Dkk1 impairs the homing of HSCs, but not pre-LSCs and LSCs. (A) HSCs homed 10.5 μm (median) from osteoblasts in WT recipient mice and 27.6 μm from osteoblasts in Dkk1-transgenic mice (P < .01) (n = 3 biologic replicates). (B) Pre-LSCs homed 12.5 μm (median; range, 0.5-28 μm) from osteoblasts in WT and 11.5 μm (median; range, 0.5-22.2 μm) in Dkk1-transgenic mice (P = not significant; n = 2 biologic replicates). (C) LSCs homed slightly more closely to osteoblasts in Dkk1-transgenic mice (median, 18.2 μm; range, 0-94.4 μm) compared with WT recipient mice (median, 23.7 μm; range, 0-79.2 μm; n = 3 biologic replicates). (D) Proliferation of individual LSCs in vivo was measured 48 hours after injection. Each LSC was identified as composed of single cells, doublets, or clusters (≥ 3 cells together) and expressed relative to the total number of cells per mouse (n = 3 for WT and Dkk1). LSC proliferation in vivo was similar between WT and Dkk1 recipients (P = .36 for doublets, P = .14 for clusters).