Fig. 8. Schematic representation of the epithelial stem cell compartment in mouse incisor and vole molar and the similar distribution of activities of some of the proposed key Notch signaling genes. The stellate reticulum and stratum intermedium are areas of high Notch expression and the putative locations of the adult stem cells. The progeny of the stem cells migrate to the inner enamel epithelium and form a population of transit-amplifying cells characterized by Lfng expression. The cells then start to differentiate into ameloblasts and enter the next domain characterized by Jag1 expression. The proliferation and the stem cells are maintained by the mesenchymal Fgf10 expression near the cervical and intercuspal loop. The identical expression of Bmp4 and Fgf10 indicate that BMP4 might work together with FGF10 in the modulation of the stem cells and their progeny. The main difference between vole molar and mouse incisor is the presence of intercuspal folds in the vole molar, which possess an identical distribution of the key regulators as in the cervical loop area.

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