The laboratory rat (Rattus norvegicus) is an indispensable tool in experimental medicine and drug development, having made inestimable contributions to human health. We report here the genome sequence of the Brown Norway (BN) rat strain. The sequence represents a high-quality 'draft' covering over 90% of the genome. The BN rat sequence is the third complete mammalian genome to be deciphered, and three-way comparisons with the human and mouse genomes resolve details of mammalian evolution. This first comprehensive analysis includes genes and proteins and their relation to human disease, repeated sequences, comparative genome-wide studies of mammalian orthologous chromosomal regions and rearrangement breakpoints, reconstruction of ancestral karyotypes and the events leading to existing species, rates of variation, and lineage-specific and lineage-independent evolutionary events such as expansion of gene families, orthology relations and protein evolution.

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.

We aimed to identify genetic variants associated with heart failure by using a rat model of the human disease. We performed invasive cardiac hemodynamic measurements in F2 crosses between spontaneously hypertensive heart failure (SHHF) rats and reference strains. We combined linkage analyses with genome-wide expression profiling and identified Ephx2 as a heart failure susceptibility gene in SHHF rats. Specifically, we found that cis variation at Ephx2 segregated with heart failure and with increased transcript expression, protein expression and enzyme activity, leading to a more rapid hydrolysis of cardioprotective epoxyeicosatrienoic acids. To confirm our results, we tested the role of Ephx2 in heart failure using knockout mice. Ephx2 gene ablation protected from pressure overload-induced heart failure and cardiac arrhythmias. We further demonstrated differential regulation of EPHX2 in human heart failure, suggesting a cross-species role for Ephx2 in this complex disease.

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Natriuretic peptides (NP) mediate their effects by activating membrane-bound guanylyl cyclase-coupled receptors A (NPR-A) or B (NPR-B). Whereas the pathophysiological role of NPR-A has been widely studied, only limited knowledge on the cardiovascular function of NPR-B is available. In vitro studies suggest antiproliferative and antihypertrophic actions of the NPR-B ligand C-type NP (CNP). Because of the lack of a specific pharmacological inhibitor, these effects could not clearly be attributed to impaired NPR-B signaling. Recently, gene deletion revealed a predominant role of NPR-B in endochondral ossification and development of female reproductive organs. However, morphological abnormalities and premature death of NPR-B-deficient mice preclude detailed cardiovascular phenotyping. In the present study, a dominant-negative mutant (NPR-B⌬KC) was used to characterize CNP-dependent NPR-B signaling in vitro and in transgenic rats. Here we demonstrate that reduced CNP-but not atrial NP-dependent cGMP response attenuates antihypertrophic potency of CNP in vitro. In transgenic rats, NPR-B⌬KC expression selectively reduced NPR-B but not NPR-A signaling. NPR-B⌬KC transgenic rats display progressive, blood pressure-independent cardiac hypertrophy and elevated heart rate. The hypertrophic phenotype is further enhanced in chronic volume overload-induced congestive heart failure. Thus, this study provides evidence linking NPR-B signaling to the control of cardiac growth.C-type natriuretic peptide ͉ knockdown