Fig. 1.

Dermo1-Cre-mediated recombination during PA development. (A) TOPGAL β-galactosidase expression was observed in the core mesenchyme of pharyngeal arch (PA)1 and PA2 and in pharyngeal mesenchyme at E9.5. β-galactosidase expression was also detected in the endocardial cushion in cells undergoing epithelial (endocardial)-mesenchymal transition. (A′) Magnified view of A showing TOPGAL expression in PA core mesenchyme (arrows). (B) E9.5 R26R^Dermo1-Cre embryo showing trace β-galactosidase activity in pharyngeal mesenchyme (arrow). R26R^Dermo1-Cre was also active in the endocardial cushion (arrowhead). However, Dermo1-Cre was not active in neural crest-derived mesenchyme in the PAs at this stage. (C) E10.5 R26R^Dermo1-Cre embryos showing β-galactosidase activity in all PA mesenchymal cells including neural crest-derived mesenchyme. No Cre activity was found in the myocardium. (D-G) Co-immunohistochemistry showing β-galactosidase (green) and β-catenin expression (red) in PA mesenchyme at E10.5. (D,E) R26R^Dermo1-Cre embryos showing that β-galactosidase expression is restricted to PA mesenchyme and does not overlap with DAPI-stained (blue) nuclei in ectoderm and endoderm (arrow). (F) Ctnnb1^+/+ embryos show staining for β-catenin in PA mesenchyme, ectoderm and endoderm. (G) In Ctnnb1^Dermo1-Cre mice, β-catenin expression was decreased in PA mesenchyme. h, heart; hm, xxx? xxx; ov, otic vesicle; pa1, first pharyngeal arch; pa2, second pharyngeal arch; pm; pharyngeal mesenchyme. Scale bar: 400 μm in C; 200 μm in A′,B,D-G.