Movie is sped up 100-fold over real time. Courtesy of Alexandra Van Keymeulen and Henry Bourne, University of California, San Francisco. Download Movie 2 (MOV)
Movie 3. Phase Contrast videomicroscopy of a cortical neuron from a Syrian golden hamster imaged over three days in culture. The growth cones at the tips of the axons explore the environment and determine the direction the axon grows. The field is approximately 400 μm wide. Movie courtesy of Katherine Kalil, University of Wisconsin. Download Movie 3 (MOV)