Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts.
Field Museum of Natural History, Chicago, Illinois.
Genome Biol Evol. 2023 Mar 3;15(3). doi: 10.1093/gbe/evad021.
Genome assemblies are growing at an exponential rate and have proved indispensable for studying evolution but the effort has been biased toward vertebrates and arthropods with a particular focus on insects. Onychophora or velvet worms are an ancient group of cryptic, soil dwelling worms noted for their unique mode of prey capture, biogeographic patterns, and diversity of reproductive strategies. They constitute a poorly understood phylum of exclusively terrestrial animals that is sister group to arthropods. Due to this phylogenetic position, they are crucial in understanding the origin of the largest phylum of animals. Despite their significance, there is a paucity of genomic resources for the phylum with only one highly fragmented and incomplete genome publicly available. Initial attempts at sequencing an onychophoran genome proved difficult due to its large genome size and high repeat content. However, leveraging recent advances in long-read sequencing technology, we present here the first annotated draft genome for the phylum. With a total size of 5.6Gb, the gigantism of the Epiperipatus broadwayi genome arises from having high repeat content, intron size inflation, and extensive gene family expansion. Additionally, we report a previously unknown diversity of onychophoran hemocyanins that suggests the diversification of copper-mediated oxygen carriers occurred independently in Onychophora after its split from Arthropoda, parallel to the independent diversification of hemocyanins in each of the main arthropod lineages.
基因组组装的发展呈指数级增长，对于研究进化来说已经不可或缺，但这方面的努力一直偏向于脊椎动物和节肢动物，特别关注昆虫。有爪动物（Onychophora）或缓步动物是一个古老的、神秘的土壤蠕虫类群，以其独特的捕食方式、生物地理模式和多样的生殖策略而闻名。它们构成了一个尚未被充分了解的完全陆生动物门，是节肢动物的姐妹群。由于这种系统发育位置，它们在理解动物最大门的起源方面至关重要。尽管它们意义重大，但该门的基因组资源却很少，仅有一个高度碎片化和不完整的基因组可供公开使用。由于其基因组较大且重复含量高，最初尝试对有爪动物基因组进行测序就遇到了困难。然而，利用长读测序技术的最新进展，我们在这里首次提供了该门的第一个注释草案基因组。Epiperipatus broadwayi 基因组的总大小为 56 亿碱基对，巨型化源于其高重复含量、内含子大小膨胀和广泛的基因家族扩张。此外，我们还报告了一种以前未知的有爪动物血蓝蛋白多样性，表明铜介导的氧载体的多样化是在有爪动物从节肢动物分支出来后独立发生的，与每个主要节肢动物谱系中血蓝蛋白的独立多样化平行。
