Expression of Type I Procollagen and Amelogenin Genes in Ectoderm-Derived Mineralized Tissue

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Ectoderm-derived hard tissues such as enamel, enameloid(produced jointly by epithelial and ectomesenchymal cells) and ganoine form an external highly mineralized layer on the teeth and scales respectively. The presence of collagen in enameloid distinguishes it clearly from true enamels, but little is known about phylogenetic relationship between these two tissues. The cellular source of enameloid collagen, however, has been remained controversial. With these considerations in mind we searched for collagen and amelogenin genes and characterized the origin of enameloid collagen. Messenger RNA encoding procollagen α 1 type I have been localized using digoxigenin-labelled synthetic oligonucleotide probes. The probe-mRNA hybrides were visualized using an anti-digoxin antibodies. Intense hybridization signals for the procollagen were detected in the fibroblasts of the oral mucosa connective tissues and perichondrium. Further, the positive hybridization signals were also observed in odontoblasts of the tooth germs of the larval urodele (Triturus pyrrhogaster) during enameloid matix formation. But no signals were detected in the oral mucosa epithelial cells including inner epithelial cells. It is highly suggestive that odontoblasts synthesize procollagen α 1 type I of the enameloid matrix.