Fig. 1. Fgf8 expression in the mandibular arch. (A,B) Fgf8 whole-mount in situ hybridization on dissected mandibular arch region of E11 wild-type (A) and Prx1^-/-Prx2^-/- (B) embryo, oral view. Dorsal side is upwards. Arrows in A indicate medial border of the Fgf8 expression domain in the wild type. In the mutant, the Fgf8 expression domain straddles the midline (arrow in B). Also visible in B is the distension at the midline (arrow), where the epithelium has detached from the mesenchyme. (C,D) Direct comparison of Fgf8 and Prx1 expression. Adjacent transversal sections through the mandibular arch area of E11 wild-type embryos were hybridized with radioactive Fgf8 and Prx1 probes. Double exposure of bright- and dark-field are shown; a red filter was used during darkfield photography. mand, mandibular arch mesenchyme; max, maxillary process mesenchyme.