Differentiation of first cell lineages in mammalian embryos – interspecies similarities and differences

The embryonic development of placental mammals takes place inside the mother’s womb, which requires the formation of appropriate supportive structures by both the mother’s organism and the developing embryo. The first stages of mammalian embryonic development, preceding implantation, are the period of differentiation of the first cell lineages – epiblast (which will give rise to the embryo proper), and extra-embryonic lineages: trophectoderm (responsible for implantation and formation of the placenta) and primitive endoderm (giving rise to the yolk sac). Their differentiation is necessary for further development, and is a common feature of the development of all placental mammals, but the timing and molecular mechanisms responsible for these processes differ between mammalian species.