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 o f type I collagen, their characteristics are determined by the nature of no ncollagenous proteins (NCPs), Among these NCPs, some proteoglycans (PGs) be long to the small leucine-rich proteoglycans (SLRPs). Recently, osteoadheri n (OSAD) has been described as a new member of this family, that is express ed by mature bovine osteoblasts, Here, we report the expression of OSAD mes senger RNA (mRNA) in human dental tissues and during the development of rat molars, using in situ hybridization. For this purpose, we constructed a pr obe fur OSAD mRNA transcripts from human odontoblast cells cultured in vitr o. Our results indicate that the mature human odontoblasts overexpress the OSAD gene as compared with cells present in the pulp core. In rat developin g molars, mRNA transcripts were first detected in alveolar hone in 19-day-o ld embryos. At the same age, no signal was detected in any cell of the firs t molar. In more mature teeth (newborn and 2-day-old rats), OSAD expression starts in the polarized odontoblasts and increases in the secretory and ma ture odontoblasts, respectively. Interestingly, a similar pattern of expres sion was observed in the ameloblast layer responsible for the deposition of enamel mineralized matrix. Together, these results lead us to speculate th at OSAD may be implicated in biomineralization processes. (C) 2000 by Elsev ier Science Inc. All rights reserved.