Boston University Department of Biology, 5 Cummington Mall, Boston, MA 02215, USA.
US Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, RI 02882, USA.
Aquat Toxicol. 2015 Feb;159:184-97. doi: 10.1016/j.aquatox.2014.12.012. Epub 2014 Dec 18.
To test the hypothesis that alternative splicing could be an adaptive mechanism for populations subject to multi-generational estrogenic exposures, we compared estrogen receptor alpha (ERα) splicing variants in two populations of killifish (Fundulus heteroclitus): one resident in an estrogenic polluted environment (New Bedford Harbor, NBH, MA, USA) and one from a relatively uncontaminated reference site (Scorton Creek, SC, MA, USA). In total we identified 19 ERα variants, each with deletions of one or more coding exons. Four of the variants with potential functional relevance were analyzed by qPCR to test for population differences in expression by tissue type, site, sex, seasonal reproductive status and estrogen treatment. Significantly, a 5'-truncated short form variant (ERαS) was highly expressed in liver and ovary, and was associated with seasonal reproductive activity in SC but not NBH fish. Both ERαS and the full-length long variant (ERαL) were estrogen-inducible (ERαS>ERαL) but the induction response was lower in NBH than in SC fish. In contrast, NBH killifish were hyper-responsive to estrogen as measured by expression of two other estrogen responsive genes: vitellogenin (Vtg) and aromatase B (AroB). Most strikingly, two ERα deletion variants (Δ6 and Δ6-8), lacking ligand binding and activation function domains, were identified in a subset of NBH fish, where they were associated with reduced responsiveness to estrogen treatment. Together, these results support the hypothesis that alternative splicing of the esr1 gene of killifish could be an autoregulatory mechanism by which estrogen modulates the differential expression of ERα, and suggests a novel and adaptive mechanistic response to xenoestrogenic exposure.
为了检验这样一个假说，即可变剪接可能是一个适应机制，使受多代雌激素暴露的种群受益，我们比较了两种花鲈（Fundulus heteroclitus）种群中的雌激素受体 α（ERα）剪接变体：一种生活在雌激素污染的环境中（美国马萨诸塞州新贝德福德港，NBH），另一种来自相对未受污染的参照点（马萨诸塞州斯考顿溪，SC）。我们总共鉴定了 19 种 ERα 变体，每种变体都缺失了一个或多个编码外显子。我们通过 qPCR 分析了四个具有潜在功能相关性的变体，以测试组织类型、地点、性别、季节性生殖状态和雌激素处理对种群表达的差异。重要的是，一种 5'-截断的短型变体（ERαS）在肝脏和卵巢中高表达，与 SC 而非 NBH 鱼类的季节性生殖活动有关。ERαS 和全长长型变体（ERαL）都可被雌激素诱导（ERαS>ERαL），但 NBH 鱼的诱导反应低于 SC 鱼。相比之下，NBH 花鲈对雌激素的反应更高，这可以通过两个其他雌激素反应基因的表达来衡量：卵黄蛋白原（Vtg）和芳香酶 B（AroB）。最引人注目的是，在一部分 NBH 鱼中发现了两种 ERα 缺失变体（Δ6 和 Δ6-8），它们缺乏配体结合和激活功能域，与对雌激素处理的反应降低有关。这些结果共同支持了这样一个假说，即花鲈 esr1 基因的可变剪接可能是雌激素调节 ERα 差异表达的一种自身调节机制，并提示了一种针对外源性雌激素暴露的新的适应性机制反应。
