In vivo Overexpression of Tuftelin in the Enamel Organic Matrix

Abstract

The primary sequences of human and mouse tuftelin are 89% identical. Both proteins comprise 390 amino acids and produce an acidic protein with an isoelectric point of 5.7, and an unmodified molecular weight of 44 kD. Using fluorescent-tagged tuftelin and amelogenin plasmid constructs we saw little evidence that these two enamel proteins colocalize in ameloblast-like LS-8 cells. Tuftelin is primarily localized to distinct ‘speckled’ domains within the cell cytoplasm. In an attempt to better define a physiological function for tuftelin during amelogenesis, we have produced transgenic mice that overexpress tuftelin in ameloblasts and subsequently the enamel matrix. Tuftelin overexpression impacts dramatically upon the enamel crystallite habit and the enamel prismatic structure. Overexpressing tuftelin results in gross imperfections in enamel that is evident both at the nanoscale and the mesoscale. The most notable difference observed in the transgenic animals, when compared to wild-type animals, is an apparent loss of restricted growth of enamel crystallites along their a-axis and b-axis. This equates to a change in the crystallite aspect ratio. In the transgenic animals the crystallite structures appear more ‘plate’-like in contrast to the symmetric, ‘ribbon’-like crystallite morphology that is a characteristic feature of mammalian enamel.