参考文献の31と32は以下よ。
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31. Takahashi, K., Mitsui, K., and Yamanaka, S. Role of ERas in promoting tumour-like properties in mouse embryonic stem cells. Nature 423, 541, 2003.
32. Ralston, A., and Rossant, J. Genetic regulation of stem cell origins in the mouse embryo. Clin Genet 68, 106, 2005.