Identification of RUNX2-dependent Programmed Cell Death Genes in Tooth Development

The developing molar is an excellent model for studying the regulation of organ morphogenesis. Tooth development is regulated by epithelial-mesenchymal interactions that are both sequential and reciprocal. A disruption of this process can lead to dental anomalies such as Cleidocranial dysplasia (CCD) which is characterized by supernumerary teeth. Mutations in the Runx2 gene have been identified as the cause for CCD. Although the molecular basis of CCD is poorly understood, a failure of programmed cell death has been hypothesized to be one of the underlying causes for the proliferation of the dental lamina in CCD. Driven by an interest in understanding the pathogenesis involving dentition in human CCD, we have analyzed the differential gene expression pattern in a Runx2 null mouse model. The objectives: of the present study were to identify apoptosis-related genes involved with Runx2 during molar formation and to study the temporal pattern of expression of these genes during odontogenesis. Analysis of differential gene expression was performed using methods: in microarray technology. RNA samples from E14.5 Runx2(+/+) and (-/-) molar organs were utilized for this study. Results: of our microarray analysis revealed a downregulation of two target genes, Programmed cell death 6 (PCD6) and Caspase 2 (CASP2). RT-PCR methods were used to determine the temporal expression pattern of these two apoptosis-related genes. RT-PCR analysis revealed expression of PCD6 at E12.5, E14.5 and E18.5 stages of gestation. However, CASP2 was detectable only at E14.5. In conclusion:, we report the downregulation of PCD6 and CASP2 genes in Runx2 (-/-) mice molar organs which previously have not been associated with tooth development. This research was supported by a grant from NIDCR/NIH DE 13368 to RDS.