Variation patterns of dentin phosphoprotein in normal human population

Objective: Dentin phosphoprotein (DPP) is the most abundant non-collagenous protein in dentin, which plays key roles in dentin biomineralization. DPP has a unique composition with rich aspartic acid and phosphoserine residues displaying exceptional extensive triplet amino acid repeat sequences. The study aims to clarify the sequence variation patterns of DPP in normal population so as to facilitate analysis on highly repetitive DPP sequence and screening disease-causing mutations in DPP. Methods: Genomic DNA was analyzed in 110 individuals from normal Chinese population. The full coding sequence of DPP was amplified by PCR and screened for variations by direct sequencing and TOPO TA-cloning sequencing. Haplotypes were constructed on the basis of the genotype data from detected variants and sequence data of each individual. The significance of deviations from Hardy-Weinberg equilibrium and the linkage disequilibrium among variants were tested using the procedures implemented in the Arlequin package. Results: A total of 25 polymorphisms with various frequencies, including 14 in-frame indels (insertion/deletion), 6 nonsynonymous and 5 synonymous single nucleotide polymorphisms (SNPs) were revealed in DPP coding region. In the investigated normal population, all variations were in Hardy-Weinberg equilibrium at the significant level of P<0.05.These variants displayed extensive linkage disequilibrium one another and constitute a total of 15 haplotypes with 3 predominant haplotypes in the investigated population. Conclusion: Our data provide the evidence that extensive in-frame indels and SNPs with specific preferred sites exist in DPP coding region in normal population, and that in-frame length variations and missense SNPs in DPP have no obvious pathogenetic effects on dentin formation. Analysis on DNA sequence variation in DPP region offers new insight into screening disease-causing mutations and understanding phenotypic variations of human teeth and teeth evolution. Supported by grant no. 30771186 from the National Natural Science Foundation of China.