Fig. 8. Asynchronous proliferation of Wt MEFs but not Rb^-/- MEFs is reduced by inhibition of MEK. Asynchronously growing populations of cells were plated at a density of 10⁴/ml. The following day cells were counted (day 1) followed by treatment with U0126 (20 µM final concentration) or vehicle control (DMSO), or LY294002 (20 µM final concentration) or vehicle control (ETOH). Growth of cells was then monitored each day for four more days (day 2-5). On each day the cells' media was changed and retreated with inhibitor(s) or vehicle control.