A transgene containing from 5' to 3', a loxP-flanked neo stop cassette, a rox-flanked stop cassette, and a 2A-NLS-ZsGreen and driven by the CAGGS promoter (chicken beta actin promoter with CMV enhancers) was inserted into intron 1. An intervening floxed neo-STOP cassette and a rox-flanked stop cassette prevents expression of the ZsGreen except in the presence of cre and dre when both the floxed neo-STOP cassette and a rox-flanked stop cassette are excised. (J:314807)