The Generation and Recognition of Positional Information in the Preimplantation Mouse Embryo

Abstract

Cell differentiation and commitment within the preimplantation mouse embryo depend on cell position (Mintz, 1965; Tarkowski and Wroblewska, 1967). Within the aggregate of cells that form the morula, the more centrally placed cluster of cells starts to differentiate as an inner cell mass (ICM), while the more peripherally placed layer of cells differentiates as trophectoderm. After these first overt signs of differentiation, the two diverging classes of cells become fixed on their courses of development and are therefore said to be committed. If cell position is changed before commitment by rearrangement of blastomeres, then both cell differentiation and fate are changed (see Rossant, 1977; Johnson, 1979; Rossant and Frels, this volume). The embryo can regulate itself.