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Activation of EGFP expression by Cre-mediated excision in a new ROSA26 reporter mouse strain.

Reporter mouse strains are important tools for monitoring Cre recombinase-mediated excision in vivo. In practice, excision may be incomplete in a given population due to threshold level or variegated expression of Cre. Hence, it is desirable in many experimental contexts to isolate cells that have undergone excision to assess the consequences of gene ablation. To generate alternative reporter mice, an enhanced green fluorescent protein (EGFP) gene was targeted to the retroviral-trapped ROSA26 locus. Upon Cre-mediated excision of "Stop" sequences, EGFP was expressed ubiquitously during embryogenesis and in adult tissues (including T cells, B cells, and myeloid cells). Using this new reporter strain, separation of excised from nonexcised cells in vitro was achieved in thymocytes in a noninvasive manner based on activated EGFP expression. This new EGFP reporter strain should facilitate a variety of conditional gene-targeting experiments, including the functional studies of hematopoietic cells in lineage-specific knockout mice.

Animals↗

IgG subclass responses to Theiler's murine encephalomyelitis virus infection and immunization suggest a dominant role for Th1 cells in susceptible mouse strains.

Inbred mouse strains differ in susceptibility to Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease. A strong correlation between disease susceptibility and delayed-type hypersensitivity (DTH) has been previously demonstrated, but no strong correlation between disease susceptibility and total anti-TMEV ELISA titres was shown. Since both DTH and IgG2a antibody production are regulated by CD4+ Th1 cells, we investigated three strains of mice to determine whether antivirus IgG2a antibody levels, like DTH in previous studies, correlated with disease susceptibility. Susceptible SJL/J, intermediately susceptible C3H/HeJ, and resistant C57BL/6 mice were infected intracerebrally (i.c.) with the BeAn strain of TMEV and monitored for clinical signs of demyelination and for levels of TMEV-specific antibody of different IgG subclasses using a particle concentration fluorescence immunoassay (PCFIA). Resistant C57BL/6 mice were found to have significantly lower concentrations of total anti-TMEV antibody than susceptible SJL/J mice and intermediately susceptible C3H/HeJ mice show variable antibody responses. A predominance of anti-TMEV IgG2a (Th1 regulated) antibody was seen in susceptible and intermediately susceptible mice, whereas resistant mice displayed a predominant anti-TMEV IgG1 (Th2 regulated) response accompanied by a marked deficiency of IgG2a. In contrast, immunization of C57BL/6 mice with UV-inactivated TMEV in adjuvant revealed that this strain was not defective either in its ability to generate high levels of anti-TMEV antibody or in its ability to produce IgG2a antibody. These results suggest that the antivirus IgG subclass profile is dependent upon the immunization route, virus viability and/or the use of adjuvant and that the levels of antivirus subclasses may be predictive of disease susceptibility.

Animals↗

Differential anti-inflammatory effects of LPS in susceptible and resistant mouse strains.

Most mouse strains are highly susceptible to endotoxin (LPS) lethality and are responsive to LPS stimulation in vitro (e.g., B cell mitogenesis, macrophage activation). They are, however, capable of mounting only a small inflammatory response to LPS when it is injected i.p. The present study demonstrates that LPS is in fact a potent, anti-inflammatory agent in all of the five normally LPS susceptible strains tested. LPS was also anti-inflammatory in F1 hybrid mice from susceptible (C3HeB/FeJ) x-resistant (C3H/HeJ) parents. Anti-inflammatory effects of LPS in susceptible strains were achieved by either i.v. or i.p. treatment and were observed toward a variety of phlogistic stimuli including mitogens, C-activating substances, and nonspecific irritants. The most dramatic inhibitory effect of LPS was directed toward the accumulation of inflammatory macrophages. Kinetic studies indicated that the anti-inflammatory effect of a single dose of LPS persisted for at least 72 hr but was maximal when LPS was given simultaneously with the inflammatory stimulus. In contrast to normal mice, two mutant, LPS resistant strains (C3H/HeJ and C57BL10/ScCR) responded to increasing doses of LPS i.p. with a progressively increasing influx of inflammatory cells. In addition, in resistant strains, LPS often enhanced and never depressed the inflammatory response to other phlogistic agents. These studies demonstrate that the genetic regulation of the inflammatory responses to LPS also controls the anti-inflammatory effects of LPS. These responses may be another relevant parameter in determining strain susceptibility to LPS lethality.

Animals↗

A novel monoclonal antibody permitting recognition of NKT cells in various mouse strains.

By immunizing mouse lymphoma cell line tMK-2U derived from intermediate TCR cells of BALB/c nude mouse, U5A2-13 monoclonal antibody (mAb, a rat IgG2a) was established. U5A2-13 antigen (Ag) was expressed on around 65% of TCRint cells in the liver of the various mouse strains including both NK1.1- and NK1.1+ mouse strains, while NK1.1 Ag was expressed only in NK1.1+ C57BL/6 mouse strain. Among CD3+ cells, 26.3% cells co-expressed U5A2-13 Ag and NK1.1+ Ag, while small proportions of the CD3+ cells were U5A2-13+NK1.1- (9.2%) or U5A2-13-NK1.1+ (4.4%). Among NK1.1+ cells, 54.9% cells co-expressed CD3 and U5A2-13 Ag, while some proportions of the cells were U5A2-13+CD3- (19.4%) or U5A2-13-CD3+ (9.8%). It was found that approximately 85% of NK1.1+CD3+ cells coexpressed U5A2-13 Ag. U5A2-13 Ag with low fluorescence intensity was also expressed on 55% of NK1.1+CD3-NK cells. U5A2-13 Ag immunoprecipitated from tMK-2U cells consisted of three proteins, which were 65 kDa, 33 kDa and 32 kDa under both reducing and non-reducing conditions and these were apparently different from NK 1.1 Ag. These results indicated that U5A2-13 mAb was able to define a similar population to NK1.1+CD3+T cells and to 55% of NK1.1+CD3-NK cells in various strains, through recognizing a different molecule from NK1.1 Ag.

Animals↗

A new locus (Mtv-4) for endogenous mammary tumor virus expression and early mammary tumor development in the SHN mouse strain.

The SHN mouse strain, which has a high incidence of mammary cancer, developed by inbreeding and selection from Swiss stock mice by Dr. H. Nagasawa and co-workers (Meiji University, Tokyo, Japan), harbored an endogenous mammary tumor virus (MTV) responsible for a high frequency of mammary tumors early in life. The locus was called "Mtv-4" and was only comparable with Mtv-2 of the GR mouse strain in its inducing capacity of mammary cancer. Molecular hybridization with 32P-labeled MTV complementary DNA showed that the characteristic Mtv-2 bands of the GR strain were absent in the SHN strain.

Animals↗

Presence of unmyelinated axons in the lumbar ventral roots of the 129 mouse strain.

The 129 mouse strain has become of increasing interest to neurobiologists due to its importance in gene targeting studies. However it has been pointed out that 129 mice suffer from a number of neuroanatomical idiosyncrasies that may make them less attractive as animal models in neurobiology. Here we show that 129 mice also differ from other commonly used strains in possessing large numbers of unmyelinated axons in their lumbar motor roots. By contrast in all other strains of mice (C57BL/6, C3H, Swiss-Webster) that we studied the axons in the L5 roots are all myelinated. Additionally we show that 129 mice have smaller myelinated axons than other mouse strains and perform poorly in the rotorod test. These characteristics must be kept in mind in studies of mutant mice that are frequently performed on a mixed genetic background containing a129 contribution.

Animals↗

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.

Animals↗

Homology of p53 intronic sequences between four laboratory mouse strains and Japanese wild mouse (Mus musculus molossinus Mishima).

Strain variation in the mouse p53 gene sequences was investigated in various regions of the gene in 14 inbred strains of laboratory mice and one Japanese wild mouse strain (Mus musculus molossinus Mishima, M. MOL-MSM). Nucleotides within p53 introns 1 and 7, found to be identical in 10 of the laboratory strains (129/J, A/J, AKR/J, BALB/cJ, C3H/HeJ, C57BL/6J, CBA/J, CE/J, NZB, and SWR/J), were substituted for other nucleotide sequences in common with M. MOL-MSM and the four other strains (DBA/1J, DBA/2J, I/LnJ, and P/J). The latter were documented to have originated from a common ancestor. These observations thus suggested the possibility that the p53 gene may have become substituted by outcrossing of this ancestral strain with Asian mice; this is presumably related to the documentation that Japanese mice brought to western countries were used as laboratory mice early in this century. To establish p53 gene heterozygosity, female C3H/HeJ and male DBA/2J mice were mated to produce F1 hybrids (C3D2F1). Electrophoresis of PCR fragments including polymorphic regions with or without restriction enzyme digestion, allowed clear distinction of paternal and maternal p53 alleles. These markers, therefore, should be useful for studying the loss of heterozygosity of the p53 gene during the carcinogenic process.

Animals↗

Genetic analysis of the cause of gastroschisis in the HLG mouse strain.

An inbred mouse strain HLG shows a high incidence of gastroschisis after X-ray exposure to the zygotes. About 11% of the fetuses display this malformation after irradiation with 1 Gy. The C57BL-strain does not show the increased frequency of gastroschisis after radiation-exposure to the zygotes. The genetic background of this malformation was investigated in a backcross of HLG x C57BL females to HLG males. The pregnant HLG x C57BL females were irradiated in a stage in which the (HLG x C57BL) x HLG [BC1] embryos were in the 1-cell stage. The frequency of gastroschisis in the BC1 generation was compared with a genetic model of a single recessive mutation with 11% penetrance. This frequency does not fit a single-locus inheritance. The number of loci involved was estimated to be about two or three. HLG mouse strain may be a valuable animal model in the study of polygenic traits.

Abdominal Muscles↗

Codominant expression of genes coding for different sets of inducible salivary polypeptides associated with parotid hypertrophy in two inbred mouse strains.

Experimental mouse parotid hypertrophy has been associated with the expression of a number of isoproterenol-induced salivary proline-rich polypeptides (IISPs). Mouse salivary proline-rich proteins (PRPs) have been mapped both to chromosomes 6 and 8. Recently, mice of two inbred strains (A/Snell and A. Swiss) have been found to differ drastically in the IISPs. In this study, mice of both strains were used for cross-breeding experiments addressed to define the pattern of inheritance of the IISP phenotype and to establish whether the IISPs are coded on a single or on several chromosomes. The IISP phenotype of individual mice was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole saliva collected after three daily stimulations by isoproterenol. Parental A/Snell and A. Swiss mice were homogeneous for distinctive strain-associated IISP-patterns. First filial generation (F1) mice obtained from the cross of A/Snell with A. Swiss mice expressed with no exception both the A/Snell and A. Swiss IISPs (coexpression). In the second filial generation (F2) both parental IISP phenotypes reappeared together with a majority of mice expressing the F1-hybrid phenotype (1:2:1 ratio). Backcrosses of F1 x A/Snell and F1 x A. Swiss produced offsprings displaying the F1 and the corresponding parental phenotypes with a 1:1 ratio. No recombinants were observed among F2 mice or among mice resulting from backcrosses. Thus, genes coding for the IISPs that are expressed differentially in both mouse strains are located on the same chromosome, probably at the same locus (alleles) or at quite closely linked loci (nonalleles).

Adrenergic beta-Agonists↗

Physical performance and soleus muscle fiber composition in wild-derived and laboratory inbred mouse strains.

We compared four inbred mouse strains in their physical performance, measured as a maximal treadmill running time, characteristics of soleus muscle, anatomic character, and growth. The strains used were Mus musculus domesticus [C57BL/6 (B6) and BALB/c], Mus musculus molossinus (MSM/Ms), and Mus spretus. Maximal running time was significantly different among these four mouse strains. Running time until exhaustion was highest in MSM/Ms and lowest in M. spretus. Maximal times for the laboratory mouse strains were nearly identical. Soleus muscle fiber type and cross-sectional area also differed significantly among the species. In particular, M. spretus was significantly different from the other inbred mouse strains. Growth in the wild-derived inbred mice appeared to be complete earlier than in the laboratory mice, and the body size of the wild strains was about half that of the laboratory strains. From these results, we propose that wild-derived inbred mouse strains are useful models for enhancing phenotypic variation in physical performance and adaptability.

Anatomy, Cross-Sectional↗

A biochemical approach to the study of the transmission of mouse mammary tumor viruses in mouse strains RIII and C3H.

Mouse mammary tumor virus (MMTV) proviral sequences were detected in the cellular DNA of mammary tumors and livers of RIII and C3H mice by molecular hybridization with radioactively labelled MMTV 60-70S RNA or tritiated MMTV complementary DNA (cDNA). By means of DNA:DNA reassociation kinetics, the DNA of the mammary tumor cells of these two mouse strains were found to contain more MMTV proviral sequences than the DNA of liver cells of these same tumor-bearing mice. Evidence is also presented that the DNA of the liver cells lacks a part (approximately 25%) of the MMTV proviral sequences found in the mammary tumor cells of these mouse strains. The relationship of the extra MMTV proviral sequences found in mammary tumor cells to the early mammary tumor-igenesis seen in these mouse strains is discussed.

Animals↗

Mind the gap: analysis of marker-assisted breeding strategies for inbred mouse strains.

The development of congenic mouse strains is the principal approach for confirming and fine mapping quantitative trait loci, as well as for comparing the phenotypic effect of a transgene or gene-targeted disruption between different inbred mouse strains. The traditional breeding scheme calls for at least nine consecutive backcrosses before establishing a congenic mouse strain. Recent availability of genome sequence and high-throughput genotyping now permit the use of polymorphic DNA markers to reduce this number of backcrosses, and empirical data suggest that marker-assisted breeding may require as few as four backcrosses. We used simulation studies to investigate the efficiency of different marker-assisted breeding schemes by examining the trade-off between the number of backcrosses, the number of mice produced per generation, and the number of genotypes per mouse required to achieve a quality congenic mouse strain. An established model of crossover interference was also incorporated into these simulations. The quality of the strain produced was assessed by the probability of an undetected region of heterozygosity (i.e., "gaps") in the recipient genetic background, while maintaining the desired donor-derived interval. Somewhat surprisingly, we found that there is a relatively high probability for undetected gaps in potential breeders for establishing a congenic mouse strain. Marker-assisted breeding may decrease the number of backcross generations required to generate a congenic strain, but only additional backcrossing will guarantee a reduction in the number and length of undetected gaps harboring contaminating donor alleles.

Animals↗

Class II-restricted T cell responses in Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease. II. Survey of host immune responses and central nervous system virus titers in inbred mouse strains.

Previous studies using mouse strains with limited genetic differences and H-2 haplotypes demonstrated that susceptibility to Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease strongly correlated with chronically high levels of TMEV-specific delayed-type hypersensitivity (DTH), but not with TMEV-specific T cell proliferation (Tprlf), serum antibody responses, or with CNS virus titers. To determine if this correlation would be supported by analysis of these parameters in a more thorough genetic survey, ten inbred mouse strains, representing a wide variety of genetic backgrounds and H-2 haplotypes, were inoculated intracerebrally (i.c.) with the BeAn strain of TMEV. Significant TMEV-specific DTH was observed in all highly susceptible strains, but was not detectable in intermediate and resistant strains. TMEV-specific serum antibody titers also appeared to correlate with susceptibility to demyelinating disease, however even resistant strains had high antibody responses. Significant differences in CNS TMEV titers existed between strains, but did not correlate with disease susceptibility. DTH and Tprlf responses were observed in 3/4 resistant strains following peripheral immunization with UV-inactivated TMEV indicating that most resistant strains are genetically capable of mounting virus-specific cell-mediated immune (CMI) responses. The data extends our knowledge of host immune responses and virus titers in many different inbred mouse strains persistently infected with TMEV, supports the hypothesis that the demyelination in highly susceptible mice involves a TMEV-specific DTH response, and suggests that the genetic ability to mount specific DTH responses is necessary, but not sufficient for development of the demyelinating disease.

Animals↗

Localization of a gene for expression of mouse mammary tumor virus antigens in the GR/Mtv-2- mouse strain.

The GR/Mtv-2- mouse strain is congenic to the GR strain but lacks the Mtv-2 gene for high amounts of mouse mammary tumor virus (MMTV) virion particles in the milk and early mammary tumors. With a sensitive competition radioimmunoassay for individual viral proteins of MMTV, substantial amounts of the gag proteins p27 and p10 could still be detected in extracts of the mammary glands of GR/Mtv-2- mice, but essentially no viral envelope antigens. The genetic transmission of the MMTV gag expression in the GR/Mtv-2- strain was investigated. In a cross with the virus-negative BALB/c strain, the MMTV p27 expression behaved as a dominant feature. Double backcross analysis proved that the p27 expression was governed by a single gene located on chromosome 11, cloe to the Es-3 locus. The gene was thereby not allelic to any of the previously described MMTV induction genes, Mtv-1 and Mtv-2, and is therefore called Mtv-3. It is concluded that the total MMTV expression in the GR strain is under control of two separate loci, Mtv-2 on chromosome 18, inducing high levels of complete virus particles and also early mammary tumors; and Mtv-3 on chromosome 11, coding for partial MMTV expression.

Animals↗