Enamel gene products during murine amelogenesis in vivo and in vitro.

Epithelial-mesenchymal interactions regulate determination and differentiation of amelogenesis. Our attention has focused on identification of ameloblast gene products, the regulation of enamel mRNA synthesis, and subsequent translation into enamel proteins in vivo and in vitro. Enamel proteins are the most abundant gene products synthesized in fully-differentiated ameloblasts. Our experimental strategy has been to isolate major proteins, produce antibodies, localize enamel protein antigens during tooth development in vivo as well as in vitro (using serumless, chemically-defined medium), develop an immunoprecipitation assay, isolate poly(A)-products in a cell-free translation system, and then initiate molecular cloning of the corresponding murine enamel gene(s). The major murine enamel mRNA appears to code for a predominant polypeptide of approximately 20,000 MW. Inner-enamel epithelial cells differentiate into ameloblasts, and synthesize and secrete enamel proteins within six d when cap-stage molar tooth organs are cultured in serumless, chemically-defined medium. The regulation of epithelial differentiation under these experimental conditions indicates that epithelial-mesenchymal interactions determine and maintian ameloblast differentiation in vitro.