Identification and characterization of estrogen-responsive gene products in the liver of rainbow trout

Abstract

Injection of male rainbow trout with estradiol induced the production of a major serum protein, vitellogenin (VG), of molecular weight (MW) 170 000. This protein is immunoprecipitable by an antiserum raised against lipovitellin from the eggs. Labelling by incubation of liver cubes of estradiol-treated fish with [³⁵S]methionine and analysis of immunospecific products showed incorporation into two polypeptides of MW 170 000 and 160 000. The peptide patterns generated from these two polypeptides by Staphylococcus aureus V8 protease digestion were identical. Cytoplasmic poly(A)⁺ RNA of estradiol-treated male liver directs the synthesis of a polypeptide of 160 000 daltons in the reticulocyte cell-free protein-synthesizing system or in Xenopus oocytes. This polypeptide is chemically, immunologically, and electrophoretically identical to the authentic VG polypeptide of 160 000 daltons. Changes in mRNA populations in the liver of male fish following estradiol treatment were detected on gels and by hybridization. On methylmercuric hydroxide gels, a polyadenylated RNA species of about 6300 nucleotides was found in estradiol-treated fish which was absent from the control fish. Data from R₀t analysis revealed the presence of at least two mRNA sequences of the high frequency class in the RNA of hormone-induced fish and their sizes were determined by Northern blot analysis to be 6300 and 1800 nucleotides, respectively. These observations are consistent with the induction of vitellogenins and at least another estrogen-responsive gene product by estradiol as reported in other egg-laying vertebrates.