Monitoring of canonical BMP and Wnt activities during postnatal stages of mouse first molar root formation

OBJECTIVE: This study aimed to explore the precise temporospatial distributions of bone morphogenetic protein (BMP) and Wnt signaling pathways during postnatal development of mammalian tooth roots after the termination of crown morphogenesis. METHODOLOGY: A total of two transgenic mouse lines, BRE-LacZ mice and BAT-gal mice, were undertaken. The mice were sacrificed on every postnatal (PN) day from PN 3d up to PN 21d. Then, the first lower molars were extracted, and the dissected mandibles were stained with 5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside (X-gal) and fixed. Serial sections at 10 µm were prepared after decalcification, dehydration, and embedding in paraffin. RESULTS: We observed BMP/Smads and Wnt/β-catenin signaling activities in the dental sac, dental pulp, and apical papilla with a certain degree of variation. The position of activation of the BMP/Smad signaling pathway was located more coronally in the early stage, which then gradually expanded as root elongation proceeded and was associated with blood vessels in the pulp and developing complex apical tissues in the later stage. However, Wnt/β-catenin signaling was highly concentrated in the mesenchyme below the cusps in the early stage, gradually expanded to regions around the root in the transition/root stage, and then disappeared entirely in the later stage. CONCLUSIONS: These results further confirmed the participation of both BMP and Wnt canonical signaling pathways in tooth root development, as well as formed the basis for future studies on how precisely integrated signaling pathways regulate root morphogenesis and regeneration.