The obese gene is expressed in lean littermates of the genetically obese mouse (C57BL/6J ob/ob)

Some individuals of the mixed group of "lean" littermates (+/ ob and +/+) of (C57BL/6J ob/ob) often suggest phenotypic characteristics of ob/ob animals. Therefore, it was of interest to determine whether expression of the ob gene had physiological significance in +/ ob animals. Body weight (BW), fasting blood glucose (FBG), and body core temperature (T ) were monitored between 62 and 364 days of age in +/+ and +/ obmice. Among females but not males, +/ ob mice were heavier ( P = 0.003) and FBG levels were greater ( P = 0.04) than in +/+ animals. Comparison of T indicated differences suggesting falling T in +/ ob but rising T in +/+ mice with age in males but not females. Multivariate analysis of variance yielded genotype effects for both males ( P = 0.002) and females ( P = 0.02). BW, FBG, and T alone were sufficient at the 75% level for genotypic characterization and separation of +/? animals as +/ ob or +/+; clearly, expression of the ob gene in heterozygotes of the +/ ob animal may make the mixed +/? group inappropriate as lean controls.