During Xenopus gastrulation, Wnt and FGF signalling are known to induce posterior structures. Wnt target genes are expressed in either a ring or a horseshoe shape with a dorsal gap, but how Wnt and FGF integrate to regulate these patterns is less well understood. Now, Richard Harland and colleagues use chromatin immunoprecipitation sequencing to profile the binding of the respective Wnt and FGF pathway transcription factors: β-catenin and Ets2. They show that Ets2 binds near all Wnt target genes, whereas β-catenin binds close to the promoter of target genes with a horseshoe shape, but further from the promoter at targets with ring patterns. By manipulating the activity of both signalling pathways, the researchers show that genes expressed in a ring pattern are predominately regulated by FGF signalling. Conversely, horseshoe-shaped expression relies on the activity of β-catenin. The researchers hypothesise that, for genes expressed in a horseshoe pattern, the Wnt pathway repressor TCF is bound close to the promoter, and Ets2 is insufficient to alleviate its activity, unless β-catenin is also present to displace TCF. For ring patterns, however, TCF is further from the promoter and Ets2 is able to drive gene expression without β-catenin. These data provide a model for FGF and Wnt signal integration.
