It is concluded that the triplet repeat expansion in 3'UTR is involved in metabolic alterations as found in hHTg and WOKW rats and that the functional unknown gene, Repin1, could be a novel candidate gene for the development of facets of the metabolic syndrome.

KLÖ TING, NORA, BARBARA WILKE, AND INGRID KLÖ TING. Alleles on rat chromosome 4 (D4Got41-Fabp1/ Tacr1) regulate subphenotypes of obesity. Obes Res. 2005; 13:589 -595. Objective: The use of inbred animal models is an essential component of the genetic dissection of complex diseases. Because quantitative trait loci for serum triglycerides, total cholesterol, and body weight were mapped on chromosome 4 in a cross of BioBreeding/OttawaKarlsburg (BB/OK) and spontaneously hypertensive (SHR) rats, we established a congenic BB.SHR rat strain by introgressing a SHR segment of chromosome 4 (D4Got41-Tacr1) into a BB/OK background. The phenotype of these BB.SHR rats (BB.4S) confirmed the quantitative trait loci. To discover whether the phenotype of BB.4S can only be attributed to the SHR segment per se, we established an additional congenic BB.WOKW strain by introgressing a similar segment of chromosome 4 (D4Got41-Fabp1) of the Wistar Ottawa Karlsburg RT1 u rat into a BB/OK background, termed briefly BB.4W. (20), and BB.4W (16) rats were longitudinally studied for body weight, serum triglycerides, total and high-density lipoprotein-cholesterol, and glucose tolerance. At the end of the observation period (32 weeks), serum insulin, leptin, and adiposity index (AI) were determined. Results and Discussion: Congenic BB.4S and BB.4W were significantly heavier, and AI, serum triglycerides, and total cholesterol values were significantly elevated in BB.4S and BB.4W compared with BB/OK but more pronounced in BB.4S. The highest serum insulin was found in BB.4W and highest leptin in BB.4S. Because the body weight gain and AI were comparable between BB.4S and BB.4W, the obviously higher insulin levels in BB.4W and higher leptin values in BB.4S suggest that the two congenics most probably define two subphenotypes of obesity and provide the unique opportunity to study their genetics. Research Methods and Procedures: Male normoglycemic BB/OK (20), BB.4S

Background Congenic and subcongenic rat strains confirmed the quantitative trait loci (QTLs) for facets of the metabolic syndrome between 60.53 and 77.11 Mb on chromosome 4. The analysis of candidate genes in this region favoured the replication initiator 1 (Repin1) characterized by a SNP in the coding region and a triplet repeat (TTT) in the 3 -untranslated region (3 UTR).

A high-fat diet seems to protect BB/OK rats from T1D in a sex-specific manner. The data suggest that a high-fat diet might influence fat accumulation and/or fat metabolism and prevent T1D development in male rats, which is supported by changes in adipose tissue gene expression.

Klöting, Nora, Barbara Wilke, and Ingrid Klöting. Phenotypic and genetic analyses of subcongenic BB.SHR rat lines shorten the region on chromosome 4 bearing gene(s) for underlying facets of metabolic syndrome. Physiol Genomics 18: [325][326][327][328][329][330] 2004. First published June 1, 2004; 10.1152/physiolgenomics.00047.2004.-Congenic BB.SHR (D4Got41-Npy-Tacr1; BB.4S) rats develop an incomplete metabolic syndrome with obesity, hyperleptinemia, and dyslipidemia compared with their progenitor strain, the diabetes-prone BB/OK rat. To narrow down the underlying gene(s), two subcongenic BB.SHR rat lines, briefly termed BB.4Sa and BB.4Sb, were generated. Male BB.4S (n ϭ 20), BB.4Sa (n ϭ 24), and BB.4Sb (n ϭ 26) were longitudinally characterized for facets of the metabolic syndrome and analyzed for expression of genes located in the region of interest in liver and blood. Body weight gain was comparable, serum triglycerides and leptin were significantly increased, and total cholesterol and HDL-cholesterol ratio were decreased in BB.4S compared with both subcongenics. Serum insulin was significantly higher in BB.4S and BB.4Sa than in BB.4Sb. The adiposity index showed a graduated decrease from BB.6S to BB.4Sb. Obvious differences in relative expression were found in 6 of 10 genes in liver and in 2 of 9 genes in blood. Only one gene, the eukaryotic translation initiation factor 2␣ kinase 3 (Eif2ak3 also called Perk or Pek), was significantly less expressed in liver and in blood of both subcongenic BB.4Sa and BB.4Sb compared with their "parental" BB.4S rats. Based on the phenotype and genotype in BB.4S and its subcongenic derivatives, the most important region on chromosome 4 can be said to lie between D4Got72 and Tacr1. Eif2ak3 is mapped in this region. Considering the function of Eif2ak3, it may be a candidate gene for the development of glucose intolerance found in both subcongenics but not in BB.4S. Allelic variants between BB/OK and SHR could influence Eif2ak3 function, possibly leading not only to glucose intolerance but also to the disturbances in hepatic and renal function found in human Wolcott-Rallison syndrome. rat model; obesity; dyslipidemia; congenic mapping LINKAGE STUDIES IN RATS have revealed a number of quantitative trait loci (QTLs) for facets of the metabolic syndrome (6, 7, 10, 12, 15-18, 20, 21). However, these localizations are only preliminary steps for the identification of the underlying gene(s), and further investigations are required to confirm the existence of QTLs; to this end, the construction of congenic strains is essential. Strains that are genetically identical except for a single chromosome segment are said to be congenic. Congenic strains are usually derived by backcross breeding and genomic selection techniques, by which a specific chromosome segment is transferred from the strain A onto the genetic background of a recipient strain B and designated B.A. If such a congenic B.A strain differs from the progenitor strain B, one can conclude that there is a locus within the transferr...