Biological and Biomedical Sciences, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4 0BA, UK.
Anal Bioanal Chem. 2010 Jan;396(2):625-30. doi: 10.1007/s00216-009-3112-2. Epub 2009 Sep 30.
Environmental oestrogens are responsible for adverse effects in fish that affect reproduction. Availability of model fish to study the differential effects of endogenous and exogenous oestrogens and to test for oestrogenic activity of chemicals would be advantageous. Zebrafish could provide such a model, but the organisation and expression of vitellogenins (VTGs) and oestrogen receptors (ERs) are not completely understood. VTGs are synthesised in the liver and provide a sensitive biomarker of oestrogenic activity since they are thought to be under the regulation of the ER. There are multiple genes for VTGs and an in silico analysis of their distribution in the Zebrafish genome has identified six genes: VTG-1, VTG-2, VTG-4, VTG-5, VTG-7 located on chromosome 22 and VTG-3 on chromosome 11. VTG-specific, quantitative, real-time, reverse-transcriptase polymerase chain reaction assays were developed and used to measure differential expression in the livers of mature male and female zebrafish. Following normalisation in female fish, relative expression of VTG-5 mRNA is highest and is 1.3x, 1.6x and 2x higher than VTG-4, VTG-2 and VTG-1, respectively, while expression of VTG-3 and VTG-7 is very low. Expression of VTGs in male fish was either undetectable or very low (VTG-4 and VTG-5). ERalpha and ERbeta2 were expressed at higher levels than ERbeta1 in females, but only ERbeta2 was expressed in appreciable quantity in males. Expression of ERalpha in males was significant but only at the limit of detection (<0.1% of female fish), while ERbeta1 could not be detected. The very low level of expression of ERalpha in males raises questions about the accepted mechanism of oestrogenic induction of VTG in male fish.
环境雌激素是造成鱼类生殖系统不良反应的元凶。如果有模式鱼类可供研究，那么就能更方便地研究内源性和外源性雌激素的差异作用，并测试化学物质的雌激素活性。斑马鱼就可以提供这样一种模式生物，但卵黄蛋白原（VTG）和雌激素受体（ER）的组织和表达尚未完全清楚。VTG 是在肝脏中合成的，是雌激素活性的敏感生物标志物，因为它们被认为受 ER 调控。VTG 有多个基因，通过对斑马鱼基因组中它们的分布进行计算机分析，已鉴定出 6 个基因：位于第 22 号染色体上的 VTG-1、VTG-2、VTG-4、VTG-5 和 VTG-7，以及位于第 11 号染色体上的 VTG-3。开发了 VTG 特异性、定量、实时、逆转录聚合酶链反应检测方法，并用于测量成熟雌雄斑马鱼肝脏中的差异表达。在雌性鱼类中进行归一化后，VTG-5 mRNA 的相对表达量最高，分别比 VTG-4、VTG-2 和 VTG-1 高 1.3 倍、1.6 倍和 2 倍，而 VTG-3 和 VTG-7 的表达量非常低。雄性鱼类的 VTG 表达要么无法检测到，要么非常低（VTG-4 和 VTG-5）。在雌性鱼类中，ERalpha 和 ERbeta2 的表达水平高于 ERbeta1，但只有 ERbeta2 在雄性鱼类中以可观的量表达。雄性鱼类 ERalpha 的表达量虽然显著，但仅在检测限（<雌性鱼类的 0.1%）以下，而 ERbeta1 则无法检测到。ERalpha 在雄性鱼类中的低水平表达引发了对公认的鱼类中雌激素诱导 VTG 机制的质疑。
