Length Polymorphisms in the Porcine Dentin Phosphoprotein Coding Sequence

Porcine dentin sialophosphoprotein (DSPP) is cleaved by proteases into 3 main protein products: dentin sialoprotein (DSP), dentin glycoprotein (DGP), and dentin phosphoprotein (DPP). DPP is a highly acidic protein that migrates as a cluster of three or four distinct bands around 100-kDa on SDS-PAGE that stain strongly with stains-all, but do not stain with Coomassie Brilliant Blue. Objectives: To determine if polymorphisms in the DPP coding sequence play a role in the observed DPP size heterogeneity. Methods: Genomic DNA from 8 pigs was isolated and amplified with primers annealing to sites flanking the DPP coding sequence. The PCR amplification products were ligated into pCR2.1-topo (Invitrogen) and transfected into E. coli. Individual colonies were grown in LB broth and DNA minipreps were characterized by DNA sequencing. Results: Four distinct DPP cDNAs were generated from multiple independent PCR cloning experiments. The DPP clones correspond to allelic variations of the DPP coding sequence in Dspp. The porcine DPP coding region has 27 sequence variations among the four alleles. Eleven are point mutations (changing 5 amino acids). Sixteen are length variations ranging from 3 to 63 basepairs that maintain the open reading frame. The DPP coding regions in the four alleles are 1656, 1728, 1770, and 1785 basepairs in length. The DPP proteins encoded by these alleles have 551, 575, 589, and 594 amino acids. These commercial pigs have no apparent dental phenotype and the observed DPP sequence variations are not associated with any loss of function. Conclusion: DPP size heterogeneity is due to allelic variations in the length of the DPP coding region. Variations in the length of the DPP protein do not interfere with normal DPP function. This study was supported by NIDCR grants DE011301 and DE015846.