['During embryogenesis, the CXC chemokine ligand (CXCL)12 acts on endothelial cells to control cardiac development and angiogenesis. Although biological functions of CXCL12 are exerted in part through activation of the small GTPase Rac, the pathway leading from its receptor CXC chemokine receptor (CXCR)4 to Rac activation remains to be determined.', 'DOCK180 (dedicator of cytokinesis), an atypical Rac activator, has been implicated in various cellular functions. Here, we examined the role of DOCK180 in cardiovascular development.', 'DOCK180 associates with ELMO (engulfment and cell motility) through the N-terminal region containing a Src homology 3 domain. We found that targeted deletion of the Src homology 3 domain of DOCK180 in mice leads to embryonic lethality with marked reduction of DOCK180 expression at the protein level. These mutant mice, as well as DOCK180-deficient mice, exhibited multiple cardiovascular abnormalities resembling those seen in CXCR4-deficient mice. In DOCK180 knocked down endothelial cells, CXCL12-induced Rac activation was impaired, resulting in a marked reduction of cell motility.'] Is dOCK180 a Rac activator that regulates cardiovascular development by acting downstream of CXCR4?