title: Identification of left ventricular mass QTL in the stroke-prone spontaneously hypertensive rat
Creators: name: Gilday, Kirsten
Publisher: name: University of Glasgow
Year: 2006
Subjects: subject: Genetics, bioinformatics.

description: Left ventricular hypertrophy (LVH) is accepted as an important independent predictor of adverse cardiovascular outcome; the aetiology includes a number of well-recognized causes but there is considerable interest in the genetics underlying cardiac hypertrophy. Data from several twin studies indicates that left ventricular mass index (LVMI) has a significant genetic basis that is most likely polygenic. Given the heterogeneity of the human condition, there has been little progress made towards identification of the genes involved, in this now common disease state. As an adjuvant to current human studies, inbred animal models have been developed which in turn have led to the identification of quantitative trait loci (QTL), via investigation using a genome wide strategy. This generally involves high fidelity phenotyping of large segregating F2 populations, derived by crossing inbred strains of sufficiently differing phenotype and subsequent genotyping using a wide selection of polymorphic microsatellite markers spread across the entire rat genome. The research described in this thesis incorporated an improved analysis of a previous genome wide scan, to confirm and identify QTL containing determinants of left ventricular hypertrophy in the Glasgow SHRSP x WKY F2 cross. This genome wide scan was carried out in 134 F2 hybrids (male: female = 65:69). Systolic and diastolic blood pressure was measured by radio-telemetry at baseline and after a 3 week 1% salt challenge in addition to heart rate, motor activity and pulse pressure. Other phenotype data included body weight, heart and LV weight and plasma renin activity. QTL affecting a given phenotype were mapped relative to an improved genetic linkage map for rat chromosome 14, with the aid of JoinMap 3.0, MapManager QTXb and Windows QTL Cartographer software. The original method of single marker analysis was used initially to test previous and newly acquired genotype data and confirm the cited LVMI QTL on rat chromosome 14. More stringent and complex statistical approaches were integrated in analysis resulting in detection of a second QTL for LVMI at marker D14Got23 and a single QTL for cardiac mass at marker D14Woxl4. The identification of QTL, although a fundamental process, is only the initial step towards the end objective of gene identification. The next logical step is the physical capture and confirmation of QTL with the production of congenic strains and substrains. In this thesis, the process of verifying the chromosome 14 QTL began with the generation of congenic strains, using a marker assisted 'speed' congenic strategy, previously validated in rats by our group. This was achieved by backcross breeding two inbred rat strains (SHRSP X WKY) and introgression of marker delineated regions of chromosome 14, from one background into the recipient genome and vice versa. Complete homozygosity of the background genetic markers (n=168) was achieved after 4 backcross generations. In the time line allowed, it was not possible to achieve a fixed congenic line however based on data provided from QTL analysis it was possible to generate and analyse preliminary phenotype data from backcross 4 males on the SHRSP background. The initial readings from this pilot study provide physical evidence that substituting a portion of WKY chromosome 14 with SHRSP results in a reduced LVMI, despite equivalent systolic blood pressure. (Abstract shortened by ProQuest.).