Practice question

Embryonic stem cells originate from careful isolation and sustained culture of inner cell mass of preimplantation blastocyst, typically embryonic day 3.5 to 4.5 in mice, dependent on leukemia inhibitory factor and dual inhibition 2i blocking MAPK and GSK3 to prevent differentiation. Trophoblast comprises outer epithelium forming future placenta, expressing Cdx2 and Eomes, separated by first fate decision driven by Hippo signaling. Deriving ESCs from trophoblast contradicts established lineage; embryonic cells are not trophectoderm derivatives and cannot contribute efficiently to placenta inside chimeras.