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

In agreement with earlier studies, the CEACAM/PSG locus was found to be located near a cluster of marker genes, including TGFB1, ATP1A3, ZNF574, PAFAH1B3, TMEM145, CNFN, LIPE, ETHE1, XRCC1, TOMM40, APOE, and SIGLEC8, in a variety of eutherian genomes ( Fig. 1 , a and b) [20, 21] . In humans, chimpanzees, and Rhesus monkeys, this locus encodes 25, 18, and 24 CEACAM/PSG genes, respectively, in a 10-Mbp region on chromosome 19 ( Fig. 1a , Table S1 in File S1). These primate CEACAM/PSG genes can be physically divided into two clusters. The cluster I contained the better characterized CEACAM1,3-8 and PSG genes whereas the second cluster included the recently identified CEACAM16, 18-20, and 22-23 genes (Fig. 1a) . Although the total number of CEACAM/PSG genes in Rhesus monkeys was close to that of humans, the majority of PSG-like genes in this primate did not show a 1:1 orthologous relationship with those of apes. Instead, phylogenetic tree analysis using either Neighbor-Joining or Maximum Likelihood methods showed that most PSG-like genes in Rhesus monkeys clustered in a sub-branch in phylogenetic trees, suggesting that the expansion of PSG genes in Rhesus monkeys was independent of those in apes (Figs. 2a and 3a).