Practice question

Mouse blastocyst at embryonic day 3.5 consists of outer trophectoderm surrounding fluid cavity and inner cell mass clustered at embryonic pole expressing Oct4 and Nanog. Inner cell mass cells express Oct4, Nanog, Sox2, and are functionally pluripotent, capable of forming all somatic lineages and germ cells when tested by chimera contribution and teratoma assays, but do not generate trophoblast under normal development. After implantation, ICM diverges into epiblast and primitive endoderm. Cultured in LIF and 2i inhibitors, ICM outgrowths establish embryonic stem cell lines, confirming pluripotency not totipotency or lineage-restricted multipotency.