Fig. 2. Shh expression reveals the presence of ectopic pre-ameloblasts in Spry4^-/-;Spry2^+/-, in Spry4^-/-, and in Fst^-/- embryonic mouse incisors. (A-I) Gene expression analyzed by RNA in situ hybridization using the indicated probes on paraffin sections of wild-type and mutant embryonic incisors. The stage at which the embryos were collected is indicated. In this and subsequent figures, a dotted line outlines the incisor epithelium. In D, the Shh expression domain appears to extend slightly into the lingual epithelium, but as this was not reproducibly observed it is likely to be an artifact of the plane of section. The red arrowheads in E and H point to a domain in which Shh is ectopically expressed on the lingual side of Spry4^-/-;Spry2^+/- and Spry4^-/- incisors. A similar domain is detected in Fst null incisors (panel I), together with an additional anterior domain of ectopic Shh expression (open arrowheads). Scale bars: 100 µm.