Identification of Dentin Matrix Protein 4 in Developing Tissues

OBJECTIVES: To identify and characterise the expression of dentin matrix protein 4 (DMP4) in development, with particular focus on hard tissue formation. METHODS: Microarray gene expression analysis of mouse metatarsal long bone development from embryonic stages (E) 15 and 19 was used to screen for new and novel genes involved in hard tissue formation. 192 genes were found to be differentially expressed, of which 176 genes were up-regulated and 16 down-regulated. Of interest was the cDNA sequence BC04044, which was up-regulated 3.4 times between E15 and E19. The sequence was referenced as DMP4 in the gene databases and has been localised to chromosome 5 in the mouse, downstream from the SIBLING protein family. It is highly conserved between species, with 90% homology to the corresponding human sequence. Analysis of the sequence shows that it encodes for a protein of 579 amino acids with a theoretical molecular weight of approximately 66kDa. The presence of a signal peptide indicates that it is a secreted protein and number of potential post-translational modifications have also been identified, including N-linked glycosylation, tyrosine sulphation and phosphorylation sites. A calcium-binding domain has been localised towards the C-terminal. Samples were prepared from mouse tissues at various developmental stages E15, E17, new born and postnatal day 5. The presence of DMP4 in these tissues was screened for using a number of methods including in situ hybridisation, Northern blots and PCR analyses. RESULTS: DMP4 was detected in the odontoblasts of developing teeth and in the osteoblasts of the surrounding alveolar bone. Furthermore, DMP4 was also detected in the osteoblasts of metatarsal long bones. CONCLUSION: DMP4 may have a role in the differentiation of odontoblasts and osteoblasts.