Fig. 9. Illustration showing the expression patterns of mouse marker genes expressed in the pluripotent cell population at each embryonic stage (upper), and the subpopulation in ES cells (lower) that could be detected by expression of these marker genes. ICM-like (Rex1⁺) and early PrE-like (Rex1^-) populations have different abilities for in vitro differentiation and could convert into each other under normal conditions for ES cell maintenance.