Shh-N Signaling Promotes Cytodifferentiation and Cusp Formation in Developing Molar

Objectives: The Shh signaling pathway plays a critical role in tooth development. The present study was designed to investigate the direct role of Shh molecule on cytodifferentiation and cusp formation. Methods: Affi-gel blue beads soaked in exogenous Shh-N protein, Shh antibody or BSA control protein were placed between the epithelium and mesenchyme of cap stage tooth germs. The recombinants were grafted for culture under kidney capsules in adult male mice for 2 and 4 weeks respectively. Histological features of tooth formation were analyzed. Results: After 2 weeks of subrenal culture, the odontoblasts in the Shh-N group and the control group formed a layer of polarized and elongated cells secreting pre-dentin matrix. The ameloblasts also converted into a highly-polarized secretory cells. The polarity and organization of the ameloblast and odontoblast layers were severely disrupted in the recombinants treated with Shh antibody. Enamel and dentin matrix deposited in the Shh antibody group was significantly thinner than that in the Shh-N group and the control group. After 4 weeks of subrenal culture, the teeth dissected from the explants treated with Shh-N or control protein were multicuspid with well formed cusps. Most of the teeth harvested from the Shh antibody group were small and abnormal. A single irregularly shaped cusp was visible, and a partial crown formed. The main cusp height in this group was significantly lower than that in the Shh-N group. Conclusion:The results indicate that Shh signaling pathway promotes odontoblast and ameloblast cytodifferentiation and patterned cusp formation. This research was supported by the grants from National Natural Science Foundation of China (30171011).