Purifying selection maintains dosage-sensitive genes during degeneration of the threespine stickleback Y chromosome

Sex chromosomes are subject to unique evolutionary forces that cause suppression of recombination, leading to sequence degeneration and the formation of heteromorphic chromosome pairs (i.e., XY or ZW). Although progress has been made in characterizing the outcomes of these evolutionary processes on vertebrate sex chromosomes, it is still unclear how recombination suppression and sequence divergence typically occur and how gene dosage imbalances are resolved in the heterogametic sex. The threespine stickleback fish (Gasterosteus aculeatus) is a powerful model system to explore vertebrate sex chromosome evolution, as it possesses an XY sex chromosome pair at relatively early stages of differentiation. Using a combination of whole-genome and transcriptome sequencing, we characterized sequence evolution and gene expression across the sex chromosomes. We uncovered two distinct evolutionary strata that correspond with known structural rearrangements on the Y chromosome. In the oldest stratum,...

性染色体（sex chromosomes）会受到独特的进化力量作用，这类力量会引发重组抑制，进而导致序列退化并形成异型染色体对（heteromorphic chromosome pairs，即XY或ZW型）。尽管目前在解析脊椎动物性染色体进化过程所产生的结果方面已取得一定进展，但学界仍未明确重组抑制与序列分化通常是如何发生的，以及异配性别（heterogametic sex）中的基因剂量失衡（gene dosage imbalances）是如何得以缓解的。三棘刺鱼（threespine stickleback fish, Gasterosteus aculeatus）是探索脊椎动物性染色体进化的优质模型系统，因其拥有一对处于相对较早分化阶段的XY性染色体。本研究结合全基因组测序（whole-genome sequencing）与转录组测序（transcriptome sequencing）技术，对性染色体全域的序列进化与基因表达模式开展了系统性解析。我们揭示了两个独立的进化层（evolutionary strata），二者与Y染色体上已探明的结构重排事件一一对应。在最古老的进化层中，……