Pluripotent potential of O-iPS cells. (a) Formation of two teratomas derived from O-iPS6 cells under the skin in nude mice 4 weeks posttransplantation. Inset shows the size of teratomas harvested from nude mice. Teratomas derived from 5 different O-iPS cells and ESC-derived teratoma serves as a positive control. GFP expression was detected in an O-iPS6-derived teratoma. Scale bar: 1 cm. (b) Genotyping of teratoma tissues derived from 6 O-iPS colonies for Cre transgene. Sorted GFP+ osteoblasts serve as a positive control. (c) H&E staining of teratoma sections showed differentiation of O-iPS6 into various tissues from all three germ layers. CNS: central nervous system. Scale bar: 100 μm. (d) Genotyping of coding regions for Oct4-EGFP, Cre, and integrated retroviral vectors carrying reprogramming factor genes (Oct4, Sox2, and Klf4) on tail tissues derived from E17.5 chimera embryos. ESCs serve as a negative control. Sorted GFP+ osteoblasts and retroviral vectors carrying reprogramming factors serve as positive controls.