Fig. 7. Activation of ß-catenin and LEF/TCF signaling in skull development. Mice carrying the TOPGAL transgene, capable of responding to ß-catenin and LEF/TCF signaling, were used to monitor activation of this pathway by ß-gal staining analyses in cranial skulls at E16.5 (C,E) and P1 (D,F). Whole-mount staining shows activation of the canonical Wnt pathway during early skull formation (C-F). Arrowheads indicate the coronal sutures and arrows indicate the activation of ß-catenin and LEF/TCF signaling in medial parts of the nasal bones. The non-transgenic mice, with no background staining, indicate the specificity of the assay (A,B). Scale bars: 2 mm in A-D; 500 µm in E,F.