The main focus of transgenic animal models in the study of adipose tissue biology has been the expression or knockout of selected genes specifically in adipose tissue. Adipose-tissue-specific expression/knockout of genes became possible with the identification and characterization of promoter regions conferring adipose-tissue-specific expression. The promoters for the adipocyte lipid binding protein aP215 and for phosphoenolpyruvate carboxykinase (PEPCK)16 are commonly used to target both white and brown adipose tissue (WAT/BAT), whereas the UCP-1 promoter only targets BAT