A new genetic mechanism in snails that controls transmission of schistosomes

描述（由申请人提供）：血吸虫病是迄今为止人类最重要的寄生虫病。没有疫苗，唯一有效的治疗方法是反复使用单一药物（吡喹酮），现在耐药性是一个主要问题。血吸虫需要水生蜗牛来传播。了解蜗牛和血吸虫相互作用的分子机制是阻断传播的新策略的关键。对蜗牛-血吸虫相容性的分子基础进行了数十年的艰苦研究，只发现了少数候选基因或机制。利用全基因组关联定位方法，我们最近确定了蜗牛基因组的一个小区域，在一个未知基因的等位基因变异对对曼氏血吸虫的抗性有很强的影响。这个区域包含10个假定的编码基因，这些基因以前都不知道与软体动物的免疫相关。这项建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，候选基因将根据它们成为致病基因的可能性进行排序。排序将基于抗性单倍型和易感单倍型（区域版本）上的等位基因在(a)表达水平或(b)氨基酸序列上是否不同，以及推测的基因功能信息。然后，对于每个剩余的候选序列，我们将测试该位点的等位基因变异是否实际上控制抗性。这将通过RNA干扰（RNAi）和等位基因特异性RNAi（即在杂合子中敲除一个等位基因或另一个等位基因）来完成。这些互补的方法允许人们评估在表达水平或氨基酸序列上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图谱说明了一个新的方法在领域

DESCRIPTION (provided by applicant): 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.