The concentration-dependent response to Hh agonist of neural progenitor markers in neural plate explants. (a) The intermediate region of neural plate was dissected from stage 10-11 chick embryos and cultured in the presence of varying concentrations of Hh-Ag 1.3 (agonist) for 22 hours. Explants were then immunostained for Pax7, MNR2 and Nkx2.2 and the number of immunoreactive cells per explant was counted. (b) The average number of immunoreactive cells per explant in response to increasing concentrations of Hh-Ag 1.3 (n = 6 explants). Error bars represent standard deviations. (c-n) Confocal images of representative explants cultured in the presence of different concentrations of the agonist and stained for (c-f) Pax7; (g-j) MNR2; and (k-n) Nkx2.2. Pax7 is expressed only at the lowest concentrations of the agonist (c,d), MNR2 at intermediate and high concentrations (i,j), and Nkx2.2 only at high concentrations of agonist (n).