PubMed Health⌕ Search

Biomedical subjects

G Flouriot

Publications and source records attributed to G Flouriot.

25 records · Page 2Linked to original sources
PubMed1997

Differential regulation of two genes implicated in fish reproduction: vitellogenin and estrogen receptor genes.

In rainbow trout as well as in other species, variability of estrogen receptor (ER) gene expression according to the cell type and the physiological state reflects a differential cell and gene sensitivity to estrogen. We previously demonstrated that expression of the rainbow trout estrogen receptor (rtER) and vitellogenin (Vg) genes were induced differently by estrogens in rainbow trout liver. Therefore, these two genes offered a suitable model to study the influence of ER concentration on gene transcriptional activities. In the present study we show that the transcription rate of rtER and Vg genes during an estrogenic treatment are affected differently by variation of cellular ER concentration. We demonstrate that rtER gene exhibits a low threshold response to loaded estrogen receptor, and increasing ER amounts do not affect the transcriptional response of this gene during an estrogenic stimulation. On the contrary, Vg gene expression requires the presence of a higher loaded estrogen receptor level to be induced, and its transcriptional response is directly proportional to the amount of synthesised ER.

Animals↗
PubMed1996

Transcriptional and post-transcriptional regulation of rainbow trout estrogen receptor and vitellogenin gene expression.

Estrogen receptor (ER) and vitellogenin (Vg) gene expression are strongly up-regulated by estrogens in rainbow trout liver. In this paper, we have used primary cultured hepatocytes to examine the mechanisms implicated in estrogen regulation of ER and Vg gene expression. Treatment of hepatocytes with 1 microM estradiol (E2) led to a rapid increase in ER and mRNA level (15 fold) followed by Vg and mRNA induction. Transcription rate and mRNA half-life determination carried out in the presence or absence of E2, demonstrated that E2 increases both the ER and Vg gene transcriptional activity and mRNA stability (ca. 3 fold). The effect of E2 was inhibited by an excess of antiestrogen, showing that E2-stimulation of ER and mRNA level is mediated by the estrogen receptor. Our data show that ER and Vg genes have different hormonal sensitivity. In fact, the Vg gene required a higher concentration of E2 to be stimulated compared to the ER gene. Examination of the mechanisms involved in post-transcriptional regulation of ER mRNA showed that the setting up and maintenance of this regulation process implies that estrogen receptor and the general translational activity within the cells, suggesting that ER mRNA depends on the synthesis of an estrogen-dependent protein. However, the cis and trans elements involved in E2-stabilization process remain to be identified.

Animals↗
PubMed1995

Influence of xenobiotics on rainbow trout liver estrogen receptor and vitellogenin gene expression.

Rainbow trout hepatocyte primary culture was used to test the influence of some xenobiotics on the expression of two genes implicated in reproduction, those for the estrogen implicated in reproduction, those for the estrogen receptor (ER) and vitellogenin (Vg). We showed that chlordecone, nonylphenol, a polychlorobiphenol (PCB) mixture (Aroclor 1245) and lindane were able to induce ER and Vg mRNA accumulation. Antiestrogens, 4-hydroxytamoxifen and ICI 164,384, prevented the effects of the xenobiotics, indicating that the induction of gene expression is mediated by the ER. Among these four xenobiotics, only chlordecone and nonylphenol were able to displace the binding of [3H]estradiol to ER-enriched COS-1 extracts, and to activate an estrogen-dependent reporter gene (ERE-TK-CAT) cotransfected with an expression vector containing ER cDNA. The results suggest that chlordecone and nonylphenol are direct inducers of rainbow trout ER and Vg gene expression, whereas PCBs and lindane act through their hepatic metabolites. Moreover, pentachlorophenol acts as an antagonist of the induction by estradiol of rainbow trout ER and Vg gene expression.

Actins↗
PubMed1993

Vitellogenin synthesis in cultured hepatocytes; an in vitro test for the estrogenic potency of chemicals.

We describe here an in vitro technique to assess the estrogenic activity of chemicals. This technique is based on rainbow trout hepatocytes incubated in a basic medium free of any additional growth factors or estrogenic chemicals and uses the production of vitellogenin (VTG) as a marker for the estrogenic potency of the compounds tested. The system allows at least some of the metabolic transformations which are undertaken by the liver cells in vivo and could therefore be used for xenobiotic compounds which exhibit estrogenic activities after liver metabolic transformation. A dose-response curve was always consistently obtained using estradiol-17 beta (E2), with a mid point at around 100 nM E2 and a maximum response at around 1000 nM. Established estrogens such as 17 a 1 ethynylestradiol (EE2) or diethylstilboestrol (DES) were also tested. EE2 appeared to be equipotent with E2 and DES slightly less potent. E2 conjugates were, perhaps surprisingly, also very potent. Estradiol-3-sulfate was equipotent with E2 and estradiol-17 beta-glucuronide approx. 10% as potent. Other steroids such as androgens and progesterone, though active in the bioassay, were 3 orders of magnitude less potent than E2. Of the various steroids tested, only cortisol, at concentrations up to 50 microM, was completely inactive. Six different phytoestrogens were tested in the assay. All were weakly estrogenic, possessing approximately one thousandth the potency of E2 (they were as potent as the androgens and progesterone). All six phytoestrogens, as well as the androgens and progesterone, were tested in the presence of tamoxifen. In all cases tamoxifen reduced the production of VTG significantly, demonstrating that the estrogenic action of all of these compounds was most likely mediated by the E2 receptor. The potencies determined here may not reflect the situation in vivo but can provide complementary results about the activity of chemicals which need an hepatic metabolization to be estrogenic. Hepatocyte cultures would profitably be developed in other species to sustain these results.

Animals↗
PubMed1993

Monolayer and aggregate cultures of rainbow trout hepatocytes: long-term and stable liver-specific expression in aggregates.

An aggregate culture system for rainbow trout hepatocytes was developed to study liver-specific mRNA expression. Maintenance of differentiated functions and morphology of hepatocytes were examined using both monolayer and aggregate systems. The rainbow trout estrogen receptor and vitellogenin genes were induced by estradiol and their mRNAs used as markers of cell differentiation during cell culture. In monolayer culture, rainbow trout hepatocytes established very few cell-cell contacts in minimal media. The use of more complete media promotes cell-cell contacts and cell islet formation. Hepatocyte response to estradiol stimulation was generally lower than in vivo but a correlation between the degree of cellular organization and the intensity of the hormonal response was observed. However, in this system hepatocytes progressively lost their specific hormonal response between 5 and 10 days. In aggregates with DMEM/F12 and Ultroser SF, cell-cell contacts were maximized and stabilized during at least one month. The levels of rainbow trout estrogen receptor and vitellogenin mRNAs induced by estradiol were stable and maintained at a level comparable to in vivo levels; vitellogenin synthesis and secretion remained fully functional for the duration of the culture.

Actins↗