Fig. 8. Comparison of gene expression in the skin mesenchyme of wild-type and Ta mutant embryos. (A,E,I) Activin ßA, Bmp4 and Ptch are intensely expressed in the mesenchyme under the ectodermal placodes in E15 wild-type embryos. Ptch (Ptc) expression is seen in whole mount in situ hybridization. (C,G,K) In E17 wild-type embryos, activin ßA, Bmp4 and Ptch are expressed in the tylotrich hair follicles and awl placodes. (B,F,J) In E15 Ta mutants, no placodes have formed and no upregulation of gene expression is apparent. Activin ßA is expressed weakly throughout the mesenchyme underlying the ectoderm. (D,H,L) At E17, activin ßA, Bmp4 and Ptch are intensely expressed in the Ta mesenchyme that underlies the placodes of awl hairs. Scale bar: 100 µm.