Practice question

Blastocyst comprises outer trophectoderm epithelium and inner cell mass cluster at embryonic pole. Inner cell mass cells remain apolar, maintain active Hippo signaling with cytoplasmic YAP, express Oct4 Nanog Sox2, and retain pluripotency. During implantation ICM splits into epiblast forming fetus plus extraembryonic mesoderm and primitive endoderm forming yolk sac. Thus ICM provides progenitors of all fetal tissues and some extraembryonic membranes. Its preservation is essential for embryonic stem cell derivation, representing source of embryonic development proper, regenerative medicine, lineage plasticity and developmental potential studies.