Adipose Tissue-specific Expression of the Obese (ob) Gene in Rats and Its Marked Augmentation in Genetically Obese-hyperglycemic Wistar Fatty Rats

The obese (ob) gene has recently been isolated by positional genetics, the mutation of which causes marked obesity and diabetes in mice. In the present study, we elucidated the tissue distribution of the ob gene expression in rats and examined the gene expression in genetically obese-hyperglycemic Wistar fatty rats. Northern blot analysis using the rat ob cDNA probe identified a single mRNA species of 4.5 kilobase in size in the adipose tissue, while no significant amount of ob mRNA was detected in other tissues in Sprague-Dawley and Wistar rats. The ob gene expression occurred in the adipose tissue with region-specificities. The rank order of the ob mRNA level in the adipose tissue was epididymal, retroperitoneal, and pericardial white adipose tissue > mesenteric and subcutaneous white adipose tissue ⑥ interscapular brown adipose tissue in both rat strains. Furthermore, expression of the ob gene was augmented in all the adipose tissue examined in Wistar fatty rats at the stage of established obesity.