Immunohistochemical localisation of amelogenin-like proteins and type I collagen and histochemical demonstration of sulphated glycoconjugates in developing enameloid and enamel matrices of the larval urodele (Triturus pyrrhogaster) teeth.

The presence of collagen in enameloid distinguishes it clearly from true enamel, but little is known about the phylogenetic relationship between these 2 tissues. It has previously been reported that amelogenins are the principal proteins of the enamel matrix, that type I collagen and chondroitin sulphates are the predominant matrices in dentine, and that amphibian and reptilian aprismatic enamels, contain no sulphated glycoconjugates, although certain sulphated substances are secreted into mammalian prismatic enamel during matrix formation. The larval urodele (Triturus pyrrhogaster) teeth are known to be composed of enameloid, dentine, and enamel-like tissue. To characterise the tooth matrices, the localisation of amelogenin-like proteins, type I collagen, and sulphated glycoconjugates was investigated. Chondroitin sulphates and fine fibrils immunoreactive for type I collagen were elaborated as the enameloid matrix inside the dental basement membrane. After the matrix had been deposited in full thickness, coarse collagen fibrils also immunoreactive for type I collagen and chondroitin sulphates were deposited below as the first dentine matrix. Further, enamel-like matrix with no collagen fibrils or sulphated glycoconjugates but strongly immunoreactive for amelogenins was deposited on the dentine. Although no immunolabelling for amelogenins was found over the enameloid matrix, at least at the formation stage, the zone of coarse collagen fibrils of dentine was partially immunoreactive as observed in mammalian mantle dentine. From the ontogeny and matrix constituents of larval urodele teeth, it is suggested that enameloid is originally a dentine-like tissue.