A new genetic mechanism in snails that controls transmission of schistosomes

血吸虫病是迄今为止人类最重要的寄生虫病。疫苗是不可用的， 唯一有效的治疗方法是反复服用一种药物(吡喹酮)，现在是药物。 阻力是一个主要的担忧。血吸虫需要水生蜗牛才能传播。了解 蜗牛和血吸虫相互作用的分子机制是中断新策略的关键 变速箱。几十年来对钉螺和血吸虫相容性的分子基础进行了艰苦的研究 只产生了几个候选基因或机制。使用全基因组关联图谱 方法，我们最近发现了蜗牛基因组的一个小区域，在其中 一个未知基因的等位基因变异对曼氏血吸虫的抗性有很大的影响。这 该区域包含10个假定的编码基因，其中没有一个与免疫相关。 软体动物。这项提议的目标是明确地确定该区域的哪些基因是因果关系。 首先，候选基因将根据其成为因果基因的可能性进行排序。排名将基于以下因素 抗性单倍型和敏感单倍型(该区域的不同版本)上的等位基因是否在(A) 表达水平或(B)氨基酸序列，以及推测的基因功能的信息。然后，对于 每个剩余的候选按排名顺序，我们将功能测试该基因座的等位基因变异 实际上控制着阻力。这将使用RNA干扰(RNAi)和等位基因特异性RNAi来完成 (即在杂合子中敲除一个等位基因或另一个等位基因)。这些互补的方法使人们能够 评估表达水平或氨基酸序列不同的等位基因的因果关系。创新： 通过因果基因功能鉴定的关联作图展示了一种新的方法 生物菌属遗传学领域。利用具有RNAseq(全基因组表达)数据的自交系 而假设检验框架中的等位基因特异性RNAi也是新颖的。意义：确定新的 抗性途径将表明潜在地干扰寄生虫传播的新途径(即如何 蜗牛阻碍了血吸虫检测、穿透或在宿主内成功发育的能力？)识别 钉螺中的抗性基因也是评估是否对钉螺种群进行基因操纵的关键 可能成为一种可行的阻断传播的方法。了解蜗牛的抵抗力也应该有助于 在寄生虫中寻找控制宿主特异性的基因。最后，软体动物是 世界范围内许多具有医疗和经济重要性的疾病。在关联区中没有一个基因 此前已在软体动物中被确定为与免疫相关。因此，无论哪种基因最终被证明是因果关系， 它将在这一重要的疾病传播群体中识别一种新的抗病机制 有机体。

Schistosomiasis is by far the most important helminth parasitic disease of humans. Vaccines are unavailable, the only effective treatment involves repeated dosing with a single drug (praziquantel), and now drug resistance is a major concern. Schistosomes require aquatic snails for transmission. Understanding the molecular mechanisms by which snails and schistosomes interact is key for new strategies to interrupt transmission. Decades of painstaking research on the molecular basis of snail-schistosome compatibility have yielded just a handful of candidate genes or mechanisms. Using a genome-wide association mapping approach, we recently identified a small region of the genome of the snail, Biomphalaria glabrata, in which allelic variation at an unknown gene has a very strong effect on resistance to Schistosoma mansoni. This region contains 10 putative coding genes, none of which was previously known to be immune relevant in molluscs. The goal of this proposal is to unambiguously identify which of the genes in this region is causal. Firstly, candidate genes will be ranked by their likelihood of being the causal gene. Ranking will be based on whether or not alleles on the resistant versus susceptible haplotypes (versions of the region) differ in (a) expression levels or (b) amino acid sequence, together with information on putative gene function. Then, for each remaining candidate in ranked order, we will functionally test whether allelic variation at that locus actually controls resistance. This will be accomplished using RNA interference (RNAi) and allele-specific RNAi (i.e. knock down one allele or the other in heterozygotes). These complementary approaches allow one to evaluate causality for alleles that differ in either expression level or amino acid sequence. Innovation: Association mapping through functional identification of a causal gene illustrates a fresh new approach in the field of Biomphalaria genetics. The use of inbred lines with RNAseq (whole-genome expression) data, RNAi and allele-specific RNAi in a hypothesis testing framework is also novel. Significance: Identifying new resistance pathways will indicate new ways to potentially interfere with parasite transmission (i.e. how do some snails block schistosomes' ability to detect, penetrate or successfully develop within a host?). Identifying resistance genes in snails is also essential for evaluating whether genetic manipulation of snail populations might become a viable approach for blocking transmission. Understanding resistance in snails should also aid the search for genes in the parasite that control host specificity. Finally, molluscs are intermediate hosts for many diseases of medical and economic importance worldwide. None of the genes in the region of association have been previously identified as immune-relevant in molluscs. Thus, whichever gene turns out to be causal, it will identify a new mechanism of disease resistance in this important group of disease-transmitting organisms.