Fig. 11.

Model. Hh signals to both the endoderm (red) and neural crest (graded shades of green, with darker shades being dorsal). Signaling to the endoderm is essential for morphogenetic movements of the pharyngeal arches and likely aids in sculpting the shape of skeletal elements. Signaling to the neural crest is required for the proper dorsal/ventral patterning of the pharyngeal arches. The reception of Hh signaling by the neural crest is required for a neural crest-derived signal that maintains Hh expression in the endoderm.