Anat Cell Biol.  2012 Sep;45(3):193-202. 10.5115/acb.2012.45.3.193.

Col1a1-cre mediated activation of beta-catenin leads to aberrant dento-alveolar complex formation

• Kim TH
• Bae CH
• Jang EH
• Yoon CY
• Bae Y
• Ko SO
• Taketo MM
• Cho ES

• KMID: 2046747
• DOI: http://doi.org/10.5115/acb.2012.45.3.193

Abstract

Wnt/beta-catenin signaling plays a critical role in bone formation and regeneration. Dentin and cementum share many similarities with bone in their biochemical compositions and biomechanical properties. Whether Wnt/beta-catenin signaling is involved in the dento-alveolar complex formation is unknown. To understand the roles of Wnt/beta-catenin signaling in the dento-alveolar complex formation, we generated conditional beta-catenin activation mice through intercross of Catnb+/lox(ex3) mice with Col1a1-cre mice. In mutant mice, tooth formation and eruption was disturbed. Lower incisors and molars did not erupt. Bone formation was increased in the mandible but tooth formation was severely disturbed. Hypomineralized dentin was deposited in the crown but roots of molars were extremely short and distorted. In the odontoblasts of mutant molars, expression of dentin matrix proteins was obviously downregulated following the activation of beta-catenin whereas that of mineralization inhibitor was increased. Cementum and periodontal ligament were hypoplastic but periodontal space was narrow due to increased alveolar bone formation. While cementum matrix proteins were decreased, bone matrix proteins were increased in the cementum and alveolar bone of mutant mice. These results indicate that local activation of beta-catenin in the osteoblasts and odontoblasts leads to aberrant dento-alveolar complex formation. Therefore, appropriate inhibition of Wnt/beta-catenin signaling is important for the dento-alveolar complex formation.

Keyword

beta-catenin; Activation; Tooth deformities; Dentin hypomineralization; Short roots

MeSH Terms

Animals
beta Catenin
Bone Matrix
Crowns
Dental Cementum
Dentin
Incisor
Mandible
Mice
Molar
Odontoblasts
Osteoblasts
Osteogenesis
Periodontal Ligament
Proteins
Regeneration
Tooth
Proteins
beta Catenin

Figure

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  Fig. 1 Targeted activation of β-catenin in the dentoalveolar complex. (A) In immunohistochemistry, β-catenin is localized in the Am, Od, and Ob of developing mouse dentoalveolar complex at P8. (B) β-galactosidase activities are also found in the Od and Ob of Col1a1-cre:R26R double transgenic mouse dentoalveolar complex at P8. (C) Col1a1-cre:Catnb+/lox(ex3) mutant mice exhibit severe growth retardation with short height and small body weights. (D) Differences in body weights between WT and MT mice are appeared in 3 weeks after birth and are clearer in the mice at 4 weeks-old. (E) Genotype analysis of mutant mice after intercross with Col1a1-cre and Catnb+/lox(ex3) mice. (F-I) Gross appearance of incisors in WT and MT mice at 4 weeks-old. Both of upper and lower incisors are normally erupted in WT mice, whereas upper incisors are erupted but lower incisors (white arrow) are not erupted in MT mice. (J, K) Molars of lower jaw (white arrowheads) are not erupted into oral cavity in MT mice in contrast to normally erupted in WT mice. Am, ameloblasts; Od, odontoblasts; Ob, osteoblasts; WT, wild type; MT, mutant. *P<0.05. Scale bar=200 µm (A, B).

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  Fig. 2 Disturbances in tooth formation and eruption failure of molars in Col1a1-cre:Catnb+/lox(ex3) mice. (A, B) In microradiography, general dimensions of craniofacial skeleton in MT mice are smaller than those in WT littermates. Particularly, mandible of MT is severely retarded and resulted in malocclusion. (C, D) In the mid-sagittal view, mandibular incisor is shorter and smaller than that of WT mice. (E, F) Molars of MT mice are impacted within mandible and root formation is impaired while those of WT mice are normally formed and erupted into the oral cavity. (G, H) In H&E-stained sagittal sections of the mandibles, bone deposition is remarkably increased and molars are not erupted in the MT mice. (I, J) In MT mice, β-catenin expression is upregulated in the odontoblasts and osteoblasts. MT, mutant; WT, wild type; H&E, hematoxylin and eosin. Scale bar=100 µm (G-J).

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  Fig. 3 Mineralization defects in dentin of Col1a1-cre:Catnb+/lox(ex3) mice. (A, B) Immunohistochemistry reveal that β-catenin is localized in the Od and pulp cells of mandibular first molar of WT mice, which is restrictedly increased in the odontoblasts of MT mice. (C, D) Phex is localized in the odontoblasts of WT mice, but which is clearly reduced in the odontoblasts of MT mice. (E, F) In WT mice, Dspp is localized in the dentin as well as odontoblasts, but it is obviously decreased in the predentin and odontoblasts of MT mice. Dspp remains only in thin mineralized dentin of MT mice. (G, H) Localization of Fgf23 is not found in the dentin and odontoblasts of WT mice but which is clearly observed in the predentin of MT mice. (I-L) Bgn and Dmp1 are mainly localized in the predentin and a part of dentin in WT mice, which also decreased in the predentin of MT mice. Od, odontoblasts; WT, wild type; MT, mutant; Phex, phosphate regulating endopeptidase homologue on the X chromosome; Dspp, dentin sialophosphoprotein; Fgf23, fibroblast growth factor-23; Bgn, biglycan; Dmp1, dentin matrix protein-1. Scale bar=100 µm (A-L).

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  Fig. 4 Deformities in the roots and periodontium of Col1a1-cre:Catnb+/lox(ex3) mice. (A, B) In contrast to WT mice, RD is thin and hypomineralized in MT mice. In addition, PS is narrower due to excessive formation of alveolar bone in MT mice. (C, D) In the RD of MT mice, Dspp is decreased in the dentin. (E-J) In WT mice, Bsp, Dmp1 and Fgf23 are specifically localized in the matrix of acellular cementum (arrows) and alveolar bone, which is decreased in the MT mice. (K, L) Osteopontin is localized in the cementum and periodontal ligaments of WT mice. It is also decreased in the cementum and periodontal ligaments of MT mice. WT, wild type; RD, root dentin; H&E, hematoxylin and eosin; MT, mutant; PS, periodontal space; Dspp, dentin sialophosphoprotein; Bsp, bone sialoprotein; Dmp1, dentin matrix protein-1; Fgf23, fibroblast growth factor-23; Opn, osteopontin. Scale bar=50 µm (A-L).

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  Fig. 5 Molecular changes related with increased bone mass in the mandibles of Col1a1-cre:Catnb+/lox(ex3) mice. (A, B) In the mandible of MT mice, bone mass is increased but number of osteoblasts are decreased to compare with those of WT mice. (C-F) Bsp expression is slightly increased with increase of bone mass, but Tnap is clearly decreased in the MT. (G-J) Bgn is significantly increased in the mandible of MT mice, while Phex is almost disappeared in MT mice. (K, L) Increased expression of Dmp1 is also observed in MT mice. WT, wild type; H&E, hamatoxylin and eosin; MT, mutant; Bsp, bone sialoprotein; Tnap, tissue-nonspecific alkaline phosphatase; Bgn, biglycan; Phex, phosphate regulating endopeptidase homologue on the X chromosome; Dmp1, dentin matrix protein-1. Scale bar=50 µm (A-L).

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