Possible functions of Protogenin in the tooth development

Objectives: Protogenin (Prtg) belongs to an immunoglobulin superfamily (IgSF), and that is mainly observed at the central nervous system in the early stages of embryogenesis. Meanwhile, we have been identified Prtg as a one of the highly expressed genes in the mouse mandible at embryonic day 10.5 (E10.5). In this study, we investigated the expression pattern of Prtg in the developing tooth germ, and showed the possible functional implications of this gene in tooth germ morphogenesis of the mouse lower first molar.

Methods: Temporal expression of Prtg mRNA and protein was analyzed by semi-quantitative RT-PCR, immunoblotting, in situ hybridization and immunohistochemistry. An inhibition assay was performed using hemagglutinating virus of Japan-liposome containing Prtg antisense (AS) phosphorothioated oligodeoxynucleotide (S-ODN) in cultured mandibles at E10.5.

Results: Ptrg was a highly N-glycosylated transmembrane protein, and was preferentially expressed in the early stage of embryogenesis. Both Prtg mRNA and protein expressions were widely demonstrated not in the mesenchymal cells but in the oral epithelial cells in the mandible at E10.5. The expression intensity of Prtg after the E12.0 was remarkably reduced. Thereafter both weak signals were observed at mesenchymal and odontogenic epithelial cells throughout the tooth germ development during embryonic days. An inhibition assay using AS S-ODN showed a significant growth inhibition of tooth germ. In some cases, the basement membrane between the enamel organ and dental papilla became obscure. A disarrangement of the inner enamel epithelial layer was also observed in the arrested tooth germ, while the mandible treated with sense S-ODN developed to a similar size as the control.

Conclusions: These results demonstrated that Prtg, a member of IgSF, is involved in the development of the tooth germ, and differentiation of the odontogenic epithelial cells in the mouse lower first molar.