Natural variation of the expression pattern of the segmentation gene even-skipped in melanogaster.
Natural variation of the expression pattern of the segmentation gene even-skipped in melanogaster.
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DOI：
10.1016/j.ydbio.2015.06.019
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发表时间：
2015-09-01
影响因子：
2.7
通讯作者：
Reinitz J
中科院分区：
文献类型：
--
作者：
Jiang P;Ludwig MZ;Kreitman M;Reinitz J
渠化性状的进化是进化生物学的一个核心问题。高度保守性状的自然变异可以为它们的进化潜力提供线索。在这里，我们研究了黑腹果蝇胚胎发育的细胞囊胚阶段保守性状even-skip （eve）表达的自然变异。在一个自然种群的3个自交系中定量测定了配对规则基因eve的表达。在原肠胚开始前的50分钟内，其中一株在形成典型的七条纹图案的间隔、幅度和时间上表现出明显的差异。条纹5的振幅和条纹4和条纹5之间的条纹宽度在这条线上都减小了，而条纹3和条纹4之间的条纹距离增加了。在第10期胚胎中，mrna的表达显著增加了第6准段的长度，减少了第8和第9准段的长度。这些变化比之前报道的D. melanogaster和D. pseudoobscura之间的变化要大，这两个物种被认为是在2500万年前从一个共同的祖先分化出来的。该系在knirps的第一个内含子（kni）上有一个罕见的448bp的缺失。这一发现表明，降低的Kni水平导致了eve的异常表达，并且我们确实观察到，与其他两个品系相比，L2在14A周期早期的Kni蛋白水平较低。第三行中的第二行显示出了大约20%的表达水平，而所有7个偶数条纹。这三个系都是可育的，成年后都没有出现分割缺陷，这表明eve表达的早期变异通过发育缓冲机制在发育后期起作用而得到改善。分割途径的通路化可能会减少遗传变异的适应度后果，从而允许具有意想不到的强基因表达表型的突变持续存在。
The evolution of canalized traits is a central question in evolutionary biology. Natural variation in highly conserved traits can provide clues about their evolutionary potential. Here we investigate natural variation in a conserved trait—even-skipped (eve) expression at the cellular blastoderm stage of embryonic development in Drosophila melanogaster. Expression of the pair-rule gene eve was quantitatively measured in three inbred lines derived from a natural population of D. melanogaster. One line showed marked differences in the spacing, amplitude and timing of formation of the characteristic seven-striped pattern over a fifty-minute period prior to the onset of gastrulation. Stripe 5 amplitude and the width of the interstripe between stripes 4 and 5 were both reduced in this line, while the interstripe distance between stripes 3 and 4 was increased. Engrailed expression in stage 10 embryos revealed a statistically significant increase in the length of parasegment 6 and a decrease in the length of parasegments 8 and 9. These changes are larger than those previously reported between D. melanogaster and D. pseudoobscura, two species that are thought to have diverged from a common ancestor over 25 million years ago. This line harbors a rare 448bp deletion in the first intron of knirps (kni). This finding suggested that reduced Kni levels caused the deviant eve expression, and indeed we observed lower levels of Kni protein at early cycle 14A in L2 compared to the other two lines. A second of the three lines displayed an approximately 20% greater level of expression for all seven eve stripes. The three lines are each viable and fertile, and none display a segmentation defect as adults, suggesting that early-acting variation in eve expression is ameliorated by developmental buffering mechanisms acting later in development. Canalization of the segmentation pathway may reduce the fitness consequences of genetic variation, thus allowing the persistence of mutations with unexpectedly strong gene expression phenotypes.