Expression of EGFP-S188/190A paxillin inhibits membrane protrusion dynamics. NBT-II cells expressing either paxillin constructs were plated on collagen-coated plates (10 μg/ml) for 4 h. Images of GFP-positive cells were taken on a fluorescence inverted microscope every 15 sec for 5 min. A) Representative images of cells expressing wild type or mutant paxillin used in protrusion analysis (performed as described in Materials and Methods) were taken from time-lapse series. Arrowheads point to stable and arrows to dynamic protrusions. Note the number of protrusions and their lability in EGFP-paxillin cell compared to cell expressing mutant paxillin. B) Protrusiveness was calculated as the net change in cell area (μm2). The distribution of protrusiveness within the cell population is shown. C) The mean number of protrusions per cell ± SEM was calculated by adding the cell extensions observed in all images and dividing the resulting figure by the number of images in the movie. D) Membrane protrusion index, which was quantified as described under Materials and Methods, represents the mean activity of a single protrusion. Data are the average of three independent experiments ± SEM. ***, p < 0.001.