Islet-1 Functional Interactions and Activation by Tooth Specific Factors

The LIM homeodomain transcription factor Islet-1 (ISL-1) is expressed in the incisor regions during tooth development. Pitx2, Dlx2, Lef-1 are expressed in the dental epithelium and have overlapping expression patterns in tooth bud and cap stages as well as Islet-1. We are working to understand the coordinated control of gene expression by transcription factors that affect dental patterning and development. Objectives: we aim to explore the molecular mechanisms required for Islet-1 expression and activity during tooth development. Methods: we use transient transfections, real-time PCR, mutant mice, chromatin immunoprecipitation (ChIP) assays, electrophoretic mobility shift assays, immunochemical and biochemical assays. Results: transfection of tooth epithelial and CHO cells revealed that Islet-1 auto-regulates the ISL-1 promoter, and co-transfection of PITX2 and ISL-1 results in a synergistic activation. PITX2 regulates Islet-1 expression in vivo and Islet-1 is endogenously expressed in the tooth epithelial cell line. Immunoprecipitation showed PITX2 directly interacts with ISL-1 to synergistically activate ISL-1 expression. Dlx2 activates the ISL-1 promoter and Lef-1 can synergistically activate the ISL-1 promoter in concert with either Dlx2 or PITX2. Conclusions: We have identified ISL-1 is a downstream target of PITX2 and Dlx2 during tooth development. The interactions between PITX2, Dlx2, Lef-1 and ISL-1 regulate ISL-1 expression and provide a mechanism for the temporal and spatial expression pattern of ISL-1. ISL-1 auto-regulates its promoter and its role in tooth patterning is controlled through its interactions with other factors. We demonstrate new mechanisms for the regulated control of gene expression during tooth development. Support for this research was provided from grant DE13941 from the National Institute of Dental and Craniofacial Research.