During embryogenesis, the anterior-posterior (AP) and dorsal-ventral (DV) axes are specified by the activity of key signalling pathways. FGF, Wnt and retinoic acid together pattern the AP axis: high activity defines more posterior tissues, which are specified later in development than anterior tissues. The BMP pathway specifies ventral fate; low BMP activity defines dorsal. Whether and how these pathways intersect to coordinate patterning of the two axes is poorly understood. On , Megumi Hashiguchi and Mary Mullins provide evidence for synchronisation of DV and AP patterning in the zebrafish embryo. Upon temporally restricted inhibition of BMP in embryos anteriorised by inhibition of FGF or Wnt, the dorsalised tissue takes on the AP fate appropriate to the anteriorised embryo, rather than that corresponding to the time of BMP inhibition. The authors identify one mechanism mediating pathway cross-talk: MAPK, activated downstream of FGF, phosphorylates and inhibits the BMP effector Smad5. Thus, this work establishes the close temporal coordination of AP and DV patterning, and provides insights into how this is achieved.
