FIG. 1.

Expression of the lineage markers in twin and control embryos at day 5 postfertilization. Twin embryos generated by embryo splitting are smaller, often with no distinctive ICM. They are less cellular in comparison with nonmanipulated control embryos and most of the cells have a dual expression of ICM and TE markers. Green: ICM marker NANOG. Red: TE marker CDX2. Blue: DNA dye Hoechst 33342. In control embryo, asterisk marks ICM cell expressing NANOG and arrow TE cell expressing CDX2. In twins A and B, the arrowheads point to cells with dual expression of NANOG and CDX2. ICM, inner cell mass; TE, trophectoderm.