Estrogen and xenoestrogens upregulate the brain aromatase isoform (P450aromB) and perturb markers of early development in zebrafish (Danio rerio)

Estrogen synthesized in the brain itself by the action of cytochrome P450 a romatase (P450arom) is known to have permanent organizing effects on the de veloping CNS. In fish, estrogen upregulates the predominant brain isoform ( P450aromB), implying that xenoestrogens (XE) could act as neurodevelopmenta l toxicants by altering P450aromB. To test this hypothesis, zebrafish embry os were exposed to 17 beta -estradiol (E-2), diethylstilbestrol (DES, a pot ent agonist), and bisphenol A (BPA, a weak agonist). RT-PCR/Southern transf er analysis showed that E-2 (0.01-10 muM) upregulated P450aromB in a dose-r esponse manner. The effect of DES (0.01 muM) was similar to 1 muM E-2 (thre e- to four-fold higher than control), but BPA was less effective (< threefo ld increase at 10 muM) mRNA levels of the predominant ovarian isoform (P450 arom4) were unchanged by estrogen. Treatment with E-2 (0.1-10 muM) between 2 and 72 hpf had dose-response effects on mortality and hatching and induce d a 'curved tail down' phenotype characteristic of mutants with defects of early CNS development. The critical period of estrogen sensitivity for effe cts on mortality and curved tails was 2-24 hpf, whereas hatching effects we re both stage- and duration-dependent. Developmental effects of DES and BPA were similar to E-2 but testosterone, and S alpha -dihydrotestosterone wer e ineffective. 17 alpha -Estradiol showed a small but significant effect on curved tails. We conclude that P450aromB mRNA is a sensitive marker of XE effect during embryogenesis, but further studies are required to determine whether changes in neural aromatase expression and estrogen biosynthesis ha ve consequences for CNS development. (C) 2001 Elsevier Science Inc. All rig hts reserved.