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 showed that CEACAM family genes are also present in genomes of basal tetrapods and teleosts (Fig. 1, b and c; Table S3 in File S1). However, no CEACAM homolog was identified in the genome of chicken, turkey (M. gallopavo), zebra finch (T. guttata), sea lamprey (P. marinus), and cephalochordate (amphioxus, B. floridae) and urochordates (tunicates, C. intestinalis and C. savignyi). In the clawed frog X. tropicalis, there are at least eight homologs, and three of them (XtrCEACAMI-III) were located close to marker genes including, LIPE, CNFN, TMEM145, PAFAH1B3, and ZNF574. In pufferfish, T. rubripes encoded at least six homologs ( Fig. 1c ; Table S3 in File S1), and three of these genes (scaffold 256, TruCEACAMI-III) were 5 Kbp from a PAFAH1B3 ortholog. Likewise, the homolog on scaffold 35 (TruCEACAMIV) was 20 Kbp from an XRCC1 ortholog (Fig. 1c) . On the other hand, the closely related pufferfish T. nigroviridis contained only three homologs (TniCEACAM Ia, Ib, and II). TniCEACAM Ia and II were found near marker genes ZNF574 and ATP1A3, and PAFAH1B3, LIPE, TMEM145, and TOMM40a, respectively. By contrast, TniCEACAM Ib was located with a second TOMM40 ortholog (TOMM40b) and an ETHE1 ortholog. Based on the understanding that a WGD occurred before the divergence of teleosts and osteoglossomorphs more than 230-350 million years ago [30, 42, 43] , TniCEACAM Ia and Ib as well as the pair of TOMM40 (a and b) genes likely represent WGD-derived co-orthologs.