The C57Bl/6J mouse is the most widely used strain in studies of obesity [46], but here we used FVB/N mice because this study is a further extension of our previous studies investigating the role of HO-1 deficiency in placental vascular development, HO-1 heterozygote transgenic mice, which was created on an FVB/N background. Here, HMOX1 is linked to obesity due to melanocortin 4 receptor deficiency.