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Hen's teeth with enamel cap: from dream to impossibility
Jean-Yves Sire1, Sidney C Delgado, Marc Girondot
1Université Pierre & Marie Curie-Paris 6, UMR 7138 Systématique, Adaptation, Evolution, 7 quai St-Bernard, 75005, Paris, France. jean-yves.sire@upmc.fr
BMC Evolutionary Biology
|September 9, 2008
Summary
Birds lost the ability to form teeth millions of years ago. Genetic analysis reveals key enamel and dentin protein genes are non-functional or absent in chickens, preventing future tooth development.
Area of Science:
- Evolutionary biology
- Genomics
- Developmental biology
Background:
- Modern birds lost the capacity for tooth formation 100-80 million years ago.
- Chicken oral epithelium can reactivate odontogenic pathways when exposed to mouse mesenchyme signals.
- Rudimentary "chicken teeth" observed in mutants suggest potential for tooth development.
Purpose of the Study:
- To investigate the genetic basis for the absence of functional teeth in modern birds.
- To determine the status of genes encoding key enamel and dentin proteins in the chicken genome.
Main Methods:
- Bioinformatic analysis of the chicken genome.
- Comparative genomics using conserved gene synteny in amniotes.
- Sequence similarity searches in defined DNA regions.
Main Results:
- The chicken genome contains a full-length amelogenin (AMEL) gene but it is invalidated.
- Dentin sialophosphoprotein (DSPP) is present only as an N-terminal region and is invalidated.
- Ameloblastin (AMBN) and enamelin (ENAM) genes are absent in chickens due to chromosomal rearrangements in avian ancestors.
Conclusions:
- Functional teeth with enamel covering cannot be obtained in birds.
- The four investigated protein genes (AMEL, AMBN, ENAM, DSPP) were specific to the last toothed bird ancestor.
- These findings challenge recent questions about the specificity of these dental genes.
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