To test the possibility that BM precursor TLR4 regulates BM development in early stages of obesity, we generated chimeras in which WT BM (CD45.1) was mixed with TLR4-deficient BM (CD45.2) and co-engrafted into WT hosts (CD45.1/2). Here, TLR4 is linked to obesity due to melanocortin 4 receptor deficiency.