Fig. 1. Histological and ultrastructural analysis of the Smo mutant tooth phenotype at 1 dpp. Parasagittal sections through control (A) and mutant (B) molars showing fusion between the first (m1) and second (m2) molars in the mutant. Frontal sections through molars from control (C) and mutant (D) pups. Note the absence of the dental cord (dc) and the cellular paucity and lack of vascularization in the mutant stellate reticulum (sr). The mis-positioned red blood cells in the SR in C is an artefact and therefore does not indicate the exact location of blood vessels. High magnifications of boxed areas in C and D are included as insets. Parasagittal sections at the anterior segment of incisors from control (E) and mutant (F) pups. Note the severe alterations in the ameloblast (a) and stratum intermedium (si) layers in the mutant. TEM micrographs from control (G) and mutant (H) incisors. The white double-headed arrows indicate ameloblast length in G and H. dp, dental papilla mesenchyme; G, Golgi; o, odontoblasts; Tp, Tomes' process; tw, terminal web. Scale bars: 500 µm (A,B); 200 µm (C,D); 50 µm (E,F); 5 µm (G,H).