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

To verify that CEACAM homologs identified in lower taxonomy represent expressed genes, we analyzed the expression of select homologs in tissues of platypus, T. nigroviridis, and D. rerio using RT-PCR with gene-specific primers (Table S4 in File S1). Analyses of intestinal mRNA samples from a deceased platypus confirmed that at least two of the four platypus CEACAMs (OanCEACAM16 and 20LI) are constitutively expressed in the intestine, a tissue that exhibits pathological responses to overexpression of human CEACAMs in mice [46] (Fig. 4a) . Likewise, zebrafish homologs, including DreCEACAMI, VII, and X, were constitutively expressed in a variety of tissues (Fig. 4b, right panel) . On the other hand, analyses of eight T. nigroviridis tissues showed that the expression of three CEACAMs in this species is tissuespecific. TniCREAMIa, Ib, and II are selectively expressed in the brain, skin, and gut, respectively (Fig. 4b, left panel) .