NTRK2 and obesity due to melanocortin 4 receptor deficiency: Sim1-Cre is expressed in other brain regions in addition to the PVH40 (Supplementary Fig. 3a–f), so the obesity phenotype in Sim1-Cre;Ntrk2lox/lox mice might result from Ntrk2 deletion in non-PVH neurons or cells.