Regulation of hepatic estrogen receptor isoform mRNA expression in rainbow trout (Oncorhynchus mykiss)

The complete nuclear estrogen receptor family in rainbow trout consists of two subtypes (ERα and ERβ) each of which consists of two isoforms (α1/α2 and β 1/β2). Transcription rate and mRNA stability of ERα1 is affected by 17β-estradiol (E2) but no information on estrogen regulation exists for the other isoforms. The objective of this study was to compare the mRNA expression patterns of the four ER isoforms in the liver of male trout and in immortalized trout hepatocyte lines (RTH-149 and SOB-15) treated with E2 or 17α-ethynylestradiol (EE2) using quantitative RT-PCR. To determine the in vivo dose–response, isogenic male trout were injected intra-peritoneally with 0, 1.5, 15 or 150 μg E2 or an equimolar amount of EE2 and the liver sampled 24 h later. Treatment with either E2 or EE2 significantly (p < 0.05) increased the level of ERα1 mRNA at all doses tested compared to vehicle, while the response of mRNAs for the other three isoforms did not change. The in vitro dose–response was tested by treating both cell lines with 0, 0.1, 1.0 or 10.0 μM E2 for 48 h. In RTH-149 cells, ERα1, ERα2 and ERβ2 mRNAs were significantly higher in cells incubated with 10 μM E2 as compared to cells treated with only vehicle (p < 0.05). In SOB-15 cells, ERα2 and ERβ1 mRNAs were significantly higher in cells incubated with 1.0 μM E2 as compared to cells incubated with only vehicle (p < 0.05). These results support the conclusion that the mRNAs for the four ER isoforms respond differentially to estrogen regulation.