Identification of a Carcinoembryonic Antigen Gene Family in the Rat

The existence of a carcinoembryonic antigen (CEA)-like gene family
in rat has been demonstrated through isolation and sequencing of
the N- terminal domain exons of presumably five discrete genes
(rnCGM1-5). This finding will allow for the first time the study of
functional and clinical aspects of the tumor marker CEA and related
antigens in an animal model. Sequence comparison with the
corresponding regions of members of the human CEA gene family
revealed a relatively low similarity at the amino acid level, which
indicates rapid divergence of the CEA gene family during evolution
and explains the lack of cross- reactivity of rat CEA-like antigens
with antibodies directed against human CEA. The N-terminal domains
of the rat CEA-like proteins show structural similarity to
immunoglobulin variable domains, including the presence of
hypervariable regions, which points to a possible receptor function
of the CEA family members. Although so far only one of the five rat
CEA-like genes could be shown to be transcriptionally active,
multiple mRNA species derived from other members of the rat
CEA-like gene family have been found to be differentially expressed
in rat placenta and liver.