Are the mammalian-like uncoupling proteins 1 and 2 expressed in cold-acclimated Muscovy ducklings?

Despite their lack of brown adipose tissue (BAT), birds can exhibit nonshiv ering thermogenesis (NST) in the cold. Avian NST mainly originates from ske letal muscle and may involve fatty acid-induced uncoupling of mitochondrial respiration. In mammals, uncoupling of oxidative phosphorylation is based on the presence of uncoupling proteins (UCPs) in the inner mitochondrial me mbrane. Because both the BAT-specific UCP1 and the ubiquitous UCP2 are up-r egulated in cold-acclimated (CA) rodents, the question arises as to whether CA birds exhibiting NST express mammalian-like UCPs. Tissue expression of UCP1 and UCP2 mRNA was therefore investigated in CA Muscovy ducklings (Cair ina moschata, 5-wk old), reared at 4 degrees C from the age of l-wk and exh ibiting muscle NST. Rat fragments of UCP1 or UCP2 cDNA were used as probes in Northern blots. UCP1 mRNA was detected only in rat BAT while UCP2 mRNA w as detected in rat BAT, liver and soleus muscle. Conversely, no UCP1- or UC P2-like mRNA were detected in duckling skeletal muscle, white adipose tissu e and liver. It is concluded that CA ducklings do not express a mRNA with s ufficient homology to hybridise with rat UCP1 or UCP2 probes.