Prolonged exposure to 4 °C can be fatal to β-less mice (16);
therefore, a milder cold challenge was given by exposing these
animals to 10 °C for 20 h. As expected, the thermogenic gene
expression [including peroxisome proliferator-activated receptor
gamma coactivator 1-alpha (Pgc1a), Ucp1, and type II iodothyronine
deiodinase (Dio2)] in the classic (interscapular) BAT
was severely diminished in the β-less mice compared with the
wild-type controls (Fig. 1A).