Specific sequence deletions in two classes of murine leukemia virus-related proviruses in the mouse genome

Mouse xenotropic and polytropic leukemia viruses (XMVs and PMVs) are closely related gammaretroviruses that use the XPR1 receptor for entry. To identify amino acid residues in XPR1 important for virus entry, we tested mouse cells derived from evolutionarily divergent species for susceptibility to prototypical PMVs, XMVs, and the wild mouse isolate CasE#1. CasE#1 has a variant XMV/PMV host range, and sequence analysis of the CasE#1 env gene identifies segments related to PMVs and XMVs. Cells from the Asian mouse species Mus pahari show a unique pattern of susceptibility to these three viruses; these cells are susceptible to XMVs and CasE#1 but are resistant to PMVs, whereas NIH 3T3 cells show the reciprocal pattern, susceptibility to only PMVs. The M. pahari XPR1 gene differs from that of NIH 3T3 in the two extracellular loops The mouse gammaretroviruses can be classified into several host range groups based on receptor usage. The xenotropic and polytropic mouse virus (XMV and PMV, respectively) subgroups were initially described as distinct host range groups based on their ability to infect mouse cells (11,14,22). However, XMVs and PMVs utilize the same receptor, XPR1, and the observed host range differences are due to sequence polymorphisms in both receptor and viral envelopes. Among mouse species, three allelic variants of Xpr1 have been described: the Xpr1 n receptor found in common strains of the laboratory mouse mediates entry of PMVs but not XMVs, the Xpr1 sxv receptor variant found in many wild mouse species, such as Mus spretus, mediates entry of XMVs as well as PMVs (17), and the Xpr1 c gene of M. castaneus is defective for entry of both virus types (26). In addition to susceptibility differences due to receptor polymorphism, in some mice XPR1 is blocked by expression of endogenous interfering PMVs (the Rmcf resistance gene of DBA/2 mice) (15) or endogenous XMVs (the Rmcf2 resistance gene of M. castaneus) (25,36). Cells of many other mammalian species, such as human and mink, generally are susceptible to infection by XMVs, and many also are susceptible to PMVs (8).The XPR1 receptor has been characterized as a transmembrane protein of unknown function, although it shows homology to yeast genes involved in signal transduction and phosphate transport (4, 32, 37). XPR1 has eight predicted transmembrane domains, with the greatest sequence divergence in its fourth extracellular loop (ECL), ECL4. Mutagenesis identified two critical amino acids, K500 in ECL3 and T582 in ECL4, for XMV entry (26). Chimeras made between human XPR1 and hamster XPR1 confirm that XPR1 has two receptor determinants that independently mediate entry of XMVs in ECL3 and ECL4 and identified a receptor determinant for PMVs in the ECL4 of human XPR1 (33). The viral sequences critical for XPR1 receptor binding have not been identified, although analysis of Env chimeras indicates that the primary determinants for this specificity are in the N-terminal 118 amino acids containing the first variable domain, VRA (3), and a recent study (2) identi...

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confidence: 99%

Wild Mouse Variants of Envelope Genes of Xenotropic/Polytropic Mouse Gammaretroviruses and Their XPR1 Receptors Elucidate Receptor Determinants of Virus Entry

Yan

Knoper

Kozak

2007

“…We derived a lambda library of NFS/N genomic DNA and isolated numerous clones containing sequences homologous to those encoding the polytropic receptor-binding domain. Previous reports have indicated that some of the polytropic MLV-related proviruses contained defects, including deletions in their env genes that would preclude their participation by a simple recombination process in the generation of replication-competent polytropic MLVs (6,24,46). We wanted to limit our analyses to proviruses that could potentially contribute intact sequences to recombinant polytropic MLVs.…”

Section: Resultsmentioning

confidence: 99%

“…replication-competent polytropic MLVs (6,24,35,46). It was possible that only a few of the endogenous proviruses would be candidates for the parents of recombinant viruses and that fewer still would possess the determinants for MAb 516 or Hy 7.…”

Section: Discussionmentioning

confidence: 99%

Antigenic Subclasses of Polytropic Murine Leukemia Virus (MLV) Isolates Reflect Three Distinct Groups of Endogenous Polytropic MLV-Related Sequences in NFS/N Mice

Evans

Lavignon

Taylor

et al. 2003

Polytropic murine leukemia viruses (MLVs) are generated by recombination of ecotropic MLVs with members of a family of endogenous proviruses in mice. Previous studies have indicated that polytropic MLV isolates comprise two mutually exclusive antigenic subclasses, each of which is reactive with one of two monoclonal antibodies termed MAb 516 and Hy 7. A major determinant of the epitopes distinguishing the subclasses mapped to a single amino acid difference in the SU protein. Furthermore, distinctly different populations of the polytropic MLV subclasses are generated upon inoculation of different ecotropic MLVs. Here we have characterized the majority of endogenous polytropic MLV-related proviruses of NFS/N mice. Most of the proviruses contain intact sequences encoding the receptor-binding region of the SU protein and could be distinguished by sequence heterogeneity within that region. We found that the endogenous proviruses comprise two major groups that encode the major determinant for Hy 7 or MAb 516 reactivity. The Hy 7-reactive proviruses correspond to previously identified polytropic proviruses, while the 516-reactive proviruses comprise the modified polytropic proviruses as well as a third group of polytropic MLV-related proviruses that exhibit distinct structural features. Phylogenetic analyses indicate that the latter proviruses reflect features of phylogenetic intermediates linking xenotropic MLVs to the polytropic and modified polytropic proviruses. These studies elucidate the relationships of the antigenic subclasses of polytropic MLVs to their endogenous counterparts, identify a new group of endogenous proviruses, and identify distinguishing characteristics of the proviruses that should facilitate a more precise description of their expression in mice and their participation in recombination to generate recombinant viruses.

“…Viruses with ecotropic host range and divergent env genes have also been found in Asian and Californian mice (the Fv4-related viruses) (9, 13) and in the European species M. spicilegus (formerly M. hortulanus) (36). The AKVand Fv4-type env genes, but not the M. spicilegus virus, are endogenous in their host species.Many of the wild mouse species closely related to laboratory strains contain proviral xenotropic/polytropic env genes, but in contrast to the laboratory strains that have multiple copies of both env types, the xenotropic and polytropic proviruses are largely segregated into different Mus species (3,20). Xenotropic MLV env genes are the predominant type in M. m. musculus of Eastern Europe and Asiatic Russia and in M. castaneus and its natural hybrid, M. m. molossinus.…”

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confidence: 99%

“…Many of the wild mouse species closely related to laboratory strains contain proviral xenotropic/polytropic env genes, but in contrast to the laboratory strains that have multiple copies of both env types, the xenotropic and polytropic proviruses are largely segregated into different Mus species (3,20). Xenotropic MLV env genes are the predominant type in M. m. musculus of Eastern Europe and Asiatic Russia and in M. castaneus and its natural hybrid, M. m. molossinus.…”

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confidence: 99%

Characterization of Recombinant Nonecotropic Murine Leukemia Viruses from the Wild Mouse Species Mus spretus

Jung

Kozak

2003

The wild mouse species most closely related to the common laboratory strains contain proviral env genes of the xenotropic/polytropic subgroup of mouse leukemia viruses (MLVs). To determine if the polytropic proviruses of Mus spretus contain functional genes, we inoculated neonates with Moloney MLV (MoMLV) or amphotropic MLV (A-MLV) and screened for viral recombinants with altered host ranges. Thymus and spleen cells from MoMLV-inoculated mice were plated on Mus dunni cells and mink cells, since these cells do not support the replication of MoMLV, and cells from A-MLV-inoculated mice were plated on ferret cells. All MoMLV-inoculated mice produced ecotropic viruses that resembled their MoMLV progenitor, although some isolates, unlike MoMLV, grew to high titers in M. dunni cells. All of the MoMLV-inoculated mice also produced nonecotropic virus that was infectious for mink cells. Sequencing of three MoMLV-and two A-MLV-derived nonecotropic recombinants confirmed that these viruses contained substantial substitutions that included the regions of env encoding the surface (SU) protein and the 5 end of the transmembrane (TM) protein. The 5 recombination breakpoint for one of the A-MLV recombinants was identified in RNase H. The M. spretusderived env substitutions were nearly identical to the corresponding regions in prototypical laboratory mouse polytropic proviruses, but the wild mouse infectious viruses had a more restricted host range. The M. spretus proviruses contributing to these recombinants were also sequenced. The seven sequenced proviruses were 99% identical to one another and to the recombinants; only two of the seven had obvious fatal defects. We conclude that the M. spretus proviruses are likely to be recent germ line acquisitions and that they contain functional genes that can contribute to the production of replication-competent virus.Laboratory mice contain numerous proviruses related to the mouse leukemia viruses (MLVs), now classed as gammaretroviruses. These proviruses include the two major host range subgroups, ecotropic and xenotropic/polytropic, defined by env sequence variation and receptor usage. The use of type-specific hybridization probes shows that the common inbred strains carry, on average, zero to five copies of ecotropic env genes, most of which are associated with full-length proviruses that can be expressed as infectious virus (14,21). Proviral copies of the nonecotropic xenotropic and polytropic MLV env genes are present in larger numbers, with more than 30 copies of each type being distributed over the laboratory mouse genome (8). Very few of the xenotropic proviruses can produce infectious virus (19), while both xenotropic and polytropic proviruses contribute to the generation of pathogenic mink cell focus-forming (MCF) viruses following recombination with replication-competent ecotropic virus (11,27,31).The wild mouse species present a different picture. Few wild mouse species harbor infectious virus that are related to the MLVs found in the common strains of laboratory mice (20). ...