Developmental regulation of dentin sialophosphoprotein during ameloblast differentiation: A potential enamel matrix nucleator

The two major dentin matrix proteins, dentin sialoprotein and dentin phosph oprotein have been shown to be expressed as a single large transcript terme d dentin sialophosphoprotein (DSPP), These non-collagenous matrix proteins, identified biochemically by their unique physical-chemical properties, are specific cleavage products of a large parent acidic phosphorylated protein (pI 4.0). Previous studies have shown expression of dentin sialoprotein at the protein level by ameloblasts. The purpose of this study was to determi ne the temporal-spatial pattern of DSPP expression during amelogenesis. In situ hybridization and immunohistochemistry were performed on sections of d eveloping mouse molars, These data were correlated with RT-PCR analysis of in vitro enamel organ epithelium monolayer cell cultures enriched for amelo blasts, Our data indicates initial expression of the DSPP transcripts and p rotein during early ameloblast differentiation prior to the secretory phase when the majority of the enamel matrix is formed. Ameloblasts appear to ti ghtly down-regulate DSPP transcription as enamel matrix formation is up-reg ulated. These data demonstrate DSPP expression during amelogenesis is under highly controlled developmental regulation. Therefore, DSPP may have a pri mary role in the initial mineralization events of both enamel and dentin, a cting as a potential nucleator of hydroxyapatite crystal formation.