Graduate School of Engineering and Science, University of the Ryukyus, Senbaru 1, Nishihara, Okinawa 903-0213, Japan.
Faculty of Science, University of the Ryukyus, Senbaru 1, Nishihara, Okinawa 903-0213, Japan.
Gen Comp Endocrinol. 2019 Oct 1;282:113211. doi: 10.1016/j.ygcen.2019.113211. Epub 2019 Jun 22.
Most groupers (genus Epinephelus) inhabiting tropical and subtropical waters exhibit lunar-related reproductive cycles. Their gametes develop synchronously toward and are released around the species-selected moon phase. Periodical changes in cues from the moon are likely used as zeitgeber, and the hypothalamic-pituitary-gonadal (HPG) axis may be activated after cues are perceived by the sensory organ and transduced as internal signals. The objective of this study was to examine weekly changes in mRNA expression profiles of gonadotropin-releasing hormones (gnrh1 and gnrh2) and the β-subunit of gonadotropins (fshβ and lhβ) during the spawning season (May to June) of the female honeycomb grouper Epinephelus merra, which spawns around the full moon period. When mature females were collected based on the lunar cycle, the gonadosomatic index peaked around the full moon. Ovarian histology revealed that oocytes laden with yolk developed toward the full moon and, subsequently, ovulatory follicles appeared around the last quarter moon, confirming lunar-related spawning with a full moon preference. Real-time quantitative polymerase chain reaction analyses revealed high abundances of fshβ and lhβ toward the first quarter moon, whereas concentrations of gnrh1 and gnrh2 increased around the last quarter moon and the first quarter moon, respectively, suggesting that transcription levels of these hormones fluctuate with the lunar cycle. The measurement of melatonin in the eye around the new moon and the full moon revealed that the ocular melatonin content was higher around the new moon than around the full moon, suggesting that the honeycomb grouper can perceive changes in moonlight. In addition, implantation of an osmotic pump containing melatonin into the body cavity of E. merra reduced the transcription levels of gonadotropins, suggesting that melatonin negatively affects hormonal synthesis at the HPG axis. We concluded that melatonin plays an essential role in transducing periodical changes in moonlight and that decreases in melatonin levels from the new moon to the full moon activate the HPG axis for entrainment of gonadal development and spawning.
大多数栖息在热带和亚热带水域的石斑鱼（Epinephelus 属）表现出与月球相关的生殖周期。它们的配子同步发育，并在物种选择的月圆期前后释放。来自月球的周期性变化的线索可能被用作 Zeitgeber，并且在下丘脑中的垂体-性腺（HPG）轴可能在感觉器官感知线索并将其转导为内部信号后被激活。本研究的目的是检查在雌性蜂巢石斑鱼 Epinephelus merra 的产卵季节（5 月至 6 月）期间，促性腺激素释放激素（gnrh1 和 gnrh2）和促性腺激素的β亚基（fshβ和 lhβ）的 mRNA 表达谱的每周变化，该产卵期围绕满月期进行。当根据月相收集成熟的雌性时，性腺指数在满月时达到峰值。卵巢组织学显示，富含卵黄的卵母细胞向满月发育，随后在半月月相时出现排卵滤泡，证实了与满月相关的产卵，并偏爱满月。实时定量聚合酶链反应分析显示，在新月时 fshβ和 lhβ的丰度较高，而 gnrh1 和 gnrh2 的浓度分别在半月月相和新月月相时增加，表明这些激素的转录水平随月相波动。在新月和满月时测量眼睛中的褪黑素发现，眼睛中的褪黑素含量在新月时高于满月时，表明蜂巢石斑鱼可以感知月光的变化。此外，将含有褪黑素的渗透泵植入 E. merra 的体腔中会降低促性腺激素的转录水平，表明褪黑素会对 HPG 轴的激素合成产生负面影响。我们得出结论，褪黑素在将月光的周期性变化转化中起着至关重要的作用，并且从新月到满月褪黑素水平的降低会激活 HPG 轴以进行性腺发育和产卵的同步化。
