Figure 5

Vertebrate ancestral genes for chemokines and chemokine receptors. The vertebrate and gnathostome protochromosomes on which chemokine and chemokine receptor genes were localized are shown. Among the genes contained by sea lamprey and elephant shark, only those that are shared by vertebrate or gnathostome ancestors are shown. Because the genome sequences of sea lamprey and elephant shark are still fragmented, it is not known whether the genes are linked on the same chromosomes. The lines that link the vertebrate chemokine ancestors with the chemokine receptor ancestors indicate the ligand–receptor relationships based on the human chemokine system. The receptor for CXCL14 and the ligand(s) for CXCR3L have not yet been identified. The ligand(s) for the ancestral XCR1 is unknown. The predicted locations of HOX gene clusters on the protochromosomes are also indicated. Colocalization of HOX clusters with chemokine receptor genes on vertebrate protochromosome E shows that some of the chemokine receptor genes accompanied HOX cluster duplication (DeVries et al. 2006). HOXD, HOXA, and HOXB on gnathostome protochromosomes E0, E1, and E2, respectively, were omitted for simplicity (see also Fig. S6 in Supporting Information). 1R and 2R indicate the two successive rounds of WGD.