レター論文の最後に書かれていることね。
>>
As for STAP-cell-derived Fgf4-induced stem cells, which can also contribute to both embryonic and placental tissues, our in vitro conversion study combined with inhibitor treatments clearly indicate that the bidirectional potential of Fgf4-induced stem cells is unlikely to reflect the co-presence of separate subpopulations of ES-like and trophoblast-stem-like cells in the culture. Collectively, our study indicates that STAP-based conversion can reprogram somatic cells to acquire not only pluripotency but also the ability of trophoblast differentiation.