GR Strain Research Articles

Isolation and characterization of a novel strain of duck aviadenovirus B from Muscovy ducklings with acute hepatitis in China.

A new disease designated as Pale liver disease (PLD) has been circulating in Chinese Muscovy duck flocks since 2014, which is characterized by fatigue, diarrhoea, sudden death and acute hepatitis with pale and haemorrhagic liver. In this study, the etiological agents of PLD were isolated, causing a significant cytopathic effect (CPE) by cell rounding. Virus particles were observed by transmission electron microscopic (TEM) observation. The same disease was reproduced by experimental infection with the isolate BG61. The whole genomes of isolates were 43,842nt in length with a GC content of 47.11%, similar to French Muscovy duck adenovirus strain GR with a GC content of 46.08%. The isolates shared 99.71-99.95% and 93.31-93.33% identity with Chinese Muscovy duck adenovirus isolates and GR strain, respectively. The DNA polymerase gene of all Muscovy duck adenovirus strains formed a separate genetic lineage with 99.55-100% amino acid sequence identity. All Chinese Muscovy duck adenovirus isolates contained two fibre genes. In contrast, only one fibre gene was found in GR, the only representative strain in species Duck aviadenovirus B. Anti-DAdV-2serumantibodies had a weakneutralizingactivity against Chinese Muscovy duck adenovirus isolates. The phylogenetic trees of the complete genome, hexon and fibre proteins revealed that all Muscovy duck adenovirus strains formed a major genetic lineage consisting of two clades. Thus, both GR and Chinese Muscovy duck adenovirus strains were proposed to be included in the same species of Duck aviadenovirus B belonging to the genus Aviadenovirus. The species Duck aviadenovirus B included two serotypes or genotypes, such as GR, which represents the strain of serotype 1 or genotype 1 (DAdV B1) and Chinese Muscovy duck adenovirus strains, which belong to serotype 2 or genotype 2 (DAdV B2).

Molecular characterization and the mutation pattern of SARS-CoV-2 during first and second wave outbreaks in Hiroshima, Japan.

BackgroundIn this study, we performed molecular characterization of SARS-CoV-2 strains in Hiroshima and its mutation pattern between the first and second waves of the outbreak.MethodA total of 55 nasal swab samples from the first wave in Hiroshima and 13 from the second wave were examined quantitatively by RT-qPCR and qualitatively by nested PCR using specific primers. Four samples from each wave underwent next-generation sequencing and phylogenetic tree analysis including controls and all sequences retrieved in Japan from GISAID and GenBank. Subsequently, mutations were examined.ResultsViral load ranged 7.85 × 101−1.42 × 108 copies/ml. Of 68 samples, one was Asian type-O, 65 were European type-GR, and 2 were undetectable. Phylogenetic tree analysis indicated that Japan was infected with various Asian strains (L, S, V, O) from January through April. By second week of March, European strains (G, GH, GR) had appeared, and GR strains became predominant after mid-March. The first case in Hiroshima was classified as Asian strain O, and the rest were GR strains. Then, second wave of GR strains appeared independently with 11–15 base mutations. Comparing the first- and second-wave GR strains, mutation rate was 1.17–1.36 × 10−3 base substitutions per site per year; in addition, amino acid changes occurred at S1361P and P3371S in ORF1a, A314V in ORF1b, and P151L in N. All seven GR strains were D614G variants with R202K and G203R mutations in N. A single-nucleotide insertion in ORF8 that causes a defect in ORF8 protein was found in one isolate (S66) from the second wave.ConclusionOur findings reveal the evolutionary hierarchy of SARS-CoV-2 in Japan. The predominant D614G variants and a new form of ORF8 deletion in Hiroshima provide the clue for role of viral factor in local outbreaks of SARS-CoV-2.

Spectral Reflectance Indices and Physiological Parameters in Quinoa under Contrasting Irrigation Regimes

High temperatures, coupled with arid environments, are a major constraint to quinoa (Chenopodium quinoaWilld.) production. Here, we tested the effectiveness of multiple phenotypic and physiological parameters useful in the selection of heat‐tolerant quinoa genotypes. Initially, we screened 112 quinoa genotypes for leaf greenness index under high‐temperature greenhouse conditions. Of these, eight genotypes were selected for field evaluations under irrigated and rainfed treatments in two locations over two growing seasons (2016–2017) in Washington State. Of these eight, four genotypes were selected as potentially heat tolerant (QQ74, Baer, BGQ 352, and Pison), and four were selected as heat‐susceptible (17 GR, La Molina, 3 UISE, and Japanese Strain). Spectral reflectance indices including normalized difference vegetation index (NDVI) and green NDVI, as well as multiple physiological parameters, such as stomatal conductance, leaf temperature, and area under soil plant analysis development (SPAD) value decline curve (AUSDC), were evaluated. Results show variability in stomatal conductance among genotypes with 17 GR and BGQ 352 having the highest stomatal conductance and QQ74 the lowest. Baer, Pison, and QQ74 had the highest NDVI value across environments, and Japanese Strain had the lowest. Best linear unbiased prediction values in AUSDC showed that QQ74 had the highest leaf greenness and Japanese Strain had the lowest; these were classified as heat tolerant and heat susceptible, respectively. The NDVI is a potentially useful measure to predict grain yield in quinoa.

High prevalence of mouse mammary tumor virus-like gene sequences in breast cancer samples of Iranian women

ABSTRACTMouse mammary tumor virus (MMTV) is considered to be responsible for breast tumor development in mice. In several instances sequences homologous to the genome of this virus have been reported in human breast cancer samples.Here we aimed to evaluate MMTV involvement in human breast cancer development. DNA was extracted from 118 formalin fixed and paraffin embedded malignant (n = 59) and benign (n = 59) breast lesions. Using two sets of outer and inner MMTV-like envelope specific primers, in a nested PCR setup, MMTV genome was detected in 19 samples out of 59 (%32.2) cases of breast carcinomas, while in non-malignant breast tissue samples, only 3 samples out of 59 (%5) were positive. The difference was statistically highly significant (p < 0.001). Alignment of PCR amplified sequences with BR6, GR and C3H mouse mammary tumor virus strains emerged to be around 99% identical which is indicative of tumor tissue infection by an exogenous mouse MMTV genome.

C3H strain of mouse mammary tumour virus, like GR strain, infects human mammary epithelial cells, albeit less efficiently than murine mammary epithelial cells.

Mouse mammary tumour virus (MMTV) is a member of the genus Betaretrovirus, infects rodent cells and uses mouse tranferrin receptor 1 for cell entry. Several MMTV strains have been shown to productively infect, in addition to murine cells, various heterologous cell lines including those of human origin, albeit less efficiently than murine cells. Here, we analysed whether MMTV from C3H mice [MMTV(C3H)], reported previously to be incapable of infecting human cells, could productively infect human cells. Using a recently described high-titre MMTV-based vector carrying MMTV(C3H) envelope protein (Env), we successfully transduced cells of human origin. Furthermore, WT MMTV(C3H) was able to infect human cells, albeit less efficiently than mouse cells. The established infection was, however, sufficient to enable virus spread to every cell in culture. The infectivity of WT MMTV(C3H) and MMTV-based vectors carrying MMTV(C3H)Env was blocked by heat inactivation, an inhibitor of reverse transcription (3'-azido-3'-deoxythymidine) and pre-incubation with neutralizing anti-MMTV antibodies that did not neutralize vectors pseudotyped with amphotropic murine leukemia virus Env, providing evidence for an authentic, receptor-mediated and reverse transcriptase-dependent infection process. Persistently infected human Hs578T cells produced infectious virions capable of infecting naïve human breast cells in culture, the infectivity of which could also be blocked by neutralizing anti-MMTV antibodies, demonstrating that virus particles released by the persistently infected Hs578T cells were related antigenically to the virus produced from murine cells. Taken together, our results show that MMTV(C3H), like MMTV(GR) and MMTV(RIII), is able not only to infect but also to replicate in cultured human breast cells.

Pathobiology of Aging Mice and GEM

The use of induced and spontaneous mutant mice and genetically engineered mice (and combinations thereof) to study cancers and other aging phenotypes to advance improved functional human life spans will involve studies of aging mice. Genetic background contributes to pathology phenotypes and to causes of death as well as to longevity. Increased recognition of expected phenotypes, experimental variables that influence phenotypes and research outcomes, and experimental design options and rationales can maximize the utility of genetically engineered mice (GEM) models to translational research on aging. This review aims to provide resources to enhance the design and practice of chronic and longevity studies involving GEM. C57BL6, 129, and FVB/N strains are emphasized because of their widespread use in the generation of knockout, transgenic, and conditional mutant GEM. Resources are included also for pathology of other inbred strain families, including A, AKR, BALB/c, C3H, C57L, C58, CBA, DBA, GR, NOD.scid, SAMP, and SJL/J, and non-inbred mice, including 4WC, AB6F1, Ames dwarf, B6, 129, B6C3F1, BALB/c,129, Het3, nude, SENCAR, and several Swiss stocks. Experimental strategies for long-term cross-sectional and longitudinal studies to assess causes of or contributors to death, disease burden, spectrum of pathology phenotypes, longevity, and functional healthy life spans (health spans) are compared and discussed.

Mouse mammary tumor virus (MMTV)-like DNA sequences in the breast tumors of father, mother, and daughter

BackgroundThe diagnosis of late onset breast cancer in a father, mother, and daughter living in the same house for decades suggested the possibility of an environmental agent as a common etiological factor. Both molecular and epidemiological data have indicated a possible role for the mouse mammary tumor virus (MMTV), the etiological agent of breast cancer in mice, in a certain percentage of human breast tumors. The aim of this study was to determine if MMTV might be involved in the breast cancer of this cluster of three family members.ResultsMMTV-like envelope (env) and long terminal repeat (LTR) sequences containing the MMTV superantigen gene (sag) were detected in the malignant tissues of all three family members. The amplified env gene sequences were 98.0%–99.6% homologous to the MMTV env sequences found in the GR, C3H, and BR6 mouse strains. The amplified LTR sequences containing sag sequences segregated to specific branches of the MMTV phylogenetic tree and did not form a distinct branch of their own.ConclusionThe presence of MMTV-like DNA sequences in the malignant tissues of all three family members suggests the possibility of MMTV as an etiological agent. Phylogenetic data suggest that the MMTV-like DNA sequences are mouse and not human derived and that the ultimate reservoir of MMTV is most likely the mouse. Although the route by which these family members came to be infected with MMTV is unknown, the possibility exists that such infection may have resulted from a shared exposure to mice.

Comparative pulsed-field gel electrophoresis typing of gentamicin-resistant and -susceptible methicillin-resistantStaphylococcus aureus strains isolated in France between 1991 and 1998. Changes in antibiotic susceptibility

Using macrorestriction of genomic DNA and pulsed-field gel electrophoresis, we examined 504 non-redundant, infection-causing human isolates of methicillin-resistant Staphylococcus aureus susceptible (GS: 238 isolates) or resistant to gentamicin (GR: 266 isolates). The strains were isolated at Albert Chenevier Hospital (Créteil, France) between 1 January 1991 and 31 December 1998. Their susceptibility to erythromycin, lincomycin, tetracycline, rifampicin, fusidic acid and fosfomycin was also studied. Seventy-six genotypes were identified (percentage similarity<80). Ten types, each containing at least eight strains, predominated. GR strains showed higher genetic polymorphism than GS strains: the 266 GR isolates belonged to 67 genotypes, five of which predominated (44, 42, 38, 30 and 15 isolates); the 238 GS isolates belonged to only 18 types, four of which predominated (112, 83, 11 and 10 isolates). Fifty-six percent of GR strains (34 Gt) were resistant to erythromycin, lincomycin, tetracycline and rifampicin, and were isolated at relatively stable frequencies. Resistance to five antibiotics studied (susceptible to fusidic acid) was observed among 16.5% of GR strains. The frequency of strains with this profile diminished from 30% in the early 1990s to 10% in 1998. One hundred and twenty-six GS isolates were susceptible to all six antibiotics; this profile was only found from 1993 onwards, and was increasingly frequent (60% of GS strains in 1996). Resistance to erythromycin and lincomycin only was found in 70 GS isolates; this profile accounted for approximately half the isolates in 1992/1993 and only one-third in 1998. These results, obtained over an eight-year period, show an overall increase in antibiotic susceptibility. They confirm the spread of two major clones of MRSA-GS and support the hypotheses that GS strains derive from GR strains that have lost the aac6′-aph2″ gene; and that GS strains are genetically related to those that were present before the use of gentamicin and persisted at a low frequency until 1992–1993.

Pulmonary carcinogenesis susceptibility-associated single-nucleotide polymorphisms in K-ras intron 2 affect the binding of factor Gata-6 but not gene expression

The sequence of K-ras intron 2, which has been associated with lung tumor susceptibility in inbred mouse strains, was analyzed in susceptible strain GR and in resistant strains PT and UT. In the latter case, the intron had a tandem repeat of a 37-bp sequence with variant GC of its two single-nucleotide polymorphisms (SNPs), as earlier reported for resistant strains AKR, C57BL/c, and C3H/A. Strain GR did not differ in intron structure from susceptible strains A/He and ICR, having one copy of the 37-bp sequence with SNP variant CA. By gel retardation assay, a DNA probe corresponding to "susceptible" allele CA of K-ras region 278-307 formed an additional complex with nuclear proteins extracted from the lungs, as compared with probes corresponding to the "resistant" GC and "intermediate" CC alleles. With specific antibodies, the protein binding to the susceptible allele was identified as transcription factor GATA-6. Reverse transcription with subsequent multiplex PCR did not reveal a significant difference in K-ras expression for susceptible and resistant strains. The results suggest that SNPs of K-ras intron 2 do not affect the level of K-ras expression but do control the binding of GATA-6, which plays an important role in lung differentiation.

Endogenous Mouse Mammary Tumor VirusMtv-17 Is Involved inMtv-2-Induced Tumorigenesis in GR Mice

Mtv-2 is an endogenous mouse mammary tumor virus (MMTV) that is responsible for the induction of mammary gland tumors in the high mammary gland tumor-incidence strain GR. GR animals inherit four different endogenous MMTVs in addition toMtv-2:Mtv-3,Mtv-7,Mtv-8 andMtv-17. In this study we analyzed the involvement of these nonpathogenic endogenous proviruses in the mammary gland tumors caused byMtv-2. We showed thatMtv-17 is expressed in the mammary gland of GR mice, efficiently packaged into virions, and shed into milk. DNA isolated from both mammary gland tumors and the nonmalignant mammary gland tissues of GR mice contained amplified copies of both newly acquiredMtv-2 and recombinant proviruses with theenvgene derived fromMtv-17. A small percentage of these tumors contained predominantly recombinant viruses. These findings suggest a role forMtv-17 in the mammary gland tumors induced byMtv-2 in GR mice.

Effects of organic compounds on the degradation ofp-nitrophenol in lake and industrial wastewater by inoculated bacteria

Many microorganisms fail to degrade pollutants when introduced in different natural environments. This is a problem in selecting inocula for bioremediation of polluted sites. Thus, a study was conducted to determine the success of four inoculants to degrade p-nitrophenol (PNP) in lake and industrial wastewater and the effects of organic compounds on the degradation of high and low concentrations of PNP in these environments. Corynebacterium strain Z4 when inoculated into the lake and wastewater samples containing 20 micrograms/ml of PNP degraded 90% of PNP in one day. Addition of 100 micrograms/ml of glucose as a second substrate did not enhance the degradation of PNP and the bacterium utilized the two substrates simultaneously. Glucose used at the same concentration (100 micrograms/ml), inhibited degradation of 20 micrograms of PNP in wastewater by Pseudomonas strain MS. However, glucose increased the extent of degradation of PNP by Pseudomonas strain GR. Phenol also enhanced the degradation of PNP in wastewater by Pseudomonas strain GR, but had no effect on the degradation of PNP by Corynebacterium strain Z4. Addition of 100 micrograms/ml of glucose as a second substrate into the lake water samples containing low concentration of PNP (26 ng/ml) enhanced the degradation of PNP and the growth of Corynebacterium strain Z4. In the presence of glucose, it grew from 2 x 10(4) to 4 x 10(4) cells/ml in 3 days and degraded 70% of PNP as compared to samples without glucose in which the bacterium declined in cell number from 2 x 10(4) to 8 x 10(3) cells/ml and degraded only 30% PNP. The results suggest that in inoculation to enhance biodegradation, depending on the inoculant, second organic substrate many play an important role in controlling the rate and extent of biodegradation of organic compounds.

The mouse mammary tumor virus long terminal repeat encodes A 47 kDa Glycoprotein with a short half-life in mammalian cells

The mouse mammary tumor virus proviral DNA contains an open reading frame in the 3' long terminal repeat which can code for a 36 kDa polypeptide with a putative transmembrane sequence and five Nlinked glycosylation sites. This gene is known to code for a superantigen which deletes a specific subset of CD4 + T lymphocytes in vivo. The superantigen encoded by the exogenous mouse mammary tumor virus of the GR strain acts specifically on Vβ 14 bearing T cells. We produced recombinant vaccinia viruses to express either the complete or a truncated ORF protein after infection of primate cells in culture. The complete ORF gene in mammalian cells leads to the production of a 47 kDa protein which is specifically detected with an anti-ORF-peptide antiserum. The 47 kDa protein can be labeled with d-[2- 3H]mannose and its synthesis is inhibited by tunicamycin, an N-linked glycosylation inhibitor, indicating that it is a glycoprotein. The truncated ORF protein beginning at the second ATG of the open reading frame is also modified, but the C-terminal half of ORF, starting at the fifth ATG, has the expected size of the non modified polypeptide. Pulse-chase experiments indicate that the ORF protein has a short half-life of about 1.5–2hr.

Differential transport and processing of variant mouse mammary tumor virus glycoproteins.

The transport and proteolytic processing of two individual gene isolates of the mouse mammary tumor virus (MMTV) glycoprotein were compared in transfected rat HTC hepatoma cells. Plasmids were constructed such that the MMTV glycoprotein genes were constitutively expressed from the promoter within the Rous Sarcoma Virus 5' Long Terminal Repeat in the absence of other MMTV proteins. An isolate of the GR strain MMTV glycoprotein was efficiently transported and processed resulting in the localization of MMTV glycoproteins at the cell surface and in the extracellular environment. Moreover, the kinetics of acquisition of endoglycosidase H resistant oligosaccharide side chains and the rate of endoproteolytic cleavage of the glycosylated polyprotein expressed in transfected cells were virtually identical to that observed in viral-infected rat hepatoma cells. In contrast, a natural variant of the C3H strain MMTV glycoprotein expressed in transfected cells was retained in an intracellular compartment by a heavy chain binding protein (BiP)-independent pathway in an endoglycosidase H sensitive and uncleaved form. This MMTV glycoprotein isolate was retained early in the exocytic pathway and displayed a half-life of approximately 45 min in transfected cells. Only a minor fraction of the expressed C3H variant glycoprotein was detected at the cell surface but was not externalized. Our results suggest that the variant C3H MMTV glycoprotein contains one or more mutations that preclude its efficient transport through the exocytic pathway.

A rare common integration site of proviruses of the mouse mammary tumor virus in P-type mammary tumors of mouse strain GR

The mouse mammary tumor virus (MMTV) can induce mammary tumors in mice by proviral activation of the cellular oncogenes int-1 or int-2. Activation of these genes, however, is observed in only a few hormone- and pregnancy-dependent mammary tumors of the mouse strain GR. To study the possible involvement of other oncogenes we cloned three MMTV proviral-host fragments (MT 40, 42, and 53) from different mammary tumors of GR with a single acquired MMTV provirus. From a genomic library of normal mouse DNA we isolated phages with insert DNAs that covered 20–30 kb of the uninterrupted regions. Suitable probes devoid of repetitive DNA sequences were isolated in order to screen other mammary tumors for MMTV proviral integrations in these regions. Only two mammary tumors, MT 40 and 42, showed integration of extra MMTV proviruses within the same region. The integrations occurred only 60 bp apart. The other mammary tumors, however, did not contain MMTV proviral integrations in this region, nor in the MT 53 region. Using mouse-hamster somatic cell hybrid DNA, the MT 40 42 integration region was assigned to mouse chromosome 7, and the second region, MT 53, to chromosome 16. The two regions bear no homology to known cellular oncogenes. We did not observe any mRNA being expressed from these cloned segments either in tumors or in normal mammary glands. These findings indicate that plaque(P)-type mammary tumors in mouse strain GR do not originate from MMTV provirus insertions in a particularly favored integration region, but that there may be a variety of integration sites in these tumors.

ULTRASTRUCTURAL AND IMMUNOLOGICAL STUDIES OF VIRUS PARTICLES OBSERVED IN A T‐CELL LINE DERIVED FROM A MOUSE SPONTANEOUS LYMPHOMA

Intracytoplasmic type A virus particles in clusters, associated with budding, immature type B and mature type B-like particles were observed in a T-cell line derived from a spontaneous lymphoma of an A/J mouse. These particles shared the antigenic determinants with murine mammary tumor virus from RIII, C3H, and GR strains as revealed by both indirect immunofluorescence and immunoperoxidase methods at ultrastructural level.

Transfer, by selective breeding, of the pathogenic Mtv-2 endogenous provirus from the GR strain to a wild mouse line free of endogenous and exogenous mouse mammary tumor virus.

The GR laboratory mouse strain has five endogenous proviral copies of the mouse mammary tumor virus (MMTV). One of these, Mtv-2, is unique because it causes mammary carcinomas in virtually 100% of breeding GR females prior to 1 year of age. To facilitate studies of this locus in particular, and mammary tumorigenesis in general, we genetically tailored a new mouse line, WXG-2, which bears Mtv-2 as its only endogenous MMTV provirus. The WXG-2 line was constructed by making hybrids between the GR strain and a wild mouse line free of both endogenous and exogenous MMTV, backcrossing to the MMTV-free line, and fixing the Mtv-2 locus in a population with the desired genotype. Mammary tumors were observed in 5 of the 20 hybrid females carrying the endogenous Mtv-2 provirus. The WXG-2 line represents a new model system for studying MMTV-induced mammary tumorigenesis in the absence of multiple endogenous proviruses.

Molecular cloning, characterization, and genetic mapping of an endogenous murine mammary tumor virus proviral unit I of C3H/He mice.

We have cloned and characterized a novel endogenous murine mammary tumor virus proviral unit of the C3H/He strain of mice. The cloned proviral unit is 16 kilobase pairs (kbp) in size and is composed of a 5.6-kbp 5' EcoRI segment of an endogenous provirus with 10.4-kbp flanking cellular sequences. A comparison of the restriction map of the cloned proviral DNA with that of an endogenous provirus of the GR strain of mice has revealed minor differences in restriction sites on the two proviruses. The restriction enzyme SstI, which does not cleave the 5' EcoRI fragment of GR DNA, cleaves the C3H/He proviral sequences once; MspI has an additional site in the C3H/He proviral sequences. By using a subcloned fragment containing unique cellular sequences as a hybridization probe, we (i) mapped the C3H/He proviral unit to chromosome 14 by using mouse-hamster somatic cell hybrids, and (ii) demonstrated that this proviral unit is also present in the genome of DBA/2 mice. From these results we conclude that the C3H/He strain of mice acquired this proviral unit from DBA stock by genetic transmission. Our data also indicate that the murine mammary tumor virus sequences present in the gag-specific proviral unit of C3H/He mice extend at least 2.45 kbp downstream of the EcoRI site in the genomic DNA. Since the structural organization and chromosomal location of this proviral unit are distinct from those of previously reported proviral units represented by similar-sized (16.7-kbp) EcoRI fragments, we tentatively propose to designate this proviral unit Mtv-7a.

Rearrangements in the long terminal repeat of extra mouse mammary tumor proviruses in T-cell leukemias of mouse strain GR result in a novel enhancer-like structure.

Male GR mice develop T-cell leukemia at low frequency late in life. These leukemia cells invariably contain large amounts of mouse mammary tumor virus (MMTV) RNA and MMTV proteins and have extra MMTV proviruses integrated in their DNA. We show here that the extra MMTV proviruses are all derived from the endogenous MMTV provirus associated with the Mtv-2 locus and that the T-cell leukemias are clonal with respect to the acquired MMTV proviruses. The extra MMTV proviruses in six transplantable T-cell leukemia lines studied had rearranged, shortened long terminal repeats (LTRs); each T-cell leukemia, however, had a different LTR rearrangement within its extra MMTV provirus. The alteration within the extra LTRs of T-cell leukemia line 42 involved deletion of 453 nucleotides and generation of a tandem repeat region consisting of regions flanking the deletion. This alteration generated a sequence similar to the adenovirus enhancer core sequence. The viral RNAs in the T-cell leukemias contained corresponding alterations in their U3 regions. These results demonstrate that expression of MMTV in T-cell leukemias of GR mice may be the consequence of the generation of a novel enhancer, which could also stimulate expression of any adjacent cellular oncogene.

Rearrangements in the Long Terminal Repeat of Extra Mouse Mammary Tumor Proviruses in T-Cell Leukemias of Mouse Strain GR Result in a Novel Enhancer-Like Structure

Male GR mice develop T-cell leukemia at low frequency late in life. These leukemia cells invariably contain large amounts of mouse mammary tumor virus (MMTV) RNA and MMTV proteins and have extra MMTV proviruses integrated in their DNA. We show here that the extra MMTV proviruses are all derived from the endogenous MMTV provirus associated with the Mtv-2 locus and that the T-cell leukemias are clonal with respect to the acquired MMTV proviruses. The extra MMTV proviruses in six transplantable T-cell leukemia lines studied had rearranged, shortened long terminal repeats (LTRs); each T-cell leukemia, however, had a different LTR rearrangement within its extra MMTV provirus. The alteration within the extra LTRs of T-cell leukemia line 42 involved deletion of 453 nucleotides and generation of a tandem repeat region consisting of regions flanking the deletion. This alteration generated a sequence similar to the adenovirus enhancer core sequence. The viral RNAs in the T-cell leukemias contained corresponding alterations in their U3 regions. These results demonstrate that expression of MMTV in T-cell leukemias of GR mice may be the consequence of the generation of a novel enhancer, which could also stimulate expression of any adjacent cellular oncogene.

A new differentiation antigen (FT-1) shared with fetal thymocytes and leukemic cells in the mouse.

A mouse monoclonal antibody (IgM) was obtained by cell hybridization between X63-Ag8.653 myeloma cells and spleen cells from a BALB mouse that was immunized with GRSL leukemia cells of the GR strain. This antibody identified a unique fetal antigen, which is expressed exclusively on embryonic thymocytes of all strains tested. Therefore, the antigen defined was named fetal thymus antigen-1, FT-1. The proportion of FT-1+ fetal thymocytes detected by immunofluorescence assay sharply decreases as gestation time increases, and finally they disappear from the thymus. On the other hand, Thy-1+ cells increase in inverse proportion. The immunofluorescence studies and absorption tests showed that FT-1 antigen is not detectable on brain, liver, kidney, or lymphoid tissue cells of adult mice. However, it is expressed on some leukemia cells of various mouse strains, which demonstrated that this is the first example of an oncofetal antigen of a mouse leukemia. The molecular weight of FT-1 antigen on leukemia cells was estimated to be 130,000 by means of biosynthetic labeling with [3H]galactose and [35S]methionine. The two-dimensional gel electrophoresis pattern of FT-1 antigen shows a family of glycoproteins with extensive charge heterogeneity. It was also shown that the FT-1 antigen molecule carries the receptor for DBA lectin.