Characterization of the cyp19a1a gene from a BAC sequence in half-smooth tongue sole (Cynoglossus semilaevis) and analysis of its conservation among teleosts

The cyp19a1a gene encodes an aromatase that plays a key role in sex differentiation of the gonad. The first bacterial artificial chromosome (BAC) sequence of half-smooth tongue sole (Cynoglossus semilaevis) containing the intact cyp19a1a gene was reported and the conservation and synteny of the cyp19a1a gene among teleosts were analyzed in the study. The BAC is 107 367 bp in size, with an overall guanine-cytosine (GC) content of 43.44%, and contains 4.38% transposable elements. Nine genes were predicted, including seven functional genes and two hypothetical genes. The cyp19a1a gene of all tested teleosts has nine exons and eight introns, and potential binding sites flanking the transcriptional start site are conserved. The expression pattern among teleosts is also similar during ovarian differentiation. Synteny analysis revealed a conserved gene cluster PKH4B-SL9A5-FHOD3-CEBPG-CEBPA among teleosts. These findings suggest that, among teleosts, cyp19a1a genes not only have similar genomic structures, but also have conserved functions. The genomic environment of cyp19a1a in tongue sole is not universal in teleosts, reflecting the particular evolution of tongue sole cyp19a1a after it diverged from the other teleosts.