Nature2014-06-18 5:22 PM

封面故事:Y染色体的演化 Origins and functional evolution of Y chromosomes across mammals

论文摘要 

以其在性别决定和雄性生殖中所起作用而知名的哺乳动物Y染色体,经常含有使其比基因组中其余部分更难组装的重复序列。为了解决这一问题,Henrik Kaessman及同事建立了一个基于雄性特定的RNA/基因组测序数据的新的转录体组装方法,以此来研究代表全部主要哺乳动物分支的15个物种的Y染色体演化情况。他们发现了哺乳动物的两个独立染色体起源和鸟类的一个染色体起源的证据。他们对全部Y/W基因所做分析表明,虽然一些基因由于时空表达变化而涉及性别决定/精子形成方面的新功能,但大多数Y基因由于剂量限制可能坚持了下来,至少在最初是这样。在一项并列的研究中,Daniel Bellott及同事通过对来自几种胎生哺乳动物和一种有袋类动物的X-Y基因对的基因组序列进行全面比较分析,重建了Y染色体的演化情况。他们得出结论认为,演化过程通过选择简化了人类Y染色体的基因内容,以维持调控全身基因表达的同源X-Y基因对的先祖剂量。他们提出,这些基因使得Y染色体对雄性存活来说必不可少,并且对不同性别在健康和疾病方面的差别有所贡献。

Abstract 

Y chromosomes underlie sex determination in mammals, but their repeat-rich nature has hampered sequencing and associated evolutionary studies. Here we trace Y evolution across 15 representative mammals on the basis of high-throughput genome and transcriptome sequencing. We uncover three independent sex chromosome originations in mammals and birds (the outgroup). The original placental and marsupial (therian) Y, containing the sex-determining gene SRY, emerged in the therian ancestor approximately 180 million years ago, in parallel with the first of five monotreme Y chromosomes, carrying the probable sex-determining gene AMH. The avian W chromosome arose approximately 140 million years ago in the bird ancestor. The small Y/W gene repertoires, enriched in regulatory functions, were rapidly defined following stratification (recombination arrest) and erosion events and have remained considerably stable. Despite expression decreases in therians, Y/W genes show notable conservation of proto-sex chromosome expression patterns, although various Y genes evolved testis-specificities through differential regulatory decay. Thus, although some genes evolved novel functions through spatial/temporal expression shifts, most Y genes probably endured, at least initially, because of dosage constraints.

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