Gene expression profiles in the testis associated with testis-ova in adult Japanese medaka (Oryzias latipes) exposed to 17α-ethinylestradiol

Abstract The occurrence of oocytes in the testis (testis–ova) of several fish species is often associated with exposure of estrogenic chemicals. However, induction mechanisms of the testis–ova remain to be elucidated. To develop marker genes for detecting testis–ova in the testis, adult male medaka were exposed to nominal concentration of 100 ng L −1 of 17α-ethinylestradiol (EE2) for 3–5 weeks, and 800 ng estradiol benzoate (EB) for 3 weeks (experiment I), and a measured concentration of 20 ng L −1 EE2 for 1–6 weeks (experiment II). Histological analysis was performed for the testis, and microarray analyses were performed for the testis, liver and brain. Microarray analysis in the estrogen-exposed medaka liver showed vitellogenin and choriogenin as estrogen responsive genes. Testis–ova were induced in the testis after 4 weeks of exposure to 100 ng L −1 EE2, 3 weeks of exposure to 800 ng EB, and 6 weeks of exposure to 20 ng L −1 EE2. Microarray analysis of estrogen-exposed testes revealed up-regulation of genes related to zona pellucida (ZP) and the oocytes marker gene, 42Sp50. Using quantitative RT-PCR we confirmed that Zpc5 gene can be used as a marker for the detection of testis–ova in male medaka.