BGI-Shenzhen, Shenzhen, China.
Villum Center for Biodiversity Genomics, Section for Ecology and Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Nature. 2021 Apr;592(7856):756-762. doi: 10.1038/s41586-020-03039-0. Epub 2021 Jan 6.
Egg-laying mammals (monotremes) are the only extant mammalian outgroup to therians (marsupial and eutherian animals) and provide key insights into mammalian evolution. Here we generate and analyse reference genomes of the platypus (Ornithorhynchus anatinus) and echidna (Tachyglossus aculeatus), which represent the only two extant monotreme lineages. The nearly complete platypus genome assembly has anchored almost the entire genome onto chromosomes, markedly improving the genome continuity and gene annotation. Together with our echidna sequence, the genomes of the two species allow us to detect the ancestral and lineage-specific genomic changes that shape both monotreme and mammalian evolution. We provide evidence that the monotreme sex chromosome complex originated from an ancestral chromosome ring configuration. The formation of such a unique chromosome complex may have been facilitated by the unusually extensive interactions between the multi-X and multi-Y chromosomes that are shared by the autosomal homologues in humans. Further comparative genomic analyses unravel marked differences between monotremes and therians in haptoglobin genes, lactation genes and chemosensory receptor genes for smell and taste that underlie the ecological adaptation of monotremes.
产卵哺乳动物（单孔目动物）是唯一现存的哺乳动物外群与有袋类动物（有袋目动物和真兽类动物），为哺乳动物的进化提供了关键的见解。在这里，我们生成和分析了鸭嘴兽（Ornithorhynchus anatinus）和针鼹（Tachyglossus aculeatus）的参考基因组，它们代表了仅有的两种现存的单孔目动物谱系。几乎完整的鸭嘴兽基因组组装将整个基因组锚定在染色体上，显著提高了基因组的连续性和基因注释。结合我们的针鼹序列，这两个物种的基因组使我们能够检测到塑造单孔目动物和哺乳动物进化的祖先和谱系特异性基因组变化。我们提供的证据表明，单孔目动物的性染色体复合体起源于祖先的染色体环构象。这种独特的染色体复合体的形成可能是由人类同源染色体之间多 X 染色体和多 Y 染色体之间异常广泛的相互作用所促进的。进一步的比较基因组分析揭示了单孔目动物和真兽类动物在触珠蛋白基因、泌乳基因和化学感觉受体基因（用于嗅觉和味觉）方面存在显著差异，这些差异是单孔目动物生态适应的基础。
