PH01 Endocrine Disruption
Exhibit Hall
8:00 AM - Thursday, 13 November 2003
(PH006) Medaka partial life-cycle test for 4-tert-pentylphenol based on sex-determining gene.
Abe, T1, Seki, M1, Yokota, H1, Maeda, M1, Inamata, C1, Kobayashi, K1, 1 Chemicals Evaluation and Research Institute, Japan (CERI), Kurume, Fukuoka, Japan
ABSTRACT- We have developed a partial life-cycle test (PLC) for detecting endocrine disrupting effects of chemicals with medaka from embryos to early adult, using a sex-determining gene (DMY). The DMY was recently isolated a specific gene, which is strongly related to Y-chromosome of medaka. To verify the applicability of the DMY to the PLC, we evaluated estrogenic effects of 4-tert-pentylphenol (4-PP), which is one of the OECD reference compounds of weak estrogen. We exposed medaka to 4-PP at 62.2, 121, 238, 413 and 783 
g/L from fertilized eggs to 60-d posthatch under a flow-through condition and evaluated its endocrine disrupting effects based on the genetic sex. At 60-d posthatch, gonadal histology and hepatic vitellogenin (VTG) induction were assessed in 20 fish from each treatment group. Medaka were also individually investigated for determining the genetic sex by DMY. In genotypic males (XY), induction of testis-ova was observed in the fish exposed to 4-PP at ≥ 121 g/L. Moreover, the XY males also showed significantly high hepatic VTG at ≥ 238 g/L of 4-PP (p<0.01). In genotypic females (XX), no effects were observed on gonadal histology, but the hepatic VTG levels in fish exposed to ≥ 121 g/L 4-PP were significantly higher than those of controls (p<0.01). Thus, this PLC based on DMY allows us to confirm the formation of testis-ova in genotypic males exposed to estrogenic chemicals, although it was not clear in previous tests that fish having testis-ova were genetically male.
Key words: partial life-cycle test, medaka, vitellogenin, sex-determining gene