CXCR4 (Chemokine (C-X-C motif) Receptor-4) (CD184) is a GPCR (G Protein-Coupled Receptor) with selectivity for a single CXC-motif chemokine, called SDF1 (Stromal Cell-Derived Factor-1). The chemokine receptor CXCR4 is broadly expressed in cells of both the immune and the central nervous systems and can mediate migration of resting leukocytes and haematopoietic progenitors in response to its ligand, SDF1. SDF1 exists in 2 structural variants (SDF1a and SDF1b) that differ by 4 additional amino acids in the carboxyl-terminus of the b-form but show identical receptor binding and activity profiles. It is involved in B lympho- and myelopoiesis, cardiogenesis, blood vessel formation and cerebellar development. Ortholog CXCR4 cDNAs are described in numerous species, including monkeys, rat, mice, cat, cow and fish. The [...]