sfrp2 RNA levels are disturbed in Hh pathway mutants and after pharmacological treatments. (A, A'') In WT embryos, sfrp2 expression is evident in adaxial cells. This expression is significantly down-regulated in yot embryos (B, B''). Pharmacological treatments with pur and cyc show altered expression in pharyngeal arches (asterisk in E, compare C, D and E for different levels of RNA). Anterior is towards left, lateral views are shown. Full lateral views of embryos are shown in A' and B'.