Figure 4.

The teratogenic consequences of cyclopamine exposure are a reflection of the dynamic nature of Shh expression. (A and B) Whole-mount and histological assessments following cyclopamine exposure at St. 15 illustrate that both brain and facial structures are affected. Embryos exposed to cyclopamine have a single telencephalic vesicle (dotted yellow line, asterisks) and severe hypotelorism that results from a lack of expansion in the mediolateral facial axis (red arrows) and approximation of the maxillary primordia (black and white arrowheads; compare with HBC controls in C and D). (E and F) In contrast, embryos exposed to cyclopamine at St. 17 have defects that are limited to facial structures. The telencephalon appears normal (yellow dotted lines, asterisks) compared with HBC controls (G and H), but treated embryos still exhibit hypotelorism (red arrows) that results in the near-approximation of the maxillary primordia (black and white arrowheads). Scale bars: 200 μm (A, C, E, and G); 100 μm (B, D, F, and H).