Genetic mapping and characterization of the bleeding disorder in the fawn-hooded hypertensive rat.

Release of platelet dense granule contents occurs in response to vascular injury, playing an important role in platelet aggregation and primary hemostasis. Abnormalities of the platelet dense granules results in a bleeding disorder of variable severity termed "storage pool defect" (SPD). We have examined the fawn-hooded hypertensive (FHH) rat as a model of SPD in order to genetically map the locus (Bd) responsible for prolonged bleeding. Platelet function assays of the FHH rat confirmed the presence of a platelet dense granule SPD. However electron microscopy and lysosomal enzyme assays indicated differences between the FHH rat and other rodent models of SPD. Genetic mapping through the use of congenic FHH rats localized the Bd locus to an approximately 1 cM region on rat chromosome 1. Through the use of comparative mapping between species and analysis of the initial draft of the rat genome assembly, six known and thirty-four putative genes were identified in the Bd locus. None of these genes have been previously implicated in platelet function. Therefore positional cloning of the gene responsible for the bleeding disorder in the FHH rat will lead to new insights in platelet physiology, with implications for diagnosis and management of hemostatic and thrombotic disorders.

Implications of circadian gene expression in kidney, liver and the effects of fasting on pharmacogenomic studies.

Pharmacogenomics offers the potential to define metabolic pathways and to provide increased knowledge of drug actions. We studied relative levels of gene expression in the rat using a microarray with 8448 rat UniGenes (1928 known genes, 6520 unknown ESTs) in the liver and kidney as a function of time of day and then of feeding regime, which are common variables in preclinical pharmacogenomic studies. We identified 597 genes, including several key metabolic pathways, whose relative expression levels are significantly affected by time of day: expression of some was further modified by feeding state. These would have sparked interest in a pharmacogenomic study. Our study demonstrates that two common variables in pharmacogenomic studies can have dramatic effects on gene expression. This study provides investigators with baseline information for both kidney and liver with respect to 'normal' changes in gene expression influenced by time of day and feeding state. It also identifies 18 new genes that should be investigated for a role in circadian rhythms in peripheral tissues.

Gene expression profiling leads to identification of GLI1-binding elements in target genes and a role for multiple downstream pathways in GLI1-induced cell transformation.

The zinc finger transcription factor GLI1, which mediates Sonic hedgehog signaling during development, is expressed in several human cancers, including basal cell carcinoma, medulloblastoma, and sarcomas. We identified 147 genes whose levels of expression were significantly altered in RNA obtained from cells demonstrating a transformed phenotype with stable GLI1 expression or stable Ha-ras expression. Comparison of expression profiles from GLI1- and Ha-ras-expressing cells established a set of genes unique to GLI1-induced cell transformation. Thirty genes were altered by stable GLI1 expression, and 124 genes were changed by stable Ha-ras expression. Seven genes had altered expression levels in both GLI1- and Ha-ras-expressing cells. Genes whose expression was altered by GLI1 included cell cycle genes, cell adhesion genes, signal transduction genes, and genes regulating apoptosis. GLI1 consensus DNA-binding sequences were identified in the 5' regions of cyclin D2, IGFBP-6, osteopontin, and plakoglobin, suggesting that these genes represent immediate downstream targets. Gel shift analysis confirmed the ability of the GLI1 protein to bind these sequences. Up-regulation of cyclin D2 and down-regulation of plakoglobin were demonstrated in GLI1-amplified compared with non-amplified human rhabdomyosarcoma cells. Many of the GLI1 targets with known function identified in this study increase cell proliferation, indicating that GLI1-induced cell transformation occurs through multiple downstream pathways.

Evidence of gene-gene interactions in the genetic susceptibility to renal impairment after unilateral nephrectomy.

The number of patients with hypertension-associated end-stage renal failure (ESRF) continues to increase despite improved antihypertensive management and early detection programs. Variation for the development of renal complications in hypertension may reflect independent genetic susceptibility to ESRF. The genetically hypertensive fawn-hooded rat is characterized by the early presence of systolic hypertension, glomerular hypertension, progressive proteinuria (UPV), and focal glomerulosclerosis (FGS), resulting in premature death as a result of renal failure. In the present study, the genetic basis of hypertension-associated ESRF in an F2 intercross consisting of 337 animals, in which systolic BP, UPV, albuminuria, and FGS, were studied at 8 wk after a unilateral nephrectomy performed at 5 to 6 wk of age. A total genome scan, consisting of 418 markers, was used to identify regions that contribute to the pathogenesis of UPV and FGS. Linkage analysis revealed five loci involved in the development of renal impairment. Of these five, two (Rf-1, Rf-2) had been identified previously. There seems to be strong interactive effects between the various loci and their impact on UPV and the other parameters of renal impairment, as well as an interaction with BP. In particular, Rf-1 seems to play a major role in determining the severity of the disease. This study is the first to report the interaction of more than two loci to produce progressive renal failure, suggesting that the genetic dissection of renal failure in humans will require understanding of how multiple genes interact with each other and BP to produce ESRF.