Chromosomal mapping of the mink cell focus-inducing and xenotropic env gene family in the mouse

Structures of endogenous nonecotropic murine leukemia virus (MLV) long terminal repeats in wild mice: implication for evolution of MLVs

To develop a better understanding of the interaction between retroviruses and their hosts, we have investigated the polymorphism in endogenous murine leukemia proviruses (MLVs). We used genomic libraries of wild mouse DNAs and PCR to analyze genetic variation in the proviruses found in wild mouse species, including Mus musculus (M. m. castaneus, M. m. musculus, M. m. molossinus, and M. m. domesticus), Mus spretus, and Mus spicelegus, as well as some inbred laboratory strains. In this analysis, we detected several unique forms of sequence organization in the U3 regions of the long terminal repeats of these proviruses. The distribution of the proviruses with unique U3 structures demonstrated that xenotropic MLV-related proviruses were present only in M. musculus subspecies, while polytropic MLV-related proviruses were found in both M. musculus and M. spretus. Furthermore, one unique provirus from M. spicelegus was found to be equidistant from ecotropic provirus and nonecotropic provirus by phylogenetic analysis. This provirus, termed HEMV, was thus likely to be related to the common ancestor of these MLVs. Moreover, an ancestral type of polytropic MLV-related provirus was detected in M. spretus species. Despite their "ancestral" phylogenetic position, proviruses of these types are not widespread in mice, implying more-recent spread by infection rather than inheritance. These results imply that recent evolution of these proviruses involved alternating periods of replication as virus and residence in the germ line.

A multistep process of leukemogenesis in Moloney murine leukemia virus-infected mice that is modulated by retroviral pseudotyping and interference

Mixed retroviral infections frequently exhibit pseudotyping, in which the genome of one virus is packaged in a virion containing SU proteins encoded by another virus. Infection of mice by Moloney murine leukemia virus (M-MuLV), which induces lymphocytic leukemia, results in a mixed viral infection composed of the inoculated ecotropic M-MuLV and polytropic MuLVs generated by recombination of M-MuLV with endogenous retroviral sequences. In this report, we describe pseudotyping which occurred among the polytropic and ecotropic MuLVs in M-MuLV-infected mice. Infectious center assays of polytropic MuLVs released from splenocytes or thymocytes of infected mice revealed that polytropic MuLVs were extensively pseudotyped within ecotropic virions. Late in the preleukemic stage, a dramatic change in the extent of pseudotyping occurred in thymuses. Starting at about 5 weeks, there was an abrupt increase in the number of thymocytes that released nonpseudotyped polytropic viruses. A parallel increase in thymocytes that released ecotropic M-MuLV packaged within polytropic virions was also observed. Analyses of the clonality of preleukemic thymuses and thymomas suggested that the change in pseudotyping characteristics was not the result of the emergence of tumor cells. Examination of mice infected with M-MuLV, Friend erythroleukemia virus, and a Friend erythroleukemia virus-M-MuLV chimeric virus suggested that the appearance of polytropic virions late in the preleukemic stage correlated with the induction of lymphocytic leukemia. We discuss different ways in which pseudotypic mixing may facilitate leukemogenesis, including a model in which the kinetics of thymic infection, modulated by pseudotyping and viral interference, facilitates a stepwise mechanism of leukemogenesis.

A high-resolution map of the chromosomal region surrounding the nude gene

The nude mutation produces the apparently disparate phenotypes of hairlessness and congenital thymic aplasia. These pleiotropic defects are the result of a single, autosomal recessive mutation that was previously mapped to a 9-cM region of murine chromosome 11 bounded by loci encoding the acetylcholine receptor beta subunit and myeloperoxidase. In this study, exclusion mapping of a panel of congenic nude strains was used to place the nude locus between the microsatellite loci D11Nds1 and D11Mit8. The relative distance from nude to each of these loci was determined by analyzing a large segregating cross. Thus, nude lies 1.4 cM distal to D11Nds1 and is 0.5 cM proximal to D11Mit8. Mice that carried recombinational breakpoints between D11Nds1 and D11Mit8 were further analyzed at the loci Evi-2 and D11Mit34, which placed nu 0.2 cM proximal to these markers. D11Nds1 and Evi-2/D11Mit34 thus define the new proximal and distal boundaries, respectively, for the nu interval. We also report the typing of the above microsatellite markers in the AKXD, AKXL, BXD, CXB, and BXH recombinant inbred strains, which confirmed the relative order and separation of loci in this region.

Characterization of epitopes defining two major subclasses of polytropic murine leukemia viruses (MuLVs) which are differentially expressed in mice infected with different ecotropic MuLVs

Polytropic murine leukemia viruses (MuLVs) arise in mice by recombination of ecotropic MuLVs with endogenous retroviral envelope genes and have been implicated in the induction of hematopoietic proliferative diseases. Inbred mouse strains contain many endogenous sequences which are homologous to the polytropic env genes; however, the extent to which particular sequences participate in the generation of the recombinants is unknown. Previous studies have established antigenic heterogeneity among the env genes of polytropic MuLVs, which may reflect recombination with distinct endogenous genes. In the present study, we have examined many polytropic MuLVs and found that nearly all isolates fall into two mutually exclusive antigenic subclasses on the basis of the ability of their SU proteins to react with one of two monoclonal antibodies, termed Hy 7 and MAb 516. Epitope-mapping studies revealed that reactivity to the two antibodies is dependent on the identity of a single amino acid residue encoded in a variable region of the receptor-binding domain of the env gene. This indicated that the two antigenic subclasses of MuLVs arose by recombination with distinct sets of endogenous genes. Evaluation of polytropic MuLVs in mice revealed distinctly different ratios of the two subclasses after inoculation of different ecotropic MuLVs, suggesting that individual ecotropic MuLVs preferentially recombine with distinct sets of endogenous polytropic env genes.

Endogenous nonecotropic proviruses mapped with oligonucleotide probes from the long terminal repeat region

We characterized endogenous proviruses in C57BL/6J, DBA/2J, and C3H/HeJ mouse strains with oligonucleotide probes derived from long terminal repeat (LTR) sequences of three classes of nonecotropic murine leukemia virus. The segregation of proviral-host DNA junction fragments was followed in BXH and BXD recombinant inbred (RI) strain sets, and most fragments mapped readily to defined chromosomal regions. Most of the LTR fragments appear to correspond to proviruses mapped previously with oligonucleotide env region probes of the same viral class. At least 22 elements represent new proviral loci, no more than half of which may be solo LTRs, and an additional six may correspond to proviruses identified previously with less specific hybridization probes. Together with proviruses identified previously with env probes, the LTR probe-reactive elements represent the majority of endogenous murine leukemia proviruses in the mouse genome.

Effects of multiple retrovirus insertions on quantitative traits of mice

To assess the potential to generate quantitative genetic variation by insertional mutagenesis in a vertebrate, lines of mice in which many provirus vector inserts segregated at a low initial frequency on an inbred background (insert lines) were subjected to divergent artificial selection on body weight at 6 weeks and responses and heritability estimates compared to control lines lacking inserts. Heritability estimates were more than 1.5 times greater in the insert lines than in the controls, but because the phenotypic variance was substantially higher in the insert lines the genetic variance was about 3 times greater. Realized heritability estimates tended to be lower than heritabilities estimated by an animal model which utilizes information in covariances between all relatives in the data set. A surprisingly large response to selection occurred in the inbred control line. Insert lines were about 20% less fertile than controls. Division of the selection lines into inbred sublines in the later generations of the experiment revealed substantially greater variation among sublines of the insert lines than among the controls. Heritabilities were similar to typical estimates for the trait in outbred populations. In conclusion, there was clear evidence of extra variation deriving from inserts, which has yet to be attributed to individual genes.

Detection of quantitative trait loci from frequency changes of marker alleles under selection

A method was developed to estimate effects of quantitative trait loci (QTL) by maximum likelihood using information from changes of gene frequency at marker loci under selection, assuming an additive model of complete linkage between markers and QTL. The method was applied to data from 16 molecular and coat colour marker loci in mouse lines derived from the F2 of two inbred strains which were divergently selected on 6-week weight for 21 generations. In 4 regions of the genome, marker allele frequencies were more extreme than could be explained by sampling, implying selection at nearby QTL. An effect of about 0.5 standard deviations was located on chromosome 11, and accounted for nearly 10% of the genetic variance in the base population. QTL with effects as small as 0.2 phenotypic standard deviations could be detected. For typing of a given number of individuals, the power of detection of QTL is very high compared to, for example, analysis of an F2 population. The joint effects of linkage and selection were investigated by Monte Carlo simulation. Marker gene frequencies change little as a consequence of selection at a QTL unless the marker and QTL are less than about 20 cM apart.

Characterization of murine middle repetitive DNA

We have characterized four sequences from a small library containing a subset of the repetitive families of the mouse. Each clone has a repetition frequency of less than 1,100 copies per genome and each clone represents a unique family of middle repetitive DNA. One clone (pMR111) shares homology with mouse intracisternal A-particle (IAP) elements, a second clone (pMR89) has partial homology with a sequence in the 3' untranslated region of the human fibulin gene, while two clones (pMR6, pMR66) are new that have no homology to any reported DNA sequence. Each clone hybridizes to one or two discrete RNA transcripts from one or more tissues of the mouse. Clone pMR66 detected restriction fragment length polymorphisms (RFLPs) at three loci in genomic mouse DNA, defining loci at the distal end of chromosome 5 and the proximal end of chromosome 7. The third locus is unmapped. This study demonstrates that cloned repeats from a repetitive DNA library are a potential source of genetic markers.

Mapping of the mouse ornithine decarboxylase-related sequence family

A family of DNA sequences homologous to the mRNA encoding ornithine decarboxylase (ODC) and comprising approximately 12 members in the mouse genome has been analyzed genetically. The inheritance of variant DNA restriction fragments detected by ODC cDNA probes on Southern blots of DNA from inbred strain mice was determined in six sets of recombinant inbred (RI) mouse strains. The distributions of these variations among the RI strains were then compared with the RI strain distribution patterns (SDPs) of previously mapped loci. This allowed the identification of nine independent ODC-related loci, of which eight could be localized to specific regions of the mouse genome: Odc-rs1 near Lamb2 on Chromosome (Chr) 1; Odc-rs2 near Psp on Chr 2; Odc-rs5, a complex locus comprising at least 5-7 copies of the ODC sequence, associated with Igk on Chr 6; Odc-rs6 between Abpa and Tam-1 on proximal Chr 7; Odc-rs7 near Hbb on distal Chr 7; Odc-rs12 near Agt and Emv-2 on distal Chr 8; Odc-rs8 associated with the Igh complex on Chr 12; and Odc-rs9 near Otf-3f on Chr 14. The ODC-related sequence family thus comprises a set of genomically dispersed "marker" loci, and alleles for several of these loci can be analyzed simultaneously in DNA from mice or cell lines. DNA from mice of 70 inbred strains has been characterized for alleles at all nine Odc-rs loci.

Characterization of the endogenous nonecotropic murine leukemia viruses of NZB/B1NJ and SM/J inbred strains

We characterized 84 endogenous nonecotropic proviruses of NZB/B1NJ and SM/J inbred strains by examining proviral junction fragment segregation in recombinant inbred (RI) and backcross mice. Forty-five proviruses were shared with other laboratory strains, but 28 were unique to NZB/B1NJ or SM/J. Proviral loci were located on 17 of the 19 mouse autosomes and on both sex chromosomes. These markers will facilitate gene mapping in the NXSM RI set and contribute to the pursuit of a more complete map of the mouse genome.

Genetic linkage analysis in recombinant inbred mice of P40, a putative clone for the high-affinity laminin receptor

Recombinant inbred (RI) mice were used to genetically map sequences of a 43-kDa protein, P40, that was originally identified as a high-affinity laminin receptor. More recent data have implicated this protein in development of the retina (Rabacchi et al. Development 109: 521-531, 1990), possibly via its proposed function in protein translation (G. Brawerman, personal communication). We have identified, in Southern blots, a set of P40-related sequences in BXD recombinant inbred mouse DNA. Ten restriction fragment length polymorphisms (RFLPs) segregate among the RI strains and display strain distribution patterns (SDPs) which are linked in varying degrees to previously typed loci on Chromosomes (Chrs) 1, 3, 6, 9, 11, 14, and 19. An intronic DNA probe from an incompletely processed P40 mRNA transcript overlaps with two of these loci mapping near the cholecystokinin gene locus on the distal arm of Chr 9 and to another site on the distal arm of Chr 6, suggesting that functional genes probably reside at least at these two sites. These P40 loci comprise part of a multimember gene family that is well dispersed in the mouse genome.

Mechanism of leukemogenesis induced by mink cell focus-forming murine leukemia viruses

The Friend or Moloney mink cell focus-forming (MCF) virus encodes a recombinant-type envelope glycoprotein, gp70, that is closely related to the membrane glycoprotein, gp55, of Friend spleen focus-forming virus (SFFV). We have shown previously that gp55 has the ability to activate cell growth by binding to the cellular receptor for erythropoietin. Here we show that gp70 encoded by either the Friend or Moloney MCF virus also binds to the erythropoietin receptor and that coexpression of the receptor and gp70 in an interleukin-3 (IL-3)-dependent cell line can activate IL-3-independent growth. Furthermore, when the cDNA for the human IL-2 receptor beta chain, which is related by sequence to the erythropoietin receptor, was introduced into this cell line, it became growth factor independent after infection either with SFFV or with one of the two MCF viruses but not with an ecotropic virus. Based on these observations, we propose a mechanism for the early stage of leukemogenesis induced by the MCF-type murine leukemia viruses.

Clustering of cytokine genes on mouse chromosome 11

The presence of positionally conserved amino acid residues suggests that the mouse proteins TCA3, P500, MIP1-alpha, MIP1-beta, and JE are members of a single gene family. These proteins are activation specific and can be expressed by both myeloid and lymphoid cells. MIP1-alpha/MIP1-beta and MCAF (the putative human homologue of JE) act as chemotactic and activating agents for neutrophils and macrophages, respectively. The functions of TCA3 and P500 are unknown. We have used interspecies somatic cell hybrids and recombinant inbred mouse strains to show that the genes encoding TCA3, MIP1-alpha, MIP1-beta, and JE (provisionally termed Tca3, Mip-1a, Mip-1b, and Sigje, respectively) map as a cluster on the distal portion of mouse chromosome 11 near the Hox-2 gene complex. DNA sequence analysis indicates that the P500 and TCA3 proteins are encoded by alternative splicing products of one genomic gene. Additionally, the genes encoding TCA3 and JE are found to be strikingly similar with respect to the positions of intron-exon boundaries. Together, these data support the model that the cytokines TCA3, P500, MIP1-alpha, MIP1-beta, and JE are encoded by a single cluster of related genes. The gene encoding IL-5 (Il-5), which acts as a T cell-replacing factor, a B cell growth factor, and an eosinophil differentiation factor, is also mapped to mouse chromosome 11.Il-5 maps approximately 25 cM proximal to the Tca-3 gene and appears tightly linked to a previously described gene cluster that includes Il-3, Il-4, and Csfgm. We discuss the potential relevance of the two cytokine gene clusters described here with particular attention to specific human hematologic malignancies associated with chromosomal aberrations at corresponding locations on human chromosomes 5 and 17.

A linkage map of endogenous murine leukemia proviruses

Thirty endogenous proviruses belonging to the modified polytropic (Mpmv) class of murine leukemia virus (MLV) were identified by proviral-cellular DNA junction fragment segregation in several sets of recombinant inbred mice. Twenty-six Mpmv loci were mapped to chromosomal regions by matching proviral strain distribution patterns to those of previously assigned genes. Like other endogenous nonecotropic MLVs, Mpmv loci were present on several chromosomes in all strains examined. We pooled recombinant inbred strain linkage data from 110 MLV loci and selected marker genes in order to construct a chromosomal linkage map. Every mouse chromosome was found to harbor at least one proviral insertion, and several regions contained multiple integrations. However, the overall distribution of the 110 mapped proviruses did not deviate significantly from a random distribution. Because of their polymorphism in inbred strains of mice, and the ability to score as many as 57 proviruses per strain using only three hybridization probes, the nonecotropic MLVs mapped in common strains of mice offer a significant advantage over older methods (e.g., biochemical or individual restriction fragment polymorphisms) as genetic markers. These endogenous insertion elements should also be useful for assessing strain purity, and for studying the relatedness of common and not-so-common inbred strains.

Genetic identification of endogenous polytropic proviruses by using recombinant inbred mice

Forty-seven endogenous polytropic murine viruses (Pmv) were identified by examination of proviral-cellular DNA junction fragment segregation in recombinant inbred (RI) mice. Most Pmv loci were found in more than one of the seven RI progenitor strains analyzed, but only four were present in all strains. Chromosomal assignments for 41 Pmv loci were determined by comparing their RI strain distribution patterns with those of known genetic markers. Pmv loci were found dispersed throughout the genome, with chromosomes 1, 3, 4, 5, 7, 11, 12, 15, and 16 each carrying three or more proviruses. Linkage analysis in the AKXD RI set suggested that the gene encoding mink cell focus-forming virus resistance (Rcmfr) of DBA/2J mice is probably not a Pmv provirus. It was also deduced that no single, AKR/J-specific Pmv provirus is required as an env gene donor for thymomagenic mink cell focus-forming viruses. In addition, a Pmv provirus was very closely associated with the albino mutation on chromosome 7.

A repeated segment on the mouse Y chromosome is composed of retroviral-related, Y-enriched and Y-specific sequences

We report the isolation and characterization of two recombinant clones containing DNA derived from the Y chromosome of the C57BL/10 inbred mouse strain. Both clones were isolated from a lambda phage library derived from a partial EcoRI digest of C57BL/10 male DNA using the murine retrovirus M720. Characterization of these clones showed they were derived from a repeated segment present on the C57BL/10J Y chromosome that contains sequences found elsewhere in the genome. In addition, one clone contained a sequence, designated YB10, that is unique to the Y chromosome and present in approximately 500 copies on the C57BL/10J Y chromosome. Analysis of Southern blots containing DNAs prepared from females and males of representative species from four subgenera of Mus probed with pYB10 and the 3'LTR from one of the Y-associated retroviruses (MuRVY) revealed that, with the exception of a single fragment observed in both female and male DNA of Mus saxicola, hybridization to pYB10 was observed only to male DNA of the species Mus spretus, Mus hortulanus, Mus musculus, Mus domesticus and Mus abbotti. In addition, the pattern and intensity of hybridization to YB10 and the MuRVY-LTR indicated that sequence of divergence was followed by amplification of Y chromosome sequences containing YB10 and MuRVY. The divergence and amplification occurred separately in each of the ancestral lineages leading to M. spretus, M. hortulanus, M. abbotti, M. musculus and M. domesticus. We suggest that acquisition and amplification of DNA sequences by the mammalian Y chromosome has contributed to its evolution and may imply that the mammalian Y chromosome is evolving at a faster rate than the rest of the genome.

Genetic analysis of endogenous xenotropic murine leukemia viruses: association with two common mouse mutations and the viral restriction locus Fv-1

We have defined 40 endogenous xenotropic virus (Xmv) loci from several common inbred strains of mice by examining provirus-cell DNA junction fragments in recombinant inbred mice. Some inbred strains carried unique proviruses, but most Xmv loci were present in several strains, indicating that many Xmv integration events preexisted modern inbreeding. It was also clear that most Xmv junction fragment variation between inbred strains resulted from independent integration events and not modification or restriction site polymorphism following integration. Chromosomal assignments were determined for 32 Xmv loci by comparing their recombinant inbred strain distribution patterns to those of known genetic markers. The Xmv loci were generally dispersed throughout the genome, but several chromosomal regions contained more than one provirus. Furthermore, several close genetic associations with cellular genes were discovered. Four Xmv loci were closely linked to Fv-1b, a dominant viral resistance gene present in C57BL/6J, BALB/cJ, A/J, and several other strains. Xmv-28 was closely linked to rd (retinal degeneration), and Xmv-10 was closely linked to a (non-agouti), both of which are old mutations as inferred from their broad distribution in mice. We suggest that Xmv integration contributed to genetic diversity in the past and that much of this diversity exists today in common laboratory strains.

Expression of an endogenous retroviral transcript is associated with murine lupus

We have been investigating whether murine lupus is associated with endogenous type C retroviral expression. We used Northern blot analyses and oligonucleotide probes, which are able to distinguish the envelope genes of the xenotropic and mink cell focus-forming (MCF) classes of type C retroviruses. Xenotropic expression in the spleen varied markedly among inbred mouse strains; although all strains expressed a 1.8-kb transcript, only one-half expressed one or more larger transcripts (8.4, 7.2, and/or 3.0 kb). Autoimmune disease did not correlate with expression of any of the xenotropic transcripts. Xenotropic and MCF transcripts were expressed independently among the mouse strains studied. Splenic RNA from all strains contained 7.2-, 3.0-, and 1.8-kb MCF transcripts. Some strains also expressed 8.4-kb MCF splenic RNA. There was a strong association between murine lupus and expression of 8.4-kb MCF transcripts: 6 of 6 lupus-prone strains, but only 2 of 11 nonautoimmune strains, had detectable 8.4-kb MCF RNA. The xid and Yaa mutations had minimal effects on expression of 8.4-kb MCF-related transcripts, despite their major and opposite effects on disease. Moreover, New Zealand black mice highly expressed this RNA from day 1 of life, before disease development. The data suggest that expression of 8.4-kb MCF endogenous retroviral transcripts is a primary feature of murine lupus and is not secondary to disease expression.

Multiple endogenous xenotropic and mink cell focus-forming murine leukemia virus-related transcripts are induced by polyclonal immune activators

Northern (RNA) analyses were used to study the kinetics of induction of endogenous mink cell focus-forming (MCF) and xenotropic murine leukemia virus (MuLV)-related sequences in NFS and C57BL/6 mice injected with the polyclonal immune activators lipopolysaccharide (LPS), concanavalin A, and 8-bromoguanosine. All three mitogens induced 8.4-, 7.2-, 3.0-, and 1.8-kilobase (kb) MCF-related transcripts coordinately in the spleens of injected mice. Xenotropic MuLV-related expression was also rapidly induced in spleens by the three polyclonal immune activators, but in a noncoordinate manner: a distinct set of transcripts with different kinetics of expression was induced by each mitogen. MCF-related induction after LPS injection was both rapid and sustained; it began within 30 min and persisted for at least 8 days in the spleens of both NFS and C57BL/6 mice. LPS also caused prolonged induction of xenotropic transcripts in spleens of C57BL/6 but not NFS mice. The gld mutation, which causes polyclonal immune activation, induced 8.4-, 10.0-, and 13-kb MCF-related transcripts in C3H/HeJ mice without altering expression of 7.2-, 5.6-, 4.0-, 3.0-, or 1.8-kb MCF-related transcripts. The data demonstrate that individual endogenous MuLV-related transcripts can be induced coordinately or independently and suggest that expression of these transcripts is linked to early stages of lymphocyte activation.

Mechanism of selection of class II recombinant murine leukemia viruses in the highly leukemic strain CWD

The development of spontaneous lymphomas in CWD mice is associated with the expression of endogenous ecotropic murine leukemia viruses (MuLV) and the formation of recombinant viruses. However, the pattern of substitution of nonecotropic sequences within the envelope genes of the CWD class II recombinant viruses differs from that seen in class I recombinant MuLVs of AKR, C58, and HRS mice. To determine how CWD host genes might influence the envelope gene structure of the recombinant viruses, we characterized the responses of these mice to two different types of exogenous MuLVs. Neonatal mice injected the HRS class I recombinant PTV-1 became infected and developed T-cell lymphomas more rapidly than controls did. The inoculation of CWD mice with the leukemogenic AKR ecotropic virus SL3-3 led to the formation of recombinant MuLVs with a novel genetic structure and class II-like envelope genes, although SL3-3 generates class I recombinants in other strains. These results suggest that the absence of class I recombinant MuLVs in CWD mice is not related to the restriction of the replication or oncogenicity of class I viruses or to the absence of an appropriate ecotropic virus that can generate class I recombinants. More likely, the genes of CWD mice that direct the formation or selection of class II recombinant viruses affect the process of recombination between the ecotropic and nonecotropic envelope gene sequences.

Chromosomal organization of the cytochrome P450-2C gene family in the mouse: a locus associated with constitutive aryl hydrocarbon hydroxylase

Cytochromes P-450 represent a superfamily of enzymes with a central role in the metabolism of drugs, chemical toxins, and carcinogens. We have used genetic analysis to establish the complexity and catalytic function of a recently identified constitutively expressed murine hepatic cytochrome P-450 encoded by P450-2C. Southern blotting analysis shows that there are at least seven or eight genes within this family in the mouse and rat and that DNA restriction fragment length variants between different mouse inbred strains are observed. Analysis of recombinant inbred strains derived from these parent strains shows (i) these genes are clustered within 1 centimorgan, (ii) this gene family does not correspond to any of the known cytochrome P-450 loci or map near any well-characterized genomic markers, and (iii) this gene family segregates to within 1-2 centimorgans of a locus controlling constitutive aryl hydrocarbon hydroxylase activity in mice. With use of Chinese hamster/mouse somatic cell hybrids, the P450-2C locus was assigned to a region of mouse chromosome 19 that appears to be syntenic with the previously mapped human P450C2C locus on human chromosome 10. By in situ hybridization to mitotic mouse chromosomes, we have localized this region to the tip of chromosome 19. These results are discussed in relation to the physiological roles of this P-450 family in foreign compound metabolism and steroid oxidations.

Murine chromosomal regions correlated with longevity

In this longevity analysis of 360 BXD recombinant inbred female mice (20 different strains), 2 strains had very significantly shorter survival and 1 strain had very significantly longer survival than the other 17 strains; 4 other strains had less significant lengthening of survival compared to the other 13 strains in a proportional hazards model of survival. Mean survival on the shortest lived strain was 479 days; on the longest lived strain the mean survival was almost double (904 days). Ranges of survival within strain were very large (averaging 642 days), and strain accounted for only 29% of the variation in survival, showing that there are important environmental and/or special developmental effects on longevity even in this colony housed in a single room. Each strain had been typed for markers of 141 regions on 15 chromosomes; 101 of these markers had distinguishable distributions on the 20 strains. The two shortest lived strains had the same alleles for 63% of the markers. The single region most significantly correlated with survival (marked by P450, Coh, Xmmv-35 on chromosome 7) divided the mice into two groups with survival medians which differed by 153 days (755 days for mice with a B genotype; 602 days for mice with a D genotype). Evaluated individually, 44% of the genetic markers (including some markers on 11 of 15 chromosomes with any markers typed) were found to be significantly correlated with survival (P less than 0.05) although one would only expect 5% of the markers to be significant by chance. While studies of many markers should adjust for the multiple comparisons problem, one interpretation of these crude P values is that any experiment with only one of these "significant" markers typed would be likely to conclude that the marker was a significant predictor of survival. Two types of multiple regression models were used to examine the correlation with survival of groups of genes. When a proportional hazards model for survival was done in terms of genotype regions, a six genetic region model best correlated with survival: that marked by P450, Coh, Xmmv-35 on chromosome 7 (B allele lives longer), Ly-24 on chromosome 2 (B allele lives longer), beta 2M and H-3 on chromosome 2 (D allele lives longer) Lamb-2 on chromosome 1 (D allele lives longer), Ltw-4 on chromosome 1 (B allele lives longer), and the Igh area of chromosome 12 (Igh-Sa4, Igh-Sa2, Igh-Bgl, Igh-Nbp, Igh-Npid, Igh-Gte, Odc-8, and Ox-1; D allele lives longer).(ABSTRACT TRUNCATED AT 400 WORDS)

Mapping and gene order of U1 small nuclear RNA, endogenous viral env sequence, amylase, and alcohol dehydrogenase-3 on mouse chromosome 3

Linkage was established between a number of genes that map on chromosome 3 by studying the distribution patterns of DNA polymorphisms and protein electrophoretic mobility polymorphisms in recombinant inbred (RI) strains of mice. This analysis resulted in the following suggested gene order between the newly assigned genes and previously mapped genes: gamma-fibrinogen (Fgg), Xmmv-22 of mink cell focus-inducing (MCF) virus, U1b small nuclear RNA gene cluster (Rnu-1b), amylase (Amy-1,2), cadmium resistance (cdm), alcohol dehydrogenase-3 (Adh-3), alcohol dehydrogenase-1 (Adh-1). In situ hybridization to chromosome spreads confirmed the assignment of the Ulb small nuclear RNA (snRNA) gene cluster and the gamma-fibrinogen gene to the center of chromosome 3.

Polymorphism of murine endogenous proviruses revealed by using virus class-specific oligonucleotide probes

Inbred mice contain three classes of endogenous nonecotropic murine leukemia virus-related sequences, namely xenotropic, polytropic, and modified polytropic proviruses. Oligonucleotide probes specific for the three different classes were prepared and used to examine the diversity of endogenous sequences present in eight different strains of mice: HRS/J, BALB/cJ, A/J, AKR/J, C57BL/6J, DBA/2J, C57L/J, and C3H/HeJ. A high degree of polymorphism was observed. Overall, the strains showed between 17% (A/J and HRS/J) and 65% (C57BL/6J and C57L/J) shared proviruses, and only four proviruses were present in all eight strains. The similarity among the strains is due in part to the few proviruses present in all of the strains but also represents the independent assortment of a limited set of proviruses. These oligonucleotides provide a basis for determining the stability, distribution, and mutagenic potential of nonecotropic proviruses within the mouse genome.

Diverse wild mouse origins of xenotropic, mink cell focus-forming, and two types of ecotropic proviral genes

We analyzed wild mouse DNAs for the number and type of proviral genes related to the env sequences of various murine leukemia viruses (MuLVs). Only Mus species closely related to laboratory mice carried these retroviral sequences, and the different subclasses of viral env genes tended to be restricted to specific taxonomic groups. Only Mus musculus molossinus carried proviral genes which cross-reacted with the inbred mouse ecotropic MuLV env gene. The ecotropic viral env sequence associated with the Fv-4 resistance gene was found in the Asian mice M. musculus molossinus and Mus musculus castaneus and in California mice from Lake Casitas (LC). Both M. musculus castaneus and LC mice carried many additional Fv-4 env-related proviruses, two of which are common to both mouse populations, which suggests that these mice share a recent common ancestry. Xenotropic and mink cell focus-forming (MCF) virus env sequences were more widely dispersed in wild mice than the ecotropic viral env genes, which suggests that nonecotropic MuLVs were integrated into the Mus germ line at an earlier date. Xenotropic MuLVs represented the major component of MuLV env-reactive genes in Asian and eastern European mice classified as M. musculus molossinus, M. musculus castaneus, and Mus musculus musculus, whereas Mus musculus domesticus from western Europe, the Mediterranean, and North America contained almost exclusively MCF virus env copies. M. musculus musculus mice from central Europe trapped near the M. musculus domesticus/M. musculus musculus hybrid zone carried multiple copies of both types of env genes. LC mice also carried both xenotropic and MCF viral env genes, which is consistent with the above conclusion that they represent natural hybrids of M. musculus domesticus and M. musculus castaneus.

Genetic determinants of lung virus titers and resistance to lethal Sendai virus pneumonia

C 57 BL/6J mice are resistant to lethal Sendai virus pneumonia and have lower lung virus titers than susceptible DBA/2J mice. Linkage between these phenotypes was tested indirectly in segregant hybrids. Sas-1, B2m, and b on chromosomes 1, 2, and 4 were linked to significant (P less than .05) differences in virus-induced mortality; d on chromosome 9 was associated with a similar but smaller difference (.1 greater than P greater than .05). Mean lung virus titers were higher in F1 X DBA/2J mice that were homozygous for DBA alleles at B2m, b, and d than in heterozygotes. The difference in lung virus titers was larger between mice that were dihomozygous/diheterozygous for paired combinations; B2m-d (P less than .02), B2m-b (P less than .06), and b-d (P less than .05) and largest between mice that were trihomozygous/triheterozygous for B2m-b-d (P less than .001). The distribution of virus titers among 22 recombinant inbred strains derived from C 57 BL/6J and DBA/2J progenitors indicated 1) that the loci linked to B2m, b, and d are among at least 4 loci that regulate lung virus titers, 2) that Sas-1 may be linked to a fourth locus, 3) that the C 57 BL/6J genome contains at least one susceptibility locus, possibly within H-2, and 4) that some of these loci may be expressed through natural killer cell activity.

Assignment of the Ly-6--Ril-1--Sis--H-30--Pol-5/Xmmv-72--Ins-3--Krt-1--Int-1 --Gdc-1 region to mouse chromosome 15

Previous work has demonstrated linkage between Ly-6, H-30, and a locus, Ril-1, that affects susceptibility to radiation-induced leukemia. Results or preliminary linkage analyses suggested further that the cluster might be linked to Ly-11 on the proximal portion of mouse chromosome 2. Using molecular probes to examine somatic cell lines and recombinant inbred and congenic strains of mice, we have re-evaluated these linkage relationships. A cloned genomic DNA fragment derived from a retroviral site has been used to define a novel locus, Pol-5, that is tightly linked to both H-30 and Ril-1 as shown by analysis of the B6.C-H-30c congenic mouse strain. Following the segregation of the Pol-5 mouse-specific DNA fragment in a series of somatic cell hybrids carrying various combinations of mouse chromosomes on a rat or Chinese hamster background mapped Pol-5 to mouse chromosome 15. During the course of these studies, restriction fragment length polymorphisms were defined associated with several loci, including Pol-5, Ly-6, Sis, Ins-3, Krt-1, Int-1, and Gdc-1. Three of these loci, Sis, Int-1, and Gdc-1, have been previously mapped to chromosome 15 by others using somatic cell hybrids or isoenzyme analyses. Following the inheritance of these eight loci in recombinant inbred strains of mice allowed the definition of a linkage group on the chromosome with the order Ly-6--Ril-1--Sis--H-30--Pol-5--Ins-3--Krt-1--Int-1--Gdc-1. Analyses of alleles inherited as passengers in B6.C-H-30c, C3H.B-Ly-6b, and C57BL/6By-Eh/+ congenic mouse strains and in situ hybridization experiments support the above gene order and indicate further that the cluster is located on distal chromosome 15, with Ly-6 and Sis near Eh.