Distinct cytochrome P450 aromatase isoforms in the common carp (Cyprinus carpio): Sexual dimorphism and onset of ontogenic expression

Cytochrome P450 aromatase (CYP19) is a key enzyme in the steroidogenic pathway that catalyses the conversion of testosterone to estrogen, and therefore is thought to influence gonadal sex differentiation. In an effort to understand the role of this enzyme in ovarian differentiation, we isolated cDNA encoding the two distinct isoforms, ovarian and brain (termed cyp19a and cyp19b, respectively) of adult common carp, Cyprinus carpio. The cloned cDNA for cyp19a had an open reading frame (ORF) of 518 amino acid residues, in contrast to cyp19b with an ORF of 511 amino acids. Sequence and phylogenetic analysis showed that these CYP19 isoforms were orthologous with previously described cyp19a and cyp19b from other teleosts. Quantitative real-time PCR indicated that both isoforms are expressed in adult ovary and brain, with predominant expression of cyp19a in the ovary and cyp19b in the brain. The major aromatase expressing tissue was found to be the brain, with greatest cyp19b expression in the anterior quarter (telencephalon) in both sexes. The gonad showed sexually dimorphic expression of both genes and dimorphic expression of cyp19a was observed in the cerebellum and the liver. Ontogenic expression showed that only the ovarian aromatase transcript is inherited maternally, with lower expression observed through early larval development under warmer rearing conditions. The differential and overlapping expression suggests these two aromatase genes have different roles in reproductive physiology.