(A) Outline of generation of transgenic mice expressing rtTA, together with Oct4 (O), Sox2 (S), Klf4 (K) and Myc (M) (OSKM, 4F) under control of a tetracycline-on promoter (Tet-O). (B) Western blot analysis of 4F expression in Tet-O MEFs treated with or without Dox. (C) Alkaline phosphatase (AP)-positive colonies were counted at day12 after Dox treatment. (D) Bright field images of an iPSC colony derived from Tet-O 4F MEFs. (E-G) Staining of representative iPSC colonies with antibodies against AP, stage-specific embryonic antigen 1 (SSEA1) and Nanog. Scale bars in panels D, E, F and G, 50μm (H) Fold changes in number of AP-positive colonies generated from Tet-O 4F MEFs transduced with specific shRNA, compared with control shRNA. AP-positive colonies were counted on day14 after Dox treatment. (I) Fold changes in number of AP-positive colonies generated from Tet-O 4F MEFs transduced with Jmjd3 expression or empty vector. Ectopic expression of Jmjd3 inhibits reprogramming. The data in panels H and I are reported as the means ± SD with indicated significance (*p <0.05, **p < 0.01 ***p < 0.001 by Student's t test). See also Figure S1.