Normal FBM hematopoiesis in absence of integrin α6. E18.5 FBM from integrin α6 gene–deleted mice (α6^−/−) and wild-type littermates (α6^+/+) was analyzed for total cell number (A) total cell number (horizontal bars show mean values), and (B) competitive repopulating units (CRUs). CRUs were assayed by transplanting 2 to 4.4 × 10⁴ FBM cells together with 2 × 10⁵ adult BM cells into lethally irradiated adult mice. Three of 13 and 3 of 12 mice that received integrin α6^−/− FBM cells, and 3 of 14 and 2 of 12 mice that received wild-type FBM cells, were reconstituted with FBM cells at 8 weeks and 16 weeks, respectively. The CRU numbers/2 legs (femur and tibia) are shown as mean (± 95% confidence interval).