Fig. 6. Neural progenitor domain patterning of feedback LDA mutants at E8.5. (A-R) Immunofluorescence of neural tube sections from eight-to nine-somite stage embryos. Antibodies and genotypes of the embryos as indicated in each panel. (S-X) Analysis for ß-galactosidase activity in neural tube sections from 11- to 12-somite stage embryos. The Ptch1-null allele has the coding sequence for nucleus-localized ß-galactosidase inserted under the Ptch1 endogenous promoter (Goodrich et al., 1997), and the Hhip1 null allele has the coding sequence for cytoplasmic ß-galactosidase placed under the regulation of Hhip1 promoter (Chuang and McMahon, 1999), allowing both to serve as potential reporters of Hh signaling. However, as shown in T, the level of ß-galactosidase expression from the Hhip1^LacZ allele appears to be below the level of detection, suggesting that the staining observed in U and W is predominantly from Ptch1^LacZ. (Y) Quantification of the size of each neural progenitor population as reflected by cell numbers in wild type and feedback LDA mutants. p3/pMN, Nkx2.2⁺Olig2⁺; p1+p0+dorsal domain, Pax6⁺Nkx6.1^-. (Z) Representation of the size of each progenitor domain as a percentage of the total cell numbers in the neural tube. Scale bar: 25 µm.