Vitellogenin gene transcription is not under strict estrogen control in winter flounder.

Although it is almost axiomatic that vitellogenin gene expression is under exclusive control of estrogen in oviparous animals, our results with winter flounder demonstrate that vitellogenin gene transcription in females can continue independent of estradiol. Winter flounder were hypophysectomized in January, i.e. several months after the onset of vitellogenesis. Thirty or more days after hypophysectomy, all fish had negligible levels of estradiol in the serum, and yet vitellogenin gene transcription was quite active in the liver. Our results also suggest that a pituitary factor may be involved in the normal repression of the vitellogenin gene.