Genetics of Cryptosporidium parvum

描述（由申请人提供）：细小隐孢子虫感染艾滋病患者和其他免疫缺陷个体，是儿童腹泻的常见原因。在人类志愿者和动物中进行的研究表明，分离株之间的毒力存在显著差异，但毒力的遗传决定因素尚不清楚。我们实验室最近的一项研究为利用遗传方法研究这种病原体开辟了新的可能性。我们发现在混合小鼠感染中可以产生重组基因型的小孢子虫系，不同基因型之间的重组可以产生高毒力的后代系。由于在实验杂交中获得了具有不同毒力特性的多个重组系，因此可以使用连锁分析来确定毒力的遗传决定因素，而无需事先了解毒力决定因素。我们的中心假设是，大多数临床或生物学相关的小孢子虫表型特性是由多个基因控制的数量性状，可以通过连锁分析来识别。具体目标：1；建立小孢子虫2型多态遗传标记的高密度图谱。即将完成的小弧菌基因组序列将有助于鉴定多态微卫星、限制性片段长度多态性和单核苷酸多态性。2. 确定交配结构和遗传的染色体外元件在基因典型混合的小孢子虫感染。我们将验证在混合的小孢子虫感染中受精是由相同或不同配子的随机融合引起的，并且自交与异交的比例符合随机交配的模型。病毒RNA基因组的遗传将在这一特定目的的背景下进行研究。3. 利用定量性状位点（QTL）分析鉴定2型小恙虫毒力标记。这一目的是基于初步的观察，即小孢子虫系之间的重组产生的后代具有不同的杀死小鼠的能力。我们将测试以下两个工作假设：a)毒力是由多个遗传位点决定的。b) QTL分析可用于鉴定与毒力相关的基因组片段。

DESCRIPTION (provided by applicant): Cryptosporidium parvum infects AIDS patients and other immunodeficient individuals and is a frequent cause of childhood diarrhea. Studies in human volunteers and animals have revealed pronounced differences in virulence among isolates, but the genetic determinants of virulence are unknown. The recent development in our laboratory of a method to cross C. parvum lines in mice opens new possibilitiesfor studying this pathogen using genetic methods. We have found that C. parvum lines with recombinant genotypes are produced in mixed mouse infections and that recombination between different genotypes can produce highly virulent progeny lines. Since multiple recombinant lines with different virulence properties are obtained in experimental crosses, linkage analysis can be used to identify genetic determinants of virulence, without prior knowledge of virulence determinants. It is our central hypothesis that a majority of clinically or biologically relevant phenotypic properties in C. parvum are quantitative traits controlled by multiple genes which can be identified by linkage analysis. Specific Aims: 1. Establish a high-density map of polymorphic genetic markers for C. parvum type 2. The almost completed C. parvum genome sequence will facilitate the identification of polymorphic microsatellites, restriction fragment length polymorphisms and single nucleotide polymorphisms. 2. Determine the mating structure and the inheritance of an extrachromosomal element in genotypically mixed C. parvum infections. We will test the working hypothesis that in mixed C. parvum infections fertilization results from the random fusion of identical or dissimilar gametes, and that the ratio of self- to cross-mating conforms to the model of random mating. The inheritance of a viral RNA genome will be studied in the context of this specific aim. 3. Identify virulence markers in type 2 C. parvum using Quantitative Trait Locus (QTL) analysis. This aim is based on preliminary observations that recombination between C. parvum lines generates progeny with distinct capacities to kill mice. We will test the following two working hypotheses: a) Virulence is determined by multiple genetic loci. b) QTL analysis can be used to identify genomic segments associated with virulence.