Immunolocalization of SP6, LEF1 and Associated Factors in the Tooth Germ of Rat Molars

Abstract

Lymphoid enhancer-binding factor 1 (LEF1) is a transcription factor in the Wnt/-catenin signaling pathway. LEF1 may control odontoblast differentiation. Specificity Protein 6/Epiprofin (SP6) is a transcription factor that mediates the signaling pathway between bone morphogenetic protein (BMP) and the Wnt/-catenin. LEF1 is decreased by the overexpression of SP6. In contrast, lef1 gene expression is increased in the dental epithelium and mesenchyme of SP6-deficient mice. Thus, LEF1 and SP6 act in an antagonistic manner, being involved in tooth formation. However, this has not been investigated in detail in vivo. In the present study, the expressions of Dickkopf-related protein-1 (DKK-1) (an antagonist to the Wnt signaling pathway), SP6, and phospho-Smad1/5/8 (p-Smad1/5/8) (activated R-Smad in the BMP signaling pathway) were immunohistochemically investigated using serial sections prepared from rat first molar tooth germs in the bell stage on embryonic day 19 and days 10 and 15 after birth, in order to investigate the roles of these factors in differentiation into ameloblasts and odontoblasts. As a result, p-Smad1/5/8 was strongly expressed in preodontoblasts and odontoblasts and also in the inner enamel epithelium and ameloblasts in the secretory stage, suggesting activation of the BMP signaling pathway through p-Smad1/5/8 and involvement of the BMP signaling pathway in differentiation into odontoblasts and ameloblasts and their secretory functions. LEF1 appears in preodontoblasts and preameloblasts and disappears with differentiation, suggesting that it suppresses the differentiation into these cells. In contrast, SP6 and DKK1 expressions are enhanced with odontoblast differentiation. Therefore, the downregulation of the Wnt signaling pathway through SP6 and DKK1 is involved in the disappearance of LEF1 in odontoblasts. SP6 expression was enhanced with ameloblast differentiation, suggesting that the activated BMP signaling pathway suppressed the expression of LEF1 through SP6, thus being involved in ameloblast differentiation.

Wnt signaling during tooth replacement in zebrafish (Danio rerio): pitfalls and perspectives

“…We report a strong and dynamic expression of the soluble Wnt inhibitor dkk1 in tooth germs of zebrafish embryos between 48 and 152 hpf. Dickkopf expression in rodents (mouse, rat) has been reported mostly for late stages of tooth development (odontoblast differentiation, Fjeld et al, 2005 ; Moriguchi et al, 2013 ). In the mouse mandibular molar, expression of Dkk1 shifts from the epithelium at bud stage to the mesenchyme during further odontogenesis (Monaghan et al, 1999 ; Fjeld et al, 2005 ), a pattern that is distinct from the exclusive epithelial expression reported here.…”