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Mapping of quantitative trait loci for blood pressure and cardiac mass in the rat by genome scanning of recombinant inbred strains.

In the HXB and BXH recombinant inbred strains derived from the spontaneously hypertensive rat and the normotensive Brown Norway rat, we determined the strain distribution patterns of 500 genetic markers to scan the rodent genome for quantitative trait loci regulating cardiac mass and blood pressure. The markers spanned approximately 1,139 cM of the genome and were tested for correlations with left ventricular mass adjusted for body weight, and with systolic, diastolic, and mean arterial pressures. The marker for the dopamine 1A receptor (Drd1a) on chromosome 17 showed the strongest correlation with left ventricular heart weight (P = .00038, r = -0.59) and the relationship to heart weight was independent of blood pressure. The markers showing the strongest correlations with systolic, diastolic, and mean arterial pressure were D19Mit7 on chromosome 19 (P = .0012, r = .55), D2N35 on chromosome 2 (P = .0008, r = .56), and Il6 on chromosome 4 (P = .0018, r = .53), respectively. These studies demonstrate that the HXB and BXH strains can be effectively used for genome scanning studies of complex traits and have revealed several chromosome regions that may be involved in the genetic control of blood pressure and cardiac mass in the rat.

A genetic linkage map of the rat derived from recombinant inbred strains

We have constructed a genetic linkage map in the rat by analyzing the strain distribution patterns of 500 genetic markers in a large set of recombinant inbred strains derived from the spontaneously hypertensive rat and the Brown-Norway rat (HXB and BXH recombinant inbred strains). 454 of the markers could be assigned to specific chromosomes, and the amount of genome covered by the mapped markers was estimated to be 1151 centimorgans. By including a variety of morphologic, biochemical, immunogenetic, and molecular markers, the current map integrates and extends existing linkage data and should facilitate rat gene mapping and genetic studies of hypertension and other complex phenotypes of interest in the HXB and BXH recombinant inbred strains.

Genetic isolation of a region of chromosome 8 that exerts major effects on blood pressure and cardiac mass in the spontaneously hypertensive rat.

The spontaneously hypertensive rat (SHR) is the most widely studied animal model of essential hypertension. Despite > 30 yr of research, the primary genetic lesions responsible for hypertension in the SHR remain undefined. In this report, we describe the construction and hemodynamic characterization of a congenic strain of SHR (SHR-Lx) that carries a defined segment of chromosome 8 from a normotensive strain of Brown-Norway rats (BN-Lx strain). Transfer of this segment of chromosome 8 from the BN-Lx strain onto the SHR background resulted in substantial reductions in systolic and diastolic blood pressure and cardiac mass. Linkage and comparative mapping studies indicate that the transferred chromosome segment contains a number of candidate genes for hypertension, including genes encoding a brain dopamine receptor and a renal epithelial potassium channel. These findings demonstrate that BP regulatory gene(s) exist within the differential chromosome segment trapped in the SHR-Lx congenic strain and that this region of chromosome 8 plays a major role in the hypertension of SHR vs. BN-Lx rats.

The rat renin gene: assignment to chromosome 13 and linkage to the regulation of blood pressure.

It has recently been suggested that in the rat, sequence variation in the renin gene or closely linked genes may have the capacity to affect blood pressure and contribute to the pathogenesis of hypertension. To map the chromosomal location of the rat renin gene and to investigate its relationship to the inheritance of increased blood pressure, we studied a panel of rat x mouse somatic cell hybrids and a large set of recombinant inbred (RI) strains derived from spontaneously hypertensive rats (SHR) and normotensive Brown-Norway (BN) rats. We have found that in the rat, the renin gene is located on chromosome 13 and that it belongs to a conserved synteny group located on chromosome 1 in man and mouse. We have also found the median blood pressure of the RI strains that inherited the renin allele of the SHR to be greater than that of the RI strains that inherited the renin allele of the normotensive BN rat. These findings, together with the results of previous studies, suggest that in the rat, sequence variation in the renin gene, or in genes linked to the renin locus on chromosome 13, may have the capacity to affect blood pressure.

Mapping and sequence analysis of the gene encoding the beta subunit of the epithelial sodium channel in experimental models of hypertension.

Objective: To investigate whether mutations in the beta subunit of the epithelial sodium channel (Scnn1b) contribute to the pathogenesis of hypertension in the spontaneously hypertensive rat (SHR) and the Dahl salt-sensitive rat. Methods: Chromosome mapping was performed by somatic cell hybrid analysis and by linkage analysis in recombinant inbred strains derived from SHR and Brown-Norway rats. Cosegregation analysis was performed by testing for correlations between blood pressure and Scnn1b genotypes in these strains. DNA sequencing was performed on cDNAs prepared from reverse-transcribed messenger RNA derived from rat kidney. Results: The Scnnib gene was closely linked to the Sa gene on rat chromosome 1. Blood pressure correlated significantly with Scnn1b gene in the recombinant inbred strains. Analysis of near full-length Scnn1b cDNAs from SHR and Dahl rats failed to reveal any coding sequence mutations that could affect the predicted amino acid sequence of the Scnnib protein. Conclusion: The Scnn1b gene maps near the Sa gene in a region of rat chromosome 1 involved in the inherited control of blood pressure. If disordered activity of the epithelial cell sodium channel contributes to the pathogenesis of hypertension in the SHR or Dahl models, it must stem from genetic lesions in sequences that regulate Scnn1b function or in sequences important to the structure or function of the other sodium channel subunits.

Assignment of rat linkage group V to chromosome 19 by single-strand conformation polymorphism analysis of somatic cell hybrids

The rat provides a number of important models of human genetic disease; however, the rat genetic map has not been extensively developed. Although most rat chromosomes carry several gene assignments, some major linkage groups (LG) remain to be mapped. To determine the chromosome location of the largest unmapped linkage group in the rat (LG V containing multiple carboxylesterase loci), we used single-strand conformation polymorphism analysis to identify the rat esterase-10 gene in a panel of rat x mouse somatic cell hybrids. We found that the carboxylesterase gene family and hence LG V are located on rat chromosome 19. We have also confirmed the assignment of the angiotensinogen gene to rat chromosome 19 and have used a large set of recombinant inbred strains to map two anonymous variable number of tandem repeat (VNTR) markers to this chromosome. The current findings bring the total number of genes assigned to rat chromosome 19 from 3 to 19 and provide further evidence of substantial homology between this chromosome and chromosome 8 in the mouse.

Genetic isolation of a blood pressure quantitative trait locus on chromosome 2 in the spontaneously hypertensive rat.

Objectives Total genome scans of genetically segregating populations derived from the spontaneously hypertensive rat (SHR) and other rat models of hypertension have suggested the presence of quantitative trait loci (QTL) regulating blood pressure and cardiac mass on multiple chromosomes, including chromosome 2. The objective of the current study was to directly test for the presence of a blood pressure QTL on rat chromosome 2. Design A new congenic strain was derived by replacing a segment of chromosome 2 in the SHR between D2Rat171 and D2Arb24 with the corresponding chromosome segment from the normotensive Brown Norway rat. Arterial pressures were directly monitored in conscious rats by radiotelemetry. Results We found that the SHR congenic strain (SHR-2) carrying a segment of chromosome 2 from the Brown Norway rat had significantly lower systolic and diastolic blood pressures than the SHR progenitor strain. The attenuation of hypertension in the SHR-2 congenic strain versus the SHR progenitor strain was accompanied by significant amelioration of cardiac hypertrophy. Conclusions These findings demonstrate that gene(s) with major effects on blood pressure exist in the differential segment of chromosome 2 trapped within the new SHR.BN congenic strain.

Rat chromosome 1 : Regional localization of seven genes (Slc9a3, Srd5a1, Esr, Tcp1, Grik5, Tnnt3, Jak2) and anchoring of the genetic linkage map to the cytogenetic map

Seven genes were regionally localized on rat Chromosome (Chr) 1, from 1p11 to 1q42, and two of these genes were also included in a linkage map. This mapping work integrates the genetic linkage map and the cytogenetic map, and allows us to orient the linkage map with respect to the centromere, and to deduce the approximate position of the centromere in the linkage map. These mapping data also indicate that the Slc9a3 gene, encoding the Na+/H+ exchanger 3, is an unlikely candidate for the blood pressure loci assigned to rat Chr 1. These new localizations expand comparative mapping between rat Chr 1 and mouse or human chromosomes.