Fig. 3. The number of dct⁺ cells declines in the presence of MoTP. (A-H) The development of late-stage dct⁺ cells was further examined as the MoTP incubation continued. Larvae were reared in MoTP solution beginning at 14 hpf and fixed at selected developmental stages up until 68 hpf for in situ analysis. (A,C,E) The distribution and the number of dct⁺ cells in untreated larvae (reared in PTU solution) at 37, 42 and 61 hpf, respectively. Note that many dct⁺ cells in the untreated animals are differentiated melanocytes that remain unpigmented as a result of PTU treatment. (B,D,F) dct⁺ cells in the MoTP-treated larvae at 37, 42 and 61 hpf, respectively, revealing a gradual disappearance of dct⁺ cells during the MoTP incubation. The number of dct⁺ cells in the MoTP-treated larvae begins to decline from a maximum of 100 dct⁺ cells at 31 hpf to an average of 15 dct⁺ cells by 60 hpf (red line in H). These dct⁺ cells have a stereotyped spacing pattern in the dorsum (white arrowheads in G). By contrast, the number of dct⁺ cells steadily increases to more than 300 in the untreated larvae (blue line in H). Scale bar: in B, 500 µm for A-D; in F, 400 µm for E,F; in G, 400 µm.