Fig. 8. Comparison of gene expression and hypothesized Fgf signals (arrows) between Astyanax and the zebrafish.(A,B) Transverse views of the left side of the mandible. Lateral epithelial and mesenchymal gene expression common to both species is Fgf dependent. Loss of a medial Fgf signal to the epithelium is hypothesized to have caused cypriniform tooth loss. See text for basis of hypothesized ligand sources. (C,D) Lateral views of selected features of mandibular epithelial expression. pitx2 and shh expression common to both species is Fgf independent. The zebrafish may lack a domain of overlapping pitx2 and shh expression corresponding to a tooth germ (marked by dlx2a and dlx2b expression in Astyanax).