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 rain- 21 bowfish, M. fluviatilis. The cloned cDNA for cyp19a1a and cyp19a1b had an open reading frame (ORF) of 492 22 and 499 amino acid residues, with shared identity of up to 83% and 87% with the corresponding homologues 23 of other teleosts respectively. In contrast, the cyp19a1a and cyp19a1b of the Murray River rainbowfish had a 24 shared identity of only 61%. Not surprisingly, the phylogenetic analysis clustered the M. fluviatilis cyp19 iso- 25 forms with the corresponding isoforms of other teleosts, suggesting a shared evolutionary ancestry of the re- 26 spective isoforms. We also studied the expression of cyp19 isoforms during ontogeny and in adult fish using 27 quantitative Real-Time PCR (qPCR). Results suggest that uniquely only cyp19a1b transcripts are maternally 28 inherited, suggesting its role in early development and growth in the species. In contrast to reports in 29 many teleosts, the cyp19a1a was exclusively expressed in the ovarian tissue and completely absent in 30 other tissues examined, including testis. The cyp19a1b like in most teleosts was predominantly expressed 31 in the brain of both males and females with low level of expression in other tissues including gonads of 32 both sexes.