DBA Strain Research Articles

Intramedullary implant stability affects patterns of fracture healing in mice with morphologically different bone phenotypes

Almost all prior mouse fracture healing models have used needles or K-wires for fixation, unwittingly providing inadequate mechanical stability during the healing process. Our contention is that the reported outcomes have predominantly reflected this instability, rather than the impact of diverse biological conditions, pharmacologic interventions, exogenous growth factors, or genetic considerations. This important issue becomes obvious upon a critical review of the literature. Therefore, the primary aim of this study was to demonstrate the significance of mouse-specific implants designed to provide both axial and torsional stability (Screw and IM Nail) compared to conventional pins (Needle and K-wires), even when used in mice with differently sized marrow canals and diverse genetic backgrounds. B6 (large medullary canal), DBA, and C3H (smaller medullary canals) mice were employed, all of which have different bone morphologies. Closed femoral fractures were created and stabilized with intramedullary implants that provide different mechanical conditions during the healing process. The most important finding of this study was that appropriately designed mouse-specific implants, providing both axial and torsional stability, had the greatest influence on bone healing outcomes regardless of the different bone morphologies encountered. For instance, unstable implants in the B6 strain (largest medullary canal) resulted in significantly greater callus, with a fracture region mainly comprising trabecular bone along with the presence of cartilage 28 days after surgery. The DBA and C3H strains (with smaller medullary canals) instead formed significantly less callus, and only had a small amount of intracortical trabeculation remaining. Moreover, with more stable fracture fixation a higher BV/TV was observed and cortices were largely restored to their original dimensions and structure, indicating an accelerated healing and remodeling process. These observations reveal that the diaphyseal cortical thickness, influenced by the genetic background of each strain, played a pivotal role in determining the amount of bone formation in response to the fracture. These findings are highly important, indicating the rate and type of tissue formed is a direct result of mechanical instability, and this most likely would mask the true contribution of the tested genes, genetic backgrounds, or various therapeutic agents administered during the bone healing process.

Non-starved mucoid Pseudomonas aeruginosa isolates cause a high death rate in strains of mice.

Pseudomonas aeruginosa is an opportunistic pathogen that affects many patients in a hospital setting as well as immunocompromised patients. Pseudomonas aeruginosa is resistant to many antibiotics because of the formation of biofilms and pigmentations serving as virulence factors. Pseudomonas aeruginosa isolates are either mucoid or alginate-producing and non-alginate-producing (non-mucoid) isolates. The main objective of this experiment was to analyze the pathogenicity of mucoid and non-mucoid isolates in P. aeruginosa in a mouse model. We hypothesized that mucoid isolates are more pathogenic compared to non-pathogenic ones. Pseudomonas aeruginosa isolates PAO1 (non-mucoid) and 2192 (mucoid) were used intranasally to infect and monitor mortality rates. Isolates starved in water for at least three months were tested for infectivity. The mucoid isolate 2192 showed a 67% death rate compared to 33% of PAO1, suggesting the mucoid is more pathogenic to BALB/c mice than the non-mucoid PAO1. The death rate of mice infected with strain DBA susceptible to P. aeruginosa infection was higher than that of the BALB/c strain. The results also suggest that non-starved bacteria are more pathogenic to mice than starved bacteria. We extend our study by infecting mouse strains under hindlimb-unloading (HU) conditions with P. aeruginosa mucoid and non-mucoid isolates. Our results show that HU conditions enhance infection, suggesting the effect of stress and physiological changes could lead to susceptibility to infection. Our data indicate that the mucoid isolate is more likely to kill all mouse strains.

Variation in Host Resistance to Blastomyces dermatitidis: Potential Use of Genetic Reference Panels and Advances in Immunophenotyping of Diverse Mouse Strains.

ABSTRACTHost genetic determinants that underpin variation in susceptibility to systemic fungal infection are poorly understood. Genes responsible for complex traits can be identified by correlating variation in phenotype with allele in founder strains of wild mice with known genetic variation, assembled in genetic reference panels. In this work, we describe wide natural variation in both primary and acquired resistance to experimental pulmonary blastomycosis in eight founder strains, including 129, A/J, BL/6, CAST, NOD, NZO, PWK, and WSB of the Collaborative Cross collection, and the inbred DBA strain. These differences in susceptibility across strains were accompanied by sharp differences in the accumulation and function of immune cells in the lungs. Immune perturbations were mapped by identifying reagents that phenotypically mark immune cell populations in the distinct strains of mice. In particular, we uncovered marked differences between BL/6 and DBA/2 mouse strains in the development of acquired resistance. Our findings highlight the potential value in using genetic reference panels of mice, and particularly the BXD (recombinant inbred strains of mice from a cross of C57BL/6J and DBA/2J mice) collection harboring a cross between resistant BL/6 and susceptible DBA/2 mice, for unveiling genes linked with host resistance to fungal infection.

The Effects of Diet-induced Obesity on the Distribution of System Trace Elements (P24-059-19)

ObjectivesIron (Fe), Copper (Cu), and Manganese (Mn) are essential trace elements that are critical for health and must be maintained in an optimal physiological range. When there is a disturbance of this regulation, such as obesity, pathologies ranging from anemia to neurotoxicity can occur. The objective of this current study is to examine strain and sex differences in the distribution of systemic trace elements due to diet-induced obesity (DIO). We hypothesize that high fat DIO causes significant systemic alterations of Fe, Cu, Mn distributions compared to low fat diet with sex and strain as contributing factors. MethodsBeginning at 21 days of age, male and female C57BL/6 J (n = 36) and DBA/2 J (n = 36) mice were fed either a high-fat diet (60% Kcal from fat) or a control diet (10% Kcal from fat) for 16 weeks. Food intake and body mass were measured weekly. At the end of the 16 weeks, blood, liver, and spleen tissues were collected. Fe, Cu, and Mn concentrations were measured using graphite furnace atomic absorption spectroscopy. ResultsWhile DIO did not cause any strain or sex differences in hematocrit, differences were detected in all three metals, Mn, Cu, and Fe concentrations in the liver and spleen. Specifically, there was a statistically significant sex by diet interaction on liver Mn concentrations (P = 0.008) and strain by sex interaction on spleen Mn concentrations (P = 0.002). There was a sex by diet and strain by sex interaction on liver Cu concentrations (P = 0.01 and P = 0.006, respectively). A three-way strain, sex, and diet interaction (P = 0.003) was observed for Cu in spleen. There was a strain by sex and strain by diet interaction on liver Fe concentrations (P = 0.031 and P = 0.002, respectively). There was a statistically significant strain, sex, and diet interaction on spleen Fe concentrations (P = 0.0002). The most prominent interactive effects of sex, strain and DIO was observed with liver and spleen Fe concentrations compared to Cu or Mn. For example, male DBA and female C57 mice had greatly reduced Fe in liver and spleen but their opposite sex counterparts were largely unaffected by the impact of DIO. ConclusionsOur results expand our previous data by showing strain and sex differences not only in Fe, but Cu and Mn systemic concentrations. For females, the impact of DIO on Fe was more significant in the C57 strain whereas in males the effect of DIO was more significant in the DBA strain. Funding SourcesUNCG Health and Human Sciences Research Grant & UNCG Faculty First Award.

Occupational Noise, Job Strain and Salivary Cortisol: A Repeated-Measure Study

Background:Exposure to occupational noise and job strain have been reported to be associated with the salivary cortisol levels, but the combined effect is not clear. This study aimed to investigate individual and interactive associations between occupational noise exposure and job strain on salivary cortisol levels.Methods:We recruited 120 volunteers in an aircraft manufacturing company in Central Taiwan as study subjects. Each participant was performed 24-hour measurements of noise exposure and collected four salivary samples during different periods on the working day. The enzyme-link immunosorbent assay was applied to determine salivary cortisol levels. We also used questionnaire to obtain information related to job strain, sleep quality and other confounders. Multiple linear regression models were performed to analyze the association.Results:Workers exposed to ≥75 A-weighted decibels (dBA) had a significantly higher difference of salivary cortisol levels between 30-min waking-up and last-night sleep compared with that in workers exposed to <75 dBA and office workers, respectively. Workers exposed to high job strain (Index ≥61) had a significantly higher mean of salivary cortisol levels after 30-min waking-up and a significant difference between 30-min waking-up and last-night sleep than those with the low job strain (Index <61). Subjects co-exposed to noise levels ≥75 dBA and high job strain had a significantly higher mean of salivary cortisol levels after 30-min waking-up (0.371±0.098 mg/dL, P<0.001) and a significant difference between 30-min waking-up and last-night sleep (0.323±0.094 mg/dL, P<0.001) compared with those exposed to <75 dBA and low job strain.Conclusions:Occupational noise exposure and high job strain was associated with the increased salivary cortisol levels after 30-min waking-up. Co-exposure to noise and job strain may have a synergistic interaction with the salivary cortisol levels.

Effect of Mouse Strain on Equine Herpesvirus 9 Infection

The infectivity of equine herpesvirus (EHV)-9 has been studied in different animal models including immunocompromised animals. The current study focused on the infectivity of EHV-9 in different mouse strains (C3H, C57BL, DBA, BALB/c-nu/nu, BALB/c and ICR) by intranasal inoculation of 2×106 plaque forming units (PFU). Various organs, including head and lungs, were collected 7 days post infection (dpi) to investigate microscopical lesions and the distribution of EHV-9 antigen. Immunopositivity of tissue sections was scored using ImageJ software. Open reading frame (ORF) 30 expression in lung tissues was quantified using quantitative reverse transcriptase polymerase chain reaction. Pathological examination revealed different degrees of rhinitis in the different mouse strains. Severe rhinitis was detected in C3H and BALB/c-nu/nu strains, moderate rhinitis was observed in C57BL and DBA strains and no lesions were detected in BALB/c mice. Immunopositivity for EHV-9 antigens was detected in the olfactory epithelium of C3H and BALB/c-nu/nu strains. Compared with C57BL, DBA, BALB/c-nu/nu, ICR and BALB/c strains, the C3H strain showed greater expression of EHV-9 antigens in the brain. The proportion of areas with high positive to positive immunoreactivity for EHV-9 were 7.57, 3.42, 3.12, 2.51, 1.79 and 0.03% for C3H, C57BL, DBA, BALB/c-nu/nu, ICR and BALB/c strains, respectively. The proportions of areas with low positive to negative immunoreactivity were 92.42, 96.70, 96.87, 97.48, 98.16 and 99.96%, respectively. The highest relative expression levels for EHV-9 ORF30 in the lungs were in C3H mice. No significant differences in the expression of ORF30 were observed in other strains. In conclusion, of the strains examined, C3H, C57BL, DBA, BALB/c-nu/nu and ICR were the most susceptible to EHV-9 infection, and the BALB/c strain was less susceptible.

Quantitative trait locus on distal chromosome 1 regulates the occurrence of spontaneous spike‐wave discharges in DBA/2 mice

Most common forms of human epilepsy result from a complex combination of polygenetic and environmental factors. Quantitative trait locus (QTL) mapping is a first step toward the nonbiased discovery of epilepsy-related candidate genes. QTL studies of susceptibility to induced seizures in mouse strains have consistently converged on a distal region of chromosome 1 as a major phenotypic determinant; however, its influence on spontaneous epilepsy remains unclear. In the present study we characterized the influence of allelic variations within this QTL, termed Szs1, on the occurrence of spontaneous spike-wave discharges (SWDs) characteristic of absence seizures in DBA/2 (D2) mice. We analyzed SWD occurrence and patterns in freely behaving D2, C57BL/6 (B6) and the congenic strains D2.B6-Szs1 and B6.D2-Szs1. We showed that congenic manipulation of the Szs1 locus drastically reduced the number and the duration of SWDs in D2.B6-Szs1 mice, which are homozygous for Szs1 from B6 strain on a D2 strain background. However, it failed to induce the full expression of SWDs in the reverse congenic animals B6.D2-Szs1. Our results demonstrate that the occurrence of SWDs in D2 animals is under polygenic control and, therefore, the D2 and B6 strains might be a useful model to dissect the genetic determinants of polygenic SWDs characteristic of typical absence seizures. Furthermore, we point to the existence of epistatic interactions between at least one modifier gene within Szs1 and genes within unlinked QTLs in regulating the occurrence of spontaneous nonconvulsive forms of epilepsies.

Behavioral assessments of mouse Strain differences in response to social stress

In this study a mouse model is set up with a potentially unbiased platform to address the strain differences in response to social stress. Three different mouse strains of C57, BALB/c and DBA were submitted to 5 day and 10 day social stress (SS). Mice were kept inside an aggressor (AGG) home cage and randomly exposed to the AGG three times a day for one minute or for up to ten attacks in less than one minute, while control mice never experienced AGG proximity.Behavioral assessments were performed using the partition/barrier test. Behaviors were recorded and analyzed using Etho Vision software. Subject mice were kept in the aggressor cage separated from the aggressor by a perforated divider.Socially stressed mice persistently avoided the partition area that separated them from the aggressor mouse. C57 mice exhibited significant behavioral changes in response to stress. DBA strain mice showed lower susceptibility to SS than C57. When BABL/c mice were evaluated on the same scale of behavioral parameters, they showed intermediate levels of (SS) responses that were between the C57 and BALB/c responses.Genomic and epigenetic studies are underway to understand these differences in stress response.

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.

Can the partial deletion in the Y chromosome of male mice affect the reproductive efficiency of their daughters?

It has been previously shown that cumuli oophori around ovulated oocytes of B10.BR-Ydel female mice (sired by males with the deleted Y chromosome) are more resistant to enzymatic treatment than cumuli oophori around eggs of control B10.BR females (having fathers with the intact Y chromosome). This can imply that some genes which influence the establishment of the imprinting pattern in male gametes are located in the region covered by the deletion. We hypothesize that the Y-dependent imprinting pattern, inherited by female offspring, affects stability of periovum layers within them. In the present study, cumulus-oocyte complexes ovulated by females from consomic strains: DBA, DBA-YBR, DBA-Ydel, and CBA, CBA-YBR, CBA-Ydel were tested for their susceptibility to hyaluronidase digestion. The mean times for dispersal of cumulus cells surrounding oocytes of females from the backcross lines were convergent with the times typical for oocytes from strains being the donors of the Y chromosome (B10.BR or B10.BR-Ydel) and differed clearly from pure DBA and CBA strains. It confirmed previous findings that Y chromosomes of fathers influence the properties of cumulus-oocyte complexes ovulated by their daughters. This influence is definitely stronger than the influence of the genetic background. Additionally, it was demonstrated that the cumuli oophori surrounding oocytes of B10.BR-Ydel females exhibit increased resistance to penetration by spermatozoa in vitro, in comparison to the control B10.BR strain. This regularity was reflected in the decreased proportion of fertilized ova recovered from oviducts of B10.BR-Ydel females mated with B10.BR-Ydel males and in the lower litter sizes recorded for these pairs. The excessive stability of cumuli oophori typical for oocytes of females having Ydel fathers may negatively affect their fertility, if they have partners producing poor quality sperm.

Characterization of pharmacological and behavioral differences to nicotine in C57Bl/6 and DBA/2 mice

Approximately 50–70% of the risk for developing nicotine dependence is attributed to genetics; therefore, it is of great significance to characterize the genetic mechanisms involved in nicotine reinforcement and dependence in hopes of generating better smoking cessation therapies. The overall goal of these studies was to characterize behavioral and pharmacological responses to nicotine in C57Bl/6 (B6) and DBA/2 (D2) mice, two inbred strains commonly used for genetic studies on behavioral traits. B6 and D2 mice where subjected to a battery of behavioral tests to measure nicotine's acute effects, calcium-mediated antinociceptive responses, tolerance to chronic treatment with osmotic mini pumps, and following three days of nicotine withdrawal. In general, D2 mice were less sensitive than B6 mice to the acute effects of nicotine, but were more sensitive to blockade of nicotine-induced antinociceptive responses by a calcium/calmodulin-dependent protein kinase II (CaMKII) inhibitor. B6, but not D2 mice, developed tolerance to nicotine and nicotine conditioned place preference (CPP). While B6 and D2 mice both expressed some physical withdrawal signs, affective withdrawal signs were not evident in D2 mice. These results provide a thorough, simultaneous evaluation of the pharmacological and behavioral differences to experimenter-administered nicotine as measured in several behavioral tests of aspects that contribute to smoking behavior. The B6 and D2 strains show wide phenotypic differences in their responses to acute or chronic nicotine. These results suggest that these strains may be useful progenitors for future genetic studies on nicotine behaviors across batteries of mouse lines such as the BXD recombinant inbred panel.

Strain Specific Synaptic Modifications on Ventral Tegmental Area Dopamine Neurons After Ethanol Exposure

Genetic factors and previous alcohol experience influence alcohol consumption in both humans and rodents. Specifically, a prior experience with ethanol increases ethanol intake in both ethanol-preferring C57BL/6 (C57) and ethanol non-preferring DBA/2 (DBA) mice. Whereas the ventral tegmental area (VTA) importantly regulates dopamine levels and ethanol intake, it is unknown whether ethanol experience differentially alters synaptic properties of VTA dopamine neurons in ethanol-preferring and non-preferring mice. The properties of excitatory and inhibitory inputs and the ability to elicit long-term potentiation (LTP) were assessed with whole-cell patch-clamp recordings in VTA dopamine neurons from C57 and DBA mice 24 hours after a single ethanol (2 g/kg, IP) or equivalent saline injection. Ethanol exposure increased gamma-aminobutyric acid (GABA) release onto VTA dopamine neurons in DBA mice, as previously observed in C57 mice. However, a single ethanol exposure reduced alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) and N-methyl-D-aspartate receptor (NMDAR) function and LTP in VTA dopamine neurons from DBA but not C57 mice. A single ethanol exposure selectively reduced glutamate receptor function in VTA dopamine neurons from the ethanol non-preferring DBA strain but enhanced GABA signaling in both C57 and DBA strains. These results support the notion that VTA dopamine neurons are a central target of ethanol-induced neural plasticity, which could contribute to ethanol consumption. Furthermore, these findings highlight the possible need for specialized therapeutic interventions for alcoholism based on individual intrinsic differences.

Differences in DBA/1J and DBA/2J reveal lipid QTL genes

Recent advances in mouse genomics have revealed considerable variation in the form of single-nucleotide polymorphisms (SNPs) among common inbred strains. This has made it possible to characterize closely related strains and to identify genes that differ; such genes may be causal for quantitative phenotypes. The mouse strains DBA/1J and DBA/2J differ by just 5.6% at the SNP level. These strains exhibit differences in a number of metabolic and lipid phenotypes, such as plasma levels of triglycerides (TGs) and HDL. A cross between these strains revealed multiple quantitative trait loci (QTLs) in 294 progeny. We identified significant TG QTLs on chromosomes (Chrs) 1, 2, 3, 4, 8, 9, 10, 11, 12, 13, 14, 16, and 19, and significant HDL QTLs on Chrs 3, 9, and 16. Some QTLs mapped to chromosomes with limited variability between the two strains, thus facilitating the identification of candidate genes. We suggest that Tshr is the QTL gene for Chr 12 TG and HDL levels and that Ihh may account for the TG QTL on Chr 1. This cross highlights the advantage of crossing closely related strains for subsequent identification of QTL genes.

038 Digit Tip Regeneration and Global Gene Expression Profiling in the MRL SuperHealer Mouse

The MRL mouse is the only known strain of mouse that can regenerate cardiac lesions and completely heal ear punches without scarring. To determine if the MRL also has greater regeneration capabilities in amputated digit tips, right paw digit tips of neonatal mice were dissected, with the left front paws as uncut controls. Controls used for regeneration comparison were the DBA, B6, C3H, and 129 inbred mouse strains. Consecutive X-ray images were captured of the left and right paws at 0, 7, 14, 21, and 28 days postamputation. MRL mouse digit tips regenerated greater in comparison to all strains tested (p < 0.05). We next undertook whole genome microarray analysis to identify the genetic mechanisms that contribute to differences in digit tip regeneration. Over 400 genes out of 15,000 were significantly differentially expressed (p < 0.05) in MRL and DBA mice at day 4 in comparison to day 0 control tissue. Of these, 170 genes were upregulated and 280 were downregulated in both mouse strains. Pathway analysis reveals that genes in the BMP/TGF pathway are differentially expressed in both mouse strains (p < 0.05). Multiple differences between MRL and DBA strains were found in transcription factors that are implicated in gastrulation, including FMN2 and SHRM. Additional differentially expressed genes include NET1 in the WNT signaling pathway. Immunohistochemistry indicates that these proteins are highly expressed in the nuclei of chondrocytes in regenerating digits. We conclude that MRL mice show greater regenerative capacity to heal digit tips and that the increased regenerative capacity of MRL mice may be due to strain specific increased expression of genes involved in the WNT pathway and genes involved in embryonic pattern formation. Acknowledgments: This work was supported by Assistance Award DAMD17–03–2–0021 and is administered by the US Army Medical Research Activity, 820 Chandler St., Ft. Detrick, MD.

Global expression profiles from C57BL/6J and DBA/2J mouse lungs to determine aging-related genes

This study identified gene expression profiles that provided evidence for genomic mechanisms underlying the pathophysiology of aging lung. Aging lungs from C57BL/6 (B6) and DBA/2 (D2) mouse strains differ in physiology and morphometry. Lungs were harvested from B6 mice at 2, 18, and 26 mo and from D2 mice at 2 and 18 mo of age. Purified RNA was subjected to oligonucleotide microarray analyses, and differential expression analyses were performed for comparison of various data sets. A significant majority of differentially expressed genes were upregulated with aging in both strains. Aging D2 lungs uniquely exhibited upregulation in stress-response genes including xenobiotic detoxification cascades. In contrast, aging B6 lungs showed downregulation of heat shock-response genes. Age-dependent downregulation of genes common to both B6 and D2 strains included several collagen genes (e.g., Col1a1 and Col3a1). There was a greater elastin gene (Eln) expression in D2 mice at 2 mo, and Eln was uniquely downregulated with age in this strain. The matrix metalloproteinase 14 gene (Mmp14), critical to alveolar structural integrity, was also downregulated with aging in D2 mice only. Several polymorphisms in the regulatory and untranslated regions of Mmp14 were identified between strains, suggesting that variation in Mmp14 gene regulation contributes to accelerated aging of lungs in D2 mice. In summary, lungs of B6 and D2 mice age with variable rates at the gene expression level, and these quantifiable genomic differences provide a template for understanding the variability in age-dependent changes in lung structure and function.

Class Switch Recombination and Somatic Hypermutation in Early Mouse B Cells Are Mediated by B Cell and Toll-like Receptors

Activation-induced cytidine deaminase (AID) is required for immunoglobulin (Ig) gene class switch recombination (CSR), somatic hypermutation (SHM), and somatic hyperconversion. In general, high AID expression is found in mature B cells that are responding to antigens. However, AID expression and SHM have also been detected in developing B cells from transgenic mice that have a limited Ig repertoire. Here we demonstrate that AID expression, ongoing CSR, and active SHM occur in developing B cells from wild-type mice. Further, our results suggest that somatic variants arising from developing B cells in the bone marrow further diversify in the spleen of unimmunized mice. AID expression in developing B cells is T cell independent but involves engagement of B cell receptors and Toll-like receptors. Early AID expression can increase the preimmune repertoire of developing B cells, may provide an innate population of IgG- and IgA-expressing cells, and could be involved in receptor editing of self-reactive immature B cells.

Identification of a genetic contamination in a commercial mouse strain using two panels of polymorphic markers

Rapid detection of genetic contamination is critical in mouse studies involving inbred strains. During a Quantitative Trait Locus (QTL) study using simple sequence length polymorphism (SSLP) markers, we noticed heterozygosity at some loci of a commercially available inbred C57BL/6N mouse strain, suggesting a contamination by another mouse strain. A panel of 100 single-nucleotide polymorphism (SNP) markers was used to confirm and specify the genetic contamination suspected. Retrospective analyses demonstrated that the contamination took place as early as autumn 2003 and has persisted ever since at a fairly constant level. Contaminating alleles most probably originated from a DBA strain. Our data demonstrate the suitability of SNP markers for rapid detection and identification of the source of genetic contamination. Further, our results show the importance of a state-of-the-art genetic monitoring of the authenticity of murine inbred strains.

Digit tip regrowth and differential gene expression in MRL/Mpj, DBA/2, and C57BL/6 mice

MRL/Mpj mice are the only known strain of mouse that can regenerate cardiac lesions and completely heal ear punches without scarring. This study was undertaken to determine if MRL mice also have greater regrowth capabilities in amputated digit tips. Right paw digit tips of neonatal MRL mice were dissected, with the left front paws as uncut controls. Controls used for regrowth comparison were the DBA/2 and C57BL/6 inbred mouse strains. Consecutive x-ray images were captured of front paws at 0, 7, 14, 21, and 28 days postamputation. MRL mouse digit tips were found to distally regrow more quickly and reform nails partially and completely to a greater degree in comparison with DBA and B6 mice (p<0.05). We next undertook microarray expression analysis to identify the genes involved in digit tip regrowth. Four hundred genes out of 15,000 were significantly differentially expressed (p<0.05) in MRL, DBA, and B6 mice at day 4 in comparison with day 0 control tissue. Multiple differences between MRL, DBA, and B6 strains were found in genes that are implicated in the WNT signaling pathway and transcription. We conclude that MRL mice regrow digits distally more rapidly and partially and completely regrow nails to a greater degree than B6 and DBA strains. This enhanced regrowth is likely due to strain-specific increased expression of genes involved in growth and development.

Metabolism of oxidants by blood from different mouse strains

Haemoglobins bearing reactive sulfhydryl groups have been shown to be able to interplay with glutathione in some detoxification processes. Blood from different mouse strains commonly used as experimental animal models, i.e., C57, DBA and ICR, was treated with oxidants with the aim of evaluating: (i) the involvement of protein SH groups in oxido-reductive reactions that are commonly carried out by glutathione and (ii) the impact of this phenomenon on blood-mediated metabolism of thiol reactants. All the main forms of glutathione (reduced, disulfide, and mixed disulfide with haemoglobin) were measured after oxidant treatment. Significant differences were found among the studied strains: DBA mice formed preferably mixed disulfides instead of glutathione disulfide, whereas the opposite behaviour was shown by C57 mice. Unexpectedly, the ICR strain resulted to be composed of three different subgroups (ICRa, ICRb, and ICRc), with the ICRa behaving similarly to the DBA strain, ICRc to the C57 strain, and ICRc showing an intermediate behaviour. These results are due to the different number of haemoglobin SH groups in the studied mouse strains. In particular, additional fast-reacting SH groups were found in haemoglobin from DBA, ICRa, and ICRb mice, but not in the C57 and ICRc strain. These differences were also reflected in the susceptibility of haemoglobin to dimerize and in its ability to react with S-nitrosocysteine. Because of the widely different reactivity of haemoglobin cysteinyl residues, the mouse strains examined are an interesting but complicated model in which to study the pharmacological and toxicological action of some drugs.

Vascular injury response in mice is dependent on genetic background

Mouse models are employed to unravel the pathophysiology of vascular restenosis. Although much effort has been spent on how to apply an adequate arterial injury, the influence of the genetic background of mice has not yet received sufficient consideration. The study presented herein was designed to demonstrate the influence of the mouse strain on vascular injury response. Mice of a defined background (50% 129 strain and 50% DBA strain) were backcrossed into either the 129 strain or the DBA strain. Male offspring were subjected to a femoral artery injury model by applying an electric current. Morphometric analysis revealed that backcrossing into the 129 strain resulted in a significant (P < 0.001) 17-fold increase in neointima formation (n = 17 mice) compared with backcrossing into the DBA strain (n = 19). The values of neointima area were 9.18 x 10(3) +/- 2.13 x 10(3) and 0.54 x 10(3) +/- 0.39 x 10(3) microm2, respectively. In conjunction, the vessel wall area was enhanced by 1.8-fold (P < 0.001). In contrast, no significant differences were found for the areas of the lumen and the tunica media. Similarly, a significant increase in neointima formation was also found for mice of pure 129 strain compared with pure DBA strain. The results underline the importance of the genetic background for studies on vascular injury response. Furthermore, because the mouse genome of the various strains is well defined, serial testing of the genetic background of mice will provide candidate genes and/or genetic modifiers controlling vascular injury response.