UBC and obesity due to melanocortin 4 receptor deficiency: To exclude the possibility that the obesity of UBC-SKO mice (SMRTloxP/loxP UBCERT2-Cre) was caused by Cre-induced organ toxicity we set up a separate control mouse cohort comparing UBCERT2-Cre and Cre-negative littermates on a C57/BL6 background, which is more prone to obesity[20].