Intra- and Interspecies Analyses of the Carcinoembryonic Antigen (CEA) Gene Family Reveal Independent Evolution in Primates and Rodents

Various rodent and primate DNAs exhibit a stronger intra- than
interspecies cross-hybridization with probes derived from the
N-terminal domain exons of human and rat carcinoembryonic antigen
(CEA)-like genes. Southern analyses also reveal that the human and
rat CEA gene families are of similar complexity. We counted at
least 10 different genes per human haploid genome. In the rat,
approximately seven to nine different N-terminal domain exons that
presumably represent different genes appear to be present. We were
able to assign the corresponding genomic restriction endonuclease
fragments to already isolated CEA gene family members of both human
and rat. Highly similar subgroups, as found within the human CEA
gene family, seem to be absent from the rat genome. Hybridization
with an intron probe from the human nonspecific cross-reacting
antigen (NCA) gene and analysis of DNA sequence data indicate the
conservation of noncoding regions among CEA-like genes within
primates, implicating that whole gene units may have been
duplicated. With the help of a computer program and by calculating
the rate of synonymous substitutions, evolutionary trees have been
derived. From this, we propose that an independent parallel
evolution, leading to different CEA gene families, must have taken
place in, at least, the primate and rodent orders.