Practice question

Inner cell mass arises inside blastocyst at embryonic day 3.5 mouse, day 5 human, isolated from trophectoderm outer epithelium forming blastocoel. ICM cells express Oct4, Nanog, Sox2 pluripotency network, capable of differentiation into all three embryonic germ layers contributing to fetus but not efficiently to placenta, meeting pluripotency definition. Cultured ICM generates embryonic stem cells retaining pluripotency demonstrable via chimera and teratoma formation. Totipotent forms extraembryonic as well seen in zygote, multipotent limited to subset like blood, unipotent single lineage such as epidermal basal. ICM potency explains ES derivation.