The Role of Autonomous Wntless in Odontoblastic Differentiation of Mouse Dental Pulp Cells

PURPOSE: Wnt signaling plays an essential role in the dental epithelium and mesenchyme during tooth morphogenesis. Deletion of the Wntless (Wls) gene in odontoblasts appears to reduce canonical Wnt activity, leading to inhibition of odontoblast maturation. However, it remains unclear if autonomous Wnt ligands are necessary for differentiation of dental pulp cells into odontoblast-like cells to induce reparative dentinogenesis, one of well-known feature of pulp repair to form tertiary dentin. MATERIALS AND METHODS: To analyze the autonomous role of Wls for differentiation of dental pulp cells into odontoblast-like cells, we used primary dental pulp cells from unerupted molars of Wls-floxed allele mouse after infection with adenovirus for Cre recombinase expression to knockout the floxed Wls gene or control GFP expression. The differentiation of dental pulp cells into odontoblast-like cells was analyzed by quantitative real-time polymerase chain reaction. RESULT: Proliferation rate was significantly decreased in dental pulp cells with Cre expression for Wls knockout. The expression levels of Osterix (Osx), runt-related transcription factor 2 (Runx2), and nuclear factor I-C (Nfic) were all significantly decreased by 0.3-fold, 0.2-fold, and 0.3-fold respectively in dental pulp cells with Wls knockout. In addition, the expression levels of Bsp, Col1a1, Opn, and Alpl were significantly decreased by 0.7-fold, 0.3-fold, 0.8-fold, and 0.6-fold respectively in dental pulp cells with Wls knockout. CONCLUSION: Wnt ligands produced autonomously are necessary for proper proliferation and odontoblastic differentiation of mouse dental pulp cells toward further tertiary dentinogenesis.

Nfic regulates tooth root patterning and growth / 대한해부학회지

Molecular interactions between epithelium and mesenchyme are important for root formation. Nuclear factor I-C (Nfic) has been identified as a key regulator of root formation. However, the mechanisms of root formation and their interactions between Hertwig's epithelial root sheath (HERS) and mesenchyme remain unclear. In this study, we investigated the role of Nfic in root patterning and growth during molar root development. The molars of Nfic knockout mice exhibited an enlarged pulp chamber and apical displacement of the pulpal floor, characteristic features of taurodontism, due to delayed furcation formation. In developing molar roots of mutant mice at P14, BrdU positive cells decreased in the apical mesenchyme of the elongation region whereas those cells increased in the dental papilla of the furcation region. Whereas cytokeratin 14 and laminin were localized in HERS cells of mutant molars, Smoothened (Smo) and Gli1 were downregulated in preodontoblasts. In contrast, cytokeratin 14 and Smo were localized in the cells of the furcation region of mutant molars. These results indicate that Nfic regulates cell proliferation in the dental mesenchyme and affects the fate of HERS cells in a site-specific manner. From the results, it is suggested that Nfic is required for root patterning and growth during root morphogenesis.

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

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.

Cholinesterase Activity in the Dental Epithelium of Hamsters During Tooth Development

Cholinesterase (ChE) is one of the most ubiquitous enzymes and in addition to its well characterized catalytic function, the morphogenetic involvement of ChE has also been demonstrated in neuronal tissues and in non-neuronal tissues such as bone and cartilage. We have previously reported that during mouse tooth development, acetylcholinesterase (AChE) activity is dynamically localized in the dental epithelium and its derivatives whereas butyrylcholinesterase (BuChE) activity is localized in the dental follicles. To test the functional conservation of ChE in tooth morphogenesis among different species, we performed cholinesterase histochemistry following the use of specific inhibitors of developing molar and incisors in the hamster from embryonic day 11 (E11) to postnatal day 1 (P1). In the developing molar in hamster, the localization of ChE activity was found to be very similar to that of the mouse. At the bud stage, no ChE activity was found in the tooth buds, but was first detectable in the dental epithelium and dental follicles at the cap and bell stages. AChE activity was found to be principally localized in the dental epithelium whereas BuChE activity was observed in the dental follicle. In contrast to the ChE activity in the molars, BuChE activity was specifically observed in the secretory ameloblasts of the incisors, whilst no AChE activity was found in the dental epithelium of incisors. The subtype and localization of ChE activity in the dental epithelium of the incisor thus differed from those of the molar in hamster. In addition, these patterns also differed from the ChE activity in the mouse incisor. These results strongly suggest that ChE may play roles in the differentiation of the dental epithelium and dental follicle in hamster, and that morphogenetic subtypes of ChE may be variable among species and tooth types.

Expression of Uchl1 in the Dental Epithelium during Mouse Tooth Development / 체질인류학회지

Tooth is formed by the reciprocal interactions between the ectoderm and ectomesenchyme derived from neural crest. It has not been clear that neuronal factors involved in the morphogenesis and differentiation of tooth. To identify the roles of neuronal factors during the tooth development, the expression patterns and localization of Uchl1 were investigated in the developing mouse tooth germ by in situ hybridization and immunohistochemistry. Uchl1 transcripts were weakly expressed in the oral epithelium and dental lamina at bud stage. However, expression of Uchl1 was not found in the oral epithelium from cap stage and observed in the inner enamel epithelium, stellate reticulum and dental papilla. From the bell stage, Uchl1 was expressed in the inner enamel epithelium and ameloblasts. Uchl1, was appeared to be localized in the inner enamel epithelium and differentiating ameloblasts of molar and incisors at neonates. Uchl1 was localized strongly in the fully differentiated ameloblasts and adjacent papillary layer whereas localized weakly in the odontoblasts of the molar at postnatal day 5. From these results, Uchl1 was expressed and localized in the differentiating dental epithelium and ameloblasts during tooth development. The results suggest that neuronal protein, Uchl1 may play roles in the histo- and cyto-differentiation of non-neuronal dental epithelium.

Expression of C-type Natriuretic Peptide and Natriuretic Peptide Receptors in the Mouse Submandibular Glands Following Embryonic Development, Postnatal Differentiation and Aging / 대한해부학회지

C-type natriuretic peptide (CNP), a member of natriuretic peptide family, is mainly synthesized in the endothelium and central nervous system. But CNP is also involved in the growth and differentiation of other peripheral organs. Although we have reported the local synthesis and localization of CNP in the adult submandibular glands (SMG), it is not known that the expression and biological activity of CNP following the morphogenesis, differentiation and aging. This study aimed to examine the expression of CNP and its receptors in the developing and differentiating stages of mouse SMG, and the changes of biological activity of its receptors with aging. The SMG, obtained from 14, 16, 18 days-old embryos (E) and 1 day, 2 weeks, 1, 2, 12, and 24 month-old C57BL/6N mouse, were processed for RT-PCR, in situ hybridization, immunohistochemistry and cGMP assay. CNP was strongly expressed in the epithelial clusters of primitive SMG, which was maintained before birth but was markedly decreased after birth. CNP was localized in the intercalated duct and granular convoluted tubules of adult SMG, where NPRC was specifically expressed but NPRB was not. CNP mRNA was gradually decreased from E16 to 2 M but ANP mRNA was opposed. NPRB and NPRC were the same pattern of the expression of CNP but NPRA was weakly expressed. In addition, CNP mRNA was also expressed in the craniofacial tissues such as tooth germs, tongue, premaxilla and bone forming area in which NPRC was specifically expressed but NPRB was not. In the SMG of 2 M, the membrane of duct cells markedly produced cGMP by CNP whereas acini produced cGMP by ANP and BNP rather than CNP. The biological activity of cGMP production of SMG gradually decreased with age. cGMP production was dominant by CNP in SMG of 1M but was by ANP after 2M. These results shows that CNP may play roles both in the morphogenesis and differentiation via NPRC and in the maintenance of duct system via NPRB in the mouse SMG and that the biological activity of its receptors may decreased with aging.