Date of Award
Doctor of Philosophy (PhD)
Studies of twins, adopted children, and some human populations indicate that there is a substantial genetic influence on body composition in both children and adults. However, in no single instance in either man or animals is the precise etiology of obesity known at the molecular level. Attempts to identify the molecular basis responsible for obesity in humans have been hampered by difficulties in measuring food intake and energy expenditure to sufficient accuracy, as well as the apparent polygenic control of body composition in man. These constraints have stimulated interest in the simpler models available in certain inbred animal strains, and particularly mice. The murine diabetes, db, mutation is an autosomal recessive mutation located on mouse chromosome 4 which demonstrates a metabolic/behavioral phenotype similar to that observed in human obesity and Type II diabetes. Homozygous db animals manifest profound obesity with hyperphagia, increased metabolic efficiency, and insulin resistance. In an effort to clone this gene (and the related obese (ob) mutant on mouse chromosome 6) by the technique of "positional cloning", several studies were undertaken. A moderate resolution genetic map of mouse chromosomes 4 and 6 utilizing an interspecific laboratorius X spretus backcross was first created using RFLPs for 29 known chromosome 4 and 6 markers. These maps extended over most of the chromosomes' length and detailed large areas of mouse - human homology. Intraspecific crosses segregating the db mutation were then established, and markers from the chromosome 4 map were positioned relative to db. Several of the markers which are linked to db - (fun, Glut-l, Lmyc-l, and CBB,) map to human chromosome 1p31-p32, suggesting that db may be part of a syntenic group between human 1 p and the distal portion of mouse chromosome 4. Additionally, distributions of age-controlled plasma [glucose] and [insulin] among the intraspecific cross obese progeny were not bimodal, suggesting a role for polygenic differences between the progenitor strains (C57BL/6J and DBA/2J) in the development of overt diabetes. In order to increase the density of probes in the region of db, flowsorting of a 4:6 Robertsonian chromosome was accomplished, establishing a library -72% pure for chromosomes 4 and 6. In addition, microdissection and microcloning of the midi distal chromosome 4 region containing db produced two clones, D4Rck22 and D4Rck69, located < 0.13 cM distal to db. Cloning and mapping of the mouse phosphoglucomutase gene established that Pgm-2 is located approximately 1.5 cM proximal of db. Utilizing these flanking markers and genetic resources, pulse-field electrophoresis mapping, and YAC cloning of the region has begun. These studies should facilitate the eventual cloning and characterization of the db gene.
Bahary, Nathan, "Molecular Approaches to the Genetics of Obesity: Mapping and Characterization of the Murine Diabetes (db) Gene" (1992). Student Theses and Dissertations. 351.