UP-REGULATION OF ESTROGEN-RECEPTOR MESSENGER-RNA AND ESTROGEN-RECEPTOR ACTIVITY BY ESTRADIOL IN LIVER OF RAINBOW-TROUT AND OTHER TELEOSTEANFISH

Injection of estradiol (E(2)) into immature rainbow trout resulted in the induction of the hepatic vitellogenin gene mediated by the nuclear estrogen receptor (ER). Liver ER mRNA rose markedly on E(2) treatment in three groups of trout kept at different temperatures. Only in the group kept at 4 degrees C did the total cellular ER, as measured by [H -3]estradiol-binding activity in nuclear and cytosol fractions, parall el the ER mRNA level. In fish kept at 9 degrees C and 15 degrees C, th e ratio of total ER activity to ER mRNA fell during chronic E(2) treat ment, probably reflecting translational or post translational control mechanisms. Upregulation of ER mRNA also occurred in sea raven, sculpi n, winter flounder, and Atlantic salmon after E(2) treatment. Intrahep atic ER activity rose proportionately in Atlantic salmon kept at 6-9 d egrees C but not in sea raven, sculpin, or flounder. We conclude that the regulation of ER expression in teleosts is complex and includes tr anscriptional, translational, and posttranslational elements and is in fluenced by environmental temperature. Copyright (C) 1996 Elsevier Sci ence Inc.