EXPERIMENTAL FIGURE 17-44The wounded-cell monolayer assay can be used to dissect signaling pathways in directed cell movement. (a) A confluent layer of cells is scratched to remove a swath about three cells wide to generate a free cell border. The remaining cells detect the free space and newly exposed extracellular matrix and, over a period of hours, fill in the area. (b) Localization of actin in a wounded monolayer 5 minutes and 3 hours after scratching; after 3 hours, cells have migrated into the wounded area. (c) Effect of introducing dominant-negative Cdc42, Rac, and Rho into cells at the wound edge; all affect wound closure.