Molecular cloning of a human dentin sialophosphoprotein gene

Dentin sialoprotein (DSP) and dentin phosphoprotein (DPP; phosphophoryn) ar e two principal dentin-specific non-collagenous proteins. DPP is extremely acidic and is rich in aspartic acid and serine. By virtue of this structure , DPP may bind large amounts of calcium and may facilitate initial minerali zation of dentin matrix collagen as well as regulate the size and shape of the crystals. The function of DSP is not known. DSP and DPP are encoded by a single gene in both rat and mouse, and are uniquely expressed in odontobl asts and transiently in pre-ameloblasts. Because DSP and DPP are isolated f rom dentin as distinct proteins and appear to be present in different amoun ts, the nascent dentin sialophosphoprotein (DSPP) is likely cleaved to yiel d DSP and DPP. However, when, where and how the DSPP is cleaved into DSP an d DPP is not clear. To further elucidate the structure and function of huma n DSP and DPP, we have cloned DPP and DSP cDNA by reverse transcriptase-pol ymerase chain reaction (RT-PCR) strategies, and then cloned and initiated c haracterization of a human dentin sialophosphoprotein gene. The genomic org anization of human DSPP is very similar to that of mouse, containing five e xons and four introns, suggesting it is a homologue of mouse dentin sialoph osphoprotein (DSPP). Exons 1-4 encode for DSP, while exon 5 encodes for the C-terminus of DSP and the whole DPP. A 4.6-kb RNA transcript was detected on Northern blot analyses of total RNA extracted from immature (open root a pices) human teeth using either a human DPP or DSP probe.