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17ß-estradiol induced vitellogenesis is inhibited by cortisol at the post-transcriptional level in Arctic char (Salvelinus alpinus)
Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology). Department of Marine Science, University of Texas Marine Science Institute, University of Texas, Port Aransas, Texas, USA.
Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Department of Natural Science, Unit of Molecular Biology, Orebro University, Orebro, Sweden.
2004 (English)In: Reproductive Biology and Endocrinology, ISSN 1477-7827, E-ISSN 1477-7827, Vol. 2, no 62, p. 1-10Article in journal (Other academic) Published
Abstract [en]

This study was performed to investigate stress effects on the synthesis of egg yolk precursor, vitellogenin (Vtg) in Arctic char (Salvelinus alpinus). In particular the effect of cortisol (F) was determined since this stress hormone has been suggested to interfere with vitellogenesis and is upregulated during sexual maturation in teleosts. Arctic char Vtg was purified and polyclonal antibodies were produced in order to develop tools to study regulation of vitellogenesis. The Vtg antibodies were used to develop an enzyme-linked immunosorbent assay. The corresponding Vtg cDNA was cloned from a hepatic cDNA library in order to obtain DNA probes to measure Vtg mRNA expression. Analysis of plasma from juvenile Arctic char, of both sexes, exposed to different steroids showed that production of Vtg was induced in a dose dependent fashion by 17β-estradiol (E2), estrone and estriol. Apart from estrogens a high dose of F also upregulated Vtg. In addition, F, progesterone (P) and tamoxifen were tested to determine these compounds ability to modulate E2 induced Vtg synthesis at both the mRNA and protein level. Tamoxifen was found to inhibit E2 induced Vtg mRNA and protein upregulation. P did not alter the Vtg induction while F reduced the Vtg protein levels without affecting the Vtg mRNA levels. Furthermore the inhibition of Vtg protein was found to be dose dependent. Thus, the inhibitory effect of F on Vtg appears to be mediated at the post-transcriptional level.

Place, publisher, year, edition, pages
BioMed Central, 2004. Vol. 2, no 62, p. 1-10
National Category
Cell and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-2988DOI: 10.1186/1477-7827-2-62OAI: oai:DiVA.org:umu-2988DiVA, id: diva2:141400
Funder
Swedish Environmental Protection AgencyThe Kempe FoundationsAvailable from: 2003-11-18 Created: 2003-11-18 Last updated: 2019-01-21Bibliographically approved
In thesis
1. Teleost reproduction: Aspects of Arctic char (Salvelinus alpinus) oocyte growth and maturation
Open this publication in new window or tab >>Teleost reproduction: Aspects of Arctic char (Salvelinus alpinus) oocyte growth and maturation
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In all vertebrate species, reproduction is a hormonally controlled process, important for growth and maturation of gonads and germ cells. Production of functional germ cells is of outmost importance to secure the survival of a species. Fish comprises 50% of the known vertebrates and are found in aquatic habitats all over the world. Even though fish have evolved a wide variety of morphological and physiological characteristics, due to large differences in the living environment, the growth an maturation of germ cells follows the same pattern in all species. In this thesis the focus has been directed on oocyte growth and development in Arctic char (Salvelinus alpinus), and if stress might inflict disturbances on the reproductive systems.

All sexually mature female egg laying vertebrates produces yolky eggs surrounded by an eggshell. Production of yolk and egg shell is under estrogenic control and it is known that production of egg components can be induced in male and juvenile fish by estrogenic substances. Many manmade chemicals have been found to interfere with hormonally controlled processes. Therefore production of the egg yolk precursor, vitellogenin (VTG), and the egg shell components, vitelline envelope proteins (VEP), have been used as biomarkers for estrogenic effect. Exposure to endocrine disrupting substances (EDS) does not only give rise to hormonal effects on the organism, but in addition it also gives rise to an increase in stress hormone, cortisol (F), levels.

It is evident that a wide variety of substances may affect Arctic char oocyte growth and maturation. VTG and VEP production is found to be under dose dependent estrogenic control, but the production was directly affected by F. Under natural condition it has been found that F increases towards ovulation. Even though both VTG and VTG is under estrogenic control, these studies showed that stress lead to a decrease of VTG while the VEP production increased. These effects was only observed on protein levels indicating that a post transcriptional down regulation of VTG production is mediated by F in Arctic char.

In order for an egg to become fertilizatible, it must undergo a maturation phase. This maturation phase is primarily induced by gonadotropins, which in turn induce the production of species specific maturation inducing substances (MIS). To investigate oocyte development in Arctic char a characterization of its MIS receptor was made. The MIS receptor is localized on the oocyte surface and displays a single class of high affinity and low capacity binding sites. The binding moieties displays association and dissociation kinetics typical of steroid membrane receptors.

Even though high specificity for Arctic char MIS was observed, it was found that some EDS bind to the Arctic char oocyte membrane receptor. This suggest that certain EDS might affect oocyte maturation and thereby might alter the reproductive success. Furthermore, it was found that F did not bind to the MIS receptor in Arctic char. It is therefore suggested that oocytes are more sensitive to stress during the growth phase than during maturation

Publisher
p. 45
Keywords
Zoophysiology, Salmonid, oocyte growth, vitellogenin, vitelline envelope protein, stress, cortisol, oocyte maturation, membrane receptor, Zoofysiologi
National Category
Zoology
Research subject
Zoophysiology
Identifiers
urn:nbn:se:umu:diva-157 (URN)91-7305-557-3 (ISBN)
Public defence
2003-12-12, Major Groove, 6L, Norrlands Universitetssjukhus, Umeå, 09:00
Opponent
Supervisors
Available from: 2003-11-18 Created: 2003-11-18 Last updated: 2019-01-24Bibliographically approved

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