Identification of a congenic mouse line with obesity and body length phenotypes

Our primary objective was to discover simplified mouse models corresponding to human obesity linkages. We used the B10.UW– H3^b we Pax1^un a^t/Sn (B10.UW) congenic strain, a subcongenic strain with a reduced UW strain donor region, and their C57BL/10SnJ background strain. The congenic and subcongenic UW strain donor regions are on mouse Chr 2. We measured body length [anal-nasal (AN) length], summed fat depot weights normalized for body weight (Adiposity Index, AI), and percentage of body weight that is lipid. The B10.UW congenic and subcongenic strains have significantly smaller AN lengths (p < 0.0001) and have a significantly lower AI and percentage of body weight as fat than the background strain (p < 0.0001). In an F₂ intercross of the congenic and background strains, AN and AI were both linked to the distal half of the donor region with LOD scores greater than 19 and 5, respectively. F₂ haplotypes identified a minimal region for AN linkage of 0.8 megabases (Mb) that is estimated to express four genes in the current Celera mouse genome assembly. We narrowed the most likely location of the obesity gene to 15 Mb whose homologous genes are all located on human Chr 20 in the region surrounding the centromere. Since a previous study identified human obesity linkage peaking near the centromere, then the B10.UW mice may exhibit obesity due to the homologous gene.     

Gene-environment interaction: a significant diet-dependent obesity locus demonstrated in a congenic segment on mouse Chromosome 7

We have previously reported suggestive evidence for a locus on Chromosome (Chr) 7 that affects adiposity in F₂ mice from a CAST/Ei × C57BL/6J intercross fed a high-fat diet. Here we characterize the effect of a high-fat (32.6 Kcal% fat) diet on male and female congenic mice with a C57BL/6J background and a CAST/Ei-derived segment on Chr 7. Adiposity index (AI) and weights of certain fat pads were approximately 50% lower in both male and female congenic mice than in control C57BL/6J mice, and carcass fat content was significantly reduced. The reduction of fat depot weights was not seen, however, in congenic animals fed a low-fat chow diet (12 Kcal% fat). The congenic segment is approximately 25 cM in length, extending from D7Mit213 to D7Mit41, and includes the tub, Ucp2, and Ucp3, genes, all of which are candidate genes for this effect. Some polymorphisms have been found on comparing c-DNA sequences of the Ucp2 gene from C57BL/6J and CAST/Ei mice. These results suggest that one or more genes present in the congenic segment modulate the susceptibility to fat deposition on feeding a high-fat diet. We were unable to show any significant difference between the energy intakes of the congenic and the control C57BL/6J mice on the high-fat diet. Also, measurements of energy expenditure in male mice at 6 weeks of age, during the first 2 weeks of exposure to the high-fat diet, failed to show any differences between control and congenic animals. Received: 30 September 1998 / Accepted: 22 December 1998     

Gene expression profiles of a mouse congenic strain carrying an obesity susceptibility QTL under obesigenic diets

Genetic factors are strongly involved in the development of obesity, likely through the interactions of susceptibility genes with obesigenic environments, such as high-fat, high-sucrose (HFS) diets. Previously, we have established a mouse congenic strain on C57BL/6 J background, carrying an obesity quantitative trait locus (QTL), tabw2, derived from obese diabetic TALLYHO/JngJ mice. The tabw2 congenic mice exhibit increased adiposity and hyperleptinemia, which becomes exacerbated upon feeding HFS diets. In this study, we conducted genome-wide gene expression profiling to evaluate differentially expressed genes between tabw2 and control mice fed HFS diets, which may lead to identification of candidate genes as well as insights into the mechanisms underlying obesity mediated by tabw2. Both tabw2 congenic mice and control mice were fed HFS diets for 10 weeks beginning at 4 weeks of age, and total RNA was isolated from liver and adipose tissue. Whole-genome microarray analysis was performed and verified by real-time quantitative RT–PCR. At False Discovery Rate adjusted P < 0.05, 1026 genes were up-regulated and 308 down-regulated in liver, whereas 393 were up-regulated and 187 down-regulated in adipose tissue in tabw2 congenic mice compared to controls. Within the tabw2 QTL interval, 70 genes exhibited differential expression in either liver or adipose tissue. A comprehensive pathway analysis revealed a number of biological pathways that may be perturbed in the diet-induced obesity mediated by tabw2.     

Mapping the diabetes polygene Idd3 on mouse Chromosome 3 by use of novel congenic strains

Development of novel congenic mouse strains has allowed us to better define the location of the diabetogenic locus, Idd3, on Chromosome (Chr) 3. Congenic strains were identified by use of published and newly developed microsatellite markers, their genomes fingerprinted by a rapid, fluorescence-based approach, and their susceptibility to type 1 diabetes evaluated. The maximum interval containing Idd3 is now approximately 4 cM.     

Dissection of multigenic obesity traits in congenic mouse strains

Previous quantitative trait locus mapping (QTL) identified multigenic obesity (MOB) loci on mouse Chromosome (Chr) 2 that influence the interrelated phenotypes of obesity, insulin resistance, and dyslipidemia. To better localize and characterize the MOB locus, three congenic mouse strains were created. Overlapping genomic intervals from the lean CAST/Ei (CAST) strain were introgressed onto an obesity-susceptible C57BL/6 (BL6) background to create proximal (15 Mb–73 Mb), middle (63 Mb–165 Mb), and distal (83 Mb–182 Mb) congenic strains. The congenic strains showed differences in obesity, insulin, and lipid traits consistent with the original QTL analysis for the locus. Importantly, characterization of the MOB congenics localized the effects of genes that underlie obesity-related traits to an introgressed interval (73–83 Mb) unique to the middle MOB congenic. Conversely, significant differences between the lipid and insulin profiles of the middle and distal MOB congenics implicated the presence of at least two genes that underlie these traits. When fed an atherogenic diet, several traits associated with metabolic syndrome were observed in the distal MOB congenic, while alterations in plasma lipoproteins were observed in the middle MOB congenic strain.     

A congenic mouse and candidate gene at the Chromosome 13 locus regulating bone density

Previously, we identified two significant quantitative trait loci (QTLs) specifying the peak relative bone mass (bone mass corrected for bone size) on chromosomes (Chrs) 11 and 13 by interval mapping in two mouse strains, SAMP2 and SAMP6. The latter strain is an established murine model of senile osteoporosis and exhibits a significantly lower peak relative bone mass than SAMP2 mice. We recently designated the Chr 13 locus as Pbd2 (Peak bone density 2) and constructed a congenic strain, P6.P2-Pbd2(b), which carried a single genomic interval from the Chr 13 of SAMP2 on a SAMP6-derived osteoporotic background. In this study, we have constructed a congenic strain, P2.P6-Pbd2(a), carrying a SAMP6-derived susceptible interval on a SAMP2-derived resistance background. This congenic strain had a lower bone density than the background strain, SAMP2, based on three measurement methods, each utilizing a different principle for evaluating bone density: MD, DXA, and pQCT. Next, a candidate gene approach was used to find polymorphisms of Bmp6 (bone morphogenetic protein 6). The CAG trinucleotide repeat numbers in exon 1 of this gene differ among SAM strains. We found an association of CAG repeat length with relative peak bone mass in mice.     

Blood pressure and survival of a Chromosome 7 congenic strain bred from Dahl rats

11β-hydroxylase (Cyp11b1) mutations were previously linked to altered steroid biosynthesis and blood pressure in Dahl salt-resistant (R) and Dahl salt-sensitive (S) rats. In the present work, interval mapping identified a putative blood pressure quantitative trait locus (QTL) near Cyp11b1 in an F₁(S×R)×S population (LOD = 2.0). Congenic rats (designated S.R-Cyp11b) were constructed by introgressing the R-rat Cyp11b1 allele into the S strain. S.R-Cyp11b rats had significantly lower blood pressure and heart weight compared with S rats, proving the existence of a blood pressure QTL on Chromosome (Chr) 7 despite the fact that QTL linkage analysis of blood pressure never achieved stringent statistical criteria for significance. To test the effects of the introgressed region on blood pressure and survival, S.R.-Cyp11b and S rats were maintained on a 4% NaCl diet until they died or became moribund. Analysis of variance (ANOVA) indicated significant strain differences in blood pressure and days survived (P < 0.0001 for both) as well as gender differences in days survived (P = 0.0003). Kaplan-Meier survival analysis also found significant strain (P < 0.0001) and gender (P = 0.007) differences in days survived. However, when the effects of blood pressure were removed, significant strain differences in survival essentially disappeared. This suggests that the increased survival of S.R-Cyp11b rats was largely due to their decreased blood pressure and thus strongly corroborates the existence of a blood pressure QTL on Chr 7 near or at Cyp11b1. Received: 7 April 1997 / Accepted: 10 August 1997     

A new strain congenic for the Mtv-7/Mls-1 locus of mouse chromosome 1

Correspondence to: B. A. Taylor.     

Genetic analysis of testis weight and fertility in an interspecies hybrid congenic strain for Chromosome X

A hybrid congenic strain, C57BL/6J.SPRET-Hprt ^a , carrying 17 map units of Chromosome (Chr) X from Mus spretus on a background of C57BL/6J, has the novel phenotype of low fertility associated with small testis weight. In histological cross-section, many of the tubules in the testes of these congenic mice are empty except for Sertoli cells, while the other tubules appear to be normal. The gene, interspecific hybrid testis weight 1 (Ihtw1) causing this phenotype, has been fine mapped by using the strategy of generating subcongenic strains from recombinants within the congenic region. Genetic and phenotypic analysis of the subcongenic strains has defined a critical region of 1.8 map units for Ihtw1. This region of the genetic map is orthologous to the region on human Chr X containing the gene for the Borjeson-Forssman-Lehman syndrome, an inherited disease in which males show microorchidism. Received: 12 June 2000 / Accepted: 8 September 2000     

Peroxisome proliferator-activated receptor-alpha regulates lipid homeostasis, but is not associated with obesity: studies with congenic mouse lines

Considerable controversy exists in determining the role of peroxisome proliferator-activated receptor-alpha (PPARalpha) in obesity. Two purebred congenic strains of PPARalpha-null mice were developed to study the role of this receptor in modulating lipid transport and storage. Weight gain and average body weight in wild-type and PPARalpha-null mice on either an Sv/129 or a C57BL/6N background were not markedly different between genotypes from 3 to 9 months of age. However, gonadal adipose stores were significantly greater in both strains of male and female PPARalpha-null mice. Hepatic accumulation of lipids was greater in both strains and sexes of PPARalpha-null mice compared with wild-type controls. Administration of the peroxisome proliferator WY-14643 caused hepatomegaly, alterations in mRNAs encoding proteins that regulate lipid metabolism, and reduced serum triglycerides in a PPARalpha-dependent mechanism. Constitutive differences in serum cholesterol and triglycerides in PPARalpha-null mice were found between genetic backgrounds. Results from this work establish that PPARalpha is a critical modulator of lipid homeostasis in two congenic mouse lines. This study demonstrates that disruption of the murine gene encoding PPARalpha results in significant alterations in constitutive serum, hepatic, and adipose tissue lipid metabolism. However, an overt, obese phenotype in either of the two congenic strains was not observed. In contrast to earlier published work, this study establishes that PPARalpha is not associated with obesity in mice.     

Multiple blood pressure QTL on rat Chromosome 2 defined by congenic Dahl rats

Linkage analysis previously demonstrated a blood pressure quantitative trait locus (QTL) on rat Chromosome 2 (Chr 2) in crosses utilizing Dahl salt-sensitive (S) rats. The present work dissects this QTL by using congenic strains in which segments of Chr 2 from Wistar Kyoto rats (WKY) are placed on the S genetic background. Two distinct QTLs were found where one QTL was anticipated. These each accounted for a blood pressure of 15–20 mm Hg in rats fed 2% NaCl diet for 24 days. One QTL was in the <9-cM interval between D2Rat35 and D2Wox18 (Fgg), and the other was in the <7-cM interval between D2Wox18 (Fgg) and D2Mgh10. A third tentative QTL was suggested, but not clearly established, in the <3-cM interval between D2Mgh10 and D2Rat259. Received: 26 July 2001 / Accepted 6 September 2001     

The C5-sufficient A/J congenic mouse strain. Inflammatory response and resistance to Listeria monocytogenes

A/J mouse strain poorly responds to an inflammatory stimulus and is highly susceptible to Listeria monocytogenes (Lm) infection. This defect in the phagocyte inflammatory response caused by the C5 component of C deficiency was shown, by linkage analysis, to be the major reason for the extreme susceptibility of A/J mice to Lm infection. The importance of this genetic defect in C5 in relation to the poor macrophage inflammatory response and to the susceptibility to Lm infection was evaluated by developing a C5-sufficient congenic A/J mouse strain. This A/J.C5 mouse strain was studied for its inflammatory response and for its susceptibility to Lm infection. C5-sufficient congenic A/J.C5 mice showed a slight improvement (2X) in their level of macrophage inflammatory response; however, they did not mount an as strong response as the Listeria-resistant C57BL/6J mice which donated the C5 allele. When infected with Lm, A/J.C5 mice were found to be as resistant as C57BL/6J mice. These results suggest that the presence of C5 on an A/J background partially improves the deficient macrophage inflammatory response of that strain. This increase is sufficient to render the A/J.C5 mouse strain highly resistant to Listeria infection. A/J.C5 mouse strain represents a new tool for the study of the importance of C5 in resistance to infection and in the regulation of the macrophage inflammatory response.     

Onset and progression of behavioral and molecular phenotypes in a novel congenic R6/2 line exhibiting intergenerational CAG repeat stability

In the present study we report on the use of speed congenics to generate a C57BL/6J congenic line of HD-model R6/2 mice carrying 110 CAG repeats, which uniquely exhibits minimal intergenerational instability. We also report the first identification of the R6/2 transgene insertion site. The relatively stable line of 110 CAG R6/2 mice was characterized for the onset of behavioral impairments in motor, cognitive and psychiatric-related phenotypes as well as the progression of disease-related impairments from 4 to 10 weeks of age. 110Q mice exhibited many of the phenotypes commonly associated with the R6/2 model including reduced activity and impairments in rotarod performance. The onset of many of the phenotypes occurred around 6 weeks and was progressive across age. In addition, some phenotypes were observed in mice as early as 4 weeks of age. The present study also reports the onset and progression of changes in several molecular phenotypes in the novel R6/2 mice and the association of these changes with behavioral symptom onset and progression. Data from TR-FRET suggest an association of mutant protein state changes (soluble versus aggregated) in disease onset and progression.     

Mating preference tests with the recombinant congenic strain BALB.HTG

Tests of MHC-associated mating preference were conducted with the congenic mouse strains BALE (H-2 ^d), BALB.B (H-2 ^b), and BALB.HTG (recombinant ofH-2 ^d andH-2)^b. The results conform to a hypothesis that anRi gene (Ri-1), the expression of which influences mating preference in females, is situated to the right of theS region; and that anotherRi gene (Ri-2), the expression of which influences mating preference in males, is situated elsewhere, probably to the left ofH-2D. This hypothesis is consistent with conclusions previously reached from study of the mating preferences of B6 and B6-Tla^a congenic mice.Abbreviations according to Yamazaki et al. (1978) Ri recognition of identity