An enigmatic population of Alsodes (Anura, Alsodidae) from the Andes of central Chile with three species-level mitochondrial lineages.

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.

Plant-mediated RNAi silences midgut-expressed genes in congeneric lepidopteran insects in nature.

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 ß-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.

Isolation of a Genomic Region Affecting Most Components of Metabolic Syndrome in a Chromosome-16 Congenic Rat Model.

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.

High-resolution mapping of a novel rat blood pressure locus on chromosome 9 to a region containing the Spp2 gene and colocalization of a QTL for bone mass.

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.

Theoretical model for gene-gene, gene-environment, and gene-sex interactions based on congenic-strain analysis of blood pressure in Dahl salt-sensitive rats.

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.

Quantitative trait locus on distal chromosome 1 regulates the occurrence of spontaneous spike-wave discharges in DBA/2 mice.

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.

CD36-deficient congenic strains show improved glucose tolerance and distinct shifts in metabolic and transcriptomic profiles.

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.

Genetically alike Syrian hamsters display both bifoliate and trifoliate aortic valves.

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.

Generation of congenic and consomic rat strains.

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.

Generation of rat "supersonic" congenic/conplastic strains using superovulation and embryo transfer.

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.

Genetic mapping of vocalization to a series of increasing acute footshocks using B6.A consomic and B6.D2 congenic mouse strains.

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.

Behavioural analysis of congenic mouse strains confirms stress-responsive Loci on chromosomes 1 and 12.

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.

Fine mapping of a major QTL influencing morphine preference in C57BL/6 and DBA/2 mice using congenic strains.

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.

Interval-specific congenic animals for high-resolution quantitative trait loci mapping.

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.

Identification of candidate genes for alcohol preference by expression profiling of congenic rat strains.

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.

Reciprocal congenic lines for a major stroke QTL on rat chromosome 1.

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.

The use of mouse chromosome substitution strains to investigate the genetic regulation of pubertal timing.

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.

A set of highly informative rat simple sequence length polymorphism (SSLP) markers and genetically defined rat strains.

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.

Development of congenic rat strains for alcohol consumption derived from the alcohol-preferring and nonpreferring rats.

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.

Renal damage susceptibility and autoregulation in RF-1 and RF-5 congenic rats.

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.