Fig. 7. Summary of Tv cell specification. (A) At stage 16, when ap-neurons appear, dac, eya and sqz are expressed in different subsets of ap-neurons. At stage 17, BMP activation via the Gbb BMP ligand and the Wit BMP receptor leads to nuclear translocation of pMad and subsequent Fmrf activation. (B) In the Tv neuron, our genetic analyses support a differential role for eya and dac. eya plays multiple roles, regulating axon pathfinding, competence to respond to Gbb, and Fmrf expression in response to activated BMP signaling. dac, by contrast, regulates only Fmrf. Although the exact target of eya action downstream of pMad is not known, the dashed arrows suggest two possibilities: eya may regulate the pMad/Medea (Med) complex and/or the expression of Fmrf directly.