INS and obesity due to melanocortin 4 receptor deficiency: These observations point out the respective influences of the nuclear and mitochondrial T3 pathways demonstrating either similarities (energy expenditure, leanness after 4 months for p43−/− mice) or differences (loss of glucose-stimulated insulin secretion and high-fat-diet induced obesity), thus indicating that these two pathways are complementary and allow a fine-tuning of the thyroid hormones effects.