Investigation of the RH locus in gorillas and chimpanzees

The human Rh blood-group system is encoded by two homologous genes,RhD andRhCE. TheRH genes in gorillas and chimpanzees were investigated to delineate the phylogeny of the humanRH genes. Southern blot analysis with an exon 7-specific probe suggested that gorillas have more than twoRH genes, as has recently been reported for chimpanzees. Exon 7 was well conserved between humans, gorillas, and chimpanzees, although the exon 7 nucleotide sequences from gorillas were more similar to the humanD gene, whereas the nucleotide sequences of this exon in chimpanzees were more similar to the humanCE gene. The intron between exon 4 and exon 5 is polymorphic and can be used to distinguish the humanD gene from theCE gene. Nucleotide sequencing revealed that the basis for the intron polymorphism is anAlu element inCE which is not present in theD gene. Examination of gorilla and chimpanzee genomic DNA for this intron polymorphism demonstrated that theD intron was present in all the chimpanzees and in all but one gorilla. TheCE intron was found in three of six gorillas, but in none of the seven chimpanzees. Sequence data suggested that theAlu element might have previously been present in the chimpanzeeRH genes but was eliminated by excision or recombination. Conservation of theRhD gene was also apparent from the complete identity between the 3′-noncoding region of the human D cDNA and a gorilla genomic clone, including anAlu element which is present in both species. The data suggest that at least twoRH genes were present in a common ancestor of humans, chimpanzees, and gorillas, and that additionalRH gene duplication has taken place in gorillas and chimpanzees. TheRhCE gene appears to have diverged more thanRhD among primates. In addition, theRhD gene deletion associated with the Rh-negative phenotype in humans seems to have occurred after speciation. Correspondence to: C.M. Westhoff