Fosfato

Volume 57(3): 227–237, 2009 Journal of Histochemistry & Cytochemistry

http://www.jhc.org ARTICLE

Temporal and Spatial Localization of the Dentin Matrix Proteins During Dentin Biomineralization
Jianjun Hao, Amsaveni Ramachandran, and Anne George

The Journal of Histochemistry & Cytochemistry

Brodie Tooth Development Genetics and Regenerative Medicine Research Laboratory, Department ofOral Biology, University of Illinois at Chicago, Chicago, Illinois

SUMMARY

Formation of bone and dentin are classical examples of matrix-mediated mineralization. The mineral phase is essentially the same in these two tissues and primarily consists of a carbonated hydroxyapatite, but the difference lies in the crystal size and shape. There are three components that are necessary for propermineralization, namely the proper synthesis and secretion of the non-collagenous proteins (NCPs), self-assembly of the collagenous matrix, and delivery of calcium and phosphate ions to the extracellular matrix. Three major NCPs present in the dentin matrix are dentin matrix protein 1 (DMP1), dentin phosphophorin (DPP), and dentin sialoprotein (DSP). In this study, we show the temporal and spatiallocalization of these NCPs and correlate their expression with the presence of collagenous matrix and calcified deposits in developing mouse incisors and molars. DMP1, an acidic protein, is present predominantly at the mineralization front and in the nucleus of undifferentiated preodontoblast cells. DPP, the major NCP, is present in large amounts at the mineralization front and might function toregulate the size of the growing hydroxyapatite crystals. For the first time, we report the localization of DPP in the nucleus of preodontoblast cells, suggesting a signaling function during the odontoblast differentiation process. DSP is localized predominantly in the dentinal tubules at the site of peritubular dentin, which is highly mineralized in nature. Thus, the precise localization of DMP1,DPP, and DSP in the dentin tissue suggests that a concerted effort between several NCPs is necessary for dentin formation.
(J Histochem Cytochem 57:227–237, 2009)

KEY WORDS dentin matrix protein 1 dentin phosphophorin dentin sialoprotein mineralization

IN VERTEBRATES, the mineralization process involves a sequential and localized series of events that leads to the controlled growth andformation of carbonated apatite mineral within an extracellular matrix (Boskey 1996). Each mineralizing tissue provides both a structural and chemical framework, which acts as a scaffold for mineral deposition at specific sites (Hao et al. 2004; He and George 2004). In bone and dentin, type I collagen is intimately associated in a well-defined manner with calcium phosphate crystals. A common featureprevalent in mineralized tissues is the presence of acidic macromolecules (Linde 1989; Gorski 1992). Many of these macromolecules bind calcium ions and apatite

Correspondence to: Anne George, Brodie Tooth Development Genetics and Regenerative Medicine Research Laboratory, Department of Oral Biology, University of Illinois at Chicago, Chicago, IL 60612. E-mail: anneg@uic.edu Received forpublication June 20, 2008; accepted October 23, 2008 [DOI: 10.1369/jhc.2008.952119]. C The Histochemical Society, Inc.
0022-1554/08/$3.30

and some inhibit mineral formation from spontaneously precipitating solutions (Schinke et al. 1996; MacDougall et al. 1998; Gorski et al. 2004). Specific roles in the mineralization process have been proposed for many of these macromolecules. These include nucleationof the mineral, control of postnucleation growth, and transformation of calcium phosphate deposits to hydroxyapatite (Denhardt and Guo 1993; Wazen et al. 2007). Odontoblasts are terminally differentiated ectomesenchymal cells that synthesize several collagenous and non-collagenous proteins. The major phosphoproteins of the non-collagenous group are now known as the SIBLING (small integrin...