A Colony formation for cb9Δmyc cells infected with retroviral vectors expressing the indicated Myc proteins; all cells were expanded with doxycycline prior to the final plating step, upon which the compound was either maintained (+dox), or removed (-dox) to switch off the tet-Myc transgene. One representative experiment out of 3 is shown. B Cumulative cell counts for cb9Δmyc cells upon serial passaging with or without dox (removed at day 2). The data are presented as mean ± SD; n = 3 (biological replicates) C 