Fig. 5. lab550 can be induced by DPP signaling in the absence of the visceral mesoderm. In a twi mutant embryo, expression of the lab550 construct is absent in the endoderm (A). The endodermal expression driven by lab550 can be restored in twi mutants upon ectopic expression of an activated form of the TKV receptor, tkv^QD, under UAS control, using the endoderm-specific GAL4 line 48Y (B, arrow). When ectopic WG or MAPK signaling were induced in a similar, cell-autonomous, way in twi mutants, using 48Y and an activated form of arm, arm^S10 (C), and of Ras, ras^V12 (D) under UAS control, endodermal expression of lab550 was not restored.