Expression of gonadotropin subunit genes following 4-nonylphenol exposure in masu salmon: effects on transcript levels and promoter activities via estrogen receptor alpha.

The 4-nonylphenol (NP) group is classified as some of the most potent endocrine disrupting chemicals (EDCs) reported to have estrogenic effects on reproductive endocrine system in vertebrates. In the present study, we investigated the effect of NP on expression of gonadotropin (GTH) subunit genes in masu salmon (Oncorhynchus masou) to clarify pituitary-based reproductive impact by EDCs. Female juvenile fish were injected with NP (a mixture of ring and chain isomers; 10 or 50 mg kg−1 body weight) and maintained for 3 days post-injection. A semi-quantitative reverse transcription–polymerase chain reaction was used to analyze the pituitary GTHα, follicle-stimulating hormone β (FSHβ), and luteinizing hormone β (LHβ), and hepatic vitellogenin (VTG) mRNA levels. A low dose of NP induced the GTHα and LHβ mRNA levels. High dose of NP slightly reduced FSHβ mRNA levels in contrast to increased VTG mRNA levels. In a promoter study, NP (1–10 nM) increased the activities of luciferase reporter gene located downstream of masu salmon GTHα or LHβ 5′-flanking region depending on the estrogen receptor α (ERα) in transiently transfected mammalian cells. In contrast, the luciferase activity of FSHβ was elevated by NP in an ERα-independent manner. These results suggest that GTH subunit gene expression of masu salmon may be affected by EDCs at the transcription level and that the genes are useful markers for pituitary effects of xenoestrogens.