Sex chromosomes differentiated from different ancestral autosomes in various vertebrate lineages. Here, we trace the functional evolution of the XY Chromosomes of the green anole lizard (Anolis carolinensis), on the basis of extensive high-throughput genome, transcriptome and histone modification sequencing data and revisit dosage compensation evolution in representative mammals and birds with substantial new expression data. Our analyses show that Anolis sex chromosomes represent an ancient XY system that originated at least ≈160 million years ago in the ancestor of Iguania lizards, shortly after the separation from the snake lineage. The age of this system approximately coincides with the ages of the avian and two mammalian sex chromosomes systems. To compensate for the almost complete Y Chromosome degeneration, X-linked genes have become twofold up-regulated, restoring ancestral expression levels. The highly efficient dosage compensation mechanism of Anolis represents the only vertebrate case identified so far to fully support Ohno's original dosage compensation hypothesis. Further analyses reveal that X up-regulation occurs only in males and is mediated by a male-specific chromatin machinery that leads to global hyperacetylation of histone H4 at lysine 16 specifically on the X Chromosome. The green anole dosage compensation mechanism is highly reminiscent of that of the fruit fly, Drosophila melanogaster. Altogether, our work unveils the convergent emergence of a Drosophila-like dosage compensation mechanism in an ancient reptilian sex chromosome system and highlights that the evolutionary pressures imposed by sex chromosome dosage reductions in different amniotes were resolved in fundamentally different ways.

性染色体与各种脊椎动物谱系中的不同祖先常染色体不同。在这里，我们在广泛的高通量基因组、转录组和组蛋白修饰测序数据的基础上，追踪了绿蜥蜴 ( Anolis carolinensis ) XY 染色体的功能进化，并重新审视了代表性哺乳动物和鸟类的剂量补偿进化，并获得了大量新的信息。表达数据。我们的分析表明Anolis性染色体代表了一个古老的 XY 系统，它起源于至少大约 1.6 亿年前的鬣蜥蜥蜴的祖先，在与蛇谱系分离后不久。该系统的年龄大致与鸟类和两种哺乳动物性染色体系统的年龄一致。为了补偿几乎完全的 Y 染色体变性，X 连锁基因已成为双重上调，恢复祖先的表达水平。Anolis的高效剂量补偿机制代表迄今为止唯一确定的完全支持 Ohno 原始剂量补偿假设的脊椎动物病例。进一步的分析表明，X 上调仅发生在雄性中，并且由雄性特异性染色质机制介导，该机制导致组蛋白 H4 在 X 染色体上的第 16 位赖氨酸处发生整体过度乙酰化。Green anole 剂量补偿机制与果蝇 Drosophila melanogaster 的机制非常相似。总之，我们的工作揭示了在古代爬行动物性染色体系统中类似果蝇的剂量补偿机制的收敛出现，并强调了不同羊膜动物性染色体剂量减少所施加的进化压力以根本不同的方式得到解决。