Figure 4

Proposed ancestry of vertebrate chemokine CCL25. Vertebrate protochromosome A, on which an ancestral CCL25 gene is assumed to reside, was duplicated by the 1R and 2R WGDs and also by a fission event between the 1R and 2R, resulting in six gnathostome protochromosomes (Nakatani et al. 2007). The CCL25 gene on gnathostome protochromosome A1 was transferred to teleost and amniote protochromosomes, whereas the genes on the other gnathostome protochromosomes were lost. Fish-specific CCL44 must have been generated by tandem duplication of the ancestral CCL25 gene on teleost protochromosome m. Two copies of the teleost CCL25 gene were maintained on duplicated chromosomes, and one of the CCL44 copies on one of the duplicated chromosomes may have been lost. Tetraodon CCL44 and bird CCL25 genes have not yet been identified. The evolutionary history of other chemokine and chemokine receptor genes are shown in Fig. S6 in Supporting Information. 3R indicates the teleost-specific WGD.