Characterization of murine carcinoembryonic antigen gene family members

The carcinoembryonic antigen (CEA) is a human tumor marker whose gene belongs to a family with more than 20 members. This gene family codes for a group of proteins with in vitro cell adhesion properties and for a group of abundantly expressed pregnancy-specific glycoproteins (PSG) with unknown functions. As a basis for in vivo functional studies, we have started to analyze the murine CEA gene family and have identified five new members (Cea-2 to Cea-6). cDNA clones were isolated for Cea-2, Cea-3, and Cea-6. The deduced amino acid sequences of Cea-2 and Cea-6 indicate three IgV-like (N), followed by one IgC-like (A) domain (N1-N2-N3-A). We have also partially characterized the Cea-2 gene and two additional ones, Cea-4 and Cea-5. Cea-2 and Cea-4 are separated by only 16 kb, suggesting a close linkage of murine CEA-related genes, as found for the human CEA gene family. Cea-5 was located to the proximal region of mouse Chromosome (Chr) 7, which is syntenic to part of human Chr 19, containing the human CEA gene family cluster. Cea-2, Cea-3, and a Cea-4-like gene are differentially transcribed in the placenta during pregnancy, but not in other organs tested. This expression pattern strongly suggests that they represent counterparts of the human PSG subgroup members, despite the presence of multiple IgV-like domains, a feature not found for human PSGs. The more distantly related Cea-5 seems to be ubiquitously expressed. The putative promoter region of Cea-2 lacks typical TATA- or CAAT-boxes, but contains other conserved motifs that could play a role in the initiation of transcription.