FGF21 and obesity due to melanocortin 4 receptor deficiency: To explore whether liver-derived FGF21 is involved in OVX-induced body weight gain and obesity in females, we bilaterally ovariectomized FGF21 LKO and their wild-type (WT) littermates at 6 weeks of age and then monitored their body weight change weekly until the age of 30 weeks.