FIG. 6.

Physical separation of EGFP-expressing and non-EGFP-expressing cells revealed both stochastic and graded responses to TPA treatment. Clone HS2γEGFP-1 was grown without hygromycin for 133 or 135 days and then sorted by FACS into EGFP-expressing and non-EGFP-expressing pools. Pools were treated with 5 nM TPA (shaded) or vehicle (unshaded) for 20 h, and then the percentage of EGFP-positive cells and the mean fluorescence of viable cells were measured by flow cytometric analysis. Representative flow cytometric profiles are shown. The horizontal line represents the EGFP-expressing cells. The values represent the means of two independent experiments in which cells were grown for either 133 or 135 days without hygromycin.