Bone morphogenetic protein 4 is involved in cusp formation in molar tooth germ of mice

In order to clarify the role of BMP4 in the development of the tooth crown, we employed the antisense technique on molar tooth germs removed from the mandibles of embryonic 13.5-d-old mice. In the tooth germ explants incubated for 14 d with antisense oligodeoxynucleotide (AS-ODN) against Bmp4 (a) cusps were not formed, whereas dentin matrix was secreted in the whole region of the crown, (b) inner enamel epithelial (IEE) cells remained in the undifferentiated state in the occlusal region of the crown, though they differentiated in the proximal region (lateral surface region of tooth crown), and (c) insufficient growth of the dental papilla was observed. A 5-bromo-2'-deoxyuridine (BrdU) uptake experiment showed that, although a site-specific proliferation of IEE cells occurred in the occlusal region in the control explants, it was not found in the AS-ODN-treated explants. In the proximal region, however, the proliferation of IEE cells was detected evenly in all explants treated with or without AS-ODNs. These results suggest that AS-ODN against Bmp4 inhibited the differentiation and the site-specific proliferation of IEE cells in the occlusal region of molar tooth germs, resulting in the suppression of cusp formation. Our data thus suggest that BMP4 is involved in cusp formation and differentiation of ameloblasts in the occlusal region of molars.