性染色体在脊椎动物中的稳定性与周转：从发育基因调控网络的角度
Sex chromosome stability and turnover across vertebrates: a developmental gene regulatory network perspective
AI总结：
本文从发育基因调控网络角度探讨性染色体的稳定性与周转，比较哺乳动物与鸟类与多数两栖类、鱼类及植物的差异，提出GRN锁假说，分析性染色体在进化中的锁定与频繁周转机制。
摘要：
性染色体在进化过程中多次重复出现，但其进化命运差异显著。与哺乳动物和鸟类退化稳定的Y/W染色体不同，大多数两栖类、鱼类、非鸟类爬行类和开花植物的性染色体仍基本同源并频繁发生周转。现有的解释如进化陷阱假说、性对抗选择、突变负荷、遗传漂变和自私遗传元件等，侧重于群体遗传过程，未能完全解释这一模式。本文提出发育基因调控网络（GRN）锁假说。我们整理了脊椎动物中染色体周转的案例研究，综合了关于性别决定和剂量调节（DC）的比较发育数据。在哺乳动物和鸟类中，性别由早期由体细胞启动的完全穿透主信号决定，该信号在狭窄的热缓冲胚胎窗口内起作用。该信号在高度通道化的GRN中运作，与染色体尺度的剂量补偿相结合，替代剪接事件在初级性别决定中起很小或不起作用。这种配置使新主性别决定位点难以入侵而不会产生有害的中间状态。相比之下，许多变温脊椎动物具有灵活、整合性的阈值GRN，在较长的敏感胚胎期内，遗传、配子细胞和环境输入相互作用，缺乏或基本基于基因的DC，以及在关键调控节点附近具有环境响应的剪接，为性别决定位点的进化提供了多个进入点。本文概述了实证预测，并强调了整合发育生物学、分子机制和群体遗传学如何产生可测试的模型，以解释性染色体何时进化锁定或重复周转。
英文摘要：
Sex chromosomes have evolved repeatedly across the Tree of Life, yet their evolutionary fates differ strikingly. In sharp contrast to mammals and birds with degenerated, stable Y/W chromosomes, in most amphibians, teleosts, non avian reptiles and flowering plants, sex chromosomes remain largely homomorphic and undergo frequently turnover. Explanations such as the evolutionary trap hypothesis, sexually antagonistic selection, mutation load, genetic drift and selfish genetic elements, focus on population genetic processes and do not fully explain this pattern. Here we propose the developmental gene regulatory network (GRN) lock in hypothesis. We compile case studies of turnover across vertebrates, synthesise comparative developmental data on sex determination and dosage regulation (DC). In mammals and birds, sex is determined by an early, initiation by somatic cells, fully penetrant master signal acting within a narrow, thermally buffered embryonic window. This signal operates within highly canalised GRNs, coupled to chromosome scale dosage compensation, with alternative splicing events playing little or no causal role in primary sex determination. This configuration makes it difficult for new master sex determining loci to invade without generating deleterious intermediate states. By contrast, many ectothermic vertebrates possess flexible, integrative threshold GRNs in which genetic, germ cells and environmental inputs interact over a prolonged sensitive embryonic period, with absent or largely gene-by-gene based DC and environmentally responsive splicing near key regulatory nodes, providing many entry points for sex determining loci to evolve. We outline empirical predictions and highlight how integrating developmental biology, molecular mechanisms and population genetics can yield testable models for when sex chromosomes become evolutionarily locked-in versus repeated turnover.
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