Widespread Divergence of the CEACAM/PSG Genes in Vertebrates and Humans Suggests Sensitivity to Selection

Chang, Chia Lin; Semyonov, Jenia; Cheng, Po Jen; Huang, Shang Yu; Park, Jae Il; Tsai, Huai-Jen; Lin, Cheng-Yung; Grützner, Frank; Soong, Yung Kuei; Cai, James J.; Hsu, Sheau Yu Teddy

Syntenic mapping of chordate genomes showed that CEACAM orthologs are present in lower taxonomy, and the number of CEACAM homologs ranges from zero in amphioxus, tunicates, sea lamprey and chicken to more than three dozen in the opossum. The radical divergence of gene inventory occurred even among species under the same family, perhaps reflecting the extensive birth-and-death of CEACAM/PSG genes in response to environmental selection. Interestingly, CEACAM/PSG genes appeared to evolve in a similar manner in humans. The CECAM/PSG locus contained a higher density of nonsynonymous SNPs compared to other genes on the same chromosome. In addition, these genetic variations exhibited high population differentiation in geographically separated human populations. Similar to studies of SNPs, we found that structural variations are common at the PSG locus, and these copy number polymorphisms exhibit population differentiation. Together with earlier studies on the dN/dS ratio in primate and rodent species [22, 23] , these results indicated that CEACAM/PSG genes had a more dynamic evolutionary history than previously thought.