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, 239 (1), 140-7

Role of Wnt Signaling in the Biology of the Periodontium

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Role of Wnt Signaling in the Biology of the Periodontium

Scott M Rooker et al. Dev Dyn.

Abstract

Continuously erupting teeth have associated with them a continuously regenerating periodontal ligament, but the factors that control this amazing regenerative potential are unknown. We used genetic strategies to show that the periodontal ligament arises from the cranial neural crest. Despite their histological similarity, the periodontal ligament of continuously erupting incisor teeth differs dramatically from the periodontal ligament of molar teeth. The most notable difference was in the distribution of Wnt responsive cells in the incisor periodontal ligament, which coincided with regions of periodontal ligament cell proliferation. We discuss these findings in the context of dental tissue regeneration.

Figures

Figure 1
Figure 1
Histology, collagen distribution and embryonic origin of the periodontal ligament. (A) Incisor, pentachrome histology. (B) Molar root, pentachrome histology. (C) Collagen layout of incisor periodontal ligament (PDL) shown through picrosirius red. (D) Collagen organization in molar PDL shown through picrosirius red staining and polarized light. (E) e13.5 Wnt1Cre;R26RLacZ molar tooth bud, showing Xgal staining in dental mesenchyme. (F) e17.5 Wnt1Cre;R26RLacZ molar tooth development where Xgal staining indicates distribution of neural crest cells. (G) Adult Wnt1Cre;R26RLacZ molar tissue stained with Xgal demonstrates the PDL arises from neural crest. (H, I) GFP expression in the molar of Wnt1Cre;Z/EG mice. p, pulp; c, cementum; d, dentin; pdl, periodontal ligament; b, bone; mes, mesenchyme; eo, enamel organ; dp, dental papilla.
Figure 2
Figure 2
Differential distribution of proliferation and differentiation within the PDL of incisors and molars. (A) Alkaline phosphatase activity is present in the PDL of the incisor with a gradient of minimal activity next to the cementum, and strong activity adjacent to the bone. (B) Alkaline activity in the molar PDL is more consistent throughout the periodontal ligament. (C) Cell proliferation of the PDL of the incisor shown through Ki67 immunostaining is evident adjacent to the cementum, but lacking in the rest of the PDL. (D) Cell proliferation is minimal in the PDL of the molar without the heavy proliferation next to the cementum as seen in the incisor. (E, F) Collagen type 1 is found in the PDL of the molar next to the bone, but not adjacent to the cementum. c, cementum; d, dentin; pdl, periodontal ligament; b, bone.
Figure 3
Figure 3
Graded distribution of cell activities with in the periodontium. (A, B) Xgal activity shows cells in the PDL of the incisor display strong Wnt responsiveness adjacent to the cementum, but is sparsely distributed throughout the rest of the PDL. The same strong signal is not found adjacent to the bone of the PDL. (C) Xgal activity shows cells in the PDL of the molar are Wnt responsive, but do not display the same localization next to the cementum as seen in the incisors. (D, E) Cell proliferation of the incisor, shown through Ki67 immunostaining, is significant adjacent to the cementum but not adjacent to the bone. (F) Cell proliferation shown through Ki67 immunostaining is minimal in the PDL of the molar. (G, H) The distribution of alkaline phosphatase activity is shown to be minimal adjacent to the cementum and strongest adjacent to the bone. (I) Alkaline phosphatase activity in the PDL of the molar is more evenly distributed throughout the periodontal ligament. p, pulp; c, cementum; d, dentin; pdl, periodontal ligament; b, bone.
Figure 4
Figure 4
Differentiation is highest at PDL-bone interface. (A, B) Osteoclast activity is shown through TRAP staining adjacent to the bone, but not to the cementum. (C, D) Collagen type IV is shown adjacent to the bone, but not to the cementum. (E, F) Vascularization is displayed through PECAM immunostaining with blood vessels near the bone but not near the cementum. p, pulp; c, cementum; d, dentin; pdl, periodontal ligament; b, bone.

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