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摘要 : 4月24日,《自然》发表的两篇论文给雄性的Y染色体演化和功能提供了新见解。众所周知,Y染色体在演化历史中丢失了大量基因,不过丢失基因的过程在大约2500万年前停止了,留下了一组稳定的祖先基因。这两篇文章共同指出,由于剂量原因,这些基因被“精心”保留下来,因为它们的功能和其他基因以及其他基因的产物具有相互作用。


由于有着大量的重复序列,Y染色体的重建并不容易,但是瑞士洛桑大学的Henrik Kaessmann和同事开发出一种新测序技术,帮助他们探索15种具有代表性的哺乳动物的Y染色体演化历程。分析结果显示,虽然有些Y染色体基因演化出新功能,但大多数Y染色体基因可能受剂量限制,保留了原来的功能。

在另一项由美国麻省理工学院Daniel Bellott及其研究团队进行的对8种哺乳动物Y染色体的独立研究,同样展示了剂量限制是保留Y染色体上祖先基因的重要选择压力。该研究团队提出,Y染色体除了参与形成睾丸和生成精子外,对于雄性的存活也是必要的。他们认为,Y染色体基因在两性的健康与疾病的区别上有重要的作用。例如,他们推测特纳综合征(一种由于缺少了一条性染色体产生的染色体疾病)的表现,可能由X染色体和Y染色体上基因对的剂量决定。


Origins and functional evolution of Y chromosomes across mammals

Diego Cortez, Ray Marin, Deborah Toledo-Flores, Laure Froidevaux, Angélica Liechti, Paul D. Waters, Frank Grützner & Henrik Kaessmann

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 transcr-ptome 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 expressi0n decreases in therians, Y/W genes show notable conservation of proto-sex chromosome expressi0n patterns, although various Y genes evolved testis-specificities through differential regulatory decay. Thus, although some genes evolved novel functions through spatial/temporal expressi0n shifts, most Y genes probably endured, at least initially, because of dosage constraints.

Mammalian Y chromosomes retain widely expressed dosage-sensitive regulators

Daniel W. Bellott, Jennifer F. Hughes, Helen Skaletsky, Laura G. Brown, Tatyana Pyntikova,Ting-Jan Cho, Natalia Koutseva, Sara Zaghlul, Tina Graves, Susie Rock, Colin Kremitzki,Robert S. Fulton, Shannon Dugan, Yan Ding, Donna Morton, Ziad Khan, Lora Lewis,Christian Buhay, Qiaoyan Wang, Jennifer Watt, Michael Holder, Sandy Lee, Lynne Nazareth, Steve Rozen, Donna M. Muzny, Wesley C. Warren, Richard A. Gibbs, Richard K. Wilson & David C. Page 

The human X and Y chromosomes evolved from an ordinary pair of autosomes, but millions of years ago genetic decay ravaged the Y chromosome, and only three per cent of its ancestral genes survived. We reconstructed the evolution of the Y chromosome across eight mammals to identify biases in gene content and the selective pressures that preserved the surviving ancestral genes. Our findings indicate that survival was nonrandom, and in two cases, convergent across placental and marsupial mammals. We conclude that the gene content of the Y chromosome became specialized through selection to maintain the ancestral dosage of homologous X–Y gene pairs that function as broadly expressed regulators of transcr-ption, translation and protein stability. We propose that beyond its roles in testis determination and spermatogenesis, the Y chromosome is essential for male viability, and has unappreciated roles in Turner’s syndrome and in phenotypic differences between the sexes in health and disease.

对应Nature杂志: 2014年4月24日Nature杂志精选

来源: 中国科学报 浏览次数:100


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