Fig. 5. Blastocyst injection was performed with mouse Rex1⁺ and Rex1^- ES cell populations to compare their capacities for contributing embryonic tissue. (A-D) Rex1/Oct3/4 double-knock-in ES cells were marked by forced expression of the DsRedT4 gene driven by the CAG promoter, and EGFP⁺ and EGFP^- cells were purified after culture under puromycin selection. Some of the 10.5 dpc embryos derived from blastocysts injected with the Rex1⁺ fraction showed DsRed fluorescence. The embryo on the left has cells showing strong fluorescence. Embryos injected with the Rex1^- fraction did not show DsRed fluorescence.