Unique and Overlapping Functions of Cbfa-1-activated Tcf/Lef transcription Factors during Tooth and Periodontal Tissue Development

Core-binding factor 1 (Cbfa-1/Runx2) gene is a key-regulator of mineralized tissue formation. Cbfa-1 mutations cause the genetic disease cleidocranial dysplasia (CCD) presenting with bone and tooth hypoplasia, supernumerary teeth, and altered tooth resorption/eruption. Little is known about downstream Cbfa-1 target genes as related to the CCD dental phenotypes. Recently, our laboratory has identified Lef-1 and Tcf-7 as potential Cbfa-1 targets using CCD-derived dental pulp (DP) cells. Objectives: To characterize Lef-1 and Tcf-7 developmental tooth expression patterns in Cbfa-1 knock-out versus wild type-mice; to evaluate Lef-1 and Tcf-7 isoforms expression levels in CCD DP and periodontal ligament (PDL) cells versus normal cells; and to investigate the mechanisms of CBFA-1 control on Lef-1 and Tcf-7 differential expression. Methods: Semi-quantitative RT-PCR analysis, western-blot, and immunohistochemistry were performed comparing Lef-1/Tcf-7 isoforms and Cbfa-1 developmental expression patterns and levels present in CCD versus normal dental cells. Transient transfections were performed to evaluate CBFA-1 action on Lef-1 and Tcf-7 genes. Results: Relevant to this study, Tcf-7 and Lef-1 were detected in DP, PDL and alveolar bone similar to Cbfa-1 distribution and their expression pattern was developmentally regulated. RT-PCR and western blot analysis of the CCD cells showed low to undetectable levels of Lef-1 and Tcf-7 as compared to controls. Moreover, transient transfection of Cbfa1/Runx2 resulted in an up-regulation of both Lef-1 and Tcf-1 mRNA in the CCD cells. Conclusions: Our data shows for the first time that Cbfa1/Runx2 regulates Tcf-7 and Lef-1 expression in tooth and PDL tissue demonstrating a potentially important link related to the CCD dento-alveolar phenotype. These findings suggest cross talk between Cbfa-1 and Wnt signaling pathways during development that may be crucial for tooth initiation and PDL tissue formation. Supported by NIDCR DE13221 (MM).