Figure 1
BRE-LacZ reporter activity during M1 postnatal development in mice ranging from postnatal day (PN) 3 to PN21. A whole-mount X-gal staining of M1 showed BRE-dependent BMP signaling in the buccal/lingual view (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, and C) and in the apical view (A1, B1, C1, D1, E1, F1, G1, H1, I1, J1, K1, L1, M1, N1, O1, P1, Q1, R1, and S1). On PN3-PN5, active BMP/Smad signaling was identified in the coronal pulp and dental sac surrounding M1 (A–C) (A1–C1). On PN6–PN8, active BMP/Smad signaling could be observed in the dental papilla and root sheath (D–F) (D1–F1). On PN9–PN14, strong BMP/Smad signaling was observed in the root-forming regions, more specifically in the apical papilla and root sheath (G–L) (G1–L1). On PN15–PN21, the expression of BMP/Smad signaling was diminished around the root but existed in the apical region and along the ordered lining of blood vessels in the pulp (M–S) (M1–S1). (EE, enamel epithelium; DS, dental sac; CS, cusp; C, crown; R, root; AP, apical papilla; P, pulp).
Figure 2
BAT-gal reporter activity during M1 postnatal development in mice ranging from PN3 to PN21. A whole-mount X-gal staining of M1 showed Wnt/β-catenin signaling in the buccal/ lingual view (A, B, C, D, E, F, G, H, I, and J), in the apical view (A1, B1, C1, D1, E1, F1, G1, H1, I1, and J1), and in the occlusal view (A2, B2, C2, D2, E2, F2, G2, H2, I2, and J2). On PN3 and PN5, active Wnt/β-catenin signaling was detected in the mesenchyme directly below the cusps (A–B) (A1–B1) (A2–B2). On PN7, active Wnt/β-catenin signaling was observed in the apical region, with a decrease in the area below the cusps (C–C2). During PN9–PN14, strong Wnt/β-catenin signaling was observed in the root-forming regions not in the crown, and more specifically in the apical papilla and root sheath (D–F) (D1–F1) (D2–F2). From PN15 to PN21, the expression of Wnt/β-catenin signaling was diminished mostly, but some expression was observed in the apical region (G–J) (G1–J1) (G2–J2). (EE, enamel epithelium; DS, dental sac; CS, cusp; C, crown; R, root; AP, apical papilla; P, pulp; CL, cervical loop)
Figure 3
Selected histological sections of postnatal M1 with whole-mount X-gal staining at 10 µm thickness. Localization of active BMP/Smad signaling (A, B, and C, ×40) and Wnt/β-catenin signaling (D, E, and F, ×40) in M1 is shown. Panels A1, B1, C1, D1, E1, and F1 are high-magnification views (×100) of the red rectangular block as shown in panels A, B, C, D, E, and F, respectively. Panels A2, B2, C2, D2, E2, and F2 are high-magnification views (×100) of the blue rectangular block as shown in panels A, B, C, D, E, and F, respectively. On PN3, BMP/Smad-dependent signaling was primarily detected in the dental epithelium (A, A1, and A2); whereas active Wnt/β-catenin signaling was mainly expressed in the odontoblasts or pre-odontoblasts below the cusps and in the dental epithelium on the cusps; some expression was found in the apical region (D, D1, and D2). On PN7, BRE activity was detected in the pre-odontoblasts/odontoblasts in the crown pulp, blood vessels, and DAC (B, B1, and B2); Wnt/β-catenin activity was observed below the cusps, but none in the dental papilla and sac, nor in the vessels in the pulp (E, E1, and E2). On PN10, the same expression pattern was identified, associated with significant root elongation and advanced tooth mineralization (C, C1, and C2). Meanwhile, in BAT-gal mice, the number of X-gal-positive cells beneath the cusps decreased on PN10 (F, F1, and F2). (EE, enamel epithelium; OE, oral epithelium; DS, dental sac; CS, cusp; C, crown; R, root; DP, dental papilla; AP, apical papilla; P, pulp; CL, cervical loop; E, enamel; D, dentin; OD, odontoblast; V, vessel; HERS, Hertwig’s epithelial root sheath)