Genetic Structure Of Murine Retroviruses

包括人类和小鼠在内的哺乳动物的基因组中约有8%由在进化过程中通过生殖系细胞感染获得的逆转录病毒元件组成。我们基因组中的逆转录病毒插入数量约为40，000，与我们DNA编码的基因总数相同。许多内源性逆转录病毒元件是有缺陷的，然而一些似乎是完整的，并且一些含有在发育和某些生理或病理条件期间表达的一个或多个病毒基因。关于逆转录病毒表达的控制或这种表达对宿主的生理或病理的影响知之甚少。一组广泛研究的内源性逆转录病毒是在小鼠中产生嗜多性鼠白血病病毒（MuLV）的那些。在一些情况下，多变性MuLV直接参与发病机制，包括诱导增殖性、免疫性和神经系统疾病。多嗜性MuLV是通过外源性嗜亲性MuLV与存在于近交系小鼠品系基因组中的内源性包膜序列重组而形成的，并且它们的产生导致混合逆转录病毒感染。我们研究了逆转录病毒在体内混合感染中的相互作用，通过共接种小鼠与嗜多性和嗜亲性MuLV，并观察到不同病毒混合物引起的疾病类型和克里思的显着变化。这些包括一种多变性MuLV诱导增殖性疾病的高度显著延迟，以及另一种多变性分离株导致神经系统疾病突然发展的显著协同效应。在这两种情况下，这些影响都伴随着嗜亲性病毒粒子内的嗜多性MuLV基因组的广泛假型化以及共接种小鼠中嗜多性MuLV感染和复制的显著升高。用亲嗜性和嗜多性MuLV共感染体外细胞培养物也导致嗜多性基因组的广泛假型化和嗜多性MuLV复制的显著升高。体外共感染细胞的研究强烈表明，多变MuLV的扩增是通过亲嗜性包装系统将多变基因组RNA掺入病毒体的效率提高的结果。 我们研究的另一个方面涉及内源性逆转录病毒家族的表征，其参与重组以产生多变性MuLV。这些内源性逆转录病毒在重组中的参与不是随机的，并且在用不同的外源性病毒感染小鼠时是不同的。我们已经表征了NFS/N小鼠中可能产生重组病毒的内源性逆转录病毒，并发现每种病毒都可以通过小的核苷酸序列差异来区分。将内源性病毒与接种外源嗜亲性MuLV后衍生的重组病毒进行比较，表明大约25至30种内源性逆转录病毒中只有3种经常参与重组。在另外的研究中，我们发现感染外源性逆转录病毒的小鼠释放感染性病毒颗粒，所述感染性病毒颗粒含有完整内源性逆转录病毒的转录控制元件的特征性RNA序列。我们目前正在对这些病毒基因组进行表征，以确定它们是否对应于以前未检测到的重组逆转录病毒类型或完整的内源性逆转录病毒。完整的内源性逆转录病毒的动员或含有内源性转录控制元件的重组体的产生是前所未有的，并且可能对内源性逆转录病毒参与疾病过程具有重要意义。 2004财政年度预付款：所有哺乳动物物种在其基因组中含有大量逆转录病毒元件，这些元件在进化过程中通过生殖系感染而积累。这些元件在发育过程中和某些病理条件下以受控的方式表达，并可能在宿主中发挥生理或病理作用。我们已经确定了NFS/N小鼠中一组内源性逆转录病毒序列的特征，这些序列已知参与了增殖性疾病以及其他疾病的诱导。它们的参与是通过与外源性逆转录病毒重组来介导的，以产生新的病毒，称为多嗜性MuLV，其表现出改变的宿主感染范围。已知内源性多变性前病毒在重组中的活性不相等，并且重组与不同的外源性病毒不同。然而，究竟是哪些内源性因子参与了重组尚不清楚。由于内源性序列彼此非常接近的相似性，这一直是难以捉摸的。我们早期的发现表明，这些病毒可以通过微小的序列差异来区分。这些差异有助于精确鉴定那些经常参与重组的前病毒。发现大约25至30种内源性病毒中只有3种容易参与重组。此外，一些外源性病毒与所有三种鉴定的内源性病毒重组，而其他外源性病毒仅与三种序列中的两种重组。这些结果，加上以前的研究结果表明，内源性逆转录病毒与不同的外源性病毒重组的特异性的分子机制。Alamgir AS，Owens N，Lavignon M，Malik F，Evans LH. 2005.精确鉴定参与用莫洛尼嗜亲性鼠白血病病毒（MuLV）纯化以产生多嗜性MuLV的NFS/N小鼠的内源性前病毒。病毒学杂志：79，4664 -71

Approximately 8% of the genomes of mammals, including humans and mice, are comprised of retroviral elements acquired by infection of germ line cells during the course of evolution. Retroviral insertions in our genome number about 40,000 and are in the same range as the total number of genes encoded by our DNA. Many endogenous retrovirus elements are defective, however some appear to be intact, and several contain one or more viral genes that are expressed during development and certain physiological or pathological conditions. Little is known about the control of retrovirus expression or the influence of such expression on the physiology or pathology of the host. An extensively investigated group of endogenous retroviruses are those giving rise to polytropic murine leukemia viruses (MuLVs) in mice. In several instances polytropic MuLVs have been directly implicated in pathogenesis, including the induction of proliferative, immunological, and neurological disorders. Polytropic MuLVs are formed by recombination of exogenous ecotropic MuLVs with endogenous envelope sequences present in the genomes of inbred mouse strains and their generation results in a mixed retrovirus infection. We have investigated the interactions of retroviruses in mixed infections in vivo by co-inoculation of mice with polytropic and ecotropic MuLVs and observed remarkable alterations in the types and tempo of disease induced by different mixtures of viruses. These included a highly significant delay in the induction of proliferative disease with one polytropic MuLV and a profound synergistic effect resulting in the abrupt development of a neurological disease with another polytropic isolate. In both cases these effects were accompanied by extensive pseudotyping of the polytropic MuLV genome within ecotropic virions and a striking elevation of polytropic MuLV infection and replication in co-inoculated mice. Co-infection of in vitro cell cultures with ecotropic and polytropic MuLVs also results in extensive pseudotyping of the polytropic genome and a striking elevation in polytropic MuLV replication. Studies of the in vitro co-infected cells strongly suggest that the amplification of polytropic MuLV is the result of increased efficiency of incorporation of the polytropic genomic RNA into virions by the ecotropic packaging system. Another aspect of our studies involves the characterization of the family of endogenous retroviruses that participate in recombination to yield polytropic MuLVs. The participation of these endogenous retroviruses in recombination is not random and is different upon infection of mice with different exogenous viruses. We have characterized the endogenous retroviruses in NFS/N mice that could potentially give rise to the recombinant viruses and found that each could be distinguished by small nucleotide sequence differences. Comparison of the endogenous viruses to recombinant viruses derived after inoculation of an exogenous ecotropic MuLV indicated that only 3 of the approximately 25 to 30 endogenous retroviruses frequently participate in recombination. In additional studies we have found that mice infected with exogenous retroviruses release infectious virus particles containing RNA sequences characteristic of the transcriptional control elements of intact endogenous retroviruses. We are currently characterizing these viral genomes to determine if they correspond to previously undetected types of recombinant retroviruses or to intact endogenous retroviruses. The mobilization of intact endogenous retroviruses or the generation of recombinants containing endogenous transcriptional control elements is unprecedented and may have important implications for the involvement of endogenous retroviruses in disease processes. FY 2004 advance: All mammalian species contain a large number of retrovirus elements in their genomes that have accumulated by germ line infection over the course of evolution. The elements are expressed in a controlled manner during development and in certain pathological conditions and may play physiological or pathological roles in the host. We have characterized a group of endogenous retrovirus sequences in NFS/N mice that are known to be participants in the induction of proliferative diseases as well as other disorders. Their participation is mediated by recombination with exogenous retroviruses to generate new viruses, termed polytropic MuLVs that exhibit an altered host range of infection. It is known that the endogenous polytropic proviruses are not equally active in recombination and that recombination differs with different exogenous viruses. It was not known, however, precisely which of the endogenous elements participate in recombination. This has been elusive because of the very close similarity of the endogenous sequences to one another. Our earlier findings indicated that the viruses are distinguishable by minor sequence differences. These differences facilitated the precise identification of those proviruses that frequently participate in recombination. It was found that only 3 of approximately 25 to 30 of the endogenous viruses readily participate in recombination. Further, some exogenous viruses recombine with all three of the identified endogenous viruses whereas other exogenous viruses recombine with only two of the three sequences. These results, coupled with results of previous studies suggested a molecular mechanism for the specificity of recombination of the endogenous retroviruses with different exogenous viruses. Alamgir AS, Owens N, Lavignon M, Malik F, Evans LH. 2005. Precise Identification of Endogenous Proviruses of NFS/N Mice Participating in Recombination with Moloney Ecotropic Murine Leukemia Virus (MuLV) To Generate Polytropic MuLVs. J Virol:79,4664-71