Confirmation and characterization of murine body weight QTLs, Bwq1 and Bwq2, identified in C57BL/6J x KK-Ay/a F2-Ay/a mice

Quantitative trait loci that control body weight and obesity in an F2 intercross between C57BL/6J and DDD.Cg-Ay mice

I have developed a congenic mouse strain for the A(y) allele at the agouti locus in an inbred DDD/Sgn strain, DDD.Cg-A(y). DDD.Cg-A(y) females are extremely obese and significantly heavier than B6.Cg-A(y) females. The objectives of this study were to determine the genetic basis of obesity in DDD.Cg-A(y) mice, and to determine whether or not their high body weight was due to the presence of DDD background-specific modifiers. I performed quantitative trait locus (QTL) analyses for body weight and body mass index in two types of F(2) mice [F2 A(y) (F(2) mice carrying the A(y) allele) and F(2) non-A(y) (F2 mice without the A(y) allele)] produced by crossing C57BL/6J females and DDD.Cg-A(y) males. The results of the QTL analysis of F(2) A(y) mice were very similar to those obtained for F(2) non-A(y) mice. It was unlikely that the high body weight of DDD.Cg-A(y) mice was due to the presence of specific modifiers. When both F(2) datasets were merged and analyzed, four significant body weight QTLs were identified on chromosomes 6, 9, and 17 (2 loci) and four significant obesity QTLs were identified on chromosomes 1, 6, 9, and 17. Although the presence of DDD background-specific modifiers was not confirmed, a multifactorial basis of obesity in DDD.Cg-A(y) females was thus revealed.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

Type 2 diabetes mouse model TallyHo carries an obesity gene on chromosome 6 that exaggerates dietary obesity

The TallyHo (TH) mouse strain is a polygenic model for Type 2 diabetes with obesity. Genetic analysis in backcross progeny from a cross between F1 [C57BL/6J (B6) x TH] and TH mice mapped a quantitative trait locus (QTL) named TH-associated body weight 2 (tabw2) to chromosome 6. The TH-derived allele is associated with increased body weight. As a first step to identify the molecular basis of this obesity QTL, we constructed a congenic line of mice on the B6 genetic background that carries a genomic region from TH mice containing tabw2. Congenic mice homozygous for tabw2 (B6.TH-tabw2/tabw2) fed a chow diet exhibited slightly, but significantly, higher body weight and body fat and plasma leptin levels compared with controls (B6.TH-+/+). This difference was exacerbated when the animals were maintained on a high-fat and high-sucrose (HFS) diet. The diet-induced obesity in tabw2 congenic mice is accompanied by hyperleptinemia, mild hyperinsulinemia, impaired glucose tolerance, and reduced glucose uptake in adipose tissue in response to insulin administration. Using F2 progeny fed a HFS diet from an intercross of B6.TH-tabw2/+ mice, we were able to refine the map position of the tabw2 obesity susceptibility locus to a 15-cM region (95% confidence interval) extending distally from the marker D6Mit102. In summary, tabw2 congenic mice are a new animal model for diet-induced obesity that will be valuable for the study of gene-diet interactions.