Figure 8.

Model of the regulatory inputs onto the tinman Dpp response element. In the ectoderm, Dpp signaling activates Smads and triggers nuclear translocation of Medea/Mad heteromers (M). Smad complexes and a yet unknown CAATGT-binding factor (?) may be able to bind to the Dpp response element, but binding of a corepressor (R) prevents transactivation. However, in the mesoderm, binding of Tinman protein competes with repressor binding, which leads to the formation of an active complex that triggers transactivation. Protein–protein interactions between Tinman and Smads (S. Zaffran, X. Xu, Z. Yin, and M. Frasch, in prep.) could be important for the formation and activity of this complex.