Primary activation of the vitellogenin gene in the rooster

Vitellogenin, the precursor of egg yolk phosphoproteins, is synthesized in the liver of the laying hen but is not normally synthesized by roosters. Administration of 17β-estradiol to roosters induces the synthesis of large amounts of this protein and its messenger RNA. We have purified vitellogenin messenger RNA from the livers of estrogen-treated roosters and have characterized it as follows: it is capable of directing the synthesis of the full sized vitellogenin polypeptide [M(r)=240,000] in a cell-free translation system derived from wheat germ; its molecular weight, determined by both agarose gel electrophoresis under fully denaturing conditions and by electron microscopy, is 2.3 to 2.35 x 10⁶, which is approximately 10% (600 nucleotides) longer than is required to encode the vitellogenin polypeptide; and complementary DNA synthesized from the purified messenger RNA hybridizes to its template with the kinetics expected for a single species the size of vitellogenin messenger RNA. We have used vitellogenin complementary DNA to quantitate vitellogenin messenger RNA in the livers of normal and estrogen-treated roosters, and have found that following primary treatment of the rooster with estrogen the level of this messenger RNA rises from 0-5 molecule(s) per cell to approximately 5000 molecules per cell. The results reported here support a model in which primary hormonal induction of vitellogenin synthesis involves activation of a dormant gene in a fully differentiated and metabolically active cell.