Summary of B. pfeifferi CREPs.

BackgroundBiomphalaria pfeifferi is the world’s most widely distributed and commonly implicated vector snail species for the causative agent of human intestinal schistosomiasis, Schistosoma mansoni. In efforts to control S. mansoni transmission, chemotherapy alone has proven insufficient. New approaches to snail control offer a way forward, and possible genetic manipulations of snail vectors will require new tools. Towards this end, we here offer a diverse set of genomic resources for the important African schistosome vector, B. pfeifferi.Methodology/Principal findingsBased largely on PacBio High-Fidelity long reads, we report a genome assembly size of 772 Mb for B. pfeifferi (Kenya), smaller in size than known genomes of other planorbid schistosome vectors. In a total of 505 scaffolds (N50 = 3.2Mb), 430 were assigned to 18 large linkage groups inferred to represent the 18 known chromosomes, based on whole genome comparisons with Biomphalaria glabrata. The annotated B. pfeifferi genome reveals a divergence time of 3.01 million years with B. glabrata, a South American species believed to be similar to the progenitors of B. pfeifferi which undertook a trans-Atlantic colonization Conclusions/SignificanceThe genome for this preferentially self-crossing species is less heterozygous than related species known to be preferential out-crossers; its smaller genome relative to congeners may similarly reflect its preference for selfing. Expansions of gene families with immune relevance are noted, including the FReD gene family which is far more similar in its composition to B. glabrata than to Bulinus truncatus, a vector for Schistosoma haematobium. Provision of this annotated genome will help better understand the dependencies of trematodes on snails, enable broader comparative insights regarding factors contributing to susceptibility/ resistance of snails to schistosome infections, and provide an invaluable resource with respect to identifying and manipulating snail genes as potential targets for more specific snail control programs.【研究背景】菲氏双脐螺（Biomphalaria pfeifferi）是全球分布最广、最常被认定为人体肠道血吸虫病致病原曼氏血吸虫（Schistosoma mansoni）媒介的螺类物种。在控制曼氏血吸虫传播的现有举措中，仅靠化疗已被证实效果有限。新型螺类防控手段提供了新的突破方向，而对媒介螺开展潜在遗传改造研究，亦需配套的全新工具。基于此目标，本研究针对这一重要的非洲血吸虫媒介物种菲氏双脐螺，提供了一套多样化的基因组学资源。 【研究方法与主要结果】本研究主要依托PacBio高保真长读长测序数据，完成了肯尼亚种群菲氏双脐螺的基因组组装，组装全长772 Mb，其基因组大小小于已报道的其他扁卷螺科血吸虫媒介螺的基因组。本次组装共获得505个支架序列（N50=3.2 Mb），其中430个被锚定至18个大型连锁群；结合与光滑双脐螺（Biomphalaria glabrata）的全基因组比对分析，研究人员推断该连锁群对应菲氏双脐螺的18条已知染色体。经注释的菲氏双脐螺基因组显示，其与光滑双脐螺的分化时间为301万年；光滑双脐螺为南美物种，被认为与菲氏双脐螺的祖先类群相近，而菲氏双脐螺曾经历跨大西洋殖民扩散事件。 【研究结论与意义】该偏好自体受精的物种，其基因组杂合度低于已知偏好异体受精的近缘物种；相较于同属其他物种，其基因组更小的特征，同样反映了其自体受精的繁殖偏好。研究还发现与免疫相关的基因家族发生了扩张，其中FReD基因家族的基因组成与光滑双脐螺的相似度，远高于与埃及血吸虫（Schistosoma haematobium）媒介螺截形小泡螺（Bulinus truncatus）的相似度。本研究提供的注释化基因组，将有助于更深入地理解吸虫纲物种与螺类之间的宿主依赖关系，为解析螺类对血吸虫感染的易感性/抗性相关机制提供更广泛的比较研究视角，同时也可为鉴定、改造螺类基因以开发更具特异性的螺类防控方案提供宝贵的研究资源。