Adhesion dynamics in a migrating CHO K1 cell. CHO K1 cells expressing paxillin-mEGFP were plated onto coverslips that were preincubated with a solution of 5 ug/ml fibronectin overnight at 4o C. The cells were visualized at 60x (1.45NA) with an Olympus IX70 inverted microscope using Total Internal Reflection Optics (through the objective mode) equipped with a Qimaging Retiga Exi CCD camera (0.1073 microns/pixel). Images were acquired every 5 seconds for a total of 15 minutes. Note the formation of small, nascent adhesions near the leading edge of protrusions. These adhesions form (in the lamellipodium) and their formation is coupled to actin polymerization. Many adhesions turnover (at the lamellipodium/lamellum interface), as the protrusion proceeds. Some adhesions also elongate and grow (mature), particularly during pauses in protrusion. The fraction of adhesions that elongate, and the rate at which they do so, is cell type dependent. Note also, the sliding and disassembly of adhesions in retracting regions of the cell. The movie was taken by Colin Choi in the Rick Horwitz laboratory (University of Virginia).