Characterization of a novel ameloblast-specific gene in developing postnatal-tooth

Objectives: Several genes associated with mineralized tissue (teeth and bone) have been mapped to the q arm of human chromosome 4. These include the dentine/bone proteins (dentine sialophosphoprotein, dentine matrix protein 1, bone sialoprotein, matrix extracellular phosphoglycoprotein, osteopontin) and enamel matrix protein (enamelin, ameloblastin). The aim of this study was to explore the gene(s) associated with enamel matrix formation. Methods: Bioinformatical analysis of the genomic context on human chromosome 4q13 revealed an unreported gene (UNQ689), which is proximal to ameloblastin. The putative orthologue of UNQ689 gene in mouse by BLAST analysis was identified as Q9D3J8 gene, which has been mapped on chromosome 5 in mouse. The genomic context of Q9D3J8 gene in mouse is the same as that in human. The two proximal genes on chromosome 5 in mouse are Q9D3J8 gene and ameloblastin. The predicated protein sequences of both UNQ689(human) and Q9D3J8(mouse) contain the signal peptide sequences, which suggested that UNQ689(human)/Q9D3J8(mouse) may be a secreting protein. According to the predicated Q9D3J8 cDNA sequence, a fragment of Q9D3J8 cDNA was isolated from the mandibular tissues of postnatal mouse by RT-PCR, and was sequenced. To investigate the expression pattern of Q9D3J8 gene in mouse, cRNA probe was synthesized and in situ hybridization analysis was conducted on the tissue sections of the postnatal mice. Results: The results revealed the presence of Q9D3J8 gene mRNA expression in the secreting ameloblasts, but not in the other tissues. With the maturation of enamel, the expression of Q9D3J8 gene mRNA in ameloblasts was down-regulated. Conclusions: The results indicated UNQ689(human)/Q9D3J8(mouse) are ameloblast-specific gene. Further study will be conducted to elucidate the biological function of UNQ689(human)/Q9D3J8(mouse).