Expression pattern of two zebrafish genes, cxcr4a and cxcr4b.

We cloned and mapped two novel zebrafish genes, cxcr4a and cxcr4b, which are closely related to mammalian CXCR4. Expression analysis by reverse transcription-polymerase chain reaction and in situ hybridization demonstrated that these two genes are expressed in most cell lineages known to express Cxcr4 in mammals. These genes are co-expressed in lateral mesoderm and posterior midbrain. The transcripts of cxcr4a were detected in interneurons and endoderm, whereas cxcr4b was specifically expressed in sensory neurons, motoneurons and cerebellum. In the lateral mesoderm, cxcr4b transcripts appeared earlier than those of cxcr4a. Thus, the function of mammalian CXCR4 could be split between the two zebrafish genes. These genes probably derived from the genome duplication event, which occurred during the evolution of teleosts. Similar pairs of Cxcr4 may exist in other species, where genome duplication has occurred.