Analysis of the regulatory region of the bovine X-chromosomal amelogenin gene

The amelogenin proteins, which are crucial for normal enamel mineral formation, are secreted by ameloblasts during development of tooth enamel. In order to better understand the mechanisms involved in regulation of expression of the amelogenin genes, the bovine X-chromosomal amelogenin gene was cloned and a 3.5 KB fragment upstream of exon 1 was inserted into a beta galactosidase (beta gal) expression vector for production of transgenic mice. When tissues from these mice were treated with Xgal, a substrate for beta gal, only ameloblasts and some of the adjacent stratum intermedium cells contained blue stain. To obtain further information concerning regulation of expression, the 3.5 KB amelogenin gene fragment was evaluated in transfection experiments. Nonoverlapping 1.9 and 1.5 KB fragments of the upstream region were subcloned separately into a vector that contains the SV40 promoter and the CAT reporter gene. Each amelogenin gene fragment was able to suppress CAT activity driven by the heterologous SV40 promoter in transfected HeLa cells. We theorize that each of these gene fragments contains regulatory elements important for the tissue-specific and developmentally-regulated pattern of expression of the X-chromosomal amelogenin gene.