Department of Aquaculture, National Taiwan Ocean University, Keelung 20224, Taiwan; Center of Excellence for the Oceans, National Taiwan Ocean University, Keelung 20224, Taiwan.
Laboratory Biology of Aquatic Organisms and Ecosystems (BOREA), Muséum National d'Histoire Naturelle, CNRS, IRD, Sorbonne Université, Université de Caen Normandie, Université des Antilles, 75231 Paris Cedex 05, France.
Gen Comp Endocrinol. 2019 Sep 15;281:17-29. doi: 10.1016/j.ygcen.2019.05.008. Epub 2019 May 11.
Previous studies revealed an estradiol (E2)-dependent peak in brain activity, including neurosteroidogenesis and neurogenesis in the black porgy during the gonadal differentiation period. The brain-pituitary-gonadotropic axis is a key regulator of reproduction and may also be involved in gonadal differentiation, but its activity and potential role in black porgy during the gonadal differentiation period is still unknown. The present study analyzed the expression of regulatory factors involved in the gonadotropic axis at the time of gonadal differentiation (90, 120, 150 days after hatching [dah]) and subsequent testicular development (180, 210, 300 dah). In agreement with previous studies, expression of brain aromatase cyp19a1b peaked at 120 dah, and this was followed by a gradual increase during testicular development. The expression of gonadotropin subunits increased slightly but not significantly during gonadal differentiation and then increased significantly at 300 dah. In contrast, the expression of brain gnrh1 and pituitary gnrh receptor 1 (gnrhr1) exhibited a pattern with two peaks, the first at 120 dah, during the period of gonadal differentiation, and the second peak during testicular development. Gonad fshr and lhcgr increased during gonadal differentiation period with highest transcript level in prespawning season during testicular development. This suggests that the early activation of brain gnrh1, pituitary gnrhr1 and gths, and gonad gthrs might be involved in the control of gonadal differentiation. E2 treatment increased brain cyp19a1b expression at each sampling time, in agreement with previous studies in black porgy and other teleosts. E2 also significantly stimulated the expression of pituitary gonadotropin subunits at all sampling times, indicating potential E2-mediated steroid feedback. In contrast, no significant effect of E2 was observed on gnrh1. Moreover, treatment of AI or E2 had no statistically significant effect on brain gnrh1 transcription levels during gonadal differentiation. This indicated that the early peak of gnrh1 expression during the gonadal differentiation period is E2-independent and therefore not directly related to the E2-dependent peak in brain neurosteroidogenesis and neurogenesis also occurring during this period in black porgy. Both E2-independent and E2-dependent mechanisms are thus involved in the peak expression of various genes in the brain of black porgy at the time of gonadal differentiation.
先前的研究表明，在性腺分化期，黑鲷的大脑活动包括神经甾体生成和神经发生中存在雌二醇（E2）依赖性峰。脑垂体性腺轴是生殖的关键调节剂，也可能参与性腺分化，但它在性腺分化期的活性及其在黑鲷中的潜在作用尚不清楚。本研究分析了性腺分化期（孵化后 90、120、150 天）和随后睾丸发育（180、210、300 天）时涉及促性腺轴的调节因子的表达。与先前的研究一致，脑芳香化酶 cyp19a1b 的表达在 120 天达到峰值，随后在睾丸发育过程中逐渐增加。促性腺激素亚基的表达在性腺分化过程中略有增加，但不显著，然后在 300 天显著增加。相比之下，脑 gnrh1 和垂体 gnrh 受体 1（gnrhr1）的表达呈双峰模式，第一个峰出现在性腺分化期的 120 天，第二个峰出现在睾丸发育过程中。在性腺分化期，性腺 fshr 和 lhcgr 增加，在睾丸发育过程中，在产卵前阶段转录水平最高。这表明，脑 gnrh1、垂体 gnrhr1 和 gths 以及性腺 gthrs 的早期激活可能参与了性腺分化的控制。E2 处理在每个采样时间都增加了脑 cyp19a1b 的表达，这与黑鲷和其他硬骨鱼的先前研究一致。E2 还显著刺激了垂体促性腺激素亚基在所有采样时间的表达，表明潜在的 E2 介导的类固醇反馈。相比之下，E2 对 gnrh1 没有显著影响。此外，在性腺分化期间，AI 或 E2 处理对脑 gnrh1 转录水平没有统计学上的显著影响。这表明，性腺分化期 gnrh1 表达的早期高峰是 E2 非依赖性的，因此与黑鲷在此期间发生的脑神经甾体生成和神经发生中的 E2 依赖性峰无关。因此，E2 非依赖性和 E2 依赖性机制都参与了黑鲷在性腺分化时大脑中各种基因的高峰表达。
