The apical domain defines the trophectoderm differentiation in early mammalian embryo by regulating YAP nuclear translocation
Mammalian life initiates at the zygote, formed by the fusion of an oocyte and sperm. The first three cleavages of the mouse zygote generate eight gently connected blastomeres which show no obvious differences in developmental potencies. However, a few hours after the formation of the 8-cell stage the embryo undergoes the process of compaction, in which individual cells become tightly connected at the membranes. The first lineage specification of mouse embryos happens during the compacted 8- to 16-cell transition; these cells eventually differentiate into the extra-embryonic trophectoderm (TE) and the pluripotent inner cell mass (ICM) at blastocyst stage. In a recent study, Korotkevich and colleagues used a reduced embryo system to show that TE differentiation is driven by cell polarization and apical domain formation (1).