Construction of a Vertebrate Embryo from Two Opposing Morphogen Gradients

Designer Embryo Numerous signaling pathways have been implicated in controlling early vertebrate embryogenesis. P.-F. Xu et al. (p. 87) identify the minimal set of factors necessary to get uncommitted cells to organize a complete embryo. Two opposing gradients of the growth factors Nodal and Bone Morphogenetic Protein were sufficient to instruct zebrafish embryonic pluripotent cells to organize a complete embryo, not only in vivo but also in vitro. These findings may provide guidance for regenerative medicine studies aimed at constructing tissues and organs in vitro from cultured pluripotent cells. Opposing gradients of bone morphogenetic protein and Nodal can induce the formation of a zebrafish embryo. Development of vertebrate embryos involves tightly regulated molecular and cellular processes that progressively instruct proliferating embryonic cells about their identity and behavior. Whereas numerous gene activities have been found to be essential during early embryogenesis, little is known about the minimal conditions and factors that would be sufficient to instruct pluripotent cells to organize the embryo. Here, we show that opposing gradients of bone morphogenetic protein (BMP) and Nodal, two transforming growth factor family members that act as morphogens, are sufficient to induce molecular and cellular mechanisms required to organize, in vivo or in vitro, uncommitted cells of the zebrafish blastula animal pole into a well-developed embryo.