Identification and estrogen induction of two estrogen receptors (ER) messenger ribonucleic acids in the rainbow trout liver: sequence homology with other ERs.

The estrogen-binding region of the cDNA for chicken ER reveals a mRNA of 3.5 kilobases (kb) in rainbow trout liver. The level of this messenger, which is very low in the liver of naive male animals, can be increased by estrogen stimulation. With this chicken probe, we have isolated a clone from a lambda gt10 trout liver cDNA library. The partial cDNA sequence, which encompasses most of the coding region, shows two domains of striking amino acid homology with human, avian, and Xenopus estrogen receptors (ERs) (DNA binding region: 90%, Hormone binding region: 60%). With this specific probe rainbow trout ER, we detected another messenger (4.5 kb) that is less expressed than the 3.5 kb messenger. The kinetics of stimulation of the two messengers is compared with the kinetics of accumulation of vitellogenin mRNA after E2 administration. This report constitutes the first identification of ER mRNA from a fish.