Enamel-Related Gene Products in Calvarial Development

Enamel-related gene products (ERPs) are detected in non-enamel tissues such as bone. We hypothesized that if functional, ERP expression corresponds with distinct events during osteoblast differentiation and affects bone development and mineralization. In mouse calvariae and MC3T3 cells, expression profiles of enamel-related gene products (ERPs) correlated with key events in postnatal calvarial development and MC3T3 cell mineralization. Developing skulls from both Amel- and Ambn-deficient animals were approximately 15% shorter when compared to wild-type controls, and their sutures remained patent for a longer period of time. Analysis of Amel- and Ambn-deficient calvaria and calvarial osteoblast cultures revealed a dramatic reduction in mineralized nodules, a significant reduction in Runx2, Sp7, Ibsp, and Msx2 expression, and a reduction in Alx4 in Amel-deficient calvariae versus an increase in Alx4 in Ambn-deficient calvariae. Together, these data indicate that ERP expression follows defined developmental profiles and affects osteoblast differentiation, mineralization, and calvarial bone development. We propose that in parallel to their role in the developing enamel matrix, ERPs have retained an evolutionary conserved function related to the biomineralization of bones.