Erk2 signaling and early embryo stem cell self-renewal

Differentiation of the mammalian blastocyst generates two distinct cell lineages: the trophectoderm, which contributes to the trophoblast layers of the placenta, and the inner cell mass, which forms the embryo. We and others recently demonstrated that the MAP kinase ERK2 is essential for trophoblast development. Erk2 mutant embryos fail to form extra-embryonic ectoderm and the ectoplacental cone, suggesting a role for ERK2 activation in the proliferation of trophoblast stem (TS) cells. Previous studies have documented that ERK1/2 activity is dispensable for proliferation of embryonic stem (ES) cells and rather interferes with self-renewal. Thus, signaling by the ERK1/2 MAP kinase pathway appears to be critical for the regulation of self-renewal and propagation of early embryo stem cell populations.