Detection of modifier loci influencing the lung phenotype of cystic fibrosis knockout mice

The variable severity of lung disease associated with cystic fibrosis (CF) cannot be explained by the genotype of the cystic fibrosis transmembrane conductance regulator (CFTR) locus alone. Lung disease has been reported in a congenic CF mouse model of C57BL/6J genetic background (B6 CF), in the absence of detectable infection, but not in CF mice of mixed genetic background, nor in wild-type animals maintained in identical environments. In this report, studies are presented to show that the same CF mutation in mice of a BALB/c background (BALB CF) results in minimal lung disease. By 12 weeks of age B6 CF mice developed a lung disease consisting of mononuclear cell interstitial infiltrate and fibrosis, and BALB CF or littermate control mice developed minimal histopathology. Therefore, it is possible to identify the chromosomal locations of genes that can contribute to the susceptibility to lung disease in B6 CF mice compared with BALB CF mice by means of a quantitative trait loci (QTL) mapping strategy based on the variable histology of the (B6 × BALB) F2 CF mice. Significant linkage of the fibrotic lung phenotype was detected for a region on Chromosome (Chr) 6, defined by markers D6Mit194 to D6Mit201, and suggestive linkage was found for regions on Chr 1, 2, 10, and 17. Additional loci, suggestive of linkage, were also detected for the interstitial thickening phenotype. Most of these putative loci are specific to the sex of the animals. These results suggest that multiple genes can influence the severity of CF lung disease in mice.     

Detection of quantitative trait loci for body weight at 10 weeks from Philippine wild mice

A genome-wide scan for quantitative trait loci (QTLs) controlling body weight at 10 weeks after birth was carried out in a population of 387 intersubspecific backcross mice derived from a cross between C57BL/6J inbred mice (Mus musculus domesticus) and wild mice (M. m. castaneus) captured in the Philippines, in order to discover novel QTLs from the wild mice that have about 60% lower body weight than C57BL/6J. By interval mapping, we detected four QTLs: a highly significant QTL on Chromosome (Chr) 2, which was common in both sexes; two significant QTLs on Chr 13, one male-specific and the other female-specific; and a suggestive male-specific QTL on X Chr. By composite interval mapping, we confirmed the presence of the three QTLs on Chrs 2 and 13, but not of the male-specific X-linked QTL. The composite interval mapping analysis newly identified three QTLs: a significant male-specific QTL on Chr 11 and two highly significant female-specific QTLs on Chrs 9 and X. Individual QTLs explained 3.8–11.6% of the phenotypic variance, and all the QTL alleles derived from the wild mice decreased body weight. A two-way analysis of variance revealed a significant epistatic interaction between the Chr 2 QTL and the background marker locus D12Mit4 on Chr 12 only in males. The interaction effect unexpectedly increased body weight. The chromosomal region containing the Chr 2 QTL did not coincide with those of growth or fatness QTLs mapped in previous studies. These results suggest that a population of wild mice may play an important role as new sources of valuable QTLs. Received: 14 January 2000 / Accepted: 14 April 2000     

Influence of language and ancestry on genetic structure of contiguous populations: A microsatellite based study on populations of Orissa

Background

Although cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, the severity of disease is highly variable indicating the influence of modifier genes. The intestines of Cftr deficient mice (CF mice: Cftr ^tm1Unc ) are prone to obstruction by excessive mucus accumulation and are used as a model of meconium ileus and distal intestinal obstruction syndrome. This phenotype is strongly dependent on the genetic background of the mice. On the C57Bl/6 background, the majority of CF mice cannot survive on solid mouse chow, have inflammation of the small intestine, and are about 30% smaller than wild type littermates. In this work potential modifier loci of the CF intestinal phenotype were identified.

Results

CF mice on a mixed genetic background (95% C57Bl/6 and 5% 129Sv) were compared to CF mice congenic on the C57Bl/6 background for several parameters of the intestinal CF phenotype. CF mice on the mixed background exhibit significantly greater survival when fed dry mouse chow, have reduced intestinal inflammation as measured by quantitative RT-PCR for marker genes, have near normal body weight gain, and have reduced mucus accumulation in the intestinal crypts. There was an indication of a gender effect for body weight gain: males did not show a significant improvement at 4 weeks of age, but were of normal weight at 8 weeks, while females showed improvement at both 4 and 8 weeks. By a preliminary genome-wide PCR allele scanning, three regions were found to be potentially associated with the milder phenotype. One on chr.1, defined by marker D1Mit36, one on chr. 9 defined by marker D9Mit90, and one on chr. 10, defined by marker D10Mit14.

Conclusion

Potential modifier regions were found that have a positive impact on the inflammatory phenotype of the CF mouse small intestine and animal survival. Identification of polymorphisms in specific genes in these regions should provide important new information about genetic modifiers of the CF intestinal phenotype.     

Mapping genetic loci that regulate lipid levels in a NZB/B1NJxRF/J intercross and a combined intercross involving NZB/B1NJ, RF/J, MRL/MpJ, and SJL/J mouse strains

The NZB/B1NJ (NZB) mouse strain exhibits high cholesterol and HDL levels in blood compared with several other strains of mice. To study the genetic regulation of blood lipid levels, we performed a genome-wide linkage analysis in 542 chow-fed F2 female mice from an NZBxRF/J (RF) intercross and in a combined data set that included NZBxRF and MRL/MpJxSJL/J intercrosses. In the NZBxRF F2 mice, the cholesterol and HDL concentrations were influenced by quantitative trait loci (QTL) on chromosome (Chr) 5 [logarithm of odds (LOD) 17-19; D5Mit10] that was in the region identified earlier in crosses involving NZB mice, but two QTLs on Chr 12 (LOD 4.7; D12Mit182) and Chr 19 (LOD 5.7; D19Mit1) were specific to the NZBxRF intercross. Triglyceride levels were affected by two novel QTLs at D12Mit182 (LOD 8.7) and D15Mit13 (LOD 3.5). The combined-cross linkage analysis (1,054 mice, 231 markers) 1) identified four shared QTLs (Chrs 5, 7, 14, and 17) that were not detected in one of the parental crosses and 2) improved the resolution of two shared QTLs. In summary, we report additional loci regulating lipid levels in NZB mice that had not been identified earlier in crosses involving the NZB strain of mice. The identification of shared loci from multiple crosses increases confidence toward finding the QTL gene.     

Identification of genetic determinants of IGF‐1 levels and longevity among mouse inbred strains

The IGF‐1 signaling pathway plays an important role in regulating longevity. To identify the genetic loci and genes that regulate plasma IGF‐1 levels, we intercrossed MRL/MpJ and SM/J, inbred mouse strains that differ in IGF‐1 levels. Quantitative trait loci (QTL) analysis of IGF‐1 levels of these F2 mice detected four QTL on chromosomes (Chrs) 9 (48 Mb), 10 (86 Mb), 15 (18 Mb), and 17 (85 Mb). Haplotype association mapping of IGF‐1 levels in 28 domesticated inbred strains identified three suggestive loci in females on Chrs 2 (13 Mb), 10 (88 Mb), and 17 (28 Mb) and in four males on Chrs 1 (159 Mb), 3 (52 and 58 Mb), and 16 (74 Mb). Except for the QTL on Chr 9 and 16, all loci co‐localized with IGF‐1 QTL previously identified in other mouse crosses. The most significant locus was the QTL on Chr 10, which contains the Igf1 gene and which had a LOD score of 31.8. Haplotype analysis among 28 domesticated inbred strains revealed a major QTL on Chr 10 overlapping with the QTL identified in the F2 mice. This locus showed three major haplotypes; strains with haplotype 1 had significantly lower plasma IGF‐1 and extended longevity (P < 0.05) than strains with haplotype 2 or 3. Bioinformatic analysis, combined with sequencing and expression studies, showed that Igf1 is the most likely QTL gene, but that other genes may also play a role in this strong QTL.     

Quantitative trait locus analysis of serum insulin, triglyceride, total cholesterol and phospholipid levels in the (SM/J x A/J)F2 mice.

Quantitative trait locus (QTL) analysis of serum insulin, triglyceride, total cholesterol and phospholipid levels at 10 weeks of age was performed in 321 F2 offspring from SM/J and A/J mice. Interval mapping revealed a total of 22 suggestive QTLs affecting the four traits: two insulin QTLs on Chromosomes (Chrs) 6 and 8; six triglyceride QTLs on Chrs 4, 8, 9, 11, 12 and 19; six total-cholesterol QTLs on Chrs 1, 3, 4, 14, 17 and 19; and eight phospholipid QTLs on Chrs 2, 3, 4, 6, 8, 10 and 19. Gender influenced the expression of eight of the suggestive QTLs. The total-cholesterol QTLs on Chrs 4, 14 and 17, the triglyceride QTL on Chr 9 and the phospholipid QTL on Chr 4 were specific to females. The phospholipid QTLs on Chrs 2 and 6 and the insulin QTL on Chr 8 were specific to males. In addition, common QTLs involved in the regulation of some of the traits were identified. The female-specific QTL on Chr 4 appeared to be involved in the regulation of total cholesterol and phospholipid levels. The QTL on Chr 8 affected insulin and phospholipid levels, whereas the Chr 19 QTL was common to the three lipid parameters.     

Submucosal gland distribution in the mouse has a genetic determination localized on Chromosome 9

Submucosal glands (SMG) are important secretory glands that are present in the major airways and bronchioles of humans. In mice the structure, cellular composition, and density of SMG are similar to those seen in humans, but the glands are present only in the trachea. Characterization of SMG is important as they secrete bacteriocidal products such as lactoferrin, lysozyme, and defensins believed to be of importance in the innate defense system. Serous cells in SMG are the primary site of cystic fibrosis transmembrane conductance regulator (CFTR) gene expression and the initial site of histological abnormality in cystic fibrosis (CF) individuals. In this study, we examined four inbred strains of mice (A/J, C57BL/6N, FVB/N, and BALB/CAnN) and revealed that the extent to which glands descend in the mouse trachea varied between inbred strains. In particular, the A/J and C57BL/6N strains exhibited few SMG extending further than the first or second intercartilaginous space (mean depth of 0.4 ± 0.11 and 1.5 ± 0.32 tracheal rings respectively) in the trachea, whereas the FVB/N and BALB/CAnN strains had SMG extending beyond the fourth space (mean depths of 3.3 ± 0.46 and 5.6 ± 0.45 rings respectively). We have previously shown that in congenic C57Bl/6N Cftr mutant mice (CF mice), the SMG are distributed more distally than in wild-type C57Bl/6N but are indistinguishable from BALB/CAnN wild-type or CF mice. The implication that SMG distribution is influenced by Cftr gene expression (or a gene closely linked to Cftr) led us to investigate the genetic difference between C57Bl6/N and BALB/CAnN mice. In recombinant inbred strain (RIS) analysis (with BALB/CJ and C57BL/6J progenitors), two loci were identified as being linked to the SMG phenotype (peak likelihood statistic levels of 8.8 and 9.9 on Chrs 9 and 10 respectively, indicating suggestive linkage). A subsequent segregation analysis of an F₂ intercross between the C57BL/6N and BALB/CAnN mice indicated that there were at least two major genetic factors responsible for SMG distribution. The loci indicated in the RI analysis were included in a targeted genome scan involving 235 F₂ intercross animals (C57BL/6N and BALB/CAnN strain intercross). The genome scan confirmed the locus on Chr 9 (between genetic markers D9Mit11 and D9Mit182), designated Smgd1, as significantly linked to the SMG distribution phenotype (peak LOD score 5.8) within a 95% confidence interval of 12 cM. Received: 26 June 2000 / Accepted: 18 September 2000     

Integration of QTL and bioinformatic tools to identify candidate genes for triglycerides in mice

To identify genetic loci influencing lipid levels, we performed quantitative trait loci (QTL) analysis between inbred mouse strains MRL/MpJ and SM/J, measuring triglyceride levels at 8 weeks of age in F2 mice fed a chow diet. We identified one significant QTL on chromosome (Chr) 15 and three suggestive QTL on Chrs 2, 7, and 17. We also carried out microarray analysis on the livers of parental strains of 282 F2 mice and used these data to find cis-regulated expression QTL. We then narrowed the list of candidate genes under significant QTL using a "toolbox" of bioinformatic resources, including haplotype analysis; parental strain comparison for gene expression differences and nonsynonymous coding single nucleotide polymorphisms (SNP); cis-regulated eQTL in livers of F2 mice; correlation between gene expression and phenotype; and conditioning of expression on the phenotype. We suggest Slc25a7 as a candidate gene for the Chr 7 QTL and, based on expression differences, five genes (Polr3 h, Cyp2d22, Cyp2d26, Tspo, and Ttll12) as candidate genes for Chr 15 QTL. This study shows how bioinformatics can be used effectively to reduce candidate gene lists for QTL related to complex traits.     

Intestinal phenotype of variable-weight cystic fibrosis knockout mice

Cystic fibrosis (CF) transmembrane conductance regulator (Cftr) knockout mice present the clinical features of low body weight and intestinal disease permitting an assessment of the interrelatedness of these phenotypes in a controlled environment. To identify intestinal alterations that are affected by body weight in CF mice, the histological phenotypes of crypt-villus axis height, goblet cell hyperplasia, mast cell infiltrate, crypt cell proliferation, and apoptosis were measured in a population of 12-wk-old (C57BL/6 x BALB/cJ) F2 Cftr(tm1UNC) and non-CF mice presenting a range of body weight. In addition, cardiac blood samples were assessed, and gene expression profiling of the ileum was completed. Crypt-villus axis height decreased with increasing body weight in CF but not control mice. Intestinal crypts from CF mice had fewer apoptotic cells, per unit length, than did non-CF mice, and normalized cell proliferation was similar to control levels. Goblet cell hyperplasia and mast cell infiltration were increased in the CF intestine and identified to be independent of body weight. Blood triglyceride levels were found to be significantly lower in CF mice than in control mice but were not dependent on CF mouse weight. By expression profiling, genes of DNA replication and lipid metabolism were among those altered in CF mice relative to non-CF controls, and no differences in gene expression were measured between samples from CF mice in the 25th and 75th percentile for weight. In this CF mouse model, crypt elongation, due to an expanded proliferative zone and decreased apoptosis, was identified to be dependent on body weight.     

Loci on Chromosomes 2, 4, 9, and 16 for body weight,body length,and adiposity identified in a genome scan of an F<Subscript>2</Subscript> intercross between the 129P3/J and C57BL/6ByJ mouse strains

Mice have proved to be a powerful model organism for understanding obesity in humans. Single gene mutants and genetically modified mice have been used to identify obesity genes, and the discovery of loci for polygenic forms of obesity in the mouse is an important next step. To pursue this goal, the inbred mouse strains 129P3/J (129) and C57BL/6ByJ (B6), which differ in body weight, body length, and adiposity, were used in an F₂ cross to identify loci affecting these phenotypes. Linkages were determined in a two-phase process. In the first phase, 169 randomly selected F₂ mice were genotyped for 134 markers that covered all autosomes and the X Chromosome (Chr). Significant linkages were found for body weight and body length on Chr 2. In addition, we detected several suggestive linkages on Chr 2 (adiposity), 9 (body weight, body length, and adiposity), and 16 (adiposity), as well as two suggestive sex-dependent linkages for body length on Chrs 4 and 9. In the second phase, 288 additional F₂ mice were genotyped for markers near these regions of linkage. In the combined set of 457 F₂ mice, six significant linkages were found: Chr 2 (Bwq5, body weight and Bdln3, body length), Chr 4 (Bdln6, body length, males only), Chr 9 (Bwq6, body weight and Adip5, adiposity), and Chr 16 (Adip9, adiposity), as well as several suggestive linkages (Adip2, adiposity on Chr 2; Bdln4 and Bdln5, body length on Chr 9). In addition, there was a suggestive linkage to body length in males on Chr 9 (Bdln4). For adiposity, there was evidence for epistatic interactions between loci on Chr 9 (Adip5) and 16 (Adip9). These results reinforce the concept that obesity is a complex trait. Genetic loci and their interactions, in conjunction with sex, age, and diet, determine body size and adiposity in mice.     

Generation of a conditional null allele for Cftr in mice

The cystic fibrosis transmembrane conductance regulator (CFTR) gene encodes a cAMP-regulated chloride channel that is important in controlling the exchange of fluid and electrolytes across epithelial cells. Mutation of CFTR can lead to cystic fibrosis (CF), the most common lethal genetic disease in Caucasians. CF is a systemic illness with multiple organ systems affected including pulmonary, gastrointestinal, pancreatic, immune, endocrine, and reproductive systems. To understand the role of CFTR in the various tissues in which it is expressed, we generated a murine conditional null allele of Cftr (Cftr(fl10)) in which loxP sites were inserted around exon 10 of the Cftr gene. The Cftr(fl10) allele was validated by generating constitutive Cftr null (Cftr(Delta10)) mice using the protamine-cre system. The Cftr(Delta10/Delta10) mice displayed almost identical phenotypes to previously published CF mouse models, including poor growth, decreased survival, intestinal obstruction, and loss of Cftr function as assessed by electrophysiology measurements on gut and nasal epithelium. Mice containing the conditional null Cftr allele will be useful in future studies to understand the role of Cftr in specific tissues and developmental time points and lead to a better understanding of CF disease.     

Genetics of obesity in KK mouse and effects of A y allele on quantitative regulation

KK mouse is known as a polygenic model for non-insulin-dependent diabetes mellitus with moderate obesity. To identify the quantitative trait loci (QTLs) responsible for the body weight in KK, linkage analysis with 97 microsatellite markers was carried out into 192 F₂ progeny, comprising 93 mice with a/a genotype at agouti locus and 99 mice with A ^y /a genotype, of a cross between C57BL/6J female and KK-A^y (A^y congenic) male, thereby the influence of A ^y allele on the quantitative regulation of body weight was also examined. In F₂ a/a mice, we identified a QTL on Chromosome (Chr) 4, and two loci with suggestive linkage on Chrs 15 and 18. In F₂ A ^y /a mice, a QTL was identified on Chr 6, and two loci with suggestive linkage were identified on Chrs 4 and 16. That the QTL on Chr 4 was held in common between F₂ a/a and F₂ A ^y /a progenies implies that this locus may be a primary component regulating body weight in KK and KK-A^y. These results suggest that the body weight in KK is controlled by multiple genes, and the different combination of loci is involved in the presence of A ^y allele. The QTL on Chr 6 seemed to determine the body weight by controlling fat deposition, because the linkage was identified on body weight and adiposity, and is suggested to be a component involved in the metabolic pathway in obesity caused by the A ^y allele. Received: 16 December 1997 / Accepted: 16 March 1998     

Cystic fibrosis growth retardation is not correlated with loss of Cftr in the intestinal epithelium

Maldigestion due to exocrine pancreatic insufficiency leads to intestinal malabsorption and consequent malnutrition, a mechanism proposed to cause growth retardation associated with cystic fibrosis (CF). However, although enzyme replacement therapy combined with increased caloric intake improves weight gain, the effect on stature is not significant, suggesting that growth retardation has a more complex etiology. Mouse models of CF support this, since these animals do not experience exocrine pancreatic insufficiency yet are growth impaired. Cftr absence from the intestinal epithelium has been suggested as a primary source of growth retardation in CF mice, a concept we directly tested by generating mouse models with Cftr selectively inactivated or restored in intestinal epithelium. The relationship between growth and functional characteristics of the intestines, including transepithelial electrophysiology, incidence of intestinal obstruction, and histopathology, were assessed. Absence of Cftr exclusively from intestinal epithelium resulted in loss of cAMP-stimulated short-circuit current, goblet cell hyperplasia, and occurrence of intestinal obstructions but only slight and transient impaired growth. In contrast, specifically restoring Cftr to the intestinal epithelium resulted in restoration of ion transport and completely protected against obstruction and histopathological anomalies, but growth was indistinguishable from CF mice. These results indicate that absence of Cftr in the intestinal epithelium is an important contributor to the intestinal obstruction phenotype in CF but does not correlate with the observed growth reduction in CF.     

Congenic strain confirms putative quantitative trait locus for body weight in the rat

Quantitative trait loci (QTLs) affecting body weight were investigated in the backcross population derived from nondiabetic BB/OK and spontaneously hypertensive rat (SHR) strains. The F₁ hybrids were backcrossed onto SHR rats, and QTL analysis was performed separately with the resulting backcross populations for each sex on Chromosomes (Chrs) 1, 3, 4, 10, 13, and 18. The body weight was determined at the age of 14 weeks, and the statistical analysis was performed with MAPMAKER/QTL 1.1b computer program. According to the stringent threshold for a lod score of 3.0, markers on Chr 1 were found to be linked with body weight. The QTL with a peak lod score (5.1) on Chr 1 for a male population was located within markers Igf2 and D1Mgh12. In contrast, in the female population the body weight affecting QTL (lod = 5.7) on Chr 1 was located between the D1Mit3 and Lsn markers. The existence of QTLs on Chr 1 affecting body weight in the male population was confirmed by congenic BB.Sa rats, carrying chromosomal region of SHR (Sa-Igf2) on the genetic background of BB rat. Received: 14 July 1997 / Accepted: 22 December 1997     

Quantitative trait locus analysis of ovarian cysts derived from rete ovarii in MRL/MpJ mice

MRL/MpJ (MRL) is a model mouse for autoimmune diseases such as dermatitis, vasculitis, arthritis, and glomerulonephritis. In addition to these immune-associated disorders, we found that older MRL mice develop ovarian cysts originating from the rete ovarii, which is lined by ciliated or nonciliated epithelium and considered remnants of mesonephric tubules. Ovarian cysts, which are reported to have several sources, are associated with female infertility, but information regarding the genetic etiology of ovarian cysts originating from the rete ovarii is rare. In this study, to elucidate the genetic background of development of ovarian cysts, we performed quantitative trait locus (QTL) analysis using 120 microsatellite markers, which cover the whole genome of murine chromosomes, and 213 backcross progenies between female MRL and male C57BL/6N mice. The quantitative trait measured was the circumferences of rete ovarii or ovarian cysts. As a result, suggestive linkages were detected on Chrs 3, 4, 6, and 11, but significant linkages were located on Chr 14 by interval mapping. We thereby designated the 27.5-cM region of Chr 14 “MRL Rete Ovarian Cysts (mroc).” The peak regions of Chrs 4 and 14 in particular showed a close additive interaction (p < 0.00001). From these results we concluded that multiple loci on Chrs 3, 4, 6, 11, and 14 interact to result in development of ovarian cysts in MRL mice.     

Mapping quantitative trait loci mediating sensitivity to etomidate

Long- and Short-Sleep (LS and SS) mice were selectively bred for differences in ethanol-induced loss of the righting reflex (LORR) and have been found to differ in LORR induced by various anesthetic agents. We used a two-stage mapping strategy to identify quantitative trait loci (QTLs) affecting duration of LORR caused by the general anesthetic etomidate and brain levels of etomidate (BEL) following regain of the righting reflex. Analysis of recombinant-inbred strains derived from a cross between LS and SS mice (LSXSS) yielded a heritability estimate of 0.23 for etomidate-induced LORR and identified one marker that showed suggestive linkage for a QTL, on mouse Chromosome (chr) 12. Mapping in an F(2) population derived from a cross between inbred LS and SS (ILS and ISS) revealed a significant QTL for etomidate-induced LORR on Chr 12, and two significant QTLs mediating BEL on Chrs 6 and 12. Several QTLs showing suggestive linkage for etomidate-induced LORR and BEL were also identified in the F(2) population. Brain levels of etomidate in the RI and F(2) mice suggested that differences in LORR were due to differential central nervous system sensitivity, rather than differential etomidate metabolism. Interestingly, the region on Chr 7 has also been identified as a region influencing ethanol-induced LORR, suggesting the possibility of a common genetic mechanism mediating etomidate and ethanol sensitivity. These QTL regions need to be further narrowed before the testing of candidate genes is feasible.     

Genetic dissection of ``OLETF', a rat model for non-insulin-dependent diabetes mellitus

To elucidate the genetic factors underlying non-insulin-dependent diabetes mellitus (NIDDM), we performed genome-wide quantitative trait locus (QTL) analysis, using the Otsuka Long-Evans Tokushima Fatty (OLETF) rat. The OLETF rat is an excellent animal model of NIDDM because the features of the disease closely resemble human NIDDM. Genetic dissection with two kinds of F2 intercross progeny, from matings between the OLETF rat and non-diabetic control rats F344 or BN, allowed us to identify on Chromosome (Chr) 1 a major QTL associated with features of NIDDM that was common to both crosses. We also mapped two additional significant loci, on Chrs 7 and 14, in the (OLETF × F344)F₂ cross alone, and designated these three loci as Diabetes mellitus, OLETF type Dmo 1, Dmo2 and Dmo3 respectively. With regard to suggestive QTLs, we found loci on Chrs 10, 11, and 16 that were common to both crosses, as well as loci on Chrs 5 and 12 in the (OLETF × F344)F₂ cross and on Chrs 4 and 13 in the (OLETF × BN)F₂ cross. Our results showed that NIDDM in the OLETF rat is polygenic and demonstrated that different genetic backgrounds could affect ``fitness' for QTLs and produce different phenotypic effects from the same locus. Received: 9 October 1997 / Accepted: 29 January 1998     

小鼠15号染色体上脊髓重数量性状基因座的精细定位

目的以前的研究结果表明,控制小鼠脊髓重的一个数量性状基因座(QTL)位于15号染色体D15Mit158附近,跨度约30cM。为分离和确认脊髓重相关基因,本文对该QTL区域进行了精细定位。方法以高级互交系小鼠A/J×C57BL/6J(F4)为研究对象,选择脊髓重偏向两极的个体,在D15Mit158位点附近作高密度局部基因组扫描,用Map Manager QTX19软件对脊髓重与基因型进行连锁不平衡分析。结果在15号染色体D15Mit107附近出现了一个很强的连锁峰,LRS值为17.3(P=1.8×10-4),变异解释率为27%,LOD值达到3.75,可以认定为一主效QTL。该QTL跨度范围为3.2cM。另一个提示可能具有连锁关系的QTL位点在D15Mit28附近,LRS值为7.6(P=0.02),变异解释率为13%,跨度范围为5.0cM。结论控制小鼠脊髓重的D15Mit158区域实际上含有两个QTL,其中一个主效QTL位于15号染色体上宽约3.2cM的D15Mit107位点附近;另一个可能的QTL位于宽约5.0cM的D15Mit28附近。     

Identification of quantitative trait loci that regulate obesity and serum lipid levels in MRL/MpJ x SJL/J inbred mice

The total body fat mass and serum concentration of total cholesterol, HDL cholesterol, and triglyceride (TG) differ between standard diet-fed female inbred mouse strains MRL/MpJ (MRL) and SJL/J (SJL) by 38-120% (P < 0.01). To investigate genetic regulation of obesity and serum lipid levels, we performed a genome-wide linkage analysis in 621 MRLx SJL F2 female mice. Fat mass was affected by two significant loci, D11Mit36 [43.7 cM, logarithm of the odds ratio (LOD) 11.2] and D16Mit51 (50.3 cM, LOD 3.9), and one suggestive locus at D7Mit44 (50 cM, LOD 2.4). TG levels were affected by two novel loci at D1Mit43 (76 cM, LOD 3.8) and D12Mit201 (26 cM, LOD 4.1), and two suggestive loci on chromosomes 5 and 17. HDL and cholesterol concentrations were influenced by significant loci on chromosomes 1, 3, 5, 7, and 17 that were in the regions identified earlier for other strains of mice, except for a suggestive locus on chromosome 14 that was specific to the MRL x SJL cross. In summary, linkage analysis in MRL x SJL F2 mice disclosed novel loci affecting TG, HDL, and fat mass, a measure of obesity. Knowledge of the genes in these quantitative trait loci will enhance our understanding of obesity and lipid metabolism.     

Long-term docosahexaenoic acid therapy in a congenic murine model of cystic fibrosis

We used a congenic C57Bl/6J cystic fibrosis transmembrane conductance regulator (Cftr)(-/-) mouse model, which develops cystic fibrosis (CF)-like pathology in all organs, to evaluate the short- and long-term therapeutic effects of dietary docosahexaenoic acid (DHA). Thirty-day-old Cftr(-/-) mice and wild-type littermates were randomized to receive a liquid diet with or without DHA (40 mg/day). Animals were killed for histological and lipid analysis after 7, 30, and 60 days of therapy. DHA had no significant therapeutic or harmful effect on the lung, pancreas, or ileum of the Cftr(-/-) mice or their wild-type littermates. In contrast, dietary DHA resulted in highly significant amelioration of the severity of liver disease in the Cftr(-/-) mice, primarily a reduction in the degree of peri-portal inflammation. Additionally, these detailed measurements confirm our previous findings that Cftr(-/-) mice have significant alterations in the pancreas (except external acinar diameter), ileum, liver, lung, and salivary (except sublingual) glands at all ages compared with their age-matched wild-type littermates. In conclusion, inhibition of cytokines and/or eicosanoid metabolism and release of endogenous inhibitors of inflammation by DHA may account for the anti-inflammatory effects in the liver of this congenic murine model of CF. The potential therapeutic benefits of DHA in severe CF-associated liver disease remain to be explored.