Phylogeny of mammalian carcinoembryonic antigen related cell adhesion molecule ( CEACAM) genes. Phylogenetic trees were constructed from N domain exon (A) and B domain exon nucleotide sequences (B) from CEACAM (CC) of cattle, horses, dogs, humans and mice using the neighbour-joining method (MEGA 4.0 software). The reliability of a phylogenetic tree was assessed using the Bootstrap test applying 1000 replicates. The statistical support for selected nodes is shown. Values >70 and >30 are shown in (A) and (B), respectively. Due to space limitations, only selected murine and horse Ceacams/CEACAMs and Psg were included and the topology of the B domain phylogenetic tree is shown (B). N1 domain exons were used from murine Psg genes which contain multiple N domain exons. Five groups of N domain exons can be discriminated. The N domain exon sequences from the CEACAM16, CEACAM18, CEACAM19 and CEACAM20 genes each cluster together, while N exon sequences from CEACAM1-like genes including PSG genes form species-specific groups. Similar groups were discriminated using B domain exons (B). CEACAM1 genes were identified based on the presence of immunoreceptor tyrosine-based inhibition motifs (ITIM)/immunoreceptor tyrosine-based switch motif (ITSM) in the encoded cytoplasmic domains. In horse, two genes with intact ITIM/ITSM were identified and named arbitrarily CEACAM1 and CEACAM43. For abbreviation of species names see Table 1. The bar below the phylogenetic tree in (A) shows the scale for the number of substitutions per site. a, b, allelic CEACAM1 variants. Multiple B domains present in a CEACAM are indicated by numbers.