PDF(Pubmed)
Abstract：
We investigate the contribution of a candidate gene, fiz (fezzik), to complex polygenic adaptation to juvenile malnutrition in Drosophila melanogaster. Experimental populations maintained for >250 generations of experimental evolution to a nutritionally poor larval diet (Selected populations) evolved several-fold lower fiz expression compared to unselected Control populations. Here we show that this divergence in fiz expression is mediated by a cis-regulatory polymorphism. This polymorphism, originally sampled from a natural population in Switzerland, is distinct from a second cis-regulatory SNP previously identified in non-African D. melanogaster populations, implying that two independent cis-regulatory variants promoting high fiz expression segregate in non-African populations. Enzymatic analyses of Fiz protein expressed in E. coli demonstrate that it has ecdysone oxidase activity acting on both ecdysone and 20-hydroxyecdysone. Four of five fiz paralogs annotated to ecdysteroid metabolism also show reduced expression in Selected larvae, implying that malnutrition-driven selection favored general downregulation of ecdysone oxidases. Finally, as an independent test of the role of fiz in poor diet adaptation, we show that fiz knockdown by RNAi results in faster larval growth on the poor diet, but at the cost of greatly reduced survival. These results imply that downregulation of fiz in Selected populations was favored by selection on the nutritionally poor diet because of its role in suppressing growth in response to nutrient shortage. However, they suggest that fiz downregulation is only adaptive in combination with other changes evolved by Selected populations, which ensure that the organism can sustain the faster growth promoted by fiz downregulation.
摘要：
我们调查了一个候选基因的贡献，fiz(fezzik),果蝇对幼年营养不良的复杂多基因适应。与未选择的对照种群相比，维持>250代实验进化为营养差的幼虫饮食（选定种群）的实验种群进化出的fiz表达降低了几倍。在这里，我们表明fiz表达的这种差异是由顺式调节多态性介导的。这种多态性，最初是从瑞士的自然人口中取样的，与先前在非非洲D.melanogaster种群中发现的第二个顺式调节SNP不同，这意味着在非非洲人群中，两个独立的促进高fiz表达的顺式调节变体分离。在大肠杆菌中表达的Fiz蛋白的酶学分析证明其具有作用于蜕皮激素和20-羟基蜕皮激素两者的蜕皮激素氧化酶活性。注释为蜕皮类固醇代谢的五个fiz旁系同源物中的四个在选定的幼虫中也显示出表达降低，这意味着营养不良驱动的选择有利于蜕皮激素氧化酶的普遍下调。最后,作为对fiz在不良饮食适应中的作用的独立测试，我们表明，通过RNAi击倒fiz导致在不良饮食下幼虫生长更快，但以大大降低生存率为代价。这些结果表明，选择营养不良的饮食有利于对选定人群中fiz的下调，因为它在抑制营养不足的生长中具有作用。然而,他们认为fiz下调仅与选定种群进化的其他变化相结合，确保生物体能够维持由fiz下调所促进的更快生长。
