As a tooth forms in the tooth bud, specialized cells called ameloblasts secrete a protein matrix with hydroxyapatite crystals embedded within. The matrix acts like a trellis to support the patterned elongation of the crystals into hard tooth enamel. Among these matrix proteins is dentin sialophosphoprotein, or Dspp. Interestingly, ameloblasts secrete the protein transiently early in matrix formation, but only near the dentinoenamel junction, where dentin and enamel meet. There, Dspp is immediately cleaved into 2 smaller proteins, Dsp and Dpp. Because of the very specific spacial and temporal secretion of Dspp, National Institute for Dental and Craniofacial Research (NIDCR) grantees have proposed that it must play a role in producing the structurally harder, first-formed enamel that borders the dentinoenamel junction. To test this hypothesis, the scientists created transgenic mice that expressed either Dsp or Dpp throughout the enamel to measure its effect on the tissue’s hardness and/or toughness. In the February 23 issue of the Journal of Biological Chemistry, the scientists found Dpp actually weakened the enamel. However, Dsp “significantly and uniformly” increased the hardness of the enamel by about 20%, showing its unique contribution to the hardness of the dentinoenamel junction. This marks the first time that a transgenic animal has been used to engineer hard dental tissues that are superior to those found in nature. As the scientists noted, the finding could have implications for ongoing efforts to engineer replacement teeth that are resistant to decay or wear.
(Source: NIDCR, Science News in Brief, March 15, 2007)
