Enamelin Transgene Expression by Ameloblasts

Enamelin (Enam) is a critical constituent of the enamel matrix during the secretory stage of amelogenesis. Enamelin deficiency shows a dose effect. Enam+/- mice have fewer crystallites than wild type (Enam+/+) mice. Enamelin null (Enam-/-) mice do not produce enamel crystallites at all. Objectives: To generate an enamelin expression construct that specifically directs enamelin expression to secretory stage ameloblasts, to generate transgenic mice that express enamelin at levels similar to wild type mice, to mate Enam transgenics with Enam null mice to determine if the wild type enamel phenotype is recovered. Methods: An Enam recovery construct was fabricated that flanked the enamelin coding sequence with the amelogenin promoter and 3' amelogenin untranslated regions. We used this construct to generate enamelin transgenic mice. Founders were mated with wild-type C57BL6 mice. F1 offspring were sacrificed on day 5, first molars were collected, and real time RT-PCR was performed to quantify transgene expression levels in developing teeth. Enamelin transgenics (Enamtg/-) showing appropriate levels of enamelin gene expression were mated with Enam-/- mice so their enamel could be characterized. Results: Thirteen independent founders were positive for the Enam transgene; seven showed germline transmission. Real-time RT-PCR of RNA collected from day 5 (secretory stage) first molars showed a range of enamelin transgene expression levels including levels equivalent to normal wild type enamelin gene expression. Conclusion: An enamelin recovery construct has been fabricated that specifically directs the expression of enamelin by ameloblasts in transgenic mice. The enamelin transgene is expressed at different levels in different transgenics, but transgenic mice were identified that express the transgene at levels similar to endogenous enamelin expression. These mice are currently being mated to Enam-/- mice to analyze for phenotype recovery. This study was supported by NIDCR grant DE011301.