Evolution of X-Degenerate Y Chromosome Genes in Greater Apes: Conservation of Gene Content in Human and Gorilla, But Not Chimpanzee
Evolution of X-Degenerate Y Chromosome Genes in Greater Apes: Conservation of Gene Content in Human and Gorilla, But Not Chimpanzee
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DOI：
10.1007/s00239-008-9189-y
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发表时间：
2009-02-01
影响因子：
3.9
通讯作者：
Makova, Kateryna D.
中科院分区：
文献类型：
--
作者：
Goto, Hiroki;Peng, Lei;Makova, Kateryna D.
与X染色体相比，哺乳动物的Y染色体在尺寸上大大缩小，并且在进化过程中丢失了大部分祖先基因。有趣的是，对于Y染色体上的X-简并区域，人类保留了所有16个基因，而黑猩猩在两个物种分化后丢失了16个基因中的4个。为了揭示猿Y染色体退化的进化动力，我们确定了16个大猩猩Y染色体X-退化区基因的编码外显子和剪接位点的完整序列。我们发现，所有研究的阅读框架和剪接位点都是完整的，因此，这个基因组区域在大猩猩谱系中没有经历基因丢失。在黑猩猩中观察到比人类谱系更高的核苷酸差异，特别是对于具有破坏性突变的基因，这表明黑猩猩中这些基因缺乏功能限制。令人惊讶的是，我们的研究结果表明，在黑猩猩中被破坏的基因的人类和大猩猩直系同源物在放松的功能限制下进化，可能不是必需的。考虑到猿类物种的交配模式和有效人口规模，我们得出结论，由于精子竞争与正选择相关的遗传搭便车可能解释了黑猩猩Y染色体基因数量的快速下降。由于我们没有发现正选择作用于X简并基因的证据，因此这种选择可能针对黑猩猩Y染色体上的其他基因。
Compared with the X chromosome, the mammalian Y chromosome is considerably diminished in size and has lost most of its ancestral genes during evolution. Interestingly, for the X-degenerate region on the Y chromosome, human has retained all 16 genes, while chimpanzee has lost 4 of the 16 genes since the divergence of the two species. To uncover the evolutionary forces governing ape Y chromosome degeneration, we determined the complete sequences of the coding exons and splice sites for 16 gorilla Y chromosome genes of the X-degenerate region. We discovered that all studied reading frames and splice sites were intact, and thus, this genomic region experienced no gene loss in the gorilla lineage. Higher nucleotide divergence was observed in the chimpanzee than the human lineage, particularly for genes with disruptive mutations, suggesting a lack of functional constraints for these genes in chimpanzee. Surprisingly, our results indicate that the human and gorilla orthologues of the genes disrupted in chimpanzee evolve under relaxed functional constraints and might not be essential. Taking mating patterns and effective population sizes of ape species into account, we conclude that genetic hitchhiking associated with positive selection due to sperm competition might explain the rapid decline in the Y chromosome gene number in chimpanzee. As we found no evidence of positive selection acting on the X-degenerate genes, such selection likely targets other genes on the chimpanzee Y chromosome.