In vivo assays of an Hh agonist. (a-d) The Hh agonist Hh-Ag 1.2 up-regulates Hh signaling in mouse embryos in utero. Expression of Ptc1lacZ in E9.5 Ptc1lacZ/+ embryos after treatment with vehicle (a,c) or Hh-Ag 1.2 (b,d). (a,b) Lateral views of whole embryos stained with X-gal; (c,d) transverse sections through E9.5 embryos following X-gal staining. Ptc1 expression is dorsally expanded throughout the ventral neural tube and adjacent mesoderm in agonist-treated embryos (compare b,d with a,c). Note the open neural tube in the head of these embryos (b). (e-p) The agonist complements the loss of Shh but requires Smo to activate Hh signaling in utero. (e-l) Whole-mount in situ hybridization analyses of the expression of Ptc1 gene in E8.5 embryos (n = 4); (e-h) ventral anterior views, and (i-l) ventral posterior views, of embryos heterozygous (e,f,i,j) or homozygous (g,h,k,l) for an Shh-null allele. (m-p) Lateral views of X-gal staining of Ptc1lacZ expression in E8.5 Ptc1lacZ/+ embryos (n = 4) heterozygous (m,n) or homozygous (o,p) for a Smo-null allele. (e,g,i,k,m,o) Vehicle-treated embryos; (f,h,j,l,n,p) Hh-Ag 1.2- (agonist-) treated embryos. Red arrows in (e-h) indicate the partial rescue of midline structures in Shh-/- embryos (g) by agonist treatment (h). Black arrowheads in (e-l) indicate expression in the midline.