Chemokines and their receptors are important in cell migration during
inflammation(1), in the establishment of functional lymphoid microenvi
ronments(2), and in organogenesis(3). The chemokine receptor CXCR4 is
broadly expressed in cells of both the immune and the central nervous
systems(4,5) and can mediate migration of resting leukocytes and haema
topoietic progenitors in response to its ligand, SDF-1 (refs 6-9). CXC
R4 is also a major receptor for strains of human immunodeficiency viru
s-1 (HIV-1) that arise during progression to immunodeficiency and AIDS
dementia(10). Here we show that mice lacking CXCR4 exhibit haematopoi
etic and cardiac defects identical to those of SDF-1-deficient mice(3)
, indicating that CXCR4 may be the only receptor for SDF-1. Furthermor
e, fetal cerebellar development in mutant animals is markedly differen
t from that in wild-type animals, with many proliferating granule cell
s invading the cerebellar anlage. This is, to our knowledge, the first
demonstration df the involvement of a G-protein-coupled chemokine rec
eptor in neuronal cell migration and patterning in the central nervous
system. These results may be important for designing strategies to bl
ock HIV entry into cells and for understanding mechanisms of pathogene
sis in AIDS dementia.