Figure 3.

PI3K signaling hot spots tend to be localized in regions of membrane protrusion. (a) TIRF images, separated by 12-min intervals, are compared so as to determine the protruded and retracted areas. Pixels in the protruded area are associated with the cell contact area in the more recent image but were in the background in the earlier image; conversely, pixels in the retracted area were in the contact area in the earlier image but are in the background in the more recent image. Scale bar, 20 μm. (b) The enrichment, E, of a region is defined as the fraction of its pixels belonging to hot spots, compared to that of the whole-cell contact area. Circles indicate the time-averaged mean values of E in the protruded and retracted areas for each of 28 cells (see main text for further description). An E value >1 indicates that the region of interest has, on average, a higher percentage of hot-spot pixels than the entire contact area.