Modeling the Histogenetic Switch Between Enameloid and Enamel

Enamel and enameloid are hypermineralized tissues that can be found on the surface of vertebrates' dental structures. Shared developmental features suggest that minor changes could have driven multiple transitions between dentine-enamel and dentine-enameloid structures. It has been hypothesized that delayed (H1) or prolonged epithelial cell activity (H2), as well as modifications in epithelial cell production rates (H3), could explain such transitions. To test these evo-devo hypotheses, we built a cell-based histogenetic model using simplified properties common to current vertebrates. By varying secreting cell parameters, the simulations can reproduce a wide range of dentine, enameloid, and enamel proportions, allowing exploration of their role in the enameloid-enamel transition. Our exploration of 12 cellular parameters showed that H1, and H3 to a lesser extent, could account for such a transition, whereas H2 likely needs to be associated with one other modification. Our results also suggest that changes in the position and timing of the mineralization front formation are key to constraining enamel-enameloid-dentine development. Thus, beyond the gain or loss of gene function, minor developmental modifications may also have played a key role in the emergence and evolution of dental tissues.