FAS and obesity due to melanocortin 4 receptor deficiency: In order to further assess a role for myeloid-expressed Fas in the development of obesity-associated insulin resistance, myeloid-specific Fas-knockout mice (Fasf/f, LysM-Cre+/−; FasΔmye) were generated using the cre-lox system (Clausen et al, 1999; Olefsky & Glass, 2010).