Scheme for deriving Tet1 and Tet2 double knockout pre-iPSC lines. Tet1KO/KO Tet2fl/fl or Tet1WT/WT Tet2fl/fl MEFs were treated with retroviruses containing OSKM. Tet1KO/KO Tet2fl/fl or Tet1WT/WT Tet2fl/fl pre-iPSC clones were isolated and treated with either Adenoviral expressed Cre recombinase or Empty vector to generate a population of pre-iPSCs with Tet1KO/KO Tet2fl/fl, Tet1KO/KO Tet2KO/KO, Tet1WT/WT Tet2fl/fl, and Tet1WT/WT, and Tet2KO/KO. Scale bar, 50 μm. 