Coronal section of embryos stained with β-gal to show Crect lineage-marked cells in the supraorbital cranial ectoderm (A,B). Fluorescent immunohistochemistry of coronal sections showing expression of Twist1 protein in cranial bone and dermal progenitors in the conditional Wls mutants in the ectoderm (C,D) and mesenchyme (E,F). Twist1 protein expression is absent in the ectoderm Wls mutants, but not in the mesenchyme Wls mutants. In situ hybridization showing Twist1 mRNA expression requires mesenchymal β-catenin (G,H). Note that skeletogenic markers Msx2 and Dlx5 are not dependent on mesenchymal β-catenin (I–L). Control and mutants images were obtained at the same magnification. Scale bar=100um.