To use immunohistochemistry to analyse the expression of MSX1 and β-catenin proteins during parrot pseudoteeth development and goose denticulations and giant filiform papillae ontogeny.

Eggs were purchased from stockbreeders. Embryos from selected stages were removed and sliced. Immunohistochemistry using anti-MSX1 and anti-β-catenin antibodies was performed and the results were compared with each other.

For each protein, the staining predominated in the epithelial layer, with sparser labelling in the subjacent mesenchyme. Despite the unequal chronology of every appendage, the labelling became maximal around stage 40.

Although the overall pattern of labelling was similar in the three appendages, several differences were observed. These structures can be considered as homologous but not strictly similar. They are odontode derivatives, with different growing mechanisms. MSX1is considered as characteristic of progress zones and areas of epithelial-mesenchymal interactions (as β-catenin) and is closely associated with β-catenin in several models. Our observations were consistent with these features, and pseudoteeth and denticulations were found to differ from true teeth in their mechanism of development: evagination vs invagination. In true tooth germs, MSX1 express mainly in the mesenchyme. In conclusion, our findings do reinforce the homologies between all these appendages but also reveal a key difference between the development of tooth germs, pseudoteeth and denticulations. Our findings also suggest that tongue papillae differ from pseudoteeth appendages in several growing mechanisms despite the similarities found between the two.