UCP1 and obesity due to melanocortin 4 receptor deficiency: Similarly, Zietak et al. showed a marked change in microbiota composition in mice exposed to 12°C for 4 weeks, characterized by the increase and decrease in bacterial genera associated to leanness and obesity, respectively, accompanied by an increase in Ucp1 expression in BAT and WAT (Zietak et al., 2016).