ES cells containing the Gt(ROSA)26Sortm1(rtTA2S-M2)Jae mutation were retargeted. Cells were injected with a "flip-in plasmid" containing a tetracycline responsive element (TRE or tetO) and mouse Nup88 cDNA sequence with an HA tag and a Flpe-recombinase plasmid to facilitate tetO-Oct4 integration into the 3' UTR region of Col1a1. (J:231166)