CAS-Max Planck Junior Research Group, State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China.
BMC Genomics. 2012 Mar 22;13:109. doi: 10.1186/1471-2164-13-109.
Drosophila albomicans is a unique model organism for studying both sex chromosome and B chromosome evolution. A pair of its autosomes comprising roughly 40% of the whole genome has fused to the ancient X and Y chromosomes only about 0.12 million years ago, thereby creating the youngest and most gene-rich neo-sex system reported to date. This species also possesses recently derived B chromosomes that show non-Mendelian inheritance and significantly influence fertility.
We sequenced male flies with B chromosomes at 124.5-fold genome coverage using next-generation sequencing. To characterize neo-Y specific changes and B chromosome sequences, we also sequenced inbred female flies derived from the same strain but without B's at 28.5-fold.
We assembled a female genome and placed 53% of the sequence and 85% of the annotated proteins into specific chromosomes, by comparison with the 12 Drosophila genomes. Despite its very recent origin, the non-recombining neo-Y chromosome shows various signs of degeneration, including a significant enrichment of non-functional genes compared to the neo-X, and an excess of tandem duplications relative to other chromosomes. We also characterized a B-chromosome linked scaffold that contains an actively transcribed unit and shows sequence similarity to the subcentromeric regions of both the ancient X and the neo-X chromosome.
Our results provide novel insights into the very early stages of sex chromosome evolution and B chromosome origination, and suggest an unprecedented connection between the births of these two systems in D. albomicans.
果蝇 albomicans 是研究性染色体和 B 染色体进化的独特模式生物。大约在 0.12 百万年前，其包含约 40%基因组的一对常染色体与古老的 X 和 Y 染色体融合，从而创造了迄今为止报道的最年轻和基因最丰富的新型性系统。该物种还拥有最近衍生的 B 染色体，其表现出非孟德尔遗传并显著影响生育能力。
我们使用下一代测序对具有 B 染色体的雄性果蝇进行了 124.5 倍基因组覆盖的测序。为了表征新 Y 染色体特异性变化和 B 染色体序列，我们还对来自同一品系但没有 B 染色体的近交雌性果蝇进行了 28.5 倍的测序。
我们组装了一个雌性基因组，并通过与 12 个果蝇基因组进行比较，将 53%的序列和 85%的注释蛋白分配到特定的染色体上。尽管其起源非常近，但非重组的新 Y 染色体表现出各种退化迹象，与新 X 染色体相比，非功能基因显著富集，与其他染色体相比，串联重复过多。我们还对一个 B 染色体连锁支架进行了特征描述，该支架包含一个活跃转录的单位，并与古老的 X 和新 X 染色体的亚着丝粒区域具有序列相似性。
我们的研究结果为性染色体进化和 B 染色体起源的早期阶段提供了新的见解，并表明在 D. albomicans 中，这两个系统的诞生之间存在前所未有的联系。
