Odontogenesis-associated phosphoprotein truncation blocks ameloblast transition into maturation in Odaph mice.

Mutations of Odontogenesis-Associated Phosphoprotein (ODAPH, OMIM *614829) cause autosomal recessive amelogenesis imperfecta, however, the function of ODAPH during amelogenesis is unknown. Here we characterized normal Odaph expression by in situ hybridization, generated Odaph truncation mice using CRISPR/Cas9 to replace the TGC codon encoding Cys41 into a TGA translation termination codon, and characterized and compared molar and incisor tooth formation in Odaph, Odaph, and Odaph mice. We also searched genomes to determine when Odaph first appeared phylogenetically. We determined that tooth development in Odaph and Odaph mice was indistinguishable in all respects, so the condition in mice is inherited in a recessive pattern, as it is in humans. Odaph is specifically expressed by ameloblasts starting with the onset of post-secretory transition and continues until mid-maturation. Based upon histological and ultrastructural analyses, we determined that the secretory stage of amelogenesis is not affected in Odaph mice. The enamel layer achieves a normal shape and contour, normal thickness, and normal rod decussation. The fundamental problem in Odaph mice starts during post-secretory transition, which fails to generate maturation stage ameloblasts. At the onset of what should be enamel maturation, a cyst forms that separates flattened ameloblasts from the enamel surface. The maturation stage fails completely.