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Teleost reproduction: Aspects of Arctic char (Salvelinus alpinus) oocyte growth and maturation.
Umeå University, Faculty of Medicine, Molecular Biology.
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

Place, publisher, year, edition, pages
2003. , 45 p.
Keyword [en]
Zoophysiology, Salmonid, oocyte growth, vitellogenin, vitelline envelope protein, stress, cortisol, oocyte maturation, membrane receptor
Keyword [sv]
Zoofysiologi
National Category
Zoology
Research subject
Zoophysiology
Identifiers
URN: urn:nbn:se:umu:diva-157ISBN: 91-7305-557-3 (print)OAI: oai:DiVA.org:umu-157DiVA: diva2:141403
Public defence
2003-12-12, Major Groove, 6L, Norrlands Universitetssjukhus, Umeå, 09:00
Opponent
Supervisors
Available from: 2003-11-18 Created: 2003-11-18Bibliographically approved
List of papers
1. Arctic char (Salvelinus alpinus) metallothionein: cDNA sequence, expression, and tissue-specific inhibition of cadmium-mediated metallothionein induction by 17ß-estradiol, 4-OH-PCB 30, and PCB 104.
Open this publication in new window or tab >>Arctic char (Salvelinus alpinus) metallothionein: cDNA sequence, expression, and tissue-specific inhibition of cadmium-mediated metallothionein induction by 17ß-estradiol, 4-OH-PCB 30, and PCB 104.
2000 In: Environ. Tox. Chem, Vol. 19, no 3, 638-645 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2987 (URN)
Available from: 2003-11-18 Created: 2003-11-18Bibliographically approved
2. 17ß-estradiol induced vitellogenesis is inhibited by cortisol at the post-transcriptional level in Arctic char (Salvelinus alpinus).
Open this publication in new window or tab >>17ß-estradiol induced vitellogenesis is inhibited by cortisol at the post-transcriptional level in Arctic char (Salvelinus alpinus).
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-2988 (URN)
Available from: 2003-11-18 Created: 2003-11-18 Last updated: 2010-01-13Bibliographically approved
3. Regulation of Arctic char (Salvelinus alpinus) egg shell proteins and vitellogenin during reproduction and in response to 17β-estradiol and cortisol
Open this publication in new window or tab >>Regulation of Arctic char (Salvelinus alpinus) egg shell proteins and vitellogenin during reproduction and in response to 17β-estradiol and cortisol
2004 (English)In: General and Comparative Endocrinology, ISSN 0016-6480, E-ISSN 1095-6840, Vol. 135, no 3, 276-285 p.Article in journal (Refereed) Published
Abstract [en]

Estrogens induce both vitellogenin (Vtg) and egg shell (zona pellucida; ZP) protein synthesis in salmonids. However, while Vtg is strictly under estrogenic control, recent reports suggest that additional mechanisms are involved in ZP protein synthesis. During sexual maturation both estrogen and glucocorticoid levels increase in the circulation of female fish. As glucocorticoids have been shown to interfere with Vtg induction in fish we investigated whether cortisol (F) had similar effects on ZP regulation. In the present study we determined both the natural variation in Vtg and ZP during an annual reproductive cycle in female Arctic char (Salvelinus alpinus), and the effect of co-treatment of juvenile Arctic char with 17β-estradiol (E2) and F. During sexual maturation the expression of Vtg and ZP correlated to plasma levels of E2 and F. Determination of Vtg and ZP protein levels following co-treatment with E2 and F showed that F antagonized E2 induction of Vtg. However, F was observed to potentiate the expression of ZP protein in the same fish. These results indicate that in Arctic char Vtg and ZP proteins are not regulated by the same mechanisms and suggest that ZP protein expression does not necessarily imply exposure to estrogenic compounds alone, and may thus not be ideally suited as a biomarker of exposure to estrogenic compounds.

Place, publisher, year, edition, pages
Elsevier, 2004
Keyword
Arctic char, Salvelinus alpinus, Reproductive cycle, 17β-Estradiol, Vitelline envelope proteins, Zona pellucida proteins, Vitellogenin, Estrogen receptor, Cortisol
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-2989 (URN)10.1016/j.ygcen.2003.10.004 (DOI)
Available from: 2003-11-18 Created: 2003-11-18 Last updated: 2017-12-14Bibliographically approved
4. Characterization of the 17,20β-dihydroxy-4-pregnen-3-one membrane receptor in Arctic char (Salvelinus alpinus) ovaries and its upregulation during gonadotropin induction of oocyte maturation.
Open this publication in new window or tab >>Characterization of the 17,20β-dihydroxy-4-pregnen-3-one membrane receptor in Arctic char (Salvelinus alpinus) ovaries and its upregulation during gonadotropin induction of oocyte maturation.
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-2990 (URN)
Available from: 2003-11-18 Created: 2003-11-18 Last updated: 2010-01-13Bibliographically approved

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