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

The number of CEACAM homologs in wet-nosed primates (Suborder Strepsirrhin; Lemuriforme, i.e., bushbaby and mouse lemur), which split from dry-nosed primates (Suborder Haplorrhini) ,40 million years ago, was limited to 4-6 (Table S1 in File S1). Likewise, most non-primate mammals (e.g., cat, guinea pig, tree shrew, rabbit, squirrel, cow, hedgehog, microbat, shrew, elephant, small Madagascar hedgehog, and armadillo) contained 4-6 CEACAM homologs. There is an absence of PSG-like genes in these species, suggesting that PSG genes of dry-nosed primates were derived from lineage-specific duplications. Among nonprimate eutherians investigated, rodents appeared to be the only group to have a large number of CEACAM homologs (16 in rats and 27 in mice) [20, 21, 42] .