The nucleotide sequences of baboon chorionic gonadotropin β-subunit genes have diverged from the human

The placental glycopeptide hormone chorionic gonadotropin (CG) is involved in establishing and maintaining pregnancy. The hormone consists of two different non-covalently associated subunits termed α and β. In man there are seven closely linked genes coding for βCG-like peptides, but only three of these appear capable of expression in the placenta. The organization of βCG-like genes in man and baboon appears to be similar. We demonstrate here that the baboon genome contains multiple copies (at least five) of βCG-related genes, and that these genes are closely linked in the genome. Nucleotide sequence data from several βCG cDNA clones indicates that at least two of these βCG-related genes are expressed in the baboon placenta. Analysis of βCG sequences from baboons and human subjects demonstrates that these genes have diverged markedly between species. In contrast, these sequences are remarkably homogeneous within their respective genomes. Gene conversion events may be responsible for retaining the high degree of identity among the various βCG gene family members. Knowledge of βCG sequences from baboon may lead to development of a long-term antipregnancy vaccine. The ability of CG antibodies to interfere with the maintenance of pregnancy can now be investigated within a homologous system.