Abstract
The dental epithelium and extracellular matrix interact to ensure that cell growth and differentiation lead to the formation of teeth of appropriate size and quality. To determine the role of fibronectin in differentiation of the dental epithelium and tooth formation, we analyzed its expression in developing incisors. Fibronectin mRNA was expressed during the presecretory stage in developing dental epithelium, decreased in the secretory and early maturation stages, and then reappeared during the late maturation stage. The binding of dental epithelial cells derived from postnatal day-1 molars to a fibronectin-coated dish was inhibited by the RGD but not RAD peptide, and by a β1 integrin-neutralizing antibody, suggesting that fibronectin-β1 integrin interactions contribute to dental epithelial-cell binding. Because fibronectin and β1 integrin are highly expressed in the dental mesenchyme, it is difficult to determine precisely how their interactions influence dental epithelial differentiation in vivo. Therefore, we analyzed β1 integrin conditional knockout mice (Intβ1lox-/lox-/K14-Cre) and found that they exhibited partial enamel hypoplasia, and delayed eruption of molars and differentiation of ameloblasts, but not of odontoblasts. Furthermore, a cyst-like structure was observed during late ameloblast maturation. Dental epithelial cells from knockout mice did not bind to fibronectin, and induction of ameloblastin expression in these cells by neurotrophic factor-4 was inhibited by treatment with RGD peptide or a fibronectin siRNA, suggesting that the epithelial interaction between fibronectin and β1 integrin is important for ameloblast differentiation and enamel formation.
Highlights
Tooth development is regulated by epithelial–mesenchymal interactions, leading to differentiation of the dental epithelium into enamel-forming ameloblasts and of the dental mesenchyme into dentin-forming odontoblasts
Our results showed that fibronectin mRNA was expressed during the presecretory (PS), S, and late stage of maturation (LM) stages, but not the early maturation (EM) stage of ameloblasts (Fig. 1)
In the LM stage, fibronectin was detected both in ameloblasts and in the papillary layer of the dental epithelium (Fig. 1B), whereas it was expressed in odontoblasts during tooth development (Fig. 1)
Summary
Tooth development is regulated by epithelial–mesenchymal interactions, leading to differentiation of the dental epithelium into enamel-forming ameloblasts and of the dental mesenchyme into dentin-forming odontoblasts. During this interaction process, growth factors and PLOS ONE | DOI:10.1371/journal.pone.0121667. Fibronectin is an adhesive glycoprotein of the ECM that functions in cell adhesion, differentiation, and growth. Fibronectin associated with the dental basement membrane appears to play a crucial role in the terminal differentiation of neural crest-derived dental mesenchymal cells and regulates the elongation and polarization of odontoblasts through interactions between its transmembrane domain and the cytoskeleton [5,6,7]. Expression of fibronectin in the dental epithelium and its functions related to the adhesion, proliferation, and differentiation of the dental epithelium are not clearly understood
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