Distinct effects of 4-nonylphenol and estrogen-17 beta on expression of estrogen receptor alpha gene in smolting sockeye salmon

摘要

Xenoestrogens such as 4-nonylphenol (4-NP) have been shown to affect the parr-smolt transformation, but their mechanisms of action are not known. We therefore examined effects of 4-NP and estradiol-17 beta (E2) on expression of estrogen receptor (ER) alpha gene in the liver, gill, pituitary and brain of sockeye salmon to elucidate molecular mechanisms of 4-NP and E2 and developmental differences in response during smolting. Fish were treated twice within a week with 4-NP (15 and 150 mg/kg BW), E2 (2 mg/kg BW) or only vehicle at three stages of smolting, pre-smolting in March, early smolting in April and late smolting in May. The absolute amounts of ER alpha mRNA were determined by real-time PCR. The basal amounts of ER alpha mRNA peaked in April in the liver, gill and pituitary. In March, E2 extensively increased the amounts in the liver, while 4-NP had no effects at this stage. In contrast, 4-NP (but not E2) decreased liver ER alpha mRNA in April. 4-NP also decreased the amount of ER alpha mRNA in the gill in April. In the pituitary, 4-NP increased ER alpha mRNA in March but decreased it in May. There were no significant effects in the brain. Changes in basal ER alpha mRNA observed in this study indicate that estrogen responsiveness of tissues may change during salmon smolting. Furthermore, 4-NP and E2 have different effects on expression of ERa gene in the liver and gill during smolting, and the response is dependent on smolt stage. (c) 2005 Elsevier Inc. All rights reserved.