Physiological effects of housing density on C57BL/6J mice over a 9-month period.

The NRC has consistently recommended floor space for animals used in science and agriculture. For mice, the recommended floor space is 77.4 cm(2) (12 in(2)) for a 15- to 25-g mouse. The NRC noted that its recommendations were based on "best professional judgment" and encouraged alternatives that were data driven. As part of a continual effort of The Jackson Laboratory to ensure the health and well-being of production and research mice, while promoting cost-effective, state-of-the-art research, several density-driven studies have been conducted by lab researchers. The objectives of this study were to determine the effect of housing density on variables related to mouse physiology and air quality in cages and assess the value of specific measured variables in such studies. In the present study, we monitored C57BL/6J mice in individually ventilated cages from weaning until 9 mo of age. Housing densities were equivalent to 66.4 or 36.8 cm(2) per mouse (10.3 or 5.7 in(2)). Clinical physiological variables representing general health and well-being were measured. Hematological traits, plasma lipids, and glucose, growth, bone mineral density, and percent body fat did not differ between housing densities. In the more densely housed mice, however, adrenal glands were significantly smaller, heart rates were significantly less, and food consumption was less. Cage air microenvironment was evaluated for ammonia, carbon dioxide, temperature, and humidity in cages changed weekly or every 2 wk. The cage microenvironment remained within acceptable limits at the higher density of mice at both cage-changing frequencies. The results suggest that mice housed for as long as 9 mo at up to twice the density currently recommended by NRC show no measurable adverse effects. Continued re-evaluation of the recommendation by measuring additional relevant variables of health and general well-being, and studying additional strains of mice is warranted.

Genetic analysis of lung function in inbred mice suggests vitamin D receptor as a candidate gene.

Vitamin D receptor (VDR) polymorphisms are associated with an increased asthma incidence in human populations; however, observations in Vdr knockout mice are unclear. The aim of our study was to determine the influence of the genetic variation in Vdr among inbred strains on lung resistance (i.e., dynamic and airway resistance). In an intercross between the strains C57BL/6J (B6) and KK/HlJ (KK), we identified that a significant QTL for dynamic resistance on Chr X was interacting with a QTL on Chr 15. The Chr 15 QTL peak was located in close proximity to the Vdr locus. We further examined if phenotypes of several inbred strains with varying Vdr genotypes differed. Strains with a B6-like genotype on the Vdr locus had significantly lower airway resistance than strains with a KK-like genotype. Vdr knockout mice were examined for dynamic resistance and showed significantly higher resistance than mice with one (i.e., heterozygous) or both copies (i.e., wild-type) of the Vdr. In comparison to B6, the strain A/J is more resistant but carries the same genotype at the Vdr locus. Dietary vitamin D manipulation in the strain A/J did not rescue the high airway resistance phenotype. Finally, we observed that serum vitamin D does not correlate significantly with lung resistance parameters in a survey of 18 strains. Conclusively, Vdr contributes to the phenotypic variation of lung resistance in inbred mice but other molecules in the Vdr pathway and extended network [i.e., Chr X gene(s)] may contribute as well.

Combining QTL data for HDL cholesterol levels from two different species leads to smaller confidence intervals.

Quantitative trait locus (QTL) analysis detects regions of a genome that are linked to a complex trait. Once a QTL is detected, the region is narrowed by positional cloning in the hope of determining the underlying candidate gene-methods used include creating congenic strains, comparative genomics and gene expression analysis. Combined cross analysis may also be used for species such as the mouse, if the QTL is detected in multiple crosses. This process involves the recoding of QTL data on a per-chromosome basis, with the genotype recoded on the basis of high- and low-allele status. The data are then combined and analyzed; a successful analysis results in a narrowed and more significant QTL. Using parallel methods, we show that it is possible to narrow a QTL by combining data from two different species, the rat and the mouse. We combined standardized high-density lipoprotein phenotype values and genotype data for the rat and mouse using information from one rat cross and two mouse crosses. We successfully combined data within homologous regions from rat Chr 6 onto mouse Chr 12, and from rat Chr 10 onto mouse Chr 11. The combinations and analyses resulted in QTL with smaller confidence intervals and increased logarithm of the odds ratio scores. The numbers of candidate genes encompassed by the QTL on mouse Chr 11 and 12 were reduced from 1343 to 761 genes and from 613 to 304 genes, respectively. This is the first time that QTL data from different species were successfully combined; this method promises to be a useful tool for narrowing QTL intervals.

Candidate genes for obesity revealed from a C57BL/6J x 129S1/SvImJ intercross.

OBJECTIVE: To identify the genes controlling body fat, we carried out a quantitative trait locus (QTL) analysis using C57BL/6J (B6) and 129S1/SvImJ (129) mice, which differ in obesity susceptibility after consuming an atherogenic diet. METHODS: Mice were fed chow until 8 weeks and an atherogenic diet from 8 to 16 weeks; body fatness was measured by X-ray absorptiometry in 528 (B6 x 129) F(2) at 8 and 16 weeks. A high-density genome scan was performed using 508 polymorphic markers. After identifying the genetic loci, we narrowed the QTL using comparative genomics and bioinformatics. RESULTS: The percentage of body fat was significantly linked to loci on chromosomes (Chr) 1 (22, 68 and 173 Mb), 4 (74 Mb), 5 (73 Mb), 7 (88 Mb), 8 (43 and 80 Mb), 9 (55 Mb), 11 (115 Mb) and 12 (32 Mb); three suggestive loci on Chrs 6 (76 Mb), 9 (30 Mb) and 16 (26 Mb) and two pairs of interacting loci (Chr 2 at 99.8 Mb with Chr 7; Chr 1 at 68 Mb with Chr 11). Comparative genomics narrowed the QTL intervals by 20-57% depending on the chromosome; in most cases, haplotype analysis further narrowed them by about 90%. CONCLUSIONS: Our analysis identified 15 QTL for percentage of body fat. We narrowed the QTL using comparative genomics and haplotype analysis and suggest several candidate genes: Apcs on Chr 1, Ppargc1a on Chr 5, Ucp1 on Chr 8, Angptl6 on Chr 9 and Lpin1 on Chr 12.

Analysis of the QTL for sleep homeostasis in mice: Homer1a is a likely candidate.

Electroencephalographic oscillations in the frequency range of 0.5-4 Hz, characteristic of slow-wave sleep (SWS), are often referred to as the delta oscillation or delta power. Delta power reflects sleep intensity and correlates with the homeostatic response to sleep loss. A published survey of inbred strains of mice demonstrated that the time course of accumulation of delta power varied among inbred strains, and the segregation of the rebound of delta power in BxD recombinant inbred strains identified a genomic region on chromosome 13 referred to as the delta power in SWS (or Dps1). The quantitative trait locus (QTL) contains genes that modify the accumulation of delta power after sleep deprivation. Here, we narrow the QTL using interval-specific haplotype analysis and present a comprehensive annotation of the remaining genes in the Dps1 region with sequence comparisons to identify polymorphisms within the coding and regulatory regions. We established the expression pattern of selected genes located in the Dps1 interval in sleep and wakefulness in B6 and D2 parental strains. Taken together, these steps reduced the number of potential candidate genes that may underlie the accumulation of delta power after sleep deprivation and explain the Dps1 QTL. The strongest candidate gene is Homer1a, which is supported by expression differences between sleep and wakefulness and the SNP polymorphism in the upstream regulatory regions.

Cholesterol synthesis inhibition distal to squalene upregulates biliary phospholipid secretion and counteracts cholelithiasis in the genetically prone C57L/J mouse.

BACKGROUND AND AIMS: Newly synthesised cholesterol contributes poorly to biliary lipid secretion but may assume greater importance when the rate limiting enzyme 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) is upregulated. As this occurs in the gall stone susceptible C57L/J inbred mouse, we employed two cholesterol biosynthesis inhibitors, Tu 2208 and Ro 48-8071, potent inhibitors of squalene epoxidase and oxidosqualene-lanosterol cyclase, respectively, to assess their potential in preventing cholesterol cholelithiasis in the C57L/J mouse strain. Mice were fed a lithogenic diet comprising a balanced nutrient intake with 15% dairy fat, 1% cholesterol, and 0.5% cholic acid added. METHODS: We determined gall stone phenotype, HMGR activity, biliary lipid secretion rates, and counterregulatory events in male C57L/J mice and gall stone resistant AKR treated with Tu 2208 (30-60 mg/kg/day) or Ro 48-8071 (30-100 mg/kg/day), while ingesting chow or the lithogenic diet. RESULTS: Both agents reduced the gall stone prevalence rate from 73% to 17% in C57L/J mice, inhibited HMGR activity, and decreased hepatic cholesterol concentrations without appreciably influencing biliary cholesterol secretion. In C57L as well as AKR mice, both agents increased biliary phospholipid (which is mostly phosphatidylcholine) secretion rates and at the highest doses effectively reduced the biliary cholesterol saturation index. CONCLUSIONS: Cholesterol biosynthesis inhibitors acting distally to squalene do not reduce biliary cholesterol secretion rates despite reductions in cholesterol biosynthesis and hepatocellular levels. However, they effectively prevent gall stone formation through stimulation of pathways that lead to enhanced biliary phospholipid secretion.

Overexpression of Prdx6 reduces H2O2 but does not prevent diet-induced atherosclerosis in the aortic root.

The mammalian 1-Cys peroxiredoxin (Prdx6) is a unique member of the peroxiredoxin family of proteins capable of protecting cells from metal-catalyzed oxidative damage. We recently identified Prdx6 as a candidate for the quantitative trait locus Ath1, a gene responsible for a difference in diet-induced atherosclerosis susceptibility in mice. To investigate the role of Prdx6 in atherosclerosis, we generated transgenic mice that overexpress the Prdx6 allele from the Ath1-resistant 129/SvJ strain on an Ath1-susceptible C57BL/6J background. These mice expressed significantly elevated levels of Prdx6 mRNA and protein in multiple tissues including liver, aorta, and peritoneal macrophages, which accumulated significantly lower levels of hydrogen peroxide, revealing an enhanced antioxidant activity in these mice. However, overexpression of Prdx6 had no protective effect on LDL oxidation in vitro, and transgenic mice fed an atherogenic diet for 10 weeks did not possess an increased resistance to atherosclerosis nor did they maintain the high prediet plasma HDL levels consistent with the Ath1-resistant phenotype. In addition, the Prdx6 allele from the susceptible strain was shown to have a higher antioxidant activity than that of the resistant strains. These data suggest that the increased peroxidase activity attributable to Prdx6 overexpression in transgenic mice is not sufficient to protect mice from atherosclerosis, and that Prdx6 is not likely to be the gene underlying Ath1.

Mapping cholesterol gallstone susceptibility (Lith) genes in inbred mice.

The individual risk for developing cholesterol gallstones in response to specific environmental factors is determined by complex genetics involving multiple genes. In this review, we introduce inbred mice as a model to localise and identify the murine genes that harbour cholesterol gallstone susceptibility alleles (Lith genes). These genes are associated with increased risk of gallstone formation when mice are fed a lithogenic diet containing cholesterol and cholic acid. We summarise the steps involved in localising the chromosomal regions that harbour Lith genes, focusing particularly on the initial step known as quantitative trait locus mapping, which employs breeding crosses of gallstone-susceptible and gallstone-resistant inbred mouse strains. Subsequent steps to narrow the chromosomal regions of the quantitative trait loci and identify the underlying Lith genes are outlined, with particular reference to the examples of Lith1 and Lith2, the first discovered quantitative trait loci associated with murine cholesterol cholelithiasis. We have now reported five quantitative trait loci for murine cholelithogenesis, which are officially named Lith1 through Lith5. Once the genes underlying these quantitative trait loci and other chromosomal loci from ongoing mouse crosses are identified and confirmed, the 'road-map' for discovery of orthologous human LITH genes will be available and, thereafter, their putative roles in cholesterol gallstone formation can be tested in selected human populations.

Genetic factors at the enterocyte level account for variations in intestinal cholesterol absorption efficiency among inbred strains of mice.

Interindividual and interstrain variations in cholesterol absorption efficiency occur in humans and animals. We investigated physiological biliary and small intestinal factors that might determine variations in cholesterol absorption efficiency among inbred mouse strains. We found that there were significant differences in cholesterol absorption efficiency measured by plasma, fecal, and lymphatic methods: <25% in AKR/J, C3H/J, and A/J strains; 25-30% in SJL/J, DBA/2J, BALB/cJ, SWR/J, and SM/J strains; and 31-40% in C57L/J, C57BL/6J, FVB/J, and 129/SvJ strains. In (AKRxC57L)F1 mice, the cholesterol absorption efficiency (31 +/- 6%) mimicked that of the C57L parent (37 +/- 5%) and was significantly higher than in AKR mice (24 +/- 4%). Although biliary bile salt compositions and small intestinal transit times were similar, C57L mice displayed significantly greater bile salt secretion rates and pool sizes than AKR mice. In examining lymphatic cholesterol transport in the setting of a chronic biliary fistula, C57L mice displayed significantly higher cholesterol absorption rates compared with AKR mice. Because biliary and intestinal transit factors were accounted for, we conclude that genetic variations at the enterocyte level determine differences in murine cholesterol absorption efficiency, with high cholesterol absorption likely to be a dominant trait. This study provides baseline information for identifying candidate genes that regulate intestinal cholesterol absorption at the cellular level.

Phenotypic characterization of Lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice: soluble pronucleating proteins in gallbladder and hepatic biles.

BACKGROUND/AIMS: Gallstone susceptibility is high in C57L inbred mice (males > females) and low in AKR mice, related to variant lithogenic (Lith) genes. We examined the relationship between biliary crystallization-promoting proteins and gallstone susceptibility. METHODS: Biliary protein and lipid concentrations were determined at 0, 7,14, 21, 28 and 56 days on a lithogenic diet. RESULTS: Protein and soluble mucin concentrations in gallbladder biles increased markedly in males, but remained low in females of both strains and correlated with the cholesterol saturation index (CSI). In all groups, IgA and IgM concentrations decreased initially, but increased at later stages. There were no consistent changes in IgG concentrations, but aminopeptidase-N levels were higher in AKR than in C57L. During the lithogenic diet period, the CSI was > or = 2 in C57L males, approximately 1.5 in AKR males, and 1 in females of both strains. Taurodeoxycholate and taurochenodeoxycholate rose sharply in C57L, but remained low in AKR. CONCLUSIONS: Hydrophobic bile salts, cholesterol supersaturation, and possibly, high mucin concentrations are associated with gallstone formation. In vitro crystallization-promoting immunoglobulins and aminopeptidase-N do not appear to be major factors in murine gallstone pathogenesis, in line with the observation that genes encoding these proteins do not co-localize with any known Lith locus.

Intraocular pressure in genetically distinct mice: an update and strain survey.

BACKGROUND: Little is known about genetic factors affecting intraocular pressure (IOP) in mice and other mammals. The purpose of this study was to determine the IOPs of genetically distinct mouse strains, assess the effects of factors such as age, sex and time of day on IOP in specific strain backgrounds, and to assess the effects of specific candidate gene mutations on IOP. RESULTS: Based on over 30 studied mouse strains, average IOP ranges from approximately 10 to 20 mmHg. Gender does not typically affect IOP and aging results in an IOP decrease in some strains. Most tested strains exhibit a diurnal rhythm with IOP being the highest during the dark period of the day. Homozygosity for a null allele of the carbonic anhydrase II gene (Car2n) does not alter IOP while homozygosity for a mutation in the leptin receptor gene (Leprdb) that causes obesity and diabetes results in increased IOP. Albino C57BL/6J mice homozygous for a tyrosinase mutation (Tyrc-2J) have higher IOPs than their pigmented counterparts. CONCLUSIONS: Genetically distinct mouse strains housed in the same environment have a broad range of IOPs. These IOP differences are likely due to interstrain genetic differences that create a powerful resource for studying the regulation of IOP. Age, time of day, obesity and diabetes have effects on mouse IOP similar to those in humans and other species. Mutations in two of the assessed candidate genes (Lepr and Tyr) result in increased IOP. These studies demonstrate that mice are a practical and powerful experimental system to study the genetics of IOP regulation and disease processes that raise IOP to harmful levels.

Fine mapping of Ath6, a quantitative trait locus for atherosclerosis in mice.

Ath6 is a novel quantitative trait locus associated with differences in susceptibility to atherosclerosis between C57BL/6J (B6) and C57BLKS/J (BKS) inbred mouse strains. Combining data from an intercross and a backcross (1593 meioses) between mice from B6 and BKS strains and from The Jackson Laboratory interspecific backcross panels, (C57BL/6J x Mus spretus) F1 x C57BL/6J and (C57BL/6J x SPRET/Ei) F1 x SPRET/Ei, we constructed a consensus genetic map and narrowed Ath6 to a 1.07 +/- 0.26 cM interval between the anonymous DNA marker D12Pgn4 and the gene Nmyc1. This region is near the proximal end of murine Chromosome (Chr) 12, which is homologous to the human chromosomal region 2p24-p25. Marker order in the Ath6 region was concordant among the two crosses and The Jackson Laboratory interspecific backcross panels. This high resolution map rules out candidate genes encoding apolipoprotein B, syndecan 1, and Adam17. The two Ath6 crosses have a combined potential resolution of 0.06 cM.

Cytomegalovirus infection increases development of atherosclerosis in Apolipoprotein-E knockout mice.

Cytomegalovirus (CMV) infection has been associated with coronary artery disease, but it is unknown whether the virus can causally contribute to atherogenesis. To determine whether the virus has this capacity, we infected an atherosclerotic-prone mouse strain (C57BL/6J apoE-/-) with murine CMV. At 14 days of age, 30 mice received CMV (30000 pfu) ip and 30 received virus free media. At 13 and 16 weeks atherosclerotic lesion size was measured from aortic sinus cross-sections. Infection did not alter plasma levels of cholesterol, triglycerides, and high density lipoprotein (HDL); however, 4 weeks after infection IFNgamma levels were elevated (infection vs control: 156+/-49 vs 50+/-22 pg/ml, P=0.04). No differences in lesion size were present at 13 weeks post infection. However, by 16 weeks mean aortic sinus lesion area (mm(2)x10(3)+/-SEM; N=75) in the CMV-infected mice was significantly greater than in uninfected mice (74+/-6 vs 57+/-6; P=0.04). CMV caused the greatest increase (34%) in lesion size in females (103+/-9 vs 77+/-10; P=0.05; N=35). These results provide additional evidence implicating CMV as a causal agent of atherosclerosis, at least in an animal model.

Analysis of glomerulosclerosis and atherosclerosis in lecithin cholesterol acyltransferase-deficient mice.

To evaluate the biochemical and molecular mechanisms leading to glomerulosclerosis and the variable development of atherosclerosis in patients with familial lecithin cholesterol acyl transferase (LCAT) deficiency, we generated LCAT knockout (KO) mice and cross-bred them with apolipoprotein (apo) E KO, low density lipoprotein receptor (LDLr) KO, and cholesteryl ester transfer protein transgenic mice. LCAT-KO mice had normochromic normocytic anemia with increased reticulocyte and target cell counts as well as decreased red blood cell osmotic fragility. A subset of LCAT-KO mice accumulated lipoprotein X and developed proteinuria and glomerulosclerosis characterized by mesangial cell proliferation, sclerosis, lipid accumulation, and deposition of electron dense material throughout the glomeruli. LCAT deficiency reduced the plasma high density lipoprotein (HDL) cholesterol (-70 to -94%) and non-HDL cholesterol (-48 to -85%) levels in control, apoE-KO, LDLr-KO, and cholesteryl ester transfer protein-Tg mice. Transcriptome and Western blot analysis demonstrated up-regulation of hepatic LDLr and apoE expression in LCAT-KO mice. Despite decreased HDL, aortic atherosclerosis was significantly reduced (-35% to -99%) in all mouse models with LCAT deficiency. Our studies indicate (i) that the plasma levels of apoB containing lipoproteins rather than HDL may determine the atherogenic risk of patients with hypoalphalipoproteinemia due to LCAT deficiency and (ii) a potential etiological role for lipoproteins X in the development of glomerulosclerosis in LCAT deficiency. The availability of LCAT-KO mice characterized by lipid, hematologic, and renal abnormalities similar to familial LCAT deficiency patients will permit future evaluation of LCAT gene transfer as a possible treatment for glomerulosclerosis in LCAT-deficient states.

The impact of reduced frequency of cage changes on the health of mice housed in ventilated cages.

Our purpose in this investigation was to determine if we could reduce cage changing frequency without adversely affecting the health of mice. We housed mice at three different cage changing frequencies: 7, 14, and 21 days, each at three different cage ventilation rates: 30, 60 and 100 air changes per hour (ACH), for a total of nine experimental conditions. For each condition, we evaluated the health of 12 breeding pairs and 12 breeding trios of C57BL/6J mice for 7 months. Health was assessed by breeding performance, weanling weight and growth, plasma corticosterone levels, immune function, and histological examination of selected organs. Over a period of 4 months, we monitored the cage microenvironment for ammonia and carbon dioxide concentrations, relative humidity, and temperature one day prior to changing the cage. The relative humidity, carbon dioxide concentrations, and temperature of the cages at all conditions were within acceptable levels. Ammonia concentrations remained below 25 ppm (parts per million) in most cages, but, even at higher concentrations, did not adversely affect the health of mice. Frequency of cage changing had only one significant effect; pup mortality with pair matings was greater at the cage changing frequency of 7 days compared with 14 or 21 days. In addition, pup mortality with pair matings was higher at 30 ACH compared with other ventilation rates. In conclusion, under the conditions of this study, cage changes once every 14 days and ventilation rates of 60 ACH provide optimum conditions for animal health and practical husbandry.

Mouse models of blood pressure regulation and hypertension.

Human essential hypertension is recognized as a multifactorial disease involving many genes, but the causative genes have not yet been identified. For many years hypertension was studied primarily in the rat, but more recently several candidate genes for hypertension have been used to produce transgenic mice for gain of function and gene-targeted mice for loss of function studies. These genetically engineered mouse strains with hypertension or hypotension are providing insights into the mechanisms of blood pressure regulation. However, genetically engineered mice are used to study one gene at a time, and another complementary approach is needed for polygenic inheritance and gene interaction. The phenotype-driven approach to hypertension studies uses the natural variation among inbred strains and crosses to find quantitative trait loci. The four mouse crosses carried out so far have found several quantitative trait loci that are concordant with hypertension loci found in rats and humans.

Chromosomal organization of candidate genes involved in cholesterol gallstone formation: a murine gallstone map.

Epidemiologic and family studies indicate that cholesterol gallstone formation is in part genetically determined. The major contribution to our current understanding of gallstone genes derives from animal studies, particularly cross-breeding experiments in inbred mouse strains that differ in genetic susceptibility to cholesterol gallstone formation (quantitative trait loci mapping). In this review we summarize how the combined use of genomic strategies and phenotypic studies in inbred mice has proven to be a powerful means of dissecting the complex pathophysiology of this common disease. We present a "gallstone map" for the mouse, consisting of all genetic loci that have been identified to confer gallstone susceptibility as well as putative candidate genes. Translation of the genetic loci and genes between mouse and human predicts chromosomal regions in the human genome that are likely to harbor gallstone genes. Both the number and the precise understanding of gallstone genes are expected to further increase with rapid progress of the genome projects, and multiple new targets for early diagnosis and prevention of gallstone disease should become possible.

Concordance of murine quantitative trait loci for salt-induced hypertension with rat and human loci.

To investigate the genetic control of salt-induced hypertension, we performed a quantitative trait locus analysis on male mice from a reciprocal backcross between the salt-sensitive C57BL/6J and the normotensive A/J inbred mouse strains after they were provided with water containing 1% salt for 2 weeks. Genome-wide scans performed on these mice and analyzed with a combination of conventional marker-based regressions and a novel simultaneous search for pairs revealed six significant quantitative trait loci associated with salt-induced blood pressure, two of which were interacting loci. These six loci, named Bpq1-6 for blood pressure quantitative trait loci, mapped to D1Mit334, D1Mit14, D4Mit164, D5Mit31, D6Mit15, and D15Mit13. Furthermore, five of these six loci were concordant with hypertension loci in rats, and four were concordant with hypertension loci in humans, suggesting that quantitative trait loci mapping in model organisms can be used to guide the search for human blood pressure genes.

Atherosclerosis in apoE knockout mice infected with multiple pathogens.

Cytomegalovirus (CMV) and Chlamydia pneumoniae (CP) possibly contribute to atherosclerosis. Murine CMV (MCMV) and CP increase lesion size in apoE knockout mice. In this study, apoE knockout mice were infected with MCMV and CP to determine whether infection with multiple pathogens increases lesion size to a greater extent than either pathogen alone and whether infection with MCMV changes serum cytokine levels in a manner that could increase lesion development. One group of mice received MCMV at 2 weeks of age, followed by 2 doses of CP at 6 and 8 weeks of age. Additional groups received only MCMV or CP. Animals were killed at 16 weeks of age to determine lesion area. Infection with MCMV alone, CP alone, and both MCMV and CP increased lesion size 84% (P<.001), 70% (P<.0001), and 45% (P<.01), respectively. The MCMV-induced increase in circulating levels of interferon-gamma may have contributed to this increase.

Quantitative trait loci mapping for cholesterol gallstones in AKR/J and C57L/J strains of mice.

Quantitative trait locus (QTL) mapping was used to locate genes that determine the difference in cholesterol gallstone disease between the gallstone-susceptible strain C57L/J and the gallstone-resistant strain AKR/J. Gallstone weight was determined in 231 male (AKR x C57L) F(1) x AKR backcross mice fed a lithogenic diet containing 1% cholesterol, 0.5% cholic acid, and 15% butterfat for 8 wk. Mice having no stones and mice having the largest stones were genotyped at approximately 20-cM intervals to find the loci determining cholesterol gallstone formation. The major locus, Lith1, mapped near D2Mit56 and was confirmed by constructing a congenic strain, AK. L-Lith1(s). Another locus, Lith2, mapped near D19Mit58 and was also confirmed by constructing a congenic strain AK.L-Lith2(s). Other suggestive, but not statistically significant, loci mapped to chromosomes 6, 7, 8, 10, and X. The identification of these Lith genes will elucidate the pathophysiology of cholesterol gallstone formation.