Amelogenin- and Enamelysin (Mmp-20)-Deficient Mice Display Altered Birefringence in the Secretory-Stage Enamel Organic Extracellular Matrix

Dental enamel is the most mineralized tissue of vertebrate organisms. Enamel biosynthesis is initiated by the secretion, processing, and self-assembly of a complex mixture of proteins. The formation of an ordered enamel organic extracellular matrix (ECM) seems be a crucial step for the proper formation of mineral phase. Polarizing microscopy demonstrates that the ordered supramolecular structure of the secretory-stage enamel organic ECM is strongly birefringent. In the present work we analyzed the birefringence of secretory-stage enamel organic ECM in amelogenin (Amelx)- and enamelysin (Mmp20)-deficient mice. Female Amelx+/− animals showed significant reduction in optical retardation values when compared with the Amelx+/+ subgroup (p = 0.0029). The secretory-stage enamel organic ECM of the Amelx−/− subgroup did not exhibit birefringence. The secretory-stage enamel organic ECM of Mmp20−/− mice showed a significant decrease in optical retardation as compared with Mmp20+/+ and Mmp20+/− mice (p = 0.0000). Mmp20+/− and Mmp20+/+ mice exhibited similar birefringence (p = 1.0000). The results presented here support growing evidence for the idea that the birefringence of secretory-stage enamel organic ECM is influenced by the ordered supramolecular organization of its components.