Ablation of Dicer, the cytoplasmic ribonuclease type III critical for microRNA maturation (9), in mature forebrain and ARH neurons (10, 11) or in neurons expressing Cre recombinase under control of the POMC promoter (POMCCre) during development (12) results in obesity. The gene discussed is POMC; the disease is obesity due to melanocortin 4 receptor deficiency.