Preovulatory changes in the levels of three gonadotropin-releasing hormone-encoding messenger ribonucleic acids (mRNAs), gonadotropin β- subunit mRNAs, plasma gonadotropin, and steroids in the female gilthead seabream, Sparus aurata

Yoav Gothilf, Iris Meiri, Abigail Elizur, Yonathan Zohar*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Gilthead seabream females undergo daily cycles of final oocyte maturation (FOM), ovulation, and spawning throughout their spawning season. FOM consists of lipid droplet and yolk granule coalescence, germinal vesicle (GV) migration, and GV breakdown. Plasma maturational gonadotropin (GtH-II) levels fluctuate throughout the day, reaching a peak at 8 h before spawning, when the GV is at the periphery of the oocyte. The preovulatory GtH-II surge is accompanied by an increase in the plasma levels of 17α,20β-dihydroxy-4- pregnen-3-one and estradiol, while testosterone and 17α,20β,21-trihydroxy- 4-pregnen-3-one levels remain unchanged. Concurrent with the preovulatory GtH-II surge, there is an increase in pituitary GtH-II β subunit mRNA levels followed by an increase in GtH-1β mRNA levels. Gilthead seabream brain contains three different forms of GnRH: salmon (s)GnRH, seabream (sb)GnRH, and chicken (c)GnRH-II. All three GnRH-encoding mRNAs fluctuate through-out the day, reaching highest levels 8 h before spawning, concurrent with the preovulatory GtH-II surge. On the basis of these correlations and of the anatomical organization of the three GnRH systems, it is hypothesized that in the daily-spawning gilthead seabream females, preovulatory GtH-II secretion, and probably synthesis, are induced by a surge of sbGnRH secretion. The involvement of the other two GnRH forms, sGnRH and cGnRH-II, in the control of ovulation and spawning is presumed, on the basis of the elevation of their mRNA levels at the time of the preovulatory GtH-II secretion and spawning.

Original languageEnglish
Pages (from-to)1145-1154
Number of pages10
JournalBiology of Reproduction
Volume57
Issue number5
DOIs
StatePublished - Nov 1997
Externally publishedYes

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