TGFβ signaling inhibits the proliferation of ERα+ epithelial cells in mouse mammary glands [94, 95] and cultured human breast epithelial cells [96], and loss of TGFβ signaling may play a role in the observed increases in ERα+ proliferating cells in mammary tissue in obesity. Here, TGFB1 is linked to obesity due to melanocortin 4 receptor deficiency.