Ontogenic and sexually dimorphic expression of cyp19 isoforms in the rainbowfish, Melanotaenia fluviatilis (Castelnau 1878)

To investigate the role of cytochrome P450 aromatase, we isolated cyp19 isoforms in the Murray River rainbowfish, M. fluviatilis. The cloned cDNA for cyp19a1a and cyp19a1b had an open reading frame (ORF) of 492 and 499 amino acid residues, with shared identity of up to 83% and 87% with the corresponding homologues of other teleosts respectively. In contrast, the cyp19a1a and cyp19a1b of the Murray River rainbowfish had a shared identity of only 61%. Not surprisingly, the phylogenetic analysis clustered the M. fluviatilis cyp19 isoforms with the corresponding isoforms of other teleosts, suggesting a shared evolutionary ancestry of the respective isoforms. We also studied the expression of cyp19 isoforms during ontogeny and in adult fish using quantitative Real-Time PCR (qPCR). Results suggest that uniquely only cyp19a1b transcripts are maternally inherited, suggesting its role in early development and growth in the species. In contrast to reports in many teleosts, the cyp19a1a was exclusively expressed in the ovarian tissue and completely absent in other tissues examined, including testis. The cyp19a1b like in most teleosts was predominantly expressed in the brain of both males and females with low level of expression in other tissues including gonads of both sexes.