The causes and consequences of genome reduction in animals are unclear because our understanding of this process mostly relies on lineages with often exceptionally high rates of evolution. Here, we decode the compact 73.8-megabase genome of Dimorphilus gyrociliatus, a meiobenthic segmented worm. The D. gyrociliatus genome retains traits classically associated with larger and slower-evolving genomes, such as an ordered, intact Hox cluster, a generally conserved developmental toolkit and traces of ancestral bilaterian linkage. Unlike some other animals with small genomes, the analysis of the D. gyrociliatus epigenome revealed canonical features of genome regulation, excluding the presence of operons and trans-splicing. Instead, the gene-dense D. gyrociliatus genome presents a divergent Myc pathway, a key physiological regulator of growth, proliferation and genome stability in animals. Altogether, our results uncover a conservative route to genome compaction in annelids, reminiscent of that observed in the vertebrate Takifugu rubripes.

动物基因组减少的原因和后果尚不清楚，因为我们对这一过程的理解主要依赖于进化速度通常非常高的谱系。在这里，我们解码了Dimorphilus gyrociliatus的紧凑型 73.8 兆碱基基因组，这是一种小型底栖分段蠕虫。D. gyrociliatus基因组保留了通常与较大且进化较慢的基因组相关的特征，例如有序、完整的 Hox 簇、普遍保守的发育工具包和祖先双侧连锁的痕迹。与其他一些基因组较小的动物不同，对D. gyrociliatus表观基因组的分析揭示了基因组调控的典型特征，不包括操纵子和反式的存在-拼接。相反，基因密集的D. gyrociliatus基因组呈现出不同的 Myc 通路，这是动物生长、增殖和基因组稳定性的关键生理调节因子。总而言之，我们的结果揭示了环节动物基因组压缩的保守途径，让人联想到在脊椎动物红斑鲇中观察到的途径。