A novel in vivo bioassay for (xeno-)estrogens using transgenic zebrafish

Adverse trends in the reproductive health of male fish, including testis ab normalities and intersex gonads, have been increasingly reported over recen t years. These effects have been associated with the exposure of fish to na tural, synthetic, and xenobiotic estrogens present in the aquatic environme nt. A novel in vivo test system using transgenic zebrafish has been develop ed to rapidly determine the effects of estrogenic chemicals on critical lif e stages and sensitive target organs in the fish. In the transgenic zebrafi sh, an estrogen binding sequence linked to a TATA box and luciferase report er gene was stably introduced. Binding of a substance to endogenous estroge n receptors (ER) and the subsequent transactivation of the ER result in luc iferase gene induction th at is easily measured in tissue lysates. Exposure to estradiol (E2) during juvenile stages of the transgenic zebrafish revea led the period of gonad differentiation to be the most responsive early lif e stage. In adult male transgenic zebrafish, the testis was the most sensit ive and responsive target tissue to estrogens. Partial sequences of zebrafi sh estrogen receptor subtypes alpha and beta were cloned for the first time and were found to he differentially expressed in developing fish and tissu es of adult male zebrafish. The transgenic zebrafish assay is a promising n ew tool to rapidly determine the estrogenic potency of chemicals in vivo.