Rat Recombinant Inbred Strains Research Articles

Cap analysis of gene expression reveals alternative promoter usage in a rat model of hypertension.

The role of alternative promoter usage in tissue-specific gene expression has been well established; however, its role in complex diseases is poorly understood. We performed cap analysis of gene expression (CAGE) sequencing from the left ventricle of a rat model of hypertension, the spontaneously hypertensive rat (SHR), and a normotensive strain, Brown Norway to understand the role of alternative promoter usage in complex disease. We identified 26,560 CAGE-defined transcription start sites in the rat left ventricle, including 1,970 novel cardiac transcription start sites. We identified 28 genes with alternative promoter usage between SHR and Brown Norway, which could lead to protein isoforms differing at the amino terminus between two strains and 475 promoter switching events altering the length of the 5' UTR. We found that the shift in Insr promoter usage was significantly associated with insulin levels and blood pressure within a panel of HXB/BXH recombinant inbred rat strains, suggesting that hyperinsulinemia due to insulin resistance might lead to hypertension in SHR. Our study provides a preliminary evidence of alternative promoter usage in complex diseases.

Expression profiling of Nme7 interactome in experimental models of metabolic syndrome.

Nucleoside diphosphate kinase 7, non-metastatic cells 7 (NME7) is an acknowledged member of ciliome and is involved in the biogenesis or function of cilia. As obesity and diabetes are common in several ciliopathies, we aimed to analyze changes of gene expression within Nme7 interactome in genetically designed rat models of metabolic syndrome. We assessed the liver transcriptome by Affymetrix microarrays in adult males of 14 PXO recombinant inbred rat strains and their two progenitor strains, SHR-Lx and BXH2. In the strains with the lowest expression of Nme7, we have identified significant enrichment of transcripts belonging to Nme7 interactome. In the subsequent network analysis, we have identified three major upstream regulators - Hnf4a, Ppara and Nr1h4 and liver steatosis (p=0.0001) and liver necrosis/cell death (apoptosis of liver cells, p=0.0003) among the most enriched Tox categories. The mechanistic network reaching the top score showed substantial overlap with Assembly of non-motile cilium and Glucose metabolism disorder gene lists. In summary, we show in a genetic model of metabolic syndrome that rat strains with the lowest expression of Nme7 present gene expression shifts of Nme7 interactome that are perturbing networks relevant for carbohydrate and lipid metabolism as well as ciliogenesis.

Systems Genetics Approaches in Rat Identify Novel Genes and Gene Networks Associated With Cardiac Conduction.

BackgroundElectrocardiographic (ECG) parameters are regarded as intermediate phenotypes of cardiac arrhythmias. Insight into the genetic underpinnings of these parameters is expected to contribute to the understanding of cardiac arrhythmia mechanisms. Here we used HXB/BXH recombinant inbred rat strains to uncover genetic loci and candidate genes modulating ECG parameters.Methods and Results RR interval, PR interval, QRS duration, and QTc interval were measured from ECGs obtained in 6 male rats from each of the 29 available HXB/BXH recombinant inbred strains. Genes at loci displaying significant quantitative trait loci (QTL) effects were prioritized by assessing the presence of protein‐altering variants, and by assessment of cis expression QTL (eQTL) effects and correlation of transcript abundance to the respective trait in the heart. Cardiac RNA‐seq data were additionally used to generate gene co‐expression networks. QTL analysis of ECG parameters identified 2 QTL for PR interval, respectively, on chromosomes 10 and 17. At the chromosome 10 QTL, cis‐eQTL effects were identified for Acbd4, Cd300lg, Fam171a2, and Arhgap27; the transcript abundance in the heart of these 4 genes was correlated with PR interval. At the chromosome 17 QTL, a cis‐eQTL was uncovered for Nhlrc1 candidate gene; the transcript abundance of this gene was also correlated with PR interval. Co‐expression analysis furthermore identified 50 gene networks, 6 of which were correlated with PR interval or QRS duration, both parameters of cardiac conduction.ConclusionsThese newly identified genetic loci and gene networks associated with the ECG parameters of cardiac conduction provide a starting point for future studies with the potential of identifying novel mechanisms underlying cardiac electrical function.

The sequenced rat brain transcriptome--its use in identifying networks predisposing alcohol consumption.

A quantitative genetic approach, which involves correlation of transcriptional networks with the phenotype in a recombinant inbred (RI) population and in selectively bred lines of rats, and determination of coinciding quantitative trait loci for gene expression and the trait of interest, has been applied in the present study. In this analysis, a novel approach was used that combined DNA-Seq data, data from brain exon array analysis of HXB/BXH RI rat strains and six pairs of rat lines selectively bred for high and low alcohol preference, and RNA-Seq data (including rat brain transcriptome reconstruction) to quantify transcript expression levels, generate co-expression modules and identify biological functions that contribute to the predisposition of consuming varying amounts of alcohol. A gene co-expression module was identified in the RI rat strains that contained both annotated and unannotated transcripts expressed in the brain, and was associated with alcohol consumption in the RI panel. This module was found to be enriched with differentially expressed genes from the selected lines of rats. The candidate genes within the module and differentially expressed genes between high and low drinking selected lines were associated with glia (microglia and astrocytes) and could be categorized as being related to immune function, energy metabolism and calcium homeostasis, as well as glial-neuronal communication. The results of the present study show that there are multiple combinations of genetic factors that can produce the same phenotypic outcome. Although no single gene accounts for predisposition to a particular level of alcohol consumption in every animal model, coordinated differential expression of subsets of genes in the identified pathways produce similar phenotypic outcomes. The datasets supporting the results of the present study are available at http://phenogen.ucdenver.edu.

Is the Alcohol Deprivation Effect Genetically Mediated? Studies with HXB/BXH Recombinant Inbred Rat Strains

Two features of alcohol addiction that have been widely studied in animal models are relapse drinking following periods of alcohol abstinence and the escalation of alcohol consumption after chronic continuous or intermittent alcohol exposure. The genetic contribution to these phenotypes has not been systematically investigated. HXB/BXH recombinant inbred (RI) rat strains were given access to alcohol sequentially as follows: alcohol (10%) as the only fluid for 1 week; alcohol (10%) and water in a 2-bottle choice paradigm for 7 weeks ("pre-alcohol deprivation effect [ADE] alcohol consumption"); 2 weeks of access to water only (alcohol deprivation); and 2 weeks of reaccess to 10% alcohol and water ("post-ADE alcohol consumption"). The periods of deprivation and reaccess to alcohol were repeated 3 times. The ADE was defined as the amount of alcohol consumed in the first 24 hours after deprivation minus the average daily amount of alcohol consumed in the week prior to deprivation. Heritability of the phenotypes was determined by analysis of variance, and quantitative trait loci (QTLs) were identified. All strains showed increased alcohol consumption, compared to the predeprivation period, in the first 24 hours after each deprivation (ADE). Broad-sense heritability of the ADEs was low (ADE1, 9.1%; ADE2, 26.2%; ADE3, 16.3%). Alcohol consumption levels were relatively stable over weeks 2 to 7. Post-ADE alcohol consumption levels consistently increased in some strains and were decreased or unchanged in others. Heritability of pre- and post-ADE alcohol consumption was high and increased over time (week 2, 38.5%; week 7, 51.1%; week 11, 56.8%; week 15, 63.3%). QTLs for pre- and post-ADE alcohol consumption were similar, but the strength of the QTL association with the phenotype decreased over time. In the HXB/BXH RI rat strains, genotypic variance does not account for a large proportion of phenotypic variance in the ADE phenotype (low heritability), suggesting a role of environmental factors. In contrast, a large proportion of the variance across the RI strains in pre- and post-ADE alcohol consumption is due to genetically determined variance (high heritability).

Abstract 18962: MrpL48 is Associated with Impaired Mitochondrial Function and Blood Pressure Regulation in Genetic Hypertension

BACKGROUND: Aerobic metabolism has been implicated in the pathogenesis of cardiovascular diseases but the underlying genes that contribute to this process are incompletely understood. Here, we identified a novel gene within a previously mapped blood pressure QTL on rat chromosome 1 and demonstrate that the nuclear encoded mitochondrial ribosomal protein 48 (MrpL48) contributes to impaired aerobic metabolism and elevated blood pressure phenotypes in rats and mice. METHODES: We measured telemetric blood pressure and generated genome wide expression signatures in kidneys of 30 rat recombinant inbred strains that were established from the spontaneously hypertensive rat (SHR) and the BN normotensive reference strain as well as from chromosome 1 congenic rats spanning the chromosome 1 blood pressure QTL. This led to a positional candidate gene which was subsequently analyzed at the molecular level. We investigated mitochondrial bioenergetic processes and translation in vitro and ex vivo and subsequently monitored blood pressure in MrpL48 knockout mice by telemetry. RESULTS: Expression analysis in the congenic line as well as the HXB/BXH recombinant inbred panel showed that variation at the MrpL48 locus resulted in altered gene expression and significantly correlated with blood pressure levels. We demonstrated that MrpL48 plays an important role in mitochondrial translation and subsequently mitochondrial function in vitro and in vivo. MrpL48 knockout mice showed significantly increased pulse pressure levels. CONCLUSION: Our findings suggest that MrpL48 plays an important role in mitochondrial dysfunction and blood pressure regulation and identifies a so far unappreciated mechanism of blood pressure regulation.

Integrated genomic approaches to identification of candidate genes underlying metabolic and cardiovascular phenotypes in the spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) is a widely used rodent model of hypertension and metabolic syndrome. Previously we identified thousands of cis-regulated expression quantitative trait loci (eQTLs) across multiple tissues using a panel of rat recombinant inbred (RI) strains derived from Brown Norway and SHR progenitors. These cis-eQTLs represent potential susceptibility loci underlying physiological and pathophysiological traits manifested in SHR. We have prioritized 60 cis-eQTLs and confirmed differential expression between the parental strains by quantitative PCR in 43 (72%) of the eQTL transcripts. Quantitative trait transcript (QTT) analysis in the RI strains showed highly significant correlation between cis-eQTL transcript abundance and clinically relevant traits such as systolic blood pressure and blood glucose, with the physical location of a subset of the cis-eQTLs colocalizing with “physiological” QTLs (pQTLs) for these same traits. These colocalizing correlated cis-eQTLs (c3-eQTLs) are highly attractive as primary susceptibility loci for the colocalizing pQTLs. Furthermore, sequence analysis of the c3-eQTL genes identified single nucleotide polymorphisms (SNPs) that are predicted to affect transcription factor binding affinity, splicing and protein function. These SNPs, which potentially alter transcript abundance and stability, represent strong candidate factors underlying not just eQTL expression phenotypes, but also the correlated metabolic and physiological traits. In conclusion, by integration of genomic sequence, eQTL and QTT datasets we have identified several genes that are strong positional candidates for pathophysiological traits observed in the SHR strain. These findings provide a basis for the functional testing and ultimate elucidation of the molecular basis of these metabolic and cardiovascular phenotypes.

Genetical genomic determinants of alcohol consumption in rats and humans.

BackgroundWe have used a genetical genomic approach, in conjunction with phenotypic analysis of alcohol consumption, to identify candidate genes that predispose to varying levels of alcohol intake by HXB/BXH recombinant inbred rat strains. In addition, in two populations of humans, we assessed genetic polymorphisms associated with alcohol consumption using a custom genotyping array for 1,350 single nucleotide polymorphisms (SNPs). Our goal was to ascertain whether our approach, which relies on statistical and informatics techniques, and non-human animal models of alcohol drinking behavior, could inform interpretation of genetic association studies with human populations.ResultsIn the HXB/BXH recombinant inbred (RI) rats, correlation analysis of brain gene expression levels with alcohol consumption in a two-bottle choice paradigm, and filtering based on behavioral and gene expression quantitative trait locus (QTL) analyses, generated a list of candidate genes. A literature-based, functional analysis of the interactions of the products of these candidate genes defined pathways linked to presynaptic GABA release, activation of dopamine neurons, and postsynaptic GABA receptor trafficking, in brain regions including the hypothalamus, ventral tegmentum and amygdala. The analysis also implicated energy metabolism and caloric intake control as potential influences on alcohol consumption by the recombinant inbred rats. In the human populations, polymorphisms in genes associated with GABA synthesis and GABA receptors, as well as genes related to dopaminergic transmission, were associated with alcohol consumption.ConclusionOur results emphasize the importance of the signaling pathways identified using the non-human animal models, rather than single gene products, in identifying factors responsible for complex traits such as alcohol consumption. The results suggest cross-species similarities in pathways that influence predisposition to consume alcohol by rats and humans. The importance of a well-defined phenotype is also illustrated. Our results also suggest that different genetic factors predispose alcohol dependence versus the phenotype of alcohol consumption.

Evaluation of LEXF/FXLE rat recombinant inbred strains for genetic dissection of complex traits

Recombinant inbred (RI) strains are formed from an outcross between two well-characterized inbred stains followed by at least 20 generations of inbreeding. RI strains can be utilized for the analysis of many complex phenotypic traits. The LEXF/FXLE RI strain set consists of 34 RI strains derived by reciprocal crossing of LE/Stm and F344/Stm. Here we report on genetic dissections of complex traits using this RI set and their parental strains. We have developed strain distribution patterns for 232 informative simple sequence length polymorphism markers. The framework map covers the rat genome except for chromosome Y. Seventy-six phenotype parameters, which included physiological and behavioral traits, were examined for these RI lines. Quantitative trait locus (QTL) analysis of these parameters revealed 27 significant and 91 suggestive QTLs, illustrating the potential of this RI resource for the detection of underlying gene functions for various phenotypes. Although this RI set was originally developed to study susceptibility to chemical-induced tumors, it has been shown to be equally powerful for a wide spectrum of traits. The LEXF/FXLE RI strains have been deposited at the National Bio Resource Project for the Rat in Japan and are maintained under specific pathogen-free conditions. They are available at http://www.anim.med.kyoto-u.ac.jp/nbr.

Heritability and tissue specificity of expression quantitative trait loci.

Variation in gene expression is heritable and has been mapped to the genome in humans and model organisms as expression quantitative trait loci (eQTLs). We applied integrated genome-wide expression profiling and linkage analysis to the regulation of gene expression in fat, kidney, adrenal, and heart tissues using the BXH/HXB panel of rat recombinant inbred strains. Here, we report the influence of heritability and allelic effect of the quantitative trait locus on detection of cis- and trans-acting eQTLs and discuss how these factors operate in a tissue-specific context. We identified several hundred major eQTLs in each tissue and found that cis-acting eQTLs are highly heritable and easier to detect than trans-eQTLs. The proportion of heritable expression traits was similar in all tissues; however, heritability alone was not a reliable predictor of whether an eQTL will be detected. We empirically show how the use of heritability as a filter reduces the ability to discover trans-eQTLs, particularly for eQTLs with small effects. Only 3% of cis- and trans-eQTLs exhibited large allelic effects, explaining more than 40% of the phenotypic variance, suggestive of a highly polygenic control of gene expression. Power calculations indicated that, across tissues, minor differences in genetic effects are expected to have a significant impact on detection of trans-eQTLs. Trans-eQTLs generally show smaller effects than cis-eQTLs and have a higher false discovery rate, particularly in more heterogeneous tissues, suggesting that small biological variability, likely relating to tissue composition, may influence detection of trans-eQTLs in this system. We delineate the effects of genetic architecture on variation in gene expression and show the sensitivity of this experimental design to tissue sampling variability in large-scale eQTL studies.

Genetic relationship between placental and fetal weights and markers of the metabolic syndrome in rat recombinant inbred strains

Epidemiological studies have shown a clear link between fetal growth retardation and an increased propensity for later cardiovascular disease in adults. It has been hypothesized that such early fetal deprivation "programs" individuals toward a life-long metabolical "thrifty phenotype" that predisposes adults to such diseases. Here we test this hypothesis, and its possible genetic basis, in rat recombinant inbred (RI) strains that uniquely allow the longitudinal studies necessary for its testing. Placental and fetal weights were determined on day 20 of pregnancy in (at least) 6 litters from each of 25 available BXH/HXB RI strains and from their SHR and BN-Lx progenitors and were correlated with metabolic traits determined in adult rats from the same inbred lines. Quantitative trait loci (QTLs) associated with placental and fetal weights were identified by total genome scanning of RI strains using the Map Manager QTX program. Heritabilities of placental and fetal weights were 56% and 62%, respectively, and total genome scanning of RI strains revealed QTLs near the D1Rat266 marker on chromosome 1 and near the D15Rat101 marker on chromosome 15 that were significantly associated with fetal and placental weights respectively. Placental weights correlated with fetal weights (r = 0.60, P = 0.001), while reduced fetal weights correlated with increased insulin concentrations during glucose tolerance test (r = -0.71, P = 0.0001) and with increased serum triglycerides (r = -0.54, P = 0.006) in adult rats. Our results suggest that predisposition toward a thrifty phenotype associated with decreased placental weight and restricted fetal growth is in part genetically determined.

Genetic analysis of complex cardiovascular traits in the spontaneously hypertensive rat

Identification of the genetic determinants of common diseases is a major challenge for current biomedical research. Combining linkage analyses of essentially monogenic cis-regulated expression phenotypes with oligogenic intermediate physiological phenotypes represents a promising approach for identification of quantitative trait loci at the molecular level. In the present review, a genetic analysis of cardiovascular phenotypes studied at several levels of complexity in rat recombinant inbred strains is described.

Integrated transcriptional profiling and linkage analysis for identification of genes underlying disease

Integration of genome-wide expression profiling with linkage analysis is a new approach to identifying genes underlying complex traits. We applied this approach to the regulation of gene expression in the BXH/HXB panel of rat recombinant inbred strains, one of the largest available rodent recombinant inbred panels and a leading resource for genetic analysis of the highly prevalent metabolic syndrome. In two tissues important to the pathogenesis of the metabolic syndrome, we mapped cis- and trans-regulatory control elements for expression of thousands of genes across the genome. Many of the most highly linked expression quantitative trait loci are regulated in cis, are inherited essentially as monogenic traits and are good candidate genes for previously mapped physiological quantitative trait loci in the rat. By comparative mapping we generated a data set of 73 candidate genes for hypertension that merit testing in human populations. Mining of this publicly available data set is expected to lead to new insights into the genes and regulatory pathways underlying the extensive range of metabolic and cardiovascular disease phenotypes that segregate in these recombinant inbred strains.

Identification of quantitative trait Loci for anxiety and locomotion phenotypes in rat recombinant inbred strains.

Anxiety disorders are phenotypically complex and may involve multiple genetic influences on many neurotransmitter systems. Rodent tests used to investigate genetic influences on anxiety-like phenotypes have face and predictive validity as models for anxiety in humans. If multiple genes contribute additively to a trait, the trait will be continuously distributed and be amenable to detection of associations between allelic variation at specific chromosomal loci and the phenotypes being studied via quantitative trait loci (QTL) mapping. The elevated plus-maze test provides quantitative measures of both anxiety-like and locomotion phenotypes. Using this test, we assessed four phenotypes in a set of 22 rat recombinant inbred (RI) strains derived from Brown Norway (BN.Lx /Cub) and Spontaneously Hypertensive rat (SHR/Ola) progenitors. QTL analyses were used to determine whether allelic variation at specific chromosomal loci contribute significantly to RI strain-dependent variance in each phenotype. Significant QTL for an anxiety phenotype were found on chromosomes 2, 5, 6, and 7. For a phenotype reflecting both anxiety and locomotion, QTL were found on chromosomes 2, 7, and 8, while for a locomotion phenotype, significant QTL were found on chromosomes 3 and 18.

Genetic Models in Applied Physiology. HXB/BXH rat recombinant inbred strain platform: a newly enhanced tool for cardiovascular, behavioral, and developmental genetics and genomics.

This review deals with the largest set of rat recombinant inbred (RI) strains and summarizes past and recent accomplishments with this platform for genetic mapping and analyses of divergent and complex traits. This strain, derived by crossing the spontaneously hypertensive rat, SHR/Ola, with a Brown Norway congenic, BN-Lx, carrying polydactyly-luxate syndrome, is referred to as HXB/BXH. The RI strain set has been used for linkage and association studies to identify quantitative trait loci for numerous cardiovascular phenotypes, including arterial pressure, stress-elicited heart rate, and pressor response, and metabolic traits, including insulin resistance, dyslipidemia and glucose handling, and left ventricular hypertrophy. The strain's utility has been enhanced with development of a new framework marker-based map and strain distribution patterns of polymorphic markers. Quantitative trait loci for behavioral traits mapped include loci for startle motor response and habituation, anxiety and locomotion traits associated with elevated plus maze, and conditioned taste aversion. The polydactyly-luxate syndrome Lx mutation has allowed the study of alleles important to limb development and malformation phenotypes as well as teratogens. The RI strains have guided development of numerous congenic strains to test locus assignments and to study the effect of genetic background. Although these strains were originally developed to aid in studies of rat genetic hypertension and morphogenetic abnormalities, this rodent platform has been shown to be equally powerful for a wide spectrum of traits and endophenotypes. These strains provide a ready and available vehicle for many physiological and pharmacological studies.

Heart rate and blood pressure quantitative trait loci for the airpuff startle reaction.

The airpuff startle reaction is a probe of sensori-autonomic processing and is useful for studies of genetic control of stress-induced cardiovascular activity. Using a Wistar-Kyoto-Spontaneously Hypertensive Rat F2 cross, we reported an airpuff-elicited strain-dependent and trial-dependent bradycardia, the absence of which cosegregated with hypertension. Here, we use the mapping power of the HXB-BXH recombinant inbred rat strains (n=23) to locate quantitative trait loci (QTL) for this and associated cardiovascular phenotypes. Rats (12 weeks old), with indwelling femoral arterial catheters, were subjected to repeated airpuff startle stimuli (100 ms, 12.5 psi, 28 trials). Basal mean arterial pressure (MAP), delta MAP, and delta heart rate response to airpuff stimuli were analyzed as the average over 28 trials. There was a significant strain effect on the cardiovascular phenotypes measured. One QTL for the bradycardia elicited by the first airpuff stimulus was identified on chromosome 2 (D2rat 62/63; logarithm of odds [LOD] 2.9) mapping near a reported blood pressure locus. Further QTL were identified for basal MAP (RN08), stimulus-elicited tachycardia on trials 2 to 5 (RNO1 and RNO10), and delta MAP (RNO6). Our results indicate that chromosomes 1, 2, and 10 are involved in heart rate responses to airpuff startle stimulus, and chromosomes 6 and 8 are involved in pressor responses. This study is the first to identify stress-related heart rate loci and provides additional support for our prior cosegregation results. Furthermore, we have established the utility of this experimental paradigm to identify loci responsible for cardiovascular regulation during stress in genetic hypertensive models.

Mapping of quantitative trait loci (QTL) of differential stress gene expression in rat recombinant inbred strains.

Stress has been shown to be a major environmental contributor to cardiovascular diseases through its effects on blood pressure variability and cardiac function. The cellular stress response is characterized by the expression of specific heat stress genes (hsps), under the transcriptional control of heat shock transcription factors (HSTFs). The levels of hsp mRNA depend on the severity of the stress, with hstf1 acting as a stress sensor. The aim of this work was to evaluate the genetic contribution of the variability in hsp expression, and to identify its putative quantitative trait loci (QTL). Twenty recombinant inbred rat strains (RIS) were studied. The animals underwent a standardized, identical 1 h immobilization stress in restraint cages, followed by 1 h of rest before sacrifice. Total RNA was extracted from the heart kidneys and adrenals, and the mRNA levels of hsp27, hsp70, hsp84, hsp86 and hsp105 were measured. The strain distribution pattern (SDP) of hsp expression was correlated with that of 475 polymorphic markers distributed throughout the RIS genome. A polymorphism of rat hstf1 in RIS was used for its mapping in RIS. Despite an identical stress being applied to all strains, hsp expression showed up to a 1 2-fold gradient with little intra-strain variability, indicative of a strong genetic contribution to the trait Heritability ranged from 50 to 77% for most hsp genes in the three target organs. The continuous SDP of stress gene expression indicated the polygenic nature of the trait A common locus on chromosome 7 (at D7Cebrp187s3 marker) was consistently associated with all hsp expression in most of the organs [with a likelihood of odds (LOD) score of 3.0 for hsp27 expression]. We have mapped rat hstf1 on chromosome 7 at the same locus. Finally, the D4Mit19 marker was significantly associated with hsp84 expression in the heart (LOD score of 3.1). Two loci were linked with the differential expression of HSPs in response to immobilization stress in target organs of RIS. The chromosome 7 locus unveiled for all HSPs could explain up to 42% of the observed inter-strain variability of hsp levels in response to stress. We propose hstf1 as a positional candidate at this locus.

Newborn and adult recombinant inbred strains: A tool to search for genetic determinants of target organ damage in hypertension

It has been proposed that one of the primary events in the development of essential hypertension is a growth-related process initiated as early as during fetal development. Differences in kidney size have been observed between most rat models of hypertension and their respective controls. In this study, we analyzed relative kidney size (kidney weight/body wt) in a set of rat recombinant inbred strains (RIS) (N = 27) and their progenitors, the spontaneously hypertensive rat strain (SHR/Ola) and Brown Norway congenic strain (BN.1x), at two different ages, at birth and at 15 weeks. In the progenitors, the relative kidney weight was higher in the hypertensive than in the normotensive strain of both the newborn (P < 0.001) and adult (P < 0.001) animals. In the RIS, a significant correlation was found between the newborn and adult relative kidney weight (r = 0.49, P = 0.01), indicating that the two phenotypes share some of their genetic determinants. A total genome search of newborn and adult relative kidney weight was performed with a total of 453 genetic markers. These analyses revealed several suggestive quantitative trait loci (QTL), some of which were, indeed, significant for both newborn and adult relative kidney weight (such as, D3Mit9 on rat chromosome 3; r = -0.50, P < 0.01; r = -0.47, P < 0.01; respectively). Others, such as the locus on rat chromosome 1 (Rt6; r = -0.43, P < 0.05), were significant only for the adult relative kidney size. This QTL was found in close proximity to a region previously related to susceptibility to hypertensive renal disease in the fawn-hooded rat and, similarly to that study, its effect was found to be independent of blood pressure. Furthermore, a growth pattern of the kidneys after birth, evaluated as the difference between the newborn and adult relative kidney weight, was also subjected to total genome scan. Several suggestive QTL were identified. One of the most significant loci was found at the D1a marker on rat chromosome 17 (r = -0.51, P < 0.01), which was previously related to the determination of adult heart weight in the RIS. In conclusion, the current study demonstrates the usefulness of RIS in studies of hypertension-related phenotypes, some of which are abnormal before the development of high blood pressure. To better understand their role in the pathogenesis of hypertension, studies at different ages are needed, which are uniquely feasible in RIS.

A Genetic and Correlation Analysis of Liver Cholesterol Concentration in Rat Recombinant Inbred Strains Fed a High Cholesterol Diet

Liver cholesterol concentration in rats fed a high cholesterol diet, is under genetic control which is supported by significant differences observed among inbred strains. For instance, the Brown Norway (BN-Lx/Cub) rat developed a twofold higher liver cholesterol concentration than the spontaneously hypertensive rat (SHR/Ola). In the current study, we used 30 recombinant inbred (RI) strains, derived from BN-Lxand SHR progenitors, to locate quantitative trait loci (QTL) that are responsible for differences in liver cholesterol concentrations between the BN-Lxand SHR strains. The heritability of liver cholesterol was estimated to be 0.55 and a significant association was detected between concentration of liver cholesterol and theD10Cebrp1016s2marker on chromosome 10 (lod score = 3.3); this putative QTL was responsible for nearly 64% of additive genetic variability and thus represents a major genetic determinant of liver cholesterol concentration. Liver cholesterol concentrations significanrly correlated with intermediate density lipoprotein (IDL) cholesterol levels.

Impact of RT1.C-encoded MHC antigens on host-versus-graft and graft versus-host reactions in a model of small bowel transplantation in the rat

Non-classical MHC-class I antigens encoded by rat RT1.C region genes have been demonstrated to have a strong in vitro and in vivo potential to trigger natural killer (NK) cell activity. 1,2 NK cells comprise a unique entity of lymphocytes that act as an important effector arm of the innate immune response. Nevertheless, NK cells distinguish non-self MHC-class I molecules on target cells in an allospecific fashion. 3 Target cell recognition of non-self MHC-class I molecules encoded by the RTI.C-locus of the RT1 gene complex induces activation of NK cells without the need of a prior sensitization process, an immune mechanism also referred to as allogeneic lymphocyte cytotoxicity (ALC). 4 By virtue of its vast mass of lymphatic tissue, heterotopic small bowel transplantation (SBTx) was performed between intra-MHC class I recombinant inbred rat strains, differing only at the RT1.C-locus, in order to show the impact of NK-related immune responses for this model of solid organ transplantation.