Fig. 8. Mammary bud formation is impaired in Gli3^xt/xt mice and after mis-activation of the hedgehog pathway. TOP-Gal expression is seen in the developing mammary placodes number 3 and number 4 in wild-type E11 embryos (arrows) (A). TOP-Gal expression is absent from the region of bud 3 in E11 Gli3^xt/xt embryos (white arrow) but is present in the developing bud 4 (black arrow) (B). In E12.5 wild-type embryos, TOP-Gal expression reveals the development of five pairs of mammary buds (C, arrows), whereas Gli3^xt/xt embryos lack bud pairs 3 and 5 (D, predicted position of missing buds is marked by white arrows). E13.5 Gli2^1nki/1nki embryos (E) show normal development of five pairs of mammary bud, but Gli2^1nki/1nki; Gli3^xt//+ embryos (H) show loss of buds 3 and 5 (white arrows). Higher magnification of the thoracic buds (F,I) and inguinal buds (G,J). A hypoplastic bud 3 (arrowhead) is seen in some Gli2^lzki/+; Gli3^xt/xt embryos (K). Misactivation of Gli1-lacZ is seen in the stroma (str) surrounding buds 1 and 4 (arrow) in Gli3^xt/xt embryo wholemounts (L,M) and sections (N).