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Fig. 5. Cells lacking PI3K activity are out competed by wild-type cells. (A) Calculations. The chemotaxis index and speed of the cells at different distances from a pipette containing 100 µM cAMP were determined for AX3 cells in the presence and absence of the PI3K inhibitor LY294002 (see Fig. 1C; Fig. 2; supplementary material Table S1). Using these data, the displacement in the direction of the pipette due to chemotaxis and random movement was calculated (see Materials and Methods for equations). Presented is the average time needed to reach the pipette from different starting positions. The data predict that PI3K-inhibited cells always arrive later at the source than wild-type cells and perform relatively well when starting from a distance of about 100 µm, but perform increasingly worse at larger distances from the source. (B-D) Experiment. Wild-type cells were transformed with a plasmid expressing cytosolic GFP, whereas pi3k-null cells were transformed with a plasmid expressing RFP. Cells were starved, mixed (wild-type:pi3k-null ratio is 1:3) and exposed to a cAMP gradient from a pipette containing 100 µM cAMP. Confocal images were recorded before (C) and 50 minutes after (D) application of the cAMP gradient. The white dot in the centre in D indicates the position of the pipette; the field of observation is 725x725 µm, recorded as 5x5 tile scans. The cell density was measured at different distances from the pipette before and after stimulation (B). The data show the increase of cell density as means ± s.d. of four determinations.
