Current papers in oral biology (30564–30667)

Abstract

During mouse tooth development the secretory ameloblasts differentiate and produce a population of acidic glycoproteins termed ‘amelogenins’ which function in the formation of the extracellular enamel organic matrix. Amelogenin-enriched fractions were isolated from murine molar and incisor tooth organs during early postnatal enamel matrix production using an extraction procedure with acetic acid. Major polypeptides were separated by gel electrophoresis, amelogenin polypeptide bands (circa 16–20,000 molecular weight) were exicised, amelogenins were eluted from the gel bands and then used as immunogen for immunization. Rabbit antibodies raised against amelogenins showed extensive cross-reactivity with lower molecular weight polypeptides of 16,000–20,000. These antibodies were used with indirect immunofluorescence microscopy to show the specific localization of amelogenins during the synthesis and secretion of the enamel matrix in situ as well as in vitro. No staining reaction was found in keratinized or non-keratinized epidermal tissues, dental papilla mesenchyme, odontoblasts, dentine matrix, cartilage, bone, heart, brain, lung, or salivary glands.In order to detect differentiation-specific synthesis of amelogenins, we cultured early cap stage molar tooth organs (17-days gestation or Theiler stage 25) in a serumless, chemically-defined medium for periods up to 21 days. The anti-amelogenin antibodies did not stain, by indirect immunofluorescence, cap stage molar tooth organ tissues. However, within six days in vitro, explants stained with antisera and showed localization within ameloblasts and newly secreted enamel matrix. Comparisons with in situ epithelial differentiation into ameloblasts suggested that cultured explants required approximately twice as long to reach a comparable expression of amelogenins. Synthesis of amelogenins was first detected by immunoprecipitation also during the sixth day of organ culture. The family of amelogenin polypeptides may be products of structural genes which can become activated during epithelial-mesenchymal interactions, even in the absence of exogenous growth factors such as serum or neutrotrophic mediators. The expression of amelogenins, therefore, does not appear to require hormones and may be an example of mesen-chyme-directed epithelial differentiation.