Humboldt-Universität zu Berlin - Albrecht Daniel Thaer-Institut für Agrar- und Gartenbauwissenschaften

NGFN Project description

Identification of natural genetic variation linked to high fatness in selected mouse lines


The subproject is aimed at the identification of candidate genes affecting obesity and related physiological factors in mice. In particular, our goal is to identify quantitative trait genes affecting obesity in the period between weaning at the age of three weeks and adulthood at the age of 18 weeks. The focus on natural genetic variation for obesity in mice is based on the fact that many human obesity genes were originally identified in mutant mice. As a novel model for polygenic obesity, we use the unique high fatness-selected Berlin fat mouse (BFM) line. The BFM line has been selected for high fatness at 9 weeks for over 50 generations and is partially inbred. A spontaneous mutation increased the initial fat percentage of 25% to 40-45% under standard diet. Candidate genes will be selected from a joined data analysis of genetic linkage mapping in a cross-bred population, differential gene expression experiments, and comparative DNA sequencing of differentially expressed positional candidate genes. Fine mapping of chromosomal segments and changes of frequency distribution of SNPs in candidate genes as result of selection will be analysed. Functional analyses of identified candidate genes harbouring genetic variants will be performed and bioinformatically analysed. The identified murine candidate genes/polymorphisms will be provided for further analyses in human populations.

Present results

The Berlin Fat Mouse (BFM) line has been selected for high fatness at the age of nine weeks for over 50 generations. Several inbred derivates of the outbred selection line have been generated.

For phenotypic characterization three Berlin Fat Mouse inbred lines (BFMI lines) and an unselected control line (C57BL6) were systematically analysed at the age between three and 20 weeks. The body weight and body composition (fat, lean, and fluid proportion by magnetic resonance interference, MRI) of live animals was measured weekly. We demonstrated, that the fat proportion in the BFMI lines (22%-37% fat content) increases by a factor of four to six as compared to the control line B6 (6% fat content) at standard diet until the age of 20 weeks. However, the animals of the BFMI lines consumed less energy per gram body weight than B6.

To test the response to high energy diet animals were fed ad libitum with either a standard (15,6% energy from fat) or a high fat diet (44,6% energy from fat) from the age of three weeks on. The three BFM inbred derivates showed a line and sex-specific pattern: Line 856 was resistant to high fat diet and, moreover, males and females had the same fat percentages of about 30%. The two other lines 860 and 861 responded to high fat diet by additional fat deposition. The difference in the fat deposition was clearest at the age of 10 - 12 weeks. In both lines females became more obese than males (with standard as well as with high fat diet). Within these lines, the total body fat was of a greater percentage in line 860 with 28% (male) and 37% (female) than in line 861 with 22% (male) and 30% (female) fat content at standard breeding diet. The difference in the percentage of body fat is particularly due to the variations in the subcutaneous fat pad. Within the BFMI lines, the line BFMI860 exhibited the highest adiposity index and the strongest response to high fat diet. This line was therefore chosen to generate a crossbred population with B6.

The BFMI860xB6 F2-population is being used for QTL analysis to identify chromosomal regions affecting fat deposition in dependency of low and high fat diet. 470 animals of the F2-population fed with low-fat diet and 500 animals fed with high-fat diet have been phenotypically characterized and are being genotyped. At 10 weeks, the F2 animals on low-fat diet weighed on average 28.0 g, with a range from 18.5 g to 44.0 g and had a percentage of WAT of 2.2 % (range: 0.5 - 9.5 %). On high-fat diet animals weighed on average 32.9 g (with a range from 13.8 to 54.9 g) and had a WAT percentage of 15.9 % (range: 3.7 - 32.4 %). First linkage analyses revealed a major QTL effect for body weight and fat deposition under high fat diet on chromosome 3. Simultaneously comparative gene expression analyses between BFMI860 and B6 males and of F2-animals are underway to identify e QTLs. As BFMI mice and their obesity phenotypes are of polygenic nature, the BFMI lines are excellent models for the study of obesity in humans.