Positive Selection Underlies Faster-Z Evolution of Gene Expression in Birds.
Positive Selection Underlies Faster-Z Evolution of Gene Expression in Birds.
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DOI：
10.1093/molbev/msv138
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发表时间：
2015-10
影响因子：
10.7
通讯作者：
Mank JE
中科院分区：
文献类型：
--
作者：
Dean R;Harrison PW;Wright AE;Zimmer F;Mank JE
性染色体上基因的进化速率高于常染色体（Fast-X或Fast-Z进化），这可能是由于异配子性别中的正选择，也可能是由于相对有效群体大小减少的非适应性后果。最近在鸟类中的研究表明，编码序列的Fast-Z主要是由于相对有效种群大小减少而导致的宽松的纯化选择。然而，基因序列和基因表达往往受到不同的进化压力;因此，我们使用来自多个鸟类物种的下一代RNA测序数据测试了Fast-Z的基因表达。与Fast-Z在编码序列中的研究类似，我们在基因表达中恢复了Fast-Z的清晰特征;然而，与编码序列相反，我们的数据表明Fast-Z在表达中是由于主要在女性中起作用的正选择。在基因表达在性别之间高度相关的索马中，我们在两种性别中都检测到Fast-Z，尽管在女性中的比率更高，这表明女性中许多积极选择的表达变化也在男性中表达。在性腺中，表达的性间相关性要低得多，我们检测到Fast-Z的女性基因表达，但至关重要的是，不是男性。这表明大量的表达变异在性腺内的影响是性别特异性的。综上所述，我们的研究结果表明，基因表达的快速Z进化是正选择作用于异配子性别中的隐性有益等位基因的产物。更广泛地说，我们的分析表明，Z染色体基因表达的适应潜力可能比基因序列大得多，这对性染色体在物种形成和性选择中的作用具有重要意义。
The elevated rate of evolution for genes on sex chromosomes compared with autosomes (Fast-X or Fast-Z evolution) can result either from positive selection in the heterogametic sex or from nonadaptive consequences of reduced relative effective population size. Recent work in birds suggests that Fast-Z of coding sequence is primarily due to relaxed purifying selection resulting from reduced relative effective population size. However, gene sequence and gene expression are often subject to distinct evolutionary pressures; therefore, we tested for Fast-Z in gene expression using next-generation RNA-sequencing data from multiple avian species. Similar to studies of Fast-Z in coding sequence, we recover clear signatures of Fast-Z in gene expression; however, in contrast to coding sequence, our data indicate that Fast-Z in expression is due to positive selection acting primarily in females. In the soma, where gene expression is highly correlated between the sexes, we detected Fast-Z in both sexes, although at a higher rate in females, suggesting that many positively selected expression changes in females are also expressed in males. In the gonad, where intersexual correlations in expression are much lower, we detected Fast-Z for female gene expression, but crucially, not males. This suggests that a large amount of expression variation is sex-specific in its effects within the gonad. Taken together, our results indicate that Fast-Z evolution of gene expression is the product of positive selection acting on recessive beneficial alleles in the heterogametic sex. More broadly, our analysis suggests that the adaptive potential of Z chromosome gene expression may be much greater than that of gene sequence, results which have important implications for the role of sex chromosomes in speciation and sexual selection.