Developmentally regulated expression of intracellular Fgf11-13, hormone-like Fgf15 and canonical Fgf16, -17 and -20 mRNAs in the developing mouse molar tooth

Abstract

Objective. To investigate and compare the cellular expression of non-secreted Fgf11-14 and secreted Fgf15-18 and -20 mRNAs during tooth formation. Materials and methods . mRNA expression was analyzed from the morphological initiation of the mouse mandibular first molar development to the onset of crown calcification using sectional in situ hybridization. Results . This study found distinct, differentially regulated expression patterns for the Fgf11-13, -15-17 and -20, in particular in the epithelial-mesenchymal interface, whereas Fgf14 and 18 mRNAs were not detected. Fgf11, -15, -16, -17 and -20 were seen in the epithelium, whereas Fgf12 and -13 signals were restricted to the mesenchymal tissue component of the tooth. Fgf11 was observed in the putative epithelial signaling areas, the tertiary enamel knots and enamel free areas of the calcifying crown. Fgf15, Fgf17 and -20 were transiently colocalized in the thickened dental epithelium at E11.5. Later Fgf15 and -20 were exclusively expressed in the epithelial enamel knot signaling centers. In contrast, Fgf13 was present in the dental mesenchyme including odontoblasts cell lineage, whereas Fgf12 appeared transiently in the preodontoblasts. Conclusions . The expression of the Fgf11-13, -15, -17 and -20 in the epithelial signaling centers and/or epithelial–mesenchymal interfaces at key stages of the tooth formation suggest important functions in odontogenesis. Future analyses of the transgenic mice will help elucidate in vivo functions of the studied Fgfs during odontogenesis and whether any of the functions of the tooth expressed epithelial and mesenchymal Fgfs of different sub-families are redundant.

Key Words::

• tooth
• organogenesis
• tissue interactions
• fibroblast growth factor
• in situ hybridization

Acknowledgements

Ms Kjellfrid Haukanes is acknowledged for skillful technical assistance. This study has been supported by a grant from the Norwegian Cancer Society.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.