Search

The genus Alsodes is the most diverse amphibian taxon of southern Andes, where a series of endemic species occur from north to south (∼33° to 48°30'S), mainly on the western slopes (Chile), with little overlap of geographic ranges. In this study, we describe a new population of Alsodes from the western slopes of the Andes (Fundo El Rosario, 36°52'S), located in a section of this mountain range where it is not clear which congeneric species inhabit. Phylogenetic analyses show that this population presents a mix of mitochondrial DNA related to three nominal species, A. hugoi , A. igneus and A. pehuenche , although the last is mainly present. However, the population presents external characteristics attributable to A. hugoi and A. igneus , differing notably from A. pehuenche . The population inhabits a stream surrounded by temperate deciduous forests at 1130 m elevation, an environment similar to that of A. hugoi and A. igneus , but very different from that of A. pehuenche (high Andean steppe environments between 2000 and 2500 m). This finding represents an enigma from the evolutionary and biogeographical point of view, because it might involve hybridization and/or introgression phenomena between more than two species. As the taxonomic status of this population cannot be determined with the available genetic and morphological evidence, we speculate about its probable origin, taking into account the scarce knowledge of the geographic distributions of the species of Alsodes in the area.

Background: Plant-mediated RNAi (PMRi) silencing of insect genes has enormous potential for crop protection, but whether it works robustly under field conditions, particularly with lepidopteran pests, remains controversial. Wild tobacco Nicotiana attenuata and cultivated tobacco (N. tabacum) (Solanaceae) is attacked by two closely related specialist herbivores Manduca sexta and M. quinquemaculata (Lepidoptera, Sphingidae). When M. sexta larvae attack transgenic N. attenuata plants expressing double-stranded RNA(dsRNA) targeting M. sexta's midgut-expressed genes, the nicotine-ingestion induced cytochrome P450 monooxygenase (invert repeat (ir)CYP6B46-plants) and the lyciumoside-IV-ingestion induced β-glucosidase1 (irBG1-plants), these larval genes which are important for the larvae's response to ingested host toxins, are strongly silenced., Results: Here we show that the PMRi procedure also silences the homologous genes in native M. quinquemaculata larvae feeding on irCYP6B46 and irBG1-transgenic N. attenuata plants in nature. The PMRi lines shared 98 and 96% sequence similarity with M. quinquemaculata homologous coding sequences, and CYP6B46 and BG1 transcripts were reduced by ca. 90 and 80%, without reducing the transcripts of the larvae's most similar, potential off-target genes., Conclusions: We conclude that the PMRi procedure can robustly and specifically silence genes in native congeneric insects that share sufficient sequence similarity and with the careful selection of targets, might protect crops from attack by congeneric-groups of insect pests.

Through linkage analysis of the Dahl salt-sensitive (S) rat and the spontaneously hypertensive rat (SHR), a blood pressure (BP) quantitative trait locus (QTL) was previously located on rat chromosome 9. Subsequent substitution mapping studies of this QTL revealed multiple BP QTLs within the originally identified logarithm of odds plot by linkage analysis. The focus of this study was on a 14.39 Mb region, the distal portion of which remained unmapped in our previous studies. High-resolution substitution mapping for a BP QTL in the setting of a high-salt diet indicated that an SHR-derived congenic segment of 787.9 kb containing the gene secreted phosphoprotein-2 (Spp2) lowered BP and urinary protein excretion. A nonsynonymous G/T polymorphism in the Spp2 gene was detected between the S and S.SHR congenic rats. A survey of 45 strains showed that the T allele was rare, being detected only in some substrains of SHR and WKY. Protein modeling prediction through SWISSPROT indicated that the predicted protein product of this variant was significantly altered. Importantly, in addition to improved cardiovascular and renal function, high salt-fed congenic animals carrying the SHR T variant of Spp2 had significantly lower bone mass and altered bone microarchitecture. Total bone volume and volume of trabecular bone, cortical thickness, and degree of mineralization of cortical bone were all significantly reduced in congenic rats. Our study points to opposing effects of a congenic segment containing the prioritized candidate gene Spp2 on BP and bone mass., (Copyright © 2016 the American Physiological Society.)

Metabolic syndrome is a highly prevalent human disease with substantial genomic and environmental components. Previous studies indicate the presence of significant genetic determinants of several features of metabolic syndrome on rat chromosome 16 (RNO16) and the syntenic regions of human genome. We derived the SHR.BN16 congenic strain by introgression of a limited RNO16 region from the Brown Norway congenic strain (BN-Lx) into the genomic background of the spontaneously hypertensive rat (SHR) strain. We compared the morphometric, metabolic, and hemodynamic profiles of adult male SHR and SHR.BN16 rats. We also compared in silico the DNA sequences for the differential segment in the BN-Lx and SHR parental strains. SHR.BN16 congenic rats had significantly lower weight, decreased concentrations of total triglycerides and cholesterol, and improved glucose tolerance compared with SHR rats. The concentrations of insulin, free fatty acids, and adiponectin were comparable between the two strains. SHR.BN16 rats had significantly lower systolic (18-28 mmHg difference) and diastolic (10-15 mmHg difference) blood pressure throughout the experiment (repeated-measures ANOVA, P < 0.001). The differential segment spans approximately 22 Mb of the telomeric part of the short arm of RNO16. The in silico analyses revealed over 1200 DNA variants between the BN-Lx and SHR genomes in the SHR.BN16 differential segment, 44 of which lead to missense mutations, and only eight of which (in Asb14, Il17rd, Itih1, Syt15, Ercc6, RGD1564958, Tmem161a, and Gatad2a genes) are predicted to be damaging to the protein product. Furthermore, a number of genes within the RNO16 differential segment associated with metabolic syndrome components in human studies showed polymorphisms between SHR and BN-Lx (including Lpl, Nrg3, Pbx4, Cilp2, and Stab1). Our novel congenic rat model demonstrates that a limited genomic region on RNO16 in the SHR significantly affects many of the features of metabolic syndrome.

There is a significant literature describing quantitative trait loci (QTL) controlling blood pressure (BP) in the Dahl salt-sensitive (S) rat. In studies to identify the genes underlying BP QTL it has been common practice to place chromosomal segments from low BP strains on the genetic background of the S rat and then reduce the congenic segments by substitution mapping. The present work suggests a model to simulate genetic interactions found using such congenic strains. The QTL are considered to be switches that can be either in series or in parallel represented by the logic operators AND or OR, respectively. The QTL switches can be on/off switches but are also allowed specific leak properties. The QTL switches are represented by a "universal" switch consisting of two molecules binding to form a complex. Genetic inputs enter the model as allelic products of one of the binding molecules and environmental variation (including dietary salt- and sex-related differences) enters as an influence on the concentration of the other binding molecule. The pairwise interactions of QTL are very well simulated and fall into recognizable patterns. There is, however, often more than one assumed model to predict a given pattern so that all patterns do not necessarily have a unique solution. Nevertheless, the models obtained provide a framework for placing the QTL in pathways relative to one another. Moreover, based on their leak properties pairs of QTL could be identified in which one QTL may alter the properties of the other QTL.

Purpose: Most common forms of human epilepsy result from a complex combination of polygenetic and environmental factors. Quantitative trait locus (QTL) mapping is a first step toward the nonbiased discovery of epilepsy-related candidate genes. QTL studies of susceptibility to induced seizures in mouse strains have consistently converged on a distal region of chromosome 1 as a major phenotypic determinant; however, its influence on spontaneous epilepsy remains unclear. In the present study we characterized the influence of allelic variations within this QTL, termed Szs1, on the occurrence of spontaneous spike-wave discharges (SWDs) characteristic of absence seizures in DBA/2 (D2) mice., Methods: We analyzed SWD occurrence and patterns in freely behaving D2, C57BL/6 (B6) and the congenic strains D2.B6-Szs1 and B6.D2-Szs1., Key Findings: We showed that congenic manipulation of the Szs1 locus drastically reduced the number and the duration of SWDs in D2.B6-Szs1 mice, which are homozygous for Szs1 from B6 strain on a D2 strain background. However, it failed to induce the full expression of SWDs in the reverse congenic animals B6.D2-Szs1., Significance: Our results demonstrate that the occurrence of SWDs in D2 animals is under polygenic control and, therefore, the D2 and B6 strains might be a useful model to dissect the genetic determinants of polygenic SWDs characteristic of typical absence seizures. Furthermore, we point to the existence of epistatic interactions between at least one modifier gene within Szs1 and genes within unlinked QTLs in regulating the occurrence of spontaneous nonconvulsive forms of epilepsies., (Wiley Periodicals, Inc. © 2012 International League Against Epilepsy.)

Deficiency of fatty acid translocase Cd36 has been shown to have a major role in the pathogenesis of metabolic syndrome in the spontaneously hypertensive rat (SHR). We have tested the hypothesis that the effects of Cd36 mutation on the features of metabolic syndrome are contextually dependent on genomic background. We have derived two new congenic strains by introgression of limited chromosome 4 regions of SHR origin, both including the defective Cd36 gene, into the genetic background of a highly inbred model of insulin resistance and dyslipidemia, polydactylous (PD) rat strain. We subjected standard diet-fed adult males of PD and the congenic PD.SHR4 strains to metabolic, morphometric and transcriptomic profiling. We observed significantly improved glucose tolerance and lower fasting insulin levels in PD.SHR4 congenics than in PD. One of the PD.SHR4 strains showed lower triglyceride concentrations across major lipoprotein fractions combined with higher levels of low-density lipoprotein cholesterol compared with the PD progenitor. The hepatic transcriptome assessment revealed a network of genes differentially expressed between PD and PD.SHR4 with significant enrichment by members of the circadian rhythmicity pathway (Arntl (Bmal1), Clock, Nfil3, Per2 and Per3). In summary, the introduction of the chromosome 4 region of SHR origin including defective Cd36 into the PD genetic background resulted in disconnected shifts of metabolic profile along with distinct changes in hepatic transcriptome. The synthesis of the current results with those obtained in other Cd36-deficient strains indicates that the eventual metabolic effect of a deleterious mutation such as that of SHR-derived Cd36 is not absolute, but rather a function of complex interactions between environmental and genomic background, upon which it operates.

The bifoliate, or bicuspid, aortic valve (BAV) is the most frequent congenital cardiac anomaly in man. It is a heritable defect, but its mode of inheritance remains unclear. Previous studies in Syrian hamsters showed that BAVs with fusion of the right and left coronary leaflets are expressions of a trait, the variation of which takes the form of a phenotypic continuum. It ranges from a trifoliate valve with no fusion of the coronary leaflets to a bifoliate root devoid of any raphe. The intermediate stages are represented by trifoliate valves with fusion of the coronary aortic leaflets, and bifoliate valves with raphes. The aim of this study was to elucidate whether the distinct morphological variants rely on a common genotype, or on different genotypes. We examined the aortic valves from 1 849 Syrian hamsters belonging to a family subjected to systematic inbreeding by full-sib mating. The incidence of the different trifoliate aortic valve (TAV) and bifoliate aortic valve (BAV) morphological variants widely varied in the successive inbred generations. TAVs with extensive fusion of the leaflets, and BAVs, accounted for five-sixths of the patterns found in Syrian hamsters considered to be genetically alike or virtually isogenic, with the probability of homozygosity being 0.999 or higher. The remaining one-sixth hamsters had aortic valves with a tricuspid design, but in most cases the right and left coronary leaflets were slightly fused. Results of crosses between genetically alike hamsters, with the probability of homozygosity being 0.989 or higher, revealed no significant association between the valvar phenotypes in the parents and their offspring. Our findings are consistent with the notion that the BAVs of the Syrian hamster are expressions of a quantitative trait subject to polygenic inheritance. They suggest that the genotype of the virtually isogenic animals produced by systematic inbreeding greatly predisposes to the development of anomalous valves, be they bifoliate, or trifoliate with extensive fusion of the leaflets. We infer that the same underlying genotype may account for the whole range of valvar morphological variants, suggesting that factors other than genetic ones are acting during embryonic life, creating the so-called intangible variation or developmental noise, and playing an important role in the definitive anatomic configuration of the valve. The clinical implication from our study is that congenital aortic valves with a trifoliate design, but with fusion of coronary aortic leaflets, may harbour the same inherent risks as those already recognised for BAVs with fusion of right and left coronary leaflets., (© 2011 The Authors. Journal of Anatomy © 2011 Anatomical Society of Great Britain and Ireland.)

Congenic and consomic rat strains are inbred strains containing in their genome a given genomic region (congenic) or a whole chromosome (consomic) from another strain. They are nowadays invaluable tools for the identification of genes and mechanisms of multifactorial diseases, one of the main goals in biomedicine. They are produced by repeated backcrosses from a donor inbred strain to a recipient inbred strain, and thereafter maintained by conventional brother-x-sister mating. Although their production is lengthy and costly, it only requires a zootechny unit for breeding and tools for genotyping.

Congenic strains are routinely used for positional mapping of quantitative trait loci; while conplastic strains, derived by substitution of different mitochondrial genomes on the same nuclear genetic background of inbred rodent strains, provide a way to unambiguously isolate effects of the mitochondrial genome on complex traits. Derivation of congenic or conplastic strains using a traditional backcross breeding strategy (10 backcrosses) takes more than 3 years. There are two principal strategies to speed up this process: (1) marker-assisted derivation of "speed" congenic/conplastic strains and (2) derivation of "supersonic" congenic/conplastic strains using in each backcross generation embryos obtained from 4-week-old superovulated females; thus, each backcross generation takes only 7 weeks. Both strategies could also be combined. In the current chapter, a method for derivation of "supersonic" congenic/conplastic rat strains is described.

C57BL/6J (B6) and DBA/2J (D2) mice differ in behaviors related to substance abuse, including voluntary morphine consumption and preference in a two-bottle choice paradigm. Two major quantitative trait loci (QTL) for morphine consumption and preference exist between these strains on chromosomes (Chrs.) 6 and 10 when the two-bottle choice involves morphine in saccharin vs quinine in saccharin. Here, we report the refinement of the Chr. 10 QTL in subcongenic strains of D2.B6-Mop2 congenic mice described previously. With these subcongenic mouse strains, we have divided the introgressed region of Chr. 10 containing the QTL gene(s) into two segments, one between the acromere and Stxbp5 (in D2.B6-Mop2-P1 mice) and the other between marker D10Mit211 and marker D10Mit51 (in D2.B6-Mop2-D1 mice). We find that, similar to B6 mice, the D2.B6-Mop2-P1 congenic mice exhibit a strong preference for morphine over quinine, whereas D2.B6-Mop2-D1 congenic mice avoid morphine (similar to D2 mice). We have also created a line of double congenic mice, B6.D2-Mop2.Qui, which contains both Chr. 10 and Chr. 6 QTL. We find that they are intermediate in their morphine preference scores when compared with B6 and D2 animals. Overall, these data suggest that the gene(s) involved in morphine preference in the morphine-quinine two-bottle choice paradigm are contained within the proximal region of Chr. 10 (which harbors Oprm1) between the acromere and Stxbp5, as well as on distal Chr. 6 between marker D6Mit10 and the telomere.

Footshock response is used to study a variety of biological functions in mammals including drug self-administration, learning and memory and nociception. However, the genetics underlying variability in footshock sensitivity are not well understood. In the current studies, a panel of B6.A consomic mouse strains, two B6.D2 genome-tagged mouse lines, and the progenitor strains were screened for footshock sensitivity as measured by audible vocalization. It was found that A/J (A) mice and C57BL/6J (B6) mice with an A Chromosome 1 (Chr 1) were less sensitive to footshock compared to B6 animals. Furthermore, the offspring of Chr 1 consomic mice crossed with B6 mice had vocalization levels that were intermediate to A/J and B6 animals. A F2 mapping panel revealed two significant QTLs for footshock vocalization centered around D1Mit490 and D1Mit206 on Chr 1. The role of these Chr 1 loci in footshock sensitivity was confirmed in B6.D2 genome-tagged mouse lines.

The way in which animals respond to stressful environments correlates with anxiety-related behaviour. To begin identifying the genetic factors that influence anxiety, we have studied the stress-responsiveness of inbred mouse strains using a modified form of the open field activity test (OFA), termed the elevated (e) OFA. In particular, two strains show high (DBA/2J) or low (C57BL/6J) stress-responsiveness in the eOFA. Genetic studies of an F(2) intercross between these two strains previously identified two regions, on chromosomes (Chr) 1 and 12, linked to anxiety-related behaviour. To confirm that these regions contain loci for stress-responsiveness, we established separate congenic mouse strains for the linked Chr1 and Chr12 regions. Each congenic strain harbours a DBA/2J-derived interval encompassing the linked region on the C57BL/6J genetic background: the congenic intervals are between, but not including approximately 48.6 Mb and approximately 194.8 Mb on Chr1, and approximately 36.2 Mb and the distal end of Chr12. Cohorts of DBA/2J, C57BL/6J and congenic mice were analysed for a series of stress-responsive phenotypes using the eOFA test. Both congenic strains had significantly different stress-responsive phenotypes compared to the low-stress C57BL/6J parental strain, but the DBA/2J-derived Chr12 interval had a greater genetic effect than the DBA/2J-derived Chr1 interval for changing the behavioral phenotype of the parental C57BL/6J mouse strain. These results confirmed the presence of stress-responsive loci on Chr1 and Chr12. New stress-related phenotypes were also identified, which aided in comparing and differentiating DBA/2J, C57BL/6J and congenic mice.

Behavioral phenotypes (e.g., drug responses and withdrawal) are typically quantitative traits-characteristics that differ along a spectrum in the extent to which an individual possesses that characteristic. Such traits are determined by multiple genes, as well as by environmental factors and interactions among genes and environmental factors. The chromosomal regions containing these genes are commonly referred to as quantitative trait loci (QTLs). As described in the preceding article by Hitzemann and colleagues (pp. 270- 271), researchers have developed a variety of strategies to attain greater precision when mapping QTLs (Darvasi 1998; Talbot et al. 1999), which is necessary for unbiased genomewide approaches such as QTL mapping to be successful in ultimately identifying which gene(s) underlies a QTL's phenotypic influence. Among these, some approaches are clearly superior for fine mapping QTLs associated with behavioral traits. One such strategy employs specially bred animals known as interval-specific congenics (ISCs) (sometimes called small donor segment congenics). This article introduces the use of these animals in mapping QTLs associated with certain responses to alcohol.

Background: A highly significant quantitative trait locus (QTL) on chromosome 4 that influenced alcohol preference was identified by analyzing crosses between the iP and iNP rats. Congenic strains in which the iP chromosome 4 QTL interval was transferred to the iNP (NP.P) exhibited the expected increase in alcohol consumption compared with the iNP background strain. This study was undertaken to identify genes in the chromosome 4 QTL interval that might contribute to the differences in alcohol consumption between the alcohol-naïve congenic and background strains., Methods: RNA from 5 brain regions from each of 6 NP.P and 6 iNP rats was labeled and analyzed separately on an Affymetrix Rat Genome 230 2.0 microarray to look for both cis-regulated and trans-regulated genes. Expression levels were normalized using robust multi-chip average (RMA). Differential gene expression was validated using quantitative real-time polymerase chain reaction. Five individual brain regions (nucleus accumbens, frontal cortex, amygdala, hippocampus, and striatum) were analyzed to detect differential expression of genes within the introgressed QTL interval, as well as genes outside that region. To increase the power to detect differentially expressed genes, combined analyses (averaging data from the 5 discrete brain regions of each animal) were also carried out., Results: Analyses within individual brain regions that focused on genes within the QTL interval detected differential expression in all 5 brain regions; a total of 35 genes were detected in at least 1 region, ranging from 6 genes in the nucleus accumbens to 22 in the frontal cortex. Analysis of the whole genome detected very few differentially expressed genes outside the QTL. Combined analysis across brain regions was more powerful. Analysis focused on the genes within the QTL interval confirmed 19 of the genes detected in individual regions and detected 15 additional genes. Whole genome analysis detected 1 differentially expressed gene outside the interval., Conclusions: Cis-regulated candidate genes for alcohol consumption were identified using microarray profiling of gene expression differences in congenic animals carrying a QTL for alcohol preference.

We previously identified a quantitative trait locus (QTL) for stroke proneness between the kallikrein (Klk) and Mt1pa markers on rat chromosome 1. To gain functional insights, we constructed congenic strains by introgressing either the whole or selected chromosomal segments from the stroke-prone (SHRsp) onto the stroke-resistant (SHRsr) spontaneously hypertensive rat genome and vice versa. The phenotype was the latency to develop stroke under a Japanese high-salt, low-potassium diet for 3 mo [known as Japanese diet (JD)]. Blood pressure (BP) was measured by tail cuff throughout the experiment. Urinary protein excretion was monitored in all lines under JD. The SHRsp-derived lines carrying the SHRsr allele, and particularly the D1Rat134-Mt1pa chromosomal segment, had a significant delay of stroke occurrence and improved survival compared with SHRsp (P < 0.001). On the other hand, a significant occurrence of stroke events (20%) was detected in the reciprocal lines by the end of the 3-mo treatment with JD (P = 0.003). The stroke phenotype was also associated with increased proteinuria. Our results underscore the functional importance of the Chr 1 stroke QTL. Furthermore, they underscore the utility of stroke/congenic lines in dissecting the genetics of stroke.

Identification of genes underlying complex traits such as pubertal timing, is vital to our understanding of fundamental human developmental processes. Animal models can provide an important adjunct to more traditional human investigations. Within this review, we discuss the use and advantages of chromosome substitution strains in the investigation of factors that regulate the timing of the onset of puberty.

Background: The National Bio Resource Project for the Rat in Japan (NBRP-Rat) is focusing on collecting, preserving and distributing various rat strains, including spontaneous mutant, transgenic, congenic, and recombinant inbred (RI) strains. To evaluate their value as models of human diseases, we are characterizing them using 109 phenotypic parameters, such as clinical measurements, internal anatomy, metabolic parameters, and behavioral tests, as part of the Rat Phenome Project. Here, we report on a set of 357 simple sequence length polymorphism (SSLP) markers and 122 rat strains, which were genotyped by the marker set., Results: The SSLP markers were selected according to their distribution patterns throughout the whole rat genome with an average spacing of 7.59 Mb. The average number of informative markers between all possible pairs of strains was 259 (72.5% of 357 markers), showing their high degree of polymorphism. From the genetic profile of these rat inbred strains, we constructed a rat family tree to clarify their genetic background., Conclusion: These highly informative SSLP markers as well as genetically and phenotypically defined rat strains are useful for designing experiments for quantitative trait loci (QTL) analysis and to choose strategies for developing new genetic resources. The data and resources are freely available at the NBRP-Rat web site 1.

A genome scan of the F2 generation from an inbred alcohol-preferring (iP) and inbred alcohol-nonpreferring (iNP) rat cross identified a significant quantitative trait locus (QTL) on chromosome 4 with a lod score of 9.2. To confirm this QTL and to create animals for fine mapping of the QTL region, chromosome 4 reciprocal congenic strains were developed by transferring the chromosome 4 QTL interval into the respective iP or iNP backgrounds. The iP strain was crossed with the iNP strain to create iPiNP F1 animals, which were backcrossed to either iNP or iP animals to produce the N2 generation. Using marker-assisted selection, 10 generations of backcrossing were performed. The selection was followed by an intercross between the N10 animals to produce homozygous animals (N10F1), resulting in the finished congenic strains. Congenic strains in which the iP chromosome 4 QTL interval was transferred to the iNP (NP.P) and the iNP chromosome 4 QTL was transferred to the iP (P.NP) exhibited the expected effect on alcohol consumption of the donor strain. Development of these congenic strains further indicates that the chromosome 4 QTL region is, in part, responsible for the disparate alcohol consumption observed between the iP and iNP rats. These congenic animals will be an invaluable resource for fine mapping the QTL region and for the identification of the gene(s) that influences the drinking behavior of the iP and iNP rats.

LEC rats constitute an animal model of high susceptibility to X-rays. We developed congenic LEC rat lines (recipient strain, Fischer 344 (F344)) and performed genome-wide genotyping to identify radiation susceptibility genes. We mapped seven positional candidate genes, Bmp10, Gpr73, Gp9, Cnbp, Copg, Rab7, and Rpn1, to an approximately 1.2-Mb region located between loci D4Got85 and D4Got148 on chromosome 4. None of the seven genes has been reported to be associated with radiation susceptibility. Comparison of the coding sequences for these seven genes in F344 and LEC rats showed no changes in deduced amino acid sequences. We determined gene expression differences in Gp73, Gp9, and Cnbp as well as strain-specific variations in upstream sequences of these genes. Our results suggest that radiation susceptibility in the LEC rat is primarily attributable to one of the genes within this approximately 1.2-Mb region; however, expression analysis gave no clear indication as to which gene is responsible.

This study sought to identify the mechanisms of vascular relaxation that are rescued in middle cerebral arteries (MCA) of SS.13BN consomic rats by substituting chromosome 13 containing the renin gene from Brown Norway (BN) rats into the Dahl salt-sensitive (SS) genetic background. Isolated MCA from SS rats exhibited an indomethacin-sensitive constriction in response to acetylcholine (ACh) and hypoxia. ACh-induced dilation was NO dependent and hypoxic dilations were cyclooxygenase (COX) dependent in BN and SS.13BN rats. In SS rats, hypoxic dilation was restored by indomethacin and abolished by inhibiting cytochrome P-450 epoxygenases, suggesting a role for epoxyeicosatrienoic acids. MCA from SS and SS.13BN rats constricted and MCA from BN rats dilated in response to the stable prostacyclin analog iloprost. MCA from SS.13BN and BN rats (but not SS rats) dilated in response to the prostaglandin E2 receptor agonist butaprost. Hypoxia increased prostacyclin release in cerebral arteries from all the strains, whereas thromboxane A2 production was reduced in BN rat vessels only. These data suggest that SS rats may be less sensitive to vasodilator prostaglandins and that normalization of renin-angiotensin system regulation causes a switch from production of COX-derived vasoconstrictor metabolites (in SS rats) toward NO-dependent relaxation in response to ACh- and prostaglandin-dependent dilation in response to hypoxia in SS.13(BN) rats.

Our previous work demonstrated 2 quantitative trait loci (QTLs), C2QTL1 and C2QTL2, for blood pressure (BP) located on chromosome (Chr) 2 of Dahl salt-sensitive (DSS) rats. However, for a lack of markers, the 2 congenic strains delineating C2QTL1 and C2QTL2 could not be separated. The position of the C2QTL1 was only inferred by comparing 2 congenic strains, one having and another lacking a BP effect. Furthermore, it was not known how adjacent QTLs would interact with one another on Chr 2. In the current investigation, first, a critical chromosome marker was developed to separate 2 C2QTLs. Second, a congenic substrain was created to cover a chromosome fragment thought to harbor C2QTL1. Finally, a series of congenic strains was produced to systematically and comprehensively cover the entire Chr 2 segment containing C2QTL2 and other regions previously untested. Consequently, a total of 3 QTLs were discovered, with C2QTL3 located between C2QTL1 and C2QTL2. C2QTL1, C2QTL2, and C2QTL3 reside in chromosome segments of 5.7 centiMorgan (cM), 3.5 cM, and 1.5 cM, respectively. C2QTL1 interacted epistatically with either C2QTL2 or C2QTL3, whereas C2QTL2 and C2QTL3 showed additive effects to each other. These results suggest that BP QTLs closely linked in a segment interact epistatically and additively to one another on Chr 2.

The Ca(2+) channel alpha(1B) subunit is a pore-forming component capable of generating N-type Ca(2+) channel activity. Although the N-type Ca(2+) channel plays a role in a variety of neuronal functions, alpha(1B)-deficient mice with a CBA/JN genetic background show no apparent behavioral or anatomical-histological abnormality, presumably owing to compensation by other Ca(2+) channels. In this study, we examined the mRNA expression of the alpha(1A), alpha(1C), alpha(1D), alpha(1E), beta(1), beta(2), beta(3) and beta(4) subunits in the olfactory bulb, cerebral cortex, hippocampus and cerebellum of alpha(1B)-deficient mice. We found that the mRNA expression levels of the alpha(1A), alpha(1C), alpha(1D), alpha(1E), beta(1), beta(2), beta(3) and beta(4) subunits were the same in the olfactory bulbs of wild, heterozygous and homozygous alpha(1B)-deficient mice. In the cerebral cortex, alpha(1A) mRNA in homozygous alpha(1B)-deficient mice was expressed at a higher level than in wild or heterozygous mice, but no difference in the expression levels of the alpha(1C), alpha(1D), alpha(1E), beta(1), beta(2), beta(3) and beta(4) subunits was found among wild, heterozygous and homozygous mice. In hippocampus and cerebellum, beta(4) mRNA in homozygous alpha(1B)-deficient mice was expressed at a higher level than in wild or heterozygous mice, but no difference in the expression levels of the alpha(1A), alpha(1C), alpha(1D), alpha(1E), beta(1), beta(2) and beta(3) subunits was found among wild, heterozygous and homozygous mice. These results suggest that the compensatory mechanisms differ in different brain regions of alpha(1B)-deficient mice with a CBA/JN genetic background.

Background: Linkage analyses of crosses of rats susceptible to renal damage, fawn-hooded hypertensive (FHH), and those resistant to kidney damage, August x Copenhagen Irish (ACI), indicated that five quantitative trait loci (QTLs), Rf-1 to Rf-5, influence proteinuria (UPV), albuminuria (UAV) and focal glomerulosclerosis (FGS). Here we present data obtained in congenic rats to directly assess the role of the Rf-1 and Rf-5 QTLs., Methods: Renal damage (UPV, UAV, and FGS) was assessed in ACI, ACI.FHH-(D1Rat324-D1Rat156)(Rf-1B), and ACI.FHH-(D17Rat117-D17Arb5)(D17Rat180-D17Rat51) (Rf-5) congenic rats in the two-kidney (2K) control situation, and following L-NAME-induced hypertension, unilateral nephrectomy (UNX), and UNX combined with L-NAME. In addition we investigated renal blood flow (RBF) autoregulation in 2K congenic and parental ACI and FHH rats., Results: Compared to ACI, Rf-1B congenic rats showed a significant increase in susceptibility to renal damage after all three treatments. The increase was most pronounced after UNX with L-NAME. In contrast, the degree of renal damage in Rf-5 congenic rats was not different from the ACI. Like FHH, Rf-1B rats had impaired renal autoregulation. In contrast, RBF autoregulation of Rf-5 rats does not differ from ACI., Conclusion: The Rf-5 QTL does not show any direct effect. The Rf-1 QTL carries one or more genes impairing renal autoregulation and influencing renal damage susceptibility. Whether these are the same genes remains to be established., (Copyright 2005 S. Karger AG, Basel.)

Aims/hypothesis: Genetic investigations in the spontaneously diabetic (Type 2) Goto Kakizaki (GK) rat have identified quantitative trait loci (QTL) for diabetes-related phenotypes. The aims of this study were to refine the chromosomal mapping of a QTL ( Nidd/gk5) identified in chromosome 8 of the GK rat and to define a pathophysiological profile of GK gene variants underlying the QTL effects in congenics., Methods: Genetic linkage analysis was carried out with chromosome 8 markers genotyped in a GKxBN F2 intercross previously used to map diabetes QTL. Two congenic strains were designed to contain GK haplotypes in the region of Nidd/gk5 transferred onto a Brown Norway (BN) genetic background, and a broad spectrum of diabetes phenotypes were characterised in the animals., Results: Results from QTL mapping suggest that variations in glucose-stimulated insulin secretion in vivo, and in body weight are controlled by different chromosome 8 loci (LOD3.53; p=0.0004 and LOD4.19; p=0.00007, respectively). Extensive physiological screening in male and female congenics at 12 and 24 weeks revealed the existence of GK variants at the locus Nidd/gk5, independently responsible for significantly enhanced insulin secretion and increased levels of plasma triglycerides, phospholipids and HDL, LDL and total cholesterol. Sequence polymorphisms detected between the BN and GK strains in genes encoding ApoAI, AIV, CIII and Lipc do not account for these effects., Conclusions/interpretation: We refined the localisation of the QTL Nidd/gk5 and its pathophysiological characteristics in congenic strains derived for the locus. These congenic strains provide novel models for testing the contribution of a subset of GK alleles on diabetes phenotypes and for identifying diabetes susceptibility genes.

Congenic BB.SHR rat strains were established by crossing of spontaneously diabetic BB/OK rats and diabetes-resistant SHR rats. Chromosomal regions on which the genes Iddm 4 (BB.6s), Iddm6 (BB.Xs) and Iddm 2 (BB.LL) are located were exchanged. As a result of genetic manipulation diabetes incidence was markedly reduced from 80% in BB/OK to 50% in BB.SHR (Chr. X), to 14% in BB.SHR (Chr. 6) and to 0% in BB.LL rats. Pancreata of these newly generated BB.SHR rats were investigated histologically. In newly diagnosed diabetic rats of congenic strains pancreatic insulin content (BB.6s: p < 0.05; BB.Xs p < 0.01) and relative volume of insulin-positive cells (BB.Xs: p < 0.001) were significantly higher than in BB/OK rats. The degree of insulitis was not different in 90-day-old and newly diagnosed diabetic animals. Surprisingly, in 30-day-old rats we observed an increase of the degree of insulitis with decreasing diabetes incidence. We suppose that by an earlier occurrence of the immunological beta-cell destruction, a part of the animals is able to develop a secondary diabetes resistance. The exchange of the BB-lymphopenia gene by that of SHR-rats prevented the development of hyperglycaemia without altering the auto-reactive immune response, which could be observed in all animals investigated.

Homozygous mu-opioid receptor (MOR) knockout (KO) mice developed on a chimeric C57B6/129SV background lack morphine-induced antinociception, locomotion and reward. Therefore it appears that MOR largely mediates these morphine actions. However, one factor that could affect the extent of knockout deficits in morphine-induced behavior is the genetic background against which the gene deletion is expressed. To examine the effect of genetic background chimeric C57B6/129SV MOR knockout mice from the 15th generation of those developed in our laboratory were backcrossed for 10 successive generations with C57BL/6 mice, a strain which is more sensitive to many of the properties of morphine, to produce congenic MOR (con-MOR) KO mice. Heterozygote conMOR KO mice display attenuated morphine locomotion and reduced morphine analgesia compared to wild-type mice. Homozygote con-MOR KO mice display baseline hyperalgesia, no morphine place preference, no morphine analgesia and no morphine locomotion. These results are not qualitatively different from those observed in the MOR KO strain with a chimeric C57B6/129SV background, and suggest that although the strain has separate influences on these functions, it does not substantially interact with deletion of the mu opiate receptor gene.

We previously detected by linkage analysis in segregating populations derived from crosses between the Sabra hypertension-prone rat (SBH/y) and the hypertension-resistant strain (SBN/y) two QTLs for salt susceptibility on chromosome 1, with sex specificity: in males SS1a and SS1b, and in females SS1b only. To provide support for a functional role of these QTLs in relation to hypertension, we constructed congenic strains by replacing most of or selected segments from chromosome 1 from SBN/y with the homologous chromosomal regions of SBH/y, or reciprocally from SBH/y with segments of SBN/y, leaving the other chromosomes unperturbed. Genetic screening with over 150 microsatellite markers confirmed the homozygosity of the targeted genomic inserts and of the remainder of the genomic background. The phenotype of the congenic strains was tested by salt loading with DOCA-salt over a 4-wk period and measuring blood pressure by tail-cuff (in all animals) or radiotelemetry (in select groups) at baseline and during salt loading. In the congenic strains in which a chromosomal segment incorporating QTL SS1a from SBN/y was introgressed onto the genomic background of SBH/y, the blood pressure response to salt loading, as measured by tail-cuff, was decreased by 16 mmHg in both males and females compared with the parental SBH/y; replacing the QTL SS1b reduced the blood pressure response by 30 and 21 mmHg, respectively. In the congenic strains in which both SS1a and SS1b were introgressed from SBN/y onto the genomic background of SBH/y, the reduction in blood pressure was 34 mmHg in males and 38 mmHg in females; these latter results were confirmed by radiotelemetry. When either one or both QTLs together were introgressed from SBH/y onto the SBN/y genomic background, tail-cuff measurements failed to detect an increase in blood pressure above baseline; telemetric measurements in the congenic strains introgressing both QTLs together, however, detected a significant rise in blood pressure after 3 and 4 wk of salt loading. Neither the origin of the Y chromosome nor the sex of the parental strain had any significant impact on the magnitude of the blood pressure response to salt loading. We conclude that the congenic rat strains that we constructed for the chromosome 1 QTLs provide functional evidence for the role of gene systems within QTLs SS1a and SS1b in the blood pressure response to salt loading. The unexpected finding was that QTL SS1a contributes to the hypertensive response also in females. The data indicate the lack of a Y chromosomal effect or of parental imprinting.

The nonobese diabetic (NOD) mouse is genetically predisposed for the spontaneous development of type 1 diabetes. Linkage analyses have identified at least 19 susceptibility loci (Idd1-Idd19) that contribute to disease pathogenesis in which lymphocytes mediate the specific destruction of insulin-producing beta-cells. Interestingly, nondiabetic mouse strains have been shown to confer susceptibility alleles to affected progeny in NOD outcrosses for some of the Idd loci. In particular, we noted that diabetic backcross progeny, derived from NOD and C57BL/6 (B6) mouse strains, demonstrated increased heterozygousity for an interval encompassing Idd14 on chromosome 13. This result suggested that B6 mice harbor a more diabetogenic allele(s) than NOD mice for this locus. To confirm this observation, a NOD congenic mouse strain, containing a B6-derived interval covering the majority of chromosome 13, was generated. Adding to the combination of already potent susceptibility alleles elsewhere in the NOD genome, the chromosome 13 B6-derived interval was able to increase the overall risk of developing type 1 diabetes, which resulted in an earlier onset and increased incidence of type 1 diabetes in congenic mice as compared with NOD mice. Furthermore, this B6-derived interval, in combination with the NOD genetic background, was able to overcome environmental conditions that typically suppressed type 1 diabetes in the NOD mouse strain.

Objective: Collagen-induced arthritis (CIA) is a model of inflammatory arthritis with many similarities to rheumatoid arthritis (RA). We previously mapped in F(2) offspring of CIA-susceptible DA and CIA-resistant F344 rats, 5 quantitative trait loci (QTLs) for which F344 alleles were associated with reduced CIA severity. In the present study, we sought to characterize the independent arthritis-modulating effects of these 5 QTLs., Methods: CIA-regulatory regions were transferred from the F344 genome to the DA background or vice versa by repeated backcrossing. The arthritis-modulating effects of the transferred alleles were determined by comparing the severity of experimentally induced arthritis in congenic rats with that in DA rats., Results: Congenic lines with either the F344 major histocompatibility complex (MHC) on the DA background or the DA MHC on the F344 background were resistant to CIA, confirming both MHC and non-MHC contributions to the genetic regulation of CIA. F344 alleles at the Cia3 and Cia5 regions of chromosomes 4 and 10 reduced CIA severity relative to that observed in DA rats. F344 Cia4 and Cia6 regions of chromosomes 7 and 8 failed to significantly alter CIA severity. Arthritis-modifying effects of Cia4 and Cia6 were, however, detected in pristane-induced and/or Freund's incomplete adjuvant oil-induced arthritis. The arthritis-modifying effects of the non-MHC CIA-regulatory loci differed in males and females., Conclusion: These congenic lines confirmed the existence and location of genes that regulate the severity of experimental arthritis in rats. Mechanisms responsible for the sex-specificity of individual arthritis-regulatory loci may explain some of the sex differences observed in RA and other autoimmune diseases in humans.

The BB (BioBreeding) rat is one of the best models of spontaneous autoimmune diabetes and is used to study non-MHC loci contributing to Type 1 diabetes. Type 1 diabetes in the diabetes-prone BB (BBDP) rat is polygenic, dependent upon mutations at several loci. Iddm1, on chromosome 4, is responsible for a lymphopenia (lyp) phenotype and is essential to diabetes. In this study, we report the positional cloning of the Iddm1/lyp locus. We show that lymphopenia is due to a frameshift deletion in a novel member (Ian5) of the Immune-Associated Nucleotide (IAN)-related gene family, resulting in truncation of a significant portion of the protein. This mutation was absent in 37 other inbred rat strains that are nonlymphopenic and nondiabetic. The IAN gene family, lying within a tight cluster on rat chromosome 4, mouse chromosome 6, and human chromosome 7, is poorly characterized. Some members of the family have been shown to be expressed in mature T cells and switched on during thymic T-cell development, suggesting that Ian5 may be a key factor in T-cell development. The lymphopenia mutation may thus be useful not only to elucidate Type 1 diabetes, but also in the function of the Ian gene family as a whole.

Although genetic mapping of quantitative trait loci (QTL) for complex traits related to hypertension is relatively straightforward, the identification of QTL at the molecular level has proven far more difficult. By combining techniques of gene mapping and gene expression profiling with studies in congenic and transgenic strains, a specific molecular defect in the Cd36 fatty acid transporter has been identified that contributes to the pathogenesis of 2 complex traits in the spontaneously hypertensive rat (SHR), namely, insulin resistance and disordered fatty acid metabolism. After mapping QTL linked to insulin resistance and dyslipidemia to the telomeric region of SHR chromosome 4, gene expression studies were used to identify candidate genes within the target chromosome segment that were differentially expressed in white adipose tissue between SHR congenic strains. This led to the identification of a major mutation in the SHR gene encoding Cd36, a fatty acid transporter involved in the transmembrane transport of long-chain fatty acids. The role for mutant Cd36 in the pathogenesis of insulin resistance and dyslipidemia was confirmed by rescuing the abnormal metabolic phenotypes through transgenic expression of wild-type Cd36 on the SHR background. These findings show that a primary defect in fatty acid transport can promote disordered carbohydrate metabolism in the SHR and show the power of advanced genome technologies for identifying QTL at the molecular level., (Copyright 2002, Elsevier Science (USA). All rights reserved.)

The identification of mutated genes and the characterization of disease pathways in monogenetic forms of human arterial hypertension has been very successful during the past decade, although only little progress has been made with regard to the genetic analysis of essential hypertension. Inbred rat strains that display hypertension as an inherited trait represent an attractive substitute for the dissection of the polygenetic basis of human essential hypertension. The power of studying these inbred models with natural allelic variation is that each strain can be thought of as a different subtype of essential hypertension. Thus, to study the genetics of hypertension using a potpourri of inbred hypertensive rat strains may help to identify a set of genes that can give rise to hypertension in the heterogeneous clinical situation of essential hypertension. Indeed, multiple blood pressure quantitative trait loci (QTL) have been identified in the rat genome and a few of those have been implicated in the human disease by homology mapping already. Here, we discuss the role of congenic breeding strategies to further dissect the genetics of hypertension in the rat. Based on recent accomplishments it can be anticipated that by using congenic strains, the genetic sifting of the collection of blood pressure QTLs identified so far will lead to the identification of additional and new candidate genes. This will open the possibility for the development of new diagnostic and therapeutic means contributing to a better control of human essential hypertension., (Copyright 2002, Elsevier Science (USA). All rights reserved.)

Studies on genetic determination of the insulin resistance syndrome in rat models revealed several susceptibility loci for features of this complex phenotype, i.e. dyslipidemia, insulin resistance and obesity. We analysed the influence of introgression of the RNO4, RNO20 segments of SHR origin and RNO8 segment of PD/Cub origin (all previously shown to be involved in (dys)regulation of carbohydrate and lipid metabolism) onto the genetic background of a common progenitor, the Brown Norway (BN/Cub) rat. The differential segments were genetically characterized in the BN.PD-D8Rat39/D8Rat35 (BN-Lx, RNO8 congenic), BN.SHR-Il6/Cd36 (BN.SHR4, RNO4 congenic) and BN.PD-D8Rat39/D8Rat3, SHR-D4Mgh2/Cd36,SHR-D20Wox3/D20Mgh5 (BN-Lx 1K, RNO4, 8, 20 triple congenic) strains and their metabolic profiling was performed. After one week of high-sucrose diet, all congenic strains showed substantially higher levels of serum triglycerides and free fatty acids as well as impaired glucose tolerance in comparison with the BN/Cub progenitor strain. The BN-Lx 1K triple congenic strain displayed the most profound dyslipidemia, glucose intolerance and highest increase of triglyceridemia in response to high-sucrose diet overall, though accompanied with the significantly lowest adiposity index. These results further support the role of genes present within the studied chromosomal regions in observed metabolic disturbances. Furthermore, these findings point to the studied loci within the gene-gene and gene-environment interactions involved in pathogenesis of the insulin resistance syndrome. The set of defined congenic strains provides a possibility of assessing individual features of such a complex phenotype.

Objective: To localize quantitative trait loci (QTL) in an animal model that is potentially relevant to human hypertension., Design and Methods: Four congenic strains have been constructed by replacing various segments of the Dahl salt-sensitive (S) rat by those of the Lewis (LEW) rat. A marker-assisted approach was employed to facilitate this process. When these congenic strains were established, their blood pressures (BPs) were measured by telemetry and compared with that of the S rat. Moreover, a search was conducted to find possible intermediate phenotypes linking the BP effects of the QTL and other physiological traits., Results: Two BP QTL, designated as QTL1 and QTL2, have been mapped to the regions of 4.2 centiMorgans (cM) and less than 12.1 cM respectively on rat chromosome 10. The effects of both QTL correlate with cardiac, left ventricular and aortic hypertrophy. The effect of QTL1 is also associated with renal hypertrophy., Conclusion: The current study proved that multiple QTL exist in the region of Dahl rat chromosome 10. The identification of these QTL may help unravel the mechanisms underlying the pathogenesis of certain QTL in humans.

A congenic rat has a small genomic fragment transferred from a donor strain into a recipient strain. It is therefore possible to make a hypertensive congenic strain with a single unknown hypertensive gene originating from a genetic hypertensive model rat such as SHR. Such a congenic strain is useful in the search for hypertension genes in rats. It can be applied (1) to further dissection of QTL regions, (2) to determination of the boundaries of QTL regions, which is necessary for selection of positional candidate genes, and (3) to physiological and biochemical studies to get intermediate phenotypes.

The rat is a well-established model for hypertension research, in both physiologic and pharmacologic study. Quantitative trait loci (QTL) for blood pressure and related phenotypes have been described on every rat chromosome; therefore, more simplified models must be generated to identify and study the function of the gene(s) located by QTL analysis. Designer rat strains, such as congenic and consomic strains, which share phenotypic and genotypic characteristics with humans but with a greatly simplified genetic background, would yield a powerful platform for functional studies, especially when combined with microarray technologies. Development of these designer rats would result in better-defined disease models that can be used in physiologic and applied pharmacologic studies to better treat human essential hypertension.

A marker assisted selection protocol is presented that allows for the generation of congenic or consomic strains derived from a C57BL/6J:129S6/SvEvTac mixed strain background. The protocol uses defined primer pairs to generate amplicons that can be distinguished by non-denaturing agarose electrophoresis. Use of this application should result in substantial savings in time, effort, and cost for investigators in all areas of transgenic mouse research.

An increasing number of scientific articles report that the phenotype of a given single gene mutation in mice is modulated by the genetic background of the inbred strain in which the mutation is maintained. This effect is attributable to so-called modifier genes, which act in combination with the causative gene. The modulation of the phenotype can be major, as exemplified in the case of several mouse models of polycystic kidney disease. Because of the existence of inbred strains and the possibility of developing congenic strains, the effect of the genetic background can be analyzed in mice, including the identification of major modifier genes. Furthermore, by transferring a given mutation into different genetic backgrounds, mouse models can be manipulated with the aim of more accurately mimicking specific features of human diseases.

The laboratory rat is an important laboratory animal with multiple well-defined inbred strains, including some of the most widely used animal models of human diseases. Recent advances in the development of rat genetic resources will enable the exploitation of the full potential of rat models of human diseases and, in addition, the rat can provide useful information for comparative genomics of humans and mice. In the current review, we describe the development of congenics strains by introgression of differential chromosome segments from the Brown Norway (BN) rat to the genetic background of the spontaneously hypertensive rat (SHR). These SHR.BN-congenic strains and recombinant sublines derived from them were developed as a model system for genetic analysis of multifactorially determined pathophysiological and morphological conditions.

Previously, linkage analysis in several experimental crosses between hypertensive rat strains and their contrasting reference strains have identified a major quantitative trait locus (QTL) for blood pressure on rat chromosome 1 (Chr 1) spanning the Sa gene locus. In this study, we report the further dissection of this Chr 1 blood pressure QTL with congenic substitution mapping. To address whether the Sa gene represents a candidate gene for the Chr 1 blood pressure QTL, congenic strains were developed by introgressing high blood pressure QTL alleles from the stroke-prone spontaneously hypertensive rat (SHRSP) into the normotensive Wistar-Kyoto (WKY-1) reference strain. Congenic animals carrying a chromosomal segment from stroke-prone spontaneously hypertensive rats between genetic markers Mt1pa and D1Rat200 (including the Sa gene locus) show a significant increase in basal systolic and diastolic blood pressure compared with their normotensive Wistar-Kyoto progenitors (P<0.001, respectively), whereas congenic animals carrying a subfragment of this Chr 1 region defined by markers Mt1pa and D1Rat57 (also spanning the Sa gene) do not show elevated basal blood pressure levels (P=0.83 and P=0.9, respectively). Similar results were obtained for NaCl-induced blood pressure values. Thus, the blood pressure QTL on Chr 1 is located centromeric to the Sa gene locus in a region that is syntenic to human chromosome 11p15.4-p15.3. This region excludes the Sa as a blood pressure-elevating candidate gene locus on the basis of congenic substitution mapping approaches.

Genetic markers throughout the genome can be used to speed up 'recovery' of the recipient genome in the backcrossing phase of the construction of a congenic strain. The prediction of the genomic proportion during backcrossing depends on the assumptions regarding the distribution of chromosome segments, the population structure, the marker spacing and the selection strategy. In this study simulation was used to investigate the rate of recovery of the recipient genome for a mouse, Drosophila and Arabidopsis genome. It was shown that an incorrect assumption of a binomial distribution of chromosome segments, and failing to take account of a reduction in variance in genomic proportion due to selection, can lead to a downward bias of up to two generations in the estimation of the number of generations required for the formation of a congenic strain.

Recent evidence suggests that neurokinin (NK)-receptor activation may have a protective role in maintaining lung integrity when challenged by airborne toxicants such as sulfur dioxide, ozone, acrolein, or hydrocarbons. To investigate the effect of NK1-receptor activation on hydrocarbon-induced lung injury, B6.A.D. (Ahr d/Nats) mice received subchronic exposures to JP-8 jet fuel (JP-8). Lung injury was assessed by the analysis of pulmonary physiology, bronchoalveolar lavage fluid, and morphology. Hydrocarbon exposure to target JP-8 concentrations of 50 mg/m3, with saline treatment, was characterized by enhanced respiratory permeability to 99mTc-labeled diethylenetriaminepentaacetic acid, alveolar macrophage toxicity, and bronchiolar epithelial damage. Mice administered [Sar9,Met(O2)11]substance P, an NK1-receptor agonist, after each JP-8 exposure had the appearance of normal pulmonary values and tissue morphology. In contrast, endogenous NK1-receptor antagonism by CP-96345 administration exacerbated JP-8-enhanced permeability, alveolar macrophage toxicity, and bronchiolar epithelial injury. These data indicate that NK1-receptor activation may have a protective role in preventing the development of hydrocarbon-induced lung injury, possibly through the modulation of bronchiolar epithelial function.

The most difficult step in dissecting the molecular basis of a quantitative trait is proceeding from chromosomal locations associated with this trait (i.e., quantitative trait locus, QTL) to determining what gene(s) in the QTL region is causative. Using standard positional cloning methodology to identify candidate genes for a particular QTL has three drawbacks: 1) it is labor intensive; 2) defining variants in genes causing quantitative variation from sequence information alone is difficult or impossible; and 3) many (or most) genes in a particular chromosomal interval will not be relevant for a specific disease/trait because they are not expressed in critical candidate organs. Instead of positional cloning, we propose using a panel of congenic strains, where each carries an allele for a different QTL on a similar genetic background, in conjunction with identification of differentially-expressed genes in target organs of inbred strains of contrasting phenotype. This will identify genes having altered expression in organs critical to regulating blood pressure and the development of hypertension. Radiation hybrid mapping of such genes will result in a transcription map of differentially-expressed genes in a target organ of a rat model of genetic hypertension. This approach could rapidly identify genes mapping to genomic regions near QTL, which will be strong candidates to explain, in part, the observed strain differences in blood pressure. This novel approach, which uses a panel of congenic strains to facilitate the mapping and subsequent identification of differentially-expressed and QTL-associated genes, should be applicable to any genetic model for identifying candidate genes located near QTL, given the availability of a panel of congenic strains.