Sequential expression of matrix protein genes in developing rat teeth

Tooth organogenesis is dependent on reciprocal and sequential epithelial-me senchymal interactions and is marked by the appearance of phenotypic matrix macromolecules in both dentin and enamel. The organic matrix of enamel is composed of amelogenins, ameloblastin/amelin, enamelins and tuftelin. Denti n is mainly composed of type I collagen, but its specificity arises from th e nature of the non-collagenous proteins (NCPs) involved in mineralization, phosphophoryn (DPP), dentin sialoprotein (DSP), osteocalcin, bone sialopro tein and dentin matrix protein-1 (Dmp1). In this paper, we studied the patt ern of expression of four mineralizing protein genes (type I collagen, amel ogenin, DSPP and osteocalcin) during the development of rat teeth by in sit u hybridization on serial sections. For this purpose, we used an easy and r apid procedure to prepare highly-specific labeled single-stranded DNA probe s using asymmetric polymerase chain reaction (PCR). Our results show that t ype I collagen is primarily expressed in polarizing odontoblasts, followed by the osteocalcin gene expression in the same polarized cells. Concomitant ly, polarized ameloblasts start to accumulate amelogenin mRNAs and transien tly express the DSPP gene. This latter expression switches over to odontobl asts whereas mineralization occurs. At the same time, osteocalcin gene expr ession decreases in secretory odontoblasts. Osteocalcin may thus act as an inhibitor of mineralization whereas DSP/DPP would be involved in more advan ced steps of mineralization. Amelogenin and type I collagen gene expression increases during dentin mineralization. Their expression is spatially and temporally controlled, in relation with the biological role of their cognat e proteins in epithelial-mesenchymal interactions and mineralization. (C) 1 999 Elsevier Science B.V./International Society of Matrix Biology. All righ ts reserved.