FIGURE 1.

Comparison of peri‐implantation embryos in human and mouse. Epiblast and trophoblast directly interact in mice, but not in human. In mice, FGF4 from the epiblast is required for trophoblast proliferation. In humans, epiblasts and trophoblasts are separated by mesenchymal cells and cannot interact directly. Therefore, human trophoblast proliferation is likely to be epiblast (FGF4) EVT independent (maintenance of human TS cells requires EGF, not FGF). EPI: epiblast; PE: primitive endoderm; TE: trophectoderm; TSCs: trophoblast stem cells; TGCs: trophoblast giant cells