Expression survey of genes critical for tooth development in the human embryonic tooth germ

In the developing murine tooth, the expression patterns of numerous regulatory genes have been examined and their roles have begun to be revealed. To unveil the molecular mechanisms that regulate human tooth morphogenesis, we examined the expression patterns of several regulatory genes, including BMP4, FGF8, MSX1, PAX9, PITX2, and SHOX2, and compared them with that found in mice. All of these genes are known to play critical roles in murine tooth development. Our results show that these genes exhibit basically similar expression patterns in the human tooth germ compared with that in the mouse. However, slightly different expression patterns were also observed for some of the genes at certain stages. For example, MSX1 expression was detected in the inner enamel epithelium in addition to the dental mesenchyme at the bell stage of the human tooth. Moreover, FGF8 expression remained in the dental epithelium at the cap stage, while PAX9 and SHOX2 expression was detected in both dental epithelium and mesenchyme of the human tooth germ. Our results indicate that, although slight differences exist in the gene expression patterns, the human and mouse teeth not only share considerable homology in odontogenesis but also use similar underlying molecular networks.