Fig. 5. The Tcf- and Smad-binding sites are required for dorsal telencephalic enhancer activity. (A) Embryo transgenic for the 4.6 kb enhancer (construct 2) shows staining in the dorsal telencephalon and ventral diencephalon. (B,C) Mutations of the Tcf- and Smad-binding sites lead to weak enhancer activity in the ventral diencephalon. lacZ staining in the dorsal telencephalon is completely abolished (B) or drastically reduced (arrowhead) (C). (D) Staining in embryos with a transgene carrying a mutation of the Tcf-binding site is restricted to the dorsomedial telencephalon. (E) Embryo carrying a transgene with a mutated Smad-binding site shows weak ß-galactosidase activity throughout the cortical neuroepithelium with higher expression levels in the dorsomedial telencephalon (arrowheads).