Fig. 4. Reversible phenotypes of mouse Rex1⁺ and Rex1^- populations. (A) Rex1⁺/Oct3/4⁺ and Rex1^-/Oct3/4⁺ fractions were sorted, cultured and analyzed by flow cytometry. Oct3/4-CFP/Rex1-GFP double-knock-in ES cells were cultured under puromycin selection, then Rex1⁺ and Rex1^- populations were purified at more than 98% purity. Rex1^- cells emerged from the purified Rex1⁺ population, and Rex1⁺ cells also appeared from purified Rex1^- populations within 1-2 days. It was confirmed that GFP fluorescence reflected Rex1 expression by RT-PCR. (B) Clonal analysis of reversibility of Rex1⁺ and Rex1^- cells. Scale bar: 50 µm.