Cdkn2a, the cyclin-dependent kinase inhibitor encoding p16INK4a and p19ARF, is a candidate for the plasmacytoma susceptibility locus, Pctr1

Plasma cell tumor induction in mice by pristane is under multigenic control. BALB/c mice are susceptible to tumor development; whereas DBA/2 mice are resistant. Restriction fragment length polymorphisms between BALB/c and DBA/2 for Cdkn2a(p16) and Cdkn2b(p15), and between BALB/c and Mus spretus for Cdkn2c(p18(INK4c)) were used to position these loci with respect to the Pctr1 locus. These cyclin-dependent kinase (CDK) inhibitors mapped to a 6 cM interval of chromosome 4 between Ifna and Tal1. C.D2-Chr 4 congenic strains harboring DBA/2 alleles associated with the Pctr1 locus contained DBA/2 "resistant" alleles of the CDK4/CDK6 inhibitors p16 and p15. On sequencing p16 and p18 cDNAs, two different allelic variants within ankyrin repeat regions of p16 were found between BALB/c and DBA/2 mice. By using an assay involving PCR amplification and restriction enzyme digestion, allelic variants were typed among several inbred strains of mice. One of the variants, G232A, was specific to two inbred strains, BALB/cAn and ABP/Le, of mice and occurred in a highly conserved amino acid in both human and rat p16. When tested with wild-type (DBA/2) p16, both A134C and G232A BALB/c-specific variants of p16 were inefficient in their ability to inhibit the activity of cyclin D2/CDK4 in kinase assays with retinoblastoma protein, suggesting this defective, inherited allele plays an important role in the genetic susceptibility of BALB/c mice for plasmacytoma induction and that p16(INK4a) is a strong candidate for the Pctr1 locus.     

A locus on chromosome 7 determines myocardial cell necrosis and calcification (dystrophic cardiac calcinosis) in mice

Dystrophic cardiac calcinosis, an age-related cardiomyopathy that occurs among certain inbred strains of mice, involves myocardial injury, necrosis, and calcification. Using a complete linkage map approach and quantitative trait locus analysis, we sought to identify genetic loci determining dystrophic cardiac calcinosis in an F2 intercross of resistant C57BL/6J and susceptible C3H/HeJ inbred strains. We identified a single major locus, designated Dyscalc, located on proximal chromosome 7 in a region syntenic with human chromosomes 19q13 and 11p15. The statistical significance of Dyscalc (logarithm of odds score 14.6) was tested by analysis of permuted trait data. Analysis of BxH recombinant inbred strains confirmed the mapping position. The inheritance pattern indicated that this locus influences susceptibility of cells both to enter necrosis and to subsequently undergo calcification.     

Inherited resistance to Corynebacterium kutscheri in mice

An analysis of the factors responsible for inherited resistance to Corynebacterium kutscheri was undertaken. Various inbred mouse strains were examined; these included the Swiss Lynch and C57Bl/l mice, their F1 and F2 progeny, and the progeny of the F1 backcrossed to each parent strain. Two modes of inherited resistance are described. An examination suggested that resistance as measured by the mean lethal dose of C. kutscheri was under polygenic control and was inherited continuously. However, the efficiency with which C. kutscheri was eliminated by the mononuclear phagocyte cells of the liver over 3 days differed markedly among strains. A genetic analysis of this mononuclear phagocyte microbicidal efficiency (MPME) in Swiss Lynch and C57Bl/6 mice was undertaken. The trait, MPME, was present, but did not segregate, in the F1 progeny or in the progeny of the backcross to the resistant C57Bl/6 parent; this was clear evidence of dominance. Moreover, MPME segregated in a ratio of 1:1 in the progeny of the backcross to the sensitive Swiss Lynch parent and in a ratio of 3:1 in the F2 progeny. It was concluded that MPME was inherited discontinuously and was controlled by a single dominant autosomal gene (or closely linked group); the recessive allele was assigned the gene symbol ack. Linkage experiments showed there to be no association between the ack locus and any of the immune-response genes.     

Delivered dialysis dose is suboptimal in hospitalized patients

Resistance to the action of endotoxin varies among inbred strains of mice, indicating that a component of this resistance has a genetic basis. Different responses to endotoxin that are characteristic of individual inbred strains represent phenotypes that can be used to genetically map the response modifier genes. This study compares the acute histologic lesions in 8-week-old male A/J and C57BL/6J (B6) mice injected intraperitoneally with endotoxin of E. coli O265:B6 (15 mg/kg). Animals of both strains exhibited splenitis, splenic lymphoid hyperplasia, splenic lymphoid necrosis, and sequestration of neutrophils in the pulmonary alveoli. The B6 mice showed increased margination of white blood cells to the pulmonary vascular endothelium relative to A/J mice. A large number of degenerating neutrophils was observed in the liver sinusoids of most B6 animals, while this lesion was much less severe in A/J mice. This difference was quantified, demonstrating a highly significant difference in neutrophil infiltration in B6 mice relative to A/J mice. Analysis of this phenotype in F1 mice demonstrates that major genes encoding the trait are not X-linked, imprinted, or maternally inherited and do not show the codominant inheritance expected if Lps(d) were primarily responsible. The distinctive, quantitative nature of these differences provides a useful assay for mapping genes that modify endotoxin responsiveness using the AXB and BXA recombinant inbred (RI) strains derived from A/J and B6 mice.     

Genetic influences on electrical seizure threshold

C57BL/6J (B6) and DBA/2J (D2) mice have been characterized previously as seizure-resistant and seizure-sensitive, respectively, a distinction based primarily upon a differential response to the convulsant effects of various drugs. In the present study, electroconvulsive shock (ECS) was used to assess maximal electroshock threshold (MET) in B6, D2 and hybrid mice. Results revealed that D2 mice have a significantly lower MET compared to B6 mice. There was also a significant gender effect for B6 and F2 mice with females exhibiting a lower MET compared to males. METs for F1 and F2 intercross mice were intermediate between the two parental strains. The difference in variance between F2 and F1 generation mice indicated that about three-quarters of the total variance is due to genetic influence. Taken together, results of this study suggest that the large difference in MET between B6 and D2 mice is a highly heritable trait which may yield to genetic dissection through use of quantitative trait locus mapping.     

Cardiac chronotropic mechanisms of dimethyl sulphoxide: inhibition of acetylcholinesterase and antagonism of negative chronotropy by atropine

Phenobarbital, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), benzpyrene, 3-methylcholanthrene (3-MC) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were administered i.p. for 1 or 3 days to genetically "responsive" (C57BL/6J) and genetically "non-responsive" (DBA/2J) mice. 3-MC or benzpyrene stimulated aryl hydrocarbon hydroxylase (AHH) activity in C57BL/6J (B6) mice but not in DBA/2J (D2) mice. TCDD induced AHH activity in both B6 and D2 mice. Time-course studies showed that in the first 12 h after a single injection of 3-MC to B6 mice there was no shift in the reduced cytochrome P-450-CO complex absorption spectra from 450 to 448 nm, although AHH activity increased 4-5 times over (above) that of the control group. The relationship between induction of AHH activity by polycyclic hydrocarbons in B6 mice and the concomitant synthesis of cytochrome P-448 is discussed.     

Genetic mapping of lung cancer modifier loci specifically affecting tumor initiation and progression

Mouse inbred strains with inherited predisposition and resistance to lung cancer provide a tool for the dissection of the complex genetics of this disease. In the present report, we have crossed the BALB/c with the SWR/J strain and performed whole-genome scanning for loci affecting lung tumor development in their F2 progeny. Both parental strains carry the pulmonary adenoma susceptibility 1 (Pas1) locus, a major locus affecting predisposition to lung cancer in mice. On distal chromosome 18 and on centromere of chromosome 6, we have mapped two pulmonary adenoma resistance loci (Par2 and Par4, respectively), which reduce lung tumor multiplicity strongly, up to 15-fold. Par2 and Par4, however, do not affect lung tumor size, which is instead controlled by an additional locus that we have mapped on the central region of chromosome 4. We designated this locus as "pulmonary adenoma progression 1" (Papg1), because it specifically modifies lung tumor size but not multiplicity. The present results, therefore, provide evidence for the existence of cancer modifier loci acting on specific stages of lung tumorigenesis.     

Murine susceptibility to radiation-induced pulmonary fibrosis is influenced by a genetic factor implicated in susceptibility to bleomycin-induced pulmonary fibrosis

From evidence of interpatient variability in normal tissue sensitivity to radiotherapy and from radiation studies using inbred mouse strains, it is hypothesized that individual variation in susceptibility to radiation-induced pulmonary fibrosis is genetically controlled. A genetic model has been developed from the fibrosis-prone C57BL/6J and the fibrosis-resistant C3Hf/Kam mouse strains. Inheritance of the fibrotic phenotype was characterized in F1 and F2 (F1 intercross) generations derived from the parental strains. Genetic mapping was used to determine whether the quantitative trait loci (QTL), which influence susceptibility to bleomycin-induced lung fibrosis in these progenitor strains, could be implicated in susceptibility to radiation-induced lung fibrosis. Mice were treated with 14 or 16 Gy (60Co) to the whole thorax. The doses were selected to investigate the response at the LD50 and LD100 of C3Hf/Kam mice. The animals were sacrificed 33 weeks after treatment or when moribund. The percentage of lung with fibrosis for each mouse was quantified with image analysis of a histological section of the lung. For both the 14- and 16-Gy data sets, heritability was estimated at 38 +/- 11%, and the number of genetic factors influencing susceptibility to pulmonary fibrosis was estimated to be one or two. Two hundred fifty-five F2 intercross mice were genotyped with markers at the bleomycin loci on chromosomes 11 and 17 (chromosome 17 marker is at the major histocompatibility complex). Genetic linkage was established for the marker on chromosome 17 (P = 3.0 x 10(-6)), which accounts for 6.6% of the F2 phenotypic variance but not for the markers surrounding the QTL on chromosome 11 (P = 0.37). The inheritance data suggested that susceptibility to radiation-induced pulmonary fibrosis is a heritable trait controlled by two genetic loci, and through genomic mapping, a QTL on chromosome 17 was identified as one of the loci.     

New genetic loci that control susceptibility and symptoms of experimental allergic encephalomyelitis in inbred mice

Experimental allergic encephalomyelitis (EAE), the principal animal model of multiple sclerosis, is a genetically determined phenotype. In this study, analyses of the cumulative disease frequencies in parental, F1 hybrid, and F2 mice, derived from the EAE-susceptible SJL/J strain and the EAE-resistant B10.S/DvTe strain, confirmed that susceptibility to EAE is not inherited as a simple Mendelian trait. Whole genome scanning, using 150 informative microsatellite markers and a panel of 291 affected and 390 unaffected F2 progeny, revealed significant linkage of EAE susceptibility to marker loci on chromosomes 7 (eae4) and 17, distal to H2 (eae5). Quantitative trait loci for EAE severity, duration, and onset were identified on chromosomes 11 (eae6, and eae7), 2 (eae8), 9 (eae9), and 3 (eae10). While each locus reported in this study is important in susceptibility or disease course, interactions between marker loci were not statistically significant in models of genetic control. One locus, eae7, colocalizes to the same region of chromosome II as Orch3 and Idd4, susceptibility loci in autoimmune orchitis and insulin-dependent diabetes mellitus, respectively. Importantly, eae5 and eae7 are syntenic with human chromosomes 6p21 and 17q22, respectively, two regions of potential significance recently identified in human multiple sclerosis genome scans.     

Multigenic and imprinting control of ovarian granulosa cell tumorigenesis in mice

Spontaneous juvenile ovarian granulosa cell (GC) tumors that occur in young girls are similar to GC carcinomas that develop in SWR-derived inbred mice. We analyzed female offspring from a series of matings among SWR and SJL inbred mice for chromosomal loci underlying tumor susceptibility. Intercross F2 female mice were produced by reciprocal matings of (SWR x SJL)F1 and (SJL x SWR)F1 parents. Tumorigenesis in these F2 mice as well as in SWXJ recombinant inbred and congenic strains of mice derived from SWR and SJL showed significant (P < 0.001) association with Gct1, a dominant susceptibility locus on chromosome (CHR) 4 and with Gct2 on CHR 12. Suggestive (P < 0.01) association was found with Gct3 on CHR 15. A fourth susceptibility locus, Gct4 on CHR X, was demonstrated with a strong parent-of-origin effect associated with the paternal genotype. Imprinting and complex interactions among these four loci combine to establish the probability for GC tumorigenesis in this mouse model.     

Genetic analysis of the corticosterone response to ethanol in BXD recombinant inbred mice.

The genetic control over the corticosterone response to ethanol (EtOH) and its possible relationship to other EtOH-related traits was examined using BXD recombinant inbred (RI) strains derived from an F2 cross of C57BL/6J (B6) and DBA/2J (D2) progenitor strains. Quantitative trait locus (QTL) analysis of corticosterone levels 1 hr following EtOH suggested the influence of a single major gene on this trait. Two loci were predicted to account for 47% of the genetic variance in plasma corticosterone levels 6 hr following EtOH, whereas 3 loci were predicted to account for 78% of the genetic variance in corticosterone levels 7 hrs following EtOH. Markers associated with corticosterone levels 7 hrs following EtOH and corrected corticosterone levels 6 hrs post-EtOH overlapped with ones found to influence acute and chronic EtOH withdrawal severity, suggesting some degree of common genetic determination between these traits. Overall these results indicate that gene action significantly influences stress responsiveness and suggest possible chromosomal locations of these genes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Host genes affecting survival period of chemically induced bladder cancer in mice

Treatment of C57BL/6 J (B6) and NON male mice with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) resulted in a high incidence of bladder cancer. The mean survival period, however, differed significantly by strain: 481+/-219 days in B6 (n = 31) and 203+/-119 days in NON (n = 30) (P < 0.0001). Major causes of death were renal failure due to obstruction of the urinary tract, or local invasion of tumors. The fact that the BBN-treated NON x B6 reciprocal F1 mice had survival periods as short as those of the parental NON mice suggests a genetically dominant susceptibility in NON or recessive resistance in B6. A linkage analysis of 248 back-cross mice to B6 suggested at least two quantitative trait loci determining the length of the survival period: one was mapped close to D2Mit260 (logarithm of odds, LOD, score 2.21), a microsatellite marker locus 83 cM from the centromere on chromosome 2, and another was close to D6Mit159, 7 cM from the centromere on chromosome 6 (LOD score 2.51).     

Hippocampal lesions cause learning deficits in inbred mice in the Morris water maze and conditioned-fear task.

This study examined the effect of hippocampal lesions on acquisition of the Morris water maze and conditioned-fear task in inbred mice. C57BL/6J, DBA/2J, and B6D2F1 hybrid mice were given hippocampal lesions or sham surgery and then tested. The lesioned C57BL/6J and B6D2F1 mice failed to learn the Morris task relative to sham-operated controls, and no DBA group learned the task. In the contextual component of conditioned fear, lesions decreased freezing in all strains. But the lesions only affected freezing to the conditioned stimulus in the DBA/2J and B6D2F1 strains. These data demonstrate that C57BL/6J and B6D2F1 mice use the hippocampus to solve the Morris water maze and conditioned-fear task, and the DBA mice use the hippocampus, to some degree, in the conditioned-fear task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic control of differential baseline breathing pattern

The purpose of the present study was to determine the genetic control of baseline breathing pattern by examining the mode of inheritance between two inbred murine strains with differential breathing characteristics. Specifically, the rapid, shallow phenotype of the C57BL/6J (B6) strain is consistently distinct from the slow, deep phenotype of the C3H/HeJ (C3) strain. The response distributions of segregant and nonsegregant progeny were compared with the two progenitor strains to determine the mode of inheritance for each ventilatory characteristic. The BXH recombinant inbred (RI) strains derived from the B6 and C3 progenitors were examined to establish strain distribution patterns for each ventilatory trait. To establish the mode of inheritance, baseline breathing frequency (f), tidal volume, and inspiratory time (TI) were measured five times in each of 178 mature male animals from the two progenitor strains and their progeny by using whole body plethysmography. With respect to f and TI, the two progenitor strains were consistently distinct, and segregation analyses of the inheritance pattern suggest that the most parsimonious genetic model for response distributions of f and TI is a two-loci model. In similar experiments conducted on 82 mature male animals from 12 BXH RI strains, each parental phenotype was represented by one or more of the RI strains. Intermediate phenotypes emerged to confirm the likelihood that parental strain differences in f and TI were determined by more than one locus. Taken together, these studies suggest that the phenotypic difference in baseline respiratory timing between male B6 and C3 mice is best explained by a genetic model that considers at least two loci as major determinants.     

Parallel strain-dependent effect of amphetamine on locomotor activity and dopamine release in the nucleus accumbens: an in vivo study in mice

Vulnerability to develop drug abuse could be related to differential sensitivity to some central effects of such drugs. Several results point to mesoaccumbens dopamine release elicited by psychostimulants as the rate-limiting factor of their reinforcing, hence addictive, effects and to locomotor stimulation as an indirect index of such a response. In this paper, we report parallel differences in sensitivity to amphetamine-induced locomotor stimulation and mesoaccumbens dopamine release in two inbred strains of mice characterized by differential susceptibility to develop drug self-administration. Thus, mice of the C57BL/6 strain responded with a simultaneous increase of locomotor activity and mesoaccumbens dopamine release measured by intracerebral microdialysis to amphetamine challenge. On the contrary, mice of the DBA/2 strain did not present either response. No strain differences in mesoaccumbens dopamine outflow or 3,4-dihydroxyphenylacetic acid concentration were found in basal conditions or following saline challenges. However, mice of the C57BL/6 strain were characterized by higher levels of accumbal homovanillic acid in basal conditions, in line with the results obtained in rats rendered more sensitive to the locomotor effects of psychostimulants by repeated administration. Finally, in both strains amphetamine decreased accumbal levels of the two metabolites. These results suggest that genotype modulates the locomotor effects of amphetamine through sensitivity of the mesoaccumbens system to amphetamine-stimulated dopamine release. Moreover, they provide a basis to test the hypothesis of mesoaccumbens dopamine involvement in individual susceptibility to the addictive effects of drugs by quantitative trait loci analysis in recombinant inbred strains.     

Listeria monocytogenes-infected human umbilical vein endothelial cells: internalin-independent invasion, intracellular growth, movement, and host cell responses

Tissue concentrations of mercury were determined by cold vapor atomic absorption spectrometry in different inbred mouse strains after continuous treatment with HgCl2 (3 weekly sc injections of 0.5 mg/kg bw) for up to 12 weeks. Except for the thymus, in which steadily increasing mercury concentrations were found, in steady state levels of mercury were reached in blood and liver after 4 weeks and in spleen and kidney after 8 weeks. In the closely related strains C57BL/6, B10.D2, and B10.S, which differ only or primarily at the major histocompatibility complex, mercury concentrations in blood and liver were about twofold lower and renal concentrations were about three- to fivefold lower than those detected in strains A.SW and DBA/2. Another strain difference was observed in the spleen: after 8 and 12 weeks of continuous HgCl2 treatment, mercury concentrations in the spleen of strains A.SW, C57BL/6, and B10.S were significantly higher than those in strains DBA/2 and B10.D2. The strain difference in the spleen, an organ of the immune system, correlates with the susceptibility to the HgCl2-induced systemic autoimmune syndrome in mice in that the strains showing a higher mercury accumulation in the spleen are susceptible to this form of chemically induced autoimmunity, whereas the strains with lower mercury concentrations in the spleen are resistant.     

High-resolution linkage map in the vicinity of the host resistance locus Bcg

The mouse chromosome 1 locus Bcg determines natural resistance/susceptibility of inbred mouse strains to infection with antigenically unrelated intracellular parasites, including several Mycobacterium species, Salmonella typhimurium, and Leishmania donovani. In our effort to clone Bcg, we have constructed a high-resolution genetic linkage map in the vicinity of the gene. We have developed eight new highly polymorphic markers (simple sequence repeats) corresponding to cloned genes (Vil, Inha, Des), microdissected chromosome 1 anonymous probes (lambda Mm1C136, lambda Mm1C163, lambda Mm1C165), or novel DNA markers from the region obtained by chromosome walking (D1Mcg101 and D1Mcg105). We have followed the cosegregation of these markers with respect to Bcg in a novel panel of 1000 (C57L/J x C57BL/6J) x C57BL/6J segregating backcross mice. Additional segregation analyses were carried out in preexisting panels of intra- and interspecific backcross mice and recombinant inbred strains. Three of these markers were found to be very tightly linked to Bcg: lambda Mm1C165 did not show recombination with Bcg in 1424 meioses analyzed, while D1Mcg105 and lambda Mm1C136 were located 0.1 cM proximal and 0.2 cM distal to Bcg, respectively. This analysis enabled us to define further the proximal and distal boundaries of the Bcg interval: the proximal limit was defined by a single crossover occurring between D1Mcg105 and Bcg/lambda Mm1C165/Vil, and the distal limit by 1 cross-over between Bcg/lambda Mm1C165/Vil and lambda Mm1C136 in 1683 and 575 informative meioses, respectively, for a maximal interval of 0.3 cM.(ABSTRACT TRUNCATED AT 250 WORDS)     

Host modifier genes affect mouse autoimmunity induced by the lpr gene

A defect in apoptotic signal transmission through CD95 is an essential genetic mechanism for lymphoproliferation and autoimmunities in lpr or gld mice. However, disease manifestations are largely affected by the host genetic background. To identify and map such host genes modifying lpr gene effect, ie, the lpr modifier (Lprm) genes, 82 MRL/lpr x (MRL/lpr x C3H/lpr) F1 mice were subjected to immunopathological and genetical analyses. High-grade vasculitis and glomerulonephritis among backcross mice were observed in separate groups of mice. Microsatellite analysis revealed that there were two host genes affecting the occurrence of vasculitis, Lprm1 (chromosome 4) and Lprm2 (chromosome 3). A recessive MRL allele at Lprm1 enhanced vasculitis to occur in both sexes, whereas that of Lprm2 inhibited its development selectively in females. Genotype combinations of these two genes explained the severity of vasculitis in crosses of MRL/lpr and C3H/lpr mice and also the vasculitis-prone recombinant inbred strain McH5/lpr. A recessive MRL allele at Lprm3 (chromosome 14) suppressed glomerulonephritis. The weight of the spleen was increased by a recessive MRL allele at Lprm4 (chromosome 5) yielding a logarithm of odds score of 2.02 in a quantitative trait locus analysis. In contrast, the weight of axillary lymph nodes was increased by a recessive MRL allele at a locus on chromosome 2, but its presence was not supported by the quantitative trait locus analysis. The titer of anti-dsDNA autoantibody was controlled by the locus Lprm5 on chromosome 16, which had an logarithm of odds score of 3.41. Possible candidate genes for Lprm genes deduced from their map locations are discussed and compared with the autoimmunity genes reported thus far. In conclusion, autoimmune disease manifestations by the lpr mutation are affected by multiple host genes separately.     

A model of peptide-induced lupus autoimmune B cell epitope spreading is strain specific and is not H-2 restricted in mice

Anti-Sm is a common and specific autoantibody found in systemic lupus erythematosus. The peptide PPPGMRPP from Sm B/B' is an early target of the autoimmune response in some anti-Sm-positive human patients. After immunization with this peptide on a MAP backbone, rabbits develop anti-Sm autoantibodies with B cell epitope spreading of the autoimmune response as well as other features of lupus autoimmunity. Various strains of inbred mice have been immunized with peptide PPPGMRPP or PSQQVMTP (nonantigenic region of Sm B/B') in Freund's adjuvant or with no peptide. All peptide-immunized mouse strains eventually develop high titers of specific anti-peptide of immunization Abs. Mice immunized with Freund's adjuvant alone have no measurable Ab binding to the PPPGMRPP peptide. With time, nearly half the mouse strains tested develop Abs that react with additional regions of Sm B/B' and Sm D. All the regions bound by mouse serum are major epitopes of the human systemic lupus erythematosus anti-Sm response. These same strains also develop significant anti-Sm and anti-nuclear ribonucleoprotein titers. In addition, some of these strains demonstrate positive anti-nuclear Abs and anti-dsDNA Abs. Experiments with congenic H-2 mice demonstrate that the H-2 region does not play a role in spreading the immune response from the peptide of immunization to other epitopes of the spliceosome. These results present a new murine model of B cell epitope spreading and lupus autoimmunity induced by peptide immunization that is strain specific and not apparently dependent upon the loci at H-2.