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Results for “Expression quantitative trait locus”

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Computational and biological analysis of 680 kb of DNA sequence from the human 5q31 cytokine gene cluster region.

With the human genome project advancing into what will be a 7- to 10-year DNA sequencing phase, we are presented with the challenge of developing strategies to convert genomic sequence data, as they become available, into biologically meaningful information. We have analyzed 680 kb of noncontiguous DNA sequence from a 1-Mb region of human chromosome 5q31, coupling computational analysis with gene expression studies of tissues isolated from humans as well as from mice containing human YAC transgenes. This genomic interval has been noted previously for containing the cytokine gene cluster and a quantitative trait locus associated with inflammatory diseases. Our analysis identified and verified expression of 16 new genes, as well as 7 previously known genes. Of the total of 23 genes in this region, 78% had similarity matches to sequences in protein databases and 83% had exact expressed sequence tag (EST) database matches. Comparative mapping studies of eight of the new human genes discovered in the 5q31 region revealed that all are located in the syntenic region of mouse chromosome 11q. Our analysis demonstrates an approach for examining human sequence as it is made available from large sequencing programs and has resulted in the discovery of several biomedically important genes, including a cyclin, a transcription factor that is homologous to an oncogene, a protein involved in DNA repair, and several new members of a family of transporter proteins.

Animals↗

Identification of complement factor 5 as a susceptibility locus for experimental allergic asthma.

The prevalence and severity of allergic asthma continue to rise, lending urgency to the search for environmental triggers and genetic substrates. Using microarray analysis of pulmonary gene expression and single nucleotide polymorphism-based genotyping, combined with quantitative trait locus analysis, we identified the gene encoding complement factor 5 (C5) as a susceptibility locus for allergen-induced airway hyperresponsiveness in a murine model of asthma. A deletion in the coding sequence of C5 leads to C5-deficiency and susceptibility. Interleukin 12 (IL-12) is able to prevent or reverse experimental allergic asthma. Blockade of the C5a receptor rendered human monocytes unable to produce IL-12, mimicking blunted IL-12 production by macrophages from C5-deficient mice and providing a mechanism for the regulation of susceptibility to asthma by C5. The role of complement in modulating susceptibility to asthma highlights the importance of immunoregulatory events at the interface of innate and adaptive immunity in disease pathogenesis.

Animals↗

PolymiRTS Database: linking polymorphisms in microRNA target sites with complex traits.

Polymorphism in microRNA Target Site (PolymiRTS) database is a collection of naturally occurring DNA variations in putative microRNA target sites. PolymiRTSs may affect gene expression and cause variations in complex phenotypes. The database integrates sequence polymorphism, phenotype and expression microarray data, and characterizes PolymiRTSs as potential candidates responsible for the quantitative trait locus (QTL) effects. It is a resource for studying PolymiRTSs and their implications in phenotypic variations. PolymiRTS database can be accessed at http://compbio.utmem.edu/miRSNP/.

Animals↗

MHC2TA is associated with differential MHC molecule expression and susceptibility to rheumatoid arthritis, multiple sclerosis and myocardial infarction.

Antigen presentation to T cells by MHC molecules is essential for adaptive immune responses. To determine the exact position of a gene affecting expression of MHC molecules, we finely mapped a previously defined rat quantitative trait locus regulating MHC class II on microglia in an advanced intercross line. We identified a small interval including the gene MHC class II transactivator (Mhc2ta) and, using a map over six inbred strains combined with gene sequencing and expression analysis, two conserved Mhc2ta haplotypes segregating with MHC class II levels. In humans, a -168A --> G polymorphism in the type III promoter of the MHC class II transactivator (MHC2TA) was associated with increased susceptibility to rheumatoid arthritis, multiple sclerosis and myocardial infarction, as well as lower expression of MHC2TA after stimulation of leukocytes with interferon-gamma. We conclude that polymorphisms in Mhc2ta and MHC2TA result in differential MHC molecule expression and are associated with susceptibility to common complex diseases with inflammatory components.

Animals↗

The role of ACE2 in cardiovascular physiology.

The renin-angiotensin system (RAS) is critically involved in cardiovascular and renal function and in disease conditions, and has been shown to be a far more complex system than initially thought. A recently discovered homologue of angiotensin-converting enzyme (ACE)--ACE2--appears to negatively regulate the RAS. ACE2 cleaves Ang I and Ang II into the inactive Ang 1-9 and Ang 1-7, respectively. ACE2 is highly expressed in kidney and heart and is especially confined to the endothelium. With quantitative trait locus (QTL) mapping, ACE2 was defined as a QTL on the X chromosome in rat models of hypertension. In these animal models, kidney ACE2 messenger RNA and protein expression were markedly reduced, making ACE2 a candidate gene for this QTL. Targeted disruption of ACE2 in mice failed to elicit hypertension, but resulted in severe impairment in myocardial contractility with increased angiotensin II levels. Genetic ablation of ACE in the ACE2 null mice rescued the cardiac phenotype. These genetic data show that ACE2 is an essential regulator of heart function in vivo. Basal renal morphology and function were not altered by the inactivation of ACE2. The novel role of ACE2 in hydrolyzing several other peptides-such as the apelin peptides, opioids, and kinin metabolites-raises the possibility that peptide systems other than angiotensin and its derivatives also may have an important role in regulating cardiovascular and renal function.

Angiotensin II↗

Molecular cloning and endometrial expression of porcine amphiregulin.

The porcine amphiregulin gene was previously reported to be within the quantitative trait locus (QTL) for uterine capacity on chromosome 8. Because amphiregulin stimulates cell proliferation, the amphiregulin gene might be responsible for this QTL. The objectives of this study were to clone amphiregulin cDNA and compare endometrial expression of its mRNA in pregnant Meishan (M) and White composite (WC) pigs. We obtained two amphiregulin cDNAs, one with 1,221 bp and another with 1,109 bp. The 112 bp difference corresponded to exon 5 of the human amphiregulin gene, which codes for the cytoplasmic domain. Endometrial mRNA expression of amphiregulin was significantly lower in M pigs than in WC pigs during early pregnancy (day 15 - 40 of gestation). Amphiregulin mRNA expression in the endometrium of both M and WC pigs increased (P < 0.01) from days 15 to 20, decreased (P = 0.01) from days 20 to 30, and did not change between days 30 and 40. This may result in reduced amphiregulin protein production leading to the slower development of M conceptuses, contributing to greater uterine capacity and litter size in prolific Chinese M pigs. Porcine genomic sequences isolated from a bacterial artificial chromosome genomic library contained exon 5, suggesting that the deletion of exon 5 in the mRNA may be due to differential splicing. The amphiregulin gene consisted of six exons and five introns spanning 10.3 kb. Mol.

Amino Acid Sequence↗

Gene expression profile in diabetic KK/Ta mice.

BACKGROUND: To identify susceptibility genes for diabetic nephropathy, GeneChip Expression Analysis was employed to survey the gene expression profile of diabetic KK/Ta mouse kidneys. METHODS: Kidneys from three KK/Ta and two BALB/c mice at 20 weeks of age were dissected. Total RNA was extracted and labeled for hybridizing to the Affymetrix Murine Genome U74Av2 array. The gene expression profile was compared between KK/Ta and BALB/c mice using GeneChip expression analysis software. Competitive reverse transcription-polymerase chain reaction (RT-PCR) was used to confirm the results of GeneChip for a selected number of genes. RESULTS: Out of 12,490 probe pairs present on GeneChip, 98 known genes and 31 expressed sequence tags (ESTs) were found to be differentially expressed between KK/Ta and BALB/c kidneys. Twenty-one known genes and seven ESTs that increased in expression and 77 known genes and 24 ESTs that decreased in KK/Ta kidneys were identified. These genes are related to renal function, extracellular matrix expansion and degradation, signal transduction, transcription regulation, ion transport, glucose and lipid metabolism, and protein synthesis and degradation. In the vicinity of UA-1 (quantitative trait locus for the development of albuminuria in KK/Ta mice), candidate genes that showed differential expression were identified, including the Sdc4 gene for syndecan-4, Ahcy gene for S-adenosylhomocysteine hydrolase, Sstr4 gene for somatostatin receptor 4, and MafB gene for Kreisler leucine zipper protein. CONCLUSION: The gene expression profile in KK/Ta kidneys is different from that in age-matched BALB/c kidneys. Altered gene expressions in the vicinity of UA-1 may be responsible for the development of albuminuria in diabetic KK/Ta mice.

Adenosylhomocysteinase↗

Estrogen-dependent growth of a rat pituitary tumor involves, but does not require, a high level of vascular endothelial growth factor.

Long-term (10-week) treatment of Fischer 344 (F344) rats with the synthetic estrogen diethylstilbestrol (DES) increases the level of vascular endothelial growth factor (VEGF) in the pituitary. This is concurrent with the development of a large tumor of the pituitary of F344 rats. A role for VEGF in estrogen-dependent pituitary tumor growth is also supported by the fact that pituitary VEGF level is not increased by estrogen treatment in rats of the tumor-resistant Brown Norway (BN) strain. However, VEGF is not increased by estrogen treatment in an F(1) hybrid of F344 and BN, even though F(1) hybrid rats do form pituitary tumors in response to estrogen. Quantitative trait locus (QLT) mapping reveals that control of estrogen-dependent VEGF expression is linked to the Edpm5 QTL, which was previously identified as a QTL for estrogen-dependent pituitary tumor growth. In contrast, the QTL Edpm2-1 and Edpm9-2, which have been shown to each have a significant effect on estrogen-dependent pituitary mass of a magnitude similar to Edpm5, do not have any effect on VEGF level. Taken together, our results support the association of VEGF expression with growth of the estrogen-induced rat pituitary tumor, as has been reported by others, but they also indicate that there is significant pathways of growth regulation that are independent of high-level VEGF expression.

Animals↗

Genetic dissection of cardiac iron regulation using transcriptome network analysis and systems genetics in BXD mice.

Cardiac iron homeostasis is essential for myocardial energy metabolism and contractile function, yet the genetic and molecular mechanisms governing iron levels within the heart remain poorly understood. We used a systems genetics approach to dissect the transcriptional regulation of cardiac iron homeostasis. Myocardial iron level varies substantially across BXD strains (40-112 &#x3bc;g/g) and is under heritable genetic control (H2 = 0.38). Elevated cardiac iron is associated with reduced ventricular mass, increased ventricular ectopy, and prolonged atrioventricular conduction in the BXD population. Weighted gene co-expression network analysis of the BXD heart transcriptome identified a co-expression module that was significantly and negatively correlated with cardiac iron levels in both young and old BXD mice and enriched for pathways related to metabolic regulation, cyclic AMP (cAMP) signaling, circadian entrainment, and cardiovascular physiology. The module showed substantial overlap with a curated cardiac iron gene set, and cross-species enrichment analysis confirmed its conservation in human cardiomyopathy differentially expressed genes (enrichment ratio = 1.49; false discovery rate [FDR] = 0.0342). Quantitative trait locus (QTL) mapping of the first principal component of the overlapping module iron genes (n = 38), corroborated by individual gene mapping, identified trans-eQTL hotspots on multiple chromosomes, implicating Fcho2, Gcc2, and Rmdn1 as candidate upstream regulators operating through sequential steps of intracellular iron trafficking. Together, these findings establish a systems-level map of cardiac iron gene regulation, identify candidate genetic regulators, and provide a molecular framework linking disruption of iron-related transcriptional networks to structural and electrical cardiac dysfunction with implications for iron-related heart diseases.

BXD mouse population↗

Genetic resistance to chemical carcinogen-induced preneoplastic hepatic lesions in DRH strain rats.

DRH strain rats were established by inbreeding a closed colony of Donryu rats continuously fed the chemical hepatocarcinogen 3'-methyl-4-dimethylaminoazobenzene for over 10 years. They are highly resistant to chemical induction of liver cancer and preneoplastic lesions. We studied the genetic basis of DRH resistance to preneoplastic lesions by analyzing 108 (F344 x DRH)F2 male rats fed 3'-methyl-4-dimethylaminoazobenzene for 7 weeks. Five parameters of preneoplastic liver lesions were selected for quantitative analysis: (a) number of glutathione S-transferase placental form-positive foci per unit area of liver section; (b) percentage area occupied by the foci; (c) average size of foci; (d) glutathione S-transferase placental form mRNA level; and (e) gamma-glutamyltranspeptidase mRNA level. Furthermore, O6-methylguanine DNA methyltransferase and mannose 6-phosphatase/insulin-like growth factor 2 receptor mRNA levels were quantified. Composite interval mapping analysis showed that there were two remarkably significant clusters of quantitative trait loci affecting preneoplastic liver lesions on chromosomes 1 and 4. These clusters were designated collectively as Drh1 and Drh2, respectively. The functions of the recessive DRH allele of Drh1 and the semidominant DRH allele of Drh2 were to suppress the phenotypes of precancerous lesions. Each cluster showed two to three subpeaks in linkage likelihood plots, suggesting the presence of several closely linked quantitative trait loci affecting preneoplastic lesions. Possible candidate genes at each locus will be discussed. Expression of O6-methylguanine DNA methyltransferase and mannose 6-phosphatase/insulin-like growth factor 2 receptor did not affect DRH resistance to hepatocarcinogenesis, although they were polymorphic between DRH and F344 rats.

Alleles↗

Genotype by smoking interaction for leptin levels in the San Antonio Family Heart Study.

Recent studies reported a marked inverse effect of smoking on serum levels of leptin (an adipocyte derived protein), offering a possible explanation for variation in body weight between smokers and non-smokers. The goal of this study was to examine the genetic architecture of the response to smoking in leptin levels using data from the San Antonio Family Heart Study. We employed a variance decomposition analysis using maximum likelihood methods to model genotype by smoking interactions for leptin levels, examined the impact of the exclusion of smokers in a subsequent linkage analysis, and incorporated the QTL identified in the linkage analysis in a model of genotype by smoking interaction. We found significant evidence (P = 0.001) for a genotype by smoking status interaction for serum leptin levels. In the subsequent linkage analysis with smokers excluded, we obtained a maximum LOD score of 3.1 (P = 0.00008) near D8S1102. Using this QTL in a model of genotype by smoking status interaction, we identified significant evidence for an interaction at this specific locus (P = 0.04). Given these results, we hypothesize that a quantitative trait locus in this vicinity of chromosome 8 may have a differential effect on the expression of leptin in smokers versus non-smokers.

Adult↗

Identification of a quantitative trait locus for ileitis in a spontaneous mouse model of Crohn's disease: SAMP1/YitFc.

BACKGROUND & AIMS: The SAMP1/Yit mouse strain develops spontaneous ileitis with histologic features of Crohn's disease. Disease expression in the SAMP1/YitFc subline (SAMP1/Fc) is partially inhibited by outcross to C57BL/6J (B6) mice, suggesting complex genetic control of disease susceptibility with both dominant and recessive determinants. We performed a genetic analysis of a (B6 x SAMP1/Fc)F(2) cross to localize the genes regulating intestinal inflammation in this model. METHODS: A genome-wide scan was performed using a panel of microsatellite loci determined to be informative for this cross. Quantitative trait loci were identified with Map Manager QT using a serial regression approach. Positional candidate genes were selectively sequenced at the genomic level to identify potential susceptibility genes for functional screening. RESULTS: A genome-wide scan of (B6 x SAMP1/Fc)F(2) mice identified a SAMP-derived quantitative trait loci with additive effects on chromosome 9 in a region likely to have been inherited from the AKR mouse strain. The candidate interval contains several genes of interest because of their potential role in either immune system function, intestinal epithelial function, or both. Suggestive evidence for additional loci was also observed on chromosomes 6 and X. CONCLUSIONS: The SAMP1/Fc allele for a locus, designated Ibdq1, promotes inflammation-associated epithelial damage in these mice. Consistent with persistent mild ileitis in (B6 x SAMP1/Fc)F(1) mice, this locus appears to function in an additive fashion. Two genes in this interval, encoding the interleukin 10 receptor alpha chain and interleukin 18, are excellent candidates for Ibdq1.

Alleles↗

Expression of IKKalpha mRNA in the suprachiasmatic nucleus and circadian rhythms of mice lacking IKKalpha.

In our previous study, quantitative trait locus (QTL) analysis using mice with abnormal circadian rhythm detected a suggestive QTL, which affects the length of free-running period, on the distal region of Chromosome 19. Among the candidate genes, we have focused on Ikkalpha gene and found that Ikkalpha mRNA is expressed in the mammalian circadian pacemaker, the suprachiasmatic nucleus (SCN) in the present study. Expression of Ikkalpha mRNA in the SCN indicated the possibility that IKKalpha is involved in the regulation of circadian clock. Therefore, to examine the role of IKKalpha in the regulation of circadian rhythms, we have further examined wheel-running activity rhythms under light-dark cycle and constant darkness, and circadian response to light. However, we could not detect any statistically significant difference between IKKalpha(+/-) mice and wild type mice. Roles of IKKalpha in the regulation of circadian system remains to be clarified in the future study.

Analysis of Variance↗

mRNA expression in mouse hypothalamus and basal forebrain during influenza infection: a novel model for sleep regulation.

After influenza infection, C57BL/6J mice develop increased slow-wave sleep (SWS) during the dark phase of the day-night cycle, whereas BALB/cByJ mice develop decreased SWS during the light phase. A previous analysis of CXB recombinant inbred mice revealed a quantitative trait locus (QTL) designated Srilp (sleep response to influenza, light phase) that was related to expression of the BALB/cByJ sleep phenotype. Srilp was localized to the 10- to 12-cM region of mouse Chr 6 between D6Mit74 and D6Mit188. Temt (thioether S-methyltransferase), which is located at region B3 of Chr 6, is a potential candidate gene for Srilp. We evaluated the expression of Temt and other Srilp candidate genes in hypothalamus and basal forebrain of uninfected and influenza-infected C57BL/6J and BALB/cByJ mice. We report here that Temt expression varies significantly with respect to mouse strain, health status, brain region, and day-night phase. C57BL/6J mice show day-night variation in Temt expression in hypothalamus, but BALB/cByJ mice do not. Temt expression in basal forebrain is much higher in C57BL/6J mice than in BALB/cByJ mice. During influenza infection, both C57BL/6J and BALB/cByJ mice show reduced Temt mRNA in basal forebrain at 30 h postinoculation, but expression remains much lower in the BALB/cByJ strain. In contrast, prostaglandin-D-synthase (Ptgds) and lipocalin 2 (Lcn2) mRNA increase in basal forebrain of both strains after influenza infection. Administration of the TEMT inhibitor sinefungin reduces sleep in uninfected BALB/cByJ mice and attenuates influenza-induced sleep enhancement in C57BL/6J mice. These data suggest that strain- and infection-related alterations in sleep may be influenced by Temt expression and perhaps by subsequent effects on prostaglandin metabolism.

Acute-Phase Proteins↗

Prioritization of causal genes from genome-wide association studies by Bayesian data integration across loci.

MOTIVATION: Genome-wide association studies (GWAS) have identified genetic variants, usually single-nucleotide polymorphisms (SNPs), associated with human traits, including disease and disease risk. These variants (or causal variants in linkage disequilibrium with them) usually affect the regulation or function of a nearby gene. A GWAS locus can span many genes, however, and prioritizing which gene or genes in a locus are most likely to be causal remains a challenge. Better prioritization and prediction of causal genes could reveal disease mechanisms and suggest interventions. RESULTS: We describe a new Bayesian method, termed SigNet for significance networks, that combines information both within and across loci to identify the most likely causal gene at each locus. The SigNet method builds on existing methods that focus on individual loci with evidence from gene distance and expression quantitative trait loci (eQTL) by sharing information across loci using protein-protein and gene regulatory interaction network data. In an application to cardiac electrophysiology with 226 GWAS loci, only 46 (20%) have within-locus evidence from Mendelian genes, protein-coding changes, or colocalization with eQTL signals. At the remaining 180 loci lacking functional information, SigNet selects 56 genes other than the minimum distance gene, equal to 31% of the information-poor loci and 25% of the GWAS loci overall. Assessment by pathway enrichment demonstrates improved performance by SigNet. Review of individual loci shows literature evidence for genes selected by SigNet, including PMP22 as a novel causal gene candidate.

Genome-Wide Association Study↗

Behavioral genomics and the study of speciation at a porous species boundary.

Porous species boundaries are characterized by differential gene flow, where some regions of the genome experience divergent evolution while others experience the homogenizing effects of gene flow. If species can arise or remain distinct despite gene flow between them, speciation can only be understood on a gene by gene level. To understand the genetics of speciation, we therefore must identify the targets of selection that cause divergent evolution and identify the genetic architecture underlying such "speciation phenotypes". This will enable characterization of genomic regions that are "free to flow" between species, and those that diverge in the face of gene flow. We discuss this problem in the genus Laupala, a morphologically cryptic, flightless group of crickets that has radiated in Hawaii. Because songs are used in courtship and always distinguish close relatives of Laupala as well as species in sympatry, we argue that songs in Laupala are speciation phenotypes. Here, we present our approaches to identify the underlying genomic regions and song genes that differentiate closely related species. We discuss what is known about the genetic basis of this species difference derived from classic quantitative genetics and quantitative trait locus mapping experiments. We also present a model of the molecular expression of cricket song to assist in our goal to identify the genes involved in song variation. As most species are sympatric and exchange genes with congeners, we discuss the importance of understanding the genetic and genomic architecture of song as a speciation phenotype that must be characterized to identify differential patterns of gene flow at porous species boundaries.

Journal Article↗

Defective Fc gamma RII gene expression in macrophages of NOD mice: genetic linkage with up-regulation of IgG1 and IgG2b in serum.

A quantitative trait locus for increased IgG serum levels in the NOD mouse strain was mapped to distal chromosome 1, close to the fcgr2 locus encoding the low-affinity type II receptor for the Fc portion of IgG (Fc gamma RII). Expression of membrane-inserted (b2) and soluble (b3) isoforms of Fc gamma RII was strongly decreased in macrophages of NOD compared with C57BL/6 (B6) mice. In contrast, B cell-specific (Fc gamma RIIb1) isoform was only slightly decreased and Fc gamma RIII was not altered. This Fc gamma RII regulatory defect was cis-encoded by fcgr2 or by a closely linked locus, occurred at the mRNA level, and was associated with multiple mutations in the fcgr2 gene promoter. In relation with this defect, binding of IgG1- and IgG2b- but not IgG2a-opsonized RBC by macrophages of NOD and congenic B6.NOD-fcgr2 mice was severely impaired, but was normal in macrophages of NOD.B6-fcgr2 congenic mice, indicating that Fc gamma RII plays a nondispensable role in binding of IgG1 and IgG2b isotypes. Likewise, serum levels of IgG1 and IgG2b but not IgG2a were up-regulated in NOD compared with NOD.B6-fcgr2 congenic mice. These findings indicate that macrophage Fc gamma RII may regulate serum IgG1 and IgG2b through their catabolism, and validate the NOD strain as a model to investigate the functions of Fc gamma RII isoforms.

Animals↗

Synergistic gene interactions control the induction of the mitochondrial uncoupling protein (Ucp1) gene in white fat tissue.

Among a selected group of mouse strains susceptible to dietary obesity, those with an enhanced capacity for Ucp1 and brown adipocyte induction in white fat preferentially lost body weight following adrenergic stimulation. Based on the generality of this mechanism for reducing obesity, a genetic analysis was initiated to identify genes that control brown adipocyte induction in white fat depots in mice. Quantitative trait locus (QTL) analysis was performed using the variations of retroperitoneal fat Ucp1 mRNA expression in progeny of genetic crosses between the A/J and C57BL/6J parental strains and selected AXB recombinant inbred strains. Three A/J-derived loci on chromosomes 2, 3, and 8 and one C57BL/6J locus on chromosome 19 were linked to Ucp1 induction in retroperitoneal fat. Although A/J-derived alleles seemed to contribute to elevated Ucp1 expression, the C57BL/6J allele on chromosome 19 increased Ucp1 mRNA to levels higher than parental values. Thus, novel patterns of C57BL/6J and A/J recombinant genotypes among the four mapped loci resulted in a transgressive variation of Ucp1 phenotypes. Although the extent of the interchromosomal interactions have not been fully explored, strong synergistic interactions occur between a C57BL/6J allele on chromosome 19 and an A/J allele on chromosome 8. In addition to selective synergistic interactions between loci, variations in recessive and dominant effects also contribute to the final levels of Ucp1 expression.

Adipose Tissue↗