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

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 100ngL^-1 of 17α-ethinylestradiol (EE2) for 3-5weeks, and 800ng estradiol benzoate (EB) for 3weeks (experiment I), and a measured concentration of 20ngL^-1 EE2 for 1-6weeks (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 4weeks of exposure to 100ngL^-1 EE2, 3weeks of exposure to 800ngEB, and 6weeks of exposure to 20ngL^-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.