Hepatic Vitellogenin Synthesis Research Articles

The condensing action of Mg 2+, hexamminecobalt 3+ and spermidine 3+ on chromatin with gene regions activated by 17-β estradiol

1. 1. Hepatic vitellogenin synthesis was induced by injecting 17-β estradiol into fish. Liver nuclei were incubated with the endonuclease EcoRI at an increasing concentration of Mg 2+ (0.15–1.50mM), hexamminecobalt 3+ or spermidine 3+ (0.10–1.00 mM). Chromatin was separated into a 5000 g supernatant, S-fraction, and pellet fraction. 2. 2. The release of chromatin into the S-fraction was higher for the induced than the control chromatin. Hybridization of the vitellogenin gene retained in the pellet fraction of the controls was unaffected by the individual cations. After activation of the vitellogenin gene, Mg 2+ at its lowest concentration retained a high amount of the vitellogenin gene in the pellet fraction. The level of hybridization decreased by increasing the Mg 2+ concentration. Retention of the gene rose by adding hexamminecobalt 3+ and more so by adding spermidine 3+. 3. 3. The condensing action of spermidine 3+ was extended to the activated vitellogenin gene regions of chromatin.

In vitro induction of vitellogenin synthesis in Rana esculenta: Role of the pituitary

Vitellogenin (VTG), a complex protein, is a precursor of yolk proteins (lipovitellin and phosvitin) in all oviparous vertebrates studied to date. In amphibians, as in other oviparous vertebrates, VTG synthesis is hormonally dependent; estradiol-17β (E 2) is especially important, although in vivo in the frog Rana esculenta the pituitary may be involved in hepatic VTG synthesis and secretion. The present in vitro experiments carried out during the main phases of the annual reproductive cycle of this frog showed that homologous pituitary homogenate (HPH), as well as E 2, stimulated VTG synthesis in male and female livers, although their patterns of VTG secretion showed some differences with respect to the induction time and the rate of VTG secretion. The hepatic response to HPH occurred after a longer time than that of E 2 VTG induction, and no cooperation between HPH and E 2 was found in the VTG synthesizing response. It should be emphasized that during the refractory period (July), hepatic VTG synthesis in males and females could only be induced by HPH. These data demonstrate, for the first time, a direct action of HPH on VTG synthesis in male and female frog livers in all the periods tested; hepatic responsiveness to HPH and E 2 varies with season and sex.

Role of the Corpus Luteum and Progesterone in the Evolution of Vertebrate Viviparity

For the past 25 years we have used a comparative strategy designed to identify anddescribe the endocrine parameters of the oviparous-vivparous transition and subsequent gradual reduction in hepatic yolk protein precursor (vitellogenin) synthesis associated with placental viviparity. Our approach has been to study vertebrate groups in which both oviparous and viviparous modes are common (reptiles, elasmobranchs). We have provided evidence for the control of follicular (granulosa/theca) and luteal steroidogenesis, and the cellular basis of gonadal steroid hormone action on the key target tissues (oviduct, liver). Our results, some of which are summarized below, have led us to suggest that ovarian progesterone (follicular or luteal in origin) has a dual role in the evolution of viviparity: 1. To inhibit myometrial contractions, thus providing a primary condition for egg retention and viviparity. 2. To inhibit estrogen-induced hepatic vitellogenin synthesis as part of both normal oviparous cycles and as a concomitant of placental evolution.

The estrogenic activity of certain phytoestrogens in the siberian sturgeon Acipenser baeri

Various phytoestrogens such as formononetin, daidzein, genistein and equol were synthesized. Their purity was assessed by various analytical techniques including melting point determination, thin-layer chromatography (TLC), infra-red spectra (i.r. spectra), nuclear magnetic resonance ( 1H- and 13C-NMR) and gas chromatography coupled with mass spectrometry (GC-MS). The estrogenic activity of these compounds, as well as biochanin A and coumestrol, was biologically tested by the induction of vitellogenin secretion in yearling sturgeon and compared to the activity of estradiol-17β. Pure daidzein, biochanin A, genistein, equol and coumestrol all had estrogenic activity as assessed by their induction of hepatic synthesis of vitellogenin when administrated intraperitoneally to yearling Siberian sturgeon. Coumestrol seemed to be the most potent compound, inducing the most vitellogenin secretion with the lowest dose administered. Formononetin was inactive when administered by the intraperitoneal route. All the phytoestrogens tested were considerably less potent than estradiol-17β.

Vitellogenin induction by estradiol in channel catfish, Ictalurus punctatus

In oviparous vertebrates estrogens induce hepatic synthesis of vitellogenin (VG), a blood protein sequestered in vitellogenic oocytes and from which lipovitellin (LV) and phosvitin are derived. Our objective was to identify VG in the channel catfish, Ictalurus punctatus. An intraperitoneal injection of estradiol-17β into adult male fish induced a dose-dependent accumulation of a 150 kDa protein (EP) in the plasma. EP was detectable in Coomassie blue-stained polyacrylamide gels within 24 hr after injection of 2 mg hormone/100 g body weight. During the next 4 days, EP increased from 5 to about 25% of the total plasma protein. Electrophoretic mobility, peptide mapping, and immunological crossreactivity showed EP to be indistinguishable from a plasma protein in adult females with vitellogenic ovaries. Two major yolk polypeptides, YP1 (120 kDa) and YP2 (29.6 kDa), were precipitated by (NH 4) 2SO 4 from a yolk protein extract. YP1 but not YP2 reacted with an anti-EP polyclonal antiserum in Western blots. Peptide mapping after proteolysis with trypsin showed YPs 1 and 2 to be unique and revealed structural homologies between YP1 and EP. Liver but not pancreatic explants from an estradiol-treated male synthesized and secreted a [ 35S]methionine-labeled, 150 kDa protein beginning about 2 hr after initial exposure to the label. We tentatively conclude that EP and YP1 represent VG and LV, respectively. YP2 remains unidentified.

Vitellogenin hormonal control in the green frog, Rana esculenta. Interplay between estradiol and pituitary hormones.

1. The effect of estradiol and pituitary hormones on the titre of serum vitellogenin has been studied in Rana esculenta by rocket immunoelectrophoresis. 2. Hepatic synthesis of vitellogenin depends on physiological doses of estradiol. 3. Gonadotrophins enhance the uptake, presumably by acting directly on the oocyte plasma membrane. 4. In addition, our data support direct pituitary intervention on liver synthesis and/or release of vitellogenin. 5. Hormonal response, as evaluated by vitellogenin serum titres, tends to increase from November to July. This could be the expression of a modification, throughout the sexual cycle, of liver sensitivity to the hormones.

Differential responsiveness of avian vitellogenin I and vitellogenin II during primary and secondary stimulation with estrogen

Avian vitellogenin consists of two major species, VTG I and VTG II, which show major differences in structure and immunological properties suggesting that VTG I and VTG II are distinct gene products. During primary stimulation with estrogen, VTG I was found to accumulate in plasma much more slowly than VTG II. At 1 day after hormone treatment VTG I was only 1–3% of VTG II, but by day 5 VTG I increased to approximately 25% of VTG II. Measurements of hepatic vitellogenin synthesis confirmed the slower induction and reduced expression of VTG I. A further difference was noted in the amnestic or memory response to secondary estrogen treatment. Measurements of VTG I and VTG II accumulation and synthesis after primary and secondary estrogen treatment showed that the memory response occurs to a much greater extent for VTG I than VTG II. These differences indicate that the inductions of VTG I and VTG II are not tightly coupled.

Role of hormones in oocyte maturation.

Role of hormones in oocyte maturation.