FIG. 8.

Forkhead-induced G₀ is reversible. (A) DL23 cells were seeded to approximately 5% confluency. Confluency was monitored during the experiment, as described for Fig. 6A, but none of the dishes at any of the indicated time points required splitting. Cells were given fresh medium without 4OHT (−4OHT) or with 500 nM 4OHT (+4OHT) every day. When 4OHT was removed (at day 6), cells were washed twice with medium without 4OHT before the fresh medium was added. Similarly, when cells were again given 4OHT (at day 9), they were washed twice with medium containing 4OHT before the fresh medium was added. Samples were taken at days 0, 1, 2, 3, 4, 6, 9, and 11, and BrdU incorporation was measured. (B) Samples of primary wild-type MEFs from two independent infections with either a control virus (puro) or an FKHR-L1.A3-encoding retrovirus were analyzed for p19^arf expression by immunoblotting.