Genetic relationship between placental and fetal weights and markers of the metabolic syndrome in rat recombinant inbred strains.

Epidemiological studies have shown a clear link between fetal growth retardation and an increased propensity for later cardiovascular disease in adults. It has been hypothesized that such early fetal deprivation "programs" individuals toward a life-long metabolical "thrifty phenotype" that predisposes adults to such diseases. Here we test this hypothesis, and its possible genetic basis, in rat recombinant inbred (RI) strains that uniquely allow the longitudinal studies necessary for its testing. Placental and fetal weights were determined on day 20 of pregnancy in (at least) 6 litters from each of 25 available BXH/HXB RI strains and from their SHR and BN-Lx progenitors and were correlated with metabolic traits determined in adult rats from the same inbred lines. Quantitative trait loci (QTLs) associated with placental and fetal weights were identified by total genome scanning of RI strains using the Map Manager QTX program. Heritabilities of placental and fetal weights were 56% and 62%, respectively, and total genome scanning of RI strains revealed QTLs near the D1Rat266 marker on chromosome 1 and near the D15Rat101 marker on chromosome 15 that were significantly associated with fetal and placental weights respectively. Placental weights correlated with fetal weights (r = 0.60, P = 0.001), while reduced fetal weights correlated with increased insulin concentrations during glucose tolerance test (r = -0.71, P = 0.0001) and with increased serum triglycerides (r = -0.54, P = 0.006) in adult rats. Our results suggest that predisposition toward a thrifty phenotype associated with decreased placental weight and restricted fetal growth is in part genetically determined.

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 x B and B x 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.

PMEDAP and its N6-substituted derivatives: genotoxic effect and apoptosis in in vitro conditions.

Genotoxic properties expressed as acquired chromosomal aberrations and induction of apoptosis after treatment with acyclic nucleoside phosphonates PMEG, PMEDAP and its N6-substituted derivatives Me2NEt-PMEDAP, allyl-PMEDAP, Me2-PMEDAP and cypr-PMEDAP, were studied in in vitro conditions. The genotoxic and antiproliferative effect of compounds was investigated on CCRF-CEM, HeLa S3, MRC-5 and Reh cell lines. PMEG and cypr-PMEDAP exhibit high genotoxic and cytostatic effect. PMEDAP and its N6-substituted derivatives Me2NEt-PMEDAP, allyl-PMEDAP and Me2-PMEDAP are considerably less genotoxic. Time- and dose-dependent suppression of proliferation by these nucleotide analogues is accompanied by induction of apoptosis, which is dependent on cell line type. However, an increased proliferation was observed after treatment of the cell culture with very low dose of PMEDAP. The sensitivity of cell lines to PMEDAP decreased in the order: CCRF-CEM > Reh > HeLa > MRC-5. The potential embryotoxic or teratogenic effect of PMEDAP and cypr-PMEDAP was examined in inbred rats involving the mutant allele Lx that determines the polydactyly-luxate syndrome. While the prevalent effect of cypr-PMEDAP during fetus development is embryolethality, PMEDAP did not induce any embryo-lethal or teratogenic effect.

Genetic analysis of metabolic defects in the spontaneously hypertensive rat.

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.

Chromosomal mapping of a major quantitative trait locus regulating compensatory renal growth in the rat.

Despite extensive research conducted over the past century, the mechanisms of compensatory renal growth (CRG) remain a mystery. Insight into the mechanisms that regulate CRG might be gained by identifying genetic factors that influence this complex phenotype. In a large set of recombinant inbred strains derived from the spontaneously hypertensive rat and the Brown Norway rat, a genome scan for quantitative trait loci (QTL) that regulate CRG was performed. The CRG score was expressed as a ratio of the weight of the remnant right kidney at 8 wk of age to the weight of the left kidney at 5 wk of age, both adjusted for body weight. QTL mapping was performed using Map Manager QT and the strain distribution patterns of more than 600 genetic markers. It was found that CRG after unilateral nephrectomy is a multifactorially determined trait with a substantial genetic component. The heritability of CRG approached 40%. Genome wide scan analysis revealed significant evidence of linkage to a region of rat chromosome 4 designated Crg 1 that accounted for more than 50% of the additive genetic variance of CRG in the recombinant inbred strains. The detection of a major QTL influencing CRG in the rat should provide new opportunities for identifying mechanisms that regulate this historically enigmatic phenomenon and may also have implications for research on the pathogenesis of end-stage kidney disease.