Vitellogenesis and its hormonal regulation in the Pacific hagfish, Eptatretus stouti L

Abstract

Vitellogenesis and its control by steroid hormones were studied in the Pacific hagfish, Eptatretus stouti. Active incorporation of inorganic 32P into plasma vitellogenin was identified in vitellogenic females following immunoprecipitation by antiserum against whole egg yolk protein. In contrast, males, or sexually immature females, had little or no 32P activity in blood plasma immunoprecipitates. Autoradiography of the Ouchterlony immunodiffusion plates confirmed that the specific vitellogenin precipitin line contained high activity of 32P. Such data indicate also that vitellogenin in hagfish, as in higher oviparous vertebrates, is a phosphorus-rich protein. The 32P radioactivity was detected also in yolk protein from eggs 48 hr following injection of radioactive inorganic phosphate. The incorporation of plasma yolk proteins into ovarian egg yolk appeared to be greater in eggs at later stages of vitellogenesis. Pellets of different steroids were implanted into sexually immature female and male hagfish, or into mature males, for 4 weeks. This was followed by immunodiffusional identification of plasma vitellogenin by immunoprecipitation with anti-hagfish egg yolk serum. Estradiol or estrone were both 100% effective in induction of a vitellogenic female-specific yolk protein; progesterone was partially effective while testosterone or corticosterone were without any effect. It is concluded that the vitellogenin in hagfish, persisting representatives of the most primitive vertebrates, is a phosphorus-rich protein and that its synthesis is inducible by estrogens. The regulation of hepatic vitellogenesis by estrogen thus appears to be a universal phenomenon in oviparous vertebrates from cyclostomes through birds.