Jeng Shan-Ru, Yueh Wen-Shiun, Pen Yi-Ting, Lee Yan-Horn, Chen Guan-Ru, Dufour Sylvie, Chang Ching-Fong
Department of Aquaculture, National Kaohsiung Marine University, Kaohsiung 811, Taiwan.
Department of Aquaculture, National Kaohsiung Marine University, Kaohsiung 811, Taiwan.
Gen Comp Endocrinol. 2014 Sep 15;206:8-15. doi: 10.1016/j.ygcen.2014.08.001. Epub 2014 Aug 12.
Silvering is a prepubertal metamorphosis preparing the eel to the oceanic reproductive migration. A moderate gonad development occurs during this metamorphosis from the sedentary yellow stage to the migratory silver stage. The aim of this study was to elucidate the molecular aspects of various endocrine parameters of BPG axis at different ovarian developmental stages in wild yellow and silver female Japanese eels. The GSI of the sampled female eels ranged between 0.18 and 2.3%, corresponding to yellow, pre-silver and silver stages. Gonad histology showed changes from previtellogenic oocytes in yellow eels to early vitellogenic oocytes in silver eels. Both serum E2 and T concentrations significantly increased with ovarian development indicating a significant activation of steroidogenesis during silvering. In agreement with previous studies, significant increases in pituitary gonadotropin beta subunits FSH-β and LH-β transcripts were also measured by qPCR, supporting that the activation of pituitary gonadotropin expression is likely responsible for the significant ovarian development observed during silvering. We investigated for the first time the possible brain neuroendocrine mechanisms involved in the activation of the pituitary gonadotropic function during silvering. By analyzing the expression of genes representative of the stimulatory GnRH control and the inhibitory dopaminergic control. The transcript levels of mGnRH and the three GnRH receptors did not change in the brain and pituitary between yellow and silver stages, suggesting that gene expression of the GnRH system is not significantly activated during silvering. The brain transcript levels of tyrosine hydroxylase, limiting enzyme of DA synthesis did not change during silvering, indicating that the DA synthesis activity was maintained. In contrast, a significant decrease in DA-D2B receptor expression in the forebrain and pituitary was observed, with no changes in DA-D2A receptor. The decrease in the pituitary expression of DA-D2BR during silvering would allow a reduced inhibitory effect of DA. We may raise the hypothesis that this regulation of D2BR gene expression is one of the neuroendocrine mechanisms involved in the slight activation of the pituitary gonadotropin and gonadal activity that occur at silvering.
银化是青春期前的一种变态过程，使鳗鱼为海洋生殖洄游做好准备。在从定居的黄色阶段到洄游的银色阶段的这种变态过程中，性腺会适度发育。本研究的目的是阐明野生黄色和银色雌性日本鳗鱼在不同卵巢发育阶段BPG轴各种内分泌参数的分子层面情况。所采样的雌性鳗鱼的性腺指数在0.18%至2.3%之间，分别对应黄色、前银色和银色阶段。性腺组织学显示，从黄色鳗鱼的初级卵母细胞到银色鳗鱼的早期卵黄生成卵母细胞发生了变化。血清E2和T浓度均随着卵巢发育而显著增加，表明银化过程中类固醇生成被显著激活。与先前的研究一致，通过qPCR也检测到垂体促性腺激素β亚基FSH-β和LH-β转录本显著增加，支持垂体促性腺激素表达的激活可能是银化过程中观察到的性腺显著发育的原因。我们首次研究了银化过程中垂体促性腺功能激活可能涉及的脑内神经内分泌机制。通过分析代表刺激性GnRH控制和抑制性多巴胺能控制的基因表达。mGnRH和三种GnRH受体的转录水平在黄色和银色阶段的脑和垂体中没有变化，表明GnRH系统的基因表达在银化过程中没有被显著激活。酪氨酸羟化酶（DA合成的限速酶）的脑转录水平在银化过程中没有变化，表明DA合成活性得以维持。相反，在前脑和垂体中观察到DA-D2B受体表达显著下降，而DA-D2A受体没有变化。银化过程中垂体DA-D2BR表达的下降将使DA的抑制作用减弱。我们可以提出这样的假设，即D2BR基因表达的这种调节是参与银化过程中垂体促性腺激素和性腺活动轻微激活的神经内分泌机制之一。
