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• Ovarian fluid in the three-spined stickleback, Gasterosteus aculeatus

  Chrysoula Roufidou, Bertil Borg.

  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.

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• Vitellogenesis in the three-spined stickleback, Gasterosteus aculeatus, over the spawning cycle and at egg overripening

  Chrysoula Roufidou, Anna Mentor, Bertil Borg.

  Vitellogenesis was studied in the female three-spined stickleback, Gasterosteus aculeatus, a multiple-spawning fish producing several egg batches during the breeding season, over the spawning cycle and at overripening of eggs. For the spawning cycle, the females were sampled when they were ’’ready to spawn’’ and 6, 24, 48, and 72 hours post-spawning (hps). For the overripening of eggs, non-overripe (mature non-ovulated and ovulated) and overripe females were sampled from nature in the breeding season. Liver tissues were collected for relative vitellogenin mRNA levels measurements by real-time qPCR. vitellogenin mRNA was expressed at all time-points over the 3-day spawning cycle and the levels were significantly increased at 24 and 48 hps, a day before ovulation, compared to the ’’ready to spawn’’ and 6 hps females. Changes over the cycle were, however, small. The highest sample point was only 1.4 times higher than the lowest. The vitellogenin mRNA levels were positively correlated with both circulating estradiol and testosterone levels over the cycle. Overripe females had 1.5 times lower vitellogenin mRNA levels than the non-overripe non-ovulated but not than the non-overripe ovulated females. These findings suggest that vitellogenesis is rather continuous over the stickleback spawning cycle, which could be an advantage for a multiple spawner, and that overripening condition reduces vitellogenin production but does not eliminate it.

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• Hormonal changes over the spawning cycle in the female three-spined stickleback, Gasterosteus aculeatus

  2017. Chrysoula Roufidou (et al.). General and Comparative Endocrinology

  Artikel

  Female three-spined sticklebacks are batch spawners laying eggs in a nest built by the male. We sampled female sticklebacks at different time points, when they were ready to spawn and 6, 24, 48 and 72 hours post-spawning (hps) with a male. Following spawning, almost all females (15 out of 19) had ovulated eggs again at Day 3 post-spawning (72hps). At sampling, plasma, brain and pituitaries were collected, and the ovary and liver were weighed. Testosterone (T) and estradiol (E2) were measured by radioimmunoassay. Moreover, the mRNA levels of follicle-stimulating hormone (fsh-β) and luteinizing hormone (lh-β) in the pituitary, and of the gonadotropin-releasing hormones (GnRHs: gnrh2, gnrh3) and kisspeptin (kiss2) and its G protein-coupled receptor (gpr54) in the brain were measured by real-time qPCR. Ovarian weights peaked in “ready to spawn” females, dropped after spawning, before again progressively increasing from 6 to 72hps. Plasma T levels showed peaks at 24 and 48hps and decreased at 72hps, while E2 levels increased already at 6hps and remained at high levels up to 48hps. There was a strong positive correlation between T and E2 levels over the spawning cycle. Pituitary lh-β mRNA levels showed a peak at 48hps, while fsh-β did not change. The neuropeptides and gpr54 did not show any changes. The changes in T and E2 over the stickleback spawning cycle were largely consistent with those found in other multiple-spawning fishes whereas the marked correlation between T and E2 does not support T having other major roles over the cycle than being a precursor for E2.

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