In mammals, proper placental development is essential for growth and viability of the embryo. The transcription factor TFAP2C is known to be important for specification and maintenance of trophoblast stem cells (placental progenitors), but whether this factor also plays roles at later stages of placental development is less well understood. On 787, Hubert Schorle and co-workers provide insights into the role of TFAP2C in a subset of placental progenitors, the TPBPA-expressing population that forms the junctional zone of the placenta. Loss of Tfap2c from this population leads to growth defects in the junctional zone, with reduced numbers of TPBPA+ cell-derived trophoblasts. Microarray analysis and follow-up experiments provide evidence that TFAP2C controls several key aspects of placental development: it inhibits Cdkn1a, a cell cycle inhibitor; promotes expression and activation of Akt to regulate glycogen synthesis; and promotes MAPK pathway activity – important for trophoblast proliferation and differentiation – by repressing the Dusp family of MAPK inhibitors. Importantly, this conditional mouse mutant provides a model for intrauterine growth retardation, as mutant embryos show lower foetal and birth weight. Preliminary data in a human trophoblast cell model suggests that this important role of TFAP2C may be conserved.