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Abstract：
It is widely known that reproduction in vertebrates is regulated by the hypothalamus-pituitary-gonadal (HPG) axis. Although the mechanism of the HPG axis has been well documented in mammals, it cannot be always applied to that in non-mammalian species, which is a great disadvantage in understanding reproduction of vertebrates in general. Recently, transgenic and genome editing tools have rapidly been developed in small teleosts, and thus these species are expected to be useful for the understanding of general mechanism of reproduction in vertebrates. One of the major sex steroid hormones in female vertebrates 17β-Estradiol (E2) plays crucial roles in the formation of sexual dimorphism and the HPG axis regulation. In spite of the importance of E2 in reproductive regulation, only a few studies have analyzed blood E2 levels in small teleosts that are easily amenable to genetic manipulation. In the present study, we analyzed blood E2 concentration in medaka and demonstrated that female medaka show diurnal changes in blood E2 concentration. We then examined the best method for manipulating the circulating E2. First, we found that ovariectomy (OVX) drastically removes endogenous E2 in a day in female medaka. We examined different methods for E2 administration and revealed that feeding administration of E2-containing food is the most convenient and physiological method for mimicking the diurnal E2 changes of female medaka. On the other hand, the medaka exposed to E2 containing water showed high blood E2 concentrations, which exceeds those of environmental water, suggesting that E2 may cause bioconcentration.
摘要：
众所周知，脊椎动物的繁殖受下丘脑-垂体-性腺（HPG）轴的调节。尽管HPG轴的机制已经在哺乳动物中得到了很好的证明,它不能总是应用于非哺乳动物物种，这在一般理解脊椎动物的繁殖方面是一个很大的缺点。最近,转基因和基因组编辑工具在小型硬骨鱼中得到了迅速发展，因此，这些物种有望有助于理解脊椎动物的一般繁殖机制。雌性脊椎动物17β-雌二醇（E2）中主要的性类固醇激素之一在性二态的形成和HPG轴的调节中起着至关重要的作用。尽管E2在生殖调节中很重要，只有少数研究分析了易于遗传操作的小型硬骨鱼的血液E2水平。在本研究中,我们分析了medaka中的血液E2浓度，并证明女性medaka显示血液E2浓度的昼夜变化。然后，我们研究了操纵循环E2的最佳方法。首先,我们发现,卵巢切除术(OVX)在一天内可显著去除雌性田鼠的内源性E2.我们研究了E2给药的不同方法，并发现喂食含E2的食物是模仿雌性田鼠昼夜E2变化的最方便和最生理的方法。另一方面,暴露于含有E2的水中的田鼠显示出很高的血液E2浓度，超过环境水，这表明E2可能导致生物富集。
