Molecular characterization and expression of two cyp19 (P450 aromatase) genes in embryos, larvae, and adults of Atlantic halibut (Hippoglossus hippoglossus).

P450aromatase (CYP19) is an essential part of the enzyme complex catalyzing the conversion of androgens into estrogens, which is a key reaction in the sex differentiation in vertebrates. Two full-length cDNAs encoding the genetic distinct CYP19A and CYP19B isozymes were isolated from Atlantic halibut (Hippoglossus hippoglossus) by RT-PCR of ovarian and brain RNA, respectively. The deduced enzymes CYP19A and CYP19B of 523 and 508 residues, respectively, showed less sequence homology with each other than with their orthologs in other teleost species. This indicates an ancient duplication of the common cyp19 gene that was supported by the constructed phylogenetic tree. Whereas cyp19b mRNA was ubiquitously expressed in the adult male and female, the cyp19a expression was more restricted and showed sex specificity in the gonads as verified by RT-PCR. The detection of transcripts encoding both CYP19A and CYP19B in the embryo clearly preceding any morphological gonadal sex differentiation provides evidence that these genes play important roles in early developmental stages in teleosts. The distinct temporal and spatial expression of the two cyp19 genes in larvae and adults, respectively, together with their low sequence similarity strongly indicate that the genes are differently regulated and that the encoding isozymes have adopted distinct functional roles in Atlantic halibut.