Molecular biology of channel catfish brain cytochrome P450 aromatase (CYP19A2): cloning, preovulatory induction of gene expression, hormonal gene regulation and analysis of promoter region.

Cytochrome P450 aromatase (CYP19) converts androgens to estrogens. Unlike mammals, teleosts have two CYP19 genes, expressed differentially in ovary (CYP19A1) and neuronal tissues (CYP19A2). The primary purpose of this study was to demonstrate the potential involvement of CYP19A2 in the reproductive endocrinology of teleosts. Channel catfish CYP19A2 (ccCYP19A2) cDNAs were isolated from the brain using a PCR-based strategy. The ccCYP19A2 cDNA putatively encodes 500 amino acids which conferred aromatase activity in transfected COS-7 cells. Additionally, an alternatively spliced transcript was isolated which lacks the first 122 amino acids and is catalytically inactive. The brain and the pituitary were predominant sources of ccCYP19A2 transcript and the abundance in both tissues acutely increased prior to spawning. This preovulatory induction of ccCYP19A2 gene in the pituitary is remarkably similar to the pattern of gene expression for luteinizing hormone-beta (LHbeta). Estradiol-17beta (E(2)) and testosterone enhanced the transcript abundance of ccCYP19A2 and LHbeta in catfish pituitary cells cultured in vitro but the stimulatory effects of testosterone were abolished by an aromatase inhibitor, indicating an important role of E(2), the product of CYP19A2 activity, in the regulation of CYP19A2 and LHbeta. Structural and functional analysis of the 5'-flanking region of the gene suggested that the sequence from -1076 to - 435 bp is critical for the basal promoter activity in the pituitary. This report demonstrates that CYP19A2 functions as an important factor in the reproductive endocrinology of teleosts through the brain-pituitary-gonadal axis.