Expression of the small leucine-rich proteoglycan osteoadherin/osteomodulin in human dental pulp and developing rat teeth.

Because the extracellular matrices of dentin and bone are composed mainly of type I collagen, their characteristics are determined by the nature of noncollagenous proteins (NCPs). Among these NCPs, some proteoglycans (PGs) belong to the small leucine-rich proteoglycans (SLRPs). Recently, osteoadherin (OSAD) has been described as a new member of this family, that is expressed by mature bovine osteoblasts. Here, we report the expression of OSAD messenger RNA (mRNA) in human dental tissues and during the development of rat molars, using in situ hybridization. For this purpose, we constructed a probe for OSAD mRNA transcripts from human odontoblast cells cultured in vitro. Our results indicate that the mature human odontoblasts overexpress the OSAD gene as compared with cells present in the pulp core. In rat developing molars, mRNA transcripts were first detected in alveolar bone in 19-day-old embryos. At the same age, no signal was detected in any cell of the first molar. In more mature teeth (newborn and 2-day-old rats), OSAD expression starts in the polarized odontoblasts and increases in the secretory and mature odontoblasts, respectively. Interestingly, a similar pattern of expression was observed in the ameloblast layer responsible for the deposition of enamel mineralized matrix. Together, these results lead us to speculate that OSAD may be implicated in biomineralization processes.