Spatiotemporal Expression of the Tcfap2b gene in Mouse Tooth Morphogenesis

Objective: The Tcfap2b gene (human homolog TFAP2B) encodes a neural crest-derived transcription factor. TFAP2B mutations in humans result in Char Syndrome, an autosomal dominant genetic disorder characterized by several abnormalities including tooth agenesis. In addition, our recent microarray analysis revealed that Tcfap2b transcripts were reduced in the arrested tooth organs of both Msx1- and Pax9-deficient embryos. However, how Tcfap2b is involved in tooth morphogenesis has not been determined yet. In order to gain a better understanding of Tcfap2b’s role, we sought to determine the spatial-temporal expression profile of theTcfap2b gene during tooth morphogenesis in wild-type as well as in Msx1- and Pax9-deficient mouse embryos.

Methods: Immunohistochemistry was used to investigate the spatiotemporal expression profile of Tcfap2b in developing teeth at various embryonic stages. Both immunohistochemistry and real-time PCR were used to examine the Tcfap2b expression in Msx1- and Pax9-deficient tooth organs.

Results: Immunohistochemistry showed that Tcfap2b is highly expressed in the dental mesenchyme at E14.5. As tooth development proceeds, the staining signal was observed in the dental papilla and in the inner dental epithelium, but was absent in the secondary enamel knot at E16.5. By 17.5, the staining signal became restricted to the cervical pulp in the dental papilla, but was continuously present in the ameloblast layers; in addition, strong signal was also noted in the dental follicle. Moreover, immunohistochemistry showed that Tcfap2b protein was reduced in the dental mesenchyme of Msx1- and Pax9-deficient mouse embryos, which apparently resulted from decreased levels of its transcripts as revealed by real-time PCR analysis. 

Conclusion: These findings suggest that Tcfap2b together with Msx1 and Pax9 might be involved in the same signaling pathway during early tooth morphogenesis.