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Ovarian fluid in the three-spined stickleback, Gasterosteus aculeatus: effects of egg overripening and sex steroid treatment
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0003-0022-0698
Stockholm University, Faculty of Science, Department of Zoology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In most fishes, including the three-spined stickleback, Gasterosteus aculeatus, the ovulated eggs are surrounded by the ovarian fluid (OF). OF is probably secreted by the ovarian lumen epithelium under stimulation by sex steroids. OF is believed to have several biological functions, including the maintance of the egg viability after ovulation. Female sticklebacks produce eggs in batches, and if spawning or spontaneous dropping of the eggs does not happen, they can become overripe. In the present study, OF properties were studied in overripe and non-overripe ovulated female sticklebacks, and the effects of testosterone (T), estradiol (E2), 17,20β-dihydroxypregn-4-en-3-one (17,20β-P) and progesterone (P4) on OF properties in females that were implanted with Silastic capsules into the abdominal cavity, after having spawned naturally were investigated. Overripe females had a diminished amount of OF, that had a higher percentage dry weight, higher protein levels and lower viscocity compared to OF from non-overripe ovulated females. T delayed the next ovulation. Both T and 17,20β-P induced a significant increase of OF amount. However, the OF protein concentration was significantly increased only in 17,20β-P females. 1-D SDS-PAGE analysis showed that OF contains several proteins, with high individual variability but with no consistent differences between groups. Some of the OF proteins appeared to correspond to proteins from the eggs. The results suggest that secretion of OF may be under the control of 17,20β-P and that changes in its properties are related to the overripening of eggs.

Keyword [en]
ovarian fluid, overripening, sex steroids, stickleback, teleosts
National Category
Biological Sciences
Research subject
Functional Zoomorphology
Identifiers
URN: urn:nbn:se:su:diva-143276OAI: oai:DiVA.org:su-143276DiVA: diva2:1097592
Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2017-08-03Bibliographically approved
In thesis
1. Reproductive physiology of the female three-spined stickleback, Gasterosteus aculeatus
Open this publication in new window or tab >>Reproductive physiology of the female three-spined stickleback, Gasterosteus aculeatus
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Reproduction in vertebrates, including fishes, is under control of the brain-pituitary-gonad (BPG) axis. The female three-spined stickleback, Gasterosteus aculeatus, produces egg clutches at intervals of a few days and spawns them in a nest built by male. Following ovulation, eggs are stored in the ovarian cavity surrounded by the ovarian fluid (OF). If spawning or spontaneous release do not occur, the eggs can undergo overripening, a phenomenon occurring both in nature and captivity.

In this PhD thesis, the changes of reproductive hormones and vitellogenesis were studied at overripening of eggs and over the natural spawning cycle. OF properties were also examined at overripening of eggs and after treatment with sex steroids.

Plasma levels of steroids: testosterone (T), estradiol (E2), 17,20β-dihydroxypregn-4-en-3-one (17,20β-P) and 17,20β,21-trihydroxypregn-4-en-3-one (17,20β,21-P) were measured by radioimmunoassay, and relative mRNA levels of the pituitary gonadotropins (fsh-β/lh-β), brain gonadotropin-releasing hormones (gnrh2/gnrh3) and kisspeptin and its receptor (kiss2/gpr54) by qPCR. Overripening of eggs was accompanied with a significant reduction in most of endocrine parameters of BPG axis (T, E2, 17,20β-P; lh-β; kiss2, gpr54). Low level of hormones could be advantageous for the overripe egg-bound females, since this would reduce further ovulations giving higher chances to survive and reproduce again. Over the 3-day spawning cycle, T and E2 were highly correlated, showed cyclicity with low levels at ovulation and increasing from 24 and 6 hours post-spawning (hps), respectively. Spawning may give rise to this increase as these rises did not occur if release of the eggs does not happen (overripe females). A peak at pituitary lh-β mRNA levels appeared 48 hps, a day before the next ovulation. No significant changes were found for the other studied hormones.

Vitellogenesis was studied by measurement of the vitellogenin mRNA levels in the liver by qPCR. The levels were highest at 24 and 48 hps and were positively correlated to both E2 and T over the cycle. However, changes were small suggesting a rather continuous vitellogenesis over the stickleback spawning cycle which could be an advantage for a multiple spawner with a limited spawning season. Overripening reduced vitellogenin mRNA levels but did not abolish it.

OF amount was diminished in overripe females and had a lower viscocity but higher dry weight and protein levels than in non-overripe ovulated females, suggesting that changes in OF properties are related to the egg overripening. The effects of steroids were studied using Silastic capsules. T and 17,20β-P induced an increase of OF amount, but protein levels were only increased in 17,20β-P-treated females, proposing a role of this steroid in the control of OF secretion. 1-D SDS-PAGE showed that OF contained several proteins, some of them came from eggs, but no consistent differences between groups.

Concluding, the knowledge of the reproductive physiological changes is important for understanding their essential roles in the production of viable eggs in this species but also in the reproductive physiology of female fishes in general.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2017. 65 p.
Keyword
overripening of eggs, spawning cycle, brain-pituitary-gonad (BPG) axis, vitellogenin, ovarian fluid, sex steroids, reproduction, three-spined stickleback, Gasterosteus aculeatus, fish
National Category
Biological Sciences Zoology Other Biological Topics
Research subject
Functional Zoomorphology
Identifiers
urn:nbn:se:su:diva-143279 (URN)978-91-7649-854-5 (ISBN)978-91-7649-855-2 (ISBN)
Public defence
2017-09-08, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2017-08-16 Created: 2017-05-22 Last updated: 2017-08-14Bibliographically approved

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