Genetic Screening of F2 WKY/WKHA Crosses Reveals That the Traits of High Ventricular Mass and Low Ventricular ANF Concentration Are Linked to a Locus on Chromosome 5 That Overlaps with the Locus of the Natriuretic Peptide Precusor A (Nppa) Gene.
The cardiac ventricular mass of WKHA inbred rats is higher than that of WKY rats, yet both strains exhibit normal and identical values of blood pressure (as verified by telemetry). We have shown previously in the F2 male progeny of WKY/WKHA crosses that low ventricular concentration of atrial natriuretic factor (ANF) co-segregated significantly with high cardiac ventricular mass (Circ. Res. 84:1453-1458, 1999). To extend these findings, we have performed a scan of the whole genome of 158 rats originating from the male F2 progeny of the WKY/WKHA cross. By linkage analysis, we have identified on chromosome 5 one QTL that was linked to left ventricular ANF concentration (QTLANF) with a LOD score of 17, and one QTL that was was linked to left ventricular mass (QTLLVM) with a LOD score of 3.5. The 2-LOD confidence interval for the location of QTLANF ranged from positions 94 to 104 cM, which overlaps partly with the 2-LOD confidence interval for the location of QTLLVM between positions 80 to 103 cM. The locus of the natriuretic peptide precursor A (Nppa) gene (at about 100 cM) is located within an interval covered by both QTL’s. Sequencing of a 600 bp fragment of the promoter regions of the Nppa genes from WKY and WKHA revealed that there were single nucleotide polymorphisms within two different regions of the promoters. These mutations lie within regions known to contain response elements to transcription factors, but the results of ongoing experiments are needed to determine whether they can affect the ability of the respective promoters to drive the expression of reporter genes in transfected cardiomyocytes. Altogether, these data suggest that the Nppa gene may be considered as a candidate gene to explain, at least in part, the variance of left ventricular ANF concentration and/or left ventricular mass in WKY and WKHA rats. They also define the region that will be studied in congenic lines to obtain a better spatial resolution of the QTL’s, and in particular to determine whether QTLANF andQTLLVM are identical or adjacent.