Dentin Matrix Protein (Dmp1) is Regulated by Different Mechanisms in Tooth compared to Bone

Dmp1 is highly expressed in odontoblasts, osteoblasts, and osteocytes during development. Overexpression of Dmp1 in pluripotent mesenchymal cells induces the odontoblast-like  phenotype. Objectives: The purpose of this research was to determine if Dmp1 is regulated differently in teeth compared to bone.  Methods: Using in situ hybridization, we determined the expression profile of Dmp1 in teeth and bones of developing normal mice. In addition, Dmp1 expression levels were determined in mice lacking genes involved in bone formation such as Cbfa1, and genes responsible for osteoclast formation such as NFkB. Results: Examination of the spatial and temporal expression patterns during development from day 11 embryos to 12-week-old mice indicated that Dmp1 expression in bone occurs earlier (day 13.5) than in teeth (day 17).  Dmp1 is expressed in both early and mature osteoblasts, osteocytes and lining cells. In contrast, Dmp1 is only detected late in tooth development in mature odontoblasts and ameloblasts.  As anticipated, no Dmp1 signal was observed in bone cells of embryos lacking Cbfa1, however, Dmp1 was still expressed in the tooth even though the tooth bud is reduced in size in these embryos.  The signal for Dmp1 in tooth from embryos lacking NFkB was similar to that of wild-type, however, reduction of Dmp1 expression was observed in bone. Lastly, our initial in situ hybridization data suggests that Dmp1 may be expressed in osteoclasts.  Conclusions: The results indicate that 1) Dmp1 is differentially regulated in bones compared to teeth and 2) NFkB may enhance expression of Dmp-1 in bone cells directly or indirectly through the generation of osteoclasts. This work is supported by NIH/NIDCR research grant DE13480 and DE00455 (JQF).