Department of Biology and Biochemistry, University of Houston, 3455 Cullen Blvd., Houston, 77204, TX, USA.
Department of Ecology and Evolution, University of California, Davis, One Shields Ave, Davis, 95616, CA, USA.
BMC Biol. 2019 Dec 5;17(1):100. doi: 10.1186/s12915-019-0721-x.
Sex chromosome evolution is a dynamic process that can proceed at varying rates across lineages. For example, different chromosomes can be sex-linked between closely related species, whereas other sex chromosomes have been conserved for > 100 million years. Cases of long-term sex chromosome conservation could be informative of factors that constrain sex chromosome evolution. Cytological similarities between the X chromosomes of the German cockroach (Blattella germanica) and most flies suggest that they may be homologous-possibly representing an extreme case of long-term conservation.
To test the hypothesis that the cockroach and fly X chromosomes are homologous, we analyzed whole-genome sequence data from cockroaches. We found evidence in both sequencing coverage and heterozygosity that a significant excess of the same genes are on both the cockroach and fly X chromosomes. We also present evidence that the candidate X-linked cockroach genes may be dosage compensated in hemizygous males. Consistent with this hypothesis, three regulators of transcription and chromatin on the fly X chromosome are conserved in the cockroach genome.
Our results support our hypothesis that the German cockroach shares the same X chromosome as most flies. This may represent the convergent evolution of the X chromosome in the lineages leading to cockroaches and flies. Alternatively, the common ancestor of most insects may have had an X chromosome that resembled the extant cockroach and fly X. Cockroaches and flies diverged ∼ 400 million years ago, which would be the longest documented conservation of a sex chromosome. Cockroaches and flies have different mechanisms of sex determination, raising the possibility that the X chromosome was conserved despite the evolution of the sex determination pathway.
性染色体的进化是一个动态的过程，在不同的谱系中可以以不同的速度进行。例如，在亲缘关系密切的物种之间，不同的染色体可能是性连锁的，而其他性染色体已经保守了超过 1 亿年。长期的性染色体保守的情况可能为限制性染色体进化的因素提供信息。德国蟑螂（Blattella germanica）和大多数蝇类的 X 染色体之间的细胞学相似性表明它们可能是同源的-可能代表了长期保守的极端情况。
为了检验蟑螂和蝇类 X 染色体同源的假设，我们分析了蟑螂的全基因组序列数据。我们在测序覆盖率和杂合性方面都发现了证据，表明相同数量的基因在蟑螂和蝇类的 X 染色体上都有显著的过剩。我们还提供了证据表明，候选的 X 连锁蟑螂基因可能在半合子雄性中剂量补偿。与这一假设一致，在蝇类 X 染色体上的三个转录和染色质调节剂在蟑螂基因组中是保守的。
我们的结果支持我们的假设，即德国蟑螂与大多数蝇类共享相同的 X 染色体。这可能代表了蟑螂和蝇类谱系中 X 染色体的趋同进化。或者，大多数昆虫的共同祖先可能有一个类似于现存的蟑螂和蝇类 X 染色体的 X 染色体。蟑螂和蝇类分化于 4 亿年前，这是有记录以来最长的性染色体保守。蟑螂和蝇类有不同的性别决定机制，这增加了尽管性别决定途径发生了进化，但 X 染色体仍被保守的可能性。
Zotero 插件
