Adult teeth lack the ability to reconstruct and/or regenerate missing tissues. As a result tooth loss is currently being treated by a variety of traditional clinical therapies using prostheses and implants. One of the major problems in reconstruction and/or regeneration of tooth structures is the lack of clearly identified progenitor cells from adult tissues that are able to replace or regenerate the mature cells and structures. Objectives: The objective of our studies is to directly examine the possibility that dental pulp contains progenitor/stem cells that upon receiving the appropriate signal(s) are capable of forming odontoblast-like structures. Methods: We used transgenic mice that carry a Green Fluorescent Protein (GFP) reporter gene fused to 3.6kb and 2.3kb fragments of rat Col1a1 regulatory sequences. Pulps free of odontoblasts from the coronal portions of first mandibular molars were isolated from 5-day-old transgenic mice and transplanted for 7-10 days under the kidney capsule of CD-1 female hosts. Tissues were processed for paraffin embedding and analyzed by epifluorescence and in situ hybridization. Results: In these transgenic mice the expression of Col3.6GFP and Col2.3GFP transgenes closely follow the expression pattern of a1(I)collagen in developing teeth and bone. High levels of GFP expression were detected in developing craniofacial bones and in functional and differentiated odontoblasts expressing dentin sialophosphoprotein (DSPP). Our histological analyses of post-implantation explants showed the presence of odontoblast-like and osteocyte-like GFP-expressing cells in grafted tissue. The odontoblast-like cells were polarized and associated with mineralized matrix, whereas osteocyte-like cells were surrounded by mineralized matrix. Our preliminary observations show expression of DSPP by the odontoblast-like cells in the grafted tissue. Conclusions: Pulp cells are capable of giving rise to both odontoblast- and osteoblast-like cells and mineralized tissues that resemble dentin and bone. This work was supported by NIH grant DE13363.

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