AMBN and ENAM disappeared after chromosomal rearrangements occurred in the candidate region in a bird ancestor.
We found the full-length chicken AMEL and the only N-terminal region of DSPP, and both are invalidated genes. Conservation of gene synteny in amniotes allowed definition of target DNA regions in which we searched for sequence similarity. Using bioinformatics, we assessed the fate of the four dental proteins thought to be specific to enamel (amelogenin, AMEL ameloblastin, AMBN enamelin, ENAM) and to dentin (dentin sialophosphoprotein, DSPP) in the chicken genome. The next odontogenetic step would have been tooth differentiation, involving deposition of dental proteins. These "chicken teeth" did not develop further, but the question remains whether functional teeth with enamel cap would have been obtained if the experiments had been carried out over a longer time period or if the chicken mutants had survived.
Recently, tooth germs similar to crocodile rudimentary teeth were found in a chicken mutant. However, experiments in chicken have revealed that the oral epithelium can respond to inductive signals from mouse mesenchyme, leading to reactivation of the odontogenic pathway. The ability to form teeth was lost in an ancestor of all modern birds, approximately 100-80 million years ago.
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