Comparative expression of the four enamel matrix protein genes, amelogenin, ameloblastin, enamelin and amelotin during amelogenesis in the lizard Anolis carolinensis

Abstract

Background: In a recent study, we have demonstrated that amelotin (AMTN) gene structure and its expression during amelogenesis have changed during tetrapod evolution. Indeed, this gene is expressed throughout enamel matrix deposition and maturation in non-mammalian tetrapods, while in mammals its expression is restricted to the transition and maturation stages of amelogenesis. Previous studies of amelogenin (AMEL) gene expression in a lizard and a salamander have shown similar expression pattern to that in mammals, but to our knowledge there are no data regarding ameloblastin (AMBN) and enamelin (ENAM) expression in non-mammalian tetrapods. The present study aims to look at, and compare, the structure and expression of four enamel matrix protein genes, AMEL, AMBN, ENAM and AMTN during amelogenesis in the lizard Anolis carolinensis.

Results: We provide the full-length cDNA sequence of A. carolinensis AMEL and AMBN, and show for the first time the expression of ENAM and AMBN in a non-mammalian species. During amelogenesis in A. carolinensis, AMEL, AMBN and ENAM expression in ameloblasts is similar to that described in mammals. It is noteworthy that AMEL and AMBN expression is also found in odontoblasts.

Conclusions: Our findings indicate that AMTN is the only enamel matrix protein gene that is differentially expressed in ameloblasts between mammals and sauropsids. Changes in AMTN structure and expression could be the key to explain the structural differences between mammalian and reptilian enamel, i.e. prismatic versus non-prismatic.

Keywords: Enamel matrix protein; Evolution; Gene expression; Tooth.

Fig. 1

Structure of AMEL and AMBN in A. carolinensis and in representatives of main tetrapod lineages. Exons are represented by boxes and introns by lines (not at scale). Coding regions are in dark green; signal peptide in light green; non-coding regions in white. Asterisk potential phosphorylated Ser residue

Fig. 2

In situ hybridization of AMEL, AMBN, ENAM and AMTN during amelogenesis in A. carolinensis. Early secretory stage (a, e, i, m), secretory stage (b, f, j, n), early maturation stage (c, g, k, o) and late maturation stage (d, h, l, p). A interpretative drawing indicating the various cell populations shown in the pictures, am ameloblasts, dp dental papilla, ide inner dental epithelium, od odontoblasts, ode outer dental epithelium, Asterisk dentin, arrowhead enamel. Scale bars 50 µm