The expression of nr0b1, the earliest gene in zebrafish tooth development, is a marker for human tooth and ameloblastoma formation.

Zebrafish teeth develop on pharyngeal jaws in the 5th branchial arch, but early tooth development is remarkably similar to mammals (Borday-Birraux et al., Evol Dev 8:130, 2006). Recently, eve1 has been shown to be associated with the primary tooth (4V(1)) and early ameloblast development, the enamel organ precursor (Laurenti et al., Dev Dyn 230:727, 2004). dax1 is initially expressed in the 5th branchial arch in zebrafish at approximately 26 h postfertilization (hpf) and colocalizes with eve1 expression at approximately 48 hpf. Embryos injected with dax1 morpholino show downregulation of eve1 expression. Based on the zebrafish observations, we demonstrated novel DAX1 expression in normal human dental, benign ameloblastoma, and malignant ameloblastoma tissues. The association of NR0B1 and its protein product DAX1 with primary tooth development and ameloblastoma tumorigenesis is an association not previously described.