Congenic Mouse Strains Research Articles

A Role for the Non-Receptor Tyrosine Kinase Abl2/Arg in Experimental Neuroinflammation

Multiple sclerosis is a neuroinflammatory degenerative disease, caused by activated immune cells infiltrating the CNS. The disease etiology involves both genetic and environmental factors. The mouse genetic locus, Eae27, linked to disease development in the experimental autoimmune encephalomyelitis (EAE) model for multiple sclerosis, was studied in order to identify contributing disease susceptibility factors and potential drug targets for multiple sclerosis. Studies of an Eae27 congenic mouse strain, revealed that genetic variation within Eae27 influences EAE development. The Abl2 gene, encoding the non-receptor tyrosine kinase Arg, is located in the 4,1 megabase pair long Eae27 region. The Arg protein plays an important role in cellular regulation and is, in addition, involved in signaling through the B- and T-cell receptors, important for the autoimmune response. The presence of a single nucleotide polymorphism causing an amino acid change in a near actin-interacting domain of Arg, in addition to altered lymphocyte activation in the congenic mice upon immunization with myelin antigen, makes Abl2/Arg a candidate gene for EAE. Here we demonstrate that the non-synonymous SNP does not change Arg’s binding affinity for F-actin but suggest a role for Abl kinases in CNS inflammation pathogenesis by showing that pharmacological inhibition of Abl kinases ameliorates EAE, but not experimental arthritis.

Loss of disease tolerance during Citrobacter rodentium infection is associated with impaired epithelial differentiation and hyperactivation of T cell responses

Citrobacter rodentium is an intestinal mouse pathogen widely used as a model to study the mucosal response to infection. Inbred mouse strains suffer one of two fates following infection: self-limiting colitis or fatal diarrheal disease. We previously reported that Rspo2 is a major genetic determinant of the outcome of C. rodentium infection; Rspo2 induction during infection of susceptible mice leads to loss of intestinal function and mortality. Rspo2 induction does not impact bacterial colonization, but rather, impedes the ability of the host to tolerate C. rodentium infection. Here, we performed deep RNA sequencing and systematically analyzed the global gene expression profiles of C. rodentium-infected colon tissues from susceptible and resistant congenic mice strains to determine the common responses to infection and the Rspo2-mediated dysfunction pathway signatures associated with loss of disease tolerance. Our results highlight changes in metabolism, tissue remodeling, and host defence as common responses to infection. Conversely, increased Wnt and stem cell signatures, loss of epithelial differentiation, and exaggerated CD4+ T cell activation through increased antigen processing and presentation were specifically associated with the response to infection in susceptible mice. These data provide insights into the molecular mechanisms underlying intestinal dysfunction and disease tolerance during C. rodentium infection.

The Type 1 Diabetes-Resistance Locus Idd22 Controls Trafficking of Autoreactive CTLs into the Pancreatic Islets of NOD Mice.

Type 1 diabetes (T1D) has a strong genetic component. The insulin dependent diabetes (Idd)22 locus was identified in crosses of T1D-susceptible NOD mice with the strongly T1D-resistant ALR strain. The NODcALR-(D8Mit293-D8Mit137)/Mx (NOD-Idd22) recombinant congenic mouse strain was generated in which NOD mice carry the full Idd22 confidence interval. NOD-Idd22 mice exhibit almost complete protection from spontaneous T1D and a significant reduction in insulitis. Our goal was to unravel the mode of Idd22-based protection using in vivo and in vitro models. We determined that Idd22 did not impact immune cell diabetogenicity or β cell resistance to cytotoxicity in vitro. However, NOD-Idd22 mice were highly protected against adoptive transfer of T1D. Transferred CTLs trafficked to the pancreatic lymph node and proliferated to the same extent in NOD and NOD-Idd22 mice, yet the accumulation of pathogenic CTLs in the islets was significantly reduced in NOD-Idd22 mice, correlating with disease resistance. Pancreatic endothelial cells from NOD-Idd22 animals expressed lower levels of adhesion molecules, even in response to inflammatory stimuli. Lower adhesion molecule expression resulted in weaker adherence of T cells to NOD-Idd22 endothelium compared with NOD-derived endothelium. Taken together, these results provide evidence that Idd22 regulates the ability of β cell-autoreactive T cells to traffic into the pancreatic islets and may represent a new target for pharmaceutical intervention to potentially prevent T1D.

Verification of a genetic locus for methamphetamine intake and the impact of morphine.

A quantitative trait locus (QTL) on proximal chromosome (Chr) 10 accounts for > 50% of the genetic variance in methamphetamine (MA) intake in mice selectively bred for high (MAHDR) and low (MALDR) voluntary MA drinking. The µ-opioid receptor (MOP-r) gene, Oprm1, resides at the proximal end of Chr 10, and buprenorphine reduces MA intake in MAHDR mice. However, this drug has only partial agonist effects at MOP-r. We investigated the impact of a full MOP-r agonist, morphine, on MA intake and saccharin intake, measured MOP-r density and affinity in several brain regions of the MA drinking lines and their C57BL/6J (B6) and DBA/2J (D2) progenitor strains, and measured MA intake in two congenic strains of mice to verify the QTL and reduce the QTL interval. Morphine reduced MA intake in the MAHDR line, but also reduced saccharin and total fluid intake. MOP-r density was lower in the medial prefrontal cortex of MAHDR, compared to MALDR, mice, but not in the nucleus accumbens or ventral midbrain; there were no MOP-r affinity differences. No significant differences in MOP-r density or affinity were found between the progenitor strains. Finally, Chr 10 congenic results were consistent with previous data suggesting that Oprm1 is not a quantitative trait gene, but is impacted by the gene network underlying MA intake. Stimulation of opioid pathways by a full agonist can reduce MA intake, but may also non-specifically affect consummatory behavior; thus, a partial agonist may be a better pharmacotherapeutic.

Aging deteriorates quality of sperm produced by male mice with partial Yq deletion

ABSTRACTThe aim of the study was to assess the cumulative effects of aging and Y-chromosome long arm deletion on sperm quality parameters. Motility, mitochondrial activity, and head morphology were evaluated for sperm of 3- and 12-month-old males from B10.BR-Ydel and B10.BR congenic mouse strains. The study revealed that quality and fertilizing potential of sperm produced by younger and older B10.BR males persist on similar levels, but worsen significantly with age of B10.BR-Ydel males. The findings imply that partial Yq deletions might be more harmful for spermiogenesis in advancing age and may be applicable to other species including humans.Abbreviations: AZF: azoospermia factor; MSYq: male-specific region of the Y-chromosome long arm

Congenic mice demonstrate the presence of QTLs conferring obesity and hypercholesterolemia on chromosome 1 in the TALLYHO mouse.

The TALLYHO (TH) mouse presents a metabolic syndrome of obesity, type 2 diabetes, and hyperlipidemia. Highly significant quantitative trait loci (QTLs) linked to adiposity and hypercholesterolemia were previously identified on chromosome (Chr) 1 in a genome-wide scan of F2 mice from C57BL/6J (B6) x TH. In this study, we generated congenic mouse strains that carry the Chr 1 QTLs derived from TH on a B6 background; B6.TH-Chr1-128Mb (128Mb in size) and B6.TH-Chr1-92Mb (92Mb in size, proximally overlapping). We characterized these congenic mice on chow and high fat (HF) diets. On chow, B6.TH-Chr1-128Mb congenic mice exhibited a slightly larger body fat mass compared with B6.TH-Chr1-92Mb congenic and B6 mice, while body fat mass between B6.TH-Chr1-92Mb congenic and B6 mice was comparable. Plasma total cholesterol levels were significantly higher in B6.TH-Chr1-128Mb congenics compared to B6.TH-Chr1-92Mb congenic and B6 mice. Again, there was no difference in plasma total cholesterol levels between B6.TH-Chr1-92Mb congenic and B6 mice. All animals gained more body fat and exhibited higher plasma total cholesterol levels when fed HF diets than fed chow, but these increases were greater in B6.TH-Chr1-128Mb congenics than in B6.TH-Chr1-92Mb congenic and B6 mice. These results confirmed the effect of the 128Mb TH segment from Chr 1 on body fat and plasma cholesterol values and showed that the distal segment of Chr 1 from TH is necessary to cause both phenotypes. Through bioinformatic approaches, we generated a list of potential candidate genes within the distal region of Chr 1 and tested Ifi202b and Apoa2. We conclude that Chr 1 QTLs largely confer obesity and hypercholesterolemia in TH mice and can be promising targets for identifying susceptibility genes. Congenic mouse strains will be a valuable resource for gene identification.

HDAC11 as a candidate therapeutic target in multiple myeloma.

8029 Background: Histone deacetylase (HDAC) inhibitors (HDI) have a therapeutic niche in multiple myeloma (MM) due to their ability to salvage proteasome inhibitor and immunomodulatory drug responsiveness in refractory patients, thus raising interest in this therapeutic class. Selective HDI may further improve therapeutic efficacy. Methods: B cell lymphopoiesis was evaluated using Tg-HDAC11-eGFP mice expressing eGFP regulated by the HDAC11 promoter and congenic mouse strains deficient in HDAC11 expression globally (B6.HDAC11-/-) or targeted to the B cell lineage (CD19Cre.HDAC11-/-). Molecular and pharmacologic means were used to impair HDAC11 in established MM cell lines. Viability was measured by activated caspase-3, Annexin/PI (A/PI) staining, and CCK-8 viability assay. Subcellular localization changes induced by HDI and identification of the novel binding partner IRF4 were assessed by proximity ligation assay (PLA). Results: Profound eGFP increases in PC of Tg-HDAC11-eGFP mice suggest HDAC11 influences late stage B cell development. In addition, HDAC11 deficiency results in dramatically reduced PC in the bone marrow and periphery. PC depletion in CD19Cre.HDAC11-/-mice suggests activity inherent in B cells rather than via externally derived signals. Quisinostat (QS), an HDI with enhanced HDAC11 selectivity, showed dose-dependent cytotoxicity in 10 MM cell lines (EC50 1-10nM). This activity was synergistic with bortezomib (BTZ) and carfilzomib (CFZ) in RPMI-8226 cells, while synergism was amplified in the BTZ-resistant RPMI-8226-B25 cell line. Exposure of RPMI-8226 cells to QS decreased detection of nuclear, but not cytosolic, HDAC11. Targeted siRNA–mediated silencing of HDAC11 in RPMI-8226 cells activated caspase-3 and reduced viability by A/PI staining. PLA of MM cell lines showed a novel interaction between HDAC11 and IRF4, an essential regulator of PC differentiation and MM survival, unmasking a potential mechanism for HDAC11-induced cytotoxicity in MM. This interaction was disrupted by QS. Conclusions: We show that HDAC11 inhibition reduces MM cell survival in vitro. Furthermore, we identify IRF4 as a binding partner for HDAC11 and propose this interaction as a candidate mechanism regulating PC maturation and MM survival.

NK cells require both inhibitory and activation Ly49 receptors to mediate MHC I Dk-dependent MCMV resistance.

Abstract The MHC class I molecule, Dk, is a key genetic factor of murine cytomegalovirus (MCMV) resistance. NK cells expressing the C57L-derived inhibitory receptor Ly49G2 (G2) mediate Dk-dependent MCMV control, however, a precise in vivo role for activation receptors has not been delineated. We studied a role for activation receptors in Dk-disparate B6.NKCc57l congenic mice by injecting neutralizing mAbs prior to infection. We found that only Ly49R (R) blockade specifically, and completely, abrogated host resistance. R+ NK cells had a differentiated phenotype (CD27−, CD11b+, KLRG1+, DNAM1−) and displayed higher granzyme B during MCMV infection, in comparison to R− NK cells. R+ G2+ NK cells responding to MCMV also showed higher proliferative potential and cytokine responsiveness compared to R+ G2− NK cells. To further interrogate the role of these NK cell subsets in vivo, we exploited differences in expression of Nkrp1 (NK1.1) and Ly49 receptor alleles in our NKC congenic mouse strains. Endogenous NK cells in H-2 matched host B6.Dk mice were either selectively depleted with mAb PK136 (NK1.1) or neutralized with mAb 3D10 (a-Ly49H), rendering them susceptible to MCMV infection, prior to adoptive transfer of donor B6.NKCc57l NK cells. We found that responding donor NK cells were mostly R+ G2+ and actively expanding in contrast to R+ G2− NK cells. Ongoing adoptive transfer experiments with sorted NK cell populations suggest MCMV control coincides with donor R+ G2+ NK cells. We are continuing to investigate how inhibitory Ly49 receptors modify NK cell responsiveness via activation Ly49 receptors. We infer from these data that inhibitory and activation Ly49 receptors work in tandem to deliver specific NK cell-dependent virus control.

Characterization Of Expression Levels Of Genes Involved In Adipogenesis And Inflammation In Congenic Mice Carrying Obesity and Hyperlipidemia QTL on Chromosome 1

Obesity is an international health crisis and is considered the leading cause of preventable death. The development of obesity is likely due to interactions of susceptibility genes with obesity‐promoting environments such as high fat diets (HFD). These interactions lead to an expansion of adipose tissue, through an increase in adipocyte size and/or number. Adipose tissue inflammation is a well‐recognized characteristic of obesity. Previously, we identified quantitative trait loci (QTL) linked to obesity and hyperlipidemia on mouse chromosome (Chr) 1 in an intercross of obese and diabetic TALLYHO/Jng (TH) mice with C57BL/6 (B6) mice. Subsequently, we established a congenic mouse strain carrying the Chr1 QTL, 128 Mb in size, derived from TH on a B6 background (B6.TH‐Chr1–128Mb). The congenic mice were found to be more susceptible to diet‐induced obesity and hyperlipidemia than their B6 counterparts. The purpose of this study was to characterize the congenic mice by examining mRNA and protein levels of adipocyte differentiation and inflammation markers in white adipose tissue and liver. B6.TH‐Chr1–128Mb congenic and B6 mice were weaned onto chow and HFD and maintained until 16 weeks of age. Total RNA was isolated from adipose tissue and reverse‐transcribed with SUPERSCRIPT RT using oligo dT as primer to synthesize first‐strand cDNA. mRNA levels of peroxisome proliferator‐activated receptor gamma (Pparg), CCAAT/enhancer binding protein beta (Cebpb), preadipocyte factor 1 (Pref‐1), and Interleukin 6 (Il‐6) genes were measured by real‐time quantitative RT‐PCR. For protein levels, adipose tissue and liver were lysed in RIPA buffer and lysates subjected to SDA‐PAGE and Western blotting. Blots were probed with specific antibodies against PPARG and IL‐6, and detection of immunoreactive bands performed using enhanced chemiluminescence. Data analysis was conducted by ANOVA with GraphPad Prism 7. Congenic mice had a 2‐fold increase in gene expression level of Pparg, a major regulator of adipogenesis and lipogenesis, in adipose tissue compared to B6 mice on chow. HFD significantly increased the gene expression level of Pparg in both B6 and congenic mice, with greater degree in congenic mice. This trend was also the case for the protein expression level of PPARG in adipose tissue, as well as in liver, but it did not reach statistical significance. There were no significant differences in gene expression levels of Pref‐1, the most upstream repressor to adipocyte differentiation, and Cebpb, a major transcription factor during an early stage of adipogenesis, in adipose tissue between congenic and B6 mice for either diet. The gene expression level of Il‐6, a proinflammatory marker, was increased by HFD in both congenic and B6 mice, without genotype difference. A similar trend was also shown in IL‐6 protein levels in adipose tissue, as well as in liver, but it did not reach statistical significance. Collectively, we demonstrated that gene expression levels of Pparg were significantly upregulated in adipose tissue of B6.TH‐Chr1–128Mb congenic mice on chow and HFD.Support or Funding InformationThis work was supported by NASA WVSGC Graduate Fellowship to JKP and in part by NIH/NIDDK Grant R01DK077202 and institutional start‐up funding from Marshall University to JHK.

Role of Genetic Variation in Collateral Circulation in the Evolution of Acute Stroke: A Multimodal Magnetic Resonance Imaging Study.

No studies have determined the effect of differences in pial collateral extent (number and diameter), independent of differences in environmental factors and unknown genetic factors, on severity of stroke. We examined ischemic tissue evolution during acute stroke, as measured by magnetic resonance imaging and histology, by comparing 2 congenic mouse strains with otherwise identical genetic backgrounds but with different alleles of the Determinant of collateral extent-1 (Dce1) genetic locus. We also optimized magnetic resonance perfusion and diffusion-deficit thresholds by using histological measures of ischemic tissue. Perfusion, diffusion, and T2-weighted magnetic resonance imaging were performed on collateral-poor (congenic-Bc) and collateral-rich (congenic-B6) mice at 1, 5, and 24 hours after permanent middle cerebral artery occlusion. Magnetic resonance imaging-derived penumbra and ischemic core volumes were confirmed by histology in a subset of mice at 5 and 24 hours after permanent middle cerebral artery occlusion. Although perfusion-deficit volumes were similar between strains 1 hour after permanent middle cerebral artery occlusion, diffusion-deficit volumes were 32% smaller in collateral-rich mice. At 5 hours, collateral-rich mice had markedly restored perfusion patterns showing reduced perfusion-deficit volumes, smaller infarct volumes, and smaller perfusion-diffusion mismatch volumes compared with the collateral-poor mice (P<0.05). At 24 hours, collateral-rich mice had 45% smaller T2-weighted lesion volumes (P<0.005) than collateral-poor mice, with no difference in perfusion-diffusion mismatch volumes because of penumbral death occurring 5 to 24 hours after permanent middle cerebral artery occlusion in collateral-poor mice. Variation in collateral extent significantly alters infarct volume expansion, transiently affects perfusion and diffusion magnetic resonance imaging signatures, and impacts salvage of ischemic penumbra after stroke onset.

Effects of C2ta genetic polymorphisms on MHC class II expression and autoimmune diseases.

Antigen presentation by the MHC-II to CD4+ T cells is important in adaptive immune responses. The class II transactivator (CIITA in human and C2TA in mouse) is the master regulator of MHC-II gene expression. It coordinates the transcription factors necessary for the transcription of MHC-II molecules. In humans, genetic variations in CIITA have been associated with differential expression of MHC-II and susceptibility to autoimmune diseases. Here we made use of a C2ta congenic mouse strain (expressing MHC-II haplotype H-2q ) to investigate the effect of the natural genetic polymorphisms in type I promoter of C2ta on MHC-II expression and function. We demonstrate that an allelic variant in the type I promoter of C2ta resulted in an increased expression of MHC-II on macrophages (72-151% higher mean florescence intensity) and conventional dendritic cells (13-65% higher mean florescence intensity) in both spleen and peripheral blood. The increase in MHC-II expression resulted in an increase in antigen presentation to T cells in vitro and increased T-cell activation. The differential MHC-II expression in B6Q.C2ta, however, did not alter the disease development in models of rheumatoid arthritis (collagen-induced arthritis and human glucose-6-phosphate-isomerase325-339 -peptide-induced arthritis), or multiple sclerosis (MOG1-125 protein-induced and MOG79-96 peptide-induced experimental autoimmune encephalomyelitis). This is the first study to address the role of an allelic variant in type I promoter of C2ta in MHC-II expression and autoimmune diseases; and shows that C2ta polymorphisms regulate MHC-II expression and T-cell responses but do not necessarily have a strong impact on autoimmune diseases.

The circadian gene Arntl2 on distal mouse chromosome 6 controls thymocyte apoptosis.

Nonobese diabetic (NOD) mice are a model for type 1 diabetes that displays defects in central immune tolerance, including impairment of thymocyte apoptosis and proliferation. Thymocyte apoptosis is decreased in NOD/Lt mice compared to nondiabetic C3H/HeJ and C57BL/6 mice. Analysis of a set of NOD.C3H and NOD.B6 congenic mouse strains for distal chromosome 6 localizes the phenotype to the 700kb Idd6.3 interval. Idd6.3 contains the type 1 diabetes candidate gene aryl hydrocarbon receptor nuclear translocator-like 2 (Arntl2), encoding a circadian rhythm-related transcription factor. Newly generated Arntl2 -/- mouse strains reveal that inactivation of the B6 allele of Arntl2 is sufficient to both decrease thymocyte apoptosis and proliferation. When expressed from C3H or B6 alleles, ARNTL2 inhibits the transcription of interleukin 21 (Il21), a major player in the regulation of immune responses. IL-21 injection abolishes the B6 allele-mediated decrease of apoptosis and proliferation. Interestingly, IL-21 also leads to an increase in thymic proinflammatory Th17 helper cells. Our results identify Arntl2 as a gene controlling thymocyte apoptosis and proliferation along with Th17 development through the IL-21 pathway.

Single targeted exon mutation creates a true congenic mouse for competitive hematopoietic stem cell transplantation: the C57BL/6-CD45.1stem mouse

Defining the molecular regulators of hematopoietic stem and progenitor cells (HSPCs) requires in vivo functional analyses. Competitive bone marrow transplants (BMTs) compare control and test HSPCs to demonstrate the functional role of a genetic change or chemical perturbation. Competitive BMT is enabled by antibodies that specifically recognize hematopoietic cells from congenic mouse strains due to variants of the cell surface protein CD45, designated CD45.1 and CD45.2. The current congenic competitor strain, B6.SJL-Ptprc(a) Pepc(b)/BoyJ (CD45.1), has a substantial inherent disadvantage in competition against the C57BL/6 (CD45.2) strain, confounding experimental interpretation. Despite backcrossing, the congenic interval over which the B6.SJL-Ptprc(a) Pepc(b)/BoyJ strain differs is almost 40 Mb encoding ∼300 genes. Here, we demonstrate that a single amino acid change determines the CD45.1 epitope. Further, we report on the single targeted exon mutant (STEM) mouse strain, CD45.1(STEM), which is functionally equivalent to CD45.2 cells in competitive BMT. This strain will permit the precise definition of functional roles for candidate genes using in vivo HSPC assays.

Decreased expression levels of Ifi genes is associated to the increased resistance to spontaneous arthritis disease in mice deficiency of IL-1RA.

BackgroundThe mouse strain BALB/c deficient in IL-1 receptor antagonist protein (Il-1ra) develops spontaneous arthritis disease (SAD) while the strain DBA/1 IL1rn-/- with the same deficiency does not. Previously, we mapped a QTL on chromosome 1 for SAD and then developed a congenic mouse strain BALB.D1-1-/- that contains the QTL genomic fragment associated with resistance from DBA/1-/- on a BALB/c-/- background. The congenic strain was relatively resistant to spontaneous arthritis and had delayed onset and reduced severity of disease. We obtained whole genome expression profiles from the spleen of the congenic strain BALB.D1-1-/- and four other strains, the wild type BALB/c, DBA/1 and the deficient DBA/1 IL1rn-/- and the BALB/c IL1rn-/-. We then compared the similarities and differences between the congenic strain and the four parental strains. Here we report the selected potential causal genes based on differential expression levels as well as function of genes.ResultsThere is a considerable number of genes that are differentially expressed between the congenic strain and the three parental strains, BALB/c, DBA/1, and DBA/1-/-. However there only a few differentially expressed genes were identified by comparing the congenic strain and the BALB/c-/-strain. These differentially expressed genes are mainly from T-cell receptor beta chain (Tcrb) and interferon-activatable protein (Ifi) genes. These genes are also differentially expressed between congenic strain and BALB/c strains. However, their expression levels in the congenic strain are similar to that in DBA/1 and DBA/1-/-. The expression level of Tcrb-j gene is positively associated with two genes of Ifi gene 200 cluster.ConclusionsDecreased expression levels of Ifi genes is associated to the increased resistance to spontaneous arthritis disease and with down regulation of expressions of Tcrb genes in the mouse congenic strain. Ifi genes may play an important role in the susceptibility to SAD in mice.Electronic supplementary materialThe online version of this article (doi:10.1186/s12865-016-0163-y) contains supplementary material, which is available to authorized users.

Genetics: Mitochondrial DNA in evolution and disease.

Cellular organelles called mitochondria contain their own DNA. The discovery that variation in mitochondrial DNA alters physiology and lifespan in mice has implications for evolutionary biology and the origins of disease. See Letter p.561 Jose Antonio Enriquez and colleagues look into the effects of mitochondrial DNA sequence variation by using congenic mice strains that share the same nuclear genome, but have different mitochondrial DNA. They show that the mitochondrial genome has a profound influence on many aspects of physiology — including insulin signalling, obesity and telomere shortening — and results in differences in median lifespan. Thus non-pathological mitochondrial DNA variants have a broad effect on metabolism, with the differences more pronounced later in life. The authors suggest that the interplay of mitochondrial and nuclear genomes may be an important factor influencing this phenomenon, which may have implications for the field of mitochondrial replacement.

Comparison of the acute ultraviolet photoresponse in congenic albino hairless C57BL/6J mice relative to outbred SKH1 hairless mice

Hairless albino Crl:SKH1-Hr(hr) mice are commonly utilized for studies in which hair or pigmentation would introduce an impediment to observational studies. Being an outbred strain, the SKH1 model suffers from key limitations that are not seen with congenic mouse strains. Inbred and congenic C57BL/6J mice are commonly utilized for modified genetic mouse models. We compare the acute UV-induced photoresponse between outbred SKH1 mice and an immune competent, hairless, albino C57BL/6J congenic mouse line [B6.Cg-Tyr(c-2J) Hr(hr) /J]. Histologically, B6.Cg-Tyr(c-2J) Hr(hr) /J skin is indistinguishable from that of SKH1 mice. The skin of both SKH1 and B6.Cg-Tyr(c-2J) Hr(hr) /J mice exhibited a reduction in hypodermal adipose tissue, the presence of utricles and dermal cystic structures, the presence of dermal granulomas and epidermal thickening. In response to a single 1500 J/m(2) ultraviolet B dose, the oedema and apoptotic responses were equivalent in both mouse strains. However, B6.Cg-Tyr(c-2J) Hr(hr) /J mice exhibited a more robust delayed sunburn reaction, with an increase in epidermal erosion, scab formation and myeloperoxidase activity relative to SKH1 mice. Compared with SKH1 mice, B6.Cg-Tyr(c-2J) Hr(hr) /J also exhibited an aberrant proliferative response to this single UV exposure. Epidermal Ki67 immunopositivity was significantly suppressed in B6.Cg-Tyr(c-2J) Hr(hr) /J mice at 24 h post-UV. A smaller non-significant reduction in Ki67 labelling was observed in SKH1 mice. Finally, at 72 h post-UV, SKH1 mice, but not B6.Cg-Tyr(c-2J) Hr(hr) /J mice, exhibited a significant increase in Ki67 immunolabelling relative to non-irradiated controls. Thus, B6.Cg-Tyr(c-2J) Hr(hr) /J mice are suitable for photobiology experiments.

Single Targeted Exon Mutation Creates a True Congenic Mouse for Competitive Hematopoietic Stem Cell Transplantation: The C57BL/6-CD45.1(STEM) Mouse.

SummaryDefining the molecular regulators of hematopoietic stem and progenitor cells (HSPCs) requires in vivo functional analyses. Competitive bone marrow transplants (BMTs) compare control and test HSPCs to demonstrate the functional role of a genetic change or chemical perturbation. Competitive BMT is enabled by antibodies that specifically recognize hematopoietic cells from congenic mouse strains due to variants of the cell surface protein CD45, designated CD45.1 and CD45.2. The current congenic competitor strain, B6.SJL-Ptprca Pepcb/BoyJ (CD45.1), has a substantial inherent disadvantage in competition against the C57BL/6 (CD45.2) strain, confounding experimental interpretation. Despite backcrossing, the congenic interval over which the B6.SJL-Ptprca Pepcb/BoyJ strain differs is almost 40 Mb encoding ∼300 genes. Here, we demonstrate that a single amino acid change determines the CD45.1 epitope. Further, we report on the single targeted exon mutant (STEM) mouse strain, CD45.1STEM, which is functionally equivalent to CD45.2 cells in competitive BMT. This strain will permit the precise definition of functional roles for candidate genes using in vivo HSPC assays.

Identification of a locus on chromosome 1 regulating IL-17-producing γδ T cells and mortality after influenza infection.

Abstract γδ T cells are an evolutionary conserved T cell subset with innate-like effector functions. We had previously identified a locus on chromosome 1 encompassing the Slam gene family that regulates the innate-like T cell compartment. To characterize this region further, we generated a B6.129 congenic mouse strain in which a 1.1 Mbp region (chr. 1: 171.05–172.12) from the 129X1/SvJ strain was introgressed onto the C57BL/6J background, and evaluated its effect on the host immune response in influenza-infected mice. Upon infection, we observed a significant and sustained increase in the number of lung γδ T cells in B6.129c2 congenic mice. A comparison of γδ T cell function revealed that a significantly greater fraction of B6.129c2 γδ T cells were producing IL-17A versus their B6 counterparts. These differences were subset-specific as they were observed in Vγ4 and at least one other Vγ subset, but not in Vγ1 T cells. Those IL-17-producing Vγ subsets accounted for most of the increase in B6.129c2 lung γδ T cell numbers and they displayed an attenuated cell surface expression profile of Slam family receptors. Finally, since enhanced IL-17 responses have been associated with immunopathology after influenza infection, we assessed the effect of the congenic interval on survival. We found that the survival of B6.129c2 congenic mice is significantly lower compared with B6 mice after influenza infection. Taken together, our data suggest that natural genetic variations at this locus significantly impact both IL-17A production by lung γδ T cells and mortality after influenza infection.

Mucosal-associated invariant T cell-rich congenic mouse strain allows functional evaluation.

Mucosal-associated invariant T cells (MAITs) have potent antimicrobial activity and are abundant in humans (5%-10% in blood). Despite strong evolutionary conservation of the invariant TCR-α chain and restricting molecule MR1, this population is rare in laboratory mouse strains (≈0.1% in lymphoid organs), and lack of an appropriate mouse model has hampered the study of MAIT biology. Herein, we show that MAITs are 20 times more frequent in clean wild-derived inbred CAST/EiJ mice than in C57BL/6J mice. Increased MAIT frequency was linked to one CAST genetic trait that mapped to the TCR-α locus and led to higher usage of the distal Vα segments, including Vα19. We generated a MAIThi congenic strain that was then crossed to a transgenic Rorcgt-GFP reporter strain. Using this tool, we characterized polyclonal mouse MAITs as memory (CD44+) CD4-CD8lo/neg T cells with tissue-homing properties (CCR6+CCR7-). Similar to human MAITs, mouse MAITs expressed the cytokine receptors IL-7R, IL-18Rα, and IL-12Rβ and the transcription factors promyelocytic leukemia zinc finger (PLZF) and RAR-related orphan receptor γ (RORγt). Mouse MAITs produced Th1/2/17 cytokines upon TCR stimulation and recognized a bacterial compound in an MR1-dependent manner. During experimental urinary tract infection, MAITs migrated to the bladder and decreased bacterial load. Our study demonstrates that the MAIThi congenic strain allows phenotypic and functional characterization of naturally occurring mouse MAITs in health and disease.

Protection from Severe Influenza Virus Infections in Mice Carrying the Mx1 Influenza Virus Resistance Gene Strongly Depends on Genetic Background.

ABSTRACTInfluenza virus infections represent a serious threat to human health. Both extrinsic and intrinsic factors determine the severity of influenza. The MX dynamin-like GTPase 1 (Mx1) gene has been shown to confer strong resistance to influenza A virus infections in mice. Most laboratory mouse strains, including C57BL/6J, carry nonsense or deletion mutations in Mx1 and thus a nonfunctional allele, whereas wild-derived mouse strains carry a wild-type Mx1 allele. Congenic C57BL/6J (B6-Mx1r/r) mice expressing a wild-type allele from the A2G mouse strain are highly resistant to influenza A virus infections, to both mono- and polybasic subtypes. Furthermore, in genetic mapping studies, Mx1 was identified as the major locus of resistance to influenza virus infections. Here, we investigated whether the Mx1 protective function is influenced by the genetic background. For this, we generated a congenic mouse strain carrying the A2G wild-type Mx1 resistance allele on a DBA/2J background (D2-Mx1r/r). Most remarkably, congenic D2-Mx1r/r mice expressing a functional Mx1 wild-type allele are still highly susceptible to H1N1 virus. However, pretreatment of D2-Mx1r/r mice with alpha interferon protected them from lethal infections. Our results showed, for the first time, that the presence of an Mx1 wild-type allele from A2G as such does not fully protect mice from lethal influenza A virus infections. These observations are also highly relevant for susceptibility to influenza virus infections in humans. IMPORTANCE Influenza A virus represents a major health threat to humans. Seasonal influenza epidemics cause high economic loss, morbidity, and deaths each year. Genetic factors of the host strongly influence susceptibility and resistance to virus infections. The Mx1 (MX dynamin-like GTPase 1) gene has been described as a major resistance gene in mice and humans. Most inbred laboratory mouse strains are deficient in Mx1, but congenic B6-Mx1r/r mice that carry the wild-type Mx1 gene from the A2G mouse strain are highly resistant. Here, we show that, very unexpectedly, congenic D2-Mx1r/r mice carrying the wild-type Mx1 gene from the A2G strain are not fully protected against lethal influenza virus infections. These observations demonstrate that the genetic background is very important for the protective function of the Mx1 resistance gene. Our results are also highly relevant for understanding genetic susceptibility to influenza virus infections in humans.