Function of DLX3 in amelogenesis

DLX3 belongs to a family of homeodomain proteins that are known to play functional and regulatory roles during important developmental processes. A highly conserved sequence of 60 amino acids comprises the homeodomain and is responsible for sequence-specific interactions with DNA. Six Dlx genes play essential roles in vertebrates and are expressed in spatially and temporally restricted patterns. Dlx family members are organized into three pairs of closely linked, convergently transcribed loci named Dlx 2-1, Dlx 5-6, Dlx 3-4. Distal-less 3 (DLX3) gene is unique in its expression in differentiating epidermal cells, neural crest, hair follicles, dental epithelium and mesenchyme, skelettogenic cells, limb bud, placenta, and in the cement gland, however its expression has not been detected in the central nervous system. Importance of DLX3 is emphasized by targeted disruption of the mouse Dlx3 gene resulting in an early embryonic lethal phenotype at day 9.5-10. In humans, mutations of Dlx3 gene located on chromosome 17q21 are associated with the pathogenesis of two autosomal dominant human diseases: Tricho-dento-osseous (TDO) syndrome and Amelogenesis Imperfecta Hypoplastic-Hypomaturation with taurodontism (AIHHT). The most distinct manifestation of both TDO and AIHHT include enamel hypoplasia and taurodontism supporting the key role of DLX3 in mineralized tissue and suggesting a potential regulatory role of DLX3 during enamel and dentin formation.;This dissertation examined the spatial and temporal expression of DLX3 during different stages of tooth development, particularly late stages associated with amelogenesis and dentinogenesis. We analyzed DLX3 expression at both RNA and protein levels, in mouse tissue and established dental and non-dental cell lines. Time and tissue specific DLX3 expression led us to believe that DLX3 has a potent regulatory role during amelogenesis. We examined potential DLX3 target genes and their regulation. The major focus of DLX3 interaction was on Amelogenin, the most important enamel matrix protein. This dissertation proved that DLX3 is an active transcriptional regulator of Amelogenin. In order for us to examine human diseases associated with the DLX3 mutations, we introduced mutations linked to TDO and AIHHT into the wild type DLX3 and constructed expression vectors for cell line studies. Our studies showed that mutated DLX3 acts as a transcriptional activator and wild type DLX3 downregulates transcription of its targets. We examined the role of DLX3 as a potent promoter regulator and analyzed the results of the differential regulation at the RNA and protein levels. This study enhanced our understanding of the expression pattern and functional role of DLX3 as a transcriptional regulator during tooth development. This information is critical in providing new insight into the importance of this gene in the pathogenesis of altered tooth structure associated with TDO and AIHHT.