Vlasta Bílá

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.

Quantitative trait loci influencing cholesterol and phospholipid phenotypes map to chromosomes that contain genes regulating blood pressure in the spontaneously hypertensive rat.

The frequent coincidence of hypertension and dyslipidemia suggests that related genetic factors might underlie these common risk factors for cardiovascular disease. To investigate whether quantitative trait loci (QTLs) regulating lipid levels map to chromosomes known to contain genes regulating blood pressure, we used a genome scanning approach to map QTLs influencing cholesterol and phospholipid phenotypes in a large set of recombinant inbred strains and in congenic strains derived from the spontaneously hypertensive rat and normotensive Brown-Norway (BN.Lx) rat fed normal and high cholesterol diets. QTLs regulating lipid phenotypes were mapped by scanning the genome with 534 genetic markers. A significant relationship (P < 0.00006) was found between basal HDL2 cholesterol levels and the D19Mit2 marker on chromosome 19. Analysis of congenic strains of spontaneously hypertensive rat indicated that QTLs regulating postdietary lipid phenotypes exist also on chromosomes 8 and 20. Previous studies in the recombinant inbred and congenic strains have demonstrated the presence of blood pressure regulatory genes in corresponding segments of chromosomes 8, 19, and 20. These findings provide support for the hypothesis that blood pressure and certain lipid subfractions can be modulated by linked genes or perhaps even the same genes.

Genetic analysis of metabolic defects in the spontaneously hypertensive rat

Abstract. Abnormalities in carbohydrate and lipid metabolism are common in patients with essential hypertension and in the spontaneously hypertensive rat (SHR). To identify chromosome regions contributing to this clustering of cardiovascular risk factors in the SHR, we searched for quantitative trait loci (QTL) associated with insulin resistance, glucose intolerance, and dyslipidemia by using the HXB/BXH recombinant inbred (RI) strains. Analysis of variance in RI strains suggested significant effects of genetic factors. A genome screening of the RI strains with more than 700 markers revealed QTL significantly associated with insulin resistance on Chromosomes (Chrs) 3 and 19. The Chr 19 QTL was confirmed by testing a previously derived SHR-19 congenic strain: transfer of a Chr 19 segment delineated by markers D19Rat57 and D19Mit7 from the Brown Norway (BN/Cr) strain onto the genetic background of the SHR/Ola was associated with decreased insulin and glucose concentrations and ameliorated insulin resistance at the tissue level. These findings suggest that closely linked genes on Chr 19, or perhaps even a single gene with pleiotropic effects, influence the clustering of metabolic disturbances in the SHR-BN model.

Genetic map of AFLP markers in the rat (Rattus norvegicus) derived from the H x B/Ipcv and B x H/Cub sets of recombinant inbred strains.

The amplified fragment length polymorphism (AFLP) technique has been used to enhance marker density in a large set of recombinant inbred strains (H × B and B × H) derived from a spontaneously hypertensive rat (SHR/OlaIpcv) and a Brown-Norway (BN.lx/Cub) inbred strain. Thirteen different primer combinations were tested and a total of 191 polymorphic bands were detected. From these polymorphic bands 89 AFLP markers could be assigned to specific chromosomes. Several of these AFLP markers were mapped to regions with low marker density, thus filling up gaps in the existing genetic map of these recombinant inbred strains. These results substantiate the value of the AFLP technology in increasing marker density in genetic maps.

A new set of recombinant inbred strains complementary to HXB and BXH sets

Summary A new set of recombinant inbred [RI]strains has been developed complementary to the original RI strains BXH/HXB using the BXH2 RI strain and the SHR- Lx congenic strain as progenitors, both homozygous in Lx locus. The reason behind the production of this lies in a special SHR/BN gene combination in the BXH2 strain which is increasing the expressivity of the Lx gene and sensitizes this strain to teratogenic effects. On the contrary, the SHR genetic background minimizes the Lx gene expression as well as the teratogenic action of retinoic acid. There are 10 PXO strains in 17 th up to 21 st generation of inbreeding. The variability of leg malformation on PXO strains is similar to that in BXH/HXB polydactylous RI strains. The genotyping of PXO RI set has been started showing relatively high degree of homozygosity [over 90%] in individual RI strains. After inbreeding is accomplished the PXO will have become a useful complement to the original RI strain system. In preliminary teratologic testing, variable sensitivity to retinoic acid has been shown in 3 PXO strains.

Genetics of rat hypodactyly

Summary Rat hypodactyly was originally described by Moutier et al. (1973) as an autosomal recessive trait. The determining gene Hd has been recently mapped to rat chromosome 10 and is closely linked to the D10Rat31/32, D10Rat30 , and Myh3 loci ( Křenova et al. 1998). In homozygous state (Hd/Hd) , there is a variable reduction in the number of fingers and metacarpals — metatarsals of front and hind feet in males and females. Moreover, there is a male sterility in homozygotes whereas male heterozygotes are fertile. The light and electron microscopic examination confirmed disorder of spermatogenesis, loosening and vacuolization of seminiferous epithelium accompanied with a significantly decreased number of germ cells in testes of homozygotes. In an intercross population (Wistar Hd×BN-Lx)F2, an independent segregation of the major genes Lx , coding for the PLS (polydactyly-luxate syndrome), and Hd — hypodactyly was found together with irregular interactions of Hd and Lx genes in double homozygotes ( Hd/Hd, Lx/Lx ). The variable phenotype manifestation of foot malformation in double homozygous animals indicated modifying influences of genes of the genetic background. In order to study more precisely the role of the determining major gene Hd as well as the role of the putative modifying genes in the development of the foot malformation and male sterility, we started the production of two congenic strains by introgressing the Hd mutant gene onto the genetic backgrounds of the BN and SHR inbred strains.