Expression of obese mRNA in genetically lean and fat selection lines of sheep.

Genetically separate lines of Coopworth sheep have been bred by selecting for (fat genotype) or against (lean genotype) backfat depth. Typically, the total fat content, adjusted for carcass weight, is 21.2 and 29.3% for the lean and fat lines, respectively. As a homologue of the obese gene, which shows altered expression in several forms of obesity, is also expressed in sheep, it was decided to determine whether the obese gene was differentially expressed in each line of sheep. The relative level of expression of obese mRNA was approximately twofold higher in the fat line compared with the lean line in back, omental and perirenal fat depots of ram lambs fed ad libitum or fasted for 48 h. This elevation in the fat line is most likely a secondary consequence of obesity rather than a cause. Fasting for 48 h decreased obese mRNA levels by 8.9-, 8.5-, and 4.2-fold in back, omental and perirenal fat, respectively, in the lean line, and by 8.3-, 5.7-, and 3.5-fold in back, omental and perirenal fat, respectively, in the fat line. The lean and fat lines of sheep, therefore, responded in a similar way to fasting.