PARENT SESSION

PH01 Endocrine Disruption
Exhibit Hall
8:00 AM - Thursday, 13 November 2003

(PH005) Effects of 4-tert-pentylphenol on the gene expression of P450 11-hydroxylase in medaka.

Yokota, H¹, Abe, T¹, Nakai, M¹, Murakami, H¹, Eto, C¹, Yakabe, Y¹, ¹ Chemicals Evaluation and Research Institute, Japan

ABSTRACT- Alkylphenols including 4-tert-pentylphenol (4-PP) have been shown to alter sexual differentiation in fish related to their estrogenic properties. However, little work has been done on the molecular mechanism of morphological and gonadal feminization in male fish by estrogenic substances. Cytochrome P450 11-hydroxylase (P450₁₁) is a key steroidogenic enzyme in production of 11-ketotestosterone, which is the predominant androgen in male fish. In this study, we cloned a cDNA encoding medaka (Oryzias latipes) testicular P450₁₁, and then investigated the gene expression of P450₁₁ in the testis of genetically male medaka exposed to 4-PP. The cDNA contains 1,740 nucleotides that encode a protein of 543 amino acids, which shares high homology with those from other fish. COS-7 cells transfected with an expression vector containing the medaka P450₁₁ cDNA open reading frame showed 11-hydroxylating activity in the presence of exogenous testosterone. Analysis of tissue distribution by RT-PCR showed great abundance of P450₁₁ mRNA in testis. In the partial life-cycle exposure with 4-PP, morphologically sex-reversal was observed in XY medaka exposed to 4-PP concentrations of ≥ 238 g/L. Furthermore, exposure to 4-PP completely inhibited P450₁₁ mRNA expression in the gonad of sex-reversed XY fish at 60-day posthatch. This result clearly demonstrates that xeno-estrogen 4-PP have profound effects on testicular steroidogenesis of XY medaka. The decrease in P450₁₁ mRNA, and subsequently inhibition of the synthesis of testicular 11-oxygenated androgens, may be a critical process in the morphological feminization of the genetically male fish exposed to xeno-estrogens.

Key words: Gene expression, Endocrine disruption, Sex differentiation, Estrogens