Genetic Aspects Of Viral Oncogenesis In Inbred Strains and Wild Mouse Species

小鼠白血病病毒(MLV)是一种伽玛逆转录病毒，与肿瘤的诱发以及神经和免疫缺陷疾病有关。近交系实验室小鼠和野生小鼠对小鼠伽马逆转录病毒感染和病毒诱导的疾病的易感性不同，它们携带的MLV类型也不同。敏感性差异是由于特定宿主基因的差异，我们一直在进行一项持续的努力，以识别和表征参与病毒抗性或有助于疾病过程的宿主基因。有两种类型的宿主基因参与病毒诱导的疾病。首先，小鼠基因组包含小鼠伽玛逆转录病毒基因组的副本，其中许多可以产生传染性和致病性病毒。其次，还有直接干扰病毒感染和复制的宿主因素，我们特别感兴趣的是那些抑制病毒进入和进入病毒复制周期的早期后阶段的因素。在进入水平上，抗性可由细胞表面受体的多态引起。在伽玛逆转录病毒进入受体细胞后，病毒抗性因子Fv1、mApobec3和TRIM5α可以抑制或改变逆转录和核转位。我们目前的目标是表征这些活跃的内源性逆转录病毒和宿主编码的抗性因子及其病毒靶标。最终目标是确定MUS进化过程中抗病毒活性的来源和程度，并阐明其相关机制。这项工作在很大程度上依赖于野生老鼠，因为实验室菌株只提供了小鼠遗传多样性的有限样本。此外，野生老鼠物种使我们能够检查携带病毒的自然种群的生存策略，并跟踪耐药基因的进化。这些小鼠还提供了新的抗性基因和病毒变种的来源。 其中一组项目旨在确定负责病毒结合和进入的病毒和细胞受体决定因素。我们目前正在研究XPR1受体对异向性/多向性MLV(XP-MLV)的作用。我们已经确定，在暴露于传染性病毒的小鼠群体中，病毒耐药性是由细胞表面受体的多态介导的。我们在野鼠身上共鉴定了6个XPR1易感变种，并描述了这些Mus Xpr1变种的地理和物种分布。这些受体中的五个限制了两个或更多依赖XPR1的病毒宿主范围变体的进入，所有这些受体都是在暴露于X-MLV的人群中进化的。 几乎所有的哺乳动物物种都有一个功能性的XPR1受体，并且可以被X-MLV感染。在我们最近关于X/P-MLV进入的研究中，我们将注意力从限制性受体转移到了介导所有X/P-MLV进入的许可的XPR1受体。大多数Mus物种和一些实验室毒株携带允许的Xpr1-sxv等位基因，在各种非啮齿动物物种中也有其他XPR1受体，尽管受体决定区域的序列存在相当大的差异，但它们是完全允许的。我们在病毒干扰试验中检测了四种哺乳动物(小鼠、人、水貂、兔)的允许细胞，以确定9个不同的X/P-MLV分离株是否在这4个多态但完全允许的受体上使用相同的不同受体决定簇。结果表明，一些病毒产生独特的物种特异性干扰谱，在某些情况下，可能与特定的受体序列变异相关。这表明，这些MLV变异体的进化是为了适应宿主受体的多态性，绕过竞争病毒的阻挡，或者避免为防御而获得的宿主编码的包膜糖蛋白。 在另一系列实验中，我们使用系统发育和分子生物学方法描述了从野鼠身上分离的传染性X/P-MLV的序列多样性和来源。这些MLV都来自内源性逆转录病毒(ERV)，这些病毒是大约100万年前由实验室小鼠的野鼠祖细胞获得的。对来自欧亚大陆和美洲野鼠的10种MLV的分析表明，这些病毒都是亚型间重组体。大多数MLV与一种独特的、主要与Y染色体连锁的MLV ERV亚型有关。对病毒包膜的检查进一步确定了3种亚型的生态型MLV，这是由于不同大小和位置的复制所致。这一分析有助于确定这些病毒的关系和起源，并强调重组在它们进化过程中的重要性。

Mouse leukemia viruses (MLVs) are gammaretroviruses linked to induction of neoplasms and to neurological and immunodeficiency diseases. Inbred strains of laboratory mice and wild mouse species differ in their susceptibility to mouse gammaretrovirus infection and to virus-induced diseases, and they also differ in the types of MLVs that they carry. Susceptibility differences are due to variations in specific host genes, and we have been engaged in an ongoing effort to identify and characterize host genes that are either involved in virus resistance or that contribute to the disease process. There are two types of host genes involved in virus-induced disease. First, the mouse genome contains copies of mouse gammaretrovirus genomes, many of which can produce infectious and pathogenic viruses. Second, there are also host factors that interfere directly with virus infection and replication, and we are particularly interested in those factors that inhibit virus entry and the early post-entry stages of the virus replicative cycle. At the level of entry, resistance can be caused by polymorphisms in the cell surface receptors. After the gammaretrovirus enters the receptive cell, reverse transcription and translocation to the nucleus can be inhibited or altered by virus resistance factors Fv1, mApobec3, and TRIM5alpha. Our current aim is to characterize these active endogenous retroviruses and the host encoded resistance factors and their viral targets. The ultimate goal is to define the origin and extent of antiviral activity in Mus evolution, and elucidate the responsible mechanisms. This work relies heavily on wild mice because laboratory strains provide only a limited sampling of the genetic diversity in Mus. Also, wild mouse species allow us to examine survival strategies in natural populations that harbor virus and to follow the evolution of the resistance genes. These mice additionally provide a source of novel resistance genes and virus variants. One set of projects aims to identify viral and cell receptor determinants responsible for virus binding and entry. We are currently working on the XPR1 receptor for the xenotropic/polytropic MLVs (XP-MLVs). We have determined that, in mouse populations exposed to infectious virus, virus resistance is mediated by polymorphisms of the cell surface receptor. We have identified a total of six XPR1 susceptibility variants in wild mice and described the geographic and species distribution of these Mus Xpr1 variants. Five of these receptors restrict entry by two or more of the virus host range variants that rely on XPR1, and all of these receptors evolved in populations exposed to X-MLVs. Virtually all mammalian species have a functional XPR1 receptor and can be infected by X-MLVs. In our most recent study on X/P-MLV entry, we shifted our attention from restrictive receptors to the permissive XPR1 receptors that mediate entry of all X/P-MLVs. Most Mus species and some laboratory strains carry the permissive Xpr1-sxv allele, and there are other XPR1 receptors in various non-rodent mammalian species that are fully permissive despite considerable sequence variation in the receptor-determining regions. We examined permissive cells from four mammalian species (Mus dunni, human, mink, rabbit) in virus interference assays to determine if 9 different X/P-MLV isolates use the same of different receptor determinants in these 4 polymorphic, but fully permissive receptors. Results showed that some viruses produce distinctive species-specific interference profiles that can, in some cases, be correlated with specific receptor sequence variations. This suggests these MLV variants evolved to adapt to host receptor polymorphisms, to circumvent blocks by competing viruses or to avoid host-encoded envelope glycoproteins acquired for defense. In another series of experiments, we used phylogenetic and molecular biological methods to describe the sequence diversity and origins of infectious X/P-MLVs isolated from wild mice. These MLVs all derive from endogenous retroviruses (ERVs) that were acquired by the wild mouse progenitors of laboratory mice about 1 million years ago. Analysis of ten MLVs from Eurasian and American wild mice indicated that all of these viruses are intersubtype recombinants. Most of these MLVs are related to a distinctive, largely Y-chromosome-linked MLV ERV subtype. Examination of the viral envelope further identifies 3 subtypes of ecotropic MLVs due to duplications of different sizes and locations. This analysis helps define the relationships and origins of these viruses and emphasizes the importance of recombination in their evolution.