Axis specification and the induction of endoderm and mesoderm in early embryos are dependent on signals generated by members of the transforming growth factor-β (TGF-β) family called Nodal that are produced by a set of cells called "the node" in mammals or "Spemann's organizer" in frogs. Niederländer et al. and Episkopou et al. show that the nuclear-localized protein Arkadia is involved in modulating the responsiveness of cells to Nodal, and thus may represent one of the molecules that allow the same signal to be interpreted differently by cells in different locations. Niederländer et al. investigated the role of Arkadia in Xenopus embryos and found that Arkadia enhanced the formation of endoderm at the expense of mesoderm when coexpressed in an animal cap assay with TGF-β members Activin, BVg, Xnr1, and Xnr2. Episkopou et al. showed that in mice with a disrupted Arkadia gene, the node does not form and anterior structures are lost during embryogenesis. Arkadia also exhibits a genetic interaction with Nodal in mice, further supporting the theory that Arkadia and Nodal are in the same signaling pathway. C. Niederländer, J. J. Walsh, V. Episkopou, C. M. Jones, Arkadia enhances nodal-related signaling to induce mesendoderm. Nature 410 , 830-834 (2001). [Online Journal] V. Episkopou, R. Arkell, P. M. Timmons, J. J. Walsh, R. L. Andrew, D. Swan, Induction of the mammalian node requires Arkadia function in the extraembryonic lineages. Nature 410 , 825-830 (2001). [Online Journal]