Strategies for Tracking the Origin and Fate of Odontoblasts and Pulp Cell Progenitors
Odontoblasts are exclusively dentin-producing cells that are morphologically and functionally distinct from osteoblasts secreting the bone matrix. Although much has been learned about the cellular and molecular mechanisms that regulate the progression of
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Strategies for Tracking the Origin and Fate of Odontoblasts and Pulp Cell Progenitors Mina Mina
4.1
Odontoblasts and Dentinogenesis
Dentinogenesis is regulated by a single layer of highly differentiated postmitotic odontoblasts originating from the cranial neural crest-derived cells of the dental papilla [1, 2]. The terminal differentiation of odontoblasts from the dental papilla occurs independently in each cusp and is dependent on inductive signals derived from the inner dental epithelium and its associated basement membrane [1, 2]. This differentiation involves a series of change in the morphology, transcriptional profile, and expression of proteins secreted by cells in the odontoblast lineage. During this process, the dental papilla cells in close proximity to the epithelial–mesenchymal interface first form cuboidal pre-odontoblasts. The differentiation of pre-odontoblasts occurs at the bell stage of tooth development and is regulated by signals from inner enamel epithelium and secondary enamel knots [3, 4]. Further differentiation proceeds in a graded fashion from cusp tips toward the intercuspal areas and cervical loops and includes the withdrawal of preodontoblasts from cell cycle and the formation of
M. Mina, DMD, MSD, PhD Division of Pediatric Dentistry, School of Dental Medicine, University of Connecticut Health Center, 263 Farmington Ave, Farmington, CT 06030-4081, USA e-mail: [email protected]
polarized odontoblasts in close contact with the epithelial–mesenchymal interface. The formation polarizing odontoblasts that display cytological polarization with nucleus occupying the proximal part of the cell body is followed by the formation of secretory/functional odontoblasts and finally the formation of mature and terminally differentiated odontoblasts [5]. Functional/secretory odontoblasts are engaged in the secretion of unmineralized predentin matrix, composed primarily of type I collagen (Col1a1) secreted at their apical end [6]. As odontoblasts continue their differentiation, they secrete many non-collagenous proteins (NCP) including SIBLINGs proteins (osteopontin, bone sialoprotein, dentin matrix protein 1 (DMP1), dentin sialophosphoprotein, osteonectin, and MEPE) and the proteoglycans (biglycan, decorin, fibromodulin, lumican, and osteoadherin) shown to be essential for initiating the mineralization of the type 1 collagen network in the predentin matrix [7]. Many of the NCPs of dentin are also found in the bone. However, dentin is characterized by the presence of two dentin-specific NCPs, dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) [8]. These two dentin-specific NCPs are encoded by a single gene and are specific cleavage products of a larger protein called dentin sialophosphoprotein (DSPP) [8]. Although low levels of Dspp have been detected in the bones by RT-PCR, high level of Dspp expression is specific to odontoblasts [8]. At the same time, odontoblasts recede toward pulp and leave behind cell processes that extend
M. Goldberg (ed.), The Dental Pulp, DOI 10.1007/978-3-642-55160-
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