Figure 2. c-kit⁺-enriched bone marrow cells acquired characteristics of ameloblasts. (A,B) In situ hybridization for amelogenin (Amg) and ameloblastin (Amb) shows strong expression in the ameloblast (Am) layer from post-natal day 7 (P7), in the mouse first lower molar. (C,E) c-kit⁺-enriched bone marrow cells are present in the newly formed tooth structure from re-associations cultured for 20 days. (D,F) Superimposition of in situ hybridization for amelogenin and ameloblastin with EGFP labeling shows that c-kit⁺-enriched bone marrow cells engrafted in the inner dental epithelium (IDE) layer expressed the two genes. (G,K) Ameloblasts and dental matrix in the P7 mouse first lower molar were characterized by indirect immunofluorescence with antibodies to amelogenin (AMG) (G) and MMP-20 (K). (H–J) The c-kit⁺-enriched bone marrow cells in the ameloblast layer secreted amelogenin. (L–N) They also secreted MMP-20. (O–Q) Cultured re-association in the presence of BrdU from day 6 to day 8 shows that the engrafted c-kit⁺-enriched bone marrow cells in the inner dental epithelium (see Fig. 1g) still divided at this early stage. (R–T) BrdU incorporation for 48 hrs before harvesting showed that engrafted c-kit⁺-enriched bone marrow cells in the inner dental epithelium were no longer dividing when polarized. BrdU-labeled epithelial cells were observed only in the cervical loop (CL) region. DM, Dental Matrix; E, Enamel; Mes, Dental Mesenchyme. Bar = 40 µm (A–F, O–T) and 10 µm (G–N).