The activation of adipose tissue by FGF21 through FGFR1 was suggested by genetic deletion of FGFR1 in adipocytes in mice used in the current study [18], and this tissue- and molecule-specific actions of FGF21 underlies the breadth of its in vivo beneficial effects on treatment of obesity and diabetes a. Here, FGF21 is linked to obesity due to melanocortin 4 receptor deficiency.