Brain aromatase in Japanese medaka (Oryzias latipes): Molecular characterization and role in xenoestrogen-induced sex reversal.

In female fish estrogen is required for the development of primary and secondary sex characteristics and is derived from the aromatization of androgens by aromatase. There are two isoforms of aromatase in several teleost species, brain and ovarian. The objective of this study was two-fold: clone and sequence the coding and promoter region of brain aromatase in medaka, and determine the effects of exposure to an environmental estrogen (o,p-DDT) on sex determination and brain aromatase transcription and activity. The brain aromatase coding sequence was obtained by reverse transcription polymerase chain reaction (RT-PCR) and PCR-based genomic DNA walking was used to clone the promoter of the brain aromatase gene. The promoter sequence revealed potential binding sites for the estrogen receptor and for transcription factors involved in primary neurogenesis and sex determination. Medaka fry were exposed to increasing o,p-DDT concentrations (0-5.5 microg/L) from days 1 to 15 after hatch and brain aromatase expression and activity were measured on days 5, 9, and 14. A complete male-to-female sex reversal occurred at 5.5 microg/L o,p-DDT and aromatase activity and expression data showed a significant five-fold increase at this concentration at day 14. This information suggests that brain aromatase is involved in the abnormal sexual differentiation of fish treated with xenoestrogens.