Sex-biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution
Sex-biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution
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DOI：
10.1073/pnas.1217027110
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发表时间：
2013-04-16
影响因子：
11.1
通讯作者：
Bachtrog, Doris
中科院分区：
文献类型：
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作者：
Vicoso, Beatriz;Kaiser, Vera B.;Bachtrog, Doris
性染色体起源于常染色体。在原性染色体上积累的性拮抗突变选择了重组的丧失，并启动了产生异形性染色体的进化过程。重组抑制和分化通常被认为是性染色体进化的默认途径，而古老的、同态的性染色体的出现，如平地鸟的性染色体，仍然是一个谜。在这里，我们分析了Eromaius novaehollandiae(Dromaius Novaehollandiae)的基因组和转录组，证实了性染色体上的大多数基因都在Z和W之间共享。然而，令人惊讶的是，所有与性别相关的基因相对于常染色体的表达水平通常是性别偏见的，包括假常染色体区域的基因，并且性腺形成后男性偏见增加。这种表达偏差表明，即使在没有ZW分化的情况下，鸵鸟的性染色体也已经男性化。因此，鸟类可能采取了不同的进化解决方案，以将性对抗突变带来的有害影响降至最低：一些谱系消除了原性染色体上的重组，以物理上将性对抗等位基因限制在一种性别上，而Ratites进化出性别偏见表达，将性对抗等位基因的产物限制在它所受益的性别上。冲突解决方面的这种差异可能解释了在其他谱系中保留重组、同态的性染色体的原因，并说明了性拮抗突变驱动性染色体进化的重要性。
Sex chromosomes originate from autosomes. The accumulation of sexually antagonistic mutations on protosex chromosomes selects for a loss of recombination and sets in motion the evolutionary processes generating heteromorphic sex chromosomes. Recombination suppression and differentiation are generally viewed as the default path of sex chromosome evolution, and the occurrence of old, homomorphic sex chromosomes, such as those of ratite birds, has remained a mystery. Here, we analyze the genome and transcriptome of emu (Dromaius novaehollandiae) and confirm that most genes on the sex chromosome are shared between the Z and W. Surprisingly, however, levels of gene expression are generally sex-biased for all sex-linked genes relative to autosomes, including those in the pseudoautosomal region, and the male-bias increases after gonad formation. This expression bias suggests that the emu sex chromosomes have become masculinized, even in the absence of ZW differentiation. Thus, birds may have taken different evolutionary solutions to minimize the deleterious effects imposed by sexually antagonistic mutations: some lineages eliminate recombination along the protosex chromosomes to physically restrict sexually antagonistic alleles to one sex, whereas ratites evolved sex-biased expression to confine the product of a sexually antagonistic allele to the sex it benefits. This difference in conflict resolution may explain the preservation of recombining, homomorphic sex chromosomes in other lineages and illustrates the importance of sexually antagonistic mutations driving the evolution of sex chromosomes.