The amelogenin story: origin and evolution

Genome sequencing and gene mapping have permitted the identification of HEVIN (SPARC-Like1) as the probable ancestor of the enamel matrix proteins (EMPs), amelogenin (AMEL), ameloblastin (AMBN) and enamelin (ENAM). We have undertaken a phylogenetic analysis to elucidate their relationships. AMEL genes available in databases, and new sequences obtained in blast searching genomes or expressed sequence tags, were compiled (22 full-length sequences), aligned, and the ancestral sequence calculated and used to search for similarities using psi - blast . Hits were obtained with the N-terminal region of AMBN, ENAM, and HEVIN. We retrieved all available AMBN ( n  = 8), ENAM ( n  = 3), and HEVIN ( n  = 4) sequences. The sequences of the four proteins were aligned and analyzed phylogenetically. AMEL and AMBN are sister genes, which diverged after duplication of a common ancestor issued from ENAM . The latter derived from a copy of HEVIN . Comparisons of gene organization, amino acid sequences and location of ENAM and AMBN , adjacent on the same chromosome, suggest that AMBN is closer to ENAM than AMEL . This supports AMEL as being derived from AMBN duplication. This duplication occurred long before tetrapod differentiation, probably in an ancestral osteichthyan. The story of AMEL origin is completed as follows: SPARC → HEVIN → ENAM → AMBN → AMEL .