Genetic Analysis of Host Specificity in Schistosoma mansoni

曼氏血吸虫宿主特异性的遗传分析

• 批准号: 8586839
• 负责人: Tim J Anderson
• 金额: $ 58.09万
• 依托单位: TEXAS BIOMEDICAL RESEARCH INSTITUTE
• 依托单位国家: 美国
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-12-15 至 2016-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8586839
• 关键词: Alleles; American; Behavior; Behavioral; Binding; Biomphalaria; Chemicals; Chromosome Mapping; Development; Epidemiology; Evolution; Funding; Gene Expression; Gene Frequency; Genes; Genetic; Genetic Crosses; Genetic Variation; Genome; Genome Mappings; Genotype; Helminths; Human; Hybrids; Immune response; Individual; Infection; Inheritance Patterns; Laboratories; Larva; Location; Malaria; Maps; Measures; Methods; Molecular; Molecular Genetics; Parasites; Parents; Penetration; Phase; Physiological; Proliferating; Publishing; Quantitative Trait Loci; RNA Interference; Relative (related person); Resistance; Resources; Schistosoma; Schistosoma mansoni; Schistosome Parasite; Snails; Species Specificity; Specificity; Staging; System; Transfection; Work; Yeasts; base; gene function; genetic analysis; genetic linkage analysis; genome sequencing; genome-wide; novel; positional cloning; research study; response; segregation; tool; trait; transmission process; vector

DESCRIPTION (provided by applicant): Parasites characteristically show strong specificity to particular hosts, but the genetic basis for this host specificity is poorly understood. In Schistosoma mansoni, one of three medically important schistosome species infecting humans, elegant experimental work demonstrates that both chemical recognition of the intermediate snail host and survival of parasites within snails follow a simple Mendelian pattern of inheritance. While Egyptian parasites show strong chemical recognition of the sympatric snail Biomphalaria alexandrina, Brazilian parasites show no specificity and are attracted to even non-vector snail hosts. Similarly, while both Egyptian and Brazilian parasites infect and proliferate in their sympatric snail hosts, F1 hybrids develop only in S. American B. glabrata snails. New molecular tools allow us to determine the parasite genes that determine host specificity in this host-parasite system, providing a means to understand key molecular interactions between parasites and snail vector. Using R21 funding we have (a) developed a 5 cM linkage map for S. mansoni, and (b) demonstrated the utility of linkage mapping by identifying a strong QTL (LOD = 21) for oxamniquine resistance to a short region of chr 6. We now propose to exploit the genetic map, together with the recently published genome sequence of S. mansoni identify the genome region(s) that underlie host specificity in the S. mansoni - Biomphalaria system. Host specificity involves two components (a) chemical location of snails by miracidia and (b) penetration and clonal proliferation of schistosome larvae within snails. For both traits, we will conduct genetic crosses between Brazilian and Egyptian S. mansoni, using snail infections with single miracidia to generate single genotype infections in snails. We will quantify chemical recognition behavior of single F2 miracidia to both B. glabrata and B. alexandrina, and then genotype individual miracidia using SNPs spaced at ~4 cM (2Mb) intervals across the S. mansoni genome to identify QTLs for this trait. Genetic mapping of survival and clonal proliferation within the snail host is not possible using classical linkage mapping methods, because parasites that do not grow within snails cannot be genotyped. We will therefore use extreme QTL (X-QTL) methods, developed by malaria and yeast geneticists, to examine allele frequencies of F2 cercariae emerging from either B. glabrata or B. alexandrina snails. At the causative loci, we expect alleles from the Egyptian S. mansoni parent to be overrepresented in F2 cercariae emerging from B. alexandrina relative to those emerging from B. glabrata. Hence locus specific deviation from normal Mendelian segregation allows QTL location. Having fine mapped QTL regions for both traits, we will use RNAi disruption of gene function or retroviral based transfection to aid identification of causative loci. Understanding the genetic and molecular basis of host specificity in the S. mansoni - Biomphalaria system is critical for control efforts that aim to disrupt this step in the parasite lifecycle and provides a key to understanding evolution of host specificity in the most important of the human helminth parasites.

描述（由申请人提供）：寄生虫对特定宿主表现出强烈的特异性，但人们对这种宿主特异性的遗传基础知之甚少。曼氏血吸虫是感染人类的​​三种医学上重要的血吸虫物种之一，优雅的实验工作表明，对中间蜗牛宿主的化学识别和蜗牛体内寄生虫的生存都遵循简单的孟德尔遗传模式。埃及寄生虫对同域蜗牛亚历山大生物表现出强烈的化学识别能力，而巴西寄生虫则没有表现出特异性，甚至会被非媒介蜗牛宿主所吸引。同样，虽然埃及和巴西寄生虫都能在同域蜗牛宿主中感染和增殖，但 F1 杂交体仅在南美光滑蜗牛中发育。新的分子工具使我们能够确定决定宿主-寄生虫系统中宿主特异性的寄生虫基因，从而提供一种了解寄生虫和蜗牛载体之间关键分子相互作用的方法。利用 R21 资金，我们 (a) 开发了曼氏沙门氏菌的 5 cM 连锁图谱，(b) 通过确定对 6 号短区域的奥沙尼喹抗性的强 QTL (LOD = 21) 证明了连锁图谱的实用性。我们现在建议利用遗传图谱，结合最近发表的曼氏沙门氏菌基因组序列，识别曼氏沙门氏菌 - 生物脐带系统中宿主特异性的基因组区域。宿主特异性涉及两个组成部分（a）通过毛蚴对蜗牛进行化学定位，以及（b）血吸虫幼虫在蜗牛体内的渗透和克隆增殖。对于这两个性状，我们将在巴西和埃及曼氏曼氏蜗牛之间进行遗传杂交，利用具有单一毛毛虫的蜗牛感染来在蜗牛中产生单一基因型感染。我们将量化单个 F2 miracidia 对光滑 B. glabrata 和 B. alexandrina 的化学识别行为，然后使用 S. mansoni 基因组中以约 4 cM (2Mb) 间隔的 SNP 对单个 miracidia 进行基因分型，以识别该性状的 QTL。使用经典的连锁作图方法不可能对蜗牛宿主内的生存和克隆增殖进行遗传作图，因为不能对不在蜗牛体内生长的寄生虫进行基因分型。因此，我们将使用由疟疾和酵母遗传学家开发的极端 QTL (X-QTL) 方法来检查来自光滑 B. glabrata 或 B. alexandrina 蜗牛的 F2 尾蚴的等位基因频率。在致病基因座上，我们预计来自埃及曼氏曼氏曼氏菌亲本的等位基因在亚历山大拟杆菌产生的 F2 尾蚴中相对于光滑拟杆菌产生的尾蚴的比例较高。因此，与正常孟德尔分离的基因座特异性偏差允许 QTL 定位。有了这两个性状的精细定位的 QTL 区域，我们将使用 RNAi 破坏基因功能或基于逆转录病毒的转染来帮助识别致病位点。了解曼氏链球菌 - 生物脐带虫系统中宿主特异性的遗传和分子基础对于旨在破坏寄生虫生命周期中这一步骤的控制工作至关重要，并为了解最重要的人类蠕虫中宿主特异性的进化提供了关键寄生虫。