Fig. 6. NF-B is essential and sufficient to induce placode down growth and Shh expression. (A) Embryonic skin explants of E13.5 Gal x tabby matings were incubated for 24 hours with recombinant Fc-Eda A1, Fc-Eda A2, TNF or PMA or left untreated (nt). Upper row, X-Gal staining of skin explants. Lower row, whole-mount in situ hybridization of skins using an Shh antisense probe. Placode down growth was induced more or less strongly by any stimulator of NF-B activity, except for Eda A2. (B) In situ hybridization of sagittal embryonic wild-type and c^IBN (N) skin sections at indicated time points (E14.5-P0) using a Shh antisense probe. Broken lines indicate the boundary between epidermis and dermis. Arrows indicate Shh-positive follicles.