The first priority of a mammalian embryo is to establish an intimate relationship with its
mother. This is accomplished by precocious differentiation of the trophoblast lineage, which
mediates uterine implantation and initiates the process of placentation. Surprisingly little is
known about the molecular mechanisms that drive trophectoderm differentiation from the
equipotent blastomeres of the morula. Somewhat more is known about the maintenance of
trophoblast stem cells, once this lineage has been established. The first half of this review …