Enamel: Molecular identity of its transepithelial ion transport system

•Enamel is the most calcified tissue in the vertebrate body.•Transepithelial ion transport is cell regulated.•Enamel cells are known as ameloblasts, form and mineralize hydroxyapatite-like crystals.•De novo crystal formation is mediated by ameloblasts as is extracellular pH.•Models for ion transport generally lack functional testing.

Enamel is the most calcified tissue in vertebrates. It differs from bone in a number of characteristics including its origin from ectodermal epithelium, lack of remodeling capacity by the enamel forming cells, and absence of collagen. The enamel-forming cells known as ameloblasts, choreograph first the synthesis of a unique protein-rich matrix, followed by the mineralization of this matrix into a tissue that is ∼95% mineral. To do this, ameloblasts arrange the coordinated movement of ions across a cell barrier while removing matrix proteins and monitoring extracellular pH using a variety of buffering systems to enable the growth of carbonated apatite crystals. Although our knowledge of these processes and the molecular identity of the proteins involved in transepithelial ion transport has increased in the last decade, it remains limited compared to other cells. Here we present an overview of the evolution and development of enamel, its differences with bone, and describe the ion transport systems associated with ameloblasts.

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