Molecular Mechanisms Of The Dlx1 And Dlx2 Gene During Tooth Development

The developing tooth is a particularly good model for studies on the regulation of organogenesis,including morphogenesis as well as cell differentiation.An interesting feature of the epithelial-mechenchymal interactions that govern early tooth morphogenesis is that the capacity to instruct morphogenesis appears to shift between the epitheliurn and mesenchyme. Important work has begun to elucidate some of the genes that are involved in these histogenic interactions. A likely class of genes for regulating dental morphogenesis is the homeobox genes.These transcription regulators are expressed in many complex differentiating systems in invertebrates and vertebrates,in particular,systems that are morphologieally segmented along a linear anatomic axis. The term 揾omeodomain?has evolved to define a class of protein domains that has recognizable similarity to a 60 amino acid motif(encoded by 180 bp homeobox sequences)originally recognized in three Drosophila homeotic and segmentation proteins.The horneodomains that have been tested contain sequence-specific DNA binding activities and are part of larger proteins that function as transcriptional regulators. The homeobox genes were named after the homeobox part of their sequence that codes for a helix-turn-helix motif~ the motif which is called homeodomain, binds DNA in a sequence-specific maner.The nucleotide sequence that codes for the homeodomain in hoineobox genes has been highly conserved for millions of years. Our studies focus on two homeobox genes, Dlxi and D1x2 ,which are now .5. known to play important regulatory roles in tooth development. We investigated the effects of Dlx genes on rat ectomesenchymal cells and tooth germs in this thesis. 1. Expression of Dlxi and D1x2 genes during the development of the rat dentition. To investigate the roles of Dlxi and D1x2 gene during early tooth development, we examined the expressions of Dlxi and D1x2 in tooth germs by using in situ hybridization.In bud stage,Dlxl and D1x2 were expressed in the dental mesenchyme,and in dental epithelium.In cap stage,Dlxl and D1x2 were expressed in the inner and outer enamel epithelia,stellate reticulum,and dental papilla.The expression patterns of Dlxi and D1x2 in the early bell stage were the same as in cap stage.In late bell stage,the expression of Dlxi was negative,while D1x2 was expressed in the outer enamel epithelia, steilate reticulum,stratum intermedium,preameloblasts and dental papilla cell,and dentin tnatrix.The temporal-spatial expression patterns of Dlx gene within tooth germs suggest Dlx genes are likely to play multiple roles in tooth development. 2. Expression of Dlxi and Dlx2 gene in the ectomesenchymal cells. Rat ectomesenchymal cells were cultured using tissue explant culture techniques.Cells were identified by immunohistochemical method.It proved that the cells were ectomesenchyme oringine.The successful culture of provided the fundament of subsequent studies. in situ hybridization and RNA dot blot hybridization were used to study the effects of Dlxi and Dlx2 gene on culture of ectomesenchymal cells, dental papilla cell,and dental pulp cells.The results indicated that the expressions of Dlxi and DM2 is higher in the ectomesenchymal cells and dental papilla cell than dental pulp cells.Dlx genes are likely to play role in undifferentiational cells.