Nestin expression is differently regulated between odontoblasts and the subodontoblastic layer in mice

The Nestin gene encodes type VI intermediate filament and is known to be expressed in undifferentiated cells during neurogenesis and myogenesis. To regulate Nestin expression, the first or second intron enhancer is activated in a tissue-dependent manner, for example, the former in mesodermal cells and the latter in neural stem cells. Although Nestin has also been used as a differentiation marker for odontoblasts during tooth development, how Nestin expression is regulated in odontoblasts remains unclear. Therefore, this study aimed to compare the expression patterns of Nestin-GFP (green fluorescent protein) with that of endogenous Nestin in developing teeth of Nestin-EGFP (enhanced GFP) transgenic mice, in which the second intron enhancer is connected with the EGFP domain, at postnatal 7d, 3w, and 8w. Immunohistochemical and in situ hybridization analyses revealed that endogenous Nestin protein and Nestin mRNA were intensely expressed in differentiated odontoblasts, while GFP immunoreactivity, which reflects the activity of Nestin second intron enhancer-mediated transcription, was mainly observed in the subodontoblastic layer. These results indicate that the first intron enhancer may be activated in differentiated odontoblasts. Intriguingly, Nestin-GFP expression in the subodontoblastic layer was found to be restricted to the coronal pulp of molars, which is susceptible to tooth injuries. Because the subodontoblastic layer serves as a reservoir of newly differentiated odontoblast-like cells upon exogenous stimuli to dentin, our findings suggest that the original odontoblasts and regenerated odontoblast-like cells may differently regulate Nestin expression.