Genetics of ethanol-induced locomotor activation: detection of QTLs in a C57BL/6J x DBA/2J F2 intercross

Moderate doses of ethanol (1-2 g/kg) markedly increase locomotor activity in some inbred mouse strains, for example, the DBA/2J (D2), but have relatively little effect in other strains, for example, the C57BL/6J (B6). In the present study, we conducted a genome-wide search in a B6D2 F2 intercross (N = 925) for quantitative trait loci (QTLs) associated with the locomotor response. A QTL with a LOD score of 8.4 was detected on Chromosome (Chr) 2; this QTL accounted for 11.4% of the phenotypic variance and approximately 30% of the genetic variance. The QTL on Chr 2 is in the same general region as QTLs previously described for ethanol preference/consumption (Rodriguez et al. Alcohol Clin Exp Res 19, 367, 1995; Melo et al. Nat Genet 13, 147, 1996; Phillips et al. Mamm Genome, in press), acute ethanol withdrawal (Buck et al. J. Neurosci 17, 3946, 1997) and nitrous oxide withdrawal severity (Belknap et al. Behav Genet 23, 213, 1993). A logical candidate gene in the region of interest is the enzyme which synthesizes GABA, glutamic acid decarboxylase 1 (GadI).     

Developmental loss of effect of a Chromosome 15 QTL on alcohol acceptance

Human alcohol abuse and alcoholism have clear developmental features, suggesting the possibility of changes over time in heritability and in quantitative genetic architecture, and raising prospects of identifying individual genes or quantitative trait loci (QTLs) that display different influence on alcohol-related phenotypes at different ages. The identification of specific loci showing such age-related changes will open up opportunities of focused association studies and of genotype manipulation by various mating procedures. Most animal model research in alcohol assesses the phenotypes of the animals at an early age; developmental studies are rare. Here we report on a QTL on Chromosome (Chr) 15 of the mouse that has been shown in several populations, including BXD recombinant inbred strains, an F2, and genotypically selected lines, to affect a measure of alcohol consumption. In the present study, we measured alcohol acceptance in the genotypically selected animals and in an F4 sample at about 100 days and again at about 300 days of age. In both groups, and in both sexes, significant differences were observed at 100 days between animals that were homozygous for the "increasing" haplotype defining the QTL region and those homozygous for the "decreasing" haplotype. At 300 days of age, the effect is absent in females and has diminished or disappeared in males. The results provide a further confirmation of the Chr 15 QTL in young mice, offer a new perspective on the development of alcohol-related phenotypes, and have strong implications for research design.     

Voluntary alcohol consumption in BXD recombinant inbred mice: relationship to alcohol metabolism

Studies were initiated to characterize behaviorally and biochemically C57BL/6J and DBA/2J inbred mice, as well as BXD Recombinant Inbred (RI) strains derived from them. The C57BL/6J, DBA/2J, and 7 BXD RI strains were tested for voluntary alcohol consumption (VAC) by receiving 4 days of forced exposure to a 10% (w/v) solution of alcohol, followed by 3 weeks of free choice between water and 10% alcohol. Measures of VAC included the absolute intake of alcohol (g/kg), as well as alcohol preference. A wide range of VAC was displayed by the various BXD RI strains with a continuous (rather than bimodal) distribution, indicating that there is likely to be additive effects of several genes involved in regulating alcohol-related behaviors. Kinetic characteristics of aldehyde dehydrogenase and catalase in liver and brain of the C57BL/6J, DBA/2J, and BXD strains of mice were determined to test the hypothesis that the genetic regulation of the levels of alcohol-metabolizing enzymes mediate differences in VAC. Aldehyde dehydrogenase activity was determined spectrophotometrically by observing the change in absorption at 340 nm. Catalase activity was determined by measuring oxygen production with a Yellow Springs Biological Oxygen monitor and oxygen electrode. There was a strong negative relationship between VAC and brain catalase activity in the BXD RI and parental strains. These data suggest that RI strains are likely to be useful genetic models in the examination of quantitative trait loci controlling VAC and other responses to alcohol.     

Female mate choice and male behaviour in domestic fowl

An F2 intercross derived from C57BL/6 and DBA/2 progenitor inbred strains was used to test for replication of quantitative trait loci (QTLs) for alcohol preference nominated by a previous study using BXD recombinant inbred (RI) strains (Rodriguez et al., Alcohol. Clin. Exp. Res. 19:367-379, 1995). Fourteen provisional QTLs were nominated in the original RI study with a p < 0.05 criterion. In the present study, a genome scan (101 microsatellite markers) was conducted on an F2 population (n = 218). Three significant QTLs were detected on chromosomes 1, 4, and 9, and three suggestive QTLs were detected on chromosomes 2, 3, and 10. Of these six QTLs, four were consistent with the previous RI nominations. The replication rate of 28.6% (4 of 14) is in agreement with the results of simulation studies performed by Belknap et al. (Behav. Genet. 26:149-160, 1996) and supports the methodological argument for a multistage research design for nominating and replicating QTLs.     

Genetic analysis of the corticosterone response to ethanol in BXD recombinant inbred mice.

The genetic control over the corticosterone response to ethanol (EtOH) and its possible relationship to other EtOH-related traits was examined using BXD recombinant inbred (RI) strains derived from an F2 cross of C57BL/6J (B6) and DBA/2J (D2) progenitor strains. Quantitative trait locus (QTL) analysis of corticosterone levels 1 hr following EtOH suggested the influence of a single major gene on this trait. Two loci were predicted to account for 47% of the genetic variance in plasma corticosterone levels 6 hr following EtOH, whereas 3 loci were predicted to account for 78% of the genetic variance in corticosterone levels 7 hrs following EtOH. Markers associated with corticosterone levels 7 hrs following EtOH and corrected corticosterone levels 6 hrs post-EtOH overlapped with ones found to influence acute and chronic EtOH withdrawal severity, suggesting some degree of common genetic determination between these traits. Overall these results indicate that gene action significantly influences stress responsiveness and suggest possible chromosomal locations of these genes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social relations and extent and severity of coronary artery disease. The Stockholm Female Coronary Risk Study

Peak bone mass is a major determinant of risk of osteoporotic fracture. Family and twin studies have found a strong genetic component to the determination of bone mineral density (BMD). However, BMD is a complex trait whose expression is confounded by environmental influences and polygenic inheritance. The number, locations, and effects of the individual genes contributing to natural variation in this trait are all unknown. Experimental animal models provide a means to circumvent complicating environmental factors, and the development of dense genetic maps based on molecular markers now provides opportunities to resolve quantitative genetic variation into individual regions of the genome influencing a given trait (quantitative trait loci, QTL). To begin to identify the heritable determinants of BMD, we have examined genetically distinct laboratory mouse strains raised under strict environmental control. Mouse whole-body bone mineral content by dual-energy X-ray absorptiometry (DXA) correlated strongly with skeletal calcium content by ashing, and peak whole-body BMD by DXA in female mice occurred at approximately 80-90 days of age. We therefore determined mean body weight and peak whole body BMD values in 12-week-old female mice from a panel of 24 recombinant inbred (RI) BXD strains, derived from a cross between C57BL/6 and DBA/2 progenitors. The distribution of body weight and BMD values among the strains clearly indicated the presence of strong genetic influences on both of these traits, with an estimated narrow sense heritability of 60% and 35%, respectively. The patterns of differences in body weight and peak whole body BMD in the BXD strains were then integrated with a large database of genetic markers previously defined in the RI BXD strains to generate chromosome map sites for QTL. After correction for redundancy among the significant correlations, QTL analysis of the BXD RI strain series provisionally identified 10 chromosomal sites linked to peak bone mass development in the female. Several of the identified sites map near genes encoding hormones, structural proteins, and cell surface receptors that are intricately involved in skeletal homeostasis. Four QTL for body weight were also identified. One of these loci was also strongly linked to inherited variation in BMD. This finding suggests that body weight and peak BMD may be influenced by linked genes or perhaps by common genes with pleiotropic effects. Our phenotyping in the RI BXD strains has allowed us to map a number of specific genetic loci strongly related to the acquisition of peak BMD. Confirmation of these findings will likely result in the understanding of which genes control skeletal health.     

Quantitative trait loci (QTL) analyses and alcohol-related behaviors

Recombinant inbred (RI) strains can make an important contribution toward the merger of molecular genetics and quantitative genetics in the quest for quantitative trait loci (QTL). We present preliminary analyses of alcohol-related processes from our ongoing research using the BXD RI series. Issues concerning reliability, genetic correlations, and RI QTL analysis are discussed. Several strategies for replication and extension of QTL candidate regions are considered: F1 crosses between RI strains, F2 crosses, heterogeneous stock, interspecific backcrosses, QTL selection, and the use of murine QTL in chromosomal regions syntenic to human chromosomes as candidate chromosomal regions for human QTL.     

Genetic analysis of susceptibility to dextran sulfate sodium-induced colitis in mice

The genetic basis for differential sensitivity of inbred mice to inflammatory bowel disease induced by dextran sulfate sodium (DSS) is unknown. Susceptible C3H/HeJ were outcrossed to partially resistant C57BL/6J mice. F2 and N2 progeny were phenotyped by evaluating histopathologic lesions in large intestine detected 16 days after a 5-day period of feeding 3.5% DSS. Screening for DSS colitis (Dssc) loci revealed quantitative trait loci (QTL) on Chr 5 (Dssc1) and Chr 2 (Dssc2). These traits contributed additively, explaining 17.5% of the variation in total colonic lesions. Additional QTL on Chr 18 and 1 that collectively explained 11% of the variation in total colon lesions were indicated. In the cecum, only a putative QTL on Chr 11 was associated with pathology (lesion severity) in the cecum. Reduced DSS susceptibility was observed in congenic stocks in which the highly susceptible NOD/Lt strain carried putative resistance alleles from either B6 on Chr 2 or from the highly resistant NON/Lt strain on Chr 9. We conclude that multiple genes control susceptibility to DSS colitis in mice. Possible Dssc candidate genes are discussed in terms of current knowledge of inflammatory bowel disease susceptibility loci in humans.     

A quantitative trait locus for alcohol consumption in selectively bred rat lines

Selective breeding for high and low alcohol consumption led to the establishment of alcohol-preferring (P) and alcohol-nonpreferring (NP) rat lines that differ greatly in their alcohol consumption. These lines were inbred and F2 intercross progenies were generated to detect quantitative trait loci (QTLs) influencing alcohol consumption. A QTL on chromosome 4 was identified with a maximum lod score of 8.6. This QTL acts in an additive fashion and accounts for 11% of the total phenotypic variability and approximately one-third of the genetic variability. Neuropeptide Y, an endogenous anxiolytic and neuromodulator, has been mapped to this same region of chromosome 4. This study is an advance in genome analyses, demonstrating that crosses between divergent, selectively bred rat lines can be used to identify QTLs. Localization of a gene influencing alcohol consumption may have important implications for the etiology of alcohol abuse and alcoholism in humans.     

Genetic modifiers of Leprfa associated with variability in insulin production and susceptibility to NIDDM

In an attempt to identify the genetic basis for susceptibility to non-insulin-dependent diabetes mellitus within the context of obesity, we generated 401 genetically obese Leprfa/Leprfa F2 WKY13M intercross rats that demonstrated wide variation in multiple phenotypic measures related to diabetes, including plasma glucose concentration, percentage of glycosylated hemoglobin, plasma insulin concentration, and pancreatic islet morphology. Using selective genotyping genome scanning approaches, we have identified three quantitative trait loci (QTLs) on Chr. 1 (LOD 7.1 for pancreatic morpholology), Chr. 12 (LOD 5.1 for body mass index and LOD 3.4 for plasma glucose concentration), and Chr. 16 (P < 0.001 for genotype effect on plasma glucose concentration). The obese F2 progeny demonstrated sexual dimorphism for these traits, with increased diabetes susceptibility in the males appearing at approximately 6 weeks of age, as sexual maturation occurred. For each of the QTLs, the linked phenotypes demonstrated sexual dimorphism (more severe affection in males). The QTL on Chr. 1 maps to a region vicinal to that previously linked to adiposity in studies of diabetes susceptibility in the nonobese Goto-Kakizaki rat, which is genetically closely related to the Wistar counterstrain we employed. Several candidate genes, including tubby (tub), multigenic obesity 1 (Mob1), adult obesity and diabetes (Ad), and insulin-like growth factor-2 (Igf2), map to murine regions homologous to the QTL region identified on rat Chr. 1.     

Identification of quantitative trait loci involved in contextual and auditory-cued fear conditioning in BXD recombinant inbred strains.

Fear conditioning shows associations formed between contextual or auditory stimuli with an unconditioned stimulus. Inbred mouse strains differ in their ability to demonstrate fear conditioning, suggesting at least a partial genetic influence. The present study identified the possible chromosomal loci regulating fear conditioning in BXD recombinant inbred strains using quantitative trait loci (QTL) analysis. Estimates of heritability for all 3 measures of conditioning were about .28. Correlational analyses between genetic markers and strain means identified multiple putative QTLs. The strongest associations were on Chromosomes 1 and 17 for freezing to the context, Chromosome 12 for freezing to an altered context, and Chromosome 1 for freezing to the auditory stimulus. Overlapping QTLs may indicate some common genes that underlie aspects of this learning task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 non-diabetic 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.     

Concomitant chemoradiotherapy for incompletely resected supratentorial low-grade astrocytoma in children: preliminary report

Interval mapping was used to identify putative quantitative trait loci (QTL) for blood pressure and cardiac mass on Chromosome (Chr) 3 in F1(S x R) x S population of 150 rats raised on an 8% NaCl diet. Two genetic markers 95.7 cM apart, D3Wox3 and D3Mco5 (tightly linked to Edn3), showed "suggestive" linkage to blood pressure (LOD = 2.0 and 1.8 respectively). In addition, D3Wox3 showed "suggestive" linkage to heart weight (LOD = 2.5), and D3Mco5 showed "suggestive" linkage to body weight-adjusted heart weight (LOD = 2.1). Congenic rats (designated S.R-Edn3) were constructed by introgressing the R-rat Edn3 allele (and flanking loci) into the S strain. On a 2% NaCl diet, S.R-Edn3 rats had lower blood pressure (21.4 mm Hg, P = 0. 0005) and heart weight (59 mg, P = 0.0038) compared with S rats, confirming the existence of a blood pressure QTL on Chr 3 near Edn3 even though QTL linkage analysis of blood pressure did not achieve stringent statistical criteria for significance. The results of the congenic experiment and the large distance between the two putative QTL suggest the presence of at least two independent blood pressure/cardiac mass QTL detectable on Chr 3 in the Dahl rat model of genetic hypertension.     

Analytical and clinical performance of an automated immunoassay system (Immulite) for estradiol in serum

Mouse strains congenic for individual quantitative trait loci (QTLs) conferring hypnotic sensitivity to ethanol were constructed by backcrossing genotypically selected ILS x ISS N2 individuals to either inbred Long Sleep (ILS) or inbred Short Sleep (ISS) mice. We used a novel "speed congenic" approach in which N2 mice were genotyped for markers flanking each of the five originally identified QTLs. Genotypic selection for ISS regions at four of the five QTLs, and for ILS/ISS at the fifth QTL, allowed rapid fixation of the genetic background. We call this strategy "QTL-Marker-Assisted Counter Selection" or QMACS. By the N4 generation, phenotypic assessments showed that in some sublines the QTL had not been captured; these sublines were discarded and positive lines split to create new replicate sublines. One QTL, on Chromosome (Chr) 8, was not confirmed. At the N8, virtually all sublines on the remaining QTLs retained the phenotypic difference between heterozygotes and ISS homozygotes. Small numbers of interim congenics were produced at the N6 and later generations in which the ILS QTL was made homozygous on the ISS background; as expected, these congenic mice showed an increased sleep time. For later backcrosses (after the N4), the parents were selected on the basis of phenotype as well as genotype. The parent-offspring correlation over all QTLs was significant, supporting the use of phenotypic selection in congenic construction.     

A major influence of sex-specific loci on alcohol preference in C57Bl/6 and DBA/2 inbred mice

C57Bl/6 mice reproducibly prefer to ingest more 10% ethanol in a two-bottle choice paradigm than do DBA/2J mice. In this paper we report the identification of two new sex-specific alcohol preference (Alcp) loci. Melo and associates (1996) identified two loci: Alcp1, a male-specific locus on Chromosome (Chr) 2, and Alcp2, a female- and cross-specific locus on Chr 11. We have additionally identified Alcp3, a male-specific locus on Chr 3, and Alcp4, a female-specific locus on Chr 1. We have also performed a statistical analysis to exclude the possibility of undiscovered major alcohol preference loci that are not sex-specific in our backcross paradigm. Our results indicate that alcohol preference in C57BL/6 mice, as measured in our backcross, is largely controlled in a sex-specific manner.     

Mapping quantitative trait loci for immune capacity in the pig

Immune capacity traits show considerable genetic variation in outbred populations. To identify quantitative trait loci (QTLs) for immune capacity in the pig, various measures of immune function (total and differential leukocyte counts, neutrophil phagocytosis, mitogen-induced proliferation, IL-2 production, and virus induced IFN-alpha production in whole blood cultures, and Ab responses to two Escherichia coli antigens) were determined in 200 F2 animals from a wild pig-Swedish Yorkshire intercross. The pedigree has been typed for 236 genetic markers covering all autosomes, the X chromosome and the X/Y pseudoautosomal region. Through interval mapping using a least-squares method, four QTLs with significant effects were identified; one for total leukocyte counts, one for mitogen-induced proliferation, one for prevaccination levels of Abs to E. coli Ag K88, and one for Ab response to the O149 Ag. In addition, several putative QTLs were indicated. The results from the present study conclusively show that it is possible to identify QTLs for immune capacity traits in outbred pig populations by genome analysis.     

A nonparametric bootstrap method for testing close linkage vs. pleiotropy of coincident quantitative trait loci

A novel method using the nonparametric bootstrap is proposed for testing whether a quantitative trait locus (QTL) at one chromosomal position could explain effects on two separate traits. If the single-QTL hypothesis is accepted, pleiotropy could explain the effect on two traits. If it is rejected, then the effects on two traits are due to linked QTLs. The method can be used in conjunction with several QTL mapping methods as long as they provide a straightforward estimate of the number of QTLs detectable from the data set. A selection step was introduced in the bootstrap procedure to reduce the conservativeness of the test of close linkage vs. pleiotropy, so that the erroneous rejection of the null hypothesis of pleiotropy only happens at a frequency equal to the nominal type I error risk specified by the user. The approach was assessed using computer simulations and proved to be relatively unbiased and robust over the range of genetic situations tested. An example of its application on a real data set from a saline stress experiment performed on a recombinant population of wheat (Triticum aestivum L. ) doubled haploid lines is also provided.     

Identification of peak bone mass QTL in a spontaneously osteoporotic mouse strain

The whole genome scan for quantitative trait loci (QTLs) specifying peak bone mass was performed with the F2 intercrosses of SAMP6, an established murine model of senile osteoporosis, exhibiting a significantly lower peak bone mass, and SAMP2, exhibiting a higher peak bone mass. Cortical thickness index (CTI), a parameter of bone mass of femurs, was measured in 488 F2 progeny at 4 months of age, when the animals attained peak bone mass by microphotodensitometry. Genetic markers were typed at 90 loci spanning all chromosomes except the Y. By interval mapping of 246 male F2 mice, two loci were identified with significant linkage to peak bone mass, one on Chromosome (Chr) 11 and another on Chr 13, with a maximum lod score of 10.8 (22.2% of the total variance) and 5.8 (10.0%), respectively. Another locus on the X Chr was suggestive of a QTL associated oppositely with a low peak bone mass to the SAMP2 allele. This association was consistent with the distribution of peak bone mass in the F1 and F2. These findings should be useful to elucidate the genetics of osteoporosis.     

Alternative algorithms for prevention of perinatal group B streptococcal infections

The well-known association of hypertension and diabetes mellitus and the lack of suitable animal models to study diabetic hypertension prompted us to transfer 4 chromosomal regions with quantitative trait loci (QTLs) for blood pressure of the spontaneously hypertensive SHR rat onto the genetic background of the diabetes-prone and normotensive BB/OK rat. Four congenic strains developed are named as BB. Sa (Chr.1), BB.Bp2 (Chr.18), BB.1K (Chr.20) and BB.Xs (Chr.X). Because the systolic blood pressure is significantly elevated in all congenics, renal related traits were investigated in serum and urine. Comparing BB/OK and their congenic derivatives, significant differences were found in all serum and in 7 out of 8 urine constituents studied. Most significant differences were found between BB/OK and BB.Bp2 rats. Significant differences were also found between the different congenic strains indicating that each congenic strain has its own phenotype and that each chromosomal region contains most probably further QTLs for some of the traits studied.     

Quantitative trait loci affecting differences in floral morphology between two species of monkeyflower (Mimulus)

Conspicuous differences in floral morphology are partly responsible for reproductive isolation between two sympatric species of monkeyflower because of their effect on visitation of the flowers by different pollinators. Mimulus lewisii flowers are visited primarily by bumblebees, whereas M. cardinalis flowers are visited mostly by hummingbirds. The genetic control of 12 morphological differences between the flowers of M. lewisii and M. cardinalis was explored in a large linkage mapping population of F2 plants n = 465 to provide an accurate estimate of the number and magnitude of effect of quantitative trait loci (QTLs) governing each character. Between one and six QTLs were identified for each trait. Most (9/12) traits appear to be controlled in part by at least one major QTL explaining >/=25% of the total phenotypic variance. This implies that either single genes of individually large effect or linked clusters of genes with a large cumulative effect can play a role in the evolution of reproductive isolation and speciation.