Expression of Avian UCP and ANT in Skeletal Muscle of Cold-exposed Laying and Meat-type Chickens

Most bird species studied thus far have no distinct brown adipose tissue (BAT) or a related type of thermogenic tissue ; however, our recent studies on cold (4- 6°C)-acclimatized chickens suggest that simultaneous increments in mRNA levels of the mitochondrial anion carriers, avian adenine nucleotide translocator (avANT) and avian uncoupling protein (avUCP), may be involved in the regulation of thermogenesis in avian skeletal muscle (FEBS Lett. 529 : 313-318, 2002). The present experiments were conducted to compare the responses of laying- and meat-type chickens in regard to the expression of avUCP and avANT when they undergo acute (24-48h) mild cold (8°C) exposure. Twenty-four male laying- and twelve meat-type chickens (3-wk old) were used. Groups from each species were exposed to mild cold for 24 and 48h, while the control group remained at 23°C. In laying-type chickens, weight gain and feed efficiency were both compensated in some degree after 48h of cold exposure. In contrast, meat-type chickens exhibited a linear decrease in weight gain corresponding to the duration of cold exposure. There were differences in the expression of avANT mRNA in Pectoralis superficialis muscle, between laying- and meat-type chickens, i.e. expression of avANT mRNA was significantly increased in laying-type chickens exposed to cold for 48h, but not in meat-type chickens. However, no differences were observed in the expression of avUCP mRNA in pectoral muscle between control and mild cold groups for both type of chickens, showing that acute mild cold exposure was not sufficient to induce increased expression of avUCP mRNA in skeletal muscle of either laying- or meat-type chickens. Up-regulation of avANT mRNA, but not avUCP mRNA, in laying-type chickens exposed to acute mild cold suggested that avANT might be involved in thermogenesis and adaptation to acute mild cold exposure. These findings will contribute to our understanding of potential differences in the responses of laying- and meat-type chickens to cold exposure at the molecular level.