Molecular Mechanisms of msp2 Variation in Rickettsiae

描述(申请人提供)：这项建议的目的是提高我们对硬质立克次体病原体致病机制的了解，这些病原体会导致人和动物的埃立克次体病和无浆体病。这些病原体有效地利用一个小基因组(~lt；1.5Mb)来逃避免疫反应并在哺乳动物宿主中建立持续感染，在扁虱中肠和唾液腺中定居和复制，并在重新摄食扁虱后发展感染性以实现继续传播。MSP2最初定义在边缘无浆体中，感染这种病原体的牛和扁虱为发现修饰表面蛋白质组的机制提供了一个很好的模型。在之前的项目中，我们发现MSP2单一表达位点的节段性基因转换和相关的表面类似物MSP3是产生表面多样性的主要机制，并证明了操纵子编码的蛋白质在哺乳动物宿主和壁虱载体之间的差异表达。吞噬细胞无形体使用了类似的基因转换机制来表达人类患者的大量外膜蛋白，其他人的研究支持来自多个基因座的表达，以产生表面多样性。对边缘毛滴虫基因组的分析揭示了与msp2相关的一个复杂的外膜蛋白基因家族。这个msp2超家族由32个类似物组成，包括两个msp2和msp3操纵子连锁的表达位点，一个msp4基因位点，多个msp2和msp3假基因，以及其他未鉴定的类似msp2的类似物。我们假设，这些类似物的差异表达和它们之间的重组产生了病原体表面的多样性，并提供了生物适应和维持不同宿主和细胞环境的能力。本建议的具体目的是：1)确定msp2超家族基因在哺乳动物和无脊椎动物宿主感染过程中是否存在差异表达；2)确定msp2超家族基因簇中操纵子的结构和多样性的产生；3)确定msp2超家族蛋白在哺乳动物和无脊椎动物宿主中的差异调控机制；以及4)比较msp2超家族蛋白在边际藻和吞噬细胞中的表达调控。

DESCRIPTION (provided by applicant): The objective of this proposal is to improve our understanding of the mechanisms of pathogenesis of tick borne rickettsial pathogens that cause ehrlichiosis and anaplasmosis of humans and animals. These pathogens efficiently utilize a small genome (<1.5 Mb) to evade the immune response and establish persistent infection in the mammalian reservoir host, to colonize and replicate in the tick midgut and salivary glands, and to develop infectivity upon renewed feeding of the tick to effect onward transmission. MSP2 was initially defined in Anaplasma marginale and infections of cattle and ticks with this pathogen provide an excellent model for discovering the mechanisms used to modify the surface proteome. In the prior project period, we identified segmental gene conversion of single expression sites for MSP2, and a related surface paralogue MSP3, as a primary mechanism for generating surface diversity and demonstrated differential expression of operon-encoded proteins between the mammalian host and tick vector. A similar gene conversion mechanism is used by Anaplasma phagocytophilum to express a large repertoire of outer membrane proteins in human patients and studies by others support expression from multiple loci to generate surface diversity. Analysis of the A. marginale genome reveals a complex family of outer membrane protein genes related to msp2. This msp2 superfamily is comprised of 32 paralogues, comprising the two msp2 and msp3 operon-linked expression sites, a single msp4 gene locus, multiple msp2 and msp3 pseudogenes, and other uncharacterized msp2-like paralogues. We hypothesize that differential expression of these paralogues and recombination between them generates diversity in the pathogen surface and provides the ability of organisms to adapt to and persist in different hosts and cellular environments. The specific aims of the present proposal are: 1] Determine if msp2 superfamily genes are differentially expressed during infection of the mammalian and invertebrate hosts; 2] Determine the operon structure and generation of diversity within msp2 superfamily gene clusters; 3] Identify the mechanisms for differential regulation of the msp2 superfamily proteins in the mammalian and invertebrate hosts; and 4] Compare regulation of expression of msp2 superfamily proteins in A. marginale and A. phagocytophilum.