BMP4 and teratoma: In contrast, mESCs cultured in CDSF with Bmp4 or the Gsk3β inhibitor maintained Oct3/4 expression (supporting information Fig. S3D, S3E), increased the number of cell doublings (Fig. 5A) and formed teratomas in 17% or 67% of transplantations by 7 months, respectively (Fig. 5B, 5C and supporting information Fig. S1F, S1G).