Dock2 has been shown to be indispensable for chemotaxis of mature lymphocytes as a critical Rac activator. However, the functional expression of Dock2 in immature hernatopoietic cells is unclear. In this study, we demonstrate that Dock2 is broadly expressed in bone marrow (BM) hernatopoietic compartment, including hernatopoietic stem/progenitor cell (HSC/HPC) fraction. Response of Dock2-/- HPCs to CXCL12 in chemotaxis and actin polymerization in vitro was impaired, although alpha 4 integrin activation by CXCL12 was not altered. Myelosuppressive stress on HSCs in vivo, such as consecutive 5-FU administration and serial bone marrow transplantation, did not show hernatopoietic defect in Dock2-/- mice. Long-term engraftment of transplanted Dock2-/- BM cells was severely impaired in competitive reconstitution. However, this was not intrinsic to HSCs but originated from the defective competition of Dock2-/- lymphoid precursors. These results suggest that Dock2 plays a significant role in BM lymphopoiesis, but is dispensable for HSC engraftment and self-renewal. (C) 2007 Elsevier Inc. All rights reserved.