PARENT SESSION

2C (1) - Biomarkers
Hall 7
1:45 PM - 3:30 PM, Tuesday, 29 April 2003
Chair: Hansen, P.D.¹, ¹
Co-chair: Vindimian, E.², ²

(TU7/13) Altering gonadal differentiation of zebrafish by affecting aromatase function.

Fenske, Martina¹, Segner, Helmut², Tyler, Charles R.¹, ¹ School of Biological Sciences, University of, Exeter, Devon, UK² Centre for Fish and Wildlife Health, University of, Bern, canton of Bern, Switzerland

ABSTRACT- Expression of the ovarian-derived and brain-derived CYP19 mRNA transcripts (CYP19A and CYP19B, respectively) was measured in juvenile and sexually maturing zebrafish (Danio rerio), using semi-quantitative RT-PCR. In juveniles, expression of CYP19A mRNA was highest in gonads (fish body trunks) and CYP19B mRNA was the dominant transcript in the brain (head tissue). In adult fish, CYP19A mRNA showed a sexual dimorphic pattern of expression in gonads, with the highest expression in the ovary. There were no gender differences in the expression of CYP19B mRNA in the brain. Exposure to fadrozole (500 g/g of food) between day 35 and day 71 post fertilization (pf- encompassing the period of gonadal sex differentiation) induced testicular differentiation and suppressed gonad expression of CYP19A mRNA . Methyl testosterone (MT) treatment (10 g/L via the water) during the same period resulted in ovarian-like gonads in all fish at 71dpf (paradoxical feminisation) and an elevated expression of CYP19B mRNA in the brain/head. Continued exposure to MT to 161dpf resulted in the maintenance of an elevated level of brain CYB 19B mRNA expression. Despite the feminising or masculinising effects of fadrozole or MT treatment on gonad development there was still a (sexual) dimorphic pattern of CYP19A mRNA expression in the gonads. These data show that alterations in aromatase as a consequence of chemical exposure can lead to alterations in sexual development and gender assignment. Moreover, by in-situ hybridisation it could be shown that the function of the CYP19 expression in the brain is strongly correlated with its anatomical and cellular localisation during differentiation.

Key words: zebrafish, P450 aromatase, fadrozole, methyl testosterone